In Situ Forming Injectable Silk Fibroin Hydrogel Promotes Skin Regeneration in Full Thickness Burn Wounds

Chondroitin sulfate/silk fibroin hydrogel incorporating graphene oxide quantum dots with photothermal-effect promotes type H vessel-related wound healing

Chronic wounds with bacterial infection present formidable clinical challenges. In this study, a versatile hydrogel dressing with antibacterial and angiogenic activity composite of silk fibroin (SF), chondroitin sulfate (CS), and graphene oxide quantum dots (GOQDs) is fabricated. GOQDs@SF/CS (GSC) hydrogel is rapidly formed through the enzyme catalytic action of horseradish peroxidase. With the incorporation of GOQDs both gelation speed and mechanical properties have been enhanced, and the photothermal characteristics of GOQDs in GSC hydrogel enabled bacterial killing through photothermal treatment (PTT) at ∼51 °C. In vitro studies show that the GSC hydrogels demonstrate excellent antibacterial performance and induce type H vessel differentiation of endothelial cells via the activated ERK1/2 signaling pathway and upregulated SLIT3 expression. In vivo results show that the hydrogel significantly promotes type H vessels formation, which is related to the collagen deposition, epithelialization and, ultimately, accelerates the regeneration of infected skin defects. Collectively, this multifunctional GSC hydrogel, with dual action of antibacterial efficacy and angiogenesis promotion, emerges as an innovative skin dressing with the potential for advancing in infected wound healing.

A Novel Food Bore Protein Hydrogel with Silver Ions for Promoting Burn Wound Healing

Hydrogels have emerged as a promising option for treating local scald wounds due to their unique physical and chemical properties. This study aims to evaluate the efficacy of ovalbumin/gelatin composite hydrogels in repairing deep II-degree scald wounds using a mouse dorsal skin model. Trauma tissues collected at various time points are analyzed for total protein content, hydroxyproline content, histological features, and expression of relevant markers. The results reveal that the hydrogel accelerates the healing process of scalded wounds, which is 17.27% higher than the control group. The hydrogel treatment also effectively prevents wound enlargement and redness of the edges caused by infection during the initial stage of scalding. The total protein and hydroxyproline content of the treated wounds are significantly elevated. Additionally, the hydrogel up-regulates the expression of VEGF (a crucial angiogenic factor) and down-regulates CD68 (a macrophage marker). In summary, this study provides valuable insights into the potential of multifunctional protein-based hydrogels in wound healing.

Hemostatic and Ultrasound-Controlled Bactericidal Silk Fibroin Hydrogel via Integrating a Perfluorocarbon Nanoemulsion

Excessive blood loss and infections are the prominent risks accounting for mortality and disability associated with acute wounds. Consequently, wound dressings should encompass adequate adhesive, hemostatic, and bactericidal attributes, yet their development remains challenging. This investigation presented the benefits of incorporating a perfluorocarbon nanoemulsion (PPP NE) into a silk-fibroin (SF)-based hydrogel. By stimulating the β-sheet conformation of the SF chains, PPP NEs drastically shortened the gelation time while augmenting the elasticity, mechanical stability, and viscosity of the hydrogel. Furthermore, the integration of PPP NEs improved hemostatic competence by boosting the affinity between cells and biomacromolecules. It also endowed the hydrogel with ultrasound-controlled bactericidal ability through the inducement of inner cavitation by perfluorocarbon and reactive oxygen species (ROS) generated by the sonosensitizer protoporphyrin. Ultimately, we employed a laparotomy bleeding model and a Staphylococcus aureus-infected trauma wound to demonstrate the first-aid efficacy. Thus, our research suggested an emulsion-incorporating strategy for managing emergency wounds.

Microneedle Patch for Transdermal Sequential Delivery of KGF-2 and aFGF to Enhance Burn Wound Therapy

Severe burn wounds usually destroy key cells' functions of the skin resulting in delayed re-epithelization and wound regeneration. Promoting key cells' activities is crucial for burn wound repair. It is well known that keratinocyte growth factor-2 (KGF-2) participates in the proliferation and morphogenesis of epithelial cells while acidic fibroblast growth factor (aFGF) is a key mediator for fibroblast and endothelial cell growth and differentiation. However, thick eschar and the harsh environment of a burn wound often decrease the delivery efficiency of fibroblast growth factor (FGF) to the wound site. Therefore, herein a novel microneedle patch for sequential transdermal delivery of KGF-2 and aFGF is fabricated to enhance burn wound therapy. aFGF is first loaded in the nanoparticle (NPaFGF) and then encapsulated NPaFGF with KGF-2 in the microneedle patch (KGF-2/NPaFGF@MN). The result shows that KGF-2/NPaFGF@MN can successfully get across the eschar and sequentially release KGF-2 and aFGF. Additional data demonstrated that KGF-2/NPaFGF@MN achieved a quicker wound closure rate with reduced necrotic tissues, faster re-epithelialization, enhanced collagen deposition, and increased neo-vascularization. Further evidence suggests that improved wound healing is regulated by significantly elevated expressions of hypoxia-inducible factor-1 alpha (HIF-1ɑ) and heat shock protein 90 (Hsp90) in burn wounds. All these data proved that KGF-2/NPaFGF@MN is an effective treatment for wound healing of burns.

Hybrid gelatin-ascorbyl phosphate scaffolds accelerate diabetic wound healing via ROS scavenging, angiogenesis and collagen remodeling

Skin wound healing, particularly diabetic wound healing, is challenging in clinical management. Impaired wound healing is associated with persistent oxidative stress, altered inflammatory responses, unsatisfactory angiogenesis and epithelialization. Magnesium ascorbyl phosphate (MAP), which is an ascorbic acid derivative and active ingredient in cosmetics, has been reported to scavenge reactive oxygen species (ROS), and is considered a potential therapeutic agent for diabetic wounds. Herein, we report a hybrid gelatin-MAP scaffolds that can reduces oxidative stress damage, enhances angiogenesis and collagen remodeling to accelerate diabetic wound repair. Preliminary insights based on network pharmacology indicate that MAP may accelerate wound repair through multiple biological pathways, including extracellular matrix remodeling and anti-apoptosis. In vitro studies showed that the hybrid hydrogel scaffold had suitable mechanical properties, excellent biocompatibility and bioactivity. Further animal experiments demonstrated that the hydrogel accelerated full-thickness wound repair in diabetic mice (repair rate MAP vs Control=91.791±3.306 % vs 62.962±6.758 %) through antioxidant, neuroangiogenesis, collagen remodeling, and up-regulated the expression of the related factors COL-1, CD31, VEGF, and CGRP. Overall, we developed a bioactive hybrid hydrogel encapsulating MAP that synergistically promotes diabetic wound repair through multiple biological effects. This potentially integrated therapeutic scaffold may enrich future surgical approaches for treating diabetic wounds.

Bioactive nanomaterials kickstart early repair processes and potentiate temporally modulated healing of healthy and diabetic wounds

Slow-healing and chronic wounds represent a major global economic and medical burden, and there is significant unmet need for novel therapies which act to both accelerate wound closure and enhance biomechanical recovery of the skin. Here, we report a new approach in which bioactives that augment early stages of wound healing can kickstart and engender effective wound closure in healthy and diabetic, obese animals, and set the stage for subsequent tissue repair processes. We demonstrate that a nanomaterial dressing made of silk fibroin and gold nanorods (GNR) stimulates a pro-neutrophilic, innate immune, and controlled inflammatory wound transcriptomic response. Further, Silk-GNR, lasered into the wound bed, in combination with exogeneous histamine, accelerates early-stage processes in tissue repair leading to effective wound closure. Silk-GNR and histamine enhanced biomechanical recovery of skin, increased transient neoangiogenesis, myofibroblast activation, epithelial-to-mesenchymal transition (EMT) of keratinocytes and a pro-resolving neutrophilic immune response, which are hitherto unknown activities for these bioactives. Predictive and temporally coordinated delivery of growth factor nanoparticles that modulate later stages of tissue repair further accelerated wound closure in healthy and diabetic, obese animals. Our approach of kickstarting healing by delivering the "right bioactive at the right time" stimulates a multifactorial, pro-reparative response by augmenting endogenous healing and immunoregulatory mechanisms and highlights new targets to promote tissue repair.

