NIR-controlled photothermal intelligent nanozyme synergizes catalysis and gas therapy for multidimensional treatment of inflammatory bowel disease

Abstract

The vicious feedback loop between reactive oxygen species (ROS)-triggered mucosal inflammation and intestinal epithelial barrier disruption represents a critical mechanism driving the onset and progression of inflammatory bowel disease (IBD). Traditional nanozymes primarily focus on scavenging ROS to suppress excessive immune responses, but generally lack intrinsic functionality for direct intestinal barrier restoration. Given the substantial potential of mild photothermal effects and nitric oxide (NO) gas in restoring barrier integrity, we engineered a near-infrared (NIR)-controlled photothermal intelligent nanozyme (FU/PBN@CUR) by loading curcumin (CUR) into NO donor-doped Prussian blue nanozymes (PBN), which were further encapsulated within a pH-responsive fucoidan/chitosan (FU/CS) hydrogel. In cytological and pharmacodynamic studies, the P-selectin-targeting and pH-responsive properties of FU/CS hydrogel remarkably enhanced FU/PBN@CUR accumulation in inflamed colon. The intrinsic enzymatic activity of the PBN effectively scavenged ROS in macrophages, driving their phenotypic conversion from the M1 to the M2 subtype. Notably, NIR triggered hyperthermia-induced autophagy and NO release from PBN, which synergistically promoted intestinal epithelial cell proliferation and tight junction protein expression, thereby restoring the integrity of the intestinal epithelial barrier. Collectively, our designed nanoplatform synergistically accomplished ROS elimination-autophagy activation-NO gas delivery behaviors, providing a novel “one stone, three birds” therapeutic strategy for IBD treatment.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-025-03878-x.

Introduction

Inflammatory bowel disease (IBD) is a chronic, immune-mediated intestinal disorder that includes ulcerative colitis and Crohn’s disease, and has emerged as a global health concern due to its significant impact on patients’ quality of life [1, 2]. Non-specific inflammation of the colon and disruption of the intestinal mucosal barrier are the two principal pathological features of IBD [3]. Owing to the constant exposure of the intestinal mucosa to the external environment, harmful flora and pathogens in the intestinal lumen can destroy the mucosal barrier, causing increased mucosal permeability [4]. This change leads to the translocation of antigenic molecules from the intestinal lumen to the lamina propria and drives the accumulation of reactive oxygen species (ROS), which activate M1-type macrophages and disrupt the balance between pro- and anti-inflammatory factors, thereby triggering persistent mucosal inflammation [5, 6]. Furthermore, excessive ROS accumulation oxidizes intestinal epithelial cells and disrupts intercellular tight junctions, compromising intestinal barrier integrity and forming a vicious positive feedback loop that exacerbates IBD progression [7]. Given these challenges, the development of an integrated therapeutic platform that scavenges ROS, modulates inflammatory cascade, and restores the integrity of the intestinal barrier emerges as a crucial research imperative for enhancing clinical efficacy in IBD management.

As one of the most promising therapeutic agents for ROS elimination, nanozymes combine the distinctive properties of nanomaterials with intrinsic catalytic activity, enabling them to effectively mimic natural enzymatic functions while exhibiting simplified synthesis, flexible structural design, and exceptional stability [8]. These advantages have led to their increasing use as substitutes for natural antioxidant enzymes in biomedical applications. Traditional nanozymes primarily focus on scavenging ROS to suppress excessive immune responses. However, they fail to achieve effective restoration of the intestinal barrier, which significantly limits their therapeutic potential in addressing the multifactorial pathology of IBD [9–11]. This underscores the pressing need to explore novel materials or innovative strategies that can directly empower nanozymes with barrier-repairing capabilities.

Recently, photothermal therapy (PTT) has achieved remarkable progress in disease treatment due to its high selectivity and minimally invasive nature [12]. Specifically, mild photothermal therapy (mPTT) has emerged as an appealing approach that avoids nonspecific damage to normal tissues and vascular systems often associated with conventional PTT [13–15]. Emerging evidence suggests that mPTT can mediate autophagy and promote the expression of tight junction proteins in intestinal epithelial cells, facilitating the repair of the impaired intestinal barrier [16, 17]. However, the development of cellular thermotolerance and the upregulation of heat shock proteins may attenuate the barrier-restoring effects of mPTT, highlighting the necessity for developing strategies to enhance its therapeutic efficacy [18]. As an emerging therapeutic modality, gas therapy offers unique advantages such as rapid diffusion, fast onset of action, and a low risk of resistance [19]. This approach utilizes endogenous gaseous mediators, such as nitric oxide (NO), hydrogen, and hydrogen sulfide, to modulate multiple physiological and pathological processes, and is regarded as a green treatment with minimal toxicity to healthy tissues [20]. Among these, the water-soluble radical gas NO plays a critical role as a biological signaling molecule in maintaining the homeostasis of the organism. Notably, previous studies have demonstrated that low concentrations of NO can help restore intestinal barrier integrity through inducing the proliferation and migration of intestinal epithelial cells [21].

Leveraging the complementary strengths of these therapies, an engineered nanozyme integrating enzymatic activity, mild photothermal effects, and NO delivery offers a breakthrough strategy to address the therapeutic limitations of conventional nanozymes. Our previous work on mesoporous Prussian blue (PB) nanoparticles revealed their exceptional capability for ROS elimination and significant efficacy in mitigating oxidative stress [22, 23]. In addition, we validated the outstanding mild photothermal characteristics of PB, attributed to its strong near-infrared (NIR) absorption, making it an optimal candidate as a nanozyme. Given the proven role of NO in promoting barrier repair, achieving effective NO delivery remains a critical challenge. Sodium nitroprusside (SNP), a classical NO donor, shares fundamental structural motifs with potassium ferricyanide, the essential iron precursor used in PB fabrication. On this basis, we developed a multifunctional nanozyme (PBN) by incorporating SNP into the PB crystalline matrix. The resulting PBN maintained the original ROS-scavenging capacity and photothermal conversion efficiency of PB, while simultaneously enabling NIR laser-responsive NO release [24, 25].

