Regulation of Mitochondrial Homeostasis: Applications of Nanobiomaterials in Age-Related Bone Diseases

Abstract

Age-related bone diseases are a heterogeneous group of metabolic disorders characterized by progressive degenerative changes. Although nanobiomaterials have emerged as a promising means of regulation at the cellular level, their therapeutic efficacy remains very limited due to the lack of treatment strategies that directly target mitochondrial pathology. In recent years, nanobiomaterial therapies centered on mitochondria have attracted widespread attention. This review aims to critically evaluate the latest advances in this emerging field and categorize them into four main strategies: enhancing mitochondrial autophagy, optimizing the mitochondrial microenvironment, repairing mitochondrial structure, and implementing mitochondrial transfer therapy. Based on existing research, we have preliminarily established a multi-level intervention framework ranging from the clearance of dysfunctional mitochondria to the regulation of the microenvironment, and from the repair of structural components to the transplantation of healthy mitochondria, which has demonstrated encouraging proof-of-concept results in vitro and in animal models. However, this field remains in the preclinical exploration phase: the vast majority of studies are based on rodent models, the efficiency of mitochondrial-targeted delivery is generally low, and long-term biosafety and the feasibility of large-scale production have not yet been systematically evaluated. This review discusses the latest advances in mitochondrial-based nanobiomaterial therapies for age-related bone diseases. Furthermore, this review explores potential drugs and targets for the development of more effective nanobiomaterials, focusing on the key challenges facing the transition from the laboratory to clinical applications in this field, and is expected to provide novel insights into the future development of mitochondria-based nanobiomaterial therapies.

Introduction

Aging has become one of the most widely discussed health topics in the world today. As we grow older, our bodies are prone to various health issues, including cardiovascular and cerebrovascular diseases, digestive disorders, urinary tract conditions, oral diseases, and skeletal disorders, among others. The World Health Organization predicts that the global population aged 60 and older will increase from 12% in 2015 to 22% in 2050, rising from 900 million to 2 billion.¹ Therefore, actively addressing aging and the associated issues it brings has become an unavoidable topic for us. Among these, bone aging poses a significant challenge to people worldwide and severely impacts their quality of life. From a macroscopic perspective, bone tissue serves not only as the cornerstone of our structural support and body shape but also as the lever and fulcrum for functional movement; from a microscopic perspective, it acts as a reservoir for the storage and balance of minerals in the human body.^2–4 Age-related bone diseases are characterized by increased resorption, decreased formation, osteoporosis, osteoarthritis, and impaired fracture healing, among other conditions.^5–10 These manifestations are associated with pathological mechanisms, including a decline in the osteogenic differentiation capacity of bone marrow mesenchymal stem cells due to aging, oxidative stress, the polarization of macrophages toward the M1 phenotype, and reduced bone vascularization.^11–15 Currently, clinical treatment strategies for bone-related age-related conditions primarily involve drug therapy, such as bisphosphonates and raloxifene.^16,17 Although bisphosphonates can delay bone resorption to some extent by inhibiting osteoclast activity, their long-term use is associated with serious complications such as osteonecrosis of the jaw and atypical femoral fractures; while raloxifene, as a selective estrogen receptor modulator, can reduce the risk of vertebral fractures, it increases the incidence of hot flashes and venous thromboembolism, and has limited efficacy in preventing non-vertebral fractures. More broadly speaking, current pharmacological interventions mostly focus on inhibiting bone resorption—a single aspect of the process—and fail to simultaneously address impaired bone formation, which is a core pathological feature of age-related bone disease.^18–21 Furthermore, while tissue engineering and cell therapy show promise for tissue regeneration, they are hampered by bottlenecks such as low cell survival rates, poor targeting, and difficulties in large-scale production. Therefore, developing proactive and effective treatment strategies for age-related bone diseases is crucial to ensuring patients’ quality of life.

Mitochondria, as one of the most important organelles in the cell, play an indispensable role in maintaining cellular longevity and normal function.^22,23 More than 95% of the adenosine triphosphate (ATP) in cells is produced by mitochondria through oxidative phosphorylation.²⁴ ATP is the foundation of all bodily functions—from DNA replication to muscle contraction, and from nerve signal transmission to the synthesis of substances.²⁵ Mitochondria serve as the “master monitor” of cellular health. As metabolic hubs, they provide the common pathway for the final oxidation and breakdown of the three major nutrients: carbohydrates, fats, and proteins. At the same time, the self-renewal and differentiation of stem cells are significantly influenced by the metabolic state of mitochondria.^26–28 It is now widely accepted that mitochondrial dysfunction is a key marker of cellular aging, as evidenced by imbalances in the mitochondrial microenvironment, impaired mitochondrial autophagy, and disruptions in mitochondrial homeostasis.^29–32 Therefore, precise regulation of mitochondrial mass and function is of critical importance for the treatment of bone aging and related age-related bone diseases.^33,34

In the field of bone regenerative medicine, the design philosophy of Nanobiomaterials is undergoing a profound paradigm shift: moving from simply providing mechanical support to evolving into intelligent therapeutic platforms capable of actively regulating cellular behavior.^35–37 For example, compared with traditional scaffold materials—which retain only 50–70% of their initial mechanical strength after implantation and lack bioactivity.^38,39 In contrast, a new generation of functionalized nanomaterials can increase the adhesion efficiency of bone marrow-derived mesenchymal stem cells by 2–3 times through surface modification (such as RGD peptide grafting). By slowly releasing bioactive factors (which mediate the restoration of mitochondrial function), these materials continuously regulate osteogenic differentiation signaling pathways (such as BMP/Smad and Wnt/β-catenin), thereby enhancing in situ bone regeneration efficiency by more than 40%.⁴⁰ However, interventions limited to the cellular level alone are increasingly unable to meet the clinical needs for the definitive treatment of age-related bone diseases. Against this backdrop, turning our attention to a more fundamental regulatory node within cells—the mitochondria—is emerging as a promising new avenue in biomedical research. Currently, by designing advanced materials with mitochondrial targeting capabilities, microenvironment responsiveness, and programmable functions, researchers have preliminarily established a multidimensional, systematic, and mitochondria-centric therapeutic framework, aiming to address the energy metabolism imbalances underlying skeletal aging and disease at their source. However, while fully acknowledging these advances, it is important to note the common challenges facing the clinical translation of nanomedicine: most nanomaterials accumulate in non-target organs (particularly the liver and spleen) at rates as high as 30%–90%, which significantly reduces therapeutic efficacy and poses potential long-term toxicity risks;^41,42 the efficiency of mitochondrial-targeted delivery is typically less than 10% and is severely limited by lysosomal degradation; furthermore, uncertainties regarding batch-to-batch consistency, large-scale production, and regulatory approval pathways remain bottlenecks to industrialization.^43,44 These limitations also constitute key barriers to the clinical translation of mitochondrial-targeted nanobiomaterials. Regrettably, Existing reviews have focused on the application of a single class of nanomaterials in bone repair or have merely outlined the biological mechanisms of mitochondrial dysfunction; few studies have systematically integrated the intrinsic links between material design principles and mitochondria-specific regulatory strategies. More critically, the field lacks a cross-comparison and critical evaluation of the therapeutic efficacy of different targeting strategies. For this reason, it is particularly necessary to summarize and evaluate the Nanobiomaterials underpinning existing mitochondria-targeted therapeutic strategies.

In this review, we discuss the complex relationship between mitochondria and aging bone, and we explore current advances and future opportunities for in vivo mitochondrial-targeted therapies. We examine therapeutic strategies involving various Nanobiomaterials for restoring mitochondrial dysfunction, as well as the mechanisms by which these strategies influence mitochondrial function to reverse aging and promote bone repair in aged states (Figure 1). Specifically, this review systematically summarizes and critically evaluates four core strategies: (1) enhancing mitochondrial autophagy to clear dysfunctional mitochondria; (2) optimizing the mitochondrial microenvironment, including restoring ion homeostasis and alleviating oxidative stress; (3) repairing mitochondrial structural components, encompassing the matrix network, the electron transport chain, and membrane integrity; (4) implementing mitochondrial transfer therapy, which involves directly transplanting healthy mitochondria into damaged cells. These research advances not only reveal the central role of mitochondria in the bone aging process but also provide a theoretical foundation for the development of novel anti-aging therapeutic strategies. In the future, the integration of nanomaterials, targeted delivery systems, and mitochondria-specific drugs is expected to enable precise regulation of mitochondrial function in aging cells, thereby enhancing bone tissue regenerative capacity and advancing the clinical treatment of age-related bone diseases.

Figure 1.

Schematic diagram of a biomaterial for treating bone aging based on mitochondria. © Created by biorender.

Biological Characteristics of Mitochondria in Bone Aging

Mitochondria are the organelles at the heart of cellular energy metabolism; cellular aging is often accompanied by degenerative and pathological changes in their structure and function,⁴⁵ These changes, in turn, further accelerate the aging process. During bone aging, mitochondrial dysfunction manifests as a multifaceted phenomenon. The following discussion addresses three key aspects: the accumulation of oxidative damage, the failure of homeostatic regulation, and the specific manifestations of dysfunction.

As the primary site of cellular aerobic respiration, mitochondria continuously generate reactive oxygen species (ROS) during oxidative phosphorylation, making them the primary intracellular source of ROS; however, under conditions of cellular senescence, limited oxygen supply leads to excessive ROS production. At the same time, due to a lack of histone protection and limited DNA repair capacity, mitochondrial components—particularly mitochondrial DNA—are highly susceptible to attack by excessive ROS.⁴⁶ Some researchers have proposed the classic free radical theory of aging: the continuous accumulation of oxidative damage induced by mitochondrial ROS not only leads to the decline of respiratory chain function and structural abnormalities but also drives cellular senescence through oxidative DNA damage (including mtDNA mutations and nuclear genomic instability), creating a vicious cycle of “damage—functional decline—increased ROS production”, which ultimately accelerates the body’s aging process.⁴⁷ In bone tissue, this vicious cycle is also present in bone marrow mesenchymal stem cells (BMSCs) and osteocytes, and is considered one of the key drivers of the initiation and progression of bone aging.

Mitophagy is a biological process by which cells selectively remove damaged, aged, or dysfunctional mitochondria through autophagy; it is a form of selective autophagy and plays a central regulatory role in maintaining mitochondrial quality and cellular homeostasis.⁴⁸ Studies have shown that impaired autophagy is closely associated with the aging process. Xiang et al demonstrated that inhibiting mitochondrial autophagy with fumonisin disrupted mitochondrial homeostasis, thereby triggering senescence in bone marrow mesenchymal stem cells. Similarly, mitochondrial autophagy dysfunction is also observed in the context of bone aging.⁴⁹ It is worth noting that dysfunctional mitochondria can produce excessive amounts of mitochondrial reactive oxygen species (mtROS), which in turn disrupt the microenvironmental homeostasis of neighboring healthy mitochondria, triggering a spread of dysfunction.⁵⁰ Therefore, activating mitochondrial autophagy to restore mitochondrial homeostasis is considered a potential strategy for improving age-related pathological changes in bone.

In the context of bone aging, mitochondrial dysfunction in BMSCs is one of its hallmark features,²⁹ This dysfunction often stems from instability in the mitochondria’s own structure.⁵¹ For example, changes in the permeability of mitochondrial membranes can lead to the leakage of mtDNA, which in turn activates the cGAS-STING pathway, thereby inducing the production of large amounts of pro-inflammatory cytokines and exacerbating inflammation in the bone aging microenvironment.⁵² It is worth noting that, in addition to membrane structures, the electron transport chain (ETC) within mitochondria—which serves as the primary site of energy production—exhibits impaired function during cellular senescence. This impairs cellular energy production, ultimately leading to a reduced tendency for osteoblasts to undergo osteogenic differentiation and may even result in cell death.⁵³ In addition, mitochondria in an aging environment exhibit a reduction in number, a decline in biosynthetic capacity, and disruption of the matrix network; these are also key factors contributing to mitochondrial dysfunction.⁵⁴

Removing Obstacles: Enhancing Mitochondrial Autophagy

The accumulation of damaged mitochondria is widely recognized as a driving factor in cellular senescence and impaired stem cell differentiation.⁵⁵ A major cause of this accumulation is mitochondrial autophagy dysfunction.⁵⁶ Recent studies have shown that autophagy plays a key role in maintaining bone homeostasis, and that alterations in this pathway are associated with bone aging to some extent.^57–60 Thus, restoring mitochondrial autophagy to eliminate damaged mitochondria has emerged as a promising therapeutic strategy. Although existing drugs (metformin and urolithin A) are already in clinical use, there remains a lack of agents capable of precisely activating or inhibiting specific pathways in a spatiotemporally specific manner.⁶¹ Currently, the research frontier in this field has expanded from simple drug discovery to the design and development of novel functional materials with intrinsic biological activity. The ultimate goal of these materials is to serve as therapeutic agents in their own right, directly and precisely regulating and restoring a key cellular physiological process: mitochondrial autophagy, Table 1.