Immunomodulatory hydrogels for skin wound healing: cellular targets and design strategy

Skin wounds significantly impact the global health care system and represent a significant burden on the economy and society due to their complicated dynamic healing processes, wherein a series of immune events are required to coordinate normal and sequential healing phases, involving multiple immunoregulatory cells such as neutrophils, macrophages, keratinocytes, and fibroblasts, since dysfunction of these cells may impede skin wound healing presenting persisting inflammation, impaired vascularization, and excessive collagen deposition. Therefore, cellular target-based immunomodulation is promising to promote wound healing as cells are the smallest unit of life in immune response. Recently, immunomodulatory hydrogels have become an attractive avenue to promote skin wound healing. However, a detailed and comprehensive review of cellular targets and related hydrogel design strategies remains lacking. In this review, the roles of the main immunoregulatory cells participating in skin wound healing are first discussed, and then we highlight the cellular targets and state-of-the-art design strategies for immunomodulatory hydrogels based on immunoregulatory cells that cover defect, infected, diabetic, burn and tumor wounds and related scar healing. Finally, we discuss the barriers that need to be addressed and future prospects to boost the development and prosperity of immunomodulatory hydrogels.

Multifunctional On-Demand Removability Hydrogel Dressing Based on in Situ Formed AgNPs, Silk Microfibers and Hydrazide Hyaluronic Acid for Burn Wound Healing

Elevated temperatures can deactivate tissues in the burn wound area, allowing pathogenic bacteria to multiply on the wound surface, ultimately leading to local or systemic infection. An ideal burn dressing should provide antibacterial properties and facilitate painless dressing changes. Silk microfibers coated with poly (2, 3, 4-trihydroxybenzaldehyde) (referred to as mSF@PTHB) to in situ reduce AgNO3 to silver nanoparticles (AgNPs) in a hydrazide hyaluronic acid-based hydrogel are utilized. The findings indicate a more homogeneous distribution of the silver elements compared to directly doped AgNPs, which also conferred antioxidant and antibacterial properties to the hydrogel. Moreover, hydrogels containing pH-responsive dynamic acylhydrazone bonds can undergo a gel-sol transition in a weak acid environment, leading to the painless removal of adhesive hydrogel dressings. Notably, the on-demand replaceable self-healing antioxidant hydrogel dressing exhibits antibacterial effects and cytocompatibility in vitro, and the wound-healing performance of the hydrogel is validated by treating a burn mouse model with full-thickness skin defects. It is demonstrated that hydrogel dressings offer a viable therapeutic approach to prevent infection and facilitate the healing of burn wounds.

Omentum Extracellular Matrix-Silk Fibroin Hydroscaffold Promotes Wound Healing through Vascularization and Tissue Remodeling in the Diabetic Rat Model

Nonhealing diabetic wounds are often associated with significant mortality and cause economic and clinical burdens to the healthcare system. Herein, a biomimetic hydroscaffold is developed using omentum tissue-derived decellularized-extracellular matrix (dECM) and silk fibroin (SF) proteins that associate the behavior of a collagenous fibrous scaffold and a hydrogel to reproduce all aspects of the provisional skin tissue matrix. The chemical cross-linker-free in situ gelation property of the two types of SF proteins from Bombyx mori and Antheraea assamensis ensures the adherence of dECM with surrounding tissue on the wound bed, circumventing further suturing. The physicochemical and mechanical properties of the composite hydroscaffold (SF-dECM) were thoroughly evaluated. The hydroscaffolds were found to support the growth and proliferation of human dermal fibroblasts and influence the angiogenic potential of endothelial cells under in vitro conditions. Furthermore, the healing efficacy of the composites was evaluated by generating full-thickness wounds on a streptozotocin-induced diabetic rat model. The presence of dECM components in the composite facilitated the rate of wound closure, granulation tissue formation, and re-epithelialization by providing intrinsic cues to advance the inflammatory stage and stimulating angiogenesis. Collectively, as an off-the-shelf wound dressing requiring only a single topical administration, the SF-dECM hydroscaffold is a promising, cost-effective dressing for the management of chronic diabetic wounds.

Silk Fibroin Materials: Biomedical Applications and Perspectives

The golden rule in tissue engineering is the creation of a synthetic device that simulates the native tissue, thus leading to the proper restoration of its anatomical and functional integrity, avoiding the limitations related to approaches based on autografts and allografts. The emergence of synthetic biocompatible materials has led to the production of innovative scaffolds that, if combined with cells and/or bioactive molecules, can improve tissue regeneration. In the last decade, silk fibroin (SF) has gained attention as a promising biomaterial in regenerative medicine due to its enhanced bio/cytocompatibility, chemical stability, and mechanical properties. Moreover, the possibility to produce advanced medical tools such as films, fibers, hydrogels, 3D porous scaffolds, non-woven scaffolds, particles or composite materials from a raw aqueous solution emphasizes the versatility of SF. Such devices are capable of meeting the most diverse tissue needs; hence, they represent an innovative clinical solution for the treatment of bone/cartilage, the cardiovascular system, neural, skin, and pancreatic tissue regeneration, as well as for many other biomedical applications. The present narrative review encompasses topics such as (i) the most interesting features of SF-based biomaterials, bare SF's biological nature and structural features, and comprehending the related chemo-physical properties and techniques used to produce the desired formulations of SF; (ii) the different applications of SF-based biomaterials and their related composite structures, discussing their biocompatibility and effectiveness in the medical field. Particularly, applications in regenerative medicine are also analyzed herein to highlight the different therapeutic strategies applied to various body sectors.

Piezoelectric Hydrogels: Hybrid Material Design, Properties, and Biomedical Applications

Hydrogels show great potential in biomedical applications due to their inherent biocompatibility, high water content, and resemblance to the extracellular matrix. However, they lack self-powering capabilities and often necessitate external stimulation to initiate cell regenerative processes. In contrast, piezoelectric materials offer self-powering potential but tend to compromise flexibility. To address this, creating a novel hybrid biomaterial of piezoelectric hydrogels (PHs), which combines the advantageous properties of both materials, offers a systematic solution to the challenges faced by these materials when employed separately. Such innovative material system is expected to broaden the horizons of biomedical applications, such as piezocatalytic medicinal and health monitoring applications, showcasing its adaptability by endowing hydrogels with piezoelectric properties. Unique functionalities, like enabling self-powered capabilities and inducing electrical stimulation that mimics endogenous bioelectricity, can be achieved while retaining hydrogel matrix advantages. Given the limited reported literature on PHs, here recent strategies concerning material design and fabrication, essential properties, and distinctive applications are systematically discussed. The review is concluded by providing perspectives on the remaining challenges and the future outlook for PHs in the biomedical field. As PHs emerge as a rising star, a comprehensive exploration of their potential offers insights into the new hybrid biomaterials.

