Bionic Poly(γ-Glutamic Acid) Electrospun Fibrous Scaffolds for Preventing Hypertrophic Scars

Hybrid Double-Sided Tape with Asymmetrical Adhesion and Burst Pressure Tolerance for Abdominal Injury Treatment

Patients with open abdominal (OA) wounds have a mortality risk of up to 30%, and the resulting disabilities would have profound effects on patients. Here, we present a novel double-sided adhesive tape developed for the management of OA wounds. The tape features an asymmetrical structure and employs an acellular dermal matrix (ADM) with asymmetric wettability as a scaffold. It is constructed by integrating a tissue-adhesive hydrogel composed of polydopamine (pDA), quaternary ammonium chitosan (QCS), and acrylic acid cross-linking onto the bottom side of the ADM. Following surface modification with pDA, the ADM would exhibit characteristics resistant to bacterial adhesion. Furthermore, the presence of a developed hydrogel ensures that the tape not only possesses tissue adhesiveness and noninvasive peelability but also effectively mitigates damage caused by oxidative stress. Besides, the ADM inherits the strength of the skin, imparting high burst pressure tolerance to the tape. Based on these remarkable attributes, we demonstrate that this double-sided (D-S) tape facilitates the repair of OA wounds, mitigates damage to exposed intestinal tubes, and reduces the risk of intestinal fistulae and complications. Additionally, the D-S tape is equally applicable to treating other abdominal injuries, such as gastric perforations. It effectively seals the perforation, promotes injury repair, and prevents the formation of postoperative adhesions. These notable features indicate that the presented double-sided tape holds significant potential value in the biomedical field.

Biomimetic and Wound Microenvironment-Modulating PEGylated Glycopolypeptide Hydrogels for Arterial Massive Hemorrhage and Wound Prohealing

Despite great progress in the hydrogel hemostats and dressings, they generally lack resistant vascular bursting pressure and intrinsic bioactivity to meet arterial massive hemorrhage and proheal wounds. To address the problems, we design a kind of biomimetic and wound microenvironment-modulating PEGylated glycopolypeptide hydrogels that can be easily injected and gelled in ∼10 s. Those glycopolypeptide hydrogels have suitable tissue adhesion of ∼20 kPa, high resistant bursting pressure of ∼150 mmHg, large microporosity of ∼15 μm, and excellent biocompatibility with ∼1% hemolysis ratio and negligible inflammation. They performed better hemostasis in rat liver and rat and rabbit femoral artery bleeding models than Fibrin glue, Gauze, and other hydrogels, achieving fast arterial hemostasis of <20 s and lower blood loss of 5-13%. As confirmed by in vivo wound healing, immunofluorescent imaging, and immunohistochemical and histological analyses, the mannose-modified hydrogels could highly boost the polarization of anti-inflammatory M2 phenotype and downregulate pro-inflammatory tumor necrosis factor-α to relieve inflammation, achieving complete full-thickness healing with thick dermis, dense hair follicles, and 90% collagen deposition. Importantly, this study provides a versatile strategy to construct biomimetic glycopolypeptide hydrogels that can not only resist vascular bursting pressure for arterial massive hemorrhage but also modulate inflammatory microenvironment for wound prohealing.

3D printing of Rg3-loaded hydrogel scaffolds: anti-inflammatory and scar-formation related collagen inhibitory effects for scar-free wound healing

During the process of wound healing, the stimulation of inflammatory factors often leads to abnormal proliferation of blood vessels and collagen, ultimately resulting in scar formation. To address this challenge, we fabricate a novel dermal extracellular matrix (DECM) hydrogel scaffold loaded with ginsenoside Rg3 (Rg3) using 3D printing technology. Mesoporous silica nanoparticles (MSNs) are introduced into the system to encase the Rg3 to control its release rate and enhance its bioavailability. We systematically evaluate the biological, physicochemical, and wound healing properties of this scaffold. In vitro studies demonstrate that the hydrogel exhibits excellent biocompatibility and solid-like rheological properties, ensuring its successful printing. In vivo studies reveal that the composite hydrogel scaffolds effectively accelerate wound healing and achieve scar-free wound healing within three weeks. Histological and immunohistochemical (IHC) analyses show that the composite hydrogel scaffolds reduce the inflammatory response and inhibit excessive collagen accumulation. These combined effects underscore the potential of our approach in effectively inhibiting scar formation.

Pioneering a paradigm shift in tissue engineering and regeneration with polysaccharides and proteins-based scaffolds: A comprehensive review

In the realm of modern medicine, tissue engineering and regeneration stands as a beacon of hope, offering the promise of restoring form and function to damaged or diseased organs and tissues. Central to this revolutionary field are biological macromolecules-nature's own blueprints for regeneration. The growing interest in bio-derived macromolecules and their composites is driven by their environmentally friendly qualities, renewable nature, minimal carbon footprint, and widespread availability in our ecosystem. Capitalizing on these unique attributes, specific composites can be tailored and enhanced for potential utilization in the realm of tissue engineering (TE). This review predominantly concentrates on the present research trends involving TE scaffolds constructed from polysaccharides, proteins and glycosaminoglycans. It provides an overview of the prerequisites, production methods, and TE applications associated with a range of biological macromolecules. Furthermore, it tackles the challenges and opportunities arising from the adoption of these biomaterials in the field of TE. This review also presents a novel perspective on the development of functional biomaterials with broad applicability across various biomedical applications.

