Living Nanofiber-Enabled Cardiac Patches for Myocardial Injury

Central Illustration

Highlights

• •Adverse cardiac remodeling following myocardial infarction is a leading cause of morbidity and mortality worldwide.
• •Several impediments exist with current cell therapy approaches to repair damaged myocardium following injury, highlighting the need for alternative approaches.
• •This review highlights a promising new approach of using biomaterial electrospun nanofiber patches for promoting tissue regeneration.

Summary

Because the adult heart has only minimal regenerative capacity, its inability to induce regeneration is well-known in patients with myocardial infarction. However, based on multidisciplinary approaches, it is possible to restore myocardial capability with regenerative medicine via living cardiac patches seeded with therapeutic ingredients ranging from multiple cell types to bioactive molecules, including growth factors, microRNA, and extracellular vesicles to the affected site. Biomaterials, natural and/or synthesized polymers, or in vivo sources such as collagen, fibrin, and decellularized extracellular matrix are used to form these cardiac patches. Herein, we review various techniques where seeded cells and bioactive agents are incorporated within porous nanofibers to create functional cardiac patches that provide myocardial extracellular matrix–like features, mechanical support, and a large surface-to-volume ratio for promoting cellular metabolism as well as compensation for the loss of cardiomyocytes in the infarcted region. We summarize recent advances through electrospinning-generated nanofibers of synthetic and/or natural polymers combined with biological material to create cardiac patches to repair and improve the function of infarcted myocardium. As tailoring designs on cardiac patches have been shown to exhibit deformation mechanisms and enhanced myocardial tissue regeneration, significant roles of various patterns and associated parameters are also discussed. The enhanced delivery of therapeutics offered by tailored nanofiber cardiac patches to treat myocardial infarction and overcome challenges of existing cardiac regeneration therapies such as low stability, short half-lifetime, and delivery methods may promote the potential for their clinical impact on myocardial regeneration.

Myocardial infarction (MI) is a consequence of the lack of oxygen and nutrients supply in the myocardium. It is usually associated with collagen fiber proliferation and scar tissue formation, which block electrical pulse signals in the infarcted area. It is well known that infract area thinning occurs in patients who survive MI, and almost 20% of the heart muscle is damaged if MI lasts 6 to 30 minutes. As a result, a sufficient number of cardiomyocytes undergo apoptosis or necrosis during the occurrence of cardiac remodeling. Because cardiomyocytes lose their regenerative potential early after birth in mammals, restoring myocardial structure and function in MI is the primary obstacle. Additionally, the nonmyocyte population of the heart contributes toward the effective functioning of the myocardium because of the involvement of the cardiac extracellular matrix (ECM) in the remodeling of the infarcted heart and myocardial stiffness. It is known that structural and biochemical remodeling of the heart occurs with enhanced collagen gene expression in cardiac fibroblasts. The hostile environment during the development of MI is unfavorable for natural repair and regenerative mechanisms, affecting the ejection fraction and loss of contractility in the infarcted area, eventually leading to arrhythmias, cardiac damage, and heart failure.1, 2, 3, 4, 5 The prevalence of MI in subjects <60 and >60 years of age has been reported to be 3.8% and 9.5%, respectively. Because the mortality and morbidity rates in MI-induced heart failure are high, heart transplantation in MI patients is a challenging proposition due to limited availability of donor organ supply and high risk of organ rejection.^6,7