Table 1.

A Summary of Representative Studies on Nanobiomaterials That Enhance Mitophagy

Materials System	Key Design Concepts	Biological Mechanisms and Functions	Results	Reference
Curcumin liposomes (Cur-Lip)	Drug Delivery	Cur activates mitochondrial autophagy via the Pink1/Parkin pathway	Decreased mtROS and increased mtΔψm Improving the senescence of rBMSCs	[62]
EM-eNMs	Drug Delivery	Induction of dynamin-related protein 1 (DRP1) promotes mitochondrial autophagy	Restores mitochondrial function Restores the stem cell properties of BMSCs Improves osteoporosis in aged rats	[63]
Serum-derived EVs and the bone-targeting peptide CDSS6 in bone healing in young mice	Drug delivery and targeting aged bone	Activated Tomm7-mediated Pink1/Parkin-dependent mitophagy	Enhancing mitochondrial function in senescent cells Shortening the healing time of fractures in senescent individuals	[64]
HydroWrap System—Hydrogel + H2S	Functional materials	Activation of PINK1/Parkin-mediated mitophagy	Improves macrophage senescence Improves fracture healing in patients with diabetes	[65]
A stable MOF coating was formed on a titanium substrate	Functional materials	Increase the expression of mitochondrial autophagy markers PINK1 and LC3	Enhanced osteogenic differentiation of MSCs	[66]

To address the need to clear dysfunctional mitochondria from aged bone tissue, current biomaterial development primarily follows two main approaches: the first involves drug delivery materials designed to serve as carriers that protect and target the delivery of mitochondrial autophagy inducers, thereby improving drug bioavailability and reducing systemic side effects; the second is functional materials that do not rely on drug delivery. These materials do not depend on traditional drug molecules but instead directly regulate cellular behavior through their unique physicochemical properties to activate the mitochondrial autophagy pathway.

Drug Delivery Materials

Through advanced material design and delivery strategies, certain naturally occurring bioactive molecules have been successfully integrated into functional systems, thereby marking an initial transition from “bioactive compounds” to “bioactive Nanobiomaterials”. Curcumin—a natural polyphenol that has been extensively studied for its exceptional antioxidant, anti-inflammatory, anticancer, and anti-aging properties.^67,68 In the field of tissue engineering and regenerative medicine, curcumin has been shown to promote the proliferation of mesenchymal stem cells (MSCs), activate autophagy, and induce their differentiation into osteoblasts, making it an ideal candidate molecule for applications such as bone defect repair.^69,70 However, its inherent drawbacks—including poor water solubility, chemical instability, and rapid metabolism in the body—severely limit the effectiveness and reliability of its direct application.⁷¹ To address this issue, Yu et al turned to nanotechnology, utilizing liposomes—a classic and highly biocompatible nanocarrier to synthesize a curcumin liposome (Cur-Lip) drug delivery system. Following Cur-Lip treatment, the expression of LC3B II/I, PINK1, and Parkin proteins was significantly increased, indicating the activation of mitochondrial autophagy. Subsequent experiments further confirmed that the Cur-Lip-treated group exhibited reduced mtROS and increased mitochondrial membrane potential (mtΔψm), demonstrating that Cur-Lip protected mitochondrial function and alleviated D-galactose (D-gal)-induced senescence in rBMSCs.⁶²

Current research is increasingly focused on developing intelligent, precisely targeted systemic drug delivery systems to address the unique delivery barriers inherent in bone tissue. Blood flow within bone tissue is relatively sparse, and target cells are deeply embedded in a highly mineralized matrix; the resulting physical and physiological barriers are even more significant than those of the blood-brain barrier, making it difficult for conventional drug delivery to achieve effective accumulation.⁷² In this regard, Liu et al developed a biomimetic nanomedicine that achieves active targeting by leveraging the high affinity of polyphosphate structures for bone minerals. This strategy uses ultrafine black phosphorus quantum dots as precursors to prepare engineered nanomaterials (EM-eNMs) with phosphate-rich surfaces via a contact electrocatalytic method. In vitro experiments demonstrated that treatment with EM-eNMs enhanced the colocalization of mitochondria and lysosomes, significantly increased the level of mitochondrial autophagy, and produced effects comparable to those observed in the rapamycin-treated group. Mechanistic studies confirmed that EM-eNMs improve mitochondrial autophagy via the β-subunit (ATP5B) of the F1-ATP synthase complex, thereby restoring mitochondrial function and alleviating cellular senescence. In vivo experiments further demonstrated that, in an age-induced bone loss mouse model, EM-eNMs improved bone mechanical strength, mineralization rate, and cortical bone thickness, and prevented age-related alveolar bone loss.⁶³ It is worth noting that, compared to the passive delivery of Cur-Lip, EM-eNMs achieve active bone targeting through the affinity of phosphate groups for bone minerals, offering a clear mechanistic advantage in terms of targeting efficiency. However, materials containing phosphate groups also carry the risk of nonspecific distribution in other mineralized tissues (such as teeth and calcified blood vessels). The severity of this issue and its impact on long-term safety constitute a major obstacle to the clinical translation of this strategy.

As drugs may diffuse non-specifically into other mineralized tissues via the systemic circulation, thereby reducing therapeutic efficacy, localized bone targeting has become an indispensable core design strategy in this field.⁷³ It has previously been suggested that extracellular vesicles possess significant potential for drug modification and delivery, and their inherent functional capabilities have made them a current focus of research.⁷⁴ Zheng et al found that extracellular vehicles (EVs) derived from the serum of young mice demonstrated the most effective ability to improve bone aging during the bone healing process—both reversing aging and promoting osteogenic differentiation (Figure 2a). Therefore, they isolated extracellular vehicles (EVs) from pretreated young mouse serum. Based on healing rates at different stages of the bone healing process in young mice, they identified BT-EF10d as the treatment with the best efficacy (Figure 2b). To enhance the therapeutic effect, they modified the surface of exosomes derived from young mice with a bone-targeting peptide (CDSS6). In vivo targeting experiments have demonstrated its excellent targeting efficiency (Figure 2c). Through a series of validation experiments, they found that as age increases, Tomm7 expression declines and the level of mitochondrial autophagy decreases, making it impossible to eliminate excess damaged mitochondria, which leads to mitochondrial dysfunction and skeletal ageing. In subsequent in vitro experiments, treatment with BT-EF10d increased Tomm7 expression and activated the Tomm7-mediated Pink1/Parkin mitochondrial phagocytosis pathway, thereby restoring the stemness of aged BMSCs by improving mitochondrial function (Figure 2d). In this way, the adverse conditions in the microenvironment of ageing bones are reversed, thereby achieving the observed reversal of ageing.⁶⁴

Figure 2.

Nanobiomaterials that Modulate Bone Aging by Enhancing Mitochondrial Autophagy. (a) Schematic illustration of young extracellular vesicles enhances mitochondrial autophagy and restore fracture healing in aged tissues. Red box indicates the aging bone microenvironment; Blue, yellow, and green boxes list specific factors; Upward (↑) and downward (↓) arrows denote upregulation/increase and downregulation/decrease, respectively; the cross (×) indicates blockade/suppression. (b) SA-β-galactosidase staining results in a H₂O₂-induced cellular senescence model following treatment with EV J, EF1d, EF10d, or EF21d. (c) In vivo fluorescence imaging to evaluate the bone-targeting potential of EF10d and BT-EF10d. (d) TEM observations of primary aged BMSCs treated with BT-EF10d. Red boxes denote magnified regions.⁶⁴ © The American Chemical Society, 2025. (e) bioMOF reprograms dysfunctional MSCs into functional MSCs by activating mitochondrial autophagy.⁶⁶ © The American Chemical Society, 2022. (f) HydroWrap rejuvenates senescent macrophages by activating mitochondrial autophagy, thereby accelerating fracture healing in T2DM. Flat-headed arrows (T-shaped lines) indicate inhibitory effects.⁶⁵ © Elsevier B.V. 2025.

Although the aforementioned studies demonstrate encouraging therapeutic prospects, their limitations must be viewed with caution. First, most of these strategies are still in the proof-of-concept stage and have only been evaluated for short periods in small animal models; their long-term safety and batch-to-batch consistency have not yet been systematically verified. Second, the “double-edged sword” effect of mitochondrial autophagy warrants attention—overactivation may lead to the nonspecific clearance of functional mitochondria, and systematic studies on dose-response relationships are currently lacking. Therefore, advancing these systems to the preclinical stage urgently requires standardized toxicological assessments and the design of controllable regulatory mechanisms. In summary, these studies mark the evolution of bone-targeting therapeutic strategies: from basic material loading, through the development of biomimetic intelligent systems, to the precise targeting of engineered biological carriers. Together, they point towards a core objective: to overcome extreme physiological barriers through the deep integration of materials science, nanotechnology and biology, thereby achieving the efficient, specific and controlled delivery of therapeutic agents to complex pathological sites.

Functional Materials

In addition to advanced drug delivery systems, another key strategy in the field of bone regeneration involves using functional Nanobiomaterials to directly modify the implant interface, actively modulate the bone microenvironment and simultaneously activate mitochondrial autophagy to promote the restoration of mitochondrial function. Impaired fracture healing in type 2 diabetes mellitus (T2DM) currently poses a clinical challenge, primarily due to damage to the bone microenvironment driven by senescent macrophages and their amplifying effects.⁷⁵ Feng et al developed the HydroWrap system, which consists of a hydrogel network and hydrogen sulphide (H₂S); when exposed to near-infrared (NIR) light, the rise in temperature causes the hydrogel network to contract and accelerates the release of H₂S (Figure 2f). Reduced H₂S levels are a key factor contributing to impaired fracture healing in T2DM. In vitro experiments demonstrated that HydroWrap provides sustained, glucose-responsive H₂S release within the hyperglycemic bone microenvironment of T2DM; elevated H₂S levels restored PINK1/Parkin-mediated mitochondrial autophagy, alleviated macrophage senescence, and demonstrated that the system improved wound healing rates and angiogenesis, restoring osteogenic differentiation and mineralization in MC3T3-E1 cells, as evidenced by increased ALP activity and enhanced calcium deposition. In vivo experiments revealed that X-ray imaging showed the most pronounced bone remodeling in the HydroWrap+ near-infrared (NIR) group; quantitative analysis of skeletal parameters indicated that bone marrow density (BMD), bone volume (BV) and the BV/total volume ratio (BV/TV) were all highest in the HydroWrap+ NIR group.⁶⁵ Although HydroWrap has shown promising results in both in vivo and in vitro experiments, there are still significant limitations regarding the in vivo monitoring of H₂S release, as excessive H₂S can also cause irreversible damage to mitochondria, which necessitates further improvements to the material.⁷⁶

Research into such functional materials also tends to focus on developing smart, active coatings for the surfaces of implants (such as titanium alloys), enabling them not only to promote osseointegration but also to respond to pathophysiological signals, thereby achieving the on-demand release of therapeutic functions. Cai et al have innovatively developed a strategy for the in situ construction of a bifunctional metal-organic framework (MOF) coating on medical-grade titanium surfaces that is sensitive to the bone microenvironment. Using a hydrothermal synthesis method and exploiting the coordination interactions between bisphosphonates and cerium/strontium ions, the study directly constructed a stable MOF coating on a titanium substrate (Figure 2e). The introduction of Ce confers long-lasting antioxidant and anti-inflammatory properties to the coating. In vitro experiments demonstrated that the AHT-Ce/SrMOF implant exhibited on-demand superoxide dismutase and hydrogen peroxide-like catalytic activity, reducing ROS levels by activating the AMP-activated protein kinase (AMPK) signaling pathway in MSCs. Concurrently, they observed a significant increase in the expression of mitochondrial autophagy markers (PINK1 and LC3) in MSCs cultured with AHT-Ce/SrMOF implants, suggesting that the bio-MOF can modulate mitochondrial autophagy in MSCs to improve mitochondrial function, thereby achieving the goal of reversing aging.⁶⁶ However, the clinical translation of this strategy still requires attention to the long-term structural stability of the MOF coating in vivo, the potential nephrotoxicity of cerium ion accumulation, and the off-target effects on normal cells resulting from excessive activation of mitochondrial autophagy. It is worth noting that, unlike HydroWrap’s delivery mechanism, which relies on exogenous H₂S, the MOF coating achieves its therapeutic effect by mimicking the catalytic function of endogenous antioxidant enzymes. While this offers certain advantages in avoiding the toxicity risks associated with exogenous gas molecules, the issue of long-term metal ion accumulation it causes should not be overlooked—the two strategies face different types of safety challenges, rather than a simple binary distinction between their presence or absence.