Revolutionizing Wound Healing: Exploring Scarless Solutions through Drug Delivery Innovations

Human skin is the largest organ and outermost surface of the human body, and due to the continuous exposure to various challenges, it is prone to develop injuries, customarily known as wounds. Although various tissue engineering strategies and bioactive wound matrices have been employed to speed up wound healing, scarring remains a significant challenge. The wound environment is harsh due to the presence of degradative enzymes and elevated pH levels, and the physiological processes involved in tissue regeneration operate on distinct time scales. Therefore, there is a need for effective drug delivery systems (DDSs) to address these issues. The objective of this review is to provide a comprehensive exposition of the mechanisms underlying the skin healing process, the factors and materials used in engineering DDSs, and the different DDSs used in wound care. Furthermore, this investigation will delve into the examination of emergent technologies and potential avenues for enhancing the efficacy of wound care devices.

Synthesis of Poly-γ-Glutamic Acid and Its Application in Biomedical Materials

Poly-γ-glutamic acid (γ-PGA) is a natural polymer composed of glutamic acid monomer and it has garnered substantial attention in both the fields of material science and biomedicine. Its remarkable cell compatibility, degradability, and other advantageous characteristics have made it a vital component in the medical field. In this comprehensive review, we delve into the production methods, primary application forms, and medical applications of γ-PGA, drawing from numerous prior studies. Among the four production methods for PGA, microbial fermentation currently stands as the most widely employed. This method has seen various optimization strategies, which we summarize here. From drug delivery systems to tissue engineering and wound healing, γ-PGA's versatility and unique properties have facilitated its successful integration into diverse medical applications, underlining its potential to enhance healthcare outcomes. The objective of this review is to establish a foundational knowledge base for further research in this field.

An ECM-mimicking assembled gelatin/hyaluronic acid hydrogel with antibacterial and radical scavenging functions for accelerating open wound healing

A multifunctional hydrogel dressing with hemostatic, antibacterial, and reactive oxygen species (ROS)-removing properties is highly desirable for the clinical treatment of open wounds. Although many wound dressings have been prepared, the modification of polymers is often involved in the preparation process, and the uncertainty of biological safety and stability of modified polymers hinders the clinical application of products. In this study, inspired by the composition and crosslinking pattern of extracellular matrix (ECM), a deeply ECM-mimicking multifunctional hydrogel dressing is created. Tannic acid (TA) and poly-ϵ-lysine (EPL) are added into a gelatin/hyaluronic acid (Gel/HA) matrix, and a stable hydrogel is formed due to the formation of the triple helix bundles of gelatin and hydrogen bonds between polymers. The introduction of TA and EPL endows the ECM-mimicking hydrogel with stable rheological properties, as well as antibacterial and hemostatic functions. The as-produced hydrogels have suitable swelling ratio, enzyme degradability, and good biocompatibility. In addition, it also shows a significant ability to eliminate ROS, which is confirmed by the elimination of 2,2-diphenyl-1-picrylhydrazyl free radical. Full-thickness skin wound repair experiment and histological analysis of the healing site in mice demonstrate that the developed ECM-mimicking Gel/HA hydrogels have a prominent effect on ECM formation and promotion of wound closure. Taken together, these findings suggest that the multifunctional hydrogels deeply mimicking the ECM are promising candidates for the clinical treatment of open wounds.

A multifunctional surgical suture with electroactivity assisted by oligochitosan/gelatin-tannic acid for promoting skin wound healing and controlling scar proliferation

Surgical wound closure is accomplished most frequently with sutures, optimally proceeding rapidly and without complication. However, surgical sutures can trigger foreign body reactions and incite abnormal collagen deposition. Sustained inflammation can result in abnormal wound healing with hypertrophic scar formation. Therefore, evolution of suture material to inhibit inflammation and scar formation is of great clinical significance. In the present study, commercial 3-0 PPDO [poly(p-dioxanone)] suture was used as the base material and modified by adding two layers: a drug-loaded layer and an electroactive layer. The former layer was curcumin (Cur) encapsulated by PLGA [poly (lactic-co-glycolic acid)] and the latter layer was composed of oligochitosan-gelatin/tannic acid/polypyrrole (OCS-GE/TA/PPy). The multifunctional sutures, named S@LC@CGTP, had desirable sustained-drug release properties in vitro where Cur could be released for 8 days due to the action of PLGA. The three-dimensional network structure of OCS-GE/TA ensured S@LC@CGTP against surface cracking and maintained electrical. Furthermore, using an in vivo experiment, S@LC@CGTP could attenuate inflammation and promote scar-free wound healing according to suppression of infiltrating inflammatory cells, down-regulation of TGF-β1 and collagen type I expression, and improved collagen arrangement. Cumulatively, we indicated that S@LC@CGTP suture material has great potential to facilitate optimal, nearly scarless healing of surgical incisions.

Effect of anti-skin disorders of ginsenosides- A Systematic Review

Ginsenosides are bioactive components of Panax ginseng with many functions such as anti-aging, anti-oxidation, anti-inflammatory, anti-fatigue, and anti-tumor. Ginsenosides are categorized into dammarane, oleanene, and ocotillol type tricyclic triterpenoids based on the aglycon structure. Based on the sugar moiety linked to C-3, C-20, and C-6, C-20, dammarane type was divided into protopanaxadiol (PPD) and protopanaxatriol (PPT). The effects of ginsenosides on skin disorders are noteworthy. They play anti-aging roles by enhancing immune function, resisting melanin formation, inhibiting oxidation, and elevating the concentration of collagen and hyaluronic acid. Thus, ginsenosides have previously been widely used to resist skin diseases and aging. This review details the role of ginsenosides in the anti-skin aging process from mechanisms and experimental research.