Active proliferation of cardiomyocytes and nonmyocyte cells occurs during cardiac development but such a mechanism in the adult heart seems to be impaired. However, some investigators have shown the ability of adult cardiomyocytes to proliferate, whereas others have provided evidence regarding the involvement of stem cells in myocardial regeneration after severe cardiac injury.8, 9, 10 The capability of the heart to regenerate myocardial tissue has also been reported under different conditions, including MI.^11,12 A cardiac patch made of biomaterials and biological materials or cell-seeded materials has been used for myocardial regeneration and treatment of MI (Figure 1). Such a patch is implanted onto the surface of the infarcted region of the heart by glue and suture or using a suture-free procedure to renew ischemic cells and repair infarcted myocardium to recover normal function.^13,14 The native myocardium is anisotropic, consisting of aligned cardiomyocytes at an angle of <45° and aligned capillaries organized in the direction of muscle fibers to fulfil interstitial oxygen and nutrient diffusion requirements for cell metabolism. Thus, wrapping the myocardium by mural cells ensures sufficient support for substrate transport and blood flow.¹⁵ Because the myocardium has an interwoven architecture in which coiled perimysial fibers offer the mechanical qualities for effective cardiac muscle contraction by expanding and recoiling the fibers, electrospun nanofiber cardiac patches preserve the biomimetic nanofibrous topography and provide a biological niche for activities of native ECM. These lightweight patches offer an extensive surface-to-volume ratio, interconnected pores, and permeability for myocardial regeneration after MI.¹⁶ Because the heart is a complex 3-dimensional (3D) anisotropic structure with a helically organized myocardial band and slender interlayer configuration shifting from the endocardium to the epicardium, an anisotropic aligned fibrous and micro-grooved cardiac patch can provide contact direction for cellular reorganization and functional modulation. Cardiomyocytes cultured on the anisotropic cardiac patches stretched in the structural direction to obtain a higher sarcomere length, faster Ca²⁺ propagation speed, and synchronous contraction rate have been shown to exhibit excellent electrophysiological properties in comparison to those revealed by 2-dimensional (2D) flat plate patches.17, 18, 19, 20 There is also evidence to show that anisotropy impacts electrical signal propagation by stimulating the polarization of extracellular gap junctions to the longitudinal ends of the cardiomyocytes.²¹ In this regard, electrospinning-generated in vitro nanofiber cardiac patches with anisotropic microstructures, which resemble the natural ECM, have attracted significant attention.²² In fact, the potentials of various electrospun cardiac patches made from synthetic and/or natural²³ and electroactive biomaterials loaded with bioactive molecules or drugs have been actively investigated for the regeneration of the infarcted regions of the heart.²⁴ Such patches do not limit later systolic activity but simulate the unique physical structure of native tissue with the same anisotropy and mechanical strength for myocardial regeneration. Their effectiveness has been observed in the delivery of loaded mass cells, nano-micro sized drugs, molecules, proteins, microRNA, and extracellular vesicles at the diseased site.^14,25, 26, 27, 28 These patches reinforce the matrix directly by binding to the material surface or covalently linking cell adhesion molecules to facilitate angiogenesis and cell survival.²⁹ As these cardiac patches promote a physical, structural, biochemical, and extracellular matrix-rich microenvironment, they encourage cell-cell and cell-matrix interactions and weave a regulatory network of cell signaling, compatible with elastic behavior during heart beating after implantation. By providing sufficient mechanical strength to the heart (left ventricle [LV]), these constructs reduce elevated heart wall stress, support healthy functional cardiomyocytes in the infarct areas of the heart, decrease scar size, and alter the cardiac remodeling for myocardial regeneration in addition to limiting post-infarct ventricular dilation and preventing post-infarction progression.^27,30, 31, 32 We have analyzed the existing information and discussed the role of patterned cardiac patches with respect to their efficiency, closely compared to that of natural myocardial tissue in myocardial regeneration.

Figure 1.

A Schematic Biomaterial-Based Strategy for Myocardial Tissue Regeneration After Myocardial Infarction

Cardiac Patches for Myocardial Regeneration

Over the past decade, diverse biomaterial cardiac patches have been used as carriers of stem cells, genes, growth factors, drugs, exosomes, and extracellular vesicles in the form of particles, injectable hydrogels, sprays, and nanofibers. These approaches have been used for the delivery of the bioactive agents at the infarcted zone for treating MI and reducing ventricular remodeling to promote cardiac repair, improve cardiac restoration, prevent arrhythmias, preserve ventricular function, and preclude heart failure.^27,33, 34, 35, 36 As shown in Figure 2, in the 1960s, a milestone in the history of synthetic and natural or biological biomaterial patches in cardiac tissue regeneration emerged with the placement of a cardiac graft over a wounded heart. In the recent past, engineered cardiac patches loaded with cell types, including embryonic stem cells, induced pluripotent stem cells, endothelial cells (ECs) in mono- or multi-cell–layered form, as well as decellularized cardiac patches from animal products that are re-cellularized with therapeutic cells or agents have been successfully integrated with the cardiac tissue regeneration. Seeding the infarcted region with cells before implantation, a cardiac patch allows their growth and maturation in culture or biological reactors. These synthetic and/or natural or biological biomaterial patches have not only shown high customizability and competency after MI-challenged situations but have also overcome the challenges of limited availability of hearts for transplantation and organ rejection.37, 38, 39, 40, 41, 42, 43, 44

Figure 2.

Milestones in the History of Cardiac Patches for Myocardial Infarction Repair and Regeneration

CM = cardiomyocyte; EC = endothelial cells; ECM = extracellular matrix; hESC = human embryonic stem cell; hiPSC = human induced pluripotent stem cell; siRNA = small-interfering RNA.

