Anisotropic Silk-Inspired Nerve Conduit with Peptides Improved the Microenvironment for Long-Distance Peripheral Nerve Regeneration

Recent research of peptide-based hydrogel in nervous regeneration

Neurological disorders exert significantly affect the quality of life for patients, necessitating effective strategies for nerve regeneration. Both traditional autologous nerve transplantation and emerging therapeutic approaches encounter scientific challenges due to the complex nature of the nervous system and the unsuitability of the surrounding environment for cell transplantation. Tissue engineering techniques offer a promising path for neurotherapy. Successful neural tissue engineering relies on modulating cell differentiation behavior and tissue repair by developing biomaterials that mimic the natural extracellular matrix (ECM) and establish a three-dimensional microenvironment. Peptide-based hydrogels have emerged as a potent option among these biomaterials due to their ability to replicate the structure and complexity of the ECM. This review aims to explore the diverse range of peptide-based hydrogels used in nerve regeneration with a specific focus on dipeptide hydrogels, tripeptide hydrogels, oligopeptide hydrogels, multidomain peptides (MDPs), and amphiphilic peptide hydrogels (PAs). Peptide-based hydrogels offer numerous advantages, including biocompatibility, structural diversity, adjustable mechanical properties, and degradation without adverse effects. Notably, hydrogels formed from self-assembled polypeptide nanofibers, derived from amino acids, show promising potential in engineering neural tissues, outperforming conventional materials like alginate, poly(ε-caprolactone), and polyaniline. Additionally, the simple design and cost-effectiveness of dipeptide-based hydrogels have enabled the creation of various functional supramolecular structures, with significant implications for nervous system regeneration. These hydrogels are expected to play a crucial role in future neural tissue engineering research. This review aims to highlight the benefits and potential applications of peptide-based hydrogels, contributing to the advancement of neural tissue engineering.

Photodynamic hemostatic silk fibroin film with photo-controllable modulation of macrophages for bacteria-infected wound healing

Massive hemorrhage and chronic wounds caused by bacterial infections after trauma are significant challenges in clinical practice. An ideal hemostatic wound dressing should simultaneously manage bleeding and prevent bacterial infections and also hold excellent biocompatibility and bioactivities to successfully modulate immune microenvironments to promote wound healing. In this study, a silk fibroin-based light-responsive film was demonstrated to possess effective capacity of light-induced non-compressible hemostasis on liver hemorrhage and tail bleeding in vivo by binding with blood platelets to promote the clotting cascade. The blood loss of the rats was significantly less after C-MASiF films were applied, which were 1223.33 ± 347.9 mg (liver trauma) and 363.33 ± 60.28 mg (tail trimming). Importantly, the films exhibited photo-controllable modulation activity on macrophages through repeated near-infrared irradiation to regulate the immune microenvironment to enhance photodynamic antibacterial therapy. Moreover, the light-responsive silk fibroin film effectively promoted Staphylococcus aureus infected burn wound healing in vivo. The quantity of residual bacteria in the wound sites of mice in the C-MASiF films group (0.05 ± 0.0047 × 108 CFU mL-1) was considerably less than that in the control group (3.18 ± 0.75 × 108 CFU mL-1), and the wound area in the C-MASiF group (78.03% ± 4.12%) was considerably smaller than that in the control group (60.33% ± 8.81%) after 14 days. Overall, this light-responsive silk fibroin film can provide a powerful strategy for wound healing of burns.

PLCL/SF/NGF nerve conduit loaded with RGD-TA-PPY hydrogel promotes regeneration of sciatic nerve defects in rats through PI3K/AKT signalling pathways