Polymer-Based Wound Dressings Loaded with Ginsenoside Rg3

The skin, the largest organ in the human body, mainly plays a protective role. Once damaged, it can lead to acute or chronic wounds. Wound healing involves a series of complex physiological processes that require ideal wound dressings to promote it. The current wound dressings have characteristics such as high porosity and moderate water vapor permeability, but they are limited in antibacterial properties and cannot protect wounds from microbial infections, which can delay wound healing. In addition, several dressings contain antibiotics, which may have bad impacts on patients. Natural active substances have good biocompatibility; for example, ginsenoside Rg3 has anti-inflammatory, antibacterial, antioxidant, and other biological activities, which can effectively promote wound healing. Some researchers have developed various polymer wound dressings loaded with ginsenoside Rg3 that have good biocompatibility and can effectively promote wound healing and reduce scar formation. This article will focus on the application and mechanism of ginsenoside Rg3-loaded dressings in wounds.

Fabrication and Bioactivity of Peptide-Conjugated Biomaterial Tissue Engineering Constructs

Tissue engineering combines materials engineering, cells and biochemical factors to improve, restore or replace various types of biological tissues. A nearly limitless combination of these strategies can be combined, providing a means to augment the function of a number of biological tissues such as skin tissue, neural tissue, bones, and cartilage. Compounds such as small molecule therapeutics, proteins, and even living cells have been incorporated into tissue engineering constructs to influence biological processes at the site of implantation. Peptides have been conjugated to tissue engineering constructs to circumvent limitations associated with conjugation of proteins or incorporation of cells. This review highlights various contemporary examples in which peptide conjugation is used to overcome the disadvantages associated with the inclusion of other bioactive compounds. This review covers several peptides that are commonly used in the literature as well as those that do not appear as frequently to provide a broad scope of the utility of the peptide conjugation technique for designing constructs capable of influencing the repair and regeneration of various bodily tissues. Additionally, a brief description of the construct fabrication techniques encountered in the covered examples and their advantages in various tissue engineering applications is provided.

Fibrous hydrogels by electrospinning: Novel platforms for biomedical applications

Hydrogels, hydrophilic and biocompatible polymeric networks, have been used for numerous biomedical applications because they have exhibited abilities to mimic features of extracellular matrix (ECM). In particular, the hydrogels engineered with electrospinning techniques have shown great performances in biomedical applications. Electrospinning techniques are to generate polymeric micro/nanofibers that can mimic geometries of natural ECM by drawing micro/nanofibers from polymer precursors with electrical forces, followed by structural stabilization of them. By exploiting the electrospinning techniques, the fibrous hydrogels have been fabricated and utilized as 2D/3D cell culture platforms, implantable scaffolds, and wound dressings. In addition, some hydrogels that respond to external stimuli have been used to develop biosensors. For comprehensive understanding, this review covers electrospinning processes, hydrogel precursors used for electrospinning, characteristics of fibrous hydrogels and specific biomedical applications of electrospun fibrous hydrogels and highlight their potential to promote use in biomedical applications.

High Molecular Weight Poly(glutamic acid) to Improve BMP2-Induced Osteogenic Differentiation

FDA-approved bone morphogenetic protein 2 (BMP2) has serious side effects due to the super high dose requirement. Heparin is one of the most well-studied sulfated polymers to stabilize BMP2 and improve its functionality. However, the clinical use of heparin is questionable because of its undesired anticoagulant activity. Recent studies suggest that poly(glutamic acid) (pGlu) has the potential to improve BMP2 bioactivity with less safety concerns; however, the knowledge on pGlu's contribution remains largely unknown. Therefore, we aimed to study the role of pGlu in BMP2-induced osteogenesis and its potential application in bone tissue engineering. Our data, for the first time, indicated that both low (L-pGlu) and high molecular weight pGlu (H-pGlu) were able to significantly improve the BMP2-induced early osteoblastic differentiation marker (ALP) in MC3T3-E1 preosteoblasts. Importantly, the matrix mineralization was more rapidly enhanced by H-pGlu compared to L-pGlu. Additionally, our data indicated that only α-H-pGlu could significantly improve BMP2's activity, whereas γ-H-pGlu failed to do so. Moreover, both gene expression and mineralization data demonstrated that α-H-pGlu enabled a single dose of BMP2 to induce a high level of osteoblastic differentiation without multiple doses of BMP2. To study the potential application of pGlu in tissue engineering, we incorporated the H-pGlu+BMP2 nanocomplexes into the collagen hydrogel with significantly elevated osteoblastic differentiation. Furthermore, H-pGlu-coated 3D porous gelatin and chitosan scaffolds significantly enhanced osteogenic differentiation through enabling sustained release of BMP2. Thus, our findings suggest that H-pGlu is a promising new alternative with great potential for bone tissue engineering applications.

Effect of composite biodegradable biomaterials on wound healing in diabetes

The repair of diabetic wounds has always been a job that doctors could not tackle quickly in plastic surgery. To solve this problem, it has become an important direction to use biocompatible biodegradable biomaterials as scaffolds or dressing loaded with a variety of active substances or cells, to construct a wound repair system integrating materials, cells, and growth factors. In terms of wound healing, composite biodegradable biomaterials show strong biocompatibility and the ability to promote wound healing. This review describes the multifaceted integration of biomaterials with drugs, stem cells, and active agents. In wounds, stem cells and their secreted exosomes regulate immune responses and inflammation. They promote angiogenesis, accelerate skin cell proliferation and re-epithelialization, and regulate collagen remodeling that inhibits scar hyperplasia. In the process of continuous combination with new materials, a series of materials that can be well matched with active ingredients such as cells or drugs are derived for precise delivery and controlled release of drugs. The ultimate goal of material development is clinical transformation. At present, the types of materials for clinical application are still relatively single, and the bottleneck is that the functions of emerging materials have not yet reached a stable and effective degree. The development of biomaterials that can be further translated into clinical practice will become the focus of research.