In this regard, synthetic polymers poly(ε-caprolactone) (PCL), poly(glycerol sebacate), poly(lactic-co-glycolic acid), biodegradable polyurethane, poly(l-lactide), poly(vinyl alcohol), and polyethylene glycol and/or natural materials such as chitosan, collagen, gelatin, fibrin, and silk fibroin cardiac patches, have shown potential for use in myocardial regeneration.²⁴ Cardiac patches formed from PCL/gelatin seeded with mesenchymal stem cells (MSCs) have shown effectiveness in restricting ventricular dilation and reducing adverse remodeling of the ventricular wall while protecting MSCs from the hypoxic conditions in the infarct zone in murine MI models.⁴⁵ Incorporated alginate microparticles in a collagen-based patch can provide a controlled release of hepatocyte growth factor and insulin-like growth factor-1 to enhance endogenous cardiac stem cell migration and proliferation.⁴⁶ Cardiac patches co-injected with cardiomyocytes have been shown to improve cell engraftment, myocardial wall stress, apoptosis, vascularization, metabolism, contractile function, cell viability, partial remuscularization, and LV function in MIanimal models.^47,48 Decellularized ECM bio-inks simulate tissue-specific ECM components and/or resident cytokines, providing biological and biochemical cues required for remodeling and enhancing cellular functions such as survival, maturation, differentiation, migration, and intercellular interactions, as well as a cardiac niche–like microenvironment that augments expression of endogenous vascular endothelial growth factor (VEGF) and upregulate angiogenesis-related genes promoting cardiac regeneration.⁴⁹ Likewise, PCL-based medium-chain-length polyhydroxy alkenoate porous composite myocardial patches seeded with cardiac stem cells increased delivery of cells in infarcted mice, and have been found to exhibit good biocompatibility, enhanced mechanical and physical properties, as well as 30% detectable cells even on the day 9 after transplantation.⁵⁰ Cardiac patches bridge electrical and/or mechanical stimulation across the infarct to maintain and improve cardiac function⁵¹ and myocardial regeneration. Cardiac patches with the combination of bioactive nano- and biomaterials with MSC ECM/silk proteins incorporated with gold nanoparticles indicate a promising approach for cardiac repair in MI.⁵² Three-dimensional printed gelatin/hyaluronic acid patches that mimic the myocardium’s particular 3D architecture preserved cardiac function and regenerated the intrinsically anisotropic myocardium after MI,⁵³ in addition to promoting in vitro and in vivo proliferation, differentiation, and contractility of cardiomyocytes. Using biomaterial patches directly facilitated paracrine interactions with the host myocardium to promote growth factors such as VEGF⁵⁴ and basic fibroblast growth factor (bFGF)⁵⁵ or therapeutic agents such as adenosine.³⁰ Although implementation of transplanted cells limits the therapeutic efficacy or are entirely rejected (depending on cell types) by the host immune system, there is evidence that the cells infused on the site can create an appropriate environment to develop new cardiac cells by secreting growth factors before rejection.⁵⁶

Nanofiber Cardiac Patches for Myocardial Regeneration

The electrospun biomaterial nanofiber cardiac patches have been shown to be a valuable tool for myocardial regeneration after MI. The exceptional capability of the electrospinning technique to convert polymeric biomaterials into nanofibers with tunable mixtures and different dimensions to produce cardiac patches is very well-known among several other procedures.^26,57 With a simple equipment setup of electrospinning (Central Illustration), different types of nano- and/or microscale component-loaded (growth factors, endothelial cells, stem cells, cytokines, chemokines, and ECM proteins) nanofiber cardiac patches can be produced by optimizing parameters, including solution concentration, viscosity, voltage, conductivity, collecting layout, flow rate, and nozzle diameter.⁵⁸ Consisting of a highly interconnected porous network of nanofibers, large surface area, light weight, and permeability that mimic myocardial ECM-like and in vivo cell microenvironment, nanofiber cardiac patches allow cells to fully metabolize and interact for the transportation of nutrients and metabolic wastes effectively.^26,59 Because the electrospun nano- and/or microfibers from the polymers or electrically charged polymer solution or melt⁶⁰ are oriented parallel to each other along one specific direction, the anisotropic structure of cardiac patches similar to that of the myocardium has shown to be significantly functionalized with other components to improve cell adhesion, survival, differentiation, diffusion, and mechanical support that imitates the natural environment to regenerate diseased myocardium and restore its function.^22,23,61,62

Central Illustration.

