Nanozyme‑Engineered Hydrogels for Anti‑Inflammation and Skin Regeneration

Inflammatory skin disorders can cause chronic scarring and functional impairments,posing a significant burden on patients and the healthcare system.Conventional therapies,such as corticosteroids and nonsteroidal anti-inflammatory drugs,are limited in efficacy and associated with adverse effects.Recently,nanozyme(NZ)-based hydrogels have shown great promise in addressing these challenges.NZ-based hydrogels possess unique therapeutic abilities by combining the therapeutic benefits of redox nanomaterials with enzymatic activity and the water-retaining capacity of hydrogels.The multifaceted therapeutic effects of these hydrogels include scavenging reactive oxygen species and other inflammatory mediators modulating immune responses toward a pro-regenerative environment and enhancing regenerative potential by triggering cell migration and differentiation.This review highlights the current state of the art in NZ-engineered hydrogels(NZ@hydrogels)for anti-inflammatory and skin regeneration applications.It also discusses the underlying chemo-mechano-biological mechanisms behind their effectiveness.Additionally,the challenges and future directions in this ground,particularly their clinical translation,are addressed.The insights provided in this review can aid in the design and engineering of novel NZ-based hydrogels,offering new possibilities for targeted and personalized skin-care therapies.

Regulatory T cells in skin regeneration and wound healing

As the body’s integumentary system,the skin is vulnerable to injuries.The subsequent wound healing processes aim to restore dermal and epidermal integrity and functionality.To this end,multiple tissue-resident cells and recruited immune cells cooperate to efficiently repair the injured tissue.Such temporally-and spatially-coordinated interplay necessitates tight regulation to prevent collateral damage such as overshooting immune responses and excessive inflammation.In this context,regulatory T cells(Tregs)hold a key role in balancing immune homeostasis and mediating cutaneous wound healing.A comprehensive understanding of Tregs’multifaceted field of activity may help decipher wound pathologies and,ultimately,establish new treatment modalities.Herein,we review the role of Tregs in orchestrating the regeneration of skin adnexa and catalyzing healthy wound repair.Further,we discuss how Tregs operate during fibrosis,keloidosis,and scarring.

Vascular Endothelial Growth Factor‑Recruiting Nanofiber Bandages Promote Multifunctional Skin Regeneration via Improved Angiogenesis and Immunomodulation

Tissue injury leads to gradients of chemoattractants,which drive multiple processes for tissue repair,including the inflam-matory response as well as endogenous cell recruitment.However,a limited time window for the gradients of chemoattract-ants as well as their poor stability at the injury site may not translate into healthy tissue repair.Consequently,intelligent multifunctional scaffolds with the capability to stabilize injury-induced cytokines and chemokines hold great promise for tissue repair.Vascular endothelial growth factor(VEGF)plays a significant role in wound healing by promoting angiogen-esis.The overarching objective of this research was to develop intelligent multifunctional scaffolds with the capability to endogenously recruit VEGF and promote wound healing via angiogenic and immunomodulatory dual functions.Prominin-1-derived peptide(PR1P)was encapsulated into electrospun poly(L-lactide-coglycolide)/gelatin(P/G)-based bandages.The sustained release of PR1P recruited VEGF in situ,thereby stabilizing the protein concentration peak in vivo and affording a reparative microenvironment with an adequate angiogenic ability at the wound site.Meanwhile,PR1P-recruited VEGF-induced macrophage reprogramming towards M2-like phenotypes further conferred immunomodulatory functions to the bandages.These dual functions of proangiogenesis and immunomodulation formed a cascade amplification,which regulated matrix metalloproteinases(MMP-9)as well as inflammatory factors(nuclear factor(NF)-κb,tumor necrosis factor(TNF)-α)in the wound microenvironment via the VEGF/macrophages/microenvironment axis.Consequently,the bandages realized multifunctional regeneration in splinted excisional wounds in rats,with or without diabetes,affording a higher skin append-age neogenesis,sensory function,and collagen remodeling.Conclusively,our approach encompassing in situ recruitment of VEGF at the injury site with the capability to promote immunomodulation-mediated tissue repair affords a promising avenue for scarless wound regeneration,which may also have implications for other tissue engineering disciplines.