Polysaccharide Electrospun Nanofibers for Wound Healing Applications

As a type of biological macromolecule, natural polysaccharides have been widely used in wound healing due to their low toxicity, good biocompatibility, degradability and reproducibility. Electrospinning is a versatile and simple technique for producing continuous nanoscale fibers from a variety of natural and synthetic polymers. The application of electrospun nanofibers as wound dressings has made great progress and they are considered one of the most effective wound dressings. This paper reviews the preparation of polysaccharide nanofibers by electrospinning and their application prospects in the field of wound healing. A variety of polysaccharide nanofibers, including chitosan, starch, alginate, and hyaluronic acid are introduced. The preparation strategy of polysaccharide electrospun nanofibers and their functions in promoting wound healing are summarized. In addition, the future prospects and challenges for the preparation of polysaccharide nanofibers by electrospinning are also discussed.

In situ forming injectable γ-poly(glutamic acid)/PEG adhesive hydrogels for hemorrhage control

Rapidly in situ forming adhesive hydrogels are promising candidates for efficient hemostasis due to their easy administration and minimal invasion. However, development of biocompatible and high-performance hemostatic hydrogels without any additional toxic agents remains a challenge. Herein, a series of novel injectable adhesive hydrogels based on N-hydroxysuccinimide (NHS) modified γ-poly(glutamic acid) (γPGA-NHS) and tetra-armed poly(ethylene glycol) amine (Tetra-PEG-NH₂) were developed. Among all samples, PGA₁₀-PEG₁₅ and PGA₁₀-PEG₂₀ hydrogels with higher PEG contents exhibited rapid gelation time (<20 s), strong mechanical strength (compression modulus up to ∼75 kPa), good adhesive properties (∼15 kPa), and satisfactory burst pressure (∼18-20 kPa). As a result, PGA₁₀-PEG₁₅ and PGA₁₀-PEG₂₀ hydrogels showed a remarkable reduction in hemostasis time and blood loss compared with gauze and fibrin glue. More importantly, the PGA₁₀-PEG₂₀ hydrogel was also successfully used to seal femoral arterial trauma. Subcutaneous implantation experiments indicated a good biocompatibility of the hydrogels in vivo. All these results strongly support that the developed PGA-PEG hydrogels could serve as promising hemostatic agents in emergency and clinical situations.

Poloxamer 407 and Hyaluronic Acid Thermosensitive Hydrogel-Encapsulated Ginsenoside Rg3 to Promote Skin Wound Healing

Ginsenoside Rg3 has shown beneficial effects in various skin diseases. The current interest in designing and developing hydrogels for biomedical applications continues to grow, inspiring the further development of drug-loaded hydrogels for tissue repair and localized drug delivery. The aim of the present study was to develop an effective and safe hydrogel (Rg3-Gel), using ginsenoside Rg3, and we evaluated the wound-healing potential and therapeutic mechanism of Rg3-Gel. The results indicated that the optimized Rg3-Gel underwent discontinuous phase transition at low and high temperatures. Rg3-Gel also exhibited good network structures, swelling water retention capacity, sustainable release performance, and excellent biocompatibility. Subsequently, the good antibacterial and antioxidant properties of Rg3-Gel were confirmed by in vitro tests. In full-thickness skin defect wounded models, Rg3-Gel significantly accelerated the wound contraction, promoted epithelial and tissue regeneration, and promoted collagen deposition and angiogenesis. In addition, Rg3-Gel increased the expression of autophagy proteins by inhibiting the MAPK and NF-KB pathways in vivo. It simultaneously regulated host immunity by increasing the abundance of beneficial bacteria and the diversity of the wound surface flora. From these preliminary evaluations, it is possible to conclude that Rg3-Gel has excellent application potential in wound-healing drug delivery systems.

Tissue engineering application combining epoxidized natural rubber blend and mesenchymal stem cells in in vivo response

This study aimed to investigate biocompatibility, integration, and tissue host response of the Poly (Lactic-co-Glycolic acid) (PLGA)/Poly (isoprene) (PI) epoxidized (PLGA/PIepox) innovative scaffold combined with adipose derived mesenchymal stem cells (ADSC). We implanted the scaffold subcutaneously on the back of 18 female rats and monitored them for up to 14 days. When compared to controls, PLGA/PIepox + ADSC demonstrated an earlier vascularization, a tendency of inflammation reduction, an adequate tissue integration, higher cell proliferation, and a tendency of expression of collagen decreasing. However, 14 days post-implantation we found similar levels of CD31, Ki67 and AE1/AE3 in PLGA/PIepox when compared to control groups. The interesting results, lead us to the assumption that PLGA/PIepox is able to provide an effective delivery system for ADSC on tissue host. This animal study assesses PLGA/PIepox + ADSC in in vivo tissue functionality and validation of use, serving as a proof of concept for future clinical translation as it presents an innovative and promising tissue engineering opportunity for the use in tissue reconstruction.

MXenes-integrated microneedle combined with asiaticoside to penetrate the cuticle for treatment of diabetic foot ulcer

Patients with diabetic foot ulcers usually suffer from inefficient epithelisation and angiogenesis accompanied by chronic wound healing. Diabetic foot ulcers remain a major challenge in clinical medicine; however, traditional treatments are incapable of transdermal drug delivery, resulting in a low drug delivery rate. We report the development of Ti2C3 MXenes-integrated poly-γ-glutamic acid (γ-PGA) hydrogel microneedles to release asiaticoside (MN-MXenes-AS). Asiaticoside was loaded into PGA-MXenes hydrogel to facilitate cell proliferation while regulating angiogenesis. The characterisation and mechanical strength of the microneedles were investigated in vitro, and the wound-healing efficacy of the microneedles was confirmed in diabetic mice. MXenes significantly improved the mechanical strength of microneedles, while γ-PGA hydrogels provided a moist microenvironment for wound healing. Mice treated with MN-MXenes-AS demonstrated obvious improvements in wound healing process. We successfully fabricated an MXenes-integrated microneedle that possesses sufficient rigidity to penetrate the cuticle for subcutaneous drug delivery, thereby accelerating diabetic wound healing. We demonstrated that MN-MXenes-AS is effective in promoting growth both in vivo and in vitro. Collectively, our data show that MN-MXenes-AS accelerated the healing of diabetic foot ulcers, supporting the use of these microneedles in the treatment of chronic wounds.

