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

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.

Bilayer silk fibroin/sodium alginate scaffold promotes vascularization and advances inflammation stage in full-thickness wound

An ideal wound dressing for full-thickness wound regeneration should offer desirable biocompatibility, adequate mechanical properties, barrier function, and cellular regulation. Here, a bilayer scaffold resembling the hierarchical structure of human skin was developed using silk fibroin and sodium alginate. The upper membrane was prepared through casting and functioned as the epidermis, whereas the lower porous scaffold was prepared by freeze-drying and mimicked extracellular matrix structures. The membrane had nonporous structure, desirable mechanical properties, moderate hydrophilic surface, and suitable water vapor transmission rate, whereas the porous scaffold revealed 157.61 ± 41.67 µm pore size, 86.10 ± 3.60% porosity, and capability of stimulating fibroblast proliferation. The combination of the two structures reinforced the tensile strength by 5-fold and provided protection from wound dehydration. A suitable degradation rate reduced potential administration frequency. Furthermore, an in vivo rabbit full-thickness wound healing test demonstrated that the bilayer scaffold facilitated wound closure, granulation tissue formation, re-epithelialization and skin component transition towards normal skin by providing a moist wound environment, advancing the inflammation stage, and stimulating angiogenesis. Collectively, as an off-the-shelf and cell-free wound dressing with single topical administration, the bilayer scaffold is a promising wound dressing for full-thickness wound regeneration.

Exploring bioactive peptides as potential therapeutic and biotechnology treasures: A contemporary perspective

In preceding years, bioactive peptides (BAPs) have piqued escalating attention owing to their multitudinous biological features. To date, many potential BAPs exhibiting anti-cancer activities have been documented; yet, obstacles such as their safety profiles and consumer acceptance continue to exist. Moreover, BAPs have been discovered to facilitate the suppression of Coronavirus Disease 2019 (CoVID-19) and maybe ideal for treating the CoVID-19 infection, as stated by published experimental findings, but their widespread knowledge is scarce. Likewise, there is a cornucopia of BAPs possessing neuroprotective effects that mend neurodegenerative diseases (NDs) by regulating gut microbiota, but they remain a subject of research interest. Additionally, a plethora of researchers have attempted next-generation approaches based on BAPs, but they need scientific attention. The text format of this critical review is organized around an overview of BAPs' versatility and diverse bio functionalities with emphasis on recent developments and novelties. The review is alienated into independent sections, which are related to either BAPs based disease management strategies or next-generation BAPs based approaches. BAPs based anti-cancer, anti-CoVID-19, and neuroprotective strategies have been explored, which may offer insights that could help the researchers and industries to find an alternate regimen against the three aforementioned fatal diseases. To the best of our knowledge, this is the first review that has systematically discussed the next-generation approaches in BAP research. Furthermore, it can be concluded that the BAPs may be optimal for the management of cancer, CoVID-19, and NDs; nevertheless, experimental and preclinical studies are crucial to validate their therapeutic benefits.

Static and Dynamic Biomaterial Engineering for Cell Modulation

In the biological microenvironment, cells are surrounded by an extracellular matrix (ECM), with which they dynamically interact during various biological processes. Specifically, the physical and chemical properties of the ECM work cooperatively to influence the behavior and fate of cells directly and indirectly, which invokes various physiological responses in the body. Hence, efficient strategies to modulate cellular responses for a specific purpose have become important for various scientific fields such as biology, pharmacy, and medicine. Among many approaches, the utilization of biomaterials has been studied the most because they can be meticulously engineered to mimic cellular modulatory behavior. For such careful engineering, studies on physical modulation (e.g., ECM topography, stiffness, and wettability) and chemical manipulation (e.g., composition and soluble and surface biosignals) have been actively conducted. At present, the scope of research is being shifted from static (considering only the initial environment and the effects of each element) to biomimetic dynamic (including the concepts of time and gradient) modulation in both physical and chemical manipulations. This review provides an overall perspective on how the static and dynamic biomaterials are actively engineered to modulate targeted cellular responses while highlighting the importance and advance from static modulation to biomimetic dynamic modulation for biomedical applications.

Construction and Biocompatibility Evaluation of Fibroin/Sericin-Based Scaffolds

Because tissue responses to implants determine the success or failure of tissue engineering products, fibroin/sericin-based scaffolds including bionic silk scaffolds, native silk fibers, fibroin fibers, and regenerated fibroin have been fabricated, and their biocompatibility was investigated. Fibroin/sericin-based scaffolds were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Bionic silk scaffolds were beneficial to silk fiber formation through self-assembly. Histological and immunofluorescent staining analysis demonstrated that bionic silk scaffolds did not show significant inflammatory responses. Immunization analysis showed that soluble fibroin and sericin did not show obvious immunogenicity. This work supplied an effective approach to design fibroin/sericin-based scaffolds for tissue engineering and drug delivery.

Silk-based phyto-hydrogel formulation expedites key events of wound healing in full-thickness skin defect model

Immense socio-economic burden of chronic wound demands effective, low-cost strategies for wound care. Herein, we have developed a chemical crosslinker-free phyto-hydrogel by encapsulating phytochemicals of Aloe vera mucilage extract (AVM) in the self-assembled polymeric chains of two different silk fibroin (SF) proteins (from Bombyx mori and Antheraea assamensis). Additionally, polyvinylpyrrolidone (PVP) has been used as a stabilizer that also contributed to the mucoadhesive property of the composite (SAP; made of SF, AVM, and PVP) hydrogel. The physicochemical properties of the hydrogel were evaluated and compared with SF hydrogel containing only SF proteins without any additives. The biocompatibility assessment of the hydrogel under in vitro conditions has shown improved cellular proliferative and migratory responses, suggesting faster tissue repairability of the hydrogel. A detailed in vivo comparative study with a commercially available DuoDERM® gel revealed that SAP hydrogel not only promoted wound closure but also showed better deposition and remodeling of the extracellular matrix. Moreover, the hydrogel also demonstrated its ability to downregulate pro-inflammatory markers (IL-1β, TNF-α) and upregulation of anti-inflammatory markers (IL-10, TGF-β) at the early stage of healing. Therefore, the bioactive proteins-carbohydrates composite efficiently accelerates skin regeneration and possesses great translational potential to offer a low-cost alternative wound care therapeutic.