A Schematic Electrospinning Process to Fabricate Biomaterial Based Nanofibers Patch

Moreover, the capacity of nanofibers is well known in MI for targeted drug delivery encapsulated with bioactive compounds for reversing adverse effects and myocardial tissue regeneration.^35,63, 64, 65 In this regard, the large surface area of nanofibers facilitates efficient drug loading, while their intricate pore structure enhances drug loading capacity and controlled release⁶⁶ Their stimuli-responsive ability under specific conditions such as patterning, magnetic fields, pH, or reactive oxygen species, has been shown to be efficient for localized, sustained, or on-demand drug release to accelerate the repair of infarcted tissue.⁶⁷ Tuned with topological features, cardiac patches have been shown to enhance mechanical parameters and deformation mechanisms similar to native tissue in a model of MI in vivo by responding to external and internal stimuli to induce nanofibers for drug release.^51,68 In fact, targeted delivery of nanomedicines for controllable modulation of the disease microenvironment has been shown to be beneficial by supramolecular nanofibers.⁶⁹ Also, significantly sustained delivery of exosomes at acute MI sites, expanding angiogenesis in the infarcted area, diminishing myocardial fibrosis, and preserving the function of the heart has been shown through incorporation of exosomes and transforming growth factor-β3 with a PCL/type I collagen nanofiber patch.⁶⁴ However, although the mechanisms that underlie drug-release through nanofibers may include diffusion, swelling, and degradation, they hold benefits through their structural and morphological characteristics, specifically surface area, porosity, fiber entanglements, and orientation. The surface drug molecules diffuse into the release media from the nanofibrous patch, occupying the interfibrous pores, and the polymer matrix swells, allowing drug molecules diffusion through nanofibers. This is followed by polymer degradation and enzymatic hydrolysis, which occurs at the surface, and assisted diffusion of the remaining molecules.^70,71 Nanofiber fabrication with water and nontoxic solvents can overcome the challenges of toxicity of cardiac patch material^72,73 as well as enhance angiogenesis following MI in a safe and nontoxic way.^74,75 Because of these advantages, the corresponding roles of these cardiac patches in the repair and regeneration of damaged myocardium in MI have been extensively studied (Table 1).^{26,31,36,44,62,}76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87

Table 1.

Nanofibers Cardiac Patches for Myocardial Regeneration

Biomaterials	Cellular Nanofiber Cardiac Patch	First Author
PCL-gelatin	hiPSC-CMs	Kumar et al26
PCL/GelMA-Ppy nanoparticles	Cardiomyocytes/fibroblasts	He et al31
PCL/gelatin	hiPSC-CMs	Sridharan et al36
Alginate/PCL	Cardiac progenitor cells	Karimi et al44
PCL-FN-immobilized nanofibers	UCB-MSC	Kang et al62
PLA, PEG, and PCL/collagen	HGF and IGF	Kerignard et al83
PCL	Sacrificial particles (PEO)	Wanjare et al84
Xylan (polysaccharides)/PVA	Acellular patch	Venugopal et al85
PLGA	Endothelial cells, VEGF	Fleischer et al86
β-PVDF	TiO2	Arumugam et al87
PEO	ECM	Shah et al76
PLA/PCL	Cardiomyocytes	Wei et al77
Alginate	Cardiomyocytes	Lee et al78
CNT/silk	Cardiomyocytes	Zhao et al79
PLA/PANI	Cardiomyoblast (H9c2)	Wang et al80
PCL/NO	NO2	Zhu et al81
PCL	hiPSC-CMs	Liu et al82

β-PVDF = β-phase polyvinylidene fluoride; CM = cardiomyocyte; CNT = carbon nanotubes; ECM = extracellular matrix; ECs = endothelial cells; FN = fibronectin; GelMA = methyl acrylic anhydride-gelatin; HGF = hepatocyte growth factor; hiPSC = human induced pluripotent stem cells; IGF = insulin-like growth factor; MSC = mesenchymal stem cell; NO = nitric oxide; PANI = polyaniline; PCL = polycaprolactone; PEG = poly (ethylene) glycol; PEO = polyethylene oxide; PLA = poly(lactic acid); PLGA = poly(lactic-co-glycolic acid); Ppy = polypyrrole; PVA = polyvinyl alcohol; PVDF = poly (vinylidene fluoride); TiO₂ = titanium dioxide; UCB-MSC = umbilical cord blood-derived mesenchymal stem cells; VEGF = vascular endothelial growth factor.