Graphical Abstract

A Review on Electrospun Poly(amino acid) Nanofibers and Their Applications of Hemostasis and Wound Healing

The timely and effective control and repair of wound bleeding is a key research issue all over the world. From traditional compression hemostasis to a variety of new hemostatic methods, people have a more comprehensive understanding of the hemostatic mechanism and the structure and function of different types of wound dressings. Electrospun nanofibers stand out with nano size, high specific surface area, higher porosity, and a variety of complex structures. They are high-quality materials that can effectively promote wound hemostasis and wound healing because they can imitate the structural characteristics of the skin extracellular matrix (ECM) and support cell adhesion and angiogenesis. At the same time, combined with amino acid polymers with good biocompatibility not only has high compatibility with the human body but can also be combined with a variety of drugs to further improve the effect of wound hemostatic dressing. This paper summarizes the application of different amino acid electrospun wound dressings, analyzes the characteristics of different materials in preparation and application, and looks forward to the development of directions of poly(amino acid) electrospun dressings in hemostasis.

Three-Dimensional Bioprinting of Decellularized Extracellular Matrix-Based Bioinks for Tissue Engineering

Three-dimensional (3D) bioprinting is one of the most promising additive manufacturing technologies for fabricating various biomimetic architectures of tissues and organs. In this context, the bioink, a critical element for biofabrication, is a mixture of biomaterials and living cells used in 3D printing to create cell-laden structures. Recently, decellularized extracellular matrix (dECM)-based bioinks derived from natural tissues have garnered enormous attention from researchers due to their unique and complex biochemical properties. This review initially presents the details of the natural ECM and its role in cell growth and metabolism. Further, we briefly emphasize the commonly used decellularization treatment procedures and subsequent evaluations for the quality control of the dECM. In addition, we summarize some of the common bioink preparation strategies, the 3D bioprinting approaches, and the applicability of 3D-printed dECM bioinks to tissue engineering. Finally, we present some of the challenges in this field and the prospects for future development.

Fibroblasts in Scar Formation: Biology and Clinical Translation

Scarring, which develops due to fibroblast activation and excessive extracellular matrix deposition, can cause physical, psychological, and cosmetic problems. Fibroblasts are the main type of connective tissue cells and play important roles in wound healing. However, the underlying mechanisms of fibroblast in reaching scarless wound healing require more exploration. Herein, we systematically reviewed how fibroblasts behave in response to skin injuries, as well as their functions in regeneration and scar formation. Several biocompatible materials, including hydrogels and nanoparticles, were also suggested. Moreover, factors that concern transformation from fibroblasts into cancer-associated fibroblasts are mentioned due to a tight association between scar formation and primary skin cancers. These findings will help us better understand skin fibrotic pathogenesis, as well as provide potential targets for scarless wound healing therapies.

Bio-inspired hydrogels with fibrous structure: A review on design and biomedical applications

Numerous tissues in the human body have fibrous structures, including the extracellular matrix, muscles, and heart, which perform critical biological functions and have exceptional mechanical strength. Due to their high-water content, softness, biocompatibility and elastic nature, hydrogels resemble biological tissues. Traditional hydrogels, on the other hand, have weak mechanical properties and lack tissue-like fibrous structures, limiting their potential applications. Thus, bio-inspired hydrogels with fibrous architectures have piqued the curiosity of biomedical researchers. Here, we review fabrication strategies for fibrous hydrogels and their recent progress in the biomedical fields of wound dressings, drug delivery, tissue engineering scaffolds and bioadhesives. Challenges and future perspectives are also discussed.

Recent Advances in Poly(α-L-glutamic acid)-Based Nanomaterials for Drug Delivery

Poly(α-L-glutamic acid) (PGA) is a class of synthetic polypeptides composed of the monomeric unit α-L-glutamic acid. Owing to their biocompatibility, biodegradability, and non-immunogenicity, PGA-based nanomaterials have been elaborately designed for drug delivery systems. Relevant studies including the latest research results on PGA-based nanomaterials for drug delivery have been discussed in this work. The following related topics are summarized as: (1) a brief description of the synthetic strategies of PGAs; (2) an elaborated presentation of the evolving applications of PGA in the areas of drug delivery, including the rational design, precise fabrication, and biological evaluation; (3) a profound discussion on the further development of PGA-based nanomaterials in drug delivery. In summary, the unique structures and superior properties enables PGA-based nanomaterials to represent as an enormous potential in biomaterials-related drug delivery areas.

Rational Design and Preparation of Functional Hydrogels for Skin Wound Healing

Skin wound healing often contains a series of dynamic and complex physiological healing processes. It is a great clinical challenge to effectively treat the cutaneous wound and regenerate the damaged skin. Hydrogels have shown great promise for skin wound healing through the rational design and preparation to endow with specific functionalities. In the mini review, we firstly introduce the design and construction of various types of hydrogels based on their bonding chemistry during cross-linking. Then, we summarize the recent research progress on the functionalization of bioactive hydrogel dressings for skin wound healing, including anti-bacteria, anti-inflammatory, tissue proliferation and remodeling. In addition, we highlight the design strategies of responsive hydrogels to external physical stimuli. Ultimately, we provide perspectives on future directions and challenges of functional hydrogels for skin wound healing.

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.