However, metal- or metal oxide-based nanozymes are prone to decomposition and inactivation in the gastrointestinal tract (GIT) [26]. Overcoming the delivery challenges caused by pH heterogeneity in the GIT is an essential prerequisite for achieving efficient oral administration of nanozymes. In this context, hydrogels with pH-responsive properties have emerged as particularly attractive materials for addressing the barriers. Fucoidan (FU), a natural marine-derived polysaccharide, can form a pH-responsive FU/CS hydrogel through cross-linking with chitosan (CS) for targeted intestinal delivery [27, 28]. At low pH (pKa ~ 1.5), the deprotonated sulfate groups (SO₃⁻) enable electrostatic interactions with positively charged amino groups, thereby forming a tight network. Conversely, increased pH induces deprotonation of amino groups in CS, disrupting the electrostatic crosslinking with SO₃⁻ and consequently triggering a transition of the hydrogel from a compact network to a swollen state. More importantly, FU is a specific ligand for the P-selectin receptor that is highly expressed in inflamed colonic tissues. Meanwhile, its negative charge allows it to bind electrostatically to positively charged proteins that accumulate in damaged intestinal epithelium. These two features may synergistically enhance the precise targeting of inflamed lesions [29, 30]. Moreover, the outstanding mucosal adhesion of the hydrogel increases the retention time of the active ingredients in the gut, thereby supporting sustained therapeutic effects [31, 32].

Herein, we constructed a NIR-controlled photothermal intelligent nanozyme (FU/PBN@CUR) by loading the anti-inflammatory drug curcumin (CUR) [33] into PBN, which was subsequently encapsulated within a pH-responsive FU/CS hydrogel. It is anticipated to modulate macrophage-intestinal epithelial cell crosstalk via a tripartite mechanism involving ROS elimination, autophagy activation, and NO delivery, disrupting the vicious loop between mucosal hyperimmunity and barrier dysfunction. After oral administration, the hydrogel targets the inflamed colon via FU-mediated recognition and subsequently undergoes alkaline pH-responsive swelling to enable controlled release of PBN and CUR. PBN-mediated ROS elimination synergizes with CUR to promote polarization of anti-inflammatory M2 macrophages and attenuates intestinal mucosal inflammation. Simultaneously, under NIR laser irradiation, PBN enables controlled NO release and exerts a “hot spring effect” to synergistically promote the proliferation of intestinal epithelial cells and the expression of tight junction proteins (Fig. 1). Experimental results indicated that the combination of FU/PBN@CUR and NIR laser irradiation effectively regulated the intestinal mucosal immunity by removing ROS, while synergistically promoting the repair of the intestinal epithelial barrier through the induction of autophagy and NO release. Our research pioneered a synergistic therapeutic strategy for IBD that integrates PB-enabled enzymatic catalysis, mild photothermal effects, and NO gas therapy, opening new avenues for the treatment of this disease.

Fig. 1.

Scheme of FU/PBN@CUR preparation and its application for IBD management

Materials and methods

Materials

Potassium ferricyanide (K₃[Fe(CN)₆]) and curcumin (purity ≥ 98%) were obtained from Yuanye (Shanghai, China). Polyvinylpyrrolidone (PVP, K58) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) were acquired from ACMEC (Shanghai, China). Fucoidan (purity ≥ 95%), chitosan (deacetylation degree ≥ 95%), and SNP (Na₂[Fe(CN)₅NO]·2H₂O) were purchased from Macklin (Shanghai, China). Dexosan sulfate sodium salt (DSS) was obtained from Meilunbio.

Cells and animals

RAW264.7 and colonic carcinoma cells (Caco-2, epithelial properties) were supplied by the Chinese Academy of Sciences (Shanghai, China). Male C57 BL/6 mice (20 ± 2 g) were procured from the Laboratory Animal Center of Southwest Medical University (Luzhou, China). All animal experiments were approved by the Animal Care and Ethics Committee of Southwest Medical University (NO. 20231031-003).

Preparation of PBN and PB

To prepare PBN nanoparticles, 3 g of PVP, 60 mg of K₃[Fe(CN)₆], 488.7 mg of SNP, and 40 mL of HCl (0.1 M) were mixed and heated at 80 °C for 12 h. The resulting mixture was centrifuged (13,000 rpm, 10 min) and washed three times with ultrapure (UP) water. For the synthesis of PB, the operation was the same as above except that the amount of potassium ferricyanide was 548.7 mg [24].

Synthesis of PBN@CUR and FU/PBN@CUR

A CUR ethanol solution (2 mg/mL, 5 mL) was mixed with a PBN aqueous solution (1 mg/mL, 5 mL) and stirred for 24 h. CUR was loaded into PBN through a mesoporous adsorption process facilitated by its inherent porous structure. Centrifugation was performed at 13,000 rpm for 10 min, and then the pellet was washed three times with water to obtain PBN@CUR [24].

FU/PBN@CUR was prepared at room temperature. A 3 wt% CS solution was prepared by dissolving it in UP water containing 1% acetic acid, with the pH adjusted to 5. At the same time, a 3 wt% FU solution was prepared. PBN@CUR was then added to the FU solution and mixed thoroughly. Subsequently, the mixture was added to the CS solution at a volume ratio of 1:2 (CS: FU) [34]. A three-dimensional hydrogel network was formed through physical cross-linking via electrostatic interactions between the amino groups (NH₃⁺) of CS and the sulfate groups (SO₃⁻) of FU, serving as a carrier for PBN@CUR. The resulting product was the intelligent nanozyme FU/PBN@CUR. In addition, FU/PB@CUR was prepared using the same method for subsequent experiments.

Characterization

The morphology and particle size distribution of PBN and PBN@CUR were observed by transmission electron microscopy (TEM; JEOL, Japan), and the elemental mapping of PBN was characterized by a FEI Tecnai G2 F20. The zeta potential of each preparation was examined using a Malvern Zetasizer, and the changes in PDI and particle size of PBN@CUR suspensions were determined after storage at 4 °C for 8 days. The crystalline properties of PBN and PB were evaluated by X-ray diffraction (XRD; Bruker D8 Advance, Germany). Based on the photothermal decomposition characteristics of PBN, the loading rate of SNP in PBN was determined by thermogravimetric analysis. The chemical composition in the PBN structure were tested by X-ray photoelectron spectroscopy (XPS). The spectra of PB, PBN, CUR, and PBN@CUR were scanned by Fourier transform infrared spectroscopy (FT-IR; Shimadzu Corporation, Japan). In addition, the average pore diameter and specific surface area of PBN were measured by Nitrogen (N₂) absorption-desorption experiments. The microstructure of the hydrogel was observed using scanning electron microscopy (SEM; HITACHI S4800, Japan). High-performance liquid chromatography (HPLC; Agilent 1260, USA) was employed to determine the loading content (LC) and loading efficiency (LE) of CUR in the formulations. The LC and LE were calculated using the following equations:

In vitro release assay of FU/PBN@CUR

The cumulative release of CUR from FU/PBN@CUR under different pH environments was determined using a dialysis method. Briefly, FU/PBN@CUR (containing 1 mg of CUR) was loaded into a dialysis bag with a molecular weight cut-off of 3,500 Da and placed in 20 mL of PBS solution simulating gastric fluid (pH 2.0), intestinal fluid (pH 6.5), and colonic fluid (pH 7.4). The samples were incubated at 37 ℃ with constant shaking. 1 mL of release medium was collected at 1, 2, 4, 6, 8, 10, 12, 24, and 36 h. The CUR content in the collected samples was subsequently measured using HPLC. Following the aforementioned procedure, samples were collected at 1, 2, 4, 6, 8, and 10 h. The CUR release profile of PBN@CUR was then determined under different pH conditions, with or without laser irradiation.