In summary, compared with the targeted drug delivery systems described above, this material system—which “empowers the implant itself”—offers a new and reliable approach to restoring bone regeneration by achieving long-lasting and stable recovery of mitochondrial autophagy function under complex pathological conditions.

Optimizing the Environment: Regulate the Mitochondrial Microenvironment

Although enhancing mitochondrial autophagy is intended to clear dysfunctional organelles, whether the remaining functional mitochondria can continue to operate efficiently depends largely on the homeostasis of their microenvironment.⁷⁷ During the process of bone ageing, mitochondria are not only affected by internal microenvironmental disturbances such as imbalances in intracellular biochemical ion homeostasis and reactive oxygen species (ROS), but are also subject to external environmental factors such as alterations in extracellular matrix (ECM) components and abnormalities in mechanical signal transduction.^78–80 During the process of bone ageing, mitochondria are not only affected by internal microenvironmental disturbances such as imbalances in intracellular biochemical ion homeostasis and reactive oxygen species (ROS), but are also subject to external environmental factors such as alterations in extracellular matrix (ECM) components and abnormalities in mechanical signal transduction, (Table 2).

Table 2.

A Representative Summary of Nanobiomaterials That Restore the Homeostasis of the Intracellular and Extracellular Environments of Cells Containing Mitochondria

Materials	Key Design Concepts	Functions and Mechanisms	Results	Reference
ALN/HA@TPP@TM Lipo	Reduce excess mitochondrial copper (II)	Reprogramming immune cells	Promotes the conversion of macrophages to the M2 phenotype Improves osteoporosis in mice	[81]
ED-71	Relieve mitochondrial calcium overload	Regulation of GPR75 via the VDR-PKC signaling pathway reduces MAM-mediated mitochondrial calcium overload	Improving Cellular Aging Restoring the Coupling Mechanism Between Angiogenesis and Osteogenesis	[82]
GHCZ composite-hydrogel system	ROS Responsive Release	Eliminate ROS inside and outside cells	Alleviating the ageing of BMSCs Improving the immune microenvironment	[83]
FAMG Nano Platform	ROS Responsive Release	Eliminate excess ROS	Restoration of mitochondrial morphology and function, promoting the regeneration of aged alveolar bone	[84]
Smart hydrogel-coated implants	ROS Responsive Release	Clear ROS Stimulate angiogenesis	Restore mitochondrial metabolic function Alleviate the ageing of mesenchymal stem cells	[85]
TPG@ChSMA composite hydrogel scaffold	Targeting mitochondria to scavenge ROS	Clear ROS Promote osteogenic differentiation	Restoring mitochondrial function Promoting the recovery of osteoporosis in rats	[86]
Layered porous scaffolds produced by 3D cryoprinting combined with hybrid nanoenzymes	Targeting mitochondria to scavenge ROS	Eliminates excess ROS, modulates the immunological microenvironment associated with ageing, and inhibits osteoclast differentiation	Restoration of mitochondrial function Promoting the healing of cranial defects in diabetic patients	[87]
An exosome-based GSH delivery platform	Targeted delivery of GSH	Increase the local GSH pool at the site of bone formation	Alleviates oxidative stress Improves mitochondrial function Slows down cellular ageing	[88]
A multimodal ROS logic-controlled therapeutic platform	Enhance the synthesis and metabolism of GSH	Boosts intracellular GSH pools Enhances ROS tolerance	Promoting bone regeneration in a cranial defect model in aged rats Alleviating SME-associated cellular senescence	[89]
Modified implant TNT@Met-LBL	Rebuilding the ECM to rejuvenate it	Eliminates excess ROS Promotes the deposition of healthy ECM	Reduced secretion of SASP by MSCs, with a general decrease in ROS levels both inside and outside the cells Differentiation of MSCs into osteoblasts	[90]
HM@Y-ECM	Harnessing the natural rejuvenating properties of the ECM	Reactive oxygen species (ROS) have been restored	Ageing BMSCs shift towards osteogenic differentiation, with a decrease in SASP secretion and enhanced mitochondrial function	[91]

Regulation of the Internal Environment

The homeostasis of the intracellular environment is fundamental to the maintenance of normal mitochondrial function. During bone ageing, metabolic disturbances and redox imbalances intertwine, jointly exacerbating mitochondrial damage. In response to this complex pathological environment, regulatory strategies primarily focus on two key areas: firstly, maintaining biochemical homeostasis to ensure energy metabolism and ionic balance; and secondly, restoring the homeostasis of the reactive oxygen species (ROS) microenvironment to mitigate oxidative damage.

Maintenance of Biochemical Ion Homeostasis

Disruptions in intracellular biochemical ion homeostasis are one of the key factors driving mitochondrial dysfunction and bone ageing.^92,93 Mitochondrial copper (II) drives pro-inflammatory epigenetic reprogramming in bone marrow-derived macrophages (BMDMs),⁹⁴ and perpetuates osteoporotic inflammation. Zhang et al developed a bone/mitochondria-targeting liposome system, ALN/HA@TPP@TM Lipo, for the delivery of the copper chelator tetramolybdate (Figure 3a). ALN/HA@TPP@TM Lipo is mediated by the triphenyl phosphonium cation (TPP), which utilizes the mitochondrial membrane potential to achieve intracellular mitochondrial targeting, thereby concentrating the therapeutic drug within this key organelle (Figure 3a). Its primary therapeutic mechanism relies on the copper chelator TM selectively sequestering mitochondrial copper (II) ions within target macrophages, thereby disrupting copper-dependent processes such as the NAD(H) redox cycle and acetyl-CoA biosynthesis; This disruption ultimately leads to the suppression of H3K27ac-mediated epigenetic reprogramming, thereby attenuating pro-inflammatory M1 polarization and promoting a shift towards an immunomodulatory phenotype (Figure 3a). This epigenetic reprogramming restored osteogenesis in bone marrow stromal cells (BMSCs) in co-culture; in vivo experiments demonstrated that the ALN/HA@TPP@TM lipid complex prevented osteoporosis in naturally ageing mice (Figure 3b).⁸¹ Their findings identify mitochondrial copper (II) as a key regulator of inflammation- and ageing-related osteoporosis, offering a dual-targeted therapeutic strategy to disrupt pro-inflammatory epigenetic circuits and mitigate age-related bone degeneration. However, copper is an essential cofactor for many key enzymes and, at low concentrations, promotes angiogenesis and osteogenic differentiation; excessive chelation may actually impair bone repair.⁹⁵ Although ALN/HA@TPP@TM Lipo achieves dual targeting, there is currently a lack of data on whether it can precisely control the “therapeutic window” within complex regulatory networks without disrupting copper homeostasis in non-target cells, which poses a key obstacle to its clinical translation.

Figure 3.

Nanobiomaterials that regulate mitochondrial biochemical ion homeostasis to treat age-related bone diseases. (a) Schematic illustration of the functionalization process for ALN/HA@TPP@TM liposome synthesis and its role in epigenetic remodelling of polarized macrophages in osteoporosis. Blue and black arrows indicate the synthesis pathways and mechanisms; Upward (↑) and downward (↓) arrows denote upregulation/increase and downregulation/decrease, respectively.⁸¹ © Elsevier B.V. 2025. (b) Histological examination of four groups of femur samples stained with HE.⁸¹ © Elsevier B.V. 2025. (c) Schematic diagram illustrating how ED-71 alleviates MAM-mediated mitochondrial Ca²⁺ overload and improves bone aging. (d) Results of calcium fluorescence staining using Rhod2-AM. Red fluorescence (Rhod2-AM) indicates calcium ions (Ca²⁺). (e) TEM observations of mitochondria in aged BMSCs treated with ER. Red triangles indicate mitochondria, and yellow arrows indicate the ER.⁸² © Elsevier B.V. 2026.

On the other hand, mitochondrial calcium is a double-edged sword: whilst low levels of mitochondrial calcium are crucial for maintaining optimal ATP production rates, extreme levels of calcium can exceed the mitochondria’s capacity to retain it—a condition known as calcium overload—which leads to the loss of mitochondrial function.⁹⁶ Consequently, in response to these challenges, Wang et al found that the active vitamin D analogue eldecalcitol (ED-71) can prevent GIOP by inhibiting the senescence of endothelial cells (ECs) and improving angiogenesis and osteogenesis (Figure 3c). Dexamethasone (DEX) induces senescence in H-type vascular ECS by promoting mitochondrial calcium overload (mediated by mitochondrial-associated membranes, (MAMs). ED-71 regulates glucose-regulated protein 75 (GRP75) via the vitamin D receptor (VDR)-protein kinase C (PKC) signaling pathway to regulate glucose-regulated protein 75 (GRP75), thereby reducing MAM-mediated mitochondrial calcium overload and inhibiting ECS senescence (Figure 3d). It significantly restored mitochondrial structure and function (Figure 3e) and re-established the angiogenesis-osteogenesis coupling mechanism, thereby alleviating bone loss.⁸² They have revealed a novel mechanism by which ED-71 alleviates GIOP by maintaining MAM-mediated mitochondrial calcium homeostasis; this therapeutic strategy also offers a unique approach for the future development of Nanobiomaterials targeting mitochondrial biochemical ion homeostasis. However, this study is currently limited to the level of a single drug molecule, and challenges remain in translating the MAM-mediated calcium homeostasis regulation mechanism into a design framework for nanobiomaterials. Furthermore, the risk of hypercalcemia associated with long-term use of vitamin D analogs constitutes a dose-limiting toxicity that must be considered when developing nanodelivery systems based on this pathway.⁹⁷ At the same time, the GIOP model used in this study does not fully reflect the clinical context of human GIOP, which is often accompanied by aging, diabetes, and chronic inflammation. This also represents a significant barrier to its clinical translation.

Homeostatic Regulation of Oxidative Stress

In the vicious cycle induced by oxidative stress, the accumulation of excessive reactive oxygen species (ROS) is the initiating and central mechanism driving mitochondrial dysfunction and cellular damage.⁹⁸ ROS not only directly attacks the lipids, proteins and mtDNA of the mitochondrial inner membrane, causing energy metabolism to break down, but also acts as a destructive signaling molecule, activating multiple pro-inflammatory and pro-apoptotic pathways, ultimately accelerating cellular ageing and even death.^99–101 Consequently, the efficient and specific removal of excess ROS from the affected site is a fundamental strategy for halting the oxidative stress cascade and creating a “therapeutic window” for the restoration of mitochondrial function.