Hybrid cardiac patches composed of polymer nanofibers loaded with insulin-like growth factor have shown 89% to 92% release of insulin-like growth factor in 2 days and up to 50% to 58% release of hepatocyte growth factor in 35 days, which promotes cell proliferation for cardiac muscle regeneration.⁸³ Matrix metalloproteinase-9–instructed assembly of bFGF nanofibers and slowly releasing bFGF in ischemic myocardium has been shown to promote cardiac repair, which can be applied clinically.⁵⁵ An implantable β-phase polyvinylidene fluoride-poly(methyl methacrylate-hydroxyapatite-titanium dioxide–based seeded cardiac patch developed mechanically is a durable electrospun nanocomposite for replacing the scar tissue, which can match the extracellular matrix of cardiac cells and favor the adherence, proliferation, and maturation of the cells.⁸⁷ Their capacity to generate a surface charge density when subjected to the pumping action of the heart muscles can enhance vascularization and thus support the development of newly seeded cells.⁸⁷ Improved survival rate of stem cells in repairing myocardial injury has been reported by PCL-gelatin coaxial nanofiber cardiac patches, providing better mechanical properties and mimicking ECM structure for the enhancement of cell adhesion, viability, and regeneration.²⁶ These electrospun nanofiber cardiac patches have shown improved cell attachment and biomimetic properties of myocardial tissue. The cells aligned on these patches exhibited synchronous contraction and thereby a quick response to cardiac drugs.²⁶ Prominent maturation of the myocardium and a significantly higher velocity of maximum contraction uniaxially aligned were observed in PCL nanofibers seeded with human-induced pluripotent stem cell–derived cardiomyocytes.⁸⁴ Xylan (a plant-based polysaccharide beech wood)/polyvinyl alcohol glutaraldehyde vapor cross-linked nanofibers for the culture of neonatal rat cardiac cells in infarcted regions show better mechanical strength and are suitable for the cardiac cells proliferation and use as a cardiac patch for MI.⁸⁵ Better maturation and vital contractility of cardiomyocytes mimic structural organization, mechanical support, and controlled release of different biofactors have also been shown to effectively accommodate cardiac cells and organization of endothelial cells into blood vessels and contracting tissue emulating native architecture of myocardium thereby improving cardiac function.^86,88 Mechanical properties, such as stress-strain and elastic modulus of the cardiac patch, are particularly critical in cardiac regeneration to withstand and contribute to the contractile activity of the heart. Decellularized porcine cardiac ECM–polyethylene oxide nanofibers have been shown to preserve ECM composition, to self-assemble into the same microstructure of native cardiac ECM, and to retain essential mechanical properties. Upon using a decellularized porcine myocardium slice as an acellular patch in a rat acute MI model, increased cell infiltration, macrophage accumulation, and prevention of thinning of the LV wall as well as a significant number of vessel structures on the patch and infarcted area were observed.⁷⁶ Mechanical support that facilitates cell migration, angiogenesis, and ventricular function has been reported in post-MI–induced cardiac remodeling.³⁰ Similarly, a PLA [poly(lactic acid]/PCL nanofiber patch was shown to improve cell viability and mechanical status to withstand the severe pumping effect of the myocardium.⁷⁷ An alginate-based hierarchical structured electrospun cardiac patch has also been observed to promote cardiomyocyte repair due to the tensile strength, as well as repair of the infarcted myocardial region, without limiting the cardiac-systolic activity.⁷⁸ Furthermore, electrical signals to cardiac tissue cells were directed by doping nanofibrous cardiac patches with conductive materials such as gold nanoparticles, carbon nanotubes, or graphene.^79,89, 90, 91 Improved electrical conductivity promoted cardiomyocyte maturation and reduction in infarct size were demonstrated by silk nanofiber encapsulated with carbon nanotubes.⁷⁹ In this regard, a reduction of 50% infarct size, an increase of 20% LV ejection fraction, and a 9-fold increase in the density of neovascularization in the infarcted area in a rat MI model was achieved by mussel-inspired conductive nanofibrous patches after 4 weeks of patch transplantation on the infarcted heart.³¹ Implanted blended PLA and polyaniline conductive nanofibrous patch in rats showed maturation and spontaneous beating of primary cardiomyocytes, differentiation of cardiomyoblasts, and the functional recovery of the myocardium.⁸⁰ The beating frequency of cardiomyocyte depends on the thickness of the cardiac patch, and cardiomyocytes loaded into thick multifunctional nanofiber cardiac patch were seen to beat spontaneously at a much higher frequency.^58,86 Good survival and infiltration of human cardiac stem cells, as well as efficient mechanical support, have been shown with use of a nanofiber cardiac patch of 50-μm thickness.⁹² Because remodeling of the myocardium post-injury correlates with distorted excitation-contraction coupling, nanofiber cardiac patches have been reported to mimic the anisotropic native tissue, enhance the cell assembly into contractile functional myocardial tissues, restore the contractile function of the LV, and repair the myocardium after MI.^22,84,88,93 Elongated cardiomyocytes and endothelialized myocardium were seen with a PCL nanofiber/silk/carbon nanotube network enclosed in a hydrogel matrix by providing 3D cardiac anisotropy.⁹⁴ Furthermore, upon implantation into the myocardium, a biodegradable PCL–nitric oxide cardiac patch has been shown to enhance cardiac repair in a porcine model of MI due to its efficacy in mitochondria-targeted cardioprotection.⁸¹