Collagen fibril-like injectable hydrogels from self-assembled nanoparticles for promoting wound healing

Soft hydrogels are excellent candidate materials for repairing various tissue defects, yet the mechanical strength, anti-swelling properties, and biocompatibility of many soft hydrogels need to be improved. Herein, inspired by the nanostructure of collagen fibrils, we developed a strategy toward achieving a soft but tough, anti-swelling nanofibrillar hydrogel by combining the self-assembly and chemical crosslinking of nanoparticles. Specifically, the collagen fibril-like injectable hydrogel was subtly designed and fabricated by self-assembling methylacrylyl hydroxypropyl chitosan (HM) with laponite (LAP) to form nanoparticles, followed by the inter-nanoparticle bonding through photo-crosslinking. The assembly mechanism of nanoparticles was elucidated by both experimental and simulation techniques. Due to the unique structure of the crosslinked nanoparticles, the nanocomposite hydrogels exhibited low stiffness (G'< 2 kPa), high compressive strength (709 kPa), and anti-swelling (swelling ratio of 1.07 in PBS) properties. Additionally, by harnessing the photo-crosslinking ability of the nanoparticles, the nanocomposite hydrogels were processed as microgels, which can be three-dimensionally (3D) printed into complex shapes. Furthermore, we demonstrated that these nanocomposite hydrogels are highly biocompatible, biodegradability, and can effectively promote fibroblast migration and accelerate blood vessel formation during wound healing. This work presents a promising approach to develop biomimetic, nanofibrillar soft hydrogels for regenerative medicine applications.

Natural agents as wound-healing promoters

The management of acute and chronic wounds resulting from diverse injuries poses a significant challenge to clinical practices and healthcare providers. Wound healing is a complex biological process driven by a natural physiological response. This process involves four distinct phases, namely hemostasis, inflammation, proliferation, and remodeling. Despite numerous investigations on wound healing and wound dressing materials, complications still persist, necessitating more efficacious therapies. Wound-healing materials can be categorized into natural and synthetic groups. The current study aims to provide a comprehensive review of highly active natural animal and herbal agents as wound-healing promoters. To this end, we present an overview of in vitro, in vivo, and clinical studies that led to the discovery of potential therapeutic agents for wound healing. We further elucidated the effects of natural materials on various pharmacological pathways of wound healing. The results of previous investigations suggest that natural agents hold great promise as viable and accessible products for the treatment of diverse wound types.

Hydrogels and Wound Healing: Current and Future Prospects

The care and rehabilitation of acute and chronic wounds have a significant social and economic impact on patients and global health. This burden is primarily due to the adverse effects of infections, prolonged recovery, and the associated treatment costs. Chronic wounds can be treated with a variety of approaches, which include surgery, negative pressure wound therapy, wound dressings, and hyperbaric oxygen therapy. However, each of these strategies has an array of limitations. The existing dry wound dressings lack functionality in promoting wound healing and exacerbating pain by adhering to the wound. Hydrogels, which are commonly polymer-based and swell in water, have been proposed as potential remedies due to their ability to provide a moist environment that facilitates wound healing. Their unique composition enables them to absorb wound exudates, exhibit shape adaptability, and be modified to incorporate active compounds such as growth factors and antibacterial compounds. This review provides an updated discussion of the leading natural and synthetic hydrogels utilized in wound healing, details the latest advancements in hydrogel technology, and explores alternate approaches in this field. Search engines Scopus, PubMed, Science Direct, and Web of Science were utilized to review the advances in hydrogel applications over the last fifteen years.

Advances of regenerated and functionalized silk biomaterials and application in skin wound healing

The cocoon silk of silkworms (Bombyx mori) has multiple potential applications in biomedicine due to its good biocompatibility, mechanical properties, degradability, and plasticity. Numerous studies have confirmed that silk material dressings are more effective than traditional ones in the skin wound healing process. Silk material research has recently moved toward functionalized biomaterials and achieved remarkable results. Herein, we summarize the recent advances in functionalized silk materials and their efficacy in skin wound healing. In particular, transgenic technology has realized the specific expression of human growth factors in the silk glands of the silkworms, which lays the foundation for fabricating novel and low-cost functionalized materials. Without a green and safe preparation process, the best raw silk materials cannot be made into medically safe products. Therefore, we provide an overview of green and gentle approaches for silk degumming and silk sericin (SS) extraction. Moreover, we summarize and discuss the processing methods of silk fibroin (SF) and SS materials and their potential applications, such as burns, diabetic wounds, and other wounds. This review aims to enhance our understanding of new advances and directions in silk materials and guide future biomedical research.

Multifunctional natural microneedles based methacrylated Bletilla striata polysaccharide for repairing chronic wounds with bacterial infections

The expeditious healing of chronic wounds with bacterial infections poses a formidable challenge in clinical practice because of the persistent bacterial presence, excessive inflammation, and the accumulation of reactive oxygen species (ROS) in clinical practice. Thus, in this study, natural antimicrobial material microneedles (MNs) with multifunctional properties were prepared by adding peony leaf extract (PLE) into a matrix of methacrylated Bletilla striata polysaccharide (BSPMA) and methacrylated chitosan (CSMA) via cross-linking under ultra-violet light to accelerate the rapid healing of chronic wounds with bacterial infections. Results showed that BCP-MNs effectively inhibited the growth of Escherichia coli, Staphylococcus aureus, and methicillin-resistant S. aureus (MRSA) by disrupting bacterial cell membranes and accelerated the healing of infected wounds by enhancing cell migration, epidermal regeneration, pro-collagen deposition, and angiogenesis and reducing inflammation. Furthermore, BCP-MNs not only possessed good mechanical properties, stability, and biocompatibility but also showed potent antioxidant effects to eliminate excessive ROS accumulation in the wound bed. In conclusion, BCP-MNs possess multifunctional wound-healing properties and can serve as excellent wound dressing in to treat infected wounds.

Multifunctional Hydrogels for the Healing of Diabetic Wounds

The healing of diabetic wounds is hindered by various factors, including bacterial infection, macrophage dysfunction, excess proinflammatory cytokines, high levels of reactive oxygen species, and sustained hypoxia. These factors collectively impede cellular behaviors and the healing process. Consequently, this review presents intelligent hydrogels equipped with multifunctional capacities, which enable them to dynamically respond to the microenvironment and accelerate wound healing in various ways, including stimuli -responsiveness, injectable self-healing, shape -memory, and conductive and real-time monitoring properties. The relationship between the multiple functions and wound healing is also discussed. Based on the microenvironment of diabetic wounds, antibacterial, anti-inflammatory, immunomodulatory, antioxidant, and pro-angiogenic strategies are combined with multifunctional hydrogels. The application of multifunctional hydrogels in the repair of diabetic wounds is systematically discussed, aiming to provide guidelines for fabricating hydrogels for diabetic wound healing and exploring the role of intelligent hydrogels in the therapeutic processes.

Preparation and optimization of agarose or polyacrylamide/amino acid-based double network hydrogels for photocontrolled drug release

The high water content and biocompatibility of amino-acid-based supramolecular hydrogels have generated growing interest in drug delivery research. Nevertheless, the existing dominant approach of constructing such hydrogels, the exploitation of a single amino acid type, typically comes with several drawbacks such as weak mechanical properties and long gelation times, hindering their applications. Here, we design a near-infrared (NIR) light-responsive double network (DN) structure, containing amino acids and different synthetic or natural polymers, i.e., polyacrylamide, poly(N-isopropylacrylamide), agarose, or low-gelling agarose. The hydrogels displayed high mechanical strength and high drug-loading capacity. Adjusting the ratio of Fmoc-Tyr-OH/Fmoc-Tyr(Bzl)-OH or Fmoc-Phe-OH/Fmoc-Tyr(Bzl)-OH, we could drastically shorten the gelation time of the DN hydrogels at room and body temperatures. Moreover, introducing photothermal agents (graphene oxide, carbon nanotubes, molybdenum disulfide nanosheets, or indocyanine green), we equipped the hydrogels with NIR responsivity. We demonstrated the light-triggered release of the drug baclofen, which is used in severe spasticity treatment. Rheology and stability tests confirmed the positive impact of the polymers on the mechanical strength of the hydrogels, while maintaining good stability under physiological conditions. Overall, our study contributed a novel hydrogel formulation with high mechanical resistance, rapid gel formation, and efficient NIR-controlled drug release, offering new opportunities for biomedical applications.