Given that ROS also play a crucial signaling role under physiological conditions, the ideal intervention strategy is not to eliminate them entirely, but rather to achieve precise spatiotemporal regulation.^46,102 This has driven a paradigm shift in research from broad-spectrum antioxidants towards smart, responsive ROS-scavenging materials. The core of the design of such materials lies in identifying and targeting key molecular nodes involved in ROS generation and scavenging; Sirtuin 6 (Sirt6) is one such highly promising target. Wu et al demonstrated that activation of SIRT6 can significantly mitigate ROS-induced damage to chondrocytes by influencing the expression of downstream antioxidant genes and mitochondrial homeostasis. This study not only confirms that SIRT6 is a key target for improving the pathological environment of osteoarthritis (OA), but also provides a direct theoretical basis and a clear molecular pathway for the design of targeted materials aimed at activating SIRT6.¹⁰³ At the metabolic level, Yin et al’s study revealed the mechanism by which the metabolic enzyme CPT1A regulates mitochondrial homeostasis through a unique non-metabolic function. They found that CPT1A promotes the succinylation of the key antioxidant enzyme SOD2 at the lysine residue at position 130. This modification directly enhances the stable accumulation of SOD2 within mitochondria and boosts its enzymatic activity, thereby effectively reducing the production of mtROS, mitigating BMSC senescence and promoting their osteogenic differentiation. When a mutation occurs at this site, this protective effect is reversed, confirming the precision of the CPT1A-SOD2(K130) axis as a potential intervention target.¹⁰⁴

A variety of smart materials that actively intervene in oxidative stress have emerged, and based on their design concepts, they can be classified into two major paradigms: ROS-responsive materials, which utilize ROS as an endogenous trigger signal to achieve on-demand drug release; and ROS-targeted materials, which deliver antioxidant units directly to mitochondria to eliminate excess ROS at the source. The former emphasizes “sensing and response”, while the latter emphasizes “targeted inhibition”. The following sections will evaluate the advantages and limitations of these two paradigms.

Chen et al developed a ROS-responsive hydrogel system containing HA-PBA-coated Ce-ZOL nanocomposites (GHCZ) (Figure 4a). In environments with excessive ROS, the GHCZ hydrogel system continuously releases HA-PBA-coated Ce-ZOL nanoparticles, which, through their significant enzyme-like catalytic effects, scavenge intracellular and extracellular ROS in BMSCs and macrophages; the core mechanism lies in protecting mitochondria from oxidative attack. In vitro experiments demonstrated that the GHCZ hydrogel system converted the polarized phenotype of macrophages into the anti-inflammatory M2 type and suppressed pro-inflammatory cytokines such as IL-1β, IL-6 and TNF-α. Notably, they confirmed that this was achieved through the GHCZ hydrogel system’s potent ROS scavenging efficiency. Concurrently, they found that GHCZ-catalyzed BMSCs exhibited the lowest mitochondrial ROS levels; GHCZ treatment effectively counteracted the negative effects of oxidative stress, restored basal and maximal respiratory rates, and promoted ATP production, thereby enhancing energy supply. Immunofluorescence staining confirmed downregulation of the ageing marker p21, demonstrating that GHCZ revitalized “ageing” BMSCs into “young” BMSCs. In in vivo experiments, using an OVX rat model with femoral condyle defects, new bone tissue clusters were observed in the GHCZ group extending from the periphery to the center of the defect nine weeks post-implantation, with a BV/TV ratio exceeding 40%, significantly higher than in other treatment groups. Concurrently, quantitative osteomorphometric analysis of regenerated bone in Micro-CT images revealed that the BS/TV and Tb.N parameters in the GHCZ group also showed a trend towards increase.⁸³ GHCZ represents a typical design for ROS-responsive hydrogels, whose advantage lies in utilizing ROS in the pathological environment as a release trigger, thereby achieving “sensing-response” closed-loop control. However, an inherent limitation of this design is that as ROS are continuously cleared, the trigger signal itself gradually weakens, which may lead to a decrease in subsequent drug release efficiency—the impact of this “self-attenuation” effect on long-term therapeutic efficacy has not yet been fully evaluated.

Figure 4.

Nanobiomaterials that restore the mitochondrial oxidative microenvironment. (a) Schematic illustration of the mechanism by which ROS-responsive GHCZ hydrogels improve bone regeneration by scavenging ROS. Red box indicates the ROS scavenging mechanism; Upward (↑) and downward (↓) arrows denote upregulation/increase and downregulation/decrease, respectively.⁸³ © The American Chemical Society, 2025. (b) Mechanisms by Which ROS-Responsive FMAG Improves Mitochondrial Function and Reverses Periodontal Aging. Red box indicates ROS response; Black dashed arrows indicate signaling pathways.⁸⁴ © Elsevier B.V. 2025. (c) Schematic illustration of mitochondria-targeted TPG@ChSMA hydrogels, which modulate ROS levels and mitochondrial function in aging cells for skeletal regeneration in the elderly. Red box indicates ROS-targeted polymers; Red arrows indicate the regulating and promoting effects; flat-headed arrows (T-shaped lines) indicate inhibitory effects.⁸⁶ © Elsevier B.V. 2025. (d) Schematic Diagram of the Hydrogel Coating Synthesis Process and Mechanism of Action. Red box indicates ROS responsive properties; Blue arrows indicate the synthesis and therapeutic process. (e) SEM images of Ti-PDA-PCB@CuDHM degradation under different conditions.⁸⁵ © The John Wiley and Sons. 2026.

Chronic periodontitis, a common inflammatory disease closely associated with cellular ageing, is characterized by the accumulation of senescent gingival fibroblasts (Sn-GFs). These cells persistently damage periodontal tissues and bone due to their anti-apoptotic properties, which enable them to evade clearance; the resulting senescent microenvironment (such as the accumulation of reactive oxygen species) propagates secondary senescence in normal cells via mitochondrial dysfunction.¹⁰⁵ To overcome these limitations, Wang et al employed a therapeutic strategy based on immune microenvironment reprogramming. By co-encapsulating non-fenyltetrahydrofuran liposomes (F-Lip) and MnO₂ nanozymes within boronic acid-functionalized GelMA hydrogels, they constructed a ROS-responsive nanoplatform (FMAG) (Figure 4b). F-Lip-induced senescent cell clearance and macrophage phenotypic conversion improved the local immune microenvironment. Utilizing boronic acid ester bonds to achieve ROS-responsive release, the released MnO₂ nanozymes demonstrated potent ROS scavenging activity. In vitro experiments, using MitoSOX Red probes, it was found that the FMAG group exhibited excellent mtROS scavenging efficiency. Furthermore, JC-1 dye was used to assess mitochondrial membrane potential, and MitoTracker Green dye was employed to observe mitochondrial morphology following FMAG treatment, revealing restoration of both mitochondrial membrane potential and morphology. This synergistic structural and functional repair signifies a transition of mitochondria from “energy collapse” to “regenerative steady state”. In an in vivo model of periodontal inflammatory ageing, FMAG demonstrated significant anti-ageing effects, promoting alveolar bone regeneration and collagen deposition. Mechanistic studies confirmed that FMAG disrupts the “ageing–cytokinesis dysfunction–mitochondrial dysfunction” cycle by synergistically reprogramming the ageing microenvironment.⁸⁴ In summary, this condition-responsive nanoplatform will reshape cellular proliferation to reverse periodontal ageing and sustainably improve the microenvironment associated with periodontal ageing, which may offer new insights into the treatment of age-related diseases. Compared to the aforementioned GHCZ system, FMAG integrates the function of senescent cell clearance into a ROS-responsive hydrogel, thereby achieving dual intervention: “removal of senescent cells” and “removal of ROS”. However, this strategy also introduces new complexities: the release kinetics and clearance rates of the two functional modules must be precisely matched. If ROS clearance reaches saturation before senescent cell clearance does, the remaining senescent cells may continue to induce secondary senescence through paracrine effects, partially offsetting the therapeutic effect. A comparison of the two strategies suggests that the enhanced efficacy of ROS-responsive hydrogels may not stem solely from maximizing scavenging efficiency, but rather from the orderly coordination of the functional modules over time.

Building on this foundation, materials design is evolving further towards deep integration with key aspects of tissue regeneration. Taking the ROS-responsive hydrogel-coated titanium implant developed by Cai et al as an example, in addition to achieving the fundamental objectives of ROS scavenging, mitochondrial protection and effectively delaying MSC senescence, it incorporates enhanced angiogenic capabilities (Figure 4d). The copper-dihydromyricetin nanoparticles (CuDHM NPs) loaded onto the implant are released in the presence of excessive ROS to exert an antioxidant effect (Figure 4e), effectively clearing the accumulation of excess intracellular and extracellular ROS, restoring mitochondrial metabolic function, and directly slowing the senescence of mesenchymal stem cells (MSCs), whilst the continuous release of copper ions actively stimulates angiogenesis. This not only resolves the issue of oxidative stress but also fundamentally improves the microenvironment of tissue ischemia and hypoxia by establishing a new blood supply, creating a sustainable virtuous cycle with the restoration of mitochondrial function.⁸⁵ This strategy integrates angiogenesis and antioxidant functions onto the same implant surface, bringing it closer to clinical implantation scenarios than the aforementioned hydrogel system. However, similar to FMAG, this dual-function integration also raises issues of temporal coordination—angiogenesis typically takes several days to several weeks, whereas ROS scavenging takes effect within a few hours. How to coordinate these biological processes, which operate on two different time scales, is a key challenge facing this dual-function design.

It is evident, therefore, that current material development has followed a clear evolutionary trajectory in the field of ROS-responsive materials: progressing from first-generation systems focused on eliminating ROS and restoring basic cellular functions, to intelligent composite systems that integrate regenerative elements—such as vascularization and immune modulation—with antioxidant protection in a synergistic manner. This paradigm shift from “single-target therapy” to “synergistic reconstruction” signifies that mitochondrial-targeted therapies for oxidative stress are entering a new phase characterized by greater systematicity and precision.

Building on the synergy between ROS clearance and tissue repair, research is now moving towards more precise targeting. Compared with traditional organ- or tissue-targeted approaches, directly targeting the subcellular organelles within the lesion—particularly the mitochondria—represents a more fundamental therapeutic strategy.¹⁰⁶ This strategy targets the very “epicenter” of oxidative damage, regulating ROS balance and repairing the cell’s energy powerhouse at the source, thereby more effectively reversing the pathological processes driven by mitochondrial dysfunction. Research by Zhou et al provides strong evidence for this. They developed a composite hydrogel scaffold incorporating tea polyphenol-reduced graphene (Figure 4c). By leveraging TPG’s mitochondrial targeting properties, this scaffold acts directly on the mitochondria of BMSCs, effectively scavenging ROS and inhibiting cellular senescence through the activation of the SIRT1/PI3K/AKT pathway. This direct protection and regulation of mitochondria fundamentally stabilize the cellular state and synergistically activates the ERK1/2 pathway to promote osteogenic differentiation. In an osteoporotic rat model, this scaffold significantly promoted bone regeneration and reduced the expression of ageing biomarkers, demonstrating that targeting mitochondria to correct intrinsic cellular ageing is an effective root-cause strategy for repairing age-related bone defects.⁸⁶ Combining this targeted approach with nano catalytic medicine enables smarter, more multifunctional interventions. Compared with the aforementioned ROS-responsive strategy, this mitochondria-targeting strategy shifts from a “passive response” to “active targeting” and offers a clear advantage in terms of precision at the site of action. However, the degradation pathways and long-term retention of reduced graphene in the body have not yet been fully elucidated, and the potential for physical cellular damage caused by its flake-like structure remains a safety concern worthy of attention.