Peripheral nerve defect are common clinical problem caused by trauma or other diseases, often leading to the loss of sensory and motor function in patients. Autologous nerve transplantation has been the gold standard for repairing peripheral nerve defects, but its clinical application is limited due to insufficient donor tissue. In recent years, the application of tissue engineering methods to synthesize nerve conduits for treating peripheral nerve defect has become a current research focus. This study introduces a novel approach for treating peripheral nerve defects using a tissue-engineered PLCL/SF/NGF@TA-PPy-RGD conduit. The conduit was fabricated by combining electrospun PLCL/SF with an NGF-loaded conductive TA-PPy-RGD gel. The gel, synthesized from RGD-modified tannic acid (TA) and polypyrrole (PPy), provides growth anchor points for nerve cells. In vitro results showed that this hybrid conduit could enhance PC12 cell proliferation, migration, and reduce apoptosis under oxidative stress. Furthermore, the conduit activated the PI3K/AKT signalling pathway in PC12 cells. In a rat model of sciatic nerve defect, the PLCL/SF/NGF@TA-PPy-RGD conduit significantly improved motor function, gastrocnemius muscle function, and myelin sheath axon thickness, comparable to autologous nerve transplantation. It also promoted angiogenesis around the nerve defect. This study suggests that PLCL/SF/NGF@TA-PPy-RGD conduits provide a conducive environment for nerve regeneration, offering a new strategy for peripheral nerve defect treatment, this study provided theoretical basis and new strategies for the research and treatment of peripheral nerve defect.

PEDOT-Integrated Fish Swim Bladders as Conductive Nerve Conduits

Advanced artificial nerve conduits offer a promising alternative for nerve injury repair. Current research focuses on improving the therapeutic effectiveness of nerve conduits by optimizing scaffold materials and functional components. In this study, a novel poly(3,4-ethylenedioxythiophene) (PEDOT)-integrated fish swim bladder (FSB) is presented as a conductive nerve conduit with ordered topology and electrical stimulation to promote nerve regeneration. PEDOT nanomaterials and adhesive peptides (IKVAV) are successfully incorporated onto the decellularized FSB substrate through pre-coating with polydopamine. The obtained PEDOT/IKVAV-integrated FSB substrate exhibits outstanding mechanical properties, high electrical conductivity, stability, as well as excellent biocompatibility and bioadhesive properties. In vitro studies confirm that the PEDOT/IKVAV-integrated FSB can effectively facilitate the growth and directional extension of pheochromocytoma 12 cells and dorsal root ganglion neurites. In addition, in vivo experiments demonstrate that the proposed PEDOT/IKVAV-integrated FSB conduit can accelerate defective nerve repair and functional restoration. The findings indicate that the FSB-derived conductive nerve conduits with multiple regenerative inducing signals integration provide a conducive milieu for nerve regeneration, exhibiting great potential for repairing long-segment neural defects.

Sea Cucumber-Inspired Microneedle Nerve Guidance Conduit for Synergistically Inhibiting Muscle Atrophy and Promoting Nerve Regeneration

Muscle atrophy resulting from peripheral nerve injury (PNI) poses a threat to a patient's mobility and sensitivity. However, an effective method to inhibit muscle atrophy following PNI remains elusive. Drawing inspiration from the sea cucumber, we have integrated microneedles (MNs) and microchannel technology into nerve guidance conduits (NGCs) to develop bionic microneedle NGCs (MNGCs) that emulate the structure and piezoelectric function of sea cucumbers. Morphologically, MNGCs feature an outer surface with outward-pointing needle tips capable of applying electrical stimulation to denervated muscles. Simultaneously, the interior contains microchannels designed to guide the migration of Schwann cells (SCs). Physiologically, the incorporation of conductive reduced graphene oxide and piezoelectric zinc oxide nanoparticles into the polycaprolactone scaffold enhances conductivity and piezoelectric properties, facilitating SCs' migration, myelin regeneration, axon growth, and the restoration of neuromuscular function. These combined effects ultimately lead to the inhibition of muscle atrophy and the restoration of nerve function. Consequently, the concept of the synergistic effect of inhibiting muscle atrophy and promoting nerve regeneration has the capacity to transform the traditional approach to PNI repair and find broad applications in PNI repair.

Strategies to enhance the ability of nerve guidance conduits to promote directional nerve growth

Severely damaged peripheral nerves will regenerate incompletely due to lack of directionality in their regeneration, leading to loss of nerve function. To address this problem, various nerve guidance conduits (NGCs) have been developed to provide guidance for nerve repair. However, their clinical application is still limited, mainly because its effect in promoting nerve repair is not as good as autologous nerve transplantation. Therefore, it is necessary to enhance the ability of NGCs to promote directional nerve growth. Strategies include preparing various directional structures on NGCs to provide contact guidance, and loading various substances on them to provide electrical stimulation or neurotrophic factor concentration gradient to provide directional physical or biological signals.