Bioactive strontium ions/ginsenoside Rg1-incorporated biodegradable silk fibroin-gelatin scaffold promoted challenging osteoporotic bone regeneration

Autogenous healing of osteoporotic fractures is challenging, as the regenerative capacity of bone tissues is impaired by estrogen reduction and existed pro-inflammatory cytokines. In this study, a biofunctional ginsenoside Rg1 and strontium-containing mineral (SrHPO₄, SrP)-incorporated biodegradable silk fibroin-gelatin (SG) scaffold (Rg1/SrP/SG) was developed to stimulate the osteoporotic bone repair. The incorporation of 15 wt% SrP significantly enhanced the mechanical strength, stimulated the osteogenic differentiation of mouse bone marrow mesenchymal stem cells, and suppressed the osteoclastogenesis of RAW264.7 in a concentration-related manner. The loading of Rg1 in SG and 15SrP/SG scaffolds obviously promoted the angiogenesis of human umbilical vein endothelial cells via activating the expression of vascular endothelial growth factor and basic fibroblast growth factor genes and proteins. The bioactive strontium ions (Sr²⁺) and Rg1 released from the scaffolds together mediated lipopolysaccharide-treated macrophages polarizing into M2 type. They downregulated the expression of inflammatory-related genes (interleukin (IL)-1β, tumor necrosis factor α, and IL-6) and stimulated the expression of genes related to anti-inflammation (Arginase and IL-10) as well as bone repair (BMP-2 and PDGF-BB) in the macrophages. The in vivo results also displayed that SrP and Rg1 significantly promoted the bone repair effect of SG scaffolds in osteoporotic critical-sized calvarial defects. Besides, the degradation rate of the scaffolds was close to the bone regeneration rate. Therefore, the simultaneous addition of SrP and Rg1 is a promising way for facilitating the osteoporotic bone repair activity of SG scaffolds via promoting the osteogenesis and angiogenesis, as well as inhibiting the osteoclastogenesis and inflammation.

Bio-inspired hydrogel-based bandage with robust adhesive and antibacterial abilities for skin closure

Although conventional suturing techniques are commonly used in assisting wound closure, they do pose limited conduciveness and may lead to secondary injury to wound tissues. Inspired by marine organism mussels, we designed and manufactured a bio-inspired hydrogel-based bandage with tough wet tissue adhesion to substitute traditional surgical suture, accelerate wound healing and avoid infection. Poly(γ-glutamic acid) was modified with 3,4-dihydroxyphenylalanine and glycidyl methacylate, then introduced into the acrylic acid-co-acrylamide hydrogel matrix with robust mechanical properties. The hydrogel bandage showed strong chemical linkage adhesion (70 ± 2.1 kPa), which is 2.8 times that of commercial tissue adhesive fibrin glue (25 ± 2.2 kPa). The hydrogel bandage can not only maintain the self-stability, but is also capable of self-tuning adhesive strength in the range of 14-70 kPa to achieve different adhesion effects by tuning constituent ratio. The bandage has desirable compression properties (0.7 ± 0.11 MPa) and tensile elongation (about 25 times), which ensures its resistance to damages, especially in joint spaces. Secondly, the bandage was endowed with antioxidant and endogenous broad-spectrum antibacterial properties with its catechol structure. Results also demonstrated excellent cell compatibility and blood compatibility, certifying its eligible biological safety profile. In a rat full-thickness cutaneous deficiency model, we can clearly observe that the bandage possesses the ability to promote wound healing (only need 6 days). Above all, this research provides a new strategy for the emergency treatment of liver hemostasis and myocardial repair during disaster rescue.

SUPPLEMENTARY INFORMATION

Experimental details and supporting data are available in the online version of the paper10.1007/s40843-021-1724-8.

Asiaticoside-laden silk nanofiber hydrogels to regulate inflammation and angiogenesis for scarless skin regeneration

Scarless skin regeneration remains a challenge due to the complicated microenvironment involved in wound healing. Here, the hydrophobic drug, asiaticoside (AC), was loaded inside silk nanofiber hydrogels to achieve bioactive and injectable matrices for skin regeneration. AC was dispersed in aqueous silk nanofiber hydrogels with retention of biological functions that regulated inflammatory reactions and vascularization in vitro. After implantation in full-thickness wound defects, these AC-laden hydrogel matrices achieved scarless wound repair. Inflammatory reactions and angiogenesis were regulated during inflammation and remodeling, which was responsible for wound regeneration similar to normal skin. Both in vitro and in vivo studies demonstrated promising applications of these AC-laden silk hydrogels towards scarless tissue regeneration.

Gradient chondroitin sulfate/poly (γ-glutamic acid) hydrogels inducing differentiation of stem cells for cartilage tissue engineering

Based on the gradient distribution of structure and composition in biological cartilage tissue, we designed a gradient hydrogel scaffold by the moving photomask, using chondroitin sulfate and poly (γ-glutamic acid) as crude materials. The hydrogel scaffold had a gradient distribution of cross-linking density, which can be verified from the results of SEM and swelling behavior. Besides, the hydrogel exhibited great viscoelastic, toughness (70% strain), and strength properties (600 kPa). Additionally, the gradient hydrogel's superior cell compatibility was proved through the MTT, live/dead staining assays, and 3D cell culture experiments. Remarkably, the results of in vitro stem cell differentiation experiments showed that the duration of light directly affected the differentiation extent of stem cells, demonstrating that the gradient hydrogel scaffold can better simulate the function of natural cartilage than the homogeneous one. Due to these outstanding characteristics, this gradient hydrogel is a potential scaffold for cartilage tissue engineering.

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.

