Innovations in gene and growth factor delivery systems for diabetic wound healing

Clinic-oriented injectable smart material for the treatment of diabetic wounds: Coordinating the release of GM-CSF and VEGF

Chronic wounds are often caused by diabetes and present a challenging clinical problem due to vascular problems leading to ischemia. This inhibits proper wound healing by delaying inflammatory responses and angiogenesis. To address this problem, we have developed injectable particle-loaded hydrogels which sequentially release Granulocyte-macrophage- colony-stimulating-factor (GM-CSF) and Vascular endothelial growth factor (VEGF) encapsulated in polycaprolactone-lecithin-geleol mono-diglyceride hybrid particles. GM-CSF promotes inflammation, while VEGF facilitates angiogenesis. The hybrid particles (200-1000 nm) designed within the scope of the study can encapsulate the model proteins Bovine Serum Albumin 65 ± 5 % and Lysozyme 77 ± 10 % and can release stably for 21 days. In vivo tests and histological findings revealed that in the hydrogels containing GM-CSF/VEGF-loaded hybrid particles, wound depth decreased, inflammation phase increased, and fibrotic scar tissue decreased, while mature granulation tissue was formed on day 10. These findings confirm that the hybrid particles first initiate the inflammation phase by delivering GM-CSF, followed by VEGF, increasing the number of vascularization and thus increasing the healing rate of wounds. We emphasize the importance of multi-component and sequential release in wound healing and propose a unifying therapeutic strategy to sequentially deliver ligands targeting wound healing stages, which is very important in the treatment of the diabetic wounds.

Dual Glyoxalase-1 and β-Klotho Gene-Activated Scaffold Reduces Methylglyoxal and Reprograms Diabetic Adipose-Derived Stem Cells: Prospects in Improved Wound Healing

Tissue engineering approaches aim to provide biocompatible scaffold supports that allow healing to progress often in healthy tissue. In diabetic foot ulcers (DFUs), hyperglycemia impedes ulcer regeneration, due to complications involving accumulations of cellular methylglyoxal (MG), a key component of oxidated stress and premature cellular aging which further limits repair. In this study, we aim to reduce MG using a collagen-chondroitin sulfate gene-activated scaffold (GAS) containing the glyoxalase-1 gene (GLO-1) to scavenge MG and anti-fibrotic β-klotho to restore stem cell activity in diabetic adipose-derived stem cells (dADSCs). dADSCs were cultured on dual GAS constructs for 21 days in high-glucose media in vitro. Our results show that dADSCs cultured on dual GAS significantly reduced MG accumulation (-84%; p < 0.05) compared to the gene-free controls. Similar reductions in profibrotic proteins α-smooth muscle actin (-65%) and fibronectin (-76%; p < 0.05) were identified in dual GAS groups. Similar findings were observed in the expression of pro-scarring structural proteins collagen I (-62%), collagen IV (-70%) and collagen VII (-86%). A non-significant decrease in the expression of basement membrane protein E-cadherin (-59%) was noted; however, the dual GAS showed a significant increase in the expression of laminin (+300%). We conclude that dual GAS-containing Glo-1 and β-klotho had a synergistic MG detoxification and anti-fibrotic role in dADSC's. This may be beneficial to provide better wound healing in DFUs by controlling the diabetic environment and rejuvenating the diabetic stem cells towards improved wound healing.

Advanced function, design and application of skin substitutes for skin regeneration

The development of skin substitutes aims to replace, mimic, or improve the functions of human skin, regenerate damaged skin tissue, and replace or enhance skin function. This includes artificial skin, scaffolds or devices designed for treatment, imitation, or improvement of skin function in wounds and injuries. Therefore, tremendous efforts have been made to develop functional skin substitutes. However, there is still few reports systematically discuss the relationship between the advanced function and design requirements. In this paper, we review the classification, functions, and design requirements of artificial skin or skin substitutes. Different manufacturing strategies for skin substitutes such as hydrogels, 3D/4D printing, electrospinning, microfluidics are summarized. This review also introduces currently available skin substitutes in clinical trials and on the market and the related regulatory requirements. Finally, the prospects and challenges of skin substitutes in the field of tissue engineering are discussed.

Current State and Future Perspective of Diabetic Wound Healing Treatment: Present Evidence from Clinical Trials

Diabetes is a chronic metabolic condition that is becoming more common and is characterised by sustained hyperglycaemia and long-term health effects. Diabetes-related wounds often heal slowly and are more susceptible to infection because of hyperglycaemia in the wound beds. The diabetic lesion becomes harder to heal after planktonic bacterial cells form biofilms. A potential approach is the creation of hydrogels with many functions. High priority is given to a variety of processes, such as antimicrobial, pro-angiogenesis, and general pro-healing. Diabetes problems include diabetic amputations or chronic wounds (DM). Chronic diabetes wounds that do not heal are often caused by low oxygen levels, increased reactive oxygen species, and impaired vascularization. Several types of hydrogels have been developed to get rid of contamination by pathogens; these hydrogels help to clean up the infection, reduce wound inflammation, and avoid necrosis. This review paper will focus on the most recent improvements and breakthroughs in antibacterial hydrogels for treating chronic wounds in people with diabetes. Prominent and significant side effects of diabetes mellitus include foot ulcers. Antioxidants, along with oxidative stress, are essential to promote the healing of diabetic wounds. Some of the problems that can come from a foot ulcer are neuropathic diabetes, ischemia, infection, inadequate glucose control, poor nutrition, also very high morbidity. Given the worrying rise in diabetes and, by extension, diabetic wounds, future treatments must focus on the rapid healing of diabetic wounds.

Combination therapy along with mesenchymal stem cells in wound healing; the state of the art

Mesenchymal stem cells (MSCs) are being increasingly used in various therapeutic applications including skin tissue repair and wound healing. The positive effects of the MSCs therapy are largely elicited by immunomodulation, increasing angiogenesis, supporting extracellular matrix (ECM) and thus favoring skin structure. However, the therapeutic competences of MSC-based therapies are somewhat hindered by their apparent modest clinical merits, conferring the need for methods that would rise the efficacy of such therapies. A plethora of reports have shown that therapeutic properties of MSCs could be enhanced with other strategies and compounds like biomaterial and platelet-rich plasma (PRP) to target key possessions of MSCs and properties of adjacent tissues concurrently. Manipulation of cellular stress-response mechanisms to improve cell resistance to oxidative stress prior to or during MSC injection could also improve therapeutic efficacy of MSCs. In the current review, we shed light on the recent advances in MSCs combination therapy with other ingredients and procedures to sustain MSCs-mediated effects in wound healing.

Therapeutic role of growth factors in treating diabetic wound

Wounds in diabetic patients, especially diabetic foot ulcers, are more difficult to heal compared with normal wounds and can easily deteriorate, leading to amputation. Common treatments cannot heal diabetic wounds or control their many complications. Growth factors are found to play important roles in regulating complex diabetic wound healing. Different growth factors such as transforming growth factor beta 1, insulin-like growth factor, and vascular endothelial growth factor play different roles in diabetic wound healing. This implies that a therapeutic modality modulating different growth factors to suit wound healing can significantly improve the treatment of diabetic wounds. Further, some current treatments have been shown to promote the healing of diabetic wounds by modulating specific growth factors. The purpose of this study was to discuss the role played by each growth factor in therapeutic approaches so as to stimulate further therapeutic thinking.