A Polyvinyl Alcohol/Acrylamide Hydrogel with Enhanced Mechanical Properties Promotes Full-Thickness Skin Defect Healing by Regulating Immunomodulation and Angiogenesis Through Paracrine Secretion

Hydrogel-based tissue-engineered skin has attracted increased attention due to its potential to restore the structural integrity and functionality of skin.However,the mechanical properties of hydrogel scaffolds and natural skin are substantially different.Here,we developed a polyvinyl alcohol(PVA)/acrylamide based interpenetrating network(IPN)hydrogel that was surface modified with polydopamine(PDA)and termed Dopa-gel.The Dopa-gel exhibited mechanical properties similar to native skin tissue and a superior ability to modulate paracrine functions.Furthermore,a tough scaffold with tensile resistance was fabricated using this hydrogel by three-dimensional printing.The results showed that the interpenetration of PVA,alginate,and polyacrylamide networks notably enhanced the mechanical properties of the hydrogel.Surface modification with PDA endowed the hydrogels with increased secretion of immunomodulatory and proangiogenic factors.In an in vivo model,Dopa-gel treatment accelerated wound closure,increased vascularization,and promoted a shift in macrophages from a proinflammatory M1 phenotype to a prohealing and anti-inflammatory M2 phenotype within the wound area.Mechanistically,the focal adhesion kinase(FAK)/extracellular signal-related kinase(ERK)signaling pathway may mediate the promotion of skin defect healing by increasing paracrine secretion via the Dopa-gel.Additionally,proangiogenic factors can be induced through Rho-associated kinase-2(ROCK-2)/vascular endothelial growth factor(VEGF)-mediated paracrine secretion under tensile stress conditions.Taken together,these findings suggest that the multifunctional Dopa-gel,which has good mechanical properties similar to those of native skin tissue and enhanced immunomodulatory and angiogenic properties,is a promising scaffold for skin tissue regeneration.

Programmable immune activating electrospun fibers for skin regeneration

Immune cells play a crucial regulatory role in inflammatory phase and proliferative phase during skin healing.How to programmatically activate sequential immune responses is the key for scarless skin regeneration.In this study,an“Inner-Outer”IL-10-loaded electrospun fiber with cascade release behavior was constructed.During the inflammatory phase,the electrospun fiber released a lower concentration of IL-10 within the wound,inhibiting excessive recruitment of inflammatory cells and polarizing macrophages into anti-inflammatory phenotype“M2c”to suppress excessive inflammation response.During the proliferative phase,a higher concentration of IL-10 released by the fiber and the anti-fibrotic cytokines secreted by polarized“M2c”directly acted on dermal fibroblasts to simultaneously inhibit extracellular matrix overdeposition and promote fibroblast migration.The“Inner-Outer”IL-10-loaded electrospun fiber programmatically activated the sequential immune responses during wound healing and led to scarless skin regeneration,which is a promising immunomodulatory biomaterial with great potential for promoting complete tissue regeneration.

Conditioned medium-electrospun fiber biomaterials for skin regeneration

Conditioned medium(CM)contains variety of factors secreted by cells,which directly regulate cellular processes,showing tremendous potential in regenerative medicine.Here,for the first time,we proposed a novel regenerative therapy mediated by biodegradable micro-nano electrospun fibers loaded with highly active conditioned medium of adipose-derived stem cells(ADSC-CM).ADSC-CM was successfully loaded into the nanofibers with biological protection and controllable sustained-release properties by emulsion electrospinning and protein freeze-drying technologies.In vitro,ADSC-CM released by the fibers accelerated the migration rate of fibroblasts;inhibited the over proliferation of fibroblasts by inducing apoptosis and damaging cell membrane;in addition,ADSC-CM inhibited the transformation of fibroblasts into myofibroblasts and suppressed excessive production of extracellular matrix(ECM).In vivo,the application of CM-biomaterials significantly accelerated wound closure and improved regeneration outcome,showing superior pro-regenerative performance.This study pioneered the application of CM-biomaterials in regenerative medicine,and confirmed the practicability and significant biological effects of this innovative biomaterials.