Injectable Hyaluronic Acid/Poly(γ-glutamic acid) Hydrogel with Step-by-step Tunable Properties for Soft Tissue Engineering

Injectable hydrogels as an important class of biomaterials have gained much attention in tissue engineering. However, their crosslinking degree is difficult to be controlled after being injected into body. As we all know, the crosslinking degree strongly influences the physicochemical properties of hydrogels. Therefore, developing an injectable hydrogel with tunable crosslinking degree in vivo is important for tissue engineering. Herein, we present a dual crosslinking strategy to prepare injectable hydrogels with step-by-step tunable crosslinking degree using Schiff base reaction and photopolymerization. The developed hyaluronic acid/poly(γ-glutamic acid) (HA/γ-PGA) hydrogels exhibit step-by-step tunable swelling behavior, enzymatic degradation behavior and mechanical properties. Mechanical performance tests show that the storage moduli of HA/γ-PGA hydrogels are all less than 2000 Pa and the compressive moduli are in kilopascal, which have a good match with soft tissue. In addition, NIH 3T3 cells encapsulated in HA/γ-PGA hydrogel exhibit a high cell viability, indicating a good cytocompatibility of HA/γ-PGA hydrogel. Therefore, the developed HA/γ-PGA hydrogel as an injectable biomaterial has a good potential in soft tissue engineering.

Biomimetic poly(γ-glutamic acid) hydrogels based on iron (III) ligand coordination for cartilage tissue engineering

For the problems in the research on differentiation of mesenchymal stem cells (BMSCs), such as poor differentiation tendency and low differentiation efficiency, a novel photo-crosslinked extracellular matrix (ECM) inspired double network hydrogel that composed of poly(γ-glutamic acid) (γ-PGA) hydrogel and Fe³⁺ ligand coordination was designed and manufactured. Compared with those traditional γ-PGA based hydrogels, the introduction of Fe³⁺ significantly enhanced the mechanical properties of the hydrogel and accelerated the chondrogenesis efficiency of BMSCs chondrogenesis. The experimental results confirmed that the mechanical properties of hydrogel enhanced by the introduction of metal ions Fe³⁺ could promote BMSCs proliferation, induce cartilage-specific gene expression, and increase secretion of hydroxyproline (HYP) and glycosaminoglycan (GAG). As a result, this method could promote chondrogenic differentiation of BMSCs, accelerate the regeneration of cartilage, and was prospective to be conducive to the research work of cartilage defect repair. Thus, the mechanically enhanced γ-PGA hydrogel scaffold by Fe³⁺ could mediate BMSCs differentiation and provide a scientific and theoretical basis for research and development of biomedical materials on cartilage tissue engineering field.

Synthesis of photocrosslinkable hydrogels for engineering three-dimensional vascular-like constructs by surface tension-driven assembly

Surface tension-driven assembly is a simple routine used in modular tissue engineering to create three-dimensional (3D) biomimetic tissues with desired structural and biological characteristics. A major bottleneck for this technology is the lack of suitable hydrogel materials to meet the requirements of the assembly process and tissue regeneration. Identifying specific requirements and synthesizing novel hydrogels will provide a versatile platform for generating additional biomimetic functional tissues using this approach. In this paper, we present a novel composite hydrogel system based on methacrylated gelatin and γ-polyglutamic acid by UV copolymerization as the building block for fabricating vascular-like tissue via surface tension-driven assembly. The resulting composite hydrogels exhibited the improved mechanical properties and hydrophilicity, which greatly facilitate the assembly process. Subsequent cell encapsulation experiment proved that the hydrogel could provide 3D support for cellular spreading and migration. Furthermore, based on the composite microgel building blocks, cylindrical vascular-like construct with a perfusable microchannel was generated by the needle-assisted sequential assembly. In order to construct a biomimetic vascular tissue, the endothelial cells and smooth muscle cells were encapsulated in the microgels assembly with a spatial arrangement to build a heterogeneous double-layer tubular structure and the cells could readily elongate and migrate in the hollow concentric construct over 3 days. These data suggest that this composite hydrogel is an attractive candidate for surface tension-driven assembly purposes, making the hydrogel potentially applicable in the fabrication of biomimetic vascularized tissues.

Drug-impregnated, pressurized gas expanded liquid-processed alginate hydrogel scaffolds for accelerated burn wound healing

While the benefits of both hydrogels and drug delivery to enhance wound healing have been demonstrated, the highly hydrophilic nature of hydrogels creates challenges with respect to the effective loading and delivery of hydrophobic drugs beneficial to wound healing. Herein, we utilize pressurized gas expanded liquid (PGX) technology to produce very high surface area (~200 m²/g) alginate scaffolds and describe a method for loading the scaffolds with ibuprofen (via adsorptive precipitation) and crosslinking them (via calcium chelation) to create a hydrogel suitable for wound treatment and hydrophobic drug delivery. The high surface area of the PGX-processed alginate scaffold facilitates >8 wt% loading of ibuprofen into the scaffold and controlled in vitro ibuprofen release over 12-24 h. In vivo burn wound healing assays demonstrate significantly accelerated healing with ibuprofen-loaded PGX-alginate/calcium scaffolds relative to both hydrogel-only and untreated controls, demonstrating the combined benefits of ibuprofen delivery to suppress inflammation as well as the capacity of the PGX-alginate/calcium hydrogel to maintain wound hydration and facilitate continuous calcium release to the wound. The use of PGX technology to produce highly porous scaffolds with increased surface areas, followed by adsorptive precipitation of a hydrophobic drug onto the scaffolds, offers a highly scalable method of creating medicated wound dressings with high drug loadings. STATEMENT OF SIGNIFICANCE: While medicated hydrogel-based wound dressings offer clear advantages in accelerating wound healing, the inherent incompatibility between conventional hydrogels and many poorly water-soluble drugs of relevance in wound healing remains a challenge. Herein, we leveraged supercritical fluids-based strategies to both process and subsequently impregnate alginate, followed by post-crosslinking to form a hydrogel, to create a very high surface area alginate hydrogel scaffold loaded with high hydrophobic drug contents (here, >8 wt% ibuprofen) without the need for any pore-forming additives. The impregnated scaffolds significantly accelerated burn wound healing while also promoting regeneration of the native skin morphology. We anticipate this approach can be leveraged to load clinically-relevant and highly bioavailable dosages of hydrophobic drugs in hydrogels for a broad range of potential applications.