The applications of 3D printing in wound healing: the external delivery of stem cells and antibiosis

As the global number of chronic wound patients rises, the financial burden and social pressure on patients increase daily. Stem cells have emerged as promising tissue engineering seed cells due to their enriched sources, multidirectional differentiation ability, and high proliferation rate. However, delivering them in vitro for the treatment of skin injury is still challenging. In addition, bacteria from the wound site and the environment can significantly impact wound healing. In the last decade, 3D bioprinting has dramatically enriched cell delivery systems. The produced scaffolds by this technique can be precisely localized within cells and perform antibacterial actions. In this review, we summarized the 3D bioprinting-based external delivery of stem cells and their antibiosis to improve wound healing.

Enriched adipose stem cell secretome as an effective therapeutic strategy for in vivo wound repair and angiogenesis

The therapeutic potential of adipose tissue-derived mesenchymal stem cells (ADMSCs) is well studied for use in non-healing wounds. However, concerns on the transplantable cell number requirement, cell expansion, cell viability, retained cell multipotency and the limited cell implantation time for efficient impact hinders cell therapy. Recent literature is much inclined to the superiority of the ADMSCs' secretome, pre-dominating its paracrine-mediated therapeutic impact. In this context, the possibility of attaining accelerated wound angiogenesis through non-viral mediated enrichment of the ADMSCs secretome with pro-angiogenic growth factors (AGF) seems promising. Accordingly, this study aimed to explore the effect of AGF-enriched ADMSCs secretome for accelerating wound angiogenesis and repair in acute large area full thickness excision rabbit wound model, as adopted from Salgado et al. (Chir Buchar Rom 108:706-710, 1990). Using sub-dermal single-dose injections along the margin of the dorsal wound, native ADMSCs secretome, AGF-enriched ADMSC secretome, allogenic rabbit ADMSCs and a combination of AGF-enriched ADMSC secretome with allogenic rabbit ADMSCs were transplanted independently. Twenty-eight days (28 days) post-transplantation, histopathological analysis was performed to assess the effect. Hematoxylin and eosin (H&E) staining showed enhanced epithelization, notable granulation tissue and collagen fiber deposition in AGF-enriched secretome transplanted groups. This was confirmed by elevated CD31 detection, faster wound closure time and collagen organization. The use of single-dose AGF-enriched ADMSCs' secretome for therapeutic angiogenesis and wound repair seems to be a promising cell-free therapeutic option. Further investigations using multiple doses on larger animal groups remains to be explored in order to ascertain the comparative potential of AGF-enriched ADMSCs' secretome.

EGFL7 affects the migration of epidermal stem cells in refractory diabetic wounds by regulating Notch signaling pathway

Aim: This study aimed to explore the role of EGFL7 in the healing process of refractory diabetic wounds. Methods: Epidermal stem cells (ESCs) were isolated from healthy mice and diabetic mice, identified by immunofluorescence, transfected with EGFL7 overexpression and silencing lentiviral vectors, and treated with Notch pathway inhibitor (DAPT). Results: SiEGFL7 significantly inhibited the proliferation, invasion and migration of ESCs of healthy mice. DAPT prominently inhibited the expressions of Notch1, Notch2, Hes1 and Jag1 in ESCs of healthy mice induced by overexpressed EGFL7. Overexpressed EGFL7 promoted wound healing in diabetic mice with refractory wounds. Conclusion: EGFL7 affects the proliferation and migration of ESCs in refractory diabetic wounds by regulating the Notch signaling pathway.

Immune evaluation of granulocyte-macrophage colony stimulating factor loaded hierarchically 3D nanofiber scaffolds in a humanized mice model

Background: Immune evaluation of biomaterials for tissue regeneration is a critical preclinical evaluation. The current evaluation criterion (ISO 10993-1 or GB/T 16886) uses rodents to perform the immune evaluation. However, the immune system of rodents is different from humans, the obtained results may not be reliable, which could lead directly to the failure of clinical trials. Granulocyte-macrophage colony-stimulating factor (GM-CSF) shows a great potential application in tissue regeneration by regulating local immune responses. The presented work combines the advantages of GM-CSF (immunoregulation) and hierarchically 3D nanofiber scaffolds (tissue regeneration). Methods: Firstly, we fabricated GM-CSF loaded 3D radially aligned nanofiber scaffolds, and then subcutaneous implantation was performed in humanized mice. The whole scaffold and surrounding tissue were harvested at each indicated time point. Finally, the cell infiltration and local immune responses were detected by histological observations, including H&E and Masson staining and immunochemistry. Results: We found significant cell migration and extracellular matrix deposition within the 3D radially aligned nanofiber scaffold after subcutaneous implantation. The locally released GM-CSF could accelerate the expression of human dendritic cells (CD11c) only 3 days after subcutaneous implantation. Moreover, higher expression of human cytotoxic T cells (CD3⁺/CD8⁺), M1 macrophages (CD68/CCR7) was detected within GM-CSF loaded radially aligned nanofiber scaffolds and their surrounding tissues. Conclusions: The 3D radially aligned scaffold can accelerate cell migration from surrounding tissues to regenerate the wound area. And the locally released GM-CSF enhances dendritic cell recruitment and activation of cytotoxic T cells and M1 macrophages. Taken together, the GM-CSF loaded 3D radially aligned nanofiber scaffolds have a promising potential for achieving tissue regeneration.

Growth Factor Binding Peptides in Poly (Ethylene Glycol) Diacrylate (PEGDA)-Based Hydrogels for an Improved Healing Response of Human Dermal Fibroblasts

Growth factors (GF) are critical cytokines in wound healing. However, the direct delivery of these biochemical cues into a wound site significantly increases the cost of wound dressings and can lead to a strong immunological response due to the introduction of a foreign source of GFs. To overcome this challenge, we designed a poly(ethylene glycol) diacrylate (PEGDA) hydrogel with the potential capacity to sequester autologous GFs directly from the wound site. We demonstrated that synthetic peptide sequences covalently tethered to PEGDA hydrogels physically retained human transforming growth factor beta 1 (hTGFβ1) and human vascular endothelial growth factor (hVEGF) at 3.2 and 0.6 ng/mm², respectively. In addition, we demonstrated that retained hTGFβ1 and hVEGF enhanced human dermal fibroblasts (HDFa) average cell surface area and proliferation, respectively, and that exposure to both GFs resulted in up to 1.9-fold higher fraction of area covered relative to the control. After five days in culture, relative to the control surface, non-covalently bound hTGFβ1 significantly increased the expression of collagen type I and hTGFβ1 and downregulated vimentin and matrix metalloproteinase 1 expression. Cumulatively, the response of HDFa to hTGFβ1 aligns well with the expected response of fibroblasts during the early stages of wound healing.