Antioxidant activity of PBN@CUR

The hydrogen peroxide (H₂O₂) scavenging ability of PBN@CUR was assessed by incubating different concentrations of the preparation (25, 50, 100, 200, and 400 µg/mL) in PBS containing 500 mM H₂O₂ for 2 h, followed by measurement of the residual H₂O₂ at 240 nm. The superoxide anion (O₂⁻) scavenging activity was evaluated using a superoxide dismutase (SOD) activity assay kit, while the peroxidase (POD)-like activity was evaluated using an ABTS radical assay kit. The DPPH scavenging activity was assessed by mixing different concentrations of PBN@CUR with 100 µL of 0.1 mM DPPH ethanol solution, measuring the absorbance at 517 nm.

In vitro detection of NO release

A 1 mL suspension of PBN in PBS was irradiated using an 808 nm NIR laser at a power density of 1.5 W/cm². Subsequently, NO levels were measured at 5, 10, 15, 20, and 25 min using an NO assay kit based on the Griess method. To verify the NIR-triggered controlled release of NO from PBN, the sample was first irradiated for 5 min, followed by a 5-minute interval without irradiation, and then subjected to two additional on-off irradiation cycles. The amount of released NO was measured at selected time intervals. Furthermore, we quantified the NO release profiles of PBN under different NIR power densities using an NO assay kit. Similarly, the NO release curves of FU/PBN@CUR were measured under different pH conditions, with or without laser irradiation.

Evaluation of photothermal properties

A quartz cuvette was filled with 2 mL of PBN@CUR suspension at concentrations of 0, 25, 50, 100, 200, and 500 µg/mL, and irradiated with an 808 nm NIR laser at a power density of 1.0 W/cm² for 7 min. Subsequently, a 200 µg/mL suspension of PBN@CUR was exposed to NIR laser irradiation at various power densities (0.5, 0.8, 1, or 1.5 W/cm²) for 7 min. Additionally, the photothermal cycling stability of PBN@CUR was assessed using repeated laser on/off cycles. Temperature changes were recorded throughout the experiment.

In vitro cytotoxicity evaluation

RAW264.7 cells were seeded in 96-well plates and incubated with media containing CUR, PBN@CUR, FU/PBN@CUR, or FU/PBN@CUR with NIR irradiation (named FU/PBN@CUR + L) at varying concentrations for 24 h. For the laser group, laser irradiation (808 nm, 1 W/cm²) was applied for 7 min after 4 h of incubation. After treatment, fresh medium with 10% CCK-8 was added, and cell viability was assessed by absorbance at 450 nm. In addition, the cytotoxicity of each preparation against human colon cancer Caco-2 cells were assessed using the same protocol.

In vitro cellular uptake

Cells were incubated into 24-well plates for 24 h. Subsequently, RAW264.7 and Caco-2 cells were stimulated with 10 µg/mL and 4 µg/mL LPS, respectively. The cells were then incubated with PBN@DID or FU/PBN@DID (in which DID was used instead of CUR) for 4 h. After nuclei staining with DAPI, cellular uptake was observed using a laser scanning confocal microscope (CLSM).

Intracellular ROS scavenging capacity

RAW264.7 cells were cultured in 6-well plates for 8 h, followed by overnight stimulation with 10 µg/mL LPS. The cells were then incubated with different preparations (equivalent to 30 µg/mL CUR) for 4 h. Subsequently, the cells were incubated with DCFH-DA (10 µM), and intracellular ROS levels were observed by fluorescence microscopy. For quantitative analysis, cells were measured for ROS accumulation by microplate reader using the same procedure. In a separate experiment, RAW264.7 cells in 6-well plates were stimulated overnight with 10 µg/mL LPS and then incubated with FU/PBN@CUR at 25, 50, 100, and 200 µg/mL for 4 h. The intracellular O₂⁻ levels were tested using a SOD enzyme activity test kit.

In vitro anti-inflammatory effect assay

RAW264.7 cells were cultured in 6-well plates and stimulated with 10 µg/mL LPS overnight. The cells were then cultured with different formulations (equivalent to 30 µg/mL CUR) for 24 h. After that, cellular RNA was extracted and the expression levels of anti-inflammatory cytokines (IL-10), pro-inflammatory cytokines (TNF-α, interleukin 1β (IL-1β)), M1-type macrophage marker (cluster of differentiation 68 (CD68)), and M2-type macrophage marker (Arginase-1 (Arg-1)) were detected using quantitative real-time polymerase chain reaction (qRT-PCR). Additionally, we detected the expression levels of the M1-specific marker (CD86) and the M2-specific marker (Arg-1) via western blot (WB) after treatment with different formulations.

Intestinal barrier repair and autophagy-related gene expression

Caco-2 cells were cultured in 6-well plates for 24 h and stimulated overnight with either 4 µg/mL LPS (for barrier-related assays) or 6 mM autophagy inhibitor 3-methyladenine (for autophagy-related assays). Subsequently, the cells were incubated with different preparations (equivalent to 30 µg/mL PB) for 24 h, and 1 W/cm² laser irradiation was applied to the FU/PBN@CUR group for 7 min. After treatment, cellular RNA was extracted and subjected to qRT-PCR to detect the expression of tight junction proteins (Zonula occludens 1 (ZO-1) and Occludin) and autophagy-related proteins (Beclin-1, p62, and LC3B).

Wound healing assay

Caco-2 cells were incubated in 6-well plates until approximately 80% confluence. Following mechanical wound creation using a 200 µL pipette tip, the cells were treated with FU/PBN@CUR, FU/PB@CUR + L, or FU/PBN@CUR + L for 24 h. Wound photographs were taken at 0, 12, and 24 h using a microscope and quantitatively analyzed with ImageJ software.

In vivo biodistribution evaluation

The IBD model was induced by oral administration of 3% DSS to mice for 5 consecutive days. Prolonged retention of therapeutics at the inflamed colon site is beneficial for oral drug delivery [1]. To track the distribution of the formulation in vivo, we utilized the fluorescent dye DID to replace the model drug CUR for labeling. We subsequently evaluated the accumulation of free DID, PBN@DID, and FU/PBN@DID in the mouse colon following gavage administration. Colonic targeting efficiency and tissue distribution were assessed by analyzing the fluorescence intensity of organs both in vivo and ex vivo after oral administration.