Bioactive materials for in vivo sweat gland regeneration

Loss of sweat glands (SwGs) commonly associated with extensive skin defects is a leading cause of hyperthermia and heat stroke. In vivo tissue engineering possesses the potential to take use of the body natural ability to regenerate SwGs, making it more conducive to clinical translation. Despite recent advances in regenerative medicine, reconstructing SwG tissue with the same structure and function as native tissue remains challenging. Elucidating the SwG generation mechanism and developing biomaterials for in vivo tissue engineering is essential for understanding and developing in vivo SwG regenerative strategies. Here, we outline the cell biology associated with functional wound healing and the characteristics of bioactive materials. We critically summarize the recent progress in bioactive material-based cell modulation approaches for in vivo SwG regeneration, including the recruitment of endogenous cells to the skin lesion for SwG regeneration and in vivo cellular reprogramming for SwG regeneration. We discussed the re-establishment of microenvironment via bioactive material-mediated regulators. Besides, we offer promising perspectives for directing in situ SwG regeneration via bioactive material-based cell-free strategy, which is a simple and effective approach to regenerate SwG tissue with both fidelity of structure and function. Finally, we discuss the opportunities and challenges of in vivo SwG regeneration in detail. The molecular mechanisms and cell fate modulation of in vivo SwG regeneration will provide further insights into the regeneration of patient-specific SwGs and the development of potential intervention strategies for gland-derived diseases.

Biomolecules based hydrogels and their potential biomedical applications: A comprehensive review

The need for biocompatible drug carriers has been significantly increased from the past few years. Researchers show great interest in the development of more versatile and sophisticated biomaterials based drug carriers. Hydrogels are beneficial drug carriers and easily release the controlled amount of drug at target site due to its tunable structure. The hydrogels made-up of potent biological macromolecules including collagen, gelatin, fibrin, elastin, fibroin, chitosan, starch, alginate, agarose and carrageenan have been proven as versatile biomaterials. These are three-dimensional polymeric networks, synthesized by crosslinking of hydrophilic polymers. The biological macromolecules based hydrogels containing therapeutic substances are used in a wide range of biomedical applications including wound healing, tissue engineering, cosmetics and contact lenses. However, many aspects related to hydrogels such as the mechanism of cross-linking and molecular entanglement are not clear. So, there is a need to do more research and exploration toward the extensive and cost-effective use of hydrogels. The present review article elaborately discusses the biomolecules based hydrogels and their possible biomedical applications in different fields.

Bombyx mori Silk Fibroin and Model Peptides Incorporating Arg-Gly-Asp Motifs and Their Application in Wound Dressings

Skin plays an important role in protecting the human body from the environment, dehydration, and infection. Burns, wounds, and disease cause the skin to lose its role, but tissue-engineered skin substitutes offer the opportunity to restore skin loss. Silk fibroin from Bombyx mori (SF) has proven to be an excellent wound dressing material. In this study, we aim to develop an excellent wound dressing material by introducing three-residue sequence Arg-Gly-Asp (RGD), which is the most well-known adhesion site of fibronectin, in the films of SF and the model peptide. Its usefulness as a wound dressing material was evaluated both in vitro and in vivo. First, we showed that the flexible structures of the RGD sequence are still maintained in SF with a rigid antiparallel β-sheet structure using NMR in association with excellent wound dressings of SF containing RGD. Then, in in vitro experiments, two types of normal cells derived from human skin, normal human neonatal epidermal keratinocytes and normal human neonatal dermal fibroblasts, were used to evaluate the cell adhesion. On the other hand, in in vivo experiments, the study was conducted using a rat model of a whole skin layer defect wound. The results showed that the high-functionalized SF developed here has the potential to play a significant role in the field of wound dressings.

An Overview of Recent Developments in the Management of Burn Injuries

According to the World Health Organization (WHO), around 11 million people suffer from burns every year, and 180,000 die from them. A burn is a condition in which heat, chemical substances, an electrical current or other factors cause tissue damage. Burns mainly affect the skin, but can also affect deeper tissues such as bones or muscles. When burned, the skin loses its main functions, such as protection from the external environment, pathogens, evaporation and heat loss. Depending on the stage of the burn, the patient's condition and the cause of the burn, we need to choose the most appropriate treatment. Personalization and multidisciplinary collaboration are key to the successful management of burn patients. In this comprehensive review, we have collected and discussed the available treatment options, focusing on recent advances in topical treatments, wound cleansing, dressings, skin grafting, nutrition, pain and scar tissue management.

Extracellular Matrix-Mimetic Immunomodulatory Hydrogel for Accelerating Wound Healing

Macrophages play a crucial role in the complete processes of tissue repair and regeneration, and the activation of M2 polarization is an effective approach to provide a pro-regenerative immune microenvironment. Natural extracellular matrix (ECM) has the capability to modulate macrophage activities via its molecular, physical, and mechanical properties. Inspired by this, an ECM-mimetic hydrogel strategy to modulate macrophages via its dynamic structural characteristics and bioactive cell adhesion sites is proposed. The LZM-SC/SS hydrogel is in situ formed through the amidation reaction between lysozyme (LZM), 4-arm-PEG-SC, and 4-arm-PEG-SS, where LZM provides DGR tripeptide for cell adhesion, 4-arm-PEG-SS provides succinyl ester for dynamic hydrolysis, and 4-arm-PEG-SC balances the stability and dynamics of the network. In vitro and subcutaneous tests indicate the dynamic structural evolution and cell adhesion capacity promotes macrophage movement and M2 polarization synergistically. Comprehensive bioinformatic analysis further confirms the immunomodulatory ability, and reveals a significant correlation between M2 polarization and cell adhesion. A full-thickness wound model is employed to validate the induced M2 polarization, vessel development, and accelerated healing by LZM-SC/SS. This study represents a pioneering exploration of macrophage modulation by biomaterials' structures and components rather than drug or cytokines and provides new strategies to promote tissue repair and regeneration.

Tissue engineered skin substitutes: A comprehensive review of basic design, fabrication using 3D printing, recent advances and challenges

The multi-layered skin structure includes the epidermis, dermis and hypodermis, which forms a sophisticated tissue composed of extracellular matrix (ECM). The wound repair is a well-orchestrated process when the skin is injured. However, this natural wound repair will be ineffective for large surface area wounds. Autografts-based treatment is efficient but, additional pain and secondary healing of the patient limits its successful application. Therefore, there is a substantial need for fabricating tissue-engineered skin constructs. The development of a successful skin graft requires a fundamental understanding of the natural skin and its healing process, as well as design criteria for selecting a biopolymer and an appropriate fabrication technique. Further, the fabrication of an appropriate skin graft needs to meet physicochemical, mechanical, and biological properties equivalent to the natural skin. Advanced 3D bioprinting provides spatial control of the placement of functional components, such as biopolymers with living cells, which can satisfy the prerequisites for the preparation of an ideal skin graft. In this view, here we elaborate on the basic design requirements, constraints involved in the fabrication of skin graft and choice of ink, the probable solution by 3D bioprinting technique, as well as their latest advancements, challenges, and prospects.