Electrospun hybrid nanofibers: Fabrication, characterization, and biomedical applications

Nanotechnology is one of the most promising technologies available today, holding tremendous potential for biomedical and healthcare applications. In this field, there is an increasing interest in the use of polymeric micro/nanofibers for the construction of biomedical structures. Due to its potential applications in various fields like pharmaceutics and biomedicine, the electrospinning process has gained considerable attention for producing nano-sized fibers. Electrospun nanofiber membranes have been used in drug delivery, controlled drug release, regenerative medicine, tissue engineering, biosensing, stent coating, implants, cosmetics, facial masks, and theranostics. Various natural and synthetic polymers have been successfully electrospun into ultrafine fibers. Although biopolymers demonstrate exciting properties such as good biocompatibility, non-toxicity, and biodegradability, they possess poor mechanical properties. Hybrid nanofibers from bio and synthetic nanofibers combine the characteristics of biopolymers with those of synthetic polymers, such as high mechanical strength and stability. In addition, a variety of functional agents, such as nanoparticles and biomolecules, can be incorporated into nanofibers to create multifunctional hybrid nanofibers. Due to the remarkable properties of hybrid nanofibers, the latest research on the unique properties of hybrid nanofibers is highlighted in this study. Moreover, various established hybrid nanofiber fabrication techniques, especially the electrospinning-based methods, as well as emerging strategies for the characterization of hybrid nanofibers, are summarized. Finally, the development and application of electrospun hybrid nanofibers in biomedical applications are discussed.

Stability Enhancement of Freeze-Dried Gelatin/Alginate Coacervates for bFGF Delivery

Chronic wound sites have elevated levels of proteolytic enzymes that negate the activity of topically applied growth factors. bFGF encapsulated in gelatin/alginate coacervates was protected from protease and showed better activity than bFGF in solution; however, its activity decreased with particle size and PDI increase after freeze-drying and rehydration. In this study, we aim to improve the stability of bFGF coacervates during freeze-drying to enable a topically applied growth factor delivery system for diabetic foot ulcer. Trehalose, mannitol, and Tween 80 at various concentrations were tested as cryoprotectant candidates. Trehalose improved the mechanical property of freeze-dried coacervates and physical properties after rehydration, resulting in stable size and PDI values. It also enhanced the bFGF activity in hyperglycemic human dermal fibroblasts with better cell viability, migration, and procollagen synthesis compared to the coacervates without trehalose. Hydrogen bonding interactions between trehalose and polymers probed by ATR-FTIR contribute to the stability of coacervates during freeze-drying. In conclusion, the freeze-dried gelatin/alginate coacervates encapsulating bFGF was effectively stabilized with trehalose, and the resulting coacervate composition is suggested as a potential therapeutic modality for chronic wounds including diabetic foot ulcer.

Evaluating polymeric biomaterials to improve next generation wound dressing design

Wound healing is a dynamic series of interconnected events with the ultimate goal of promoting neotissue formation and restoration of anatomical function. Yet, the complexity of wound healing can often result in development of complex, chronic wounds, which currently results in a significant strain and burden to our healthcare system. The advancement of new and effective wound care therapies remains a critical issue, with the current therapeutic modalities often remaining inadequate. Notably, the field of tissue engineering has grown significantly in the last several years, in part, due to the diverse properties and applications of polymeric biomaterials. The interdisciplinary cohesion of the chemical, biological, physical, and material sciences is pertinent to advancing our current understanding of biomaterials and generating new wound care modalities. However, there is still room for closing the gap between the clinical and material science realms in order to more effectively develop novel wound care therapies that aid in the treatment of complex wounds. Thus, in this review, we discuss key material science principles in the context of polymeric biomaterials, provide a clinical breadth to discuss how these properties affect wound dressing design, and the role of polymeric biomaterials in the innovation and design of the next generation of wound dressings.

Advances and perspective on animal models and hydrogel biomaterials for diabetic wound healing

Diabetic wounds are a common complication in diabetes patients. Due to peripheral nerve damage and vascular dysfunction, diabetic wounds are prone to progress to local ulcers, wound gangrene and even to require amputation, bringing huge psychological and economic burdens to patients. However, the current treatment methods for diabetic wounds mainly include wound accessories, negative pressure drainage, skin grafting and surgery; there is still no ideal treatment to promote diabetic wound healing at present. Appropriate animal models can simulate the physiological mechanism of diabetic wounds, providing a basis for translational research in treating diabetic wound healing. Although there are no animal models that can fully mimic the pathophysiological mechanisms of diabetic wounds in humans, it is vital to explore animal simulation models used in basic research and preclinical studies of diabetic wounds. In addition, hydrogel materials are regarded as a promising treatment for diabetic wounds because of their good antimicrobial activity, biocompatibility, biodegradation and appropriate mechanical properties. Herein, we review and discuss the different animal models used to investigate the pathological mechanisms of diabetic wounds. We further discuss the promising future application of hydrogel biomaterials in diabetic wound healing.

Immunomodulatory Bandage for Accelerated Healing of Diabetic Wounds

Diabetic foot ulcers are challenging to treat. Current strategies to treat these wounds focus on preventing infection and promoting tissue regrowth but are ineffective in many individuals. Low-grade chronic inflammation is present in individuals with diabetes, and altering the inflammatory responses at the wound site could be an alternate approach to promote healing. We hypothesized that immunomodulation of the wound microenvironment would result in accelerated healing. To test this hypothesis, we began by characterizing the changes in the myeloid cell phenotype in a mouse model [leptin receptor knockout (KO) mouse] that closely mimics the type 2 diabetes condition observed in humans. We observed increased numbers of monocytes and neutrophils in the circulation of the KO mice compared to that in wild-type control mice. We also observed several phenotypic changes in neutrophils from the KO diabetic mice, suggesting low-grade systemic inflammation. Hence, we developed a rapamycin-loaded chitosan scaffold that may be used to modulate immune responses. The use of these immunomodulatory scaffolds at a wound site resulted in accelerated healing compared to the healing using blank scaffolds. In summary, our data suggest that immunomodulation may be a viable strategy to promote the healing of wounds in individuals with diabetes.

Nrf2 Mediated Heme Oxygenase-1 Activation Contributes to Diabetic Wound Healing - an Overview

Diabetic wound healing is a complicated procedure because hyperglycemia changes the various stages of wound healing. In type 2 diabetes mellitus (T2DM), oxidative stress is proven to be a critical factor in causing non-healing wounds and aggravating the inflammatory phase, resulting in the amputation of lower limbs in T2DM patients. This makes scientists figure out how to control oxidative stress and chronic inflammation at the molecular level. Nuclear factor erythroid 2- related factor 2 (Nrf2) releases antioxidant proteins to suppress reactive oxygen species (ROS) activation and inflammation. The current review discusses the role of Nrf2 in improving diabetic wound healing by reducing the production of ROS and thus reducing oxidative stress, as well as inhibiting nuclear factor kappa B (NF-kB) dissociation and nuclear translocation, which prevents the release of inflammatory mediators and increases antioxidant protein levels, thereby improving diabetic wound healing. As a result, the researcher will be able to find a more effective diabetic wound healing therapy.