Recent advances in peptide-based bioactive hydrogels for nerve repair and regeneration: from material design to fabrication, functional tailoring and applications

The injury of both central and peripheral nervous systems can result in neurological disorders and severe nervous diseases, which has been one of the challenges in the medical field. The use of peptide-based hydrogels for nerve repair and regeneration (NRR) provides a promising way for treating these problems, but the effects of the functions of peptide hydrogels on the NRR efficiency have been not understood clearly. In this review, we present recent advances in the material design, matrix fabrication, functional tailoring, and NRR applications of three types of peptide-based hydrogels, including pure peptide hydrogels, other component-functionalized peptide hydrogels, and peptide-modified polymer hydrogels. The case studies on the utilization of various peptide-based hydrogels for NRR are introduced and analyzed, in which the effects and mechanisms of the functions of hydrogels on NRR are illustrated specifically. In addition, the fabrication of medical NRR scaffolds and devices for pre-clinical application is demonstrated. Finally, we provide potential directions on the development of this promising topic. This comprehensive review could be valuable for readers to know the design and synthesis strategies of bioactive peptide hydrogels, as well as their functional tailoring, in order to promote their practical applications in tissue engineering, biomedical engineering, and materials science.

Recent advances in photo-crosslinkable methacrylated silk (Sil-MA)-based scaffolds for regenerative medicine: A review

Silks fibroin can be chemically modified through amino acid side chains to obtain methacrylated silk (Sil-MA). Sil-MA could be processed into a variety of scaffold forms and combine synergistically with other biomaterials to form composites vehicle. The advent of Sil-MA material has enabled impressive progress in the development of various scaffolds based on Sil-MA type to imitate the structural and functional characteristics of natural tissues. This review highlights the reasonable design and bio-fabrication strategies of diverse Sil-MA-based tissue constructs for regenerative medicine. First, we elucidate modification methodology and characteristics of Sil-MA. Next, we describe characteristics of Sil-MA hydrogels, and focus on the design approaches and formation of different types of Sil-MA-based hydrogels. Thereafter, we present an overview of the recent advances in the application of Sil-MA based scaffolds for regenerative medicine, including detailed strategies for the engineering methods and materials used. Finally, we summarize the current research progress and future directions of Sil-MA in regenerative medicine. This review not only delineates the representative design strategies and their application in regenerative medicine, but also provides new direction in the fabrication of biomaterial constructs for the clinical translation in order to stimulate the future development of implants.

Zwitterionic Conductive Hydrogel-Based Nerve Guidance Conduit Promotes Peripheral Nerve Regeneration in Rats

In recent years, conductive biomaterials have been widely used to enhance peripheral nerve regeneration. However, most biomaterials use electronic conductors to increase the conductivity of materials. As information carriers, electronic conductors always transmit discontinuous electrical signals, while biological systems essentially transmit continuous signals through ions. Herein, an ion-based conductive hydrogel was fabricated by simple copolymerization of the zwitterionic monomer sulfobetin methacrylate and hydroxyethyl methacrylate. Benefiting from the excellent mechanical stability, suitable electrical conductivity, and good cytocompatibility of the zwitterionic hydrogel, the Schwann cells cultured on the hydrogel could grow and proliferate better, and dorsal root ganglian had an increased neurite length. The zwitterionic hydrogel-based nerve guidance conduits were then implanted into a 10 mm sciatic nerve defect model in rats. Morphological analysis and electrophysiological data showed that the grafts achieved a regeneration effect close to that of the autologous nerve. Overall, our developed zwitterionic hydrogel facilitates efficient and efficacious peripheral nerve regeneration by mimicking the electrical and mechanical properties of the extracellular matrix and creating a suitable regeneration microenvironment, providing a new material reserve for the repair of peripheral nerve injury.