In vivo assessment of the photothermal effect

To evaluate the in vivo photothermal conversion capability of the intelligent nanozyme, mice were orally administered saline, CUR, PBN@CUR, and FU/PBN@CUR. At 8 h, the gastrointestinal tract was irradiated with an 808 nm laser (1 W/cm²) for 3 min, and temperature changes were monitored using a thermal imaging camera.

In vivo pharmacodynamic evaluation

To establish the IBD model, mice were administered 3% DSS in their drinking water for 5 consecutive days. The model mice were randomly divided into DSS, CUR, PBN, PBN@CUR, FU/PBN@CUR, FU/PBN + L, and FU/PBN@CUR + L groups, with a healthy control group also included. On the third day after modeling, the respective preparations were administered via oral gavage at predetermined doses (CUR equivalent to 20 mg/kg). Disease activity index (DAI) scores and body weight changes were monitored daily from the start of modeling until the end of treatment. After 7 days of treatment, mice were sacrificed for macroscopic evaluation, including representative colonic pictures and quantitative analysis of colonic length. Subsequently, histological evaluation of colon tissue was performed using hematoxylin-eosin (H&E) staining, with inflammatory cell infiltration, crypt damage, goblet cell count, and mucosal epithelial injury serving as indices of therapeutic efficacy.

In vivo evaluation of anti-inflammatory and intestinal barrier repair functions

Mouse plasma and colon tissue homogenates were collected, and the levels of the anti-inflammatory cytokine (IL-10) and pro-inflammatory cytokines (TNF-α, IL-6) were measured via enzyme-linked immunosorbent assay (ELISA) kits. The infiltration of inflammatory cells in colon tissues was observed by immunohistochemistry (IHC). To examine the effect of each treatment on intestinal barrier repair, the expression levels of two key epithelial tight junction proteins (ZO-1 and Claudin) were examined by IHC. In the IHC analysis, nuclei were counterstained blue with hematoxylin, and positive expression appeared brown-yellow. Subsequently, all acquired images were subjected to quantitative analysis using Image-Pro Plus software, measuring the integrated optical density (IOD) of positive signals and the corresponding tissue area.

In vivo biosafety studies

At the end of the pharmacodynamic experiment, blood samples were collected for serum analysis of urea (UREA), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels. Major organs (heart, liver, spleen, kidneys, and lungs) were analyzed by H&E staining to evaluate histopathological changes.

Statistical analysis

Each experimental condition was performed at least three times. Data are presented as mean ± standard deviation. The student’s t test and one-way analysis of variance were used for statistical analysis. Values of *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001 were considered statistically significant.

Results

Preparation and characterization of FU/PBN@CUR

The synthesis method of PBN is displayed in Scheme 1. TEM images displayed that PBN appeared as granular, approximately cubic particles with an average size of approximately 170 nm (Fig. 2A). Furthermore, the successful synthesis of PBN was confirmed by various characterization methods. Both PB and PBN showed Fe (2P) bonding energies at 708 (2P_2/3) and 721 eV (2P_1/3), and the C (1 S) peak appeared at 284 eV (Fig. S1). For N (1 S), a peak at 399.5 eV revealed the existence of the nitroso group in PBN, indicating that SNP was successfully inserted in the lattice of PB (Fig. 2C and D). In addition, we observed a uniform distribution of element O in the elemental mapping of PBN (Fig. 2E). The successful doping of SNP in PB was further supported by the N = O oscillations located near 1945 cm^− 1 in the FT-IR spectra of both SNP and PBN (Fig. 2F). Thermogravimetric analysis confirmed the successful loading of SNP in PBN, with a loading rate of 8.6% (Fig. S2). XRD analysis further demonstrated that PBN retained the same diffraction peaks as PB, revealing that the doping of SNP did not alter the crystal structure of PB (Fig. 2G).

Fig. 2.

Synthesis and characterization of FU/PBN@CUR. TEM images of (A) PBN and (B) PBN@CUR. Scale bars, 200 nm. XPS spectra of (C) PB and (D) PBN. (E) Elemental mapping of PBN. Scale bar, 200 nm. (F) FTIR spectra of free SNP, PB, PBN, free CUR, and PBN@CUR. (G) XRD patterns of PB and PBN. (H) N₂ adsorption-desorption isotherms and pore size distribution of PBN. SEM images of (I) FU/CS blank hydrogel and (J) FU/PBN@CUR. Scale bars, 1 mm. (K) Time-dependent release profiles of CUR under different conditions

The etching effect of hydrochloric acid promoted the formation of porous structures in PBN nanoparticles, which contributed to the catalytic activity and drug-loading capacity of the nanozyme [35]. The N₂ adsorption-desorption isotherm of PBN displayed that it was a type IV mesopore material (Fig. 2H). Its surface area and average pore size were 256.81 m²/g and 8.3948 nm, respectively. To load CUR into PBN to prepare PBN@CUR, different feed ratios of PBN to CUR were screened. When the weight ratio of PBN to CUR was 1:2, the LC and LE of PBN@CUR were 47.6% and 71.6%, respectively (Fig. S3). The TEM image revealed that PBN@CUR retained a cubic morphology with a particle size of about 180 nm (Fig. 2B). The particle size and PDI of the PBN@CUR suspension showed no significant change over 8 days of storage at 4 °C, indicating good stability (Fig. S4a). Characteristic absorption peaks of CUR were observed in the FT-IR spectrum of PBN@CUR, further verifying the successful loading of CUR into PBN. As shown in Fig. 2F, the spectrum of PBN@CUR revealed characteristic peaks derived from CUR, specifically at 1603 cm^{− 1} and 1029 cm⁻¹ (attributed to C = C bending on the aromatic rings) and at 1429 cm⁻¹ (attributed to C = C stretching in aromatic rings).

Subsequently, we used a hydrogel formed by FU and CS through physical cross-linking to encapsulate PBN@CUR, yielding the NIR-controlled photothermal intelligent nanozyme FU/PBN@CUR. The SEM images of the FU/CS blank hydrogel and FU/PBN@CUR indicated that the hydrogels successfully encapsulated the nanoparticles (Fig. 2I and J). As shown in Fig. S4b, the hydrogel coating increased the negative charge of PBN@CUR to − 30.6 mV, a value that more favorably promotes the nanozyme’s subsequent electrostatic adsorption to the inflamed colon, which secretes positively charged proteins. Furthermore, the LE and LC of CUR in FU/PBN@CUR were determined to be 92.1 ± 0.1% and 4.1 ± 0.5% respectively, based on the quantification of free CUR content using HPLC. It was observed from Fig. S5a that the incorporation of the FU/CS hydrogel improved the adhesion performance of PBN@CUR. In addition, we validated the injectability of FU/PBN@CUR using a gavage needle, supporting its potential for oral administration (Fig. S5b). Next, we evaluated the in vitro release kinetics of FU/PBN@CUR. As shown in Fig. 2K, the amount of CUR released from FU/PBN@CUR was significantly lower at pH 2.0 compared to that at pH 6.5 and 7.4 during the observation period. Within 36 h, the cumulative CUR release reached 95.7% at pH 7.4, compared to 59.6% at pH 2.0. Furthermore, the release rate of PBN@CUR was consistently higher than that of FU/PBN@CUR under the same pH conditions and time points. These results indicated that FU/CS hydrogel exhibited strong pH-responsive properties, capable of protecting the nanozymes from gastric acid degradation and facilitating targeted drug delivery to the colon. Additionally, the effect of PTT on modulating and accelerating the release of CUR was explored. The release profiles indicated that the release rate of CUR from PBN@CUR and FU/PBN@CUR increased following laser irradiation.