Growth Factor and Cytokine Delivery Systems for Wound Healing

Skin wound healing is a highly coordinated process involving multiple tissue-resident and recruited cell types. Cells within the wound microenvironment respond to key secreted factors such as pro-proliferative growth factors and immunomodulatory cytokines to repair the skin and promptly restore its essential barrier role. Therefore, recombinant growth factors and cytokines are promising therapeutics for skin wounds, in particular for large acute wounds such as burns, or wounds associated with underlying pathologies such as nonhealing chronic and diabetic wounds. However, translation of growth factors and cytokines into clinically effective treatments has been limited. Short half-life, poor stability, rapid diffusion, uncontrolled signaling, and systemic side effects are currently the key challenges to developing efficient growth factor- and cytokine-based therapies. To overcome these limitations, novel delivery systems have been developed to improve the regenerative potential of recombinant growth factors and cytokines. In this review, we discuss biomaterial and protein engineering strategies used to optimize the delivery of growth factor and cytokine therapeutics for skin wound treatment.

FPR2 DNA Aptamers for Targeted Therapy of Wound Repair

Chronic wounds represent a major health problem worldwide. Some of the available therapies based on recombinant proteins usually fail owing to the hostile environment found at the wound bed. Aptamers appear as an attractive alternative to recombinant factors owing in part to their stability, sensitivity, specificity, and low-cost production. In this study, the Cell-Systematic Evolution of Ligands by EXponential Enrichment technology was employed to generate aptamers that specifically recognize and modulate the function of the FPR2, a receptor expressed in a variety of cells involved in wound repair. Three aptamers were obtained that specifically bound to FPR2 stable transfectants generated in HaCaT cells. The targeted aptamers were shown to act as FPR2 agonists in different in vitro functional assays, including wound healing assays, and elicited a similar pattern of response to that obtained with other known FPR2 peptide agonists, such as the human LL37 cathelicidin. We have also obtained in vivo evidence for the prohealing activities of one of these FPR2 aptamers in a skin-humanized mouse model developed by us, previously shown to accurately recreate the main phases of physiological human wound repair process. In conclusion, we provide evidence of the potential therapeutic value of FPR2 aptamers for cutaneous repair.

Novel Pharmaceutical Strategies for Enhancing Skin Penetration of Biomacromolecules

Skin delivery of biomacromolecules holds great advantages in the systemic and local treatment of multiple diseases. However, the densely packed stratum corneum and the tight junctions between keratinocytes stand as formidable skin barriers against the penetration of most drug molecules. The large molecular weight, high hydrophilicity, and lability nature of biomacromolecules pose further challenges to their skin penetration. Recently, novel penetration enhancers, nano vesicles, and microneedles have emerged as efficient strategies to deliver biomacromolecules deep into the skin to exert their therapeutic action. This paper reviews the potential application and mechanisms of novel skin delivery strategies with emphasis on the pharmaceutical formulations.

Recent Advances of Natural Polysaccharide-based Double-network Hydrogels for Tissue Repair

Natural polysaccharide hydrogels have been extensively explored for many years due to their outstanding biocompatibility and biodegradability, which are very promising candidates as artificial soft materials for biomedical applications. However, their inferior mechanical performances greatly limited their applications. Introduction of double-network (DN) structure has been well documented to be an efficient strategy for significant improvement of the mechanical property of hydrogels. Here, recent progress of natural polysaccharide-based DN hydrogels is reviewed from the perspective of fundamental concepts on both design rationale and preparation strategies to biomedical application in tissue repair. Retrospect of the DN-strengthened polysaccharide hydrogels can give a deep insight into the fundamental relationship of such bio-based hydrogels among structural design, mechanical properties and practical demands, thereby prompting their translation to clinical application prospects.

Smart 3D Printed Hydrogel Skin Wound Bandages: A Review

Wounds are a major health concern affecting the lives of millions of people. Some wounds may pass a threshold diameter to become unrecoverable by themselves. These wounds become chronic and may even lead to mortality. Recently, 3D printing technology, in association with biocompatible hydrogels, has emerged as a promising platform for developing smart wound dressings, overcoming several challenges. 3D printed wound dressings can be loaded with a variety of items, such as antibiotics, antibacterial nanoparticles, and other drugs that can accelerate wound healing rate. 3D printing is computerized, allowing each level of the printed part to be fully controlled in situ to produce the dressings desired. In this review, recent developments in hydrogel-based wound dressings made using 3D printing are covered. The most common biosensors integrated with 3D printed hydrogels for wound dressing applications are comprehensively discussed. Fundamental challenges for 3D printing and future prospects are highlighted. Additionally, some related nanomaterial-based hydrogels are recommended for future consideration.

Electrospun multifunctional nanofibrous mats loaded with bioactive anemoside B4 for accelerated wound healing in diabetic mice

With the worldwide prevalence of diabetes and considering the complicated microenvironment of diabetic wounds, the design and development of innovative multifunctional wound dressing materials are much wanted for the treatment of hard-to-heal wounds in diabetic patients. In the present study, anti-inflammatory ingredients loaded with nanofibrous wound dressing materials were manufactured by a promising blend-electrospinning strategy, and their capability for treating the diabetic wound was also systematically explored. A polymer blend consisting of Chitosan (CS) and polyvinyl alcohol (PVA) was electrospun into CS-PVA nanofibrous mats as control groups. In the meanwhile, a bioactive ingredient of Chinese medicine Pulsatilla, anemoside B4(ANE), with different contents were loaded into the electrospinning solution to construct CS-PVA-ANE nanofibrous mats. The developed CS-PVA-ANE wound dressing materials exhibited multifunctional properties including prominent water absorption, biomimetic elastic mechanical properties, and sustained ANE releasing behavior, as well as outstanding hemostatic properties. The in vitro studies showed that the CS-PVA-ANE nanofiber mats could significantly suppress lipopolysaccharide (LPS)-stimulated differentiation of pro-inflammatory (M1) macrophage subsets, and notably reduce the reactive oxygen species (ROS) generation, as well as obviously decrease inflammatory cytokine release. The in vivo animal studies showed that the CS-PVA-ANE nanofiber mats promoted the healing of diabetic wounds by significantly enhancing wound closure rates, accelerating excellent angiogenesis, promoting re-epithelization and collagen matrix deposition throughout all stages of wound healing. The present study demonstrated that CS-PVA-ANE nanofiber mats could effectively shorten the wound-healing time by inhibiting inflammatory activity, which makes them promising candidates for the treatment of hard-to-heal wounds caused by diabetes.