Also, the antibacterial, antimicrobial, and anti-inflammatory activities of electrospun nanofibers with incorporated therapeutic agents in various platforms have been reported.⁹⁵ Therapies targeting inflammation benefit patients with cardio-inflammatory phenotype suffering from ischemic heart disease. In the case of MI, necrosis of cardiomyocytes triggers the activation of the adaptive and innate immune system, leading to an inflammatory response.⁹⁶ Immune response modulation in post-infarction myocardial regeneration controls the inflammatory environment and significantly influences the overall outcome in repairing the damaged cardiac tissue.97, 98, 99, 100 Since the immune response to implanted devices is critical in determining their success or failure, immunomodulation may effectively mitigate adverse foreign body reactions.¹⁰¹ Therefore, the ability of biomaterial cardiac patch–mediated myocardium regeneration has been explored for their capacity to modulate immunological reactions of overlapping phases (inflammation, proliferation, and resolution) and support cardiac tissue regeneration in myocardial infarction.^102,103 Whereas natural biological materials tend to have low immunogenicity due to their limited mechanical characteristics, synthetic polymers with highly controllable mechanical properties are more likely to induce immune response. Immunomodulatory hybrid micro-nanofiber constructs have been suggested as candidates for enhancing cardiac regeneration.^104,105 Composites of nanofibers in conjunction with electrical stimulation or release of bioactive enhanced functionality and regeneration of cardiac tissue offer great potential for enhancing material-cell interactions and modulation of the immune system.^106,107 Studies have shown immunomodulatory effects of carbon-based nanofiber patches, such as graphene, in regenerating cardiac tissue after myocardial injury.^108,109 Releasing cellular components and growth factors that interact with host tissue cells influence the immune response and cardiac repair.²⁶ Incorporating dexamethasone-peptide amphiphile into nanofibers could reduce inflammation and protect the cardiac tissue from oxidative stress during regeneration, as demonstrated in vitro using a human inflammatory reporter cell line.¹¹⁰

In addition, there have been promising results in studies on immunomodulatory therapies that use dexamethasone-incorporated peptide nanofibers to induce antigen-specific responses, leading to better tolerogenic immunotherapies.¹¹¹ Moreover, aligned nanofiber patches with a balanced porousness and smooth surface have been shown to reduce foreign body response and immunomodulatory capacity, which helps modulate the host response in vivo.¹¹² Hydrophilic nanofibers with an aligned topography explored for their immunomodulatory properties have shown that activation of the NOD-like receptor thermal protein domain-associated protein 3 inflammasome facilitates the maturation and release of inflammatory factors by activating caspase-1. This mechanism regulates the macrophage-mediated foreign body response and implant integration, thereby shaping the peri-implantation immune microenvironment.¹¹³ In a preclinical study conducted on animals, a cardiac patch made of cardiomyocytes and human fibroblasts on a bioresorbable matrix was beneficial in treating ischemia-induced decreases in LV function caused by a loss of functioning cardiomyocytes. The subjects who received the treatment showed improved LV contractility/function, partially reversed cardiac remodeling, and enhanced exercise activity without any increase in ventricular arrhythmias or myocardial energy use. The mechanism of action was related to localized immune-mediated changes in gene expression at the injury site, which repaired and polarized macrophages from their pro-inflammatory state to their anti-inflammatory reparative state.¹⁰⁴ Furthermore, studies have shown that incorporating signaling molecules directly into nanofibers can lead to local immunosuppression,¹¹⁴ controlled drug delivery that responds to changes in temperature,¹¹⁵ and increased cellular proliferation, adhesion, and attachment, which promotes a biomimetic matrix¹¹⁶ and enhances biological activity for myocardium regeneration.