Incorporating redox-sensitive nanogels into bioabsorbable nanofibrous membrane to acquire ROS-balance capacity for skin regeneration

Facing the high incidence of skin diseases,it is urgent to develop functional materials with high bioactivity for wound healing,where reactive oxygen species(ROS)play an important role in the wound healing process mainly via adjustment of immune response and neovasculation.In this study,we developed a kind of bioabsorbable materials with ROS-mediation capacity for skin disease therapy.Firstly,redox-sensitive poly(N-isopropylacrylamide-acrylic acid)(PNA)nanogels were synthesized by radical emulsion polymerization method using a disulfide molecule as crosslinker.The resulting nanogels were then incorporated into the nanofibrous membrane of poly(L-lactic acid)(PLLA)via airbrushing approach to offer bioabsorbable membrane with redox-sensitive ROS-balance capacity.In vitro biological evaluation indicated that the PNA-contained bioabsorbable membrane improved cell adhesion and proliferation compared to the native PLLA membrane.In vivo study using mouse wound skin model demonstrated that PNA-doped nanofibrous membranes could promote the wound healing process,where the disulfide bonds in them were able to adjust the ROS level in the wound skin for mediation of redox potential to achieve higher wound healing efficacy.

Engineering immune-responsive biomaterials for skin regeneration

The progress of biomaterials and tissue engineering has led to significant advances in wound healing,but the clinical therapy to regenerate perfect skin remains a great challenge.The implantation of biomaterial scaffolds to heal wounds inevitably leads to a host immune response.Many recent studies revealed that the immune system plays a significant role in both the healing process and the outcome.Immunomodulation or immuno-engineering has thus become a promising approach to develop pro-regenerative scaffolds for perfect skin regeneration.In this paper,we will review recent advancements in immunomodulating biomaterials in the field of skin repair and regeneration,and discuss strategies to modulate the immune response by tailoring the chemical,physical and biological properties of the biomaterials.Understanding the important role of immune responses and manipulating the inherent properties of biomaterials to regulate the immune reaction are approaches to overcome the current bottleneck of skin repair and regeneration.

Mesenchymal stem cell-derived exosomes: A novel and potential remedy for cutaneous wound healing and regeneration

Poor healing of cutaneous wounds is a common medical problem in the field of traumatology.Due to the intricate pathophysiological processes of wound healing,the use of conventional treatment methods,such as chemical molecule drugs and traditional dressings,have been unable to achieve satisfactory outcomes.Within recent years,explicit evidence suggests that mesenchymal stem cells(MSCs)have great therapeutic potentials on skin wound healing and regeneration.However,the direct application of MSCs still faces many challenges and difficulties.Intriguingly,exosomes as cell-secreted granular vesicles with a lipid bilayer membrane structure and containing specific components from the source cells may emerge to be excellent substitutes for MSCs.Exosomes derived from MSCs(MSC-exosomes)have been demonstrated to be beneficial for cutaneous wound healing and accelerate the process through a variety of mechanisms.These mechanisms include alleviating inflammation,promoting vascularization,and promoting proliferation and migration of epithelial cells and fibroblasts.Therefore,the application of MSC-exosomes may be a promising alternative to cell therapy in the treatment of cutaneous wounds and could promote wound healing through multiple mechanisms simultaneously.This review will provide an overview of the role and the mechanisms of MSC-derived exosomes in cutaneous wound healing,and elaborate the potentials and future perspectives of MSC-exosomes application in clinical practice.