Progress in methods for evaluating Schwann cell myelination and axonal growth in peripheral nerve regeneration via scaffolds

Peripheral nerve injury (PNI) is a neurological disorder caused by trauma that is frequently induced by accidents, war, and surgical complications, which is of global significance. The severity of the injury determines the potential for lifelong disability in patients. Artificial nerve scaffolds have been investigated as a powerful tool for promoting optimal regeneration of nerve defects. Over the past few decades, bionic scaffolds have been successfully developed to provide guidance and biological cues to facilitate Schwann cell myelination and orientated axonal growth. Numerous assessment techniques have been employed to investigate the therapeutic efficacy of nerve scaffolds in promoting the growth of Schwann cells and axons upon the bioactivities of distinct scaffolds, which have encouraged a greater understanding of the biological mechanisms involved in peripheral nerve development and regeneration. However, it is still difficult to compare the results from different labs due to the diversity of protocols and the availability of innovative technologies when evaluating the effectiveness of novel artificial scaffolds. Meanwhile, due to the complicated process of peripheral nerve regeneration, several evaluation methods are usually combined in studies on peripheral nerve repair. Herein, we have provided an overview of the evaluation methods used to study the outcomes of scaffold-based therapies for PNI in experimental animal models and especially focus on Schwann cell functions and axonal growth within the regenerated nerve.

Advances in Large Gap Peripheral Nerve Injury Repair and Regeneration with Bridging Nerve Guidance Conduits

Peripheral nerve injury is a common complication of accidents and diseases. The traditional autologous nerve graft approach remains the gold standard for the treatment of nerve injuries. While sources of autologous nerve grafts are very limited and difficult to obtain. Nerve guidance conduits are widely used in the treatment of peripheral nerve injuries as an alternative to nerve autografts and allografts. However, the development of nerve conduits does not meet the needs of large gap peripheral nerve injury. Functional nerve conduits can provide a good microenvironment for axon elongation and myelin regeneration. Herein, the manufacturing methods and different design types of functional bridging nerve conduits for nerve conduits combined with electrical or magnetic stimulation and loaded with Schwann cells, etc., are summarized. It summarizes the literature and finds that the technical solutions of functional nerve conduits with electrical stimulation, magnetic stimulation and nerve conduits combined with Schwann cells can be used as effective strategies for bridging large gap nerve injury and provide an effective way for the study of large gap nerve injury repair. In addition, functional nerve conduits provide a new way to construct delivery systems for drugs and growth factors in vivo.

Self-Assembled Peptide Hydrogels in Regenerative Medicine

Regenerative medicine is a complex discipline that is becoming a hot research topic. Skin, bone, and nerve regeneration dominate current treatments in regenerative medicine. A new type of drug is urgently needed for their treatment due to their high vulnerability to damage and weak self-repairing ability. A self-assembled peptide hydrogel is a good scaffolding material in regenerative medicine because it is similar to the cytoplasmic matrix environment; it promotes cell adhesion, migration, proliferation, and division; and its degradation products are natural and harmless proteins. However, fewer studies have examined the specific mechanisms of self-assembled peptide hydrogels in promoting tissue regeneration. This review summarizes the applications and mechanisms of self-assembled short peptide and peptide hydrogels in skin, bone, and neural healing to improve their applications in tissue healing and regeneration.

Manufacture of Bilayered Composite Hydrogels with Strong, Elastic, and Tough Properties for Osteochondral Repair Applications

Layered composite hydrogels have been considered attractive materials for use in osteochondral repair and regeneration. These hydrogel materials should be mechanically strong, elastic, and tough besides fulfilling some basic requirements such as biocompatibility and biodegradability. A novel type of bilayered composite hydrogel with multi-network structures and well-defined injectability was thus developed for osteochondral tissue engineering using chitosan (CH), hyaluronic acid (HA), silk fibroin (SF), CH nanoparticles (NPs), and amino-functionalized mesoporous bioglass (ABG) NPs. CH was combined with HA and CH NPs to build the chondral phase of the bilayered hydrogel, and CH, SF, and ABG NPs were used together to construct the subchondral phase of the bilayer hydrogel. Rheological measurements showed that the optimally achieved gels assigned to the chondral and subchondral layers had their elastic moduli of around 6.5 and 9.9 kPa, respectively, with elastic modulus/viscous modulus ratios higher than 36, indicating that they behaved like strong gels. Compressive measurements further demonstrated that the bilayered hydrogel with an optimally formulated composition had strong, elastic, and tough characteristics. Cell culture revealed that the bilayered hydrogel had the capacity to support the in-growth of chondrocytes in the chondral phase and osteoblasts in the subchondral phase. Results suggest that the bilayered composite hydrogel can act as an injective biomaterial for osteochondral repair applications.

