A Dual-network Nerve Adhesive with Enhanced Adhesion Strength Promotes Transected Peripheral Nerve Repair

Transplantation of peripheral nerve tissueoid based on a decellularized optic nerve scaffold to restore rat hindlimb sensory and movement functions

Peripheral nerve injury (PNI) involving the loss of sensory and movement functions is challenging to repair. Although the gold standard of PNI repair is still the use of autologous nerve grafts, the destruction of the donor side is inevitable. In the present study, peripheral nerve tissueoids (PNTs) composed of a Schwann cell (SC)-based neurotrophin-3 (NT-3) delivery system and a decellularized optic nerve (DON) with naturally oriented channels were engineered to investigate the mechanism of PNTs in nerve regeneration. Proteomic analysis and mRNA sequencing revealed that PNTs have the advantage of promoting nerve regeneration by the three mechanisms of chemotaxis, adhesion and intrinsic mobilisation. The results demonstrated that a local NT-3-enriched pool was constructed by laminin γ3 (LAMC3) in PNTs, creating a niche for the colonization of TrkC-positive SCs, attraction of axons to the defect/graft area, and remyelination. In addition, LAMC3 in PNTs can rapidly promote axon adhesion through integrin aVβ6 and can precisely guide long projecting axons to target tissues. Furthermore, the interactions among the NT-3/TrkC, LAMC3/integrin aVβ6 and the scaffold synergistically activate the PI3K-AKT signalling pathway in damaged neurons, further stimulating the intrinsic regenerative drive within the neurons to ultimately achieve the rapid reinnervation and the improvement of sensory and movement functions in the hindlimb.

ROS-responsive injectable hydrogels loaded with exosomes carrying miR-4500 reverse liver fibrosis

The reversal of liver fibrosis requires effective strategies to reduce oxidative stress and inhibition of hepatic stellate cell (HSC) activation. MiR-4500 regulates pathological angiogenesis and collagen mRNA stability, with the potential to inhibit fibrosis. Herein, we explored the inhibition of HSC activation in vitro by exosomes (Exos) carrying miR-4500 and encapsulated ExosmiR-4500 in an intelligent injectable hydrogel with biological activity and reactive oxygen species (ROS) responsiveness for application in oxidative stress environments. Briefly, reversible boronic ester bonds were integrated into gelatin-based hydrogels through dynamic crosslinking of quaternized chitosan (QCS) and 4-carboxyphenylboronic acid (CPBA)-modified gelatin. The QCS-CPBA-Gelatin (QCG) hydrogel scavenged excess ROS from the local microenvironment and released ExosmiR-4500 through the dissociation of boronic ester bonds, providing a favorable microenvironment and in situ sustained-release drug delivery system for ExosmiR-4500. The results showed that QCG@ExosmiR-4500 hydrogel has biocompatibility, biodegradability, and slow-release ability, which could effectively clear ROS and inhibit HSC activation and pathological angiogenesis in vitro and in vivo. Furthermore, transcriptome analysis suggests that the pharmacological mechanism of the QCG@ExosmiR-4500 hydrogel is mainly related to anti-oxidation, anti-angiogenesis, anti-fibrosis processes, and signaling pathways. Thus, our study demonstrates that an intelligently responsive ExosmiR-4500 delivery system based on injectable hydrogels is a promising strategy for the treatment of liver fibrosis.

Recent Advances in Multifunctional Naturally Derived Bioadhesives for Tissue Engineering and Wound Management

Recent advancements in naturally derived bioadhesives have transformed their application across diverse medical fields, including tissue engineering, wound management, and surgery. This review focuses on the innovative development and multifunctional nature of these bioadhesives, particularly emphasizing their role in enhancing adhesion performance in wet environments and optimizing mechanical properties for use in dynamic tissues. Key areas covered include the chemical and physical mechanisms of adhesion, the incorporation of multi‐adhesion strategies that combine covalent and non‐covalent bonding, and bioinspired designs mimicking natural adhesives such as those of barnacles and mussels. Additionally, the review discusses emerging applications of bioadhesives in the regeneration of musculoskeletal, cardiac, neural, and ocular tissues, highlighting the potential for bioadhesive‐based therapies in complex biological settings. Despite substantial progress, challenges such as scaling lab‐based innovations for clinical use and overcoming environmental and mechanical constraints remain critical. Ongoing research in bioadhesive technologies aims to bridge these gaps, promising significant improvements in medical adhesives tailored for diverse therapeutic needs.