However, in more complex pathological settings—particularly the microenvironment of bone defects in diabetic patients—more precise therapeutic strategies are required. The pathological diabetic microenvironment is characterized by mitochondrial dysfunction, excessive accumulation of reactive oxygen species (ROS), cellular senescence and chronic inflammation, which impair the body’s innate ability to heal bones.¹⁰⁷ To address these challenges, Deng et al developed a 3D-printed scaffold system incorporating biomimetic nano enzymes. A layered porous scaffold (PBG) comprising carboxyl-functionalized PAEK-COOH and 45S5 bioactive glass (BG) was combined with a hybrid nanozyme composed of SS31-reinforced manganese dioxide (MnO₂)-ferritin biomimetic nanozyme (MF@S nanozyme). In vitro experiments utilizing the specific targeting of mitochondria by the MF@S nano enzyme demonstrated that, under pathological conditions simulating high concentrations of ROS, the MF@S nano enzyme not only exhibited extremely high ROS scavenging efficiency but also inhibited the production of mitochondrial ROS (mtROS), whilst simultaneously restoring the cell migration and angiogenesis capabilities of HMEC-1 cells. Subsequently, under the same conditions, they examined the osteogenic differentiation characteristics of HBMSCs. The MF@S group exhibited the highest ALP activity and the highest expression of osteogenesis-related genes, namely type I collagen A1 (COL1A1) and RUNX2. Furthermore, they discovered that this biomimetic nano enzyme possesses an anti-osteoclast differentiation effect. More notably, they applied the nanozyme to a 3D-printed scaffold system, creating a more comprehensive therapeutic system. In in vivo experiments, they evaluated the effect of the PBG-MF@S scaffold on bone regeneration in a 5-mm critical cranial defect model in diabetic rats. Not only did the PBG-MF@S scaffold treatment group demonstrate the best bone recovery efficiency compared to other groups, but the PBG-MF@S scaffold was also found to possess the strongest immunomodulatory effect.⁸⁷ The bio-inspired nano enzyme 3D-printed scaffold system they developed represents a significant advancement, moving from “clearance” to “suppression at the source”. This profound restoration of mitochondrial function not only revitalizes ageing cells but also systematically regulates the immune microenvironment (macrophage polarization) and bone metabolic balance (osteoblast/osteoclast differentiation), achieving a multi-level therapeutic effect ranging from the repair of individual organelles to the remodeling of the overall tissue microenvironment. The PBG-MF@S system is the most highly integrated example of the aforementioned strategies, combining mitochondrial targeting, nanoenzyme catalysis, 3D-printed scaffolds, and immunomodulation into a single system. The advantage of higher functional integration lies in the potential for multi-target synergistic effects; however, this is accompanied by an increased risk of interference among the various components, and it becomes difficult to trace failures back to a specific module. Furthermore, compared to the relatively simple GHCZ hydrogel mentioned earlier, this system involves a significantly greater number of components and higher manufacturing complexity, posing more pronounced challenges regarding GMP production feasibility and batch quality control.

From targeted delivery of functional scaffolds to targeted catalytic nano enzyme systems, this represents a deepening of the concept of mitochondrial-targeted therapy: specifically, an evolution from “targeting and protecting” to “targeting, regulating and remodeling”. This precise intervention, which directly targets the core of energy metabolism, goes beyond the scope of traditional tissue-targeting approaches—which primarily aim to improve delivery efficiency—and instead directly corrects the fundamental intracellular defects underlying disease development. It thus opens up a highly promising new avenue for the treatment of intractable bone diseases closely associated with ageing and oxidative stress.

Regulation of the Extracellular Environment

Whilst the focus remains on the organelles themselves, modulating the extracellular matrix (ECM) microenvironment in which mitochondria reside has emerged as another key dimension for intervening in oxidative stress and ageing at a systemic level. The ECM not only provides physical support and anchorage for cells, but also serves as a dynamic three-dimensional network that stores bioactive signals and mediates intercellular communication.¹⁰⁸ In particular, the extracellular matrix (ECM) derived from mesenchymal stem cells (MSCs) possesses components and a structure that can directly regulate cells’ antioxidant defense capabilities and metabolic state, thereby influencing mitochondrial function and bone metabolic balance.¹⁰⁹ The reconstruction or utilization of ECM with youthful characteristics through engineering approaches offers a unique microenvironmental strategy for reversing age-related bone defects. The research by Cai et al exemplifies the concept of actively reconstructing functional ECM through materials engineering. They constructed an array of metformin-loaded TiO₂ nanotubes on a titanium substrate and, through layer-by-layer self-assembly using chitosan-catechol and gelatin, ultimately formed a biomimetic, controllable microenvironment on the implant surface (Figure 5a). This system functions through a dual mechanism: firstly, the sustained release of metformin assists in the clearance of excess ROS; secondly, the surface coating mimics and promotes the deposition and reorganization of healthy ECM. Within this artificially optimized ECM microenvironment, the ageing process of MSCs was significantly delayed, manifested by reduced SASP secretion, enhanced PINK1/Parkin-mediated mitochondrial autophagy, and a comprehensive decrease in intracellular and extracellular ROS levels. Ultimately, this favorable microenvironment, created jointly by antioxidant support and ECM reconstruction, successfully guided MSCs towards osteogenic differentiation and demonstrated osteointegration capacity in animal models.⁹⁰

Figure 5.

Nanobiomaterials for restoring mitochondrial function by reestablishing ECM homeostasis. (a) Schematic diagram illustrating the preparation of modified implants and the reconstruction of the ECM to delay cellular senescence and promote osseointegration.⁹⁰ © Elsevier B.V. 2024. (b) Schematic diagram illustrating the preparation of HM@Y-ECM composites and the mechanism underlying the restoration of mitochondrial activity. Black arrows indicate the synthesis and preparation processes; green dashed arrows indicate the therapeutic/rejuvenation pathways; flat-headed arrows (T-shaped lines) indicate inhibitory/suppressive effects; Upward (↑) and downward (↓) arrows denote increase and decrease, respectively. (c) Results of mitochondrial ROS assessment following treatment with HM@Y-ECM composites using dual staining with MitoTracker (green) and MitoSOX (red). (d) Results of ATP5A and COL I staining after treatment with HM@Y-ECM composites.⁹¹ © The John Wiley and Sons. 2025.

Further research has revealed the immense potential of utilizing the natural “youthful” ECM itself as a therapeutic resource. The work of He et al found that, compared with aged-derived ECM (A-ECM), young bone marrow-derived mesenchymal stem cell-derived ECM (Y-ECM) is richer in proteins that support mitochondrial function and redox homeostasis (Figure 5b). Building on this, they innovatively developed a composite biomaterial combining hyaluronic acid methacrylate hydrogel microspheres with Y-ECM (Figure 5b). In vitro experiments involving the co-culture of aged bone marrow mesenchymal stem cells (A-BMMSCs) with Y-ECM revealed a comprehensive restoration of mitochondrial function in A-BMMSCs (Figure 5b). Interestingly, by modifying the extracellular environment, the previously unstable intracellular factor (ROS) was also restored (Figure 5c). This indicates that changes in the extracellular environment can simultaneously improve the intracellular environment. Subsequently, they observed that A-BMMSCs shifted from adipogenic differentiation to osteogenic differentiation, whilst levels of ageing markers in A-BMMSCs also decreased, thereby achieving the goal of reversing ageing. When applied to a bone defect model in aged rats, this material not only provided a physical scaffold but, more importantly, delivered a complete ECM signaling blueprint with youthful characteristics. These natural components derived from the young ECM directly improved the microenvironment of the aged host cells, significantly enhanced mitochondrial function and promoted bone defect healing, (Figure 5d).⁹¹ Compared to the former strategy, the latter approach directly utilizes naturally sourced Y-ECM rather than artificially engineered biomimetic coatings. Its advantage lies in the greater integrity of the ECM components and structure, which theoretically allows for a more comprehensive remodeling of the microenvironment. However, this strategy also faces a significant translational bottleneck: the composition of Y-ECM is highly dependent on the age, health status, and culture conditions of the donor cells, making it difficult to ensure consistency between batches—a stark contrast to the reproducibility of synthetic material systems. Furthermore, there is a lack of long-term evaluation data regarding the immunogenicity risks posed by donor cytokines, exosomes, and even nucleic acid components that may remain in natural ECM, whereas this issue is relatively controllable in artificial ECM systems.

In summary, the research perspective has evolved from “artificial reconstruction of functional ECM” to “direct delivery of natural, youthful ECM”, marking a shift from local material modification to the systematic introduction of biological signals. The common core of these strategies lies in indirectly yet systematically stabilizing the redox state of mitochondria by reshaping the extracellular microenvironment on which cells depend for survival, thereby breaking the vicious cycle between ageing and impaired bone formation. This marks a shift in bone regeneration strategies from targeting the interior of cells (mitochondria) to regulating their external ecosystem (ECM), offering a highly promising integrated solution for restoring the function of “seed” cells by improving the quality of the “soil”.

Structural Improvements: Focusing on the Overall Structure and Internal Components of Mitochondria

Whilst efforts are focused on regulating the external microenvironment of mitochondria, the restoration of their internal structure and functional homeostasis represents a more fundamental and direct therapeutic focus. The maintenance of mitochondrial homeostasis depends on a complex dynamic equilibrium, involving the precise control of key regulatory factors, the fine-tuning of energy metabolism and post-translational modifications, and the integrity of the mitochondrial membrane structure. Disruption of these intrinsic factors constitutes the underlying cause of cellular ageing and dysfunction. Therapeutic strategies targeting these intrinsic factors hold significant potential (Table 3).

Table 3.

A Summary of Representative Nanobiomaterials for Improving Mitochondrial Structure

Materials	Key Design Concepts	Functions and Mechanisms	Results	Reference
Peptide-functionalized nanocomposite hydrogels	Enhancing the expression of respiratory chain complexes	Restore mitochondrial energy metabolism	Repair cartilage damage Slow down the ageing of cartilage cells	[110]
Core-shell electrospinning scaffold	αKG restores the respiratory chain Stent-induced in situ recruitment of VEGF	Delivering αKG to restore mitochondrial energy metabolism	Reduces the expression of age-related genes Accelerates angiogenesis	[111]
Oral hydrogel microsphere system	Drug delivery via the ilio-sacral axis Active bone targeting	E7-Liposomes restore abnormalities in the respiratory chain of aged mitochondria	Significantly improves mitochondrial dysfunction Promotes the regeneration of aged bone tissue	[112]
High-potency chelating agent TAM-2LI-MAM	Improving mitochondrial dysfunction caused by uranium exposure	Enhance the activity of mitochondrial complex I	Improved mitochondrial function partially reversed uranium-induced senescence in BMSCs	[113]
Engineering a tetrahedral framework nucleic acid-based nanomedicine	Inhibited mitochondrial outer membrane permeability	Blocked the downstream activation of the cGAS-STING pathway	Reversing the ageing phenotype of BMSCs and restoring their potential for osteogenic differentiation	[114]
Implantable physical signal converter platform	Converting physical signals into thermal signals Thermal signals stimulate bone regeneration	Inhibiting BAX activation by upregulating HSP70 expression to maintain mitochondrial membrane integrity	Delaying the ageing of BMSCs Promoting bone regeneration in elderly patients with femoral condyle defects	[115]
Engineered lipid/fibre micro-clusters containing ionizable coenzyme Q10	Maintain mitochondrial membrane permeability	Reduce mtDNA leakage, restore the mitochondria-ribosome axis, and enhance mRNA translation	Stabilized the mitochondrial membrane potential of BMSCs enhanced mRNA translation	[116]

Maintaining the Mitochondrial Network and Its Dynamic Equilibrium

Interventions targeting the mitochondrial network and dynamic homeostasis have emerged as key strategies for enhancing the function of bone marrow mesenchymal stem cells and counteracting their senescence. This provides a core theoretical basis and diverse targets for the design of next-generation Nanobiomaterials aimed at regulating cell fate. For example: Research by Krzysztof Marycz et al has revealed that upregulation of the miR-21-5p can significantly enhance the viability of bone marrow mesenchymal stem cells (BMSCs) in an osteoporotic context. The core mechanism lies in the fact that miR-21-5p effectively regulates mitochondrial kinetic equilibrium—that is, it coordinates the processes of mitochondrial fission and fusion—thereby promoting the restoration of “stemness” and functional regeneration in aged, osteoporotic BMSCs.¹¹⁷ In the previous section, we mentioned that abnormalities in the extracellular microenvironment may trigger senescence and a decline in the differentiation capacity of bone marrow-derived mesenchymal stem cells (BMSCs), whilst MSCs are capable of sensing changes in extracellular matrix stiffness and responding by regulating mitochondrial function.^118–121 Zhang et al found that mitochondrial-lysosomal contact (M-L contact) regulates mitochondrial function to maintain cellular homeostasis. They also discovered that MSCs exhibit varying degrees of M-L contact intensity under different substrate stiffness conditions; for instance, enhanced M-L contact under low substrate stiffness accelerates MSC senescence. Consequently, they used the M-L contact inhibitor ML282 to alleviate MSC senescence by restoring the mitochondrial network and function. This offers hope for a mitochondria-centered cellular anti-ageing strategy, particularly in the field of stem cell therapy, and provides new insights for the design of emerging biomaterials.¹²² In contrast, exogenous bioactive substances offer greater potential for application due to factors such as their ease of access; a case in point is royal jelly (RJ), a nutrient produced by worker bees that contains large quantities of proteins beneficial to cell growth and proliferation.¹²³ In their study, Gülsemin Çiçek et al cultured human Wharton’s jelly mesenchymal stem cells (WJ-MSCs) derived from umbilical cord stroma in a medium supplemented with RJ. To their surprise, they observed that, following the addition of RJ to the MSC culture, the number of mitochondria increased after differentiation induction, ageing was reduced, and osteogenic differentiation was enhanced.¹²⁴ This also lays the groundwork for the future efficient utilization of RJ.