Recent Advances in Electrospun Nanofiber-Based Strategies for Diabetic Wound Healing Application

Diabetic ulcers are the second largest complication caused by diabetes mellitus. A great number of factors, including hyperchromic inflammation, susceptible microbial infection, inferior vascularization, the large accumulation of free radicals, and other poor healing-promoting microenvironments hold back the healing process of chronic diabetic ulcer in clinics. With the increasing clinical cases of diabetic ulcers worldwide, the design and development of advanced wound dressings are urgently required to accelerate the treatment of skin wounds caused by diabetic complications. Electrospinning technology has been recognized as a simple, versatile, and cost-reasonable strategy to fabricate dressing materials composed of nanofibers, which possess excellent extracellular matrix (ECM)-mimicking morphology, structure, and biological functions. The electrospinning-based nanofibrous dressings have been widely demonstrated to promote the adhesion, migration, and proliferation of dermal fibroblasts, and further accelerate the wound healing process compared with some other dressing types like traditional cotton gauze and medical sponges, etc. Moreover, the electrospun nanofibers are commonly harvested in the structure of nonwoven-like mats, which possess small pore sizes but high porosity, resulting in great microbial barrier performance as well as excellent moisture and air permeable properties. They also serve as good carriers to load various bioactive agents and/or even living cells, which further impart the electrospinning-based dressings with predetermined biological functions and even multiple functions to significantly improve the healing outcomes of different chronic skin wounds while dramatically shortening the treatment procedure. All these outstanding characteristics have made electrospun nanofibrous dressings one of the most promising dressing candidates for the treatment of chronic diabetic ulcers. This review starts with a brief introduction to diabetic ulcer and the electrospinning process, and then provides a detailed introduction to recent advances in electrospinning-based strategies for the treatment of diabetic wounds. Importantly, the synergetic application of combining electrospinning with bioactive ingredients and/or cell therapy was highlighted. The review also discussed the advantages of hydrogel dressings by using electrospun nanofibers. At the end of the review, the challenge and prospects of electrospinning-based strategies for the treatment of diabetic wounds are discussed in depth.

Oligochitosan and oxidized nucleoside-based bioderived hydrogels for wound healing

Herein, we report biocompatible hydrogel for wound healing that was prepared using nature-sourced building blocks. For the first time, OCS was employed as a building macromolecule to form bulk hydrogels along with the nature-sourced nucleoside derivative (inosine dialdehyde, IdA) as the cross-linker. A strong correlation was obtained between the mechanical properties and stability of the prepared hydrogels with a cross-linker concentration. The Cryo-SEM images of IdA/OCS hydrogels showed an interconnected spongy-like porous structure. Alexa 555 labeled bovine serum albumin was incorporated into the hydrogels matrix. The release kinetics studies under physiological conditions indicated that cross-linker concentration could also control the release rate. The potential of hydrogels in wound healing applications was tested in vitro and ex vivo on human skin. Topical application of the hydrogel was excellently tolerated by the skin with no impairment of epidermal viability or irritation, determined by MTT and IL-1α assays, respectively. The hydrogels were used to load and deliver epidermal growth factor (EGF), showing an increase in its ameliorating action, effectively enhancing wound closure inflicted by punch biopsy. Furthermore, BrdU incorporation assay performed in both fibroblast and keratinocyte cells revealed an increased proliferation in hydrogel-treated cells and an enhancement of EGF impact in keratinocytes.

In situ photo-crosslinking silk fibroin based hydrogel accelerates diabetic wound healing through antibacterial and antioxidant

Bacterial infection and excessive reactive oxygen species (ROS) in diabetic wounds lead to a prolonged inflammatory phase, and injuries are highly susceptible to developing into chronic wounds. Improving the poor microenvironment is vital to achieving effective diabetic wound healing. In this work, methacrylated silk fibroin (SFMA) was combined with ε-polylysine (EPL) and manganese dioxide nanoparticles (BMNPs) to form an SF@(EPL-BM) hydrogel with in situ forming, antibacterial and antioxidant properties. EPL imparted high antibacterial activity (>96 %) to the hydrogel. BMNPs and EPL showed good scavenging activity against a variety of free radicals. SF@(EPL-BM) hydrogel had low cytotoxicity and could alleviate H₂O₂-induced oxidative stress in L929 cells. In diabetic wounds infected with Staphylococcus aureus (S. aureus), the SF@(EPL-BM) hydrogel exhibited better antibacterial properties and reduced wound ROS levels more significantly than that of the control in vivo. In this process, the pro-inflammatory factor TNF-α was down-regulated, and the vascularization marker CD31 was up-regulated. H&E and Masson staining showed a rapid transition from the inflammatory to the proliferative phase of the wounds, with significant new tissue and collagen deposition. These results confirm that this multifunctional hydrogel dressing holds well potential for chronic wound healing.

Application of Silk-Fibroin-Based Hydrogels in Tissue Engineering

Silk fibroin (SF) is an excellent protein-based biomaterial produced by the degumming and purification of silk from cocoons of the Bombyx mori through alkali or enzymatic treatments. SF exhibits excellent biological properties, such as mechanical properties, biocompatibility, biodegradability, bioabsorbability, low immunogenicity, and tunability, making it a versatile material widely applied in biological fields, particularly in tissue engineering. In tissue engineering, SF is often fabricated into hydrogel form, with the advantages of added materials. SF hydrogels have mostly been studied for their use in tissue regeneration by enhancing cell activity at the tissue defect site or counteracting tissue-damage-related factors. This review focuses on SF hydrogels, firstly summarizing the fabrication and properties of SF and SF hydrogels and then detailing the regenerative effects of SF hydrogels as scaffolds in cartilage, bone, skin, cornea, teeth, and eardrum in recent years.

Release systems based on self-assembling RADA16-I hydrogels with a signal sequence which improves wound healing processes

Self-assembling peptides can be used for the regeneration of severely damaged skin. They can act as scaffolds for skin cells and as a reservoir of active compounds, to accelerate scarless wound healing. To overcome repeated administration of peptides which accelerate healing, we report development of three new peptide biomaterials based on the RADA16-I hydrogel functionalized with a sequence (AAPV) cleaved by human neutrophil elastase and short biologically active peptide motifs, namely GHK, KGHK and RDKVYR. The peptide hybrids were investigated for their structural aspects using circular dichroism, thioflavin T assay, transmission electron microscopy, and atomic force microscopy, as well as their rheological properties and stability in different fluids such as water or plasma, and their susceptibility to digestion by enzymes present in the wound environment. In addition, the morphology of the RADA-peptide hydrogels was examined with a unique technique called scanning electron cryomicroscopy. These experiments enabled us to verify if the designed peptides increased the bioactivity of the gel without disturbing its gelling processes. We demonstrate that the physicochemical properties of the designed hybrids were similar to those of the original RADA16-I. The materials behaved as expected, leaving the active motif free when treated with elastase. XTT and LDH tests on fibroblasts and keratinocytes were performed to assess the cytotoxicity of the RADA16-I hybrids, while the viability of cells treated with RADA16-I hybrids was evaluated in a model of human dermal fibroblasts. The hybrid peptides revealed no cytotoxicity; the cells grew and proliferated better than after treatment with RADA16-I alone. Improved wound healing following topical delivery of RADA-GHK and RADA-KGHK was demonstrated using a model of dorsal skin injury in mice and histological analyses. The presented results indicate further research is warranted into the engineered peptides as scaffolds for wound healing and tissue engineering.