Rapid Forming, Robust Adhesive Fungal-Sourced Chitosan Hydrogels Loaded with Deferoxamine for Sutureless Short-Gap Peripheral Nerve Repair

Clinically, conventional sutures for repair of short-distance nerve injuries (< 5 mm) may contribute to uncontrolled inflammation and scar formation, thus negatively impacting nerve regeneration. To repair transected peripheral nerves with short distances, a rapid-forming, robust adhesive chitosan hydrogel is prepared by synthesizing maleic and dopamine bi-functionalized fungal-sourced chitosan (DM) and subsequently photopolymerizing DM precursor solution. The hydrogel rapidly polymerized under UV light irradiation (≈2 s) and possessed a strong adhesive strength (273.33 ± 55.07 kPa), facilitating a fast bonding of nerve stump. Especially, its tailored degradation profile over 28 days supported both early gap bridging and subsequent nerve regeneration. Furthermore, deferoxamine (DFO), a pro-angiogenic drug, is loaded into the hydrogel to reach sustainable release, accelerating axonal growth synergistically. A 3 mm long sciatic nerve defects model in rats is used to investigate the efficacy of DM@DFO hydrogel for repairing peripheral nerve defects. After 60 days, the DM@DFO hydrogel significantly outperformed conventional sutures and fibrin glue, improving motor and sensory recovery by reducing inflammation, inhibiting scar formation, and accelerating vascular regeneration within 14 days post-repair. This work highlights the DM@DFO hydrogel as a promising tissue adhesive for effective short-distance peripheral nerve repair.

Deformation-Resistant Underwater Adhesion in a Wide Salinity Range

Conventional adhesives experience reduced adhesion when exposed to aqueous environments. The development of underwater adhesives capable of forming strong and durable bonds across various wet substrates is crucial in biomedical and engineering domains. Nonetheless, limited emphasis placed on retaining high adhesion strengths in different saline environments, addressing challenges such as elevated osmotic pressure and spontaneous dimensional alterations. Herein, a series of ionogel-based underwater adhesives are developed using a copolymerization approach that incorporates "dynamic complementary cross-linking" networks. Synergistic engineering of building blocks, cross-linking networks, pendant groups and counterions within ionogels ensures their adhesion and cohesion in brine spanning a wide salinity range. A high adhesion strength of ≈3.6 MPa is attained in freshwater. Gratifyingly, steady adhesion strengths exceeding 3.3 MPa are retained in hypersaline solutions with salinity ranging from 50 to 200 g kg-1, delivering one of the best-performing underwater adhesives suitable for diverse saline solutions. A combination of outstanding durability, reliability, deformation resistance, salt tolerance, and self-healing properties showcases the "self-contained" underwater adhesion. This study shines light on the facile fabrication of catechol-free ionogel-based adhesives, not merely boosting adhesion strengths in freshwater, but also broadening their applicability across various saline environments.

Predicting in vivo therapeutic efficacy of CelTrac1000-labeled hair follicle epidermal neural crest stem cells in models of repairing rat facial nerve defects via second near-infrared fluorescence imaging

AIMS

To detect the therapeutic efficacy of CelTrac1000-labeled hair follicle epidermal neural crest stem cells (EPI-NCSCs) on repairing facial nerve defects by second near-infrared (NIR-II) fluorescence imaging.

