Tissue engineering of skin and regenerative medicine for wound care

Chitosan alchemy: transforming tissue engineering and wound healing

Chitosan, a biopolymer acquired from chitin, has emerged as a versatile and favorable material in the domain of tissue engineering and wound healing. Its biocompatibility, biodegradability, and antimicrobial characteristics make it a suitable candidate for these applications. In tissue engineering, chitosan-based formulations have garnered substantial attention as they have the ability to mimic the extracellular matrix, furnishing an optimal microenvironment for cell adhesion, proliferation, and differentiation. In the realm of wound healing, chitosan-based dressings have revealed exceptional characteristics. They maintain a moist wound environment, expedite wound closure, and prevent infections. These formulations provide controlled release mechanisms, assuring sustained delivery of bioactive molecules to the wound area. Chitosan's immunomodulatory properties have also been investigated to govern the inflammatory reaction during wound healing, fostering a balanced healing procedure. In summary, recent progress in chitosan-based formulations portrays a substantial stride in tissue engineering and wound healing. These innovative approaches hold great promise for enhancing patient outcomes, diminishing healing times, and minimizing complications in clinical settings. Continued research and development in this field are anticipated to lead to even more sophisticated chitosan-based formulations for tissue repair and wound management. The integration of chitosan with emergent technologies emphasizes its potential as a cornerstone in the future of regenerative medicine and wound care. Initially, this review provides an outline of sources and unique properties of chitosan, followed by recent signs of progress in chitosan-based formulations for tissue engineering and wound healing, underscoring their potential and innovative strategies.

Recent advances in molecular mechanisms of skin wound healing and its treatments

The skin, being a multifaceted organ, performs a pivotal function in the complicated wound-healing procedure, which encompasses the triggering of several cellular entities and signaling cascades. Aberrations in the typical healing process of wounds may result in atypical scar development and the establishment of a persistent condition, rendering patients more vulnerable to infections. Chronic burns and wounds have a detrimental effect on the overall quality of life of patients, resulting in higher levels of physical discomfort and socio-economic complexities. The occurrence and frequency of prolonged wounds are on the rise as a result of aging people, hence contributing to escalated expenditures within the healthcare system. The clinical evaluation and treatment of chronic wounds continue to pose challenges despite the advancement of different therapeutic approaches. This is mainly owing to the prolonged treatment duration and intricate processes involved in wound healing. Many conventional methods, such as the administration of growth factors, the use of wound dressings, and the application of skin grafts, are used to ease the process of wound healing across diverse wound types. Nevertheless, these therapeutic approaches may only be practical for some wounds, highlighting the need to advance alternative treatment modalities. Novel wound care technologies, such as nanotherapeutics, stem cell treatment, and 3D bioprinting, aim to improve therapeutic efficacy, prioritize skin regeneration, and minimize adverse effects. This review provides an updated overview of recent advancements in chronic wound healing and therapeutic management using innovative approaches.

The crystallization properties of antifreeze GelMA hydrogel and its application in cryopreservation of tissue-engineered skin constructs

Gelatin methacrylate (GelMA) hydrogels are expected to be ideal skin tissue engineering dressings for a wide range of clinical treatments. Herein, we report the preparation of GelMA or antifreeze GelMA hydrogel sheets with different GelMA concentrations, crosslinking times, and cryoprotectant (CPA) concentrations. The crystallization properties of GelMA or antifreeze GelMA hydrogel sheets were studied by cryomicroscopy and differential scanning calorimetry (DSC). It was found that the growth of ice crystals was slower when GelMA hydrogel concentration was more than 7%. The 10% DMSO-7% GelMA hydrogel sheets crosslinked for 60 min showed no ice crystal formation and growth during cooling and warming. The DSC results showed that the vitrification temperature of the 10% DMSO-7% GelMA hydrogel sheet was -111°C. Furthermore, slow freezing and rapid freezing of fibroblast-laden GelMA or antifreeze GelMA hydrogel sheets, and tissue-engineered skin constructs were studied. The results showed no significant difference in cell survival between slow (88.8% ± 1.51) and rapid (89.2% ± 3.00) freezing of fibroblast-loaded 10% DMSO-7% GelMA hydrogel sheets, and significantly higher than that of 7% GelMA hydrogel sheets (33.4% ± 5.46). The cell viability was higher in tissue-engineered skin constructs after slow freezing (86.34% ± 1.45) than rapid freezing (72.74% ± 1.34). We believe that the combination of antifreeze hydrogels and tissue engineering will facilitate the cryopreservation of tissue engineering constructs.