Photopolymerized silk fibroin gel for advanced burn wound care

The future of burn wound treatment lies in developing bioactive dressings for faster and more effective healing and regeneration. Silk fibroin (SF) hydrogels have proven regenerative abilities and are being explored as a burn wound dressing. However, unfavorable gelation conditions limit the processability and clinical application. Herein a white light-responsive photopolymerization technique was adapted for gelation via photooxidation of tyrosine. To render the gel suitable for application to irregular and non-planar burn surfaces, SF gel-incorporated dressing (SFD) was fabricated. The mild gelation conditions using white light afforded the loading of drugs for local delivery. The moisture balance ability of the dressing was confirmed by the favorable measures of swelling capacity (106 ± 1 %) and moisture retention (≈10 h). The in vitro cytocompatibility of the gel was confirmed using HaCaT cells. Finally, in vivo performance of the SFD was tested on a second-degree burn in a rodent model. The gross analysis and histological assessment revealed scarless healing in SFD-treated groups. Overall, the SFD developed in this work is shown to be a promising candidate for advanced burn wound care.

Highly stretchable porous regenerated silk fibroin film for enhanced wound healing

Silk fibroin (SF) has received interest in tissue engineering owing to its biocompatibility, biodegradability, and favorable mechanical properties. However, the complex preparation, brittleness, and lack of pores in the structure of the silk fibroin film limit its application. Herein, we show that facile dissolution of SF in aqueous phosphoric acid followed by regeneration in aqueous ammonium sulfate ((NH₄)₂SO₄) could afford highly stretchable films with nano-pores formed in the nonsolvent-induced phase separation process. The named phase separation, which determines the morphology and mechanical properties of the regeneration silk fibroin (RSF) films, is highly dependent on the (NH₄)₂SO₄ concentration as well as the initial concentration of the SF solution. Therefore, the RSF films exhibit a tunable pore size ranging from 230 to 510 nm and excellent stretchability with tensile strain up to 143 ± 16%. Most interestingly, the RSF films were shown to support the proliferation of human skin fibroblasts in vitro as well as speed up full-thickness skin wound healing in a rat model. This work establishes an easy and feasible method to access porous RSF membranes that can be used for wound dressing in clinical settings.

Hyaluronic acid and chitosan-based injectable and self-healing hydrogel with inherent antibacterial and antioxidant bioactivities

Injectable dressings offering intrinsic antibacterial activity and antioxidation are required, because persistent bacterial infection and oxidative damage are common issues associated with chronic non-healing wounds. Herein, a versatile QCS-l-TA-l-OHA hydrogel is fabricated using ubiquitous nature derived biological macromolecules, quaternized chitosan (QCS), tannic acid (TA) and oxidant hyaluronic acid (OHA), driving by multiple dynamic interactions under physiological conditions. The hydrogel can serve as multiple functional wound dress with injectable and self-healing capabilities coupling with attractive antibacterial activity and antioxidation. The biocompatible and self-biodegradable hydrogel augments free radical scavenging capacity, antibacterial, angiogenesis, mature granulation tissue and collagen disposition, enabling fast wound healing of rat skin full-thickness incision model. This study highlights a wound dressing platform of hyaluronic acid and chitosan based injectable and self-healing hydrogel with inherent antibacterial and antioxidant bioactivities, thereby avoiding the use of antibiotics or antioxidant agents.

Structural and biological engineering of 3D hydrogels for wound healing

Chronic wounds have become one of the most important issues for healthcare systems and are a leading cause of death worldwide. Wound dressings are necessary to facilitate wound treatment. Engineering wound dressings may substantially reduce healing time, reduce the risk of recurrent infections, and reduce the disability and costs associated. In the path of engineering of an ideal wound dressing, hydrogels have played a leading role. Hydrogels are 3D hydrophilic polymeric structures that can provide a protective barrier, mimic the native extracellular matrix (ECM), and provide a humid environment. Due to their advantages, hydrogels (with different architectural, physical, mechanical, and biological properties) have been extensively explored as wound dressing platforms. Here we describe recent studies on hydrogels for wound healing applications with a strong focus on the interplay between the fabrication method used and the architectural, mechanical, and biological performance achieved. Moreover, we review different categories of additives which can enhance wound regeneration using 3D hydrogel dressings. Hydrogel engineering for wound healing applications promises the generation of smart solutions to solve this pressing problem, enabling key functionalities such as bacterial growth inhibition, enhanced re-epithelialization, vascularization, improved recovery of the tissue functionality, and overall, accelerated and effective wound healing.

Silk Fibroin Biomaterials and Their Beneficial Role in Skin Wound Healing

The skin, acting as the outer protection of the human body, is most vulnerable to injury. Wound healing can often be impaired, leading to chronic, hard-to-heal wounds. For this reason, searching for the most effective dressings that can significantly enhance the wound healing process is necessary. In this regard, silk fibroin, a protein derived from silk fibres that has excellent properties, is noteworthy. Silk fibroin is highly biocompatible and biodegradable. It can easily make various dressings, which can be loaded with additional substances to improve healing. Dressings based on silk fibroin have anti-inflammatory, pro-angiogenic properties and significantly accelerate skin wound healing, even compared to commercially available wound dressings. Animal studies confirm the beneficial influence of silk fibroin in wound healing. Clinical research focusing on fibroin dressings is also promising. These properties make silk fibroin a remarkable natural material for creating innovative, simple, and effective dressings for skin wound healing. In this review, we summarise the application of silk fibroin biomaterials as wound dressings in full-thickness, burn, and diabetic wounds in preclinical and clinical settings.

The role of the immune microenvironment in bone, cartilage, and soft tissue regeneration: from mechanism to therapeutic opportunity

Bone, cartilage, and soft tissue regeneration is a complex spatiotemporal process recruiting a variety of cell types, whose activity and interplay must be precisely mediated for effective healing post-injury. Although extensive strides have been made in the understanding of the immune microenvironment processes governing bone, cartilage, and soft tissue regeneration, effective clinical translation of these mechanisms remains a challenge. Regulation of the immune microenvironment is increasingly becoming a favorable target for bone, cartilage, and soft tissue regeneration; therefore, an in-depth understanding of the communication between immune cells and functional tissue cells would be valuable. Herein, we review the regulatory role of the immune microenvironment in the promotion and maintenance of stem cell states in the context of bone, cartilage, and soft tissue repair and regeneration. We discuss the roles of various immune cell subsets in bone, cartilage, and soft tissue repair and regeneration processes and introduce novel strategies, for example, biomaterial-targeting of immune cell activity, aimed at regulating healing. Understanding the mechanisms of the crosstalk between the immune microenvironment and regeneration pathways may shed light on new therapeutic opportunities for enhancing bone, cartilage, and soft tissue regeneration through regulation of the immune microenvironment.

Preparation and Characterization of Nanofibrous Membranes Electro-Spun from Blended Poly(l-lactide-co-ε-caprolactone) and Recombinant Spider Silk Protein as Potential Skin Regeneration Scaffold

Biomaterial scaffolding serves as an important strategy in skin tissue engineering. In this research, recombinant spider silk protein (RSSP) and poly(L-lactide-co-ε-caprolactone) (PLCL) were blended in different ratios to fabricate nanofibrous membranes as potential skin regeneration scaffolds with an electro-spinning process. Scanning electron microscopy (SEM), water contact angles measurement, Fourier transform infrared (FTIR) spectroscopy, wide angle X-ray diffraction (WAXD), tensile mechanical tests and thermo-gravimetric analysis (TGA) were carried out to characterize the nanofibrous membranes. The results showed that the blending of RSSP greatly decreased the nanofibers' average diameter, enhanced the hydrophilicity, changed the microstructure and thermal properties, and could enable tailored mechanical properties of the nanofibrous membranes. Among the blended membranes, the PLCL/RSSP (75/25) membrane was chosen for further investigation on biocompatibility. The results of hemolysis assays and for proliferation of human foreskin fibroblast cells (hFFCs) confirmed the membranes potential use as skin-regeneration scaffolds. Subsequent culture of mouse embryonic fibroblast cells (NIH-3T3) demonstrated the feasibility of the blended membranes as a human epidermal growth factor (hEGF) delivery matrix. The PLCL/RSSP (75/25) membrane possessed good properties comparable to those of human skin with high biocompatibility and the ability of hEGF delivery. Further studies can be carried out on such membranes with chemical or genetic modifications to make better scaffolds for skin regeneration.