MATERIALS AND METHODS

Firstly, CelTrac1000-labeled EPI-NCSCs were microinjected into the acellular nerve allografts (ANAs) to bridge a 10-mm-long gap in the buccal branch of facial nerve in adult rats. Then, Celtrac1000-labeled EPI-NCSCs were detected by NIR-II fluorescence imaging system to visualize the behavior of the transplanted cells in vivo. Additionally, the effect of the transplanted EPI-NCSCs on repairing facial nerve defect was examined.

KEY FINDINGS

Through 14 weeks of dynamic observation, the transplanted EPI-NCSCs survived in the ANAs in vivo after surgery. Meanwhile, the region of the NIR-II fluorescence signals was gradually limited to be consistent with the direction of the regenerative nerve segment. Furthermore, the results of functional and morphological analysis showed that the transplanted EPI-NCSCs could promote the recovery of facial paralysis and neural regeneration after injury.

SIGNIFICANCE

Our research provides a novel way to track the transplanted cells in preclinical studies of cell therapy for facial paralysis, and demonstrates the therapeutic potential of EPI-NCSCs combined with ANAs in bridging rat facial nerve defects.

A stretchable, electroconductive tissue adhesive for the treatment of neural injury

Successful nerve repair using bioadhesive hydrogels demands minimizing tissue-material interfacial mechanical mismatch to reduce immune responses and scar tissue formation. Furthermore, it is crucial to maintain the bioelectrical stimulation-mediated cell-signaling mechanism to overcome communication barriers within injured nerve tissues. Therefore, engineering bioadhesives for neural tissue regeneration necessitates the integration of electroconductive properties with tissue-like biomechanics. In this study, we propose a stretchable bioadhesive based on a custom-designed chemically modified elastin-like polypeptides (ELPs) and a choline-based bioionic liquid (Bio-IL), providing an electroconductive microenvironment to reconnect damaged nerve tissue. The stretchability akin to native neural tissue was achieved by incorporating hydrophobic ELP pockets, and a robust tissue adhesion was obtained due to multi-mode tissue-material interactions through covalent and noncovalent bonding at the tissue interface. Adhesion tests revealed adhesive strength ~10 times higher than commercially available tissue adhesive, Evicel®. Furthermore, the engineered hydrogel supported in vitro viability and proliferation of human glial cells. We also evaluated the biodegradability and biocompatibility of the engineered bioadhesive in vivo using a rat subcutaneous implantation model, which demonstrated facile tissue infiltration and minimal immune response. The outlined functionalities empower the engineered elastic and electroconductive adhesive hydrogel to effectively enable sutureless surgical sealing of neural injuries and promote tissue regeneration.

Biocompatible 3D-Printed Devices With Adipose Stem Cells in the Regenerative Process of Sciatic Nerve Lesions in Rodent Models: An Experimental Study

INTRODUCTION

Peripheral nerve injuries are a significant clinical challenge. The rat sciatic nerve serves as an ideal model for studying nerve regeneration. Extensive research has been conducted to unravel the intricate mechanisms involved in peripheral nerve regeneration, aiming to develop effective therapeutic strategies for nerve injury patients. Research including different types of materials that can be used as nerve guides like synthetic polymers have been investigated for their biocompatibility and molding properties. Among multiple stem cell types, adipose-derived stem cells (ASCs), bone marrow-derived mesenchymal stem cells (BM-MSCs), and induced pluripotent stem cells (iPSCs) have shown neuroprotective and regenerative important properties.

METHODS

The purposes of our study were to develop a protocol for rat sciatic nerve injury treated with 3D-printed guide and adipose stem cells to investigate nerve regeneration through histologic examination and biomechanical characteristics of muscular tissue. We use 20 (100%) male Wistar rats, measuring between 350 g ± 35 g, who underwent complete transection of the right sciatic nerve, resulting in a 1 cm defect. The group was separated into three subgroups: the first subgroup (n = 8) was treated with a 3D-printed guide with adipose stem cells, the second subgroup (n = 8) was treated with a 3D-printed guide without adipose stem cells, and the third subgroup (n = 4) was the control group. At four, eight, and 12 weeks, we measured with ultrasonography the grade of muscular atrophy. At 12 weeks, we harvested the sciatic nerve and performed a histological examination and mechanical investigation of the tibialis anterior muscle.