Thus, nanofiber cardiac patches can be seen to assist in replacing scar tissue effectively and repair the infarcted area of the heart. Together, these observations show the ability of various biomaterial-based electrospun nanofibrous patches to promote cell proliferation, adhesion, differentiation, and preservation of their phenotypic shape. Their anisotropic structure, high porosity, low density, antibacterial activities, and capacity to deliver cells or bioactive factors make them suitable tools for infarcted hearts and clinical translation. These nanofiber-based cardiac patches have the potential for clinical application as they may maintain structural and functional complexity within the human heart.

Topological Features of Nanofiber Cardiac Patches

It is well known that the cardiac patch must have a proper design, thickness, and size relevant to the typical infarct size in addition to its mechanical, physicochemical properties and electrical conductivity to improve cardiac function and myocardial regeneration in MI.^51,117 The significant roles of designed nanofiber patches to deliver seeded material are actively studied in tissue engineering. Tailored with square, rectangular, or honeycomb conventional patterns on nanofiber, patches have been shown to simulate anisotropic architecture similar to myocardium, elevate cardiomyocyte viability, promote penetration of cells, and induce expression of cardiac-related genes.^118,119 Likewise, in coiled, helical, or spring-like nanofiber patches, increased elasticity and extensibility for supporting the assembly of functional cardiac tissue with strong contraction forces have been observed.^91,120,121 Albumin electrospun nanofiber patches with laser-patterned microscale grooves and holes have been reported to exhibit anisotropic electrical signal propagation, as the microchannels pattern within the patch seeded with ECs has been shown to form closed lumens.^32,86,92 Moreover, the cage-like structures patterned on poly(lactic-co-glycolic acid) multilayered nanofibrous cardiac patch have been shown to control the release of VEGF to promote vascularization and anti-inflammatory drugs into the exterior microenvironment and integrate suitably with the native heart muscle.⁸⁶

Because most biomaterial cardiac patches have conventional patterns when stretched longitudinally, they tend to contract transversally causing mismatch with native cardiac tissue behavior during the regeneration of infarcted myocardial tissue. Thus, these patches are limited in their use due to inadequate flexibility, elongation, and poor cellular infiltration.^122,123 On the other hand, the tailored (auxetic) design of cardiac patches promotes flexibility, mechanical strength, and deformation mechanisms, enabling them to withstand stresses, improve cellular infiltration, and impart cell differentiation. Such outcomes are considered to augment the compatibility of cardiac patches to the demanding mechanics of the heart and enhance their use in myocardial regeneration after MI. The expansion of nanofiber cardiac patches with tailored designs in multiple directions that concurrently increase the surface area to promote cell adhesion and growth are essential for their use in cardiac regeneration.¹²⁴ A variety of geometries, such as re-entrant, rotating, chiral, crumpled and sinusoidal structures have been identified, which promotes a deformation mechanism allowing expansion in multiple directions simultaneously.¹²⁵ Thus, it is difficult to ensure that the cardiac patch matches with the behavior of myocardial tissue. However, it has been shown that an angled solid square geometry on an electrospun polymer nanofibrous patch coated with gold nanoparticle for conductivity was easily stretched with small tensile load compared to an electrospun nanofiber patch.¹²⁶ Expansion in multiple directions simultaneously and retaining the original shape upon forces dissipated has been shown during the cycles of applied stress and strain to these patches (Figure 3). There was an increase in tensile capacity of this designed nanofibrous patch compared to a nonpatterned nanofibrous patch, which confirms the tuned flexible nature due to tailored design. Also, the total elongation capacity of the thick patch is significantly reduced compared to the thin patch, highlighting reduced deformation ability due to increased patch thickness.¹²⁷ It indicates that patterned cardiac patches can be modified according to infarct thickness and size to support the infarcted region. In this regard, sinuous cardiac patches of poly-ethylene-glycol diacrylate film casting, embedded silver nanowires, and microarchitectures closed to chiral pattern cardiac patches using photopolymer resin via ink-jet printing have been shown to function for strain detection in cardiac muscle.¹²⁸ An excimer-lasered microablation micropatterned “re-entrant honeycomb shape” on a conducive composite of polyaniline and phytic acid cardiac patch was found to stretch according to the movement of the native heart tissue without detrimental effects.⁵¹

Figure 3.

An Angled, Square-Patterned PCL-Nanofiber Patch Provides Multidirectional Expansion and Increased Surface Area Under Stretched Conditions

PCL = poly(ε-caprolactone).