Decellularized extracellular matrix:A promising strategy for skin repair and regeneration

The skin is an important organ of the human body that resists external threats but lacks sufficient self-regeneration ability when severe damage occurs.However,most of the available skin substitutes cannot achieve ideal restoration of complex structures and multiple functions of native skin tissues.Fortunately,the advent of decellularized extracellular matrix(dECM)offers a promising approach to overcome these obstacles.The dECM,derived from the natural extracellular matrix(ECM),possesses a similar structure and composition,which constructs an environment favorable for cell performance in regeneration.Moreover,dECM retains good bioactivity,low immunogenicity,and high availability,making it a suitable biomaterial for skin repair and regeneration.In this review,various decellularization methods and subsequent evaluations of dECM are introduced first,and the main sources of dECM are then presented.Furthermore,the recent progress of dECM-based biomaterials applied in skin regeneration and future perspectives are summarized.

Hesitant steps from the artificial skin to organ regeneration

This is a historical account of the steps,both serendipitous and rational,that led my group of students and colleagues at MIT and Harvard Medical School to discover induced organ regeneration.Our research led to methods for growing back in adult mammals three heavily injured organs,skin,peripheral nerves and the conjunctiva.We conclude that regeneration in adults is induced by a modification of normal wound healing.

Fabrication and Evaluation of Porous Keratin/chitosan(KCS) Scaffolds for Effectively Accelerating Wound Healing

Objective To develop a dressing with desired antibacterial activity, good water maintaining ability and mechanical properties for wound healing and skin regeneration. Methods The chitosan with different concentrations were added in keratin solution to form porous keratin/chitosan（KCS） scaffolds. The morphological characteristics, chemical composition, wettability, porosity, swelling ratio and degradation of the scaffolds were evaluated. The antibacterial activity was tested by using S. aureus and E. coli suspension for 2 h. And L929 fibroblast cells culture was used to evaluate the cytotoxicity of the KCS scaffolds. Results The adding of chitosan could increase the hydrophobicity, decrease porosity, swelling ratio and degradation rate of the KCS porous scaffolds. Mechanical properties of KCS scaffolds could be enhanced and well adjusted by chitosan. KCS scaffolds could obviously decrease bacteria number. The proliferation of fibroblast cells in porous KCS patch increased firstly and then decreased with the increase of chitosan concentration. It was appropriate to add 400 μg/m L chitosan to form porous KCS scaffold for achieving best cell attachment and proliferation compared with other samples. Conclusion The porous KCS scaffold may be used as implanted scaffold materials for promoting wound healing and skin regeneration.

Breathable,antifreezing,mechanically skin-like hydrogel textile wound dressings with dual antibacterial mechanisms

Hydrogels are emerging as the most promising dressings due to their excellent biocompatibility,extracellular matrix mimicking structure,and drug loading ability.However,existing hydrogel dressings exhibit limited breathability,poor environmental adaptability,potential drug resistance,and limited drug options,which extremely restrict their therapeutic effect and working scenarios.Here,the current research introduces the first paradigm of hydrogel textile dressings based on novel gelatin glycerin hydrogel(glyhydrogel)fibers fabricated by the Hofmeister effect based wet spinning.Benefiting from the unique knitted structure,the textile dressing features excellent breathability(1800 times that of the commercially available 3 M dressing)and stretchability(535.51±38.66%).Furthermore,the glyhydrogel textile dressing can also withstand the extreme temperature of-80℃,showing the potential for application in subzero environments.Moreover,the introduction of glycerin endows the textile dressing with remarkable antibacterial property and expands the selection of loaded drugs(e.g.,clindamycin).The prepared glyhydrogel textile dressing shows an excellent infected wound healing effect with a complete rat skin closure within 14 days.All these functions have not been achievable by traditional hydrogel dressings and provide a new approach for the development of hydrogel dressings.