Biological scaffold as potential platforms for stem cells: Current development and applications in wound healing

Wound repair is a complex challenge for both clinical practitioners and researchers. Conventional approaches for wound repair have several limitations. Stem cell-based therapy has emerged as a novel strategy to address this issue, exhibiting significant potential for enhancing wound healing rates, improving wound quality, and promoting skin regeneration. However, the use of stem cells in skin regeneration presents several challenges. Recently, stem cells and biomaterials have been identified as crucial components of the wound-healing process. Combination therapy involving the development of biocompatible scaffolds, accompanying cells, multiple biological factors, and structures resembling the natural extracellular matrix (ECM) has gained considerable attention. Biological scaffolds encompass a range of biomaterials that serve as platforms for seeding stem cells, providing them with an environment conducive to growth, similar to that of the ECM. These scaffolds facilitate the delivery and application of stem cells for tissue regeneration and wound healing. This article provides a comprehensive review of the current developments and applications of biological scaffolds for stem cells in wound healing, emphasizing their capacity to facilitate stem cell adhesion, proliferation, differentiation, and paracrine functions. Additionally, we identify the pivotal characteristics of the scaffolds that contribute to enhanced cellular activity.

Electrospun nanofibers as advanced wound dressing materials: comparative analysis of single-layered and multilayered nanofibers containing polycaprolactone, methylcellulose, and polyvinyl alcohol

The dressing materials that provide surface protection, bacteriostatic activities, and tissue regeneration are important for the treatment and management of complex wounds. This study aimed to evaluate the wound-healing properties of electrospun nanofibers containing a blend of methylcellulose (MC) and polyvinyl alcohol (PVA). The nanofibers were tested in single-layered (S-NFs) and multilayered (M-NFs) forms (PCL/MC-PVA/PCL). In vitro scratch assay using L929 cells and in vivo experiments on Wistar rats were conducted. The results showed that both S-NFs and M-NFs significantly accelerated wound closure by promoting cell migration. M-NFs demonstrated superior wound healing activity compared to S-NFs. Additionally, M-NFs exhibited faster skin epithelization compared to S-NFs. Histopathological evaluation confirmed the absence of irritation or lesions on the healed wound surface. Overall, the study concluded that these polymeric nanofibers have the potential to be used as self-wound healing dressings. They are safe, non-toxic, biodegradable, and biocompatible.

Recent progress and treatment strategy of pectin polysaccharide based tissue engineering scaffolds in cancer therapy, wound healing and cartilage regeneration

Natural polymers and its mixtures in the form of films, sponges and hydrogels are playing a major role in tissue engineering and regenerative medicine. Hydrogels have been extensively investigated as standalone materials for drug delivery purposes as they enable effective encapsulation and sustained release of drugs. Biopolymers are widely utilised in the fabrication of hydrogels due to their safety, biocompatibility, low toxicity, and regulated breakdown by human enzymes. Among all the biopolymers, polysaccharide-based polymer is well suited to overcome the limitations of traditional wound dressing materials. Pectin is a polysaccharide which can be extracted from different plant sources and is used in various pharmaceutical and biomedical applications including cartilage regeneration. Pectin itself cannot be employed as scaffolds for tissue engineering since it decomposes quickly. This article discusses recent research and developments on pectin polysaccharide, including its types, origins, applications, and potential demands for use in AI-mediated scaffolds. It also covers the materials-design process, strategy for implementation to material selection and fabrication methods for evaluation. Finally, we discuss unmet requirements and current obstacles in the development of optimal materials for wound healing and bone-tissue regeneration, as well as emerging strategies in the field.

A potential bilayer skin substitute based on electrospun silk-elastin-like protein nanofiber membrane covered with bacterial cellulose

Skin substitutes are designed to promote wound healing by replacing extracellular matrix. Silk-elastin-like protein is a renewable extracellular matrix-like material that integrated the advantages of silk and elastin-like protein. In this study, electrospun silk-elastin-like protein (SELP) nanofiber membrane covered with bacterial cellulose (BC) was created as a potential skin substitute to mimic gradient structure of epidermis and dermis of skin. The two layers were glued together using adhesive SELP containing 3,4-dihydroxyphenylalanine (DOPA) converted from tyrosine by tyrosinase. Skin topical drugs commonly used in clinical practice can penetrate through the SELP/BC barrier, and the rate of penetration is proportional to drug concentration. BC with dense fibrous structure can act as a barrier to preserve the inner SELP layer and prevent bacterial invasion, with a blocking permeation efficiency over 99% against four species of bacteria. Cell experiments demonstrated that the reticular fibers of SELP could provide an appropriate growth environment for skin cells proliferation and adhesion, which is considered to promote tissue repair and regeneration. The promising results support this strategy to fabricate a silk-elastin-like protein-based biomaterial for skin substitutes in the clinical treatment of full skin injuries and ulcers.