RESULTS

On the examined specimen of the first subgroup, cross-sectioned nerve structures were present, surrounded by a mature fibro-adipose connective tissue, with blood vessels. In the second subgroup, no nerve structure was observed on the examined sections, but in the polymorphic inflammatory infiltrate and control group, no signs of regeneration were found.

CONCLUSIONS

The present study shows a promising potential when utilizing adipose stem cell-based therapies for promoting peripheral nerve regeneration following large (>1 cm) nerve defects knowing that at this size, regeneration is impossible with known treatments.

Paintable Decellularized-ECM Hydrogel for Preventing Cardiac Tissue Damage

The tissue-specific heart decellularized extracellular matrix (hdECM) demonstrates a variety of therapeutic advantages, including fibrosis reduction and angiogenesis. Consequently, recent research for myocardial infarction (MI) therapy has utilized hdECM with various delivery techniques, such as injection or patch implantation. In this study, a novel approach for hdECM delivery using a wet adhesive paintable hydrogel is proposed. The hdECM-containing paintable hydrogel (pdHA_t) is simply applied, with no theoretical limit to the size or shape, making it highly beneficial for scale-up. Additionally, pdHA_t exhibits robust adhesion to the epicardium, with a minimal swelling ratio and sufficient adhesion strength for MI treatment when applied to the rat MI model. Moreover, the adhesiveness of pdHA_t can be easily washed off to prevent undesired adhesion with nearby organs, such as the rib cages and lungs, which can result in stenosis. During the 28 days of in vivo analysis, the pdHA_t not only facilitates functional regeneration by reducing ventricular wall thinning but also promotes neo-vascularization in the MI region. In conclusion, the pdHA_t presents a promising strategy for MI treatment and cardiac tissue regeneration, offering the potential for improved patient outcomes and enhanced cardiac function post-MI.

Recent Advances in the Degradability and Applications of Tissue Adhesives Based on Biodegradable Polymers

In clinical practice, tissue adhesives have emerged as an alternative tool for wound treatments due to their advantages in ease of use, rapid application, less pain, and minimal tissue damage. Since most tissue adhesives are designed for internal use or wound treatments, the biodegradation of adhesives is important. To endow tissue adhesives with biodegradability, in the past few decades, various biodegradable polymers, either natural polymers (such as chitosan, hyaluronic acid, gelatin, chondroitin sulfate, starch, sodium alginate, glucans, pectin, functional proteins, and peptides) or synthetic polymers (such as poly(lactic acid), polyurethanes, polycaprolactone, and poly(lactic-co-glycolic acid)), have been utilized to develop novel biodegradable tissue adhesives. Incorporated biodegradable polymers are degraded in vivo with time under specific conditions, leading to the destruction of the structure and the further degradation of tissue adhesives. In this review, we first summarize the strategies of utilizing biodegradable polymers to develop tissue adhesives. Furthermore, we provide a symmetric overview of the biodegradable polymers used for tissue adhesives, with a specific focus on the degradability and applications of these tissue adhesives. Additionally, the challenges and perspectives of biodegradable polymer-based tissue adhesives are discussed. We expect that this review can provide new inspirations for the design of novel biodegradable tissue adhesives for biomedical applications.

In Situ-Sprayed Bioinspired Adhesive Conductive Hydrogels for Cavernous Nerve Repair