Bioactive Materials Promote Wound Healing through Modulation of Cell Behaviors

Skin wound repair is a multistage process involving multiple cellular and molecular interactions, which modulate the cell behaviors and dynamic remodeling of extracellular matrices to maximize regeneration and repair. Consequently, abnormalities in cell functions or pathways inevitably give rise to side effects, such as dysregulated inflammation, hyperplasia of nonmigratory epithelial cells, and lack of response to growth factors, which impedes angiogenesis and fibrosis. These issues may cause delayed wound healing or even non-healing states. Current clinical therapeutic approaches are predominantly dedicated to preventing infections and alleviating topical symptoms rather than addressing the modulation of wound microenvironments to achieve targeted outcomes. Bioactive materials, relying on their chemical, physical, and biological properties or as carriers of bioactive substances, can affect wound microenvironments and promote wound healing at the molecular level. By addressing the mechanisms of wound healing from the perspective of cell behaviors, this review discusses how bioactive materials modulate the microenvironments and cell behaviors within the wounds during the stages of hemostasis, anti-inflammation, tissue regeneration and deposition, and matrix remodeling. A deeper understanding of cell behaviors during wound healing is bound to promote the development of more targeted and efficient bioactive materials for clinical applications.

Silk Fibroin-Based Therapeutics for Impaired Wound Healing

Impaired wound healing can lead to local hypoxia or tissue necrosis and ultimately result in amputation or even death. Various factors can influence the wound healing environment, including bacterial or fungal infections, different disease states, desiccation, edema, and even systemic viral infections such as COVID-19. Silk fibroin, the fibrous structural-protein component in silk, has emerged as a promising treatment for these impaired processes by promoting functional tissue regeneration. Silk fibroin’s dynamic properties allow for customizable nanoarchitectures, which can be tailored for effectively treating several wound healing impairments. Different forms of silk fibroin include nanoparticles, biosensors, tissue scaffolds, wound dressings, and novel drug-delivery systems. Silk fibroin can be combined with other biomaterials, such as chitosan or microRNA-bound cerium oxide nanoparticles (CNP), to have a synergistic effect on improving impaired wound healing. This review focuses on the different applications of silk-fibroin-based nanotechnology in improving the wound healing process; here we discuss silk fibroin as a tissue scaffold, topical solution, biosensor, and nanoparticle.

Neoantigen Immunotherapeutic-Gel Combined with TIM-3 Blockade Effectively Restrains Orthotopic Hepatocellular Carcinoma Progression

Herein, we integrate the Hepa1-6 liver cancer-specific neoantigen, toll-like receptor 9 agonist and stimulator of interferon genes agonist by silk-hydrogel package, and combine with TIM-3 blockade to elicit robust antitumor immunity for effectively suppressing orthotopic hepatocellular carcinoma (HCC) progression. Unlike intradermal injection of simple mixed components with short-term immune protection, the neoantigen immunotherapeutic-gels evoke long-term immune protection to achieve significant prophylactic and therapeutic activity against HCC through only one-shot administration without any side effects. Notably, the synergized immunotherapy by further combining NGC-gels with TIM-3 antibody significantly reduces regulatory T-cells and increases the IFN-γ and IL-12p70 levels in tumor tissues for promoting the infiltration of IFN-γ+CD8+T-cells and 41BB+CD8+T-cells to achieve complete remission (4/7) and prevent pulmonary metastasis in orthotopic HCC, and establish long-term memory against tumor rechallenge with remarkably longer survival time (180 days). Overall, this study provides an attractive and promising synergistic strategy for HCC immunotherapy with possible clinical translation prospects.

Impact of silk hydrogel secondary structure on hydrogel formation, silk leaching and in vitro response

Silk can be processed into a broad spectrum of material formats and is explored for a wide range of medical applications, including hydrogels for wound care. The current paradigm is that solution-stable silk fibroin in the hydrogels is responsible for their therapeutic response in wound healing. Here, we generated physically cross-linked silk fibroin hydrogels with tuned secondary structure and examined their ability to influence their biological response by leaching silk fibroin. Significantly more silk fibroin leached from hydrogels with an amorphous silk fibroin structure than with a beta sheet-rich silk fibroin structure, although all hydrogels leached silk fibroin. The leached silk was biologically active, as it induced vitro chemokinesis and faster scratch assay wound healing by activating receptor tyrosine kinases. Overall, these effects are desirable for wound management and show the promise of silk fibroin and hydrogel leaching in the wider healthcare setting.

Covalent Organic Framework-Incorporated Nanofibrous Membrane as an Intelligent Platform for Wound Dressing

Covalent organic frameworks (COFs) possess fascinating features that have sparked increasing interest as drug carriers in biomedical applications. However, the promising properties of COFs in wound healing have rarely been reported. Herein, a facile one-pot method is reported to prepare a curcumin-loaded COF (CUR@COF) by the condensation reaction and the Schiff base reaction and to further incorporate CUR@COF into polycaprolactone (PCL) nanofibrous membranes (CUR@COF/PCL NFMs) through electrospinning to develop a pH-triggered drug release platform for wound dressing. CUR@COF has a high CUR loading capacity of 27.68%, and CUR@COF/PCL NFMs exhibit increased thermal stability, improved mechanical properties, good biocompatibility, and enhanced antibacterial and antioxidant activities. More importantly, CUR@COF-based membranes show a pH-responsive CUR release profile by protonation under acidic conditions, suggesting the promotion of CUR release from membranes under an acidic extracellular microenvironment. The histopathological analysis and immunofluorescence staining of an in vivo skin defect model indicate that CUR@COF/PCL NFMs can accelerate wound healing and skin regeneration by reducing the expression of inflammatory factors (TNF-α) and enhancing the expression of angiogenesis (VEGF). This work provides a new strategy by employing COF-based drug-encapsulated nanocomposites for wound dressing applications.