Human Placenta-Derived Mesenchymal Stem Cells Combined With Artificial Dermal Scaffold Enhance Wound Healing in a Tendon-Exposed Wound of a Rabbit Model

To overcome the difficulty of vascular regeneration in exposed tendon wounds, we combined human placenta-derived mesenchymal stem cells (hPMSCs) with an artificial dermal scaffold and assessed their role in promoting vascular regeneration and wound healing in vivo. hPMSCs were isolated from the human placenta and characterized based on their morphology, phenotypic profiles, and pluripotency. New Zealand rabbits were used to establish an exposed tendon wound model, and hPMSCs and artificial dermal scaffolds were transplanted into the wounds. The results of gross wound observations and pathological sections showed that hPMSCs combined with artificial dermal scaffold transplantation increased the vascularization area of the wound, promoted wound healing, and increased the survival rate of autologous skin transplantation. Following artificial dermal scaffold transplantation, hPMSCs accelerated the vascularization of the dermal scaffold, and the number of fibroblasts, collagen fibers, and neovascularization in the dermal scaffold after 1 week were much higher than those in the control group. Immunohistochemical staining further confirmed that the expression of the vascular endothelial cell marker, CD31, was significantly higher in the combined transplantation group than in the dermal scaffold transplantation group. Our findings demonstrated that hPMSCs seeded onto artificial dermal scaffold could facilitate vascularization of the dermal scaffold and improve tendon-exposed wound healing.

Cerium oxide nanoparticles: Synthesis methods and applications in wound healing

Wound care and treatment can be critical from a clinical standpoint. While different strategies for the management and treatment of skin wounds have been developed, the limitations inherent in the current approaches necessitate the development of more effective alternative strategies. Advances in tissue engineering have resulted in the development of novel promising approaches for accelerating wound healing. The use of various biomaterials capable of accelerating the regeneration of damaged tissue is critical in tissue engineering. In this regard, cerium oxide nanoparticles (CeO2 NPs) have recently received much attention because of their excellent biological properties, such as antibacterial, anti-inflammatory, antioxidant, and angiogenic features. The incorporation of CeO2 NPs into various polymer-based scaffolds developed for wound healing applications has led to accelerated wound healing due to the presence of CeO2 NPs. This paper discusses the structure and functions of the skin, the wound healing process, different methods for the synthesis of CeO2 NPs, the biological properties of CeO2 NPs, the role of CeO2 NPs in wound healing, the use of scaffolds containing CeO2 NPs for wound healing applications, and the potential toxicity of CeO2 NPs.

Artificial dermis combined with skin grafting for the treatment of hand skin and soft tissue defects and exposure of bone and tendon

BACKGROUND

The recovery time of hand wounds is long, which can easily result in chronic and refractory wounds, making the wounds unable to be properly repaired. The treatment cycle is long, the cost is high, and it is prone to recurrence and disability. Double layer artificial dermis combined with autologous skin transplantation has been used to repair hypertrophic scars, deep burn wounds, exposed bone and tendon wounds, and post tumor wounds.

AIM

To investigate the therapeutic efficacy of autologous skin graft transplantation in conjunction with double-layer artificial dermis in treating finger skin wounds that are chronically refractory and soft tissue defects that expose bone and tendon.

METHODS

Sixty-eight chronic refractory patients with finger skin and soft tissue defects accompanied by bone and tendon exposure who were admitted from July 2021 to June 2022 were included in this study. The observation group was treated with double layer artificial dermis combined with autologous skin graft transplantation (n = 49), while the control group was treated with pedicle skin flap transplantation (n = 17). The treatment status of the two groups of patients was compared, including the time between surgeries and hospital stay. The survival rate of skin grafts/flaps and postoperative wound infections were evaluated using the Vancouver Scar Scale (VSS) for scar scoring at 6 mo after surgery, as well as the sensory injury grading method and two-point resolution test to assess the recovery of skin sensation at 6 mo. The satisfaction of the two groups of patients was also compared.