Green tea catechin-grafted silk fibroin hydrogels with reactive oxygen species scavenging activity for wound healing applications

BACKGROUND

Overproduction of reactive oxygen species (ROS) is known to delay wound healing by causing oxidative tissue damage and inflammation. The green tea catechin, (-)-Epigallocatechin-3-O-gallate (EGCG), has drawn a great deal of interest due to its strong ROS scavenging and anti-inflammatory activities. In this study, we developed EGCG-grafted silk fibroin hydrogels as a potential wound dressing material.

METHODS

The introduction of EGCG to water-soluble silk fibroin (SF-WS) was accomplished by the nucleophilic addition reaction between lysine residues in silk proteins and EGCG quinone at mild basic pH. The resulting SF-EGCG conjugate was co-crosslinked with tyramine-substituted SF (SF-T) via horseradish peroxidase (HRP)/H2O2 mediated enzymatic reaction to form SF-T/SF-EGCG hydrogels with series of composition ratios.

RESULTS

Interestingly, SF-T70/SF-EGCG30 hydrogels exhibited rapid in situ gelation (< 30 s), similar storage modulus to human skin (≈ 1000 Pa) and superior wound healing performance over SF-T hydrogels and a commercial DuoDERM® gel dressings in a rat model of full thickness skin defect.

CONCLUSION

This study will provide useful insights into a rational design of ROS scavenging biomaterials for wound healing applications.

Electrospun nanofibers with antibacterial properties for wound dressings

The antibacterial nanofibers have been proposed as an interesting material for wound healing management, since the majority of traditional wound dressings exhibit issues and complications such as infection, pain, discomfort, and poor adhesive proprieties. It allows the organism's passage through the dressing and delay the wound healing progression. Electrospun nanofibers have been intensively investigated for wound dressings in tissue engineering applications due to their distinctive features and structural similarities to the extracellular matrix including the various available methods to load the antibacterial compounds onto the nanofiber webs. To construct an effective electrospun wound dressing, various efforts have been made to design different strategies to develop advanced polymers, such as employing synthetic and/or natural materials, modifying fiber orientation, and incorporating chemicals and metallic nanoparticles (NPs) as intriguing materials for antibacterial bandages. Thus, this review summarizes the relevant recent studies on the production of electrospun antibacterial nanofibers from a wide variety of polymers used in biomedical applications for wound dressings.

Short Peptide-Based Smart Thixotropic Hydrogels †

Thixotropy is a fascinating feature present in many gel systems that has garnered a lot of attention in the medical field in recent decades. When shear stress is applied, the gel transforms into sol and immediately returns to its original state when resting. The thixotropic nature of the hydrogel has inspired scientists to entrap and release enzymes, therapeutics, and other substances inside the human body, where the gel acts as a drug reservoir and can sustainably release therapeutics. Furthermore, thixotropic hydrogels have been widely used in various therapeutic applications, including drug delivery, cornea regeneration and osteogenesis, to name a few. Because of their inherent biocompatibility and structural diversity, peptides are at the forefront of cutting-edge research in this context. This review will discuss the rational design and self-assembly of peptide-based thixotropic hydrogels with some representative examples, followed by their biomedical applications.

Bacterial Growth-Induced Tobramycin Smart Release Self-Healing Hydrogel for Pseudomonas aeruginosa-Infected Burn Wound Healing

Burns are a common health problem worldwide and are highly susceptible to bacterial infections that are difficult to handle with ordinary wound dressings. Therefore, burn wound repair is extremely challenging in clinical practice. Herein, a series of self-healing hydrogels (QCS/OD/TOB/PPY@PDA) with good electrical conductivity and antioxidant activity were prepared on the basis of quaternized chitosan (QCS), oxidized dextran (OD), tobramycin (TOB), and polydopamine-coated polypyrrole nanowires (PPY@PDA NWs). These Schiff base cross-links between the aminoglycoside antibiotic TOB and OD enable TOB to be slowly released and responsive to pH. Interestingly, the acidic substances during the bacteria growth process can induce the on-demand release of TOB, avoiding the abuse of antibiotics. The antibacterial results showed that the QCS/OD/TOB/PPY@PDA9 hydrogel could kill high concentrations of Pseudomonas aeruginosa (PA), Staphylococcus aureus, and Escherichia coli in a short time and showed a bactericidal effect for up to 11 days in an agar plate diffusion experiment, while showing good in vivo antibacterial activity. Excellent and long-lasting antibacterial properties make it suitable for severely infected wounds. Furthermore, the incorporation of PPY@PDA endowed the hydrogel with near-infrared (NIR) irradiation assisted bactericidal activity of drug-resistant bacteria, conductivity, and antioxidant activity. Most importantly, in the PA-infected burn wound model, the QCS/OD/TOB/PPY@PDA9 hydrogel more effectively controlled wound inflammation levels and promoted collagen deposition, vascular generation, and earlier wound closure compared to Tegaderm dressings. Therefore, the TOB smart release hydrogels with on-demand delivery are extremely advantageous for bacterial-infected burn wound healing.

Synergetic integrations of bone marrow stem cells and transforming growth factor-β1 loaded chitosan nanoparticles blended silk fibroin injectable hydrogel to enhance repair and regeneration potential in articular cartilage tissue

The cartilage repair and regeneration show inadequate self-healing capability and have some complications, which are inordinate challenges in clinical therapy. Biopolymeric injectable hydrogels, a prominent type of cell-carrier as well tissue engineering scaffolding materials, establish promising therapeutic potential of stem cell-based cartilage-regeneration treatment. In addition, injectable scaffolding biomaterial should have rapid gelation properties with adequate rheological and mechanical properties. In the present investigation, we developed and fabricated the macromolecular silk fibroin blended with polylysine modified chitosan polymer (SF/PCS) using thermal-sensitive glycerophosphate (GP), which contains effective gelation ability, morphology, porosity and also has enhanced mechanical properties to induce physical applicability, cell proliferation and nutrient exchange in the cell-based treatment. The developed and optimised injectable hydrogel group has good biocompatibility with human fibroblast (L929) cells and bone marrow-derived mesenchymal stem cells (BMSCs). Additionally, it was found that SF/PCS hydrogel group could sustainably release TGF-β1 and efficiently regulate cartilage-specific and inflammatory-related gene expressions. Finally, the cartilage-regeneration potential of the hydrogel groups embedded with and without BMSCs were evaluated in SD rat models under histopathological analysis, which showed promising cartilage repair. Overall, we conclude that the TGF-β1-SF/PCS injectable hydrogel demonstrates enhanced in vitro and in vivo tissue regeneration properties, which lead to efficacious therapeutic potential in cartilage regeneration.