A General Protein Unfolding-Chemical Coupling Strategy for Pure Protein Hydrogels with Mechanically Strong and Multifunctional Properties

Protein-based hydrogels have attracted great attention due to their excellent biocompatible properties, but often suffer from weak mechanical strength. Conventional strengthening strategies for protein-based hydrogels are to introduce nanoparticles or synthetic polymers for improving their mechanical strength, but often compromise their biocompatibility. Here, a new, general, protein unfolding-chemical coupling (PNC) strategy is developed to fabricate pure protein hydrogels without any additives to achieve both high mechanical strength and excellent cell biocompatibility. This PNC strategy combines thermal-induced protein unfolding/gelation to form a physically-crosslinked network and a -NH2/-COOH coupling reaction to generate a chemicallycrosslinked network. Using bovine serum albumin (BSA) as a globular protein, PNC-BSA hydrogels show macroscopic transparency, high stability, high mechanical properties (compressive/tensile strength of 115/0.43 MPa), fast stiffness/toughness recovery of 85%/91% at room temperature, good fatigue resistance, and low cell cytotoxicity and red blood cell hemolysis. More importantly, the PNC strategy can be not only generally applied to silk fibroin, ovalbumin, and milk albumin protein to form different, high strength protein hydrogels, but also modified with PEDOT/PSS nanoparticles as strain sensors and fluorescent fillers as color sensors. This work demonstrates a new, universal, PNC method to prepare high strength, multi-functional, pure protein hydrogels beyond a few available today.

Cellular Interaction of Human Skin Cells towards Natural Bioink via 3D-Bioprinting Technologies for Chronic Wound: A Comprehensive Review

Skin substitutes can provide a temporary or permanent treatment option for chronic wounds. The selection of skin substitutes depends on several factors, including the type of wound and its severity. Full-thickness skin grafts (SGs) require a well-vascularised bed and sometimes will lead to contraction and scarring formation. Besides, donor sites for full-thickness skin grafts are very limited if the wound area is big, and it has been proven to have the lowest survival rate compared to thick- and thin-split thickness. Tissue engineering technology has introduced new advanced strategies since the last decades to fabricate the composite scaffold via the 3D-bioprinting approach as a tissue replacement strategy. Considering the current global donor shortage for autologous split-thickness skin graft (ASSG), skin 3D-bioprinting has emerged as a potential alternative to replace the ASSG treatment. The three-dimensional (3D)-bioprinting technique yields scaffold fabrication with the combination of biomaterials and cells to form bioinks. Thus, the essential key factor for success in 3D-bioprinting is selecting and developing suitable bioinks to maintain the mechanisms of cellular activity. This crucial stage is vital to mimic the native extracellular matrix (ECM) for the sustainability of cell viability before tissue regeneration. This comprehensive review outlined the application of the 3D-bioprinting technique to develop skin tissue regeneration. The cell viability of human skin cells, dermal fibroblasts (DFs), and keratinocytes (KCs) during in vitro testing has been further discussed prior to in vivo application. It is essential to ensure the printed tissue/organ constantly allows cellular activities, including cell proliferation rate and migration capacity. Therefore, 3D-bioprinting plays a vital role in developing a complex skin tissue structure for tissue replacement approach in future precision medicine.

Dual-Light-Triggered In Situ Structure and Function Regulation of Injectable Hydrogels for High-Efficient Anti-Infective Wound Therapy

Most injectable hydrogels used in biomedical engineering have unsatisfactory and untunable mechanical properties, making it difficult to match them with the mechanical strengths of different tissues and organs, which can cause a series of adverse consequences such as immune rejection and soft tissue contusion. In this contribution, dopamine-modified hyaluronic acid (HA-DA) is developed as the backbone for an injectable hydrogel using a catechol-Fe³⁺ coordination crosslinking strategy. Due to dynamic physical crosslinking, the hydrogel can be easily injected through a single syringe. Into the hydrogel, black phosphorous nanosheets loaded with a Zr-based porphyrinic metal-organic framework (PCN@BP) are introduced that could generate reactive oxygen species (ROS) under 660 nm laser irradiation, this promotes the oxidative coupling of dopamine in the presence of the ROS, introducing in situ chemical crosslinking into the hydrogel. A physical/chemical double-crosslinked hydrogel is obtained, effectively improving the hydrogel's mechanical properties, which are tuned in situ by adjusting the irradiation time to match the mechanical modulus of different biological tissues. Combining the excellent photothermal properties and photodynamic performance of the PCN@BP nanosheets yields effective sterilization under mild conditions (below 50 °C, low ROS production). The results show that this hydrogel is an excellent multifunctional wound dressing.

Recent advances of 3D hydrogel culture systems for mesenchymal stem cell-based therapy and cell behavior regulation

Mesenchymal stem cells (MSCs) have been increasingly recognized as resources for disease treatments and regenerative medicine. Meanwhile, the unique chemical and physical properties of hydrogels provide innate advantages to achieve...

Functional Hydrogel Dressings for Treatment of Burn Wounds

The therapy of burns is a challenging clinical issue. Burns are long-term injuries, and numerous patients suffer from chronic pain. Burn treatment includes management, infection control, wound debridement and escharotomy, dressing coverage, skin transplantation, and the use of skin substitutes. The future of advanced care of burn wounds lies in the development of “active dressings”. Hydrogel dressings have been employed universally to accelerate wound healing based on their unique properties to overcome the limitations of existing treatment methods. This review briefly introduces the advantages of hydrogel dressings and discusses the development of new hydrogel dressings for wound healing along with skin regeneration. Further, the treatment strategies for burns, ranging from external to clinical, are reviewed, and the functional classifications of hydrogel dressings along with their clinical value for burns are discussed.