RESULTS

Wound healing time in the observation group was significantly longer than that in the control group (P < 0.05, 27.92 ± 3.25 d vs 19.68 ± 6.91 d); there was no significant difference in the survival rate of skin grafts/flaps between the two patient groups (P > 0.05, 95.1 ± 5.0 vs 96.3 ± 5.6). The interval between two surgeries (20.0 ± 4.3 d) and hospital stay (21.0 ± 10.1 d) in the observation group were both significantly shorter than those in the control group (27.5 ± 9.3 d) and (28.4 ± 17.7 d), respectively (P < 0.05). In comparison to postoperative infection (23.5%) and subcutaneous hematoma (11.8%) in the control group, these were considerably lower at (10.2%) and (6.1%) in the observation group. When comparing the two patient groups at six months post-surgery, the excellent and good rate of sensory recovery (91.8%) was significantly higher in the observation group than in the control group (76.5%) (P < 0.05). There was also no statistically significant difference in two point resolution (P > 0.05). The VSS score in the observation group (2.91 ± 1.36) was significantly lower than that in the control group (5.96 ± 1.51), and group satisfaction was significantly higher (P < 0.05, 90.1 ± 6.3 vs 76.3 ± 5.2).

CONCLUSION

The combination of artificial dermis and autologous skin grafting for the treatment of hand tendon exposure wounds has a satisfactory therapeutic effect. It is a safe, effective, and easy to operate treatment method, which is worthy of clinical promotion.

On-Site Construction of a Full-Thickness Skin Equivalent with Endothelial Tube Networks via Multilayer Electrospinning for Wound Coverage

Novel full-thickness skin substitutes are of increasing interest due to the inherent limitations of current models lacking capillary networks. Herein, we developed a novel full-thickness skin tissue containing blood capillary networks through a layer-by-layer assembly approach using a handy electrospinning apparatus and evaluated its skin wound coverage potential in vivo. The average diameter and thickness of fabricated poly-ε-caprolactone-cellulose acetate scaffolds were easily tuned in the range of 474 ± 77-758 ± 113 nm and 9.43 ± 2.23-29.96 ± 5.78 μm by varying electrospinning distance and duration, as indicated by FE-SEM. Besides, keratinocytes exhibited homogeneous differentiation throughout the fibrous matrix prepared with electrospinning distance and duration of 9 cm and 1.5 min within five-layer (5L) epidermal tissues with thickness of 135-150 μm. Moreover, coculture of vascular endothelial cells, circulating fibrocytes, and fibroblasts within the 5L dermis displayed network formation in vitro, resulting in reduced inflammatory factor levels and enhanced integration with the host vasculature in vivo. Additionally, the skin equivalent grafts consisting of the epidermal layer, biomimetic basement membrane, and vascularized dermis layer with an elastic modulus of approximately 11.82 MPa exhibited accelerated wound closure effect indicative of re-epithelialization and neovascularization with long-term cell survival into the host, which was confirmed by wound-healing rate, bioluminescence imaging activity, and histological analysis. It is the first report of a full-thickness skin equivalent constructed using a battery-operated electrospinning apparatus, highlighting its tremendous potential in regenerative medicine.

Quality management overview for the production of a tissue-engineered human skin substitute in Malaysia

Treatments for skin injuries have recently advanced tremendously. Such treatments include allogeneic and xenogeneic transplants and skin substitutes such as tissue-engineered skin, cultured cells, and stem cells. The aim of this paper is to discuss the general overview of the quality assurance and quality control implemented in the manufacturing of cell and tissue product, with emphasis on our experience in the manufacturing of MyDerm®, an autologous bilayered human skin substitute. Manufacturing MyDerm® requires multiple high-risk open manipulation steps, such as tissue processing, cell culture expansion, and skin construct formation. To ensure the safety and efficacy of this product, the good manufacturing practice (GMP) facility should establish a well-designed quality assurance and quality control (QA/QC) programme. Standard operating procedures (SOP) should be implemented to ensure that the manufacturing process is consistent and performed in a controlled manner. All starting materials, including tissue samples, culture media, reagents, and consumables must be verified and tested to confirm their safety, potency, and sterility. The final products should also undergo a QC testing series to guarantee product safety, efficacy, and overall quality. The aseptic techniques of cleanroom operators and the environmental conditions of the facility are also important, as they directly influence the manufacturing of good-quality products. Hence, personnel training and environmental monitoring are necessary to maintain GMP compliance. Furthermore, risk management implementation is another important aspect of QA/QC, as it is used to identify and determine the risk level and to perform risk assessments when necessary. Moreover, procedures for non-conformance reporting should be established to identify, investigate, and correct deviations that occur during manufacturing. This paper provides insight and an overview of the QA/QC aspect during MyDerm® manufacturing in a GMP-compliant facility in the Centre for Tissue Engineering and Regenerative Medicine, Faculty of Medicine, Universiti Kebangsaan Malaysia.