Evaluation of photothermal property

We further investigated the photothermal property of PBN@CUR by recording temperature variations. PBN@CUR exhibited a significant concentration-dependent temperature increase under laser irradiation (Fig. 3A and B). When a 200 µg/mL solution of PBN@CUR was irradiated for 7 min, the temperature reached 51.3 °C, while the temperature of PBS displayed minimal change. Additionally, the temperature of PBN@CUR gradually increased as the laser power density increased from 0.5 to 1.5 W/cm² (Fig. 3C). These results indicated that PBN@CUR possessed a significant photothermal effect. Moreover, PBN@CUR maintained a temperature of 49.2 °C after five NIR irradiation cycles, demonstrating excellent photothermal stability (Fig. 3D). The maximum temperature also gradually increased after each cycle, due to the enhanced absorbance of PBN@CUR at 808 nm.

Fig. 3.

Evaluation of enzyme-like activity, photothermal effects, and NIR-controlled NO release. (A) Thermographic images of different concentrations of PBN@CUR (1 W/cm², 7 min). (B) Temperature change curves after 7 min of irradiation with different concentrations of PBN@CUR (1 W/cm²). (C) Temperature variation profiles of 200 µg/mL PBN@CUR under different power densities. (D) Photothermal stability of PBN@CUR. (E) NO release profile of PBN under NIR on/off switching control. (F) NO release profiles at different laser power densities. Evaluation of (G) H₂O₂ scavenging activity, (H) SOD-like activity (promoting O₂⁻ scavenging), (I) POD-like activity (promoting ABTS radical generation), and (J) DPPH scavenging activity of PBN@CUR (n = 3)

NO release from PBN and FU/PBN@CUR

We investigated the NIR-controlled release behavior of NO from PBN. When the laser was switched on, PBN rapidly released NO, while turning off the laser led to an almost complete cessation of gas release. The release rate remained relatively stable with prolonged irradiation (Fig. 3E). We then investigated the influence of laser power on NO release, revealing a positive correlation between the NO release rate and the laser power density (Fig. 3F). In addition, the NO release curves revealed that neither SNP nor PB responded to NIR laser irradiation (Fig. S6a). Similarly, the release profiles demonstrated that NO release from FU/PBN@CUR exhibited excellent NIR controllability. Furthermore, due to the pH-responsive of the hydrogel, NO release was higher at pH 7.4 than at pH 2.0 (Fig. S6b). This NIR-controlled NO release behavior of PBN could significantly contribute to its precisely targeted therapeutic application.

Enzyme-like activity and free radical scavenging activity of PBN@CUR

Previous studies have demonstrated that PBN can mimic multiple enzyme activities and exhibit potent ROS scavenging capacity [36, 37]. As observed in Fig. S7, after co-incubating different concentrations of PBN with H₂O₂ solution, numerous bubbles from H₂O₂ decomposition were found attached to the tube walls. In the comparative analysis of antioxidant activity among different formulation groups, PBN exhibited superior SOD-, CAT-, and POD-like activities compared to CUR. Moreover, the combination of PBN and CUR synergistically led to a significant enhancement in all three enzyme-mimicking activities (Fig. S8). Furthermore, quantitative analysis revealed a concentration-dependent increase in H₂O₂ scavenging efficiency by PBN@CUR. (Fig. 3G). When the concentration was 400 µg/mL, the scavenging rate reached 85%. Meanwhile, we investigated the SOD-like and POD-like activities of PBN@CUR through different catalytic mechanisms, both of which exhibited a concentration-dependent increase. The results indicated that the nanozyme possessed strong SOD-like activity (Fig. 3H), while demonstrating relatively weak POD-like activity (Fig. 3I). DPPH is a stable free radical widely used for in vitro evaluation of antioxidant activity [38]. As illustrated in Fig. 3J, the nanozyme exhibited concentration-dependent DPPH scavenging activity, achieving a scavenging rate of 68% at 400 µg/mL.

Safety evaluation of the FU/PBN@CUR

Firstly, the cytotoxicity of various nanozymes on RAW264.7 and Caco-2 cells was assessed using the CCK-8 assay (Fig. 4A and B). The results demonstrated improved cell viability of FU/PBN@CUR compared to PBN@CUR in both cell lines. Even at a high concentration (equivalent to 40 µg/mL CUR), the cellular activity was still higher than 80%. This suggested that the addition of the hydrogel improved the biocompatibility of PBN@CUR. In addition, we observed that laser irradiation had a mild inhibitory effect on RAW264.7 cell viability, but the activity remained above 80% at 40 µg/mL CUR equivalent. On the contrary, the cell viability of Caco-2 cells increased following laser irradiation. This phenomenon may be attributed to the combined effects of the PBN-mediated photothermal effect and NO, both of which promote Caco-2 cell proliferation.

Fig. 4.

Biocompatibility evaluation of FU/PBN@CUR. The cell viability of (A) RAW264.7 and (B) Caco-2 cells after treatment with different concentrations of the preparation. Plasma levels of (C) ALT, (D) AST, and (E) UREA in IBD mice (n = 3). *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 vs. Control. (F) Histological analysis of major organs. Scale bar, 100 μm

Next, we evaluated the in vivo safety of the intelligent nanozyme. The levels of ALT, AST, and UREA in both the FU/PBN@CUR and FU/PBN@CUR + L groups showed no significant differences compared to the healthy control group (Fig. 4C-E). H&E staining of major organs in all treatment groups revealed no evident tissue damage or pathological abnormalities (Fig. 4F). Collectively, these results suggested that FU/PBN@CUR exhibits a favorable safety profile in vitro and in vivo.

Uptake of FU/PBN@CUR by RAW264.7 and Caco-2 cells

To evaluate whether FU modification enhances the cellular uptake of the multifunctional nanozyme by RAW264.7 and Caco-2 cells under inflammatory conditions, we prepared PBN@DID and FU/PBN@DID using DID as a substitute for CUR. CLSM analysis revealed only weak fluorescence signals in both cell types without LPS treatment (Fig. 5A and B). However, in LPS-treated cells, FU/PBN@DID exhibited significantly stronger red fluorescence than PBN@DID. These results clearly indicate that the modification of FU/CS hydrogel substantially improves the cellular uptake of the nanozyme in both cell types, particularly following LPS activation.