Robust Alcohol Soluble Polyurethane/Chitosan/Silk Sericin(APU/CS/SS)Nanofiber Scaffolds Toward Artificial Skin Extracellular Matrices via Microfluidic Blow‑Spinning

Skin regeneration is a matter of high concern since many individuals suffer from skin damage.To date,the concept of protein-based artificial skin scaffolds have been successfully applied and proven in skin regeneration.However,realizing a skin tissue scaffold with a skin-like extracellular matrix(ECM)that combines low price,good biocompatibility,excellent antibacterial properties,good cell adhesion,and strong mechanical properties is still a major challenge.In this study,inexpensive silk sericin(SS)protein-based artificial skin nanofiber scaffolds(NFSs)with excellent biological activity,no immune rejection,and high mechanical strength were fabricated via microfluidic blow-spinning(MBS).In particular,the as-prepared NFS was transformed from a random coil structure to aβ-sheet structure by using the MBS in high-speed shear chips to improve its stability and mechanical strength.Additionally,through in vitro and in vivo studies,it was shown that SS protein-based artificial skin NFSs possessed excellent antibacterial effects and degradability properties,as well as accelerated tissue granu-lation growth,effectively promoting full skin wound healing and skin regeneration for medical problems worldwide.Thus,this skin ECM-inspired NFS offers new perspectives for accelerating wound healing and tissue regeneration and provides potential applications for clinical medicine.

A CS-based composite scaffold with excellent photothermal effect and its application in full-thickness skin wound healing

The development of natural polymer-based scaffolds with excellent biocompatibility,antibacterial activity,and blood compatibility,able to facilitate full-thickness skin wound healing,remains challenging.In this study,we have developed three chitosan(CS)-based porous scaffolds,including CS,CS/CNT(carbon nanotubes)and CS/CNT/HA(nano-hydroxyapatite,n-HA)using a freeze-drying method.All three scaffolds have a high swelling ratio,excellent antibacterial activity,outstanding cytocompatibility and blood compatibility in vitro.The introduction of CNTs exhibited an obvious increase in mechanical properties and exerts excellent photothermal response,which displays excellent healing performance as a wound dressing in mouse full-thickness skin wound model when compared to CS scaffolds.CS/CNT/HA composite scaffolds present the strongest ability to promote full-thickness cutaneous wound closure and skin regeneration,which might be ascribed to the synergistic effect of photothermal response from CNT and excellent bioactivity from n-HA.Overall,the present study indicated that CNT and n-HA can be engineered as effective constituents in wound dressings to facilitate full-thickness skin regeneration.

A TRILAYER DERMAL EQUIVALENT CONTAINING SILVER NANOPARTICLES WITH ENHANCED ANTIBACTERIAL PROPERTY

A dermal equivalent having a trilayered structure was designed by combining a silver nanoparticles incorporated chitosan film with a bilayer collagen-chitosan/silicon membrane dermal equivalent(BDE).The silver nanoparticles prepared at different conditions were characterized by UV-Vis and transmission electron microscopy(TEM).The macroscopic sharp and the microstructure of the trilayer dermal equivalent(TDE) were also studied.Then,the in vitro antibacterial property of TDE was evaluated by the antibacterial...

The biological effect of recombinant humanized collagen on damaged skin induced by UV-photoaging:An in vivo study

The application of medical devices to repair skin damage is clinically accepted and natural polymer enjoys an important role in this field,such as collagen or hyaluronic acid,etc.However,the biosafety and efficacy of these implants are still challenged.In this study,a skin damage animal model was prepared by UV-photoaging and recombinant humanized type Ⅲ collagen(rhCol Ⅲ)was applied as a bioactive material to implant in vivo to study its biological effect,comparing with saline and uncrosslinked hyaluronic acid(HA).Animal skin conditions were non-invasively and dynamically monitored during the 8 weeks experiment.Histological observation,specific gene expression and other molecular biological methods were applied by the end of the animal experiment.The results indicated that rhCol Ⅲ could alleviate the skin photoaging caused by UV radiation,including reduce the thickening of epidermis and dermis,increase the secretion of Collagen Ⅰ(Col Ⅰ)and Collagen Ⅲ(Col Ⅲ)and remodel of extracellular matrix(ECM).Although the cell-material interaction and mechanism need more investigation,the effect of rhCol Ⅲ on damaged skin was discussed from influence on cells,reconstruction of ECM,and stimulus of small biological molecules based on current results.In conclusion,our findings provided rigorous biosafety information of rhCol Ⅲ and approved its potential in skin repair and regeneration.Although enormous efforts still need to be made to achieve successful translation from bench to clinic,the recombinant humanized collagen showed superiorities from both safety and efficacy aspects.