FastSkin® Concept: A Novel Treatment for Complex Acute and Chronic Wound Management

Successful treatments for acute and chronic skin wounds remain challenging. The goal of this proof-of-concept study was to assess the technical feasibility and safety of a novel wound treatment solution, FastSkin®, in a pig model. FastSkin® was prepared from skin micrografts patterned in blood using acoustic waves. Upon coagulation, the graft was transferred on a silicone sheet and placed on wounds. Six full-thickness wounds were created at the back of two pigs and treated with either FastSkin®, split-thickness skin graft (positive control), a gauze coverage (negative control, NC1), or blood patterned without micrografts (negative control, NC2). Silicone sheets were removed after 7, 14, and 21 days. Wound healing was monitored for six weeks and evaluated macroscopically for re-epithelialization and morphometrically for residual wound area and wound contraction. Tissue regeneration was assessed with histology after six weeks. Re-epithelialization was faster in wounds covered with FastSkin® treatments compared to NC2 and in NC2 compared to NC1. Importantly, an enhanced collagen organization was observed in FastSkin® in contrast to NC treatments. In summary, two clinically approved skin wound treatments, namely micrografting and blood clot graft, were successfully merged with sound-induced patterning of micrografts to produce an autologous, simple, and biologically active wound treatment concept.

Engineered dermis loaded with confining forces promotes full-thickness wound healing by enhancing vascularisation and epithelialisation

Tissue-engineered skin is ideal for clinical wound repair. Restoration of skin tissue defects using tissue-engineered skin remains a challenge owing to insufficient vascularisation. In our previous study, we developed a 3D bioprinted model with confined force loading and demonstrated that the confined force can affect vascular branching, which is regulated by the YAP signalling pathway. The mechanical properties of the model must be optimised to suture the wound edges. In this study, we explored the ability of a GelMA-HAMA-fibrin scaffold to support the confined forces created by 3D bioprinting and promote vascularisation and wound healing. The shape of the GelMA-HAMA-fibrin scaffold containing 3% GelMA was affected by the confined forces produced by the embedded cells. The GelMA-HAMA-fibrin scaffold was easy to print, had optimal mechanical properties, and was biocompatible. The constructs were successfully sutured together after 14 d of culture. Scaffolds seeded with cells were transplanted into skin tissue defects in nude mice, demonstrating that the cell-seeded GelMA-HAMA-fibrin scaffold, under confined force loading, promoted neovascularisation and wound restoration by enhancing blood vessel connections, creating a patterned surface, growth factors, and collagen deposition. These results provide further insights into the production of hydrogel composite materials as tissue-engineered scaffolds under an internal mechanical load that can enhance vascularisation and offer new treatment methods for wound healing. STATEMENT OF SIGNIFICANCE: Tissue-engineered skin is ideal for use in clinical wound repair. However, treatment of tissue defects using synthetic scaffolds remains challenging, mainly due to slow and insufficient vascularization. Our previous study developed a 3D bioprinted model with confined force loading, and demonstrated that confined force can affect vascular branching regulated by the YAP signal pathway. The mechanical properties of the construct need to be optimized for suturing to the edges of wounds. Here, we investigated the ability of a GelMA-HAMA-fibrin scaffold to support the confined forces created by 3D bioprinting and promote vascularization in vitro and wound healing in vivo. Our findings provide new insight into the development of degradable macroporous composite materials with mechanical stimulation as tissue-engineered scaffolds with enhanced vascularization, and also provide new treatment options for wound healing.

Artificial Skin Therapies; Strategy for Product Development

Significance: Tissue-engineered artificial skin for clinical reconstruction can be regarded as an established practice. Bi-layered skin equivalents are available as established allogenic or autologous therapy, and various acellular skin replacements can support tissue repair. Moreover, there is considerable commonality between the skin and other soft tissue reconstruction products. This article presents an attempt to create a comprehensive global landscape review of advanced replacement materials and associated strategies for skin and soft tissue reconstruction. Recent Advances: There has been rapid growth in the number of commercial and pre-commercial products over the past decade. In this survey, 263 base products for advanced skin therapy have been identified, across 8 therapeutic categories, giving over 350 products in total. The largest market is in the United States, followed by the E.U. zone. However, despite these advances, and the investment of resources in each product development, there are key issues concerning the clinical efficacy, cost-benefit of products, and clinical impact. Each therapeutic strategy has relative merits and limitations. Critical Issues: A critical consideration in developing and evaluating products is the therapeutic modality, associated regulatory processes, and the potential for clinical adoption geographically, determined by regulatory territory, intellectual property, and commercial distribution factors. The survey identifies an opportunity for developments that improve basic efficacy or cost-benefit. Future Directions: The economic pressures on health care systems, compounded by the demands of our increasingly ageing population, and the imperative to distribute effective health care, create an urgent global need for effective and affordable products.