Fig. 5.

Cellular uptake and in vitro evaluation of anti-inflammatory and intestinal barrier repair effects. Uptake of PBN@DID and FU/PBN@DID by (A) RAW264.7 and (B) Caco-2 cells, with or without LPS stimulation. Scale bar, 50 and 100 μm, respectively. (C) Fluorescence images of intracellular ROS, using DCFH-DA as the probe. Scale bar, 100 μm. (D) Quantitative analysis of DCFH-DA fluorescence intensity in RAW264.7 cells (n = 3). mRNA expression levels of (E) TNF-α, (F) IL-1β, and (G) IL-10 in RAW264.7 cells treated with different preparations, detected by qRT-PCR (n = 3). mRNA expression levels of (H) Occludin and (I) ZO-1 in Caco-2 cells treated with different preparations, detected by qRT-PCR (n = 3)

Intracellular ROS scavenging by FU/PBN@CUR

By employing DCFH-DA as a fluorescent probe for ROS detection, we observed that RAW264.7 cells stimulated with LPS exhibited the strongest green fluorescence, indicating significantly elevated intracellular ROS generation. Following treatment, green fluorescence intensity gradually decreased in all groups, with the FU/PBN@CUR group showing a more pronounced reduction than PBN@CUR and PBN, likely due to the presence of targeting molecules (Fig. 5C). However, it is worth noting that the addition of laser irradiation had a negligible effect on the enhancement of ROS scavenging. Quantitative analysis using a microplate reader further validated these findings (Fig. 5D), demonstrating that FU/PBN@CUR possesses remarkable ROS-scavenging capacity. Furthermore, intracellular SOD activity was quantitatively assessed following FU/PBN@CUR treatment, revealing a concentration-dependent enhancement in enzymatic activity (Fig. S9a). These results demonstrated that PBN-loaded hydrogels could effectively alleviate oxidative stress.

Repolarization of activated macrophages by FU/PBN@CUR

Numerous studies have shown that activated macrophages produce excessive amounts of ROS, which in turn leads to a metabolic imbalance between pro-inflammatory and anti-inflammatory factors [39, 40]. To investigate whether FU/PBN@CUR could effectively mitigate the inflammatory response in activated macrophages, we quantitatively analyzed the levels of TNF-α, IL-1β, and IL-10 following treatment with various preparations. The results demonstrated that treatment with FU/PBN@CUR group significantly downregulated TNF-α and IL-1β expression while upregulating IL-10 production (Fig. 5E-G). The downregulation of intracellular ROS contributes to the repolarization of M1-type macrophages towards the M2 phenotype, thereby improving anti-inflammatory efficacy. To verify this effect, we quantified the expression levels of the M1 marker (CD68) and M2 marker (Arg-1) in the different treatment groups using qRT-PCR. The FU/PBN@CUR group significantly upregulated Arg-1 expression while downregulating CD68 levels (Fig. S9b and c). However, no statistically significant differences were detected in the expression of these inflammatory markers between laser-exposed and non-exposed groups, indicating that laser irradiation contributed little to the pro-macrophage polarization effect of FU/PBN@CUR [41, 42]. Furthermore, WB analysis demonstrated the beneficial role of PBN in promoting M1-to-M2 macrophage polarization, with the effect being most pronounced for FU/PBN@CUR (Fig. S9d). These findings collectively demonstrated that the intelligent nanozyme significantly alleviated mucosal inflammation in IBD by inducing macrophage repolarization toward the M2 phenotype. Nevertheless, the ameliorative effects of its photothermal activity and NO release on IBD pathogenesis may involve mechanisms independent of inflammation suppression.

In vitro intestinal barrier repair capacity of FU/PBN@CUR

QRT-PCR analysis revealed significant alterations in the expression levels of tight junction proteins ZO-1 and Occludin in Caco-2 cells following treatment with various preparations. As shown in Fig. 5H and I, the expression of Occludin and ZO-1 was significantly reduced in the model group after LPS-induced injury. Notably, the FU/PBN@CUR + L treatment demonstrated the most pronounced upregulation of both Occludin and ZO-1 expression. However, the addition of an autophagy inhibitor significantly decreased their expression, confirming that mPTT-induced autophagy promoted the expression of tight junction proteins. Similarly, the SNP-doped intelligent nanozyme significantly enhanced the expression of ZO-1 and Occludin compared to its undoped counterpart, with an effect comparable to that of exogenous NO. These results revealed that intestinal barrier restoration by FU/PBN@CUR + L was synergistically mediated by NO release and photothermal effects, wherein NO contributed predominantly to the therapeutic outcome. To further investigate whether the photothermal effect of PBN promotes intestinal epithelial repair through autophagy induction, we examined autophagy levels in Caco-2 cells following various treatments. Compared with the no-laser group, the mRNA expression of the autophagy-related proteins Beclin-1 and LC3B in the FU/PB@CUR + L group demonstrated a significant elevation, while p62 expression was reduced (Fig. S10), which is indicative of autophagy activation. Our findings indicated that the photothermal effect of PBN effectively induced autophagy in Caco-2 cells.

Clinical evidence has demonstrated that the proliferation and migration of intestinal epithelial cells are critical for intestinal barrier repair [43]. To further evaluate the proliferative effects of FU/PBN@CUR on Caco-2 cells, we conducted a scratch wound assay. As shown in the Fig. S11, the FU/PBN@CUR + L treatment group displayed the maximum migration rate of Caco-2 cells compared to other treatment groups. These results further validated that NIR-controlled NO release promoted the proliferation and migration of intestinal epithelial cells.

In vivo biodistribution evaluation

Significant fluorescence signals were observed in the intestinal tract of live mice 6 h post-oral administration. The fluorescence intensity in all preparation groups initially increased and then gradually decreased over time. Notably, the FU/PBN@DID group maintained consistently higher fluorescence intensity than both the PBN@DID and DID groups throughout the observation period (Fig. 6A and S12). Fluorescence analysis of isolated colon tissue also exhibited a similar trend as observed in living mice. At 24 h post-administration, fluorescence imaging of isolated colons showed that the FU/PBN@DID group still exhibited significantly higher fluorescence intensity than that of the free DID and PBN@DID groups (Fig. 6B and D). Furthermore, the fluorescence distribution across organs suggested that the liver served as the primary metabolic pathway for the intelligent nanozyme (Fig. 6C). These results demonstrated that the FU-based hydrogel significantly enhanced accumulation and prolonged retention duration in inflamed colonic tissues.

Fig. 6.