Exosome inspired photo-triggered gelation hydrogel composite on modulating immune pathogenesis for treating rheumatoid arthritis

Although exosome therapy has been recognized as a promising strategy in the treatment of rheumatoid arthritis (RA), sustained modulation on RA specific pathogenesis and desirable protective effects for attenuating joint destruction still remain challenges. Here, silk fibroin hydrogel encapsulated with olfactory ecto-mesenchymal stem cell-derived exosomes (Exos@SFMA) was photo-crosslinked in situ to yield long-lasting therapeutic effect on modulating the immune microenvironment in RA. This in situ hydrogel system exhibited flexible mechanical properties and excellent biocompatibility for protecting tissue surfaces in joint. Moreover, the promising PD-L1 expression was identified on the exosomes, which potently suppressed Tfh cell polarization via inhibiting the PI3K/AKT pathway. Importantly, Exos@SFMA effectively relieved synovial inflammation and joint destruction by significantly reducing T follicular helper (Tfh) cell response and further suppressing the differentiation of germinal center (GC) B cells into plasma cells. Taken together, this exosome enhanced silk fibroin hydrogel provides an effective strategy for the treatment of RA and other autoimmune diseases.

Aptamer engineering exosomes loaded on biomimetic periosteum to promote angiogenesis and bone regeneration by targeting injured nerves via JNK3 MAPK pathway

Repairing critical bone defects is a complex problem in the clinic. The periosteum rich in nerve plays a vital role in initiating and regulating bone regeneration. However, current studies have paid little attention to repairing nerves in the periosteum to promote bone regeneration. Thus, it is essential to construct bionic periosteum with the targeted injured nerves in the periosteum. We coupled phosphatidylserine (PS) targeted aptamers with repair Schwann cell exosomes to construct exosome@aptamer (EA). Then through PEI, EA was successfully built on the surface of the electrospun fiber, which was PCL@PEI@exosome@aptamer (PPEA). Through SEM, TEM, and other technologies, PPEA was characterized. Experiments prove in vivo and in vitro that it has an excellent repair effect on damaged nerves and regeneration of vascular and bones. In vivo, we confirmed that biomimetic periosteum has an apparent ability to promote nerve and bone regeneration by using Microcomputer tomography, hematoxylin-eosin, Masson, and Immunofluorescence. In vitro, we used Immunofluorescence, Real-Time Quantitative PCR, Alkaline phosphatase staining, and other tests to confirm that it has central nerve, blood vessel, and bone regeneration ability. The PPEA biomimetic periosteum has apparent neurogenic, angiogenic, and osteogenic effects. The PPEA biomimetic periosteum will provide a promising method for treating bone defects.

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To construct a biomimetic periosteum that can target injured axons and bone regeneration.

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PS targeted aptamer is coupled with repair Schwann cell exosomes.

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PEI self-assembly was used for the PCL electrospun biomimetic membrane loading.

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It targeted and repaired the injured axons and promoted the secretion of CGRP and SP.

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Biomimetic periosteum promotes vascular regeneration and bone regeneration.

Silk fibroin hydrogels for biomedical applications

Silk fibroin hydrogels occupy an essential position in the biomedical field due to their remarkable biological properties, excellent mechanical properties, flexible processing properties, as well as abundant sources and low cost. Herein, we introduce the unique structures and physicochemical characteristics of silk fibroin, including mechanical properties, biocompatibility, and biodegradability. Then, various preparation strategies of silk fibroin hydrogels are summarized, which can be divided into physical cross-linking and chemical cross-linking. Emphatically, the applications of silk fibroin hydrogel biomaterials in various biomedical fields, including tissue engineering, drug delivery, and wearable sensors, are systematically summarized. At last, the challenges and future prospects of silk fibroin hydrogels in biomedical applications are discussed.

The success of biomaterial-based tissue engineering strategies for peripheral nerve regeneration

Peripheral nerve injury is a clinically common injury that causes sensory dysfunction and locomotor system degeneration, which seriously affects the quality of the patients' daily life. Long gapped defects in large nerve are difficult to repair via surgery and limited donor source of autologous nerve greatly challenges the successful nerve repair by transplantation. Significantly, remarkable progress has been made in repairing the peripheral nerve injury using artificial nerve grafts and a variety of products for peripheral nerve repair have emerged been approved globally in recent years. The raw materials of these commercial products includes natural/synthetic polymers, extracellular matrix. Despite a lot of effort, the desirable functional recovery still remains great challenges in long gapped nerve defects. Thus this review discusses the recent development of tissue engineering products for peripheral nerve repair and the design of bionic grafts improving the local microenvironment for accelerating nerve regeneration against locomotor disorder, which may provide potential strategies for the repair of long gaps or thick nerve defects by multifunctional biomaterials.