It is indicated that a patch with a missing rib design fabricated by melt electrospinning writing can overcome the limited elasticity capacity seen in the conventional square patch design and adapt the strains and stresses experienced by the human myocardium during both diastole and systole. Such patches reflect anisotropic mechanical properties, as well as the anisotropic ratio of effective stiffness, and are thus compatible with the directionally dependent mechanics of the heart.¹²⁸ It has been shown that the functionality of cardiac patches for their use in myocardial regeneration is dependent on structural geometry⁸² such as nanofiber interlocking and patterned design.¹²⁹ These observations suggest that designed nanofibrous patches have the advantage of deformation behavior matching the stretchable mechanism of the native tissue, that is, the ability to be tailored and optimized according to the severity of targeted infracted region to serve as a potent cardiac patch for cardiac repair or myocardial regeneration. However, the understanding of tailoring patterns into cardiac patches for treating MI remains in the theoretical stage. Overall, although the beneficial effects of cardiac patches in animal models and their clinical feasibility by successful transplantation are supported,130, 131, 132 there are still considerable difficulties in their use.^133,134

Conclusions

It is well known that MI is a severe medical condition, and the limited regenerative potential of cardiomyocytes restricts the capacity for self-repair of cardiac tissue. Because myocardium is comprised of electroactive tissues, electrospun nanofiber cardiac patches have been actively explored as a strategy for myocardium regeneration. This targeted approach may complement pharmacological interventions, revascularization procedures, lifestyle modifications, and other existing myocardial injury and tissue repair treatments. This review highlights promising results of biomaterial electrospun nanofibers with or without tailored-design–enabled cardiac patches through controllable delivery of embedded cell loads and bioactive molecules or therapeutic agents at the infarcted region for promoting myocardial tissue regeneration.

Directly applied to damaged heart tissue, nanofiber cardiac patches mimic the mechanical properties of the native ECM and provide structural support and scaffolding for cell attachment, growth, and migration to the injury site. Their large surface area of nanofibers facilitates efficient drug loading. At the same time, their intricate pore structure enhances drug loading capacity and benefits localized, measured, and sustained delivery of therapeutic compounds to the diseased site, whereas the selection of drug-polymer–solvent systems or electrospinning techniques promotes reduced initial burst release. Their stimuli-responsive ability to release targeted and controllable drugs accelerates the repair of infarcted tissue, while their tuned topological features according to infarct size can achieve deformation mechanisms similar to native tissue. These cardiac patches provide adequate conductive and mechanical strength for maintaining the myocardium's ability to contract and relax, making them suitable platforms for the regeneration of infarcted myocardium. Combined with cellular components and growth factors, they interact with host tissue cells to influence the immune response, impacting cardiac repair. Their immunomodulatory effects, potentially reducing inflammation and scar formation, are particularly noteworthy. These patches also offer the potential for in vitro drug efficacy and toxicity testing before clinical trials.

Although the beneficial effects of cardiac patches in animal models and preclinical studies showed promising performance, their clinical feasibility is progressing, and ongoing clinical trials explore their potential and new insights into infarcted myocardial repair and regeneration.^{54,83,135,136} However, there are still many challenges with their clinical implications. For instance, the risks of open-chest surgery for implantation increases the patient's risk of death, inflammation, a lengthy recovery period, and the heavy burden of sutures for cardiac patch transplantations for an already injured heart. Without suture-free engraftment, ensuring seamless patch integration with the host tissue remains challenging. Long-term safety studies are still required because all patches are external foreign substances that may cause relevant immune rejection due to the materials used or their metabolic derivatives. Furthermore, there is a lack of large animal and human clinical studies. Their applications are limited to the laboratory scale, necessitating more in-depth preclinical and clinical evaluation to validate their effectiveness in mitigating myocardial injury and for the translation process.

Despite the challenges, with the combination of a growing understanding of the biological pathways underlying the infarcted region, nanofiber cardiac patches that can generate all cardiac cell types with appropriate electrical and calcium signal transduction events would become an increasingly feasible and transformative choice for patients suffering from MI and heart failure. However, the clinical translation is currently at a halt, like other emerging treatments, such as cell therapy for heart failure.^99,137 Therefore, it is crucial to advance research and development in this area to fully realize the potential of nanofiber cardiac patches and their benefits for patients.

Funding Support and Author Disclosures

This work was supported by a foundation grant to Dr Kirshenbaum from the Canadian Institute for Health Research (CIHR) and St Boniface Hospital Research Foundation. Dr Rabinovich-Nikitin has received grants from the St Boniface Hospital Research Foundation, Manitoba Medical Services Foundation, Winnipeg Foundation. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.