In vivo biodistribution evaluation of FU/PBN@DID. (A) Fluorescence images of DSS-induced colitis mice after oral administration of free DID, PBN@DID, and FU/PBN@DID. Ex vivo distribution of DID fluorescence in the (B) small intestine and colon, and (C) major organs at 6, 12, and 24 h post-administration. (D) Quantitative analysis of colon fluorescence intensity at 6, 12, and 24 h post-administration (n = 3)

Evaluation of in vivo photothermal performance

Effective in vivo photothermal performance serves as a fundamental prerequisite for therapeutic efficacy. To evaluate the photothermal effect of FU/PBN@CUR at IBD lesion sites, we acquired thermal images using a FLIR C3-X infrared thermal camera and recorded temperature variations. As shown in Fig. S13, the intestinal temperature in the saline group exhibited no significant increase over time. In contrast, both PBN@CUR and FU/PBN@CUR treatments induced a progressive elevation in intestinal temperature, with FU/PBN@CUR demonstrating the most pronounced photothermal response.

Evaluation of therapeutic efficacy in IBD mice

Following the treatment procedure illustrated in the Fig. 7A, we evaluated the in vivo therapeutic efficacy of FU/PBN@CUR. The principal clinical manifestations of IBD include weight loss, diarrhea, and hematochezia. Therefore, we assessed disease severity by monitoring body weight and calculating the DAI score, which was calculated based on weight variation, stool consistency, and fecal occult blood. Higher degrees of weight loss and elevated DAI scores correlate with more severe IBD progression [44]. As shown in Fig. 7B and C, mice treated with FU/PBN@CUR + L exhibited significant body weight recovery and the greatest reduction in DAI score compared to the DSS group. Colon shortening represents a common consequence of intestinal epithelial barrier injury, mucosal damage, and tissue dehydration during colitis. Representative photographs of the colon (Fig. 7D) and length measurements (Fig. 7E) revealed that the FU/PBN@CUR + L treatment group exhibited the most pronounced increase in colon length compared to the DSS group, approaching that of the healthy control group. Histopathological evaluation using H&E staining displayed that FU/PBN@CUR + L conferred superior therapeutic efficacy in ameliorating DSS-induced murine colitis compared to other intervention groups. Specifically, the healthy control group exhibited normal colonic architecture without inflammatory infiltration or tissue damage. In contrast, the DSS-treated mice demonstrated severe histopathological alterations, including crypt necrosis, reduction of cup cells, mucosal edema, and architectural distortion. Remarkably, FU/PBN@CUR + L treatment significantly ameliorated these pathological features (Fig. 7F). Collectively, these findings indicated that the intelligent nanozyme conferred superior therapeutic effects against DSS-triggered IBD mice.

Fig. 7.

Therapeutic efficiency of FU/PBN@CUR in vivo. (A) Schematic illustration of the IBD mouse model establishment and dosing regimen. (B) Body weight changes (n = 3). (C) Daily DAI scores throughout the entire process (n = 3). (D) Representative colon images and (E) length analysis in healthy and treated groups (n = 3). (F) H&E staining images of colonic tissues from healthy mice and DSS-induced colitis mice with different treatments. Scale bar, 100 μm. The levels of (G) TNF-α, (H) IL-6, and (I) IL-10 in colonic tissue after treatment in each group (n = 3)

In vivo inflammation regulation and barrier repair

To evaluate the anti-inflammatory efficacy of FU/PBN@CUR in DSS-induced IBD, we quantified inflammatory cytokine levels in both plasma and colonic tissues across treatment groups. Additionally, inflammatory cell infiltration in the colonic mucosa was assessed by immunohistochemical staining. As illustrated in the experimental results, the FU/PBN@CUR + L group indicated remarkable downregulation of pro-inflammatory factors (TNF-α and IL-6) in both plasma (Fig. S14a and b) and colonic tissues (Fig. 7G and H), along with markedly reduced M1 macrophage infiltration (Fig. 8A and B), compared to the DSS control group. Conversely, this therapeutic intervention significantly elevated the expression of anti-inflammatory IL-10 (Fig. 7I and S14c) and enhanced M2 macrophage recruitment (Fig. 8C).

Fig. 8.

Inflammatory cell infiltration and tight junction protein expression in vivo. (A) Representative immunohistochemical images of CD68, CD163, Claudin, and ZO-1 expression in the colon after various treatments. Scale bar, 40 μm. Quantitative analyses of (B) CD68, (C) CD163, (D) Claudin, and (E) ZO-1 expression levels in colonic tissues (n = 3)

As previously established, intestinal barrier restoration constitutes a critical therapeutic goal in IBD management. To investigate whether the intelligent nanozyme could accelerate barrier repair, we quantitatively analyzed the ZO-1 and Claudin expression in colonic tissues via IHC. These proteins serve as core structural components of intestinal epithelial tight junctions and are well-established biomarkers of mucosal integrity and barrier function. As shown in Fig. 8D and E, DSS treatment substantially suppressed Claudin and ZO-1 expression in colonic tissues, demonstrating severe inflammation-induced mucosal damage. In contrast, FU/PBN@CUR + L treatment elicited the most pronounced upregulation of both ZO-1 and Claudin, indicating restoration of colonic mucosal integrity and barrier function. These results collectively suggested that the integration of FU/PBN@CUR with NIR laser irradiation effectively attenuated intestinal mucosal inflammation and facilitated the regeneration of impaired intestinal barriers, contributing to IBD therapy.

Discussion

In this study, we designed an NIR-controlled photothermal intelligent nanozyme based on the enzymatic catalysis of PB, a mild photothermal effect, and NIR-controllable NO release for a multipronged intervention in reducing mucosal inflammation and repairing the damaged intestinal epithelial barrier. FU/PBN@CUR exhibited satisfactory pH-responsive behavior in vitro and preferential accumulation in inflamed colonic tissues. Furthermore, the nanozyme promoted macrophage polarization from the M1 to M2 phenotype by scavenging ROS. Compared with PB alone, PBN synergistically promoted the proliferation of intestinal epithelial cells and upregulated the expression of tight junction proteins through NO release and photothermally induced autophagy. Animal experiments further demonstrated that FU/PBN@CUR synergistically disrupted the vicious cycle between inflammation and intestinal barrier damage in DSS-induced IBD mouse models through dual mechanisms of remodeling inflammatory macrophage phenotypes and restoring intestinal barrier function.