Diverse nanocomposites as a potential dressing for diabetic wound healing

Wound healing is a programmed process of continuous events which is impaired in the case of diabetic patients. This impaired process of healing in diabetics leads to amputation, longer hospitalisation, immobilisation, low self-esteem, and mortality in some patients. This problem has paved the way for several innovative strategies like the use of nanotechnology for the treatment of wounds in diabetic patients. The use of biomaterials, nanomaterials have advanced approaches in tissue engineering by designing multi-functional nanocomposite scaffolds. Stimuli-responsive scaffolds that interact with the wound microenvironment and controlled release of bioactive molecules have helped in overcoming barriers in healing. The use of different types of nanocomposite scaffolds for faster healing of diabetic wounds is constantly being studied. Nanocomposites have helped in addressing specific issues with respect to healing and improving angiogenesis. Method: A literature search was followed to retrieve the articles on strategies for wound healing in diabetes across several databases like PubMed, EMBASE, Scopus and Cochrane database. The search was performed in May 2022 by two researchers independently. They keywords used were "diabetic wounds, nanotechnology, nanocomposites, nanoparticles, chronic diabetic wounds, diabetic foot ulcer, hydrogel". Exclusion criteria included insulin resistance, burn wound, dressing material.

Advances in bioactive glass-containing injectable hydrogel biomaterials for tissue regeneration

Successful tissue regeneration requires a scaffold with tailorable biodegradability, tissue-like mechanical properties, structural similarity to extracellular matrix (ECM), relevant bioactivity, and cytocompatibility. In recent years, injectable hydrogels have spurred increasing attention in translational medicine as a result of their tunable physicochemical properties in response to the surrounding environment. Furthermore, they have the potential to be implanted via minimally invasive procedures while enabling deep penetration, which is considered a feasible alternative to traditional open surgical procedures. However, polymeric hydrogels may lack sufficient stability and bioactivity in physiological environments. Composite hydrogels containing bioactive glass (BG) particulates, synergistically combining the advantages of their constituents, have emerged as multifunctional biomaterials with tailored mechanical properties and biological functionalities. This review paper highlights the recent advances in injectable composite hydrogel systems based on biodegradable polymers and BGs. The influence of BG particle geometry, composition, and concentration on gel formation, rheological and mechanical behavior as well as hydration and biodegradation of injectable hydrogels have been discussed. The applications of these composite hydrogels in tissue engineering are additionally described, with particular attention to bone and skin. Finally, the prospects and current challenges in the development of desirable injectable bioactive hydrogels for tissue regeneration are discussed to outline a roadmap for future research. STATEMENT OF SIGNIFICANCE: Developing a biomaterial that can be readily available for surgery, implantable via minimally invasive procedures, and be able to effectively stimulate tissue regeneration is one of the grand challenges in modern biomedicine. This review summarizes the state-of-the-art of injectable bioactive glass-polymer composite hydrogels to address several challenges in bone and soft tissue repair. The current limitations and the latest evolutions of these composite biomaterials are critically examined, and the roles of design parameters, such as composition, concentration, and size of the bioactive phase, and polymer-glass interactions on the rheological, mechanical, biological, and overall functional performance of hydrogels are detailed. Existing results and new horizons are discussed to provide a state-of-the-art review that may be useful for both experienced and early-stage researchers in the biomaterials community.

Anti-Aging β-Klotho Gene-Activated Scaffold Promotes Rejuvenative Wound Healing Response in Human Adipose-Derived Stem Cells

Wound healing requires a tight orchestration of complex cellular events. Disruption in the cell-signaling events can severely impair healing. The application of biomaterial scaffolds has shown healing potential; however, the potential is insufficient for optimal wound maturation. This study explored the functional impact of a collagen-chondroitin sulfate scaffold functionalized with nanoparticles carrying an anti-aging gene β-Klotho on human adipose-derived stem cells (ADSCs) for rejuvenative healing applications. We studied the response in the ADSCs in three phases: (1) transcriptional activities of pluripotency factors (Oct-4, Nanog and Sox-2), proliferation marker (Ki-67), wound healing regulators (TGF-β3 and TGF-β1); (2) paracrine bioactivity of the secretome generated by the ADSCs; and (3) regeneration of basement membrane (fibronectin, laminin, and collagen IV proteins) and expression of scar-associated proteins (α-SMA and elastin proteins) towards maturation. Overall, we found that the β-Klotho gene-activated scaffold offers controlled activation of ADSCs' regenerative abilities. On day 3, the ADSCs on the gene-activated scaffold showed enhanced (2.5-fold) activation of transcription factor Oct-4 that was regulated transiently. This response was accompanied by a 3.6-fold increase in the expression of the anti-fibrotic gene TGF-β3. Through paracrine signaling, the ADSCs-laden gene-activated scaffold also controlled human endothelial angiogenesis and pro-fibrotic response in dermal fibroblasts. Towards maturation, the ADSCs-laden gene-activated scaffold further showed an enhanced regeneration of the basement membrane through increases in laminin (2.1-fold) and collagen IV (8.8-fold) deposition. The ADSCs also expressed 2-fold lower amounts of the scar-associated α-SMA protein with improved qualitative elastin matrix deposition. Collectively, we determined that the β-Klotho gene-activated scaffold possesses tremendous potential for wound healing and could advance stem cell-based therapy for rejuvenative healing applications.

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.

Huiyang Shengji decoction promotes wound healing in diabetic mice by activating the EGFR/PI3K/ATK pathway

Background

Common chronic wounds include diabetic ulcers, venous ulcers, and pressure ulcers. The traditional Chinese medicine Huiyang Shengji decoction (HYSJD) has been shown to promote the healing of diabetic chronic wounds, however, its pharmacological mechanism is still unclear.

Purpose

This study aimed to determine the mechanism of HYSJD in promoting the healing of diabetic chronic skin ulcers.

Methods

Ultra-performance liquid chromatography was combined with tandem mass spectrometry (UPLC-MS/MS) to analyze the main components of HYSJD and the absorbed components in mouse serum at 30 min after oral administration of HYSJD. db/db mouse models for chronic skin ulcers were constructed by full-thickness skin resection. Wound tissues at day 7 post wound formation were used to perform microarray analysis of growth factors and chemokine expression. GO and KEGG enrichment analysis was performed on differentially expressed proteins. ELISA assays were used to measure differential expressed cytokines in the serum and Western blot analysis was used to determine the expression levels of related pathway proteins in the skin wounds.

Results

UPLC-MS/MS analysis showed that the main chemical components of HYSJD were flavonoids, terpenes, alkaloids, phenylpropanoids, and carbohydrates. At 30 min after oral administration of HYSJD, five absorbed components were detected in the serum, these included formononetin, calycosin, hypaconitine, calycosin-7-glucoside, and sinapic acid. HYSJD was found to increase the wound healing rate in chronic skin ulcers in db/db mice at days 3, 7, and 14 post wound formation, and promote the proliferation of epidermal cells. Two proteins that were differentially expressed between the different groups, i.e., IGF-1 and EGFR, were further validated. Serum ELISA assays showed that serum EGFR in the HYSJD treatment group was significantly increased. KEGG pathway analysis suggested that the PI3K/AKT pathway involved in HYSJD promoting the proliferation of epidermal cells in chronic wounds in db/db mice. Experimental verification showed that HYSJD activated the PI3K/AKT signaling pathway in mouse wound skin.