The application and progress of tissue engineering and biomaterial scaffolds for total auricular reconstruction in microtia

Microtia is a congenital deformity of the ear with an incidence of about 0.8-4.2 per 10,000 births. Total auricular reconstruction is the preferred treatment of microtia at present, and one of the core technologies is the preparation of cartilage scaffolds. Autologous costal cartilage is recognized as the best material source for constructing scaffold platforms. However, costal cartilage harvest can lead to donor-site injuries such as pneumothorax, postoperative pain, chest wall scar and deformity. Therefore, with the need of alternative to autologous cartilage, in vitro and in vivo studies of biomaterial scaffolds and cartilage tissue engineering have gradually become novel research hot points in auricular reconstruction research. Tissue-engineered cartilage possesses obvious advantages including non-rejection, minimally invasive or non-invasive, the potential of large-scale production to ensure sufficient donors and controllable morphology. Exploration and advancements of tissue-engineered cartilaginous framework are also emerging in aspects including three-dimensional biomaterial scaffolds, acquisition of seed cells and chondrocytes, 3D printing techniques, inducing factors for chondrogenesis and so on, which has greatly promoted the research process of biomaterial substitute. This review discussed the development, current application and research progress of cartilage tissue engineering in auricular reconstruction, particularly the usage and creation of biomaterial scaffolds. The development and selection of various types of seed cells and inducing factors to stimulate chondrogenic differentiation in auricular cartilage were also highlighted. There are still confronted challenges before the clinical application becomes widely available for patients, and its long-term effect remains to be evaluated. We hope to provide guidance for future research directions of biomaterials as an alternative to autologous cartilage in ear reconstruction, and finally benefit the transformation and clinical application of cartilage tissue engineering and biomaterials in microtia treatment.

Polymeric biomaterials for wound healing

Skin indicates a person's state of health and is so important that it influences a person's emotional and psychological behavior. In this context, the effective treatment of wounds is a major concern, since several conventional wound healing materials have not been able to provide adequate healing, often leading to scar formation. Hence, the development of innovative biomaterials for wound healing is essential. Natural and synthetic polymers are used extensively for wound dressings and scaffold production. Both natural and synthetic polymers have beneficial properties and limitations, so they are often used in combination to overcome overcome their individual limitations. The use of different polymers in the production of biomaterials has proven to be a promising alternative for the treatment of wounds, as their capacity to accelerate the healing process has been demonstrated in many studies. Thus, this work focuses on describing several currently commercially available solutions used for the management of skin wounds, such as polymeric biomaterials for skin substitutes. New directions, strategies, and innovative technologies for the design of polymeric biomaterials are also addressed, providing solutions for deep burns, personalized care and faster healing.

Tissue Extract from Brittle Star Undergoing Arm Regeneration Promotes Wound Healing in Rat

This study set out to evaluate the wound healing properties of brittle star extracts in vitro and in vivo. Due to the great arm regeneration potential of the brittle star, Ophiocoma cynthiae, the present study aimed to evaluate the wound healing effect of hydroalcoholic extracts of brittle star undergoing arm regeneration in wound healing models. The brittle star samples were collected from Nayband Bay, Bushehr, Iran. After wound induction in the arm of brittle stars, hydroalcoholic extracts relating to different times of arm regeneration were prepared. The GC-MS analysis, in vitro MTT cell viability and cell migration, Western blot, and computational analysis tests were performed. Based on the in vitro findings, two BSEs were chosen for in vivo testing. Macroscopic, histopathological and biochemical evaluations were performed after treatments. The results showed positive proliferative effects of BSEs. Specifically, forty-two compounds were detected in all groups of BSEs using GC-MS analysis, and their biological activities were assessed. The MTT assay showed that the 14 d BSE had a higher proliferative effect on HFF cells than 7 d BSE. The cell migration assay showed that the wound area in 7 d and 14 d BSEs was significantly lower than in the control group. Western blot analysis demonstrated an increase in the expression of proliferation-related proteins. Upon the computational analysis, a strong affinity of some compounds with proteins was observed. The in vivo analysis showed that the evaluation of wound changes and the percentage of wound healing in cell migration assay in the 7 d BSE group was better than in the other groups. Histopathological scores of the 7 d BSE and 14 d BSE groups were significantly higher than in the other groups. In conclusion, the hydroalcoholic extract of O. cynthiae undergoing arm regeneration after 7 and 14 days promoted the wound healing process in the cell and rat skin wound healing model due to their proliferative and migratory biological activity.