Traditional IBD management predominantly relies on pharmacological regulation of immunity using anti-inflammatory drugs and immunosuppressive therapies [45, 46]. However, these drugs are prone to systemic side effects due to their off-target effects [47–49]. The inflammatory cascade in IBD induces a sharp elevation of mucosal ROS levels, driving most existing studies to concentrate on antioxidant-based strategies for immunomodulatory therapy [50, 51]. Among these approaches, nanozymes can cyclically catalyze ROS decomposition and exhibit sustained antioxidant capacity compared with conventional antioxidants [52, 53]. However, traditional nanozymes primarily exert antioxidant effects and mostly indirectly regulating other pathological injuries, with relatively singular functionality [5, 54, 55]. For example, Huang et al. prepared CeO₂@S100 by encapsulating CeO₂ nanoparticles in a polyacrylic resin shell, which demonstrated efficacy in IBD treatment by modulating redox balance and the gut microbiome [10]. To address these limitations, we innovatively developed an NIR-controlled photothermal intelligent nanozyme that combines enzymatic catalysis, mPTT, and gas therapy to achieve intestinal mucosal immunomodulation and barrier repair in IBD.

PB is a highly biocompatible nanomaterial [56]. Mesoporous PB nanozymes have been shown in our previous studies to effectively reduce intracellular ROS levels and regulate the redox microenvironment [22, 23]. In recent years, unlike conventional PTT, which relies on extremely high temperatures to ablate cells, mPTT has garnered increasing attention in disease treatment due to its minimal damage to healthy tissues [57, 58]. Coincidentally, our earlier work found that PB nanoparticles possess a mild photothermal effect [59]. Notably, mild photothermal stimulation can induce autophagy in intestinal epithelial cells and promote the expression of tight junction proteins. However, the development of cellular thermotolerance and upregulation of heat shock proteins may impair the effectiveness of mPTT-based intestinal barrier repair strategies. Hence, we sought to develop novel nanotherapeutic agents based on PB. Gas therapy is an emerging green therapy with benign biocompatibility and high permeability, allowing rapid intracellular penetration and direct action on signaling pathways and biomolecules [60, 61]. Compared with traditional drug therapy, gas therapy offers higher delivery efficiency, enabling more precise targeting of lesions [62]. NO is an endogenous trace gaseous transmitter in the GIT, with low levels shown to possess outstanding intestinal barrier-repairing ability in previous studies [21]. However, in exogenous delivery strategies, the concentration and duration of local gas exposure are crucial factors affecting efficacy [63]. Therefore, a major challenge in IBD therapy remains the efficient loading and precise delivery of NO because of its short half-life and limited diffusion distance [64]. To address these challenges, we prepared a multifunctional nanozyme, PBN, by doping the NO donor SNP into mesoporous PB nanoparticles. The resulting PBN can cleave the Fe-NO coordination bond to release free NO molecules via photothermal conversion under in vitro NIR irradiation, showing NIR-controlled NO release behavior. In our studies, the developed nanozyme demonstrated remarkable multifunctionality, including ROS scavenging to inhibit intestinal mucosal inflammation, mild photothermal effects, and NO-mediated intestinal barrier repair.

Oral administration exposes the drug delivery system to obstacles in the GIT, such as first-pass metabolism, extreme pH, and enzymatic degradation, which leads to limited drug accumulation in the inflamed colon [65–67]. Microenvironment-responsive nano delivery systems offer a promising solution by leveraging the distinct pH gradients present across different GIT regions. The stomach has an acidic pH, the small intestine ranges from slightly acidic to neutral, and the colon typically has a pH range of 6.1–7.5 [68]. Taking advantage of these microenvironmental differences, we previously developed a hydrogel composed of sodium alginate and CS to deliver anti-inflammatory drugs for the treatment of IBD. However, passive targeting alone was insufficient to achieve the required drug accumulation [3]. Thus, in this study, we prepared hydrogels using FU and CS, which showed satisfactory pH-responsive properties in cumulative drug release experiments and guaranteed the smooth passage of the nanozymes through the gastric acidic environment during GIT transit. Meanwhile, in vivo biodistribution studies displayed significantly enhanced accumulation of nanozymes in the inflammatory colon due to the specific binding of FU to P-selectin, which is highly expressed in inflamed colonic tissue. Even more surprisingly, the hydrogel elevated moisture content and softness enable it to mimic the physical properties of the intestinal mucosa, demonstrating biomimetic characteristics [69].

In our study, the intelligent nanozyme demonstrated remarkable multifunctional efficacy. However, delineating the individual contributions of ROS scavenging, NO release, mPTT, and CUR to the overall therapeutic outcome remains a key challenge. We propose that implementing a comprehensive experimental matrix incorporating single-function-deficient controls would be an optimal strategy to clarify the independent roles of each component. More importantly, gut microbiota dysbiosis represents another critical pathological feature of IBD, as intestinal microorganisms produce various metabolites, including short-chain fatty acids, bile acids, and essential vitamins, that modulate immune responses and maintain metabolic homeostasis [70–72]. Therefore, future investigations should further explore the regulatory effects of FU/PBN@CUR on gut microbiota composition and function [73].

Conclusion

In summary, aiming at the pathological characteristics of the disease, we successfully synthesized an NIR-controlled photothermal intelligent nanozyme (FU/PBN@CUR) for multimodal IBD treatment. FU/PBN@CUR exhibited excellent in vitro adhesiveness and could pass smoothly through a gavage needle. It remained relatively stable in simulated gastric fluid but disintegrated in simulated colonic fluid, suggesting that this system could effectively reduce gastric acid exposure and achieve selective colonic release. More importantly, this formulation efficiently scavenged excessive ROS in activated macrophages and modulated their phenotypic polarization. In addition, NO release, synergized with the mild photothermal effect under NIR laser irradiation, induced the proliferation and migration of intestinal epithelial cells and promoted the expression of tight junction proteins. Furthermore, in vivo evaluations confirmed the excellent biosafety of the nanoplatform and revealed its preferential biodistribution in inflamed colon regions. Following NIR laser irradiation, the preparation significantly alleviated mucosal inflammation while promoting the structural reconstitution of the impaired intestinal epithelial barrier. In conclusion, this study presented a distinctive multifunctional nanozyme paradigm for IBD treatment.

Author contributions

Xiaoya Liang and Xin Yu: Methodology, Investigation, Writing–original draft. Yilin Liu and Xinghui He: Methodology, Investigation. Keyi Ding and Xiao Tan: Writing–original draft. Qi LI, Ting Zhao and Yue Lan: Conceptualization. Meiling Zhou: Conceptualization, Supervision. Chunhong Li: Writing – review & editing, Funding acquisition, Project administration.

Funding

This work was supported by the Xuyong County People’s Hospital-Southwest Medical University Joint Scientific Research Project (grant numbers 2023XYXNYD14), the Pengzhou First People’s Hospital-Southwest Medical University Cooperation Project (grant number 2023PZXNYD07), the Hejiang County People’s Hospital-Southwest Medical University Joint Scientific Research Project (grant numbers 2022HJXNYD14).

Data availability

Data will be made available on request.

Declarations

Competing interests

The authors declare no competing interests.