Using bioprinting and spheroid culture to create a skin model with sweat glands and hair follicles

Background:Sweat glands(SGs)and hair follicles(HFs)are two important cutaneous appendages that play crucial roles in homeostatic maintenance and thermoregulation,and their interaction is involved in wound healing.SGs can be regenerated from mesenchymal stem cell-laden 3D bioprinted scaffolds,based on our previous studies,whereas regeneration of HFs could not be achieved in the same model.Due to the lack of an in vitro model,the underlying molecular mechanism of the interaction between SGs and HFs in regeneration could not be fully understood.The purpose of the present study was to establish an in vitro model of skin constructs with SGs and HFs and explore the interaction between these two appendages in regeneration.Methods:To investigate the interaction effects between SGs and HFs during their regeneration processes,a combined model was created by seeding HF spheroids on 3D printed SG scaffolds.The interaction between SG scaffolds and HF spheroids was detected using RNA expression and immunofluorescence staining.The effects of microenvironmental cues on SG and HF regeneration were analysed by altering seed cell types and plantar dermis homogenate in the scaffold.Results:According to this model,we overcame the difficulties in simultaneously inducing SG and HF regeneration and explored the interaction effects between SG scaffolds and HF spheroids.Surprisingly,HF spheroids promoted both SG and HF differentiation in SG scaffolds,while SG scaffolds promoted SG differentiation but had little effect on HF potency in HF spheroids.Specifically,microenvironmental factors(plantar dermis homogenate)in SG scaffolds effectively promoted SG and HF genesis in HF spheroids,no matter what the seed cell type in SG scaffolds was,and the promotion effects were persistent.Conclusions:Our approach elucidated a new model for SG and HF formation in vitro and provided an applicable platform to investigate the interaction between SGs and HFs in vitro.This platform might facilitate 3D skin constructs with multiple appendages and unveil the spatiotemporal molecular program of multiple appendage regeneration.

HOX genes in the skin

Deep skin wounds heal by scar formation with a Joss of its original appearance, structure and function.However, when the same damage occurs to the skin of an early gestational fetus, complete regeneration can be observed. Despite significant research in the field of skin regeneration, many mysteries remain, such as the loss of wound healing ability with maturity, the differences in healing at different parts of the body, and the presence of hypertrophic scars and keloids in some races but not in others. The finding of HOX genes in the skin provides new explanations to these conundrums.

Polymeric hydrogels for burn wound care:Advanced skin wound dressings and regenerative templates

Wound closure represents a primary goal in the treatment of very deep and/or large wounds,for which the mortality rate is particularly high.However,the spontaneous healing of adult skin eventually results in the formation of epithelialized scar and scar contracture(repair),which might distort the tissues and cause lifelong deformities and disabilities.This clinical evidence suggests that wound closure attained by means of skin regeneration,instead of repair,should be the true goal of burn wound management.The traditional concept of temporary wound dressings,able to stimulate skin healing by repair,is thus being increasingly replaced by the idea of temporary scaff olds,or regenerative templates,able to promote healing by regeneration.As wound dressings,polymeric hydrogels provide an ideal moisture environment for healing while protecting the wound,with the additional advantage of being comfortable to the patient,due to their cooling eff ect and non-adhesiveness to the wound tissue.More importantly,recent advances in regenerative medicine demonstrate that bioactive hydrogels can be properly designed to induce at least partial skin regeneration in vivo.The aim of this review is to provide a concise insight on the key properties of hydrogels for skin healing and regeneration,particularly highlighting the emerging role of hydrogels as next generation skin substitutes for the treatment of fullthickness burns.