Mechanoadaptive injectable hydrogel based on poly(γ-glutamic acid) and hyaluronic acid regulates fibroblast migration for wound healing

Injectable hydrogels have shown therapeutic effects on wound repair, but most of them exhibit poor mechanical strength. The impacts of stiff injectable hydrogels on cell behavior and wound healing remain unclear. Herein, an injectable hydrogel was developed based on thiolated poly(γ-glutamic acid) (γ-PGA-SH) and glycidyl methacrylate-conjuated oxidized hyaluronic acid (OHA-GMA). Thiol-methacrylate Michael chemistry-mediated post-stabilization and increase of polymer concentration were found to improve the mechanical strength of γ-PGA-SH/OHA-GMA hydrogel. Moreover, in vitro studies confirmed its biodegradability, biocompatibility, and self-healing property. Using the mechanically-tunable hydrogel, it further showed that fibroblasts migrated faster on the surface of stiffer hydrogel, but infiltrated slowly inside it compared with softer hydrogel. In animal experiments, the injectable hydrogel could promote wound healing by increasing collagen deposition and vascularization. In summary, γ-PGA-SH/OHA-GMA hydrogel is able to regulate migration and infiltration of fibroblasts by altering stiffness and offers effective in situ forming scaffolds towards skin tissue regeneration.

In Situ-Forming Cellulose/Albumin-Based Injectable Hydrogels for Localized Antitumor Therapy

Injectable hydrogels, which are formed in situ by changing the external stimuli, have the unique characteristics of easy handling and minimal invasiveness, thus providing the advantage of bypass surgical operation and improving patient compliance. Using external temperature stimuli to realize the sol-to-gel transition when preparing injectable hydrogel is essential since the temperature is stable in vivo and controllable during ex vivo, although the hydrogels obtained possibly have low mechanical strength and stability. In this work, we designed an in situ fast-forming injectable cellulose/albumin-based hydrogel (HPC-g-AA/BSA hydrogels) that responded to body temperature and which was a well-stabilized hydrogen-bonding network, effectively solving the problem of poor mechanical properties. The application of localized delivery of chemotherapeutic drugs of HPC-g-AA/BSA hydrogels was evaluated. In vitro and in vivo results show that HPC-g-AA/BSA hydrogels exhibited higher antitumor efficacy of reducing tumor size and seem ideal for localized antitumor therapy.

Impacts of Blended Bombyx mori Silk Fibroin and Recombinant Spider Silk Fibroin Hydrogels on Cell Growth

Binary-blended hydrogels fabricated from Bombyx mori silk fibroin (SF) and recombinant spider silk protein eADF4(C16) were developed and investigated concerning gelation and cellular interactions in vitro. With an increasing concentration of eADF4(C16), the gelation time of SF was shortened from typically one week to less than 48 h depending on the blending ratio. The biological tests with primary cells and two cell lines revealed that the cells cannot adhere and preferably formed cell aggregates on eADF4(C16) hydrogels, due to the polyanionic properties of eADF4(C16). Mixing SF in the blends ameliorated the cellular activities, as the proliferation of L929 fibroblasts and SaOS-2 osteoblast-like cells increased with an increase of SF content. The blended SF:eADF4(C16) hydrogels attained the advantages as well as overcame the limitations of each individual material, underlining the utilization of the hydrogels in several biomedical applications.

Hydrogels: 3D Drug Delivery Systems for Nanoparticles and Extracellular Vesicles

Synthetic and naturally occurring nano-sized particles present versatile vehicles for the delivery of therapy in a range of clinical settings. Their small size and modifiable physicochemical properties support refinement of targeting capabilities, immune response, and therapeutic cargo, but rapid clearance from the body and limited efficacy remain a major challenge. This highlights the need for a local sustained delivery system for nanoparticles (NPs) and extracellular vesicles (EVs) at the target site that will ensure prolonged exposure, maximum efficacy and dose, and minimal toxicity. Biocompatible hydrogels loaded with therapeutic NPs/EVs hold immense promise as cell-free sustained and targeted delivery systems in a range of disease settings. These bioscaffolds ensure retention of the nano-sized particles at the target site and can also act as controlled release systems for therapeutics over a prolonged period of time. The encapsulation of stimuli sensitive components into hydrogels supports the release of the content on-demand. In this review, we highlight the prospect of the sustained and prolonged delivery of these nano-sized therapeutic entities from hydrogels for broad applications spanning tissue regeneration and cancer treatment. Further understanding of the parameters controlling the release rate of these particles and efficient transfer of cargo to target cells will be fundamental to success.

Harnessing Multifaceted Next-Generation Technologies for Improved Skin Wound Healing

Dysregulation of sequential and synchronized events of skin regeneration often results in the impairment of chronic wounds. Conventional wound dressings fail to trigger the normal healing mechanism owing to the pathophysiological conditions. Tissue engineering approaches that deal with the fabrication of dressings using various biomaterials, growth factors, and stem cells have shown accelerated healing outcomes. However, most of these technologies are associated with difficulties in scalability and cost-effectiveness of the products. In this review, we survey the latest developments in wound healing strategies that have recently emerged through the multidisciplinary approaches of bioengineering, nanotechnology, 3D bioprinting, and similar cutting-edge technologies to overcome the limitations of conventional therapies. We also focus on the potential of wearable technology that supports complete monitoring of the changes occurring in the wound microenvironment. In addition, we review the role of advanced devices that can precisely enable the delivery of nanotherapeutics, oligonucleotides, and external stimuli in a controlled manner. These technological advancements offer the opportunity to actively influence the regeneration process to benefit the treatment regime further. Finally, the clinical relevance, trajectory, and prospects of this field have been discussed in brief that highlights their potential in providing a beneficial wound care solution at an affordable cost.