Mussel-Inspired Dual-Cross-linking Hyaluronic Acid/ε-Polylysine Hydrogel with Self-Healing and Antibacterial Properties for Wound Healing

Physicians have long been calling for an inherent antimicrobial wound dressing, which will be a great progress for treating complicated infections. Here, we report a novel bioadhesive hydrogel with inherent antibacterial properties prepared by mixing modified hyaluronic acid (HA) and ε-polylysine (EPL). This hydrogel can effectively kill Gram (+) and (-) bacteria for its high positive charge density on the surface. The sol-gel transition occurs within seconds via horseradish peroxidase enzymatic cross-linking and Schiff base reaction, which also allows the hydrogel to recover completely from destruction quickly within 5 min. In an infected rat wound model, histological studies indicated that the hydrogels effectively killed bacteria on the surface of wounds and accelerated wound healing. Histological analysis indicated that the thickness of the newborn skin, the density of the newborn microvascular, granulation tissue, and the collagen of rats treated with hydrogel dressings were twice as high as those treated by commercial fibrin glue. These results indicate that the HA/EPL hydrogel has great potential as an antibacterial wound dressing for future clinical applications.

Poly(γ-glutamic acid)-based electrospun nanofibrous mats with photodynamic therapy for effectively combating wound infection

Pathogenic bacterial infections associated with wound healing progress usually result in serious complications. Herein, biocompatible and antimicrobial electrospun nanofibrous mats with photodynamic therapy (PDT) effect were fabricated to accelerate the infected wound healing. The nanofibrous mats were fabricated by co-electrospining of polyanionic poly(γ-glutamic acid) (γ-PGA) and cationic photosensitizer 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin tetra (p-toluenesulfonate) (TMPyP) in aqueous solution and stabilized by the chemical crosslinking. The as-prepared nanofibrous mats can not only confer the moist microenvironment to the wound bed, but also provide potent bactericidal activity upon visible light irradiation by releasing the cytotoxic reactive oxygen species (ROS). The antibacterial assay in vitro showed that they can effectively eradicate the board-spectrum bacteria at a relatively low loading dose of TMPyP (e.g., 0.1 wt%). Meanwhile, those nanofibrous mats showed good biocompatibility with no obvious adverse effects on mammalian cells and red blood cells (RBCs). The animal test in vivo suggested that the restrained inflammatory reaction and better wound healing could be achieved upon timely and effective antibacterial treatment with negligible local toxicities. This biocompatible and antibacterial γ-PGA-TMPyP nanofibrous mat may show great potential in practical infection-resistant applications, particularly for wound dressing applications.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

Ginsenoside Rb1/TGF-β1 loaded biodegradable silk fibroin-gelatin porous scaffolds for inflammation inhibition and cartilage regeneration

Creating a microenvironment with low inflammation and favorable for the chondrogenic differentiation of endogenous stem cells plays an essential role in cartilage repairing. In the present study, we design a novel ginsenoside Rb1/TGF-β1 loaded silk fibroin-gelatin porous scaffold (GSTR) with the function of attenuating inflammation and promoting chondrogenesis. The scaffold has porous microstructure, proper mechanical strength, degradation rate and sustained release of Rb1 and TGF-β1. Rat bone marrow-derived mesenchymal stem cells (rBMSCs) seeded into GSTR scaffolds are homogeneously distributed and display a higher proliferation rate than non-loaded scaffolds (GS). GSTR scaffolds promote the chondrogenic differentiation of rBMSCs and suppress the expression of inflammation genes. Under the stimulation of IL-1β, the inflammation level of the chondrocytes seeded in GSTR scaffolds is also significantly down-regulated. Moreover, GSTR scaffolds implanted into the osteochondral defects in rats effectively promote the regeneration of hyaline cartilage 12 weeks after surgery when compared with other groups. It is demonstrated that this scaffold loaded with Rb1 and TGF-β1 can synergistically create a microenvironment favorable for cartilage regeneration by promoting the chondrogenesis and suppressing the inflammation levels in vivo. These results prove it has a great potential to develop this Rb1/TGF-β1 releasing scaffold into a novel and promising therapeutic for cartilage repair.

Sandwich-structure hydrogels implement on-demand release of multiple therapeutic drugs for infected wounds

Wound infections bring huge challenges to clinical practice. A series of approaches are involved in the management of infected wounds including use of antibacterial agents, granulation tissue regeneration and scar prevention. In this study, we fabricated a sandwich-structure hydrogel dressing through layer-by-layer assembly of films and hydrogels. By pre-loading silver nanoparticles (AgNPs), vascular endothelial growth factors (VEGF) and ginsenoside Rg3 (Rg3) into each layer of the sandwich compound, this hydrogel could realize the sequential release of these drugs onto infected wound beds as demanded. Moreover, altering the thickness of middle layer could further change the drug delivery patterns characterized by delay at the initial releasing timepoint. When applying this dressing on infected wounds of rabbit ears, we found it could alleviate infection-induced inflammation, promote granulation tissue regeneration and inhibit scar formation. Collectively, the design of sandwich-structure hydrogels was facilitated to deliver specific drugs sequentially during their therapeutic time window for complicated diseases and has shown potential applications in infected wounds.

Wound infections bring huge challenges to clinical practice.