Improve the Function of the Mitochondrial Electron Transport Chain

Once the overall homeostasis of the mitochondrial network has been ensured, the focus of intervention shifts to its core functional unit—the electron transport chain. As the energy conversion hub located on the inner mitochondrial membrane, the efficiency of the electron transport chain directly determines the cell’s energy status and metabolic health; its functional decline is the root cause of the energy crisis underlying cellular ageing and bone metabolic disorders.^125–128 Consequently, targeting the improvement of electron transport chain function—with the aim of restoring cellular energy metabolism and synthetic capacity at the “source of energy”—constitutes a core strategy for combating stem cell dysfunction and insufficient bone formation caused by energy deficiency.

Osteoarthritis, an age-related condition driven by mitochondrial dysfunction,^129–133 One of the key features is abnormal mitochondrial energy metabolism. To address this challenge, Zhang et al designed a novel chimeric peptide (MW) by integrating the mitochondrial-protective MOTS-s (a bioactive peptide) with WYRGRL, which targets chondrocytes. The bifunctional chimeric peptide MW was immobilized on GeSe nanosheets and embedded in a multifunctional responsive hydrogel composed of HA-MAL, an MMP13-sensitive peptide and PF127 (HMP), forming a peptide-functionalized nanocomposite hydrogel (MW@GeSe@HMP) (Figure 6a). In vitro experiments revealed that MW@GeSe@HMP significantly increased the expression levels of mitochondrial respiratory chain complexes (Figure 6b), thereby restoring mitochondrial energy metabolism. Subsequently, they confirmed that this system effectively up-regulated the mitochondrial fusion proteins Mfn1 and Mfn2, whilst down-regulating the mitochondrial fission protein Drp1, thereby regulating mitochondrial dynamics (Figure 6b). Scanning electron microscopy (SEM) also confirmed that the material restored overall mitochondrial structural integrity and protected chondrocytes (Figure 6c). In in vivo experiments, MW@GeSe@HMP targeted chondrocytes, not only protecting them but also improving osteoarthritis-associated bone remodeling.¹¹⁰

Figure 6.

Nanobiomaterials for restoring the mitochondrial electron transport chain. (a) Schematic diagram of peptide-functionalized nanocomposite hydrogels for the treatment of osteoarthritis. The red boxes indicate the effects of the materials on the mitochondrial respiratory chain complexes; the blue and purple arrows represent synthetic cascades and targeted delivery; the upward (↑) and downward (↓) arrows indicate upregulation and downregulation, respectively; and the flat-headed arrows (T-shaped lines) indicate inhibition. (b) WB analysis of mitochondrial respiratory chain complex proteins and WB analysis of mitochondrial dynamics proteins. Gapdh: A housekeeping protein (c) TEM images of mitochondria with different morphologies.¹¹⁰ © The John Wiley and Sons. 2025.

At the same time, α-ketoglutarate (α-KG) also plays an unparalleled role in mitochondrial energy metabolism.^134,135 Liu et al developed a core-shell electrospun scaffold (Fn-TA-PFC/PCK), which utilizes three biomimetic strategies,¹¹¹ They utilized tannic acid (TA)-anchored fibronectin (Fn) to recruit endogenous vascular endothelial growth factor (VEGF) in situ to promote angiogenesis, Immunomodulatory factors promote the polarization of macrophages towards the regenerative M2 phenotype and reduce ROS levels, thereby synergizing with α-ketoglutarate (αKG) to preprogramme the mitochondrial metabolism of bone marrow-derived mesenchymal stem cells (BMSCs), promoting energy production. In vitro experiments demonstrated that the scaffold enhanced adenosine triphosphate (ATP) production and effectively captured VEGF. Importantly, α-ketoglutarate (α-KG) within the scaffold reduced the expression of ageing-associated genes, improved the ageing microenvironment, and restored the osteogenic potential of aged BMSCs. Further evaluation in aged mice, ovariectomized (OVX) rats, and SD rats with cranial defects demonstrated that the scaffold possesses potent angiogenic and osteogenic activity. Multiomics analysis attributed this efficacy to activated osteogenic/angiogenic pathways and metabolic reorganization. This multifunctional scaffold heralds a paradigm shift from single-factor delivery to endogenous niche engineering, offering a strategy for the repair of ageing tissues. Compared with the intra-articular local delivery of MW@GeSe@HMP, Fn-TA-PFC/PCK, as an implantable scaffold, also falls under the category of local application; however, the two differ in their mechanisms of action: the former directly supplements exogenous mitochondrial protective peptides to repair the electron transport chain, while the latter indirectly improves energy metabolism by preprogramming endogenous metabolic pathways via α-KG. The advantage of direct repair lies in its clear targeting and rapid onset of action; however, the long-term delivery of exogenous peptides may feedback-inhibit the activation of endogenous protective mechanisms. The advantage of metabolic reprogramming lies in mobilizing the host’s own regulatory networks; however, its effects manifest more slowly, and under pathological conditions of severe metabolic disruption, it remains uncertain whether upstream programming signals can be effectively transmitted to the mitochondrial level.

To improve the efficacy of disease treatment, the development of targeted delivery systems is essential. However, localized drug delivery often requires invasive procedures; the gut-bone axis offers a solution to this problem and is also a key focus in osteoporosis treatment for inhibiting bone loss.¹³⁶ Luo et al therefore utilized the gut-bone axis as a promising therapeutic target for osteoporosis. By employing gas microfluidics and ion-crosslinking technology, they developed an oral hydrogel microsphere system (E7-Lipo@Alg/Cs) to deliver the drug to bone marrow mesenchymal stem cells (BMSCs) via the gut-bone axis, thereby modulating mitochondrial senescence. In vitro experiments demonstrated that E7-Lipo@Alg/Cs restored abnormalities in the respiratory chain of aged mitochondria, as evidenced by measurements of ATP levels and the NAD+/NADH ratio. Additionally, RNA-seq analysis indicated activation of the AMPK-SIRT1 pathway, which reversed mitochondrial senescence in BMSCs and promoted the regeneration of aged bone tissue.¹¹² Evidence from multiple sources confirms that this targeted recovery strategy holds great promise and offers significant clinical potential for the treatment of osteoporosis. E7-Lipo@Alg/Cs represents an oral delivery strategy for repairing the electron transport chain, and its non-invasive advantage is clear. However, compared with the other two topical strategies, oral delivery faces multiple attenuation factors—including the intestinal absorption barrier, first-pass effect in the liver, and dilution in the systemic circulation—and the dose fraction ultimately reaching the bone marrow remains unclear. Furthermore, regulation of the gut-bone axis is highly dependent on the composition and function of the gut microbiome, which varies significantly among individuals and is influenced by multiple factors such as diet, age, and medication use. This source of variability may lead to substantial interindividual fluctuations in therapeutic efficacy under the same treatment regimen. This limitation does not pose a major issue in topical delivery strategies.

Unlike the aforementioned strategies that indirectly regulate mitochondrial function through bioactive factors or metabolites, photobiomodulation therapy (PBMT) offers a more direct physical intervention. PBMT primarily utilizes low-energy visible to near-infrared light (typically 600–1000 nm) to directly target and activate the key enzyme in the electron transport chain—cytochrome c oxidase (CCO), also known as Complex IV.^137,138 As the rate-limiting enzyme at the end of the mitochondrial respiratory chain, CCO’s absorption of photons promotes a conformational change in its catalytic center, accelerating electron transfer and thereby directly driving oxidative phosphorylation at the “energy source”, which increases the efficiency of adenosine triphosphate (ATP) synthesis. This non-invasive strategy has demonstrated unique potential for reversing mitochondrial senescence in stem cells and restoring the regenerative capacity of aged bone tissue.¹³⁹ Eroglu et al’s study precisely corroborated this concept; they found that irradiating aged mouse bone marrow mesenchymal stem cells (BMSCs) with near-infrared light at 3 J/cm² significantly restored their mitochondrial function and reversed multiple markers of aging. Crucially, through three consecutive, spaced-out irradiation sessions, this “rejuvenation” effect was sustainably maintained in aged stem cells, offering a new approach to addressing functional deficits in autologous stem cell transplantation for elderly individuals.¹⁴⁰ Furthermore, Li et al’s study revealed the underlying mechanisms by which PBMT promotes osteogenic differentiation. They confirmed that irradiation with 650-nm red LED light activates the autophagy pathway in BMSCs derived from osteoporotic rats (OP-BMSCs), thereby significantly enhancing their alkaline phosphatase activity and mineralization capacity, and upregulating the expression of key osteogenic transcription factors such as Runx-2 and OCN; however, once autophagy is inhibited, the osteogenic effects of PBMT are significantly reversed. This indicates that PBMT’s activation of mitochondrial CCO not only reignites the cell’s “energy engine” but also coordinates broader cellular repair processes by regulating mitochondrial dynamics-related processes such as reactive oxygen species (ROS) signaling and autophagy.¹⁴¹ Therefore, as a non-invasive, non-pharmacological strategy for “light-activated” mitochondrial regulation, PBMT opens up a new pathway with great potential for clinical translation in the treatment of osteoporosis by targeting energy metabolism disorders.

Stabilizing the Mitochondrial Membrane

The integrity of the mitochondrial membrane structure directly determines the functional state of the organelle and the cell’s fate.¹⁴² The mitochondrial membrane serves not only as a platform for the anchoring of electron transport chain complexes and energy conversion, but also as a critical barrier for regulating ion balance, metabolite exchange, and the release of apoptotic signals.¹⁴³ During the process of bone aging, factors such as oxidative stress, calcium overload, and lipid peroxidation often lead to increased mitochondrial membrane permeability, resulting in the dissipation of the membrane potential, impaired ATP synthesis, and even apoptosis, ultimately accelerating the degeneration of bone tissue.^30,144 Consequently, targeted repair or stabilization of mitochondrial membrane structure has become one of the key strategies for intervening in skeletal ageing. To address this need, Huang et al developed an implantable physical signal transducer platform: this platform utilizes composite nanoparticles (dopamine-coated gold nanorods [PDA@GNRs]) as its core, which possess highly efficient ultrasonic-to-thermal conversion capabilities, and is coupled with a gel methacrylate (GelMA) hydrogel microsphere carrier (GMPG) via microfluidic technology (Figure 7a). In vitro experiments revealed, via high-resolution structural imaging microscopy (HISSIM), the colocalization of cytochrome c (cyt c) and TOM20 in the GMPG/US group, significantly reducing cyt c efflux and confirming that ageing cells exhibit enhanced mitochondrial membrane permeability (Figure 7c). Subsequent SEM analysis also confirmed that it effectively maintained the intact mitochondrial network structure in aged BMSCs (Figure 7b). They subsequently found that this platform acts by increasing HSP70 expression, thereby inhibiting BAX activation and maintaining mitochondrial membrane permeability. Subsequent TOM20 labelling revealed that DNA-like substances were primarily localized to mitochondria and the nucleus, confirming that HSP70 mitigates mitochondrial DNA leakage. Western blot analysis of cyclin proteins, inflammation-related pathways and key osteogenesis markers demonstrated that HSP70 exerts an inhibitory effect on the cGAS-STING pathway (Figure 7d). In in vivo experiments, using an aged rat femoral condyle bone defect model, rats implanted with GMPG exhibited significantly lower ROS levels at the bone defect site following ultrasound stimulation compared to other groups. The bone defect region recovered, with the GMPG/US group demonstrating the best bone repair outcome.¹¹⁵

Figure 7.