Silk Fibroin Hydrogel Reinforced With Magnetic Nanoparticles as an Intelligent Drug Delivery System for Sustained Drug Release

Due to the well-known biocompatibility, tunable biodegradability, and mechanical properties, silk fibroin hydrogel is an exciting material for localized drug delivery systems to decrease the therapy cost, decrease the negative side effects, and increase the efficiency of chemotherapy. However, the lack of remote stimuli response and active drug release behavior has yet to be analyzed comparatively. In this study, we developed magnetic silk fibroin (SF) hydrogel samples through the facile blending method, loaded with doxorubicin hydrochloride (DOX) and incorporated with different concentrations of iron oxide nanoparticles (IONPs), to investigate the presumable ability of controlled and sustained drug release under the various external magnetic field (EMF). The morphology and rheological properties of SF hydrogel and magnetic SF hydrogel were compared through FESEM images and rheometer analysis. Here, we demonstrated that adding magnetic nanoparticles (MNPs) into SFH decreased the complex viscosity and provided a denser porosity with a bigger pore size matrix structure, which allowed the drug to be released faster in the absence of an EMF. Release kinetic studies show that magnetic SF hydrogel could achieve controlled release of DOX in the presence of an EMF. Furthermore, the drug release from magnetic SF hydrogel decreased in the presence of a static magnetic field (SMF) and an alternating magnetic field (AMF), and the release rate decreased even more with the higher MNPs concentration and magnetic field strength. Subsequently, Wilms’ tumor and human fibroblast cells were cultured with almost the same concentration of DOX released in different periods, and cell viability was investigated using MTT assay. MTT results indicated that the Wilms’ tumor cells were more resistant to DOX than the human fibroblasts, and the IC50 values were calculated at 1.82 ± 0.001 and 2.73 ± 0.004 (μg/ml) for human fibroblasts and Wilms’ tumor cells, respectively. Wilms’ tumor cells showed drug resistance in a higher DOX concentration, indicating the importance of controlled drug delivery. These findings suggest that the developed magnetic SFH loaded with DOX holds excellent potential for intelligent drug delivery systems with noninvasive injection and remotely controlled abilities.

Enzymatic Crosslinked Silk Fibroin Hydrogel for Biodegradable Electronic Skin and Pulse Waveform Measurements

The development of a portable, controllable, and environmentally friendly electronic skin (e-skin) is highly desirable; however, it presents a major challenge. Herein, a biocompatible, biodegradable, and easily usable hydrogel was designed and fabricated as e-skin to enable the transmission of information regarding the spatial pressure distribution. Silk fibroin (SF) was used as the hydrogel skeleton, which endowed the hydrogel with intelligent mechanical sensitivity. During its conditioning in weakly acidic media, the density of the enzymatic crosslink increased and a dense network was formed due to the formation of covalent/hydrogen bonds. Additionally, a conductive SF/polyvinyl alcohol (PVA) hybrid film was molded as a flexible electrode after graphite deposition. The above SF sensing unit based on SF hydrogels and SF/PVA hybrid films showed high strain sensitivity (4.78), fast responsiveness (<0.1 s), good cycling stability (≥10,000), excellent biocompatibility, and biodegradability. Importantly, a coplanar 8 × 8 pixel SF-based e-skin array was successfully fabricated and applied for 3D signal transmission of the object. The SF-based e-skin was capable of precisely tracking the changes in the pulse pressure, the movement of the finger joint, and the vibrations of the vocal cord. Therefore, the current findings provide a solid foundation for future studies exploring the next generation of electronic devices.

In vitro biological activities of the flexible and virus nanoparticle-decorated silk fibroin-based films

Flexible films were prepared from silk fibroin (SF) and gelatin (GA) with a presence of glycerol (Gly), followed by water vapor annealing to achieve water-insoluble matrices. The blended SF/GA/Gly films were chemically conjugated with tobacco mosaic virus (TMV), either native (TMV-wt) or genetically modified with Arg-Gly-Asp (RGD) sequences (TMV-rgd), to improve cellular responses. The attachment and proliferation of L929 cells on TMV-decorated films were improved, possibly due to enhanced surface roughness. The cellular responses were pronounced with TMV-rgd, due to the proper decoration of RGD, which is an integrin recognition motif supporting cell binding. However, the biological results were inconclusive for human primary cells because of an innate slow growth kinetic of the cells. Additionally, the cells on SF/GA/Gly films were greater populated in S and G2/M phase, and the cell cycle arrest was notably increased in the TMV-conjugated group. Our findings revealed that the films modified with TMV were cytocompatible and the cellular responses were significantly enhanced when conjugated with its RGD mutants. The biological analysis on the cellular mechanisms in response to TMV is further required to ensure the safety concern of the biomaterials toward clinical translation.

Keratin-based wound dressings: From waste to wealth

Keratin is a natural protein with a high content of cysteine residues (7-13%) and is widely found in hair, wool, horns, hooves, and nails. Keratin possesses abundant cell-binding motifs such as leucine-aspartate-valine (LDV), glutamate-aspartate-serine (EDS), and arginine-glycine-aspartate (RGD), which benefit cell attachment and proliferation. It has been confirmed that keratin plays important roles in every stage of wound healing, including hemostasis, inflammation, proliferation, and remodeling, making keratin-based materials good candidates for wound dressings. In combination with synthetic and natural polymers, keratin-based wound dressings in the forms of films, hydrogels, and nanofibers can be achieved with improved mechanical properties. This review focuses on the recent development of keratin-based wound dressings. Firstly, the physicochemical and biological properties of keratin, are systematically discussed. Secondly, the role of keratin in wound healing is proposed. Thirdly, the applications of keratin-based wound dressings are summarized, in terms of the forms and functionalization. Finally, the current challenges and future development of keratin-based wound dressings are presented.

Development of silk fibroin‑sodium alginate scaffold loaded silk fibroin nanoparticles for hemostasis and cell adhesion

During wound healing process, it is essential to promote hemostasis and cell adhesion. Herein, we incorporated a scaffold with nanoparticles to improve the hemostatic properties and stimulate cell adhesion. The nanoparticles were prepared by self-assembling of silk fibroin, and the scaffold loaded nanoparticles were synthesized by crosslinking and freeze-drying. Macroscopical images showed that the nanoparticles distributed uniformly and increased the surface roughness of scaffold pore wall. The addition of nanoparticles decreased the pore size, enhanced the compression strength, lowered the degradation rate, and maintained the resilience and water uptake capacity. Compared with pure scaffold, the scaffold loaded nanoparticles revealed higher blood clotting index and promoted platelets adhesion. Furthermore, in vitro tests showed that scaffold loaded nanoparticles exhibited excellent biocompatibility, and stimulation effects on cell proliferation, migration, and adhesion for both L929 cells and HUVECs. Therefore, the scaffold loaded nanoparticles possessed great potential as a wound dressing for efficient hemostasis and subsequent wound healing.

One-Step FRESH Bioprinting of Low-Viscosity Silk Fibroin Inks

Silk fibroin (SF) is an attractive material for composing bioinks suitable for three-dimensional (3D) bioprinting. However, the low viscosity of SF solutions obtained through common dissolution methods limits 3D-bioprinting applications without the addition of thickeners or partial gelation beforehand. Here, we report a method of 3D bioprinting low-viscosity SF solutions without additives. We combined a method of freeform reversible embedding of suspended hydrogels, known as the FRESH method, with horseradish peroxidase-catalyzed cross-linking. Using this method, we successfully fabricated 3D SF hydrogel constructs from low-viscosity SF ink (10% w/w, 50 mPa s at 1 s^-1 shear rate), which does not yield 3D constructs when printed onto a plate in air. Studies using mouse fibroblasts confirmed that the printing process was cell-friendly. Additionally, cells enclosed in printed SF hydrogel constructs maintained > 90% viability for 11 days of culture. These results demonstrate that the 3D bioprinting technique developed in this study enables new 3D bioprinting applications using SF inks and thus has a great potential to contribute to tissue engineering and regenerative medicine.