Conclusion

HYSJD promotes the proliferation of epidermal cells in chronic diabetic wounds by increasing EGFR expression in the wounds and activating the PI3K/AKT signaling pathway. Our study provides an experimental basis for the pharmacological mechanism of HYSJD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13020-021-00497-0.

Investigation of the potential therapeutic effect of cationic lipoplex mediated fibroblast growth factor-2 encoding plasmid DNA delivery on wound healing

BACKGROUND

Developing an alternative and efficient therapy for wound healing has been an important research topic for pharmaceutical sciences. A straightforward but effective system for delivering fibroblast growth factor-2 (FGF-2) encoding plasmid DNA (pFGF-2) for wound healing therapy was aimed to develop in this study.

METHODS

In order to provide the delivery of pFGF-2, a delivery vector, namely, cationic lipid nanoparticle (cLN) was developed by the melt-emulsification process, complexed with pFGF-2 to form a lipoplex system and further characterized. The pFGF-2 binding and protecting ability of lipoplexes were evaluated. The cytotoxicity and transfection efficiency of the lipoplexes, FGF-2 expression levels, and in vitro wound healing ability have been investigated on the L929 fibroblast cell line.

RESULTS

The obtained lipoplex system has a particle size of 88.53 nm with a low PDI (0.185), and zeta potential values of 27.8 mV with a spherical shape. The ability of cLNs to bind pFGF-2 and protect against nucleases was demonstrated by gel retardation assay. Furthermore, the developed FGF-2 carrying lipoplexes system showed significant transfection and FGF-2 expression ability comparing naked plasmid. Finally, scratch assay revealed that the developed system is able to promote in vitro cell proliferation/migration in 48 h.

CONCLUSION

Promising results have been achieved with the use of lipoplexes carrying pFGF-2, and this approach could be considered as a potentially applicable concept for the future gene-based wound healing therapies.

Photobiomodulation and diabetic foot and lower leg ulcer healing: A narrative synthesis

PURPOSE

To provide a comprehensive narrative review and critical appraisal of research investigating photobiomodulation (PBM), formerly known as low level laser therapy which includes lasers and light emitting diodes (LEDs), as a treatment to promote diabetic foot and lower leg ulcer (DFU) healing for humans.

MATERIALS AND METHODS

Pubmed, CINAHL, Scopus, and OVID Medline databases were used to find relevant studies published between January 2000 and January 2020. Reference lists of identified articles were scanned for additional studies that might have been missed in the database searches.

RESULTS

A total of 13 studies, with a total of 417 participants, were included in this review.

DISCUSSION

The studies were critically appraised using the PEDro scale, which revealed weaknesses in study designs such as small sample sizes and problems with reproducibility with respect to the laser protocols. Characteristics of PBM that improved wound healing were wavelengths of 630 nm-660 nm and infrared wavelengths of 850 or 890 nm, and radiant exposure levels of 3 J/cm²-7 J/cm². PBM was beneficial for superficial and deep DFUs. Controlled blood glucose levels and adherence to best practices (pressure off-loading, optimized wound dressing changes, appropriate debridement, etc.) could have been a factor in the beneficial outcomes.

CONCLUSION

Regardless of the laser characteristics chosen, in the majority of studies PBM as a treatment for DFUs improved healing rate when compared with standard wound care alone. However, weaknesses across the studies indicate that further research is required.

Heparin Microislands in Microporous Annealed Particle Scaffolds for Accelerated Diabetic Wound Healing

Mimicking growth factor-ECM interactions for promoting cell migration is a powerful technique to improve tissue integration with biomaterial scaffolds for the regeneration of damaged tissues. This has been attempted by scaffold-mediated controlled delivery of exogenous growth factors; however, the predetermined nature of this delivery can limit the scaffold's ability to meet each wound's unique spatiotemporal regenerative needs and presents translational hurdles. To address this limitation, we present a new approach to growth factor presentation by incorporating heparin microislands, which are spatially isolated heparin-containing microparticles that can reorganize and protect endogenous local growth factors via heterogeneous sequestration at the microscale in vitro and result in functional improvements in wound healing. More specifically, we incorporated our heparin microislands within microporous annealed particle (MAP) scaffolds, which allows facile tuning of microenvironment heterogeneity through ratiometric mixing of microparticle sub-populations. In this manuscript, we demonstrate the ability of heparin microislands to heterogeneously sequester applied growth factor and control downstream cell migration in vitro. Further, we present their ability to significantly improve wound healing outcomes (epidermal regeneration and re-vascularization) in a diabetic wound model relative to two clinically relevant controls.

Synergistic Effect of Biomaterial and Stem Cell for Skin Tissue Engineering in Cutaneous Wound Healing: A Concise Review

Skin tissue engineering has made remarkable progress in wound healing treatment with the advent of newer fabrication strategies using natural/synthetic polymers and stem cells. Stem cell therapy is used to treat a wide range of injuries and degenerative diseases of the skin. Nevertheless, many related studies demonstrated modest improvement in organ functions due to the low survival rate of transplanted cells at the targeted injured area. Thus, incorporating stem cells into biomaterial offer niches to transplanted stem cells, enhancing their delivery and therapeutic effects. Currently, through the skin tissue engineering approach, many attempts have employed biomaterials as a platform to improve the engraftment of implanted cells and facilitate the function of exogenous cells by mimicking the tissue microenvironment. This review aims to identify the limitations of stem cell therapy in wound healing treatment and potentially highlight how the use of various biomaterials can enhance the therapeutic efficiency of stem cells in tissue regeneration post-implantation. Moreover, the review discusses the combined effects of stem cells and biomaterials in in vitro and in vivo settings followed by identifying the key factors contributing to the treatment outcomes. Apart from stem cells and biomaterials, the role of growth factors and other cellular substitutes used in effective wound healing treatment has been mentioned. In conclusion, the synergistic effect of biomaterials and stem cells provided significant effectiveness in therapeutic outcomes mainly in wound healing improvement.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

SDF-1α gene-activated collagen scaffold enhances provasculogenic response in a coculture of human endothelial cells with human adipose-derived stromal cells

Novel biomaterials can be used to provide a better environment for cross talk between vessel forming endothelial cells and wound healing instructor stem cells for tissue regeneration. This study seeks to investigate if a collagen scaffold containing a proangiogenic gene encoding for the chemokine stromal-derived factor-1 alpha (SDF-1α GAS) could be used to enhance functional responses in a coculture of human umbilical vein endothelial cells (HUVECs) and human adipose-derived stem/stromal cells (ADSCs). Functional responses were determined by (1) monitoring the amount of junctional adhesion molecule VE-cadherin released during 14 days culture, (2) expression of provasculogenic genes on the 14th day, and (3) the bioactivity of secreted factors on neurogenic human Schwann cells. When we compared our SDF-1α GAS with a gene-free scaffold, the results showed positive proangiogenic determination characterized by a transient yet controlled release of the VE-cadherin. On the 14th day, the coculture on the SDF-1α GAS showed enhanced maturation than its gene-free equivalent through the elevation of provasculogenic genes (SDF-1α-7.4-fold, CXCR4-1.5-fold, eNOS-1.5-fold). Furthermore, we also found that the coculture on SDF-1α GAS secretes bioactive factors that significantly (p < 0.01) enhanced human Schwann cells' clustering to develop toward Bünger band-like structures. Conclusively, this study reports that SDF-1α GAS could be used to produce a bioactive vascularized construct through the enhancement of the cooperative effects between endothelial cells and ADSCs.