Autologous Skin Grafts, versus Tissue-engineered Skin Constructs: A Systematic Review and Meta-analysis

For over 100 years, autologous skin grafts have remained the gold standard for the reconstruction of wounds but are limited in availability. Acellular tissue-engineered skin constructs (acellular TCs) and cellular tissue-engineered skin constructs (cellular TCs) may address these limitations. This systematic review and meta-analysis compare outcomes between them.

Methods

A systematic review was conducted using PRISMA guidelines, querying MEDLINE, Embase, Web of Science, and Cochrane to assess graft incorporation, failure, and wound healing. Case reports/series, reviews, in vitro/in vivo work, non-English articles or articles without full text were excluded.

Results

Sixty-six articles encompassing 4076 patients were included. No significant differences were found between graft failure rates (P = 0.07) and mean difference of percent reepithelialization (p = 0.92) when split-thickness skin grafts were applied alone versus co-grafted with acellular TCs. Similar mean Vancouver Scar Scale was found for these two groups (p = 0.09). Twenty-one studies used at least one cellular TC. Weighted averages from pooled results did not reveal statistically significant differences in mean reepithelialization or failure rates for epidermal cellular TCs compared with split-thickness skin grafts (p = 0.55).

Conclusions

This systematic review is the first to illustrate comparable functional and wound healing outcomes between split-thickness skin grafts alone and those co-grafted with acellular TCs. The use of cellular TCs seems promising from preliminary findings. However, these results are limited in clinical applicability due to the heterogeneity of study data, and further level 1 evidence is required to determine the safety and efficacy of these constructs.

Return to Sports and Functional Outcomes after Autologous Platelet-Rich Fibrin Matrix (PRFM) and Debridement in Midportion Achilles Tendinopathy: A Case Series with 24-Month Follow-Up

(1) Background: Achilles tendinopathy (AT) is characterized by load-induced tendon pain, stiffness, and functional impairment that may affect the tendon midportion or insertion. Platelet-rich fibrin matrix (PRFM) is a promising adjunctive therapy for AT. We analyzed 24-month pain and functional outcomes in a cohort of patients managed by tendon debridement and autologous PRFM application to determine whether the combined treatment ensured an early return to sports/work and satisfactory clinical outcomes and functional scores. (2) Methods: The 24-month outcomes of 32 sport-practicing patients with chronic midportion AT treated with debridement and autologous PRFM were evaluated in terms of time to return to sports/work. The AOFAS and VISA-A were computed preoperatively and at 6 and 24 months. Blazina scores were evaluated preoperatively and at 6 months; ankle range of motion was assessed at 1, 6, 12, 24 months; and patient satisfaction was assessed at 24 months. (3) Results: Altogether, all patients had resumed their sport(s) activity, at the same or higher level, after 25.41 days (±5.37). Regarding work, all patients were able to return to their jobs after 16.41 days (±2.43). Ankle dorsiflexion and plantarflexion increased significantly: the AOFAS rose from 54.56 (±6.47) to 97.06 (±4.06) and 98.88 (±2.21) at 6 and 12 months, respectively, and the mean VISA-A score rose from 69.16 (±7.35) preoperatively to 95.03 (±4.67) and 97.28 (±2.43) at 6 and 12 months, respectively, after treatment. There were no complications. Most (90.62%) patients were very satisfied. (4) Conclusions: In symptomatic midportion AT, surgical debridement and autologous PRFM ensured a fast return to sports/work (4 weeks), significantly improving AOFAS and VISA-A and Blazina scores already at 6 months and providing excellent clinical outcomes at 24 months.