Nanobiomaterials for Treating Age-Related Bone Diseases by Stabilizing Mitochondrial Membranes. (a) Schematic illustration of how GelMA microspheres integrated with dopamine-coated gold nanorods (GMPG) promote the regeneration of aged bone by improving mitochondrial membrane permeability. (b) Detection of mitochondria in BMSCs using transmission electron microscopy. (c) High-resolution structural imaging microscopy (SIM) images showing cytochrome c (green) and TOM20 (red). (d) Western blot analysis of HSP70, VDAC, and BAX6A7 in young and aged BMSCs following heat stimulation.¹¹⁵ © The John Wiley and Sons. 2025. (e) Mechanism by which ionizable coenzyme-engineered lipid/fiber microwave clusters enhance mRNA translation in aging cells. Red box indicates the mRNA release process; Upward (↑) and downward (↓) arrows denote upregulation/increase and downregulation/decrease, respectively.¹¹⁶ © The John Wiley and Sons. 2025.

Similarly, as part of a strategy to stabilize the mitochondrial membrane, Ling et al developed ionizable coenzyme Q10 (iCoQ10)-engineered lipid-fibril nanostructures (iCLNP@SF) to restore the mitochondrial-ribosomal axis and enhance mRNA translation. In vitro therapeutic evaluations demonstrated that iCLNP@SF synergistically enhanced mitochondrial metabolism and mRNA translation in senescent cells. Further mechanistic studies revealed that iCLNP enhances translational capacity by stabilizing mitochondrial membrane structure, reducing mtDNA leakage, inhibiting cGAS-STING activation, and decreasing eIF2α phosphorylation. In in vivo experiments, iCLNP@SF delivery of Runx2 mRNA resulted in new bone formation (BV/TV) of approximately 40% in the defective model, a result significantly superior to that of conventional LNPs (Figure 7e).¹¹⁶

However, strategies to stabilize mitochondrial membrane structure face a core challenge: how to strike a balance between protecting membrane integrity and maintaining the permeability necessary for mPTP. Excessive stabilization may inhibit quality control mechanisms such as mitochondrial autophagy. Furthermore, the GMPG/US platform relies on ultrasound triggering, but ultrasound penetration efficiency varies significantly across different bone densities and soft tissue thicknesses, making clinical standardization difficult. Furthermore, the iCLNP@SF system reduces inflammation by inhibiting the cGAS-STING pathway; however, since this pathway is involved in antiviral and tumor immune surveillance, the potential long-term effects of its inhibition on immune function in elderly patients remain unclear. Additionally, as it has only been validated in rodent models to date, there is still a considerable distance to clinical translation.

In summary, repair strategies targeting intrinsic mitochondrial dysfunction require systematic intervention across three dimensions: network dynamics, the energy core, and structural integrity. By regulating mitochondrial fission and fusion, specifically restoring the function of the electron transport chain, and stabilizing mitochondrial membrane structure, it is possible to effectively reverse energy metabolism disorders, inhibit inflammatory pathways triggered by mtDNA leakage, and restore stem cell function and tissue regenerative capacity at their source. These strategies shift the focus from “single-target intervention” to “multidimensional endogenous homeostasis restoration”. This not only provides innovative treatment approaches for age-related bone diseases such as osteoporosis and osteoarthritis by addressing the “source of energy”, but also lays a solid theoretical and experimental foundation for the future development of tissue regeneration materials with greater potential for clinical translation.

Transfer Therapy: Mitochondrial Transfer

In the cutting-edge field of medicine, the treatment of intractable diseases is entering a new phase characterized by more precise organelle transplantation.^145–147 In particular, mitochondrial transfer—a revolutionary strategy—opens up entirely new therapeutic prospects for reversing age-related bone diseases caused by mitochondrial dysfunction, either by directly supplementing healthy mitochondria or by promoting their intercellular transfer.^79,148–150 Ding et al found that osteocytes transfer mitochondria to bone marrow cells, and that impaired mitochondrial transfer by osteocytes alters glutathione metabolism, thereby protecting cells of the osteoclast lineage from the deleterious effects of iron and promoting osteoclast activity.¹⁴⁹ In subsequent experiments, they found that mitochondria transferred from osteoblasts to osteoclasts play a role in regulating glucocorticoid-induced osteoporosis, and that glutathione depletion can alleviate the progression of glucocorticoid-induced osteoporosis. Consequently, the application of mitochondrial transfer strategies holds great promise.

Direct mitochondrial transplantation has also been shown to effectively enhance stem cell function. Deng et al were the first to investigate the extraction of mitochondria from donor BMSCs and their transfer into isogenic recipient BMSCs. The results indicate that this artificial transplantation significantly enhances the proliferation, migration capacity and osteogenic differentiation potential of recipient cells, with the effects being dependent on increased OXPHOS activity and ATP production. In animal models, BMSCs that received mitochondrial transplantation promoted more significant new bone formation, confirming the feasibility and potential of this strategy in optimizing stem cell therapies and repairing bone defects.¹⁵¹ The biological basis for this strategy stems from the physiological phenomenon of mitochondrial transfer that occurs within living organisms. Similarly, the mechanistic studies conducted by Gao et al provide valuable insights into this process: they found that stressed osteocytes release adenosine diphosphate (ADP), which triggers healthy osteocytes to donate mitochondria to them via P2Y2/P2Y6 receptor signaling, thereby restoring energy metabolism and alleviating oxidative stress.¹⁵² Importantly, ageing bone cells release more ADP due to impaired mitochondrial membrane integrity, thereby driving this “rescue” process more vigorously, revealing that intercellular mitochondrial transfer is an intrinsic regulatory mechanism for maintaining bone tissue homeostasis. This strategy demonstrates universal therapeutic potential across different types of stem cells. For example, in the field of periodontal regeneration, Gong et al found that mitochondrial supplementation in aged human periodontal ligament stem cells effectively restores their mitochondrial function and osteogenic capacity by upregulating the AKAP1 protein and activating the cAMP/PKA signaling pathway, thereby promoting the repair of bone defects in vivo.¹⁵³ To date, numerous biomaterials centered on mitochondrial transfer strategies have already been developed, Table 4.

Table 4.

A Summary of Representative Nanobiomaterials That Promote Mitochondrial Transfer

Materials	Key Design Concepts	Mechanism and Functionality	Results	Reference
MTBG	Directly promotes mitochondrial transfer	MTBG promotes the formation of tunnel nanotubes	Improve mitochondrial function Promote the regeneration of aged bone	[154]
Autophagic cerium-based nanosystems	Promoting mitochondrial transfer between different cell types	Promoting the mitochondrial transfer of S-BMDM to S-BMSC	Slowed the aging of S-BMSCs Altered the immune microenvironment Promoted the regeneration of bone defects	[155]
Functionalized Fe3O4 nanoparticles	Restore mitochondrial function in donor cells Promote mitochondrial transfer	Integrating high-quality mitochondria into aged BMSCs	Coordinates intercellular communication Improves the immune microenvironment Significantly promotes bone regeneration	[156]
Artificial cell microspheres containing mitochondria from fetal mouse mesenchymal stem cells	Artificial mitochondrial implantation	Transferring young mitochondria into aged BMSCs	Mitigating the aging of aged BMSCs Significantly improving fracture healing in the elderly	[157]
CXCR4-engineered macrophages carrying mitochondria functionalized with nanozymes	Live Mitochondrial Delivery System	Transfer of functional mitochondria to BMSCs via intercellular communication	Restore bone metabolism Improving the senescence of BMSCs	[158]

Smart biomaterials have become powerful tools for inducing and promoting mitochondrial translocation. Xiong et al developed mesoporous bioactive glass microspheres (MTBG) loaded with melatonin (Figure 8a). They first demonstrated that MTBG, through the sustained release of melatonin and bioactive ions, directly scavenges ROS, stabilizes mitochondrial membrane potential, and promotes the formation of aged skeletons. More crucially, MTBG promoted the formation of tunnel nanotubes. In vitro experiments revealed characteristic actin-tunnel nanotube (TNT) structures between cells, with longer TNT lengths observed in aged and MTBG-treated aged cells (Figure 8b). Subsequently, they co-cultured cells labelled with MitoTracker Red with cells labelled with CFDA-SE in a 1:1 ratio; MitoTracker Red-labelled mitochondria were observed in the CFDA-SE-labelled cells, confirming the occurrence of mitochondrial transfer. Results from Western blotting and immunofluorescence showed that mitochondrial Rho-GTPase 1 (Miro1), a key regulator of mitochondrial transfer, was significantly up-regulated in the MTBG group, indicating enhanced mitochondrial transfer (Figure 8c). In vivo results further demonstrated that the number of Miro1- and PGC1α-positive cells in the newly formed bone sites of the MTBG group was significantly higher than in the other groups, indicating an increase in the incidence of mitochondrial transfer and biogenesis.¹⁵⁴

Figure 8.

Nanobiomaterials that promote mitochondrial transfer. (a) Schematic diagram illustrating the mechanism by which melatonin-loaded bioactive microspheres (MTBG) promote intercellular mitochondrial transfer to accelerate the regeneration of aged bone. Red box indicates the mitochondrial transfer process. (b) Confocal image of a double stain with phalloidin (green) and MitoTracker Red (red). The red arrows indicate tunnel nanotubes (TNT). (c) Immunofluorescence images of femoral bone samples showing double staining for Miro1 and PGC1α. The bottom row shows magnified views of the white boxes in the top row; white triangular arrows indicate cells where the two markers colocalize. Abbreviation: New Bone.¹⁵⁴ © Elsevier B.V. 2024. (d) Confocal microscopy images of representative S-BMDMs and S-BMSCs incubated for 24 hours in the TW culture system. S-BMSCs were stained with Mitotracker Green (green), S-BMDMs were stained with Mitotracker Deep Red (red), and cell nuclei were stained with Hoechst 33342 (blue). (e) KGM-PEG-SPIONs enhance skeletal regeneration in the elderly through M2-like mitochondrial transfer, thereby restoring the immune-metabolic-stem cell axis. Red boxes indicate the Autophagy and Fe-S Clusters steps.¹⁵⁶ © Elsevier B.V. 2025.