CCL2 loaded microparticles promote acute patency in silk-based vascular grafts implanted in rat aortae

Cardiovascular disease is the leading cause of death worldwide, often associated with coronary artery occlusion. A common intervention for arterial blockage utilizes a vascular graft to bypass the diseased artery and restore downstream blood flow; however, current clinical options exhibit high long-term failure rates. Our goal was to develop an off-the-shelf tissue-engineered vascular graft capable of delivering a biological payload based on the monocyte recruitment factor C-C motif chemokine ligand 2 (CCL2) to induce remodeling. Bi-layered silk scaffolds consisting of an inner porous and outer electrospun layer were fabricated using a custom blend of Antherea Assama and Bombyx Mori silk (lyogel). Lyogel silk scaffolds alone (LG), and lyogel silk scaffolds containing microparticles (LGMP) were tested. The microparticles (MPs) were loaded with either CCL2 (LGMP+) or water (LGMP-). Scaffolds were implanted as abdominal aortic interposition grafts in Lewis rats for 1 and 8 weeks. 1-week implants exhibited patency rates of 50% (7/14), 100% (10/10), and 100% (5/5) in the LGMP-, LGMP+, and LG groups, respectively. The significantly higher patency rate for the LGMP+ group compared to the LGMP- group (p = 0.0188) suggests that CCL2 can prevent acute occlusion. Immunostaining of the explants revealed a significantly higher density of macrophages (CD68+ cells) within the outer vs. inner layer of LGMP- and LGMP+ constructs but not in LG constructs. After 8 weeks, there were no significant differences in patency rates between groups. All patent scaffolds at 8 weeks showed signs of remodeling; however, stenosis was observed within the majority of explants. This study demonstrated the successful fabrication of a custom blended silk scaffold functionalized with cell-mimicking microparticles to facilitate controlled delivery of a biological payload improving their in vivo performance. STATEMENT OF SIGNIFICANCE: This study outlines the development of a custom blended silk-based tissue-engineered vascular graft (TEVG) for use in arterial bypass or replacement surgery. A custom mixture of silk was formulated to improve biocompatibility and cellular binding to the tubular scaffold. Many current approaches to TEVGs include cells that encourage graft cellularization and remodeling; however, our technology incorporates a microparticle based delivery platform capable of delivering bioactive molecules that can mimic the function of seeded cells. In this study, we load the TEVGs with microparticles containing a monocyte attractant and demonstrate improved performance in terms of unobstructed blood flow versus blank microparticles. The acellular nature of this technology potentially reduces risk, increases reproducibility, and results in a more cost-effective graft when compared to cell-based options.

The antigenicity of silk-based biomaterials: sources, influential factors and applications

Silk is an ancient material with essential roles in numerous biomedical applications, such as tissue regeneration and drug delivery, because of its excellent tunable mechanical properties and diverse physical structures. In addition to the necessary functionalities for biomedical applications, another critical factor for materials applied in biology is the appropriate immune interactions with the body. This review focuses on the immune responses of silk-based materials applied in biomedical applications, specifically antigenicity. The factors affecting the antigenicity of silk-based materials are complicated and are related to the composition and structural characteristics of the materials. At the same time, the composition of silk-based materials varies with its species sources, such as silkworms, spiders, honey bees, or engineered recombinant silk. Additionally, different processing methods are used to fabricate different material formats, such as films, hydrogels, scaffolds, particles, and fibers, resulting in different structural characteristics. Furthermore, the resulting body reactions are also different with different degrees of the immune response. Silk protein typically induces a mild immune response, and immunogenicity can play active roles in osteogenesis, angiogenesis, and protection from inflammation. However, there are some rare reports of severe immune responses caused by silk, which can result in an allergic response or tissue necrosis. The source of allergenicity in silk-based materials is currently under-studied and how to regulate and eliminate the overreaction of the immune system is essential for further applications. Overall, the diverse characteristics of silk-based materials mostly show beneficial bioresponses with mild immunogenicity, and the tunable properties make it applicable in immune-related biomedical applications.

Silk biomaterials for vascular tissue engineering applications

Vascular tissue engineering is a rapidly growing field of regenerative medicine, which strives to find innovative solutions for vascular reconstruction. Considering the limited success of synthetic grafts, research impetus in the field is now shifted towards finding biologically active vascular substitutes bestowing in situ growth potential. In this regard, silk biomaterials have shown remarkable potential owing to their favorable inherent biological and mechanical properties. This review provides a comprehensive overview of the progressive development of silk-based small diameter (<6 mm) tissue-engineered vascular grafts (TEVGs), emphasizing their pre-clinical implications. Herein, we first discuss the molecular structure of various mulberry and non-mulberry silkworm silk and identify their favorable properties at the onset of vascular regeneration. The emergence of various state-of-the-art fabrication methodologies for the advancement of silk TEVGs is rationally appraised in terms of their in vivo performance considering the following parameters: ease of handling, long-term patency, resistance to acute thrombosis, stenosis and aneurysm formation, immune reaction, neo-tissue formation, and overall remodeling. Finally, we provide an update on the pre-clinical status of silk-based TEVGs, followed by current challenges and future prospects. STATEMENT OF SIGNIFICANCE: Limited availability of healthy autologous blood vessels to replace their diseased counterpart is concerning and demands other artificial substitutes. Currently available synthetic grafts are not suitable for small diameter blood vessels owing to frequent blockage. Tissue-engineered biological grafts tend to integrate well with the native tissue via remodeling and have lately witnessed remarkable success. Silk fibroin is a natural biomaterial, which has long been used as medical sutures. This review aims to identify several favorable properties of silk enabling vascular regeneration. Furthermore, various methodologies to fabricate tubular grafts are discussed and highlight their performance in animal models. An overview of our understanding to rationally improve the biological activity fostering the clinical success of silk-based grafts is finally discussed.