Cavernous nerve injury (CNI), resulting in erectile dysfunction (ED), poses a significant threat to the quality of life for men. Strategies utilizing conductive hydrogels have demonstrated promising results for the treatment of peripheral nerves with a large diameter (>2 mm). However, integrating convenient minimally invasive operation, antiswelling and immunomodulatory conductive hydrogels for treating small-diameter injured cavernous nerves remains a great challenge. Here, a sprayable adhesive conductive hydrogel (GACM) composed of gelatin, adenine, carbon nanotubes, and mesaconate designed for cavernous nerve repair is developed. Multiple hydrogen bonds provide GACM with excellent adhesive and antiswelling properties, enabling it to establish a conformal electrical bridge with the damaged nerve and aiding in the regeneration process. Additionally, mesaconate-loaded GACM suppresses the release of inflammatory factors by macrophages and promotes the migration and proliferation of Schwann cells. In vivo tests demonstrate that the GACM hydrogel repairs the cavernous nerve and restores erectile function and fertility. Furthermore, the feasibility of sprayable GACM in minimally invasive robotic surgery in beagles is validated. Given the benefits of therapeutic effectiveness and clinical convenience, the research suggests a promising future for sprayable GACM materials as advanced solutions for minimally invasive nerve repair.

Sticky and Strain-Gradient Artificial Epineurium for Sutureless Nerve Repair in Rodents and Nonhuman Primates

The need for the development of soft materials capable of stably adhering to nerve tissues without any suturing followed by additional damages is at the fore at a time when success in postoperative recovery depends largely on the surgical experience and/or specialized microsuturing skills of the surgeon. Despite fully recognizing such prerequisite conditions, designing the materials with robust adhesion to wet nerves as well as acute/chronic anti-inflammation remains to be resolved. Herein, a sticky and strain-gradient artificial epineurium (SSGAE) that overcomes the most critically challenging aspect for realizing sutureless repair of severely injured nerves is presented. In this regard, the SSGAE with a skin-inspired hierarchical structure entailing strain-gradient layers, anisotropic Janus layers including hydrophobic top and hydrophilic bottom surfaces, and synergistic self-healing capabilities enables immediate and stable neurorrhaphy in both rodent and nonhuman primate models, indicating that the bioinspired materials strategy significantly contributes to translational medicine for effective peripheral nerve repair.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

Emerging trends in the application of hydrogel-based biomaterials for enhanced wound healing: A literature review

Currently, there is a rising global incidence of diverse acute and chronic wounds, underscoring the immediate necessity for research and treatment advancements in wound repair. Hydrogels have emerged as promising materials for wound healing due to their unique physical and chemical properties. This review explores the classification and characteristics of hydrogel dressings, innovative preparation strategies, and advancements in delivering and releasing bioactive substances. Furthermore, it delves into the functional applications of hydrogels in wound healing, encompassing areas such as infection prevention, rapid hemostasis and adhesion adaptation, inflammation control and immune regulation, granulation tissue formation, re-epithelialization, and scar prevention and treatment. The mechanisms of action of various functional hydrogels are also discussed. Finally, this article also addresses the current limitations of hydrogels and provides insights into their potential future applications and upcoming innovative designs.

Inversely engineered biomimetic flexible network scaffolds for soft tissue regeneration

Graft-host mechanical mismatch has been a longstanding issue in clinical applications of synthetic scaffolds for soft tissue regeneration. Although numerous efforts have been devoted to resolve this grand challenge, the regenerative performance of existing synthetic scaffolds remains limited by slow tissue growth (comparing to autograft) and mechanical failures. We demonstrate a class of rationally designed flexible network scaffolds that can precisely replicate nonlinear mechanical responses of soft tissues and enhance tissue regeneration via reduced graft-host mechanical mismatch. Such flexible network scaffold includes a tubular network frame containing inversely engineered curved microstructures to produce desired mechanical properties, with an electrospun ultrathin film wrapped around the network to offer a proper microenvironment for cell growth. Using rat models with sciatic nerve defects or Achilles tendon injuries, our network scaffolds show regenerative performances evidently superior to that of clinically approved electrospun conduit scaffolds and achieve similar outcomes to autologous nerve transplantation in prevention of target organ atrophy and recovery of static sciatic index.