Effects of a Catechol-Functionalized Hyaluronic Acid Patch Combined with Human Adipose-Derived Stem Cells in Diabetic Wound Healing

Introduction: Chronic inflammation and impaired neovascularization play critical roles in delayed wound healing in diabetic patients. To overcome the limitations of current diabetic wound (DBW) management interventions, we investigated the effects of a catechol-functionalized hyaluronic acid (HA-CA) patch combined with adipose-derived mesenchymal stem cells (ADSCs) in DBW mouse models. Methods: Diabetes in mice (C57BL/6, male) was induced by streptozotocin (50 mg/kg, >250 mg/dL). Mice were divided into four groups: control (DBW) group, ADSCs group, HA-CA group, and HA-CA + ADSCs group (n = 10 per group). Fluorescently labeled ADSCs (5 × 10⁵ cells/100 µL) were transplanted into healthy tissues at the wound boundary or deposited at the HA-CA patch at the wound site. The wound area was visually examined. Collagen content, granulation tissue thickness and vascularity, cell apoptosis, and re-epithelialization were assessed. Angiogenesis was evaluated by immunohistochemistry, quantitative real-time polymerase chain reaction, and Western blot. Results: DBW size was significantly smaller in the HA-CA + ADSCs group (8% ± 2%) compared with the control (16% ± 5%, p < 0.01) and ADSCs (24% ± 17%, p < 0.05) groups. In mice treated with HA-CA + ADSCs, the epidermis was regenerated, and skin thickness was restored. CD31 and von Willebrand factor-positive vessels were detected in mice treated with HA-CA + ADSCs. The mRNA and protein levels of VEGF, IGF-1, FGF-2, ANG-1, PIK, and AKT in the HA-CA + ADSCs group were the highest among all groups, although the Spred1 and ERK expression levels remained unchanged. Conclusions: The combination of HA-CA and ADSCs provided synergistic wound healing effects by maximizing paracrine signaling and angiogenesis via the PI3K/AKT pathway. Therefore, ADSC-loaded HA-CA might represent a novel strategy for the treatment of DBW.

An Injectable Fibrin Scaffold Rich in Growth Factors for Skin Repair

Platelet aggregates, such as PRP, PRF, and CGF, have been used alone or in combination with other grafting materials to enhance restoration outcomes. The process for preparing these autografting materials requires two-step centrifugation or specific centrifuges. In this study, we obtained an injectable fibrin scaffold (IFS) rich in growth factors by one-step centrifugation of whole blood from rabbits. The purpose of this study is to introduce some characteristics of IFS. This scaffold was characterized using various techniques, including Masson's trichrome staining, scanning electron microscopy, porosity measurements, and cell counting. The sustained release of growth factors, including PDGF, VEGF, TGF-β1, IGF, FGF, and EGF, was quantified using ELISA assay. The obtained IFS was tested for its effects on cell proliferation, extracellular matrix deposition, and full-thickness skin defect repair. The prepared IFS is characterized by a loose fibrin network structure with white blood cells and platelets that slowly release growth factors and can promote the healing of skin defects via the promotion of cell proliferation, collagen deposition, and tissue revascularization. In addition, its liquid properties and porous structure are conducive to its application as a therapeutic component in tissue engineering.

SDF-1α Gene-Activated Collagen Scaffold Restores Pro-Angiogenic Wound Healing Features in Human Diabetic Adipose-Derived Stem Cells

Non-healing diabetic foot ulcers (DFUs) can lead to leg amputation in diabetic patients. Autologous stem cell therapy holds some potential to solve this problem; however, diabetic stem cells are relatively dysfunctional and restrictive in their wound healing abilities. This study sought to explore if a novel collagen-chondroitin sulfate (coll-CS) scaffold, functionalized with polyplex nanoparticles carrying the gene encoding for stromal-derived factor-1 alpha (SDF-1α gene-activated scaffold), can enhance the regenerative functionality of human diabetic adipose-derived stem cells (ADSCs). We assessed the impact of the gene-activated scaffold on diabetic ADSCs by comparing their response against healthy ADSCs cultured on a gene-free scaffold over two weeks. Overall, we found that the gene-activated scaffold could restore the pro-angiogenic regenerative response in the human diabetic ADSCs similar to the healthy ADSCs on the gene-free scaffold. Gene and protein expression analysis revealed that the gene-activated scaffold induced the overexpression of SDF-1α in diabetic ADSCs and engaged the receptor CXCR7, causing downstream β-arrestin signaling, as effectively as the transfected healthy ADSCs. The transfected diabetic ADSCs also exhibited pro-wound healing features characterized by active matrix remodeling of the provisional fibronectin matrix and basement membrane protein collagen IV. The gene-activated scaffold also induced a controlled pro-healing response in the healthy ADSCs by disabling early developmental factors signaling while promoting the expression of tissue remodeling components. Conclusively, we show that the SDF-1α gene-activated scaffold can overcome the deficiencies associated with diabetic ADSCs, paving the way for autologous stem cell therapies combined with novel biomaterials to treat DFUs.

Glycocalyx disruption enhances motility, proliferation and collagen synthesis in diabetic fibroblasts

Impaired wound healing represents one of the most debilitating side effects of Diabetes mellitus. Though the role of fibroblasts in wound healing is well-known, the extent to which their function is altered in the context of diabetes remains incompletely understood. Here, we address this question by comparing the phenotypes of healthy dermal fibroblasts (HDFs) and diabetic dermal fibroblasts (DDFs). We show that DDFs are more elongated but less motile and less contractile than HDFs. Reduced motility of DDFs is attributed to formation of larger focal adhesions stabilized by a bulky glycocalyx, associated with increased expression of the cell surface glycoprotein mucin 16 (MUC 16). Disruption of the glycocalyx not only restored DDF motility to levels comparable to that of HDFs, but also led to increased proliferation and collagen synthesis. Collectively, our results illustrate the influence of glycocalyx disruption on mechanics of diabetic fibroblasts relevant to cell motility.