Similarly, the use of biomaterials to facilitate mitochondrial transfer between different cell types has also emerged as a new strategy. In addition to considering the transfer channels established between cells,^159–161 Mitochondrial transfer between different cell types also faces another major challenge: in the context of ageing, where donor mitochondria exhibit functional defects and poor compatibility with the recipient, its efficacy is rather limited.^162–164 Consequently, efforts must be focused on controlling the quality of donor mitochondria. As mentioned earlier, we have outlined several methods for restoring mitochondrial dysfunction; therefore, combining these mitochondrial quality control strategies with mitochondrial transfer strategies could represent a highly promising approach to biomaterial development. For example, Wu et al designed a cerium-based Nano system for the in situ treatment of senescent macrophages. By activating the SIRT1-PGC-1α axis, to activate mitochondrial autophagy in senescent bone marrow-derived macrophages (S-BMDMs), thereby promoting the macrophages’ own mitochondrial biogenesis, improving the mitochondrial quality of the donor cells, and significantly enhancing mitochondrial transfer to surrounding senescent BMSCs. This, in turn, alleviates mitochondrial dysfunction in BMSCs, thereby improving the entire bone microenvironment and synergistically promoting bone regeneration, (Figure 8e). However, when using S-BMDMs as mitochondrial donors, one must consider the fact that, within the microenvironment of aged bone, S-BMDMs typically polarize towards the M1 pro-inflammatory phenotype,^165–167 Consequently, the quality of mitochondrial donors is compromised under these conditions. To address this challenge, Sun et al designed a more stringent quality control system for mitochondrial donors, developing a functionalized Fe₃O₄ nanoparticle—KGM-PEG-SPIONs. By activating autophagy and the biosynthesis of Fe–S clusters via the PGC-1α-NRF1-TFAM transcriptional pathway, these nanoparticles enhance the quality of donor mitochondria, promote M2 macrophage polarization, and improve compatibility with the oxidative and inflammatory environment of aged BMSCs. Having confirmed the restoration of mitochondrial quality in macrophages, they then utilized a Transwell non-contact co-culture system and found that S-BMDMs treated with KGM-PEG-SPIONs exhibited higher mitochondrial transfer efficiency than untreated aged and young control groups, (Figure 8d). To assess in vivo relevance, Mito Tracker™ Deep Red-labelled S-BMSCs were pre-treated with KGM-PEG-SPIONs and administered intravenously to aged rats. Flow cytometry analysis revealed a significant increase in red fluorescence in CD90+/CD44+ S-BMSCs, with a mitochondrial transfer efficiency approximately three times that of the untreated group, confirming the efficacy of in vivo mitochondrial transfer from macrophages to stem cells. Subsequently, they observed that M2-like mitochondria (referring to a context-dependent mitochondrial state shaped by the metabolic and immunological environment of M2-polarised macrophages) significantly reduced the accumulation of intracellular ROS in S-BMSCs, outperforming mitochondria derived from M0 and M1 macrophages, thereby confirming the critical role of mitochondrial donor quality. More crucially, they discovered that M2-like mitochondria help reawaken osteogenic potential by regulating Ca²⁺ flux. At the same time, they found that these high-quality mitochondria may integrate into S-BMSCs via Cx43-associated gap junctions. In vivo experiments further demonstrated that the KGM-PEG-SPIONs-BCP scaffold modulates the local immune environment via M2 macrophage polarization, reducing age-related signaling pathways and enhancing mitochondrial activation and potential organelle transfer. These immunometabolism effects facilitated the functional recovery of aged BMSCs and promoted robust structural and compositional regeneration of osteoporotic bone defects in an aged animal model.¹⁵⁶

Building on the potential of previous artificial mitochondrial transplantation, Nie et al constructed artificial cell microspheres (Fmito@ACs) containing mitochondria from fetal mouse mesenchymal stem cells as an efficient mitochondrial-targeted delivery system. Fmito@ACs fully leverage the anti-aging effects of young mitochondria. By artificially implanting young mitochondria and transferring them into aged BMSCs, they demonstrate potent mitochondrial protection, mitigate aging in aged BMSCs, and promote osteogenesis by enhancing mitochondrial fusion and aerobic glycolysis. In a model of fractures in the elderly, Fmito@ACs demonstrated targeted accumulation and biosafety, significantly improving bone healing. Transcriptomic sequencing revealed that Fmito@ACs enhance fracture healing in aged mice through a coordinated regulatory mechanism, boosting local energy metabolism, improving hypoxic adaptation, reducing inflammation in the bone marrow niche.¹⁵⁷

Although mitochondrial transfer strategies hold great promise, their clinical translation still faces fundamental challenges. First, there are no uniform standards for the sourcing and quality control of donor mitochondria: the yield of autologous mitochondria is limited, allogeneic sources carry a risk of immune rejection, embryonic sources are subject to ethical restrictions, and there are no universally accepted testing standards for key indicators. Second, current transfer efficiency is relatively low (5–30%), and there is a lack of ultrastructural evidence supporting functional integration. Third, the long-term safety of introducing exogenous mitochondrial DNA (mtDNA) remains unclear, and mitochondrial transfer within the tumor microenvironment may promote cancer cell metabolism, posing a potential risk to elderly patients at risk for cancer. Fourth, the extraction and purification processes rely primarily on manual procedures; the activity of the isolated mitochondria can only be maintained for a few hours.^168,169 Overall, this strategy remains in the preclinical stage, and priority must be given to addressing key bottlenecks such as donor standardization, improving transfer efficiency, and evaluating long-term safety.

In summary, mitochondrial transfer strategies—whether through direct transplantation, stimulation of endogenous transfer, or material-mediated approaches—represent a conceptual shift in bone regenerative medicine, moving from “cell replacement” to “repairing the cell’s core energy unit”. By targeting the fundamental energy deficits underlying cellular ageing, these strategies provide a highly innovative and promising toolkit for the treatment of age-related bone diseases.

Challenges and Prospects

Although mitochondria-based nanobiomaterials have opened up new avenues for the treatment of age-related bone diseases, their clinical translation still faces multiple challenges.

In terms of the maturity of therapeutic strategies, the four treatment pathways have formed a distinct hierarchical differentiation, which dictates differentiated advancement strategies. Optimization of the mitochondrial microenvironment—particularly strategies for reactive oxygen species (ROS) scavenging—has the most extensive research foundation and a relatively mature basis for translation. Strategies to enhance mitochondrial autophagy rank second; although a complete technological chain from drug delivery to functional materials has been established, evidence of long-term safety remains insufficient, constituting the primary obstacle to their advancement into clinical practice. Structural repair strategies largely remain at the stage of target identification and mechanism elucidation; they lack precision in intervention and carry a clear risk of off-target effects. Mitochondrial transfer strategies are the most innovative; however, fundamental bottlenecks exist in donor standardization, transfer efficiency, and long-term safety, placing them furthest from clinical application.

Regarding specific translational limitations, the following issues require attention. First, targeting efficiency and safety. The targeting efficiency of existing systems for mitochondrial delivery is generally less than 10%; non-targeted materials often accumulate in organs such as the liver and spleen, and the lack of long-term biosafety data makes it difficult to assess the consequences of this accumulation. Second, scalability and standardization. Most material systems rely on precisely controlled laboratory synthesis conditions, and the in vitro activity of mitochondria can only be maintained for a few hours; GMP-level production capacity and quality control systems have not yet been established. Third, model limitations. Nearly all existing evidence comes from induced aging models in rodents, which differ fundamentally from humans in skeletal structure, immune function, and metabolic characteristics; therefore, extrapolating efficacy conclusions from animal experiments to humans requires caution. Fourth, the regulatory pathway. In regulatory practice, multi-component smart materials are often classified as combination products; the complexity and cost of their commercialization pathway are far higher than those of single drugs or medical devices, and this regulatory factor increases the uncertainty of commercialization.

Resolving the aforementioned bottlenecks ultimately hinges on the spatiotemporal coordination of these four strategies. At the mechanistic level, the four strategies are complementary: enhanced autophagy improves the quality of donor mitochondria to enhance the efficacy of transfer therapy; microenvironment optimization creates conditions for structural repair; and structural integrity is a prerequisite for both autophagy and metabolic homeostasis. However, at the material design level, this complementarity translates into mutual constraints: the requirements of different strategies regarding release kinetics, targeting specificity, and degradation cycles are inconsistent and may even conflict with one another. Therefore, moving beyond the optimization framework of individual strategies to construct integrated material systems capable of multimodal regulation and sequential synergy is a key direction for advancing this field.

Conclusions

This review systematically summarizes the latest advances in the treatment of age-related bone diseases using mitochondria-based nanobiomaterials. Focusing on mitochondrial dysfunction as the core mechanism, this paper outlines four major therapeutic strategies: enhancing mitochondrial autophagy, optimizing the microenvironment, repairing structural components, and implementing mitochondrial transfer. Compared with other treatments for age-related bone diseases, these mitochondria-targeted strategies elevate the level of intervention from the cellular to the organellar level, directly addressing the energy metabolism imbalance at the core of the disease and opening new avenues for the development of novel biomaterials. These four strategies are not isolated from one another but form a synergistic network: enhancing autophagy improves the quality of graft donors; optimizing the microenvironment creates conditions for structural repair; and structural integrity, in turn, supports metabolic homeostasis. Therefore, the organic integration of these four strategies into a single biomaterial system is a key direction for achieving more effective treatment. With the deep integration of materials science, cell biology, and regenerative medicine, precision interventions based on mitochondria are expected to move from the mechanistic validation stage toward clinical application, thereby establishing a new paradigm for the treatment of age-related bone diseases.

Funding Statement

This work was supported by National Natural Science Foundation of China (82470959), Research Project Supported by Shanxi Scholarship Council of China (2024-076), the Key Open Project of the National Key Laboratory for Oral Disease Prevention and Treatment (SKLOD2025OF07), Fundamental Research Program of Shanxi Province, No. 202303021222384 and Open Research Project of the Municipal-Provincial Jointly Established Cultivation Base for the Shanxi Provincial Key Laboratory of Oral and Maxillofacial Prosthodontics, Reconstruction, and Regeneration (2025-010).

Abbreviations

ATP, adenosine triphosphate; ROS, reactive oxygen species; BMSCs, bone marrow mesenchymal stem cells; mtROS, mitochondrial reactive oxygen species; cGAS-STING, cyclic GMP-AMP synthase-Stimulator of interferon genes; ETC, electron transport chain; DRP1, dynamin-related protein 1; Cur-Lip, curcumin liposomes; MSCs, mesenchymal stem cells; mtΔψm, mitochondrial membrane potential; D-gal, D-galactose; EM-eNM, energy metabolism-engaged nanomedicine; Poly-p, polyphosphate; HSP60, mitochondrial chaperone protein; LAMP1, lysosome-associated membrane protein 1; ATP5B, β-subunit of the F1-ATP synthase complex; EVs, extracellular vehicles; CDSS6, a bone-targeting peptide; T2DM, type 2 diabetes mellitus; NIR, near-infrared; TPP, triphenyl phosphonium cation; ALN/HA@TPP@TM Lipo, alendronate/hyaluronic acid shell@ triphenyl phosphonium cation @ Tetrathiomolybdate-loaded liposomes; ED-71, vitamin D analogue eldecalcitol; MAMs, mitochondrial-associated membranes; GRP75, glucose-regulated protein 75; VDR, vitamin D receptor; PKC, protein kinase C; GHCZ, containing HA-PBA-coated Ce-ZOL nanocomposites; Sn-GFs, senescent gingival fibroblasts; FMAG, co-encapsulating non-fenyltetrahydrofuran liposomes and MnO₂ nanozymes within boronic acid-functionalized GelMA hydrogels; CuDHM NPs, copper-dihydromyricetin nanoparticles; TPG@ChSMA, tea polyphenol-reduced graphene@Chondroitin Sulfate Methacryloy; PBG-MF@S, PAEK-COOH/45S5 bioactive glass-MnO₂-ferritin nanozyme@ SS31; HM@Y-ECM, hyaluronic acid methacrylate hydrogel @Y-ECM; Y-ECM, young bone marrow-derived mesenchymal stem cell-derived ECM; TNT@Met-LBL, TiO₂ nanotubes @ Metformin-loaded-layer-by-layer; RJ, royal jelly; MW@GeSe@HMP, MOTS-c/WYRGRL chimeric@ GeSe nanosheets@ HA-MAL/MMP13-sensitive peptide/PF127 responsive hydrogel; Fn-TA-PFC/PCK, Tannic acid-anchored fibronectin and α-ketoglutarate-loaded core-shell electrospun scaffold with immunomodulatory factors; E7-Lipo@Alg/Cs, E7 peptide-modified bone-targeted liposomes@ alginate/chitosan pH-responsive hydrogel microspheres; iCLNP@SF, ionizable coenzyme Q10 lipid nanoparticles-engineered lipid@fiber microplexes system; MTBG, mesoporous bioactive glass microspheres loaded with melatonin; Miro1, mitochondrial Rho-GTPase 1; CNS, cerium-based Nano system; KGM-PEG-SPIONs, functionalized Fe₃O₄ nanoparticle; Fmito@ACs, Mitochondria from fetal mouse mesenchymal stem cells encapsulated in artificial cell microspheres; Gapdh, Glyceraldehyde-3-phosphate dehydrogenase.

Data Sharing Statement

No data were used for the research described in the article.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing financial interests or personal relationships that could have influenced the work reported in this paper.