Mimosa-Inspired Stimuli-Responsive Curling Bioadhesive Tape Promotes Peripheral Nerve Regeneration

Trauma often results in peripheral nerve injuries (PNIs). These injuries are particularly challenging therapeutically because of variable nerve diameters, slow axonal regeneration, infection of severed ends, fragility of the nerve tissue, and the intricacy of surgical intervention. Surgical suturing is likely to cause additional damage to peripheral nerves. Therefore, an ideal nerve scaffold should possess good biocompatibility, diameter adaptability, and a stable biological interface for seamless biointegration with tissues. Inspired by the curl of Mimosa pudica, this study aimed to design and develop a diameter-adaptable, suture-free, stimulated curling bioadhesive tape (SCT) hydrogel for repairing PNI. The hydrogel is fabricated from chitosan and acrylic acid-N-hydroxysuccinimide lipid via gradient crosslinking using glutaraldehyde. It closely matches the nerves of different individuals and regions, thereby providing a bionic scaffold for axonal regeneration. In addition, this hydrogel rapidly absorbs tissue fluid from the nerve surface achieving durable wet-interface adhesion. Furthermore, the chitosan-based SCT hydrogel loaded with insulin-like growth factor-I effectively promotes peripheral nerve regeneration with excellent bioactivity. This procedure for peripheral nerve injury repair using the SCT hydrogel is simple and reduces the difficulty and duration of surgery, thereby advancing adaptive biointerfaces and reliable materials for nerve repair.

Engineered hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) is a complex disease that often appears in young adults. It is characterized by a high incidence, limited treatment options, and poor clinical outcomes. This disease not only causes dysfunction and psychological disorders in patients but also brings a heavy burden to the society. Currently, autologous nerve grafting is the gold standard in clinical treatment, but complications, such as the limited source of donor tissue and scar tissue formation, often further limit the therapeutic effect. Recently, a growing number of studies have used tissue-engineered materials to create a natural microenvironment similar to the nervous system and thus promote the regeneration of neural tissue and the recovery of impaired neural function with promising results. Hydrogels are often used as materials for the culture and differentiation of neurogenic cells due to their unique physical and chemical properties. Hydrogels can provide three-dimensional hydration networks that can be integrated into a variety of sizes and shapes to suit the morphology of neural tissues. In this review, we discuss the recent advances of engineered hydrogels for peripheral nerve repair and analyze the role of several different therapeutic strategies of hydrogels in PNI through the application characteristics of hydrogels in nerve tissue engineering (NTE). Furthermore, the prospects and challenges of the application of hydrogels in the treatment of PNI are also discussed.

In situ delivery of a curcumin-loaded dynamic hydrogel for the treatment of chronic peripheral neuropathy

Patients with peripheral nerve injuries would highly likely suffer from chronic neuropathic pain even after surgical intervention. The primary reasons for this involve sustained neuroinflammatory and dysfunctional changes in the nervous system after the nerve injury. We previously reported an injectable boronic ester-based hydrogel with inherent antioxidative and nerve protective properties. Herein, we first explored the anti-neuroinflammatory effects of Curcumin on primary sensory neurons and activated macrophages in vitro. Next, we incorporated thiolated Curcumin-Pluronic F-127 micelles (Cur-M) into our boronic ester-based hydrogel to develop an injectable hydrogel that serves as sustained curcumin release system (Gel-Cur-M). By orthotopically injecting the Gel-Cur-M to sciatic nerves of mice with chronic constriction injuries, we found that the bioactive components could remain on the nerves for at least 21 days. In addition, the Gel-Cur-M exhibited superior functions compared to Gel and Cur-M alone, which includes ameliorating hyperalgesia while simultaneously improving locomotor and muscular functions after the nerve injury. This could stem from in situ anti-inflammation, antioxidation, and nerve protection. Furthermore, the Gel-Cur-M also showed extended beneficial effects for preventing the overexpression of TRPV1 as well as microglial activation in the lumbar dorsal root ganglion and spinal cord, respectively, which also contributed to its analgesic effects. The underlying mechanism may involve the suppression of CC chemokine ligand-2 and colony-stimulating factor-1 in the injured sensory neurons. Overall, this study suggests that orthotopic injection of the Gel-Cur-M is a promising therapeutic strategy that especially benefits patients with peripheral neuropathy who require surgical interventions.