Rational Design of Immunomodulatory Hydrogels for Chronic Wound Healing

With all the advances in tissue engineering for construction of fully functional skin tissue, complete regeneration of chronic wounds is still challenging. Since immune reaction to the tissue damage is critical in regulating both the quality and duration of chronic wound healing cascade, strategies to modulate the immune system are of importance. Generally, in response to an injury, macrophages switch from pro-inflammatory to an anti-inflammatory phenotype. Therefore, controlling macrophages' polarization has become an appealing approach in regenerative medicine. Recently, hydrogels-based constructs, incorporated with various cellular and molecular signals, have been developed and utilized to adjust immune cell functions in various stages of wound healing. Here, the current state of knowledge on immune cell functions during skin tissue regeneration is first discussed. Recent advanced technologies used to design immunomodulatory hydrogels for controlling macrophages' polarization are then summarized. Rational design of hydrogels for providing controlled immune stimulation via hydrogel chemistry and surface modification, as well as incorporation of cell and molecules, are also dicussed. In addition, the effects of hydrogels' properties on immunogenic features and the wound healing process are summarized. Finally, future directions and upcoming research strategies to control immune responses during chronic wound healing are highlighted.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Photocrosslinking silver nanoparticles-aloe vera-silk fibroin composite hydrogel for treatment of full-thickness cutaneous wounds

Damage to the skin causes physiological and functional issues. The most effective treatment approach is the use of wound dressings. Silk fibroin (SF) is a promising candidate biomaterial for regulating wound healing; however, its antibacterial properties and biological activity must be further improved. In this study, a photocrosslinking hydrogel was developed to treat full-thickness cutaneous wounds. The composite hydrogel (Ag–AV–SF hydrogel) was prepared by introducing the silver nanoparticles (AgNPs) and aloe vera (AV) as the modifiers. In vitro study exhibited great antibacterial ability, biocompatibility and cell-proliferation and -migration-promoting capacities. It also showed the pH-response releasing properties which release more AgNPs in a simulated chronic infection environment. The healing effect evaluation in vivo showed the healing-promoting ability of the Ag–AV–SF hydrogel was stronger than the single-modifiers groups, and the healing rate of it reached 97.02% on Day 21, higher than the commercial wound dressing, silver sulfadiazine (SS) cream on sale. Additionally, the histological and protein expression results showed that the Ag–AV–SF hydrogel has a greater effect on the pro-healing regenerative phenotype with M2 macrophages at the early stage, reconstructing the blood vessels networks and inhibiting the formation of scars. In summary, the Ag–AV–SF hydrogel developed in this study had good physical properties, overwhelming antibacterial properties, satisfactory biocompatibility and significantly promoting effect on cell proliferation, migration and wound healing. Overall, our results suggest that the Ag–AV–SF hydrogel we developed has great potential for improving the wound healing in clinical treatment.

Human Umbilical Cord Mesenchymal Stem Cell Derived Exosomes Delivered Using Silk Fibroin and Sericin Composite Hydrogel Promote Wound Healing

Recent studies have shown that the hydrogels formed by composite biomaterials are better choice than hydrogels formed by single biomaterial for tissue repair. We explored the feasibility of the composite hydrogel formed by silk fibroin (SF) and silk sericin (SS) in tissue repair for the excellent mechanical properties of SF, and cell adhesion and biocompatible properties of SS. In our study, the SF SS hydrogel was formed by SF and SS protein with separate extraction method (LiBr dissolution for SF and hot alkaline water dissolution for SS), while SF-SS hydrogel was formed by SF and SS protein using simultaneous extraction method (LiBr dissolution for SF and SS protein). The effects of the two composite hydrogels on the release of inflammatory cytokines from macrophages and the wound were analyzed. Moreover, two hydrogels were used to encapsulate and deliver human umbilical cord mesenchymal stem cell derived exosomes (UMSC-Exo). Both SF SS and SF-SS hydrogels promoted wound healing, angiogenesis, and reduced inflammation and TNF-α secretion by macrophages. These beneficial effects were more significant in the experimental group treated by UMSC-Exo encapsulated in SF-SS hydrogel. Our study found that SF-SS hydrogel could be used as an excellent alternative to deliver exosomes for tissue repair.

Self-Healing, Self-Adhesive Silk Fibroin Conductive Hydrogel as a Flexible Strain Sensor

Flexible and wearable hydrogel strain sensors have attracted tremendous attention for applications in human motion and physiological signal monitoring. However, it is still a great challenge to develop a hydrogel strain sensor with certain mechanical properties and tensile deformation capabilities, which can be in conformal contact with the target organ and also have self-healing properties, self-adhesive capability, biocompatibility, antibacterial properties, high strain sensitivity, and stable electrical performance. In this paper, an ionic conductive hydrogel (named PBST) is rationally designed by proportionally mixing polyvinyl alcohol (PVA), borax, silk fibroin (SF), and tannic acid (TA). SF can not only be a reinforcement to introduce an energy dissipation mechanism into the dynamically cross-linked hydrogel network to stabilize the non-Newtonian behavior of PVA and borax but it can also act as a cross-linking agent to combine with TA to reduce the dissociation of TA on the hydrogel network, improving the mechanical properties and viscoelasticity of the hydrogel. The combination of SF and TA can improve the self-healing ability of the hydrogel and realize the adjustable viscoelasticity of the hydrogel without sacrificing other properties. The obtained hydrogel has excellent stretchability (strain > 1000%) and shows good conformal contact with human skin. When the hydrogel is damaged by external strain, it can rapidly self-repair (mechanical and electrical properties) without external stimuli. It shows adhesiveness and repeatable adhesiveness to different materials (steel, wood, PTFE, glass, iron, and cotton fabric) and biological tissues (pigskin) and is easy to peel off without residue. The obtained PBST conductive hydrogel also has a wide strain-sensing range (>650%) and reliable stability. The hydrogel adhered to the skin surface can monitor large strain movements such as in finger joints, wrist joints, knee joints, and so on and detect swallowing, smiling, facial bulging and calming, and other micro-deformation behaviors. It can also distinguish physical signals such as light smile, big laugh, fast and slow breathing, and deep and shallow breathing. Therefore, the PBST conductive hydrogel material with multiple synergistic functions has great potential as a flexible wearable strain sensor. The PBST hydrogel has antibacterial properties and good biocompatibility at the same time, which provides a safety guarantee for it as a flexible wearable strain sensor. This work is expected to provide a new way for people to develop ideal wearable strain sensors.