Natural Polymer‐Derived Bioscaffolds for Peripheral Nerve Regeneration

In recent decades, artificial nerve scaffolds have become a promising substitute for peripheral nerve repair. Considerable efforts have been devoted to improving the therapeutic effectiveness of artificial scaffolds. Among numerous biomaterials for tissue engineering scaffolds fabrication, natural polymers are considered as tremendous candidates because of their excellent biocompatibility, low toxicity, high cell affinity, wide source, and environmental protection. With the development of engineering technology, a variety of natural polymer‐derived nerve scaffolds have emerged, which are endowed with biological properties and appropriate physicochemical performances to gradually adapt to the needs of nerve regeneration. Significantly, the intergradation of exogenous biomolecules onto the artificial scaffolds is able to avoid low stability, rapid degradation, and redistribution of direct therapeutic drugs in vivo, thereby enhancing nerve regeneration and functional reconstruction. Here, the development of nerve scaffolds derived from natural polymers, and their applications in continuous administration and peripheral nerve regeneration are comprehensively and carefully reviewed, providing an advanced perspective of the field.

The impact of physical, biochemical, and electrical signaling on Schwann cell plasticity

Peripheral nervous system (PNS) injuries are an ongoing health care concern. While autografts and allografts are regarded as the current clinical standard for traumatic injury, there are inherent limitations that suggest alternative remedies should be considered for therapeutic purposes. In recent years, nerve guidance conduits (NGCs) have become increasingly popular as surgical repair devices, with a multitude of various natural and synthetic biomaterials offering potential to enhance the design of conduits or supplant existing technologies entirely. From a cellular perspective, it has become increasingly evident that Schwann cells (SCs), the primary glia of the PNS, are a predominant factor mediating nerve regeneration. Thus, the development of severe nerve trauma therapies requires a deep understanding of how SCs interact with their environment, and how SC microenvironmental cues may be engineered to enhance regeneration. Here we review the most recent advancements in biomaterials development and cell stimulation strategies, with a specific focus on how the microenvironment influences the behavior of SCs and can potentially lead to functional repair. We focus on microenvironmental cues that modulate SC morphology, proliferation, migration, and differentiation to alternative phenotypes. Promotion of regenerative phenotypic responses in SCs and other non-neuronal cells that can augment the regenerative capacity of multiple biomaterials is considered along with innovations and technologies for traumatic injury.

Regenerative Role of T Cells in Nerve Repair and Functional Recovery

The immune system is essential in the process of nerve repair after injury. Successful modulation of the immune response is regarded as an effective approach to improving treatment outcomes. T cells play an important role in the immune response of the nervous system, and their beneficial roles in promoting regeneration have been increasingly recognized. However, the diversity of T-cell subsets also delivers both neuroprotective and neurodegenerative functions. Therefore, this review mainly discusses the beneficial impact of T-cell subsets in the repair of both peripheral nervous system and central nervous system injuries and introduces studies on various therapies based on T-cell regulation. Further discoveries in T-cell mechanisms and multifunctional biomaterials will provide novel strategies for nerve regeneration.

Light-Triggered Adhesive Silk-Based Film for Effective Photodynamic Antibacterial Therapy and Rapid Hemostasis

Successful control of massive hemorrhage in deep wounds with irregular shape and low elasticity still remains great challenges in the clinic. As the wound sites are usually at risk of bacterial infection, it is necessary to design an ideal hemostatic agent with rapid hemostasis and excellent antibacterial activity. In this study, we developed a light responsive hemostatic film for effective handling of liver bleeding with promising photodynamic therapy against S. aureus onnear infrared (NIR) irradiation. Based on silk fibroin, the film exhibited desirable biocompatibility and mechanical property as a hemostat tape. Significantly, the film tape achieved excellent tissue adhesion and hemostasis in vivo within 2 min of UV exposure, which would have a great potential as a multifunctional biomedical material in the field of tissue repair such as wound healing, bone repair, and nerve regeneration.