SDF-1α gene-activated collagen scaffold drives functional differentiation of human Schwann cells for wound healing applications

Enhancing angiogenesis is the prime target of current biomaterial-based wound healing strategies. However, these approaches largely overlook the angiogenic role of the cells of the nervous system. Therefore, we explored the role of a collagen-chondroitin sulfate scaffold functionalized with a proangiogenic gene stromal-derived factor-1α (SDF-1α)-an SDF-1α gene-activated scaffold on the functional regulation of human Schwann cells (SCs). A preliminary 2D study was conducted by delivering plasmids encoding for the SDF-1α gene into a monolayer of SCs using polyethyleneimine-based nanoparticles. The delivery of the SDF-1α gene into the SCs enhanced the production of proangiogenic vascular endothelial growth factor (VEGF). Subsequently, we investigated the impact of SDF-1α gene-activated scaffold (3D) on the SCs for 2 weeks, using a gene-free scaffold as control. The transfection of the SCs within the gene-activated scaffold resulted in transient overexpression of SDF-1α transcripts and triggered the production of bioactive VEGF that enhanced endothelial angiogenesis. The overexpression of SDF-1α also caused transient activation of the transcription factor c-Jun and supported the differentiation of SCs towards a repair phenotype. This was characterized by elevated expression of neurotrophin receptor p75NGFR. During this developmental stage, the SCs also performed an extensive remodelling of the basement matrix (fibronectin, collagen IV, and laminin) to enrich their environment with the pro-neurogenic matrix protein laminin, revealing an enhanced pro-neurogenic behavior. Together, this study shows that SDF-1α gene-activated scaffold is a highly bioinstructive scaffold capable of enhancing proangiogenic regenerative response in human SCs for improved wound healing.

Kanglexin accelerates diabetic wound healing by promoting angiogenesis via FGFR1/ERK signaling

Diabetic foot is one of the main causes of non-traumatic amputation. However, there is still lack of effective drugs to treat diabetic foot in clinical practice. Kanglexin (KLX) is a new anthraquinone compound with cardiovascular protective effects. Here we report that KLX accelerates diabetic wound healing by promoting angiogenesis via FGFR1/ERK signaling. Firstly, KM mice were injected (ip) with streptozocin to establish type 1 diabetic model. The full thickness wound with the diameter of 5 mm was prepared on the back of each mice. The wounds were treated with KLX once a day for 14 consecutive days. Results showed that KLX significantly accelerated the closure of diabetic wounds. Pathological studies of skin tissues around the wounds showed that KLX promoted the formation of granulation tissue and new blood vessels, increased collagen deposition and reduced inflammatory cell infiltration. Besides, KLX significantly alleviated advanced glycation end products (AGEs) - induced abnormal proliferation, migration and tubule formation of human umbilical vein endothelial cells (HUVECs), and up-regulated phospho-ERK1/2 both in the diabetic wound tissue and AGEs - treated HUVECs. Moreover, molecular docking results indicated that KLX had the potential to bind with FGF receptor 1 (FGFR1), and subsequent experiments confirmed that FGFR1 inhibitor PD173074 reversed the effect of KLX on promoting the phosphorylation of ERK1/2 and angiogenesis, suggesting that KLX promoted angiogenesis through FGFR1/ERK signaling. In conclusion, our study provides a new effective compound for treating diabetic wounds. More importantly, KLX has the potential to be developed as a topical drug to promote diabetic wound healing.

Nonpharmacological Management of Diabetic Foot Ulcers: An Update

Diabetic foot ulcers (DFUs) are a common and serious complication of diabetes mellitus that is associated with increased morbidity and mortality, as well as substantial economic burden for the health care system. The standard of care for DFUs includes pressure off-loading, sharp debridement, and wound moisture balance, along with infection control and management of peripheral arterial disease. A variety of advanced modalities that target distinct pathophysiological aspects of impaired wound healing in diabetes are being studied as possible adjunct therapies for difficult to heal ulcers. These modalities include growth factors, stem cells, cultured fibroblasts and keratinocytes, bioengineered skin substitutes, acellular bioproducts, human amniotic membranes, oxygen therapy, negative pressure wound therapy, and energy therapies. Additionally, the use of advanced biomaterials and gene delivery systems is being investigated as a method of effective delivery of substances to the wound bed. In the present narrative review, we outline the latest advances in the nonpharmacological management of DFUs and summarize the efficacy of various standard and advanced treatment modalities.

Skin wound healing assisted by angiogenic targeted tissue engineering: A comprehensive review of bioengineered approaches

Skin injuries and in particular, chronic wounds, are one of the major prevalent medical problems, worldwide. Due to the pivotal role of angiogenesis in tissue regeneration, impaired angiogenesis can cause several complications during the wound healing process and skin regeneration. Therefore, induction or promotion of angiogenesis can be considered as a promising approach to accelerate wound healing. This article presents a comprehensive overview of current and emerging angiogenesis induction methods applied in several studies for skin regeneration, which are classified into the cell, growth factor, scaffold, and biological/chemical compound-based strategies. In addition, the advantages and disadvantages of these angiogenic strategies along with related research examples are discussed in order to demonstrate their potential in the treatment of wounds.

Challenges and New Therapeutic Approaches in the Management of Chronic Wounds

Chronic non-healing wounds are estimated to cost the US healthcare $28-$31 billion per year. Diabetic ulcers, arterial and venous ulcers, and pressure ulcers are some of the most common types of chronic wounds. The burden of chronic wounds continues to rise due to the current epidemic of obesity and diabetes and the increase in elderly adults in the population who are more vulnerable to chronic wounds than younger individuals. This patient population is also highly vulnerable to debilitating infections caused by opportunistic and multi-drug resistant pathogens. Reduced microcirculation, decreased availability of cytokines and growth factors that promote wound closure and healing, and infections by multi-drug resistant and biofilm forming microbes are some of the critical factors that contribute to the development of chronic non-healing wounds. This review discusses novel approaches to understand chronic wound pathology and methods to improve chronic wound care, particularly when chronic wounds are infected by multi-drug resistant, biofilm forming microbes.

Size effect of human epidermal growth factor-conjugated polystyrene particles on cell proliferation

Conjugation of growth factors to a carrier is a favorable method to improve their efficacy as therapeutic molecules. Here, we report the carrier size effect on bioactivity of human epidermal growth factor (hEGF) conjugated to polystyrene particles. BALB/3T3 cells were treated with hEGF-conjugated particles (hEGF-conjs) sized from 20 to 1000 nm. At hEGF concentrations less than 0.5 ng ml^-1, free hEGF was more potent than the hEGF-conjs at inducing cell proliferation. However, cell proliferation was size-dependent at higher concentrations of hEGF i.e. hEGF-conjs sized equal to or less than 200 nm displayed lower cell proliferation, compared to free hEGF, but larger particles showed increased cell proliferation. This is in agreement with previous studies showing accumulation of activated-EGFRs in early endosomes triggers apoptosis of A431 and HeLa cells. The confocal microscopy and co-localization fluorescence staining showed the 500 and 1000 nm hEGF-conjs exclusively remained on the cell surface, probably enabling them to activate EGF receptors for a longer time. Conversely, smaller particles were mostly inside the cells, indicating their rapid endocytosis. Similarly, A431 cells treated with 20 nm hEGF-conj, endocytosed the particles and experienced decreased cell proliferation, while the 500 and 1000 nm hEGF-conjs were not internalized, and induced partial cell proliferation. Moreover, we showed multivalency of hEGF-conjs is not the cause of enhanced cell proliferation by large particles, as the degree of EGFR phosphorylation by free EGF was higher, compared to hEGF-conjs. Our results suggest the potential of micron-sized particles as a carrier for hEGF to enhance cell proliferation, which could be explored as a promising approach for topical application of growth factors for accelerating wound healing.