3D-printed antioxidant antibacterial carboxymethyl cellulose/ε-polylysine hydrogel promoted skin wound repair

Developing a wound dressing for the treatment of large and irregular-shaped wounds remains a great challenge. Herein we developed novel printable bionic hydrogels with antibacterial and antioxidant properties which could effectively overcome the challenge by inhibiting inflammation and accelerating wound healing. The CMC/PL (CP) hydrogels were customized with glycidyl methacrylate (GMA) modified carboxymethyl cellulose (CMC) and ε-polylysine (ε-PL) via ultraviolet (UV) light polymerization using a 3D printer. Except for the high compression modulus (238 kPa), stable rheological properties, and effective degradability, these CP hydrogels also had an excellent inhibitory effect (95%) on both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Remarkably, CP hydrogels could remove the excessive reactive oxygen species (ROS) and protect the fibroblasts from damage. Compared with the commercial dressing (Tegaderm ™ film), CP hydrogels showed a better ability to increase the expression of VEGF and CD31, accelerate granulation tissue regeneration, and promote wound healing. This work provides a new strategy to fabricate on-demand multi-functional hydrogels in the field of skin tissue engineering.

Preparation of Silk Fibroin/Carboxymethyl Chitosan Hydrogel under Low Voltage as a Wound Dressing

At present, silk fibroin (SF) hydrogel can be prepared by means of electrodeposition at 25 V in direct current (DC) mode. Reducing the applied voltage would provide benefits, including lower fabrication costs, less risk of high voltage shocks, and better stability of devices. Here, a simple but uncommon strategy for SF-based hydrogel preparation using 4 V in DC mode is discussed. SF was mixed and cross-linked with carboxymethyl chitosan (CMCS) through hydrogen bonding, then co-deposited on the graphite electrode. The thickness, mass, and shape of the SF/CMCS hydrogel were easily controlled by adjusting the electrodeposition parameters. Morphological characterization of the prepared hydrogel via SEM revealed a porous network within the fabricated hydrogel. This structure was due to intermolecular hydrogen bonding between SF and CMCS, according to the results of thermogravimetric analysis and rheological measurements. As a potential wound dressing, SF/CMCS hydrogel maintained a suitable moisture environment for wound healing and demonstrated distinct properties in terms of promoting the proliferation of HEK-293 cells and antibacterial activity against Escherichia coli and Staphylococcus aureus. Furthermore, histological studies were conducted on a full-thickness skin wound in rats covered with the SF/CMCS hydrogel, with results indicating that this hydrogel can promote wound re-epithelization and enhance granulation tissue formation. These results illustrate the feasibility of using the developed strategy for SF-based hydrogel fabrication in practice for wound dressing.

Sugar Functionalization of Silks with Pathway-Controlled Substitution and Properties

Silk biomaterials are important for applications in biomedical fields due to their outstanding mechanical properties, biocompatibility, and tunable biodegradation. Chemical functionalization of silk by various chemistries can be leveraged to enhance and tune these features and enable the expansion of silk-based biomaterials into additional fields. Sugars are particularly relevant for intracellular communication, signal transduction events, as well as in hydrated extracellular matrices such as in cartilage, vitreous, and brain tissues. Multiple reaction pathways are demonstrated (carboxylation of serines followed by carbodiimide coupling with glucosamine, carboxylation of tyrosines followed by carbodiimide coupling with glucosamine; direct carbodiimide coupling of the inherent carboxylic acids of silk (aspartic and glutamic acid) with glucosamine) for the covalent conjugation of glucosamine onto silk with characterization by proton nuclear magnetic resonance (1 H-NMR), liquid chromatography tandem mass spectroscopy (LC-MS), water contact angle (WCA), and Fourier transform infrared (FTIR) spectroscopy. The results indicate that different pathways substitute different amounts of glucosamine onto silk chains, with control over resulting material properties, including hydrophobicity/hydrophilicity and biological responses. The aqueous processability of these conjugates into functional material formats (films, sponges) is assessed. These new classes of bio-inspired materials can lead to multifunctional biomaterials for potential applications in different fields of biomedical engineering.

Injectable keratin hydrogels as hemostatic and wound dressing materials

Injectable hydrogels hold promise in biomedical applications due to their noninvasive administration procedure and capacity enabling the filling of irregularly shaped defects. Protein-based hydrogels provide features including good biocompatibility and inherent biofunction. However, challenges still remain to develop a protein-based injectable hydrogel in a convenient way due to the limited active groups in proteins. Keratins are a group of cysteine-rich structural proteins found abundantly in skin and skin appendages. In this work, we utilized keratin and the Au(iii) salt to develop an injectable hydrogel based on the dynamic exchange between disulfide bonds (S-S) and gold(i)-thiolates (Au-S). Such a hydrogel could be prepared at the physiological pH and applied as an injectable hydrogel for biomedical applications including hemostatic and wound dressing materials. Our findings demonstrated that this keratin injectable hydrogel showed a good hemostatic effect in both tail amputation and liver injury models. Moreover, it was proved efficient as a drug loading carrier, and the deferoxamine-loaded hydrogel showed a desirable wound healing effect in a full-thickness excision wound model.

Injectable adaptive self-healing hyaluronic acid/poly (γ-glutamic acid) hydrogel for cutaneous wound healing

The most significant challenge in designing wound dressings is to mimic the tissue microenvironment because of the pro-regenerative structural and functional properties of skin. Herein, we developed a type of bionic extracellular matrix (ECM) hydrogels based on thiol-modified poly (γ-glutamic acid) (γ-PGA-SH) and oxidized hyaluronic acid (HA-CHO). The rapid and reversible thiol-aldehyde addition reaction of thiols in γ-PGA-SH and aldehyde groups in HA-CHO provided hydrogels with a dynamic covalent network and endowed them with properties of adaptability and self-healing capability, which are conducive for initial wound coverage and for prolonging the lifespan of the dressing. Interestingly, these hydrogels also showed typical viscoelastic characteristics similar to those of natural ECM, degradation property in vitro and in vivo, and free radical scavenging capability. In addition, the gelation time, rheological behavior, mechanical property, porous structure, and degradation process of the hydrogels could be tuned by adjusting polymer content. Furthermore, the ECM-inspired hydrogels significantly enhanced the wound healing process in vivo in a full-thickness skin defect model compared to those by commercial dressing (Tegaderm™) by facilitating angiogenesis and promoting collagen deposition. The successful application of the multifunctional hydrogel as an antioxidant wound dressing for wound treatment significantly exhibited its great application potential for biomedical areas. STATEMENT OF SIGNIFICANCE: The application of tissue engineering techniques to repair full-thickness skin wounds remains a great challenge in clinical trials. Among the recent approaches used for wound healing, in situ forming injectable hydrogels have gained much attention, and few of them have shown satisfactory overall performance, such as integration into the wound bed, biodegradability, immunocompatibility, vascularization, and recapitulation of the structure and function of skin. In the present study, we designed a simple and convenient in situ forming injectable adaptable self-healing hydrogels with biodegradability and antioxidative properties, which could substantially improve wound healing quality at an affordable cost. The hydrogel-based wound dressing is expected to solve the abovementioned problems and help in promoting cutaneous wound healing.

Recent trends on burn wound care: hydrogel dressings and scaffolds

Acute and chronic wounds can cause severe physical trauma to patients and also result in an immense socio-economic burden. Thus, wound management has attracted increasing attention in recent years. However, burn wound management is still a major challenge in wound management. Autografts are often considered the gold-standard for burn care, but their application is limited by many factors. Hence, ideal burn dressings and skin substitute dressings are desirable. With the development of biomaterials and progress of tissue engineering technology, some innovative dressings and tissue engineering scaffolds, such as nanofibers, films, foams and hydrogels, have been widely used in the field of biomedicine, especially in wound management. Among them, hydrogels have attracted tremendous attention with their unique advantages. In this review, we discuss the challenges in burn wound management, several crucial design considerations with respect to hydrogels for burn wound healing, and available polymers for hydrogels in burn wound care. In addition, the potential application and plausible prospect of hydrogels are also highlighted.

Functional silk fibroin hydrogels: preparation, properties and applications

Over the past decade, the hydrogels prepared from silk fibroin have received immense research attention due to the advantages of safe nature, biocompatibility, controllable degradation and capability to combine with other materials. They have broad application prospects in biomedicine and other fields. However, the traditional silk protein hydrogels have a simple network structure and single functionality, thus, leading to poor adaptability towards complex application environments. As a result, the application fields and development have been significantly restricted. However, the development of functional silk protein hydrogels has provided the opportunities to overcome the limitations of the silk protein hydrogels. In recent years, the functional design of the silk protein hydrogels and their potential applications have attracted the attention of scholars worldwide. Nevertheless, a comprehensive review on functional silk protein hydrogels is missing so far. In order to gain an in-depth understanding of the development status of the functional silk protein hydrogels, this article reviews the current status of the preparation, properties and application of the functional silk protein hydrogels. The article first briefly introduces the current cross-linking methods (including physical and chemical cross-linking), principles, advantages and limitations of the silk protein hydrogels. Subsequently, the types of functional silk protein hydrogels (e.g., high strength, injectable, self-healing, adhesive, conductive, environmental stimuli-responsive, 3D printable, etc.) and design principles for functional implementation have been introduced. Next, based on the advantages of the various functional aspects of the silk protein hydrogels, the applications of these hydrogels in the biomedical field (tissue engineering, sustained drug release, wound repair, adhesives, etc.) and bioelectronics are reviewed. Finally, the development prospects and challenges associated with silk protein functional hydrogels have been analyzed. It is hoped that this study will contribute towards the future innovation of the silk protein hydrogels by promoting the rational design of new mechanisms and successful realization of the target applications.

Biogenetic Acellular Dermal Matrix Maintaining Rich Interconnected Microchannels for Accelerated Tissue Amendment

Given that many people suffer from extensive skin damage, wound repair has drawn tremendous attention in research. Among the various assistant dressing materials that promote healing, a porcine acellular dermal matrix (PADM), as a skin substitute, can efficiently accelerate healing by promoting cell migration and proliferation. However, a simple, low-cost preparation process remains a challenge facing PADM development, particularly because of the inferior elasticity. To overcome these drawbacks, a CaCl₂-ethanol-H₂O solution (ternary solution) combined with an additional enzyme treatment was used to obtain a transparent, porous, and elastic PADM that retained the major extracellular matrix composition of the dermis. Our results indicated that alterations in the fiber organization and secondary structural changes in the collagen occurred after treatment. Furthermore, the in vivo wound healing and histological analyses clearly revealed an extremely expedited wound repair process following the application of the biocompatible PADM. In conclusion, this study provides new insights into the development of a transparent PADM with a porous structure and good elasticity that can be used as a skin substitute to accelerate the wound healing process. Moreover, this effective technique could potentially be used to extrapolate other decellularized materials in the future.

Rapid and cytocompatible cell-laden silk hydrogel formation via riboflavin-mediated crosslinking

Bioactive hydrogels based on naturally-derived polymers are of great interest for regenerative medicine applications. Among naturally-derived polymers, silk fibroin has been extensively explored as a biomaterial for tissue engineering due to its unique mechanical properties. Here, we demonstrate the rapid gelation of cell-laden silk fibroin hydrogels by visible light-induced crosslinking using riboflavin as a photo-initiator, in presence of an electron acceptor. The gelation kinetics were monitored by in situ photo-rheometry. Gelation was achieved in minutes and could be tuned owing to its direct proportionality to the electron acceptor concentration. The concentration of the electron acceptor did not affect the elastic modulus of the hydrogels, which could be altered by varying the polymer content. Further, the biocompatible riboflavin photo-initiator combined with sodium persulfate allowed for the encapsulation of cells within silk fibroin hydrogels. To confirm the cytocompatibility of the silk fibroin formulations, three cell types (articular cartilage-derived progenitor cells, mesenchymal stem cells and dental-pulp-derived stem cells) were encapsulated within the hydrogels, which associated with a viability >80% for all cell types. These results demonstrated that fast gelation of silk fibroin can be achieved by combining it with riboflavin and electron acceptors, which results in a hydrogel that can be used in tissue engineering and cell delivery applications.