Tissue Engineering-Based Strategies for Diabetic Foot Ulcer Management

Significance: Diabetic foot ulcers (DFU) are a mounting problem with the increasingly frail population. Injuries that would otherwise heal are kept open by risk factors such as diabetes, obesity, and age-related conditions, which interferes with the natural wound healing processes. Recent Advances: This review summarizes recent advancements in the field of tissue engineering for the treatment of DFUs. FDA-approved approaches, including signaling-based therapies, stem cell therapies, and skin substitutes are summarized and cutting-edge experimental technologies that have the potential to manage chronic wounds, such as skin printing, skin organogenesis, skin self-assembly, and prevascularization, are discussed. Critical Issues: The standard of care for chronic wounds involves wound debridement, wound dressings, and resolving the underlying cause such as lowering the glycemic index and reducing wound pressure. Current DFU treatments are limited by low wound closure rates and poor regrown skin quality. New adjuvant therapies that facilitate wound closure in place of or in conjunction with standard care are critically needed. Future Directions: Tissue engineering strategies are limited by the plasticity of adult human cells. In addition to traditional techniques, genetic modification, although currently an emerging technology, has the potential to unlock human regeneration and can be incorporated in future therapeutics.

Biomaterial mediated immunomodulation: An interplay of material environment interaction for ameliorating wound regeneration

Chronic wounds are the outcome of an imbalanced inflammatory response caused by sustenance of immune microenvironment. In this context, tissue engineered graft played great role in healing wounds but faced difficulty in scar remodelling, immune rejection and poor vascularization. All the limitations faced are somewhere linked with the immune cells involved in healing. In this consideration, immunomodulatory biomaterials bridge a large gap with the delivery of modulating factors for triggering key inflammatory cells responsible towards interplay in the wound micro-environment. Inherent physico-chemical properties of biomaterials substantially determine the nature of cell-materials interaction thereby facilitating differential cytokine gradient involved in activation or suppression of inflammatory signalling pathways, and followed by surface marker expression. This review aims to systematically describe the interplay of immune cells involved in different phases in the wound microenvironment and biomaterials. Additionally, it also focuses on modulating innate immune cell responses in the context of triggering the halted phase of the wound healing, i.e., inflammatory phase. The various strategies are highlighted for modulation of wound microenvironment towards wound regeneration including stem cells, cytokines, growth factors, vitamins, and anti-inflammatory agents to induce interactive ability of biomaterials with immune cells. The last section focuses on prospective approaches and current potential strategies for wound regeneration. This includes the development of different models to bridge the gap between mouse models and human patients. Emerging new tools to study inflammatory response owing to biomaterials and novel strategies for modulation of monocyte and macrophage behaviour in the wound environment are also discussed.

Polymeric biomaterials-based tissue engineering for wound healing: a systemic review

Background

Biomaterials are vital products used in clinical sectors as alternatives to several biological macromolecules for tissue engineering techniques owing to their numerous beneficial properties, including wound healing. The healing pattern generally depends upon the type of wounds, and restoration of the skin on damaged areas is greatly dependent on the depth and severity of the injury. The rate of wound healing relies on the type of biomaterials being incorporated for the fabrication of skin substitutes and their stability in in vivo conditions. In this review, a systematic literature search was performed on several databases to identify the most frequently used biomaterials for the development of successful wound healing agents against skin damage, along with their mechanisms of action.

Method

The relevant research articles of the last 5 years were identified, analysed and reviewed in this paper. The meta-analysis was carried out using PRISMA and the search was conducted in major scientific databases. The research of the most recent 5 years, from 2017-2021 was taken into consideration. The collected research papers were inspected thoroughly for further analysis. Recent advances in the utilization of natural and synthetic biomaterials (alone/in combination) to speed up the regeneration rate of injured cells in skin wounds were summarised. Finally, 23 papers were critically reviewed and discussed.

Results

In total, 2022 scholarly articles were retrieved from databases utilizing the aforementioned input methods. After eliminating duplicates and articles published before 2017, ~520 articles remained that were relevant to the topic at hand (biomaterials for wound healing) and could be evaluated for quality. Following different procedures, 23 publications were selected as best fitting for data extraction. Preferred Reporting Items for Systematic Reviews and Meta-Analyses for this review illustrates the selection criteria, such as exclusion and inclusion parameters. The 23 recent publications pointed to the use of both natural and synthetic polymers in wound healing applications. Information related to wound type and the mechanism of action has also been reviewed carefully. The selected publication showed that composites of natural and synthetic polymers were used extensively for both surgical and burn wounds. Extensive research revealed the effects of polymer-based biomaterials in wound healing and their recent advancement.

Conclusions

The effects of biomaterials in wound healing are critically examined in this review. Different biomaterials have been tried to speed up the healing process, however, their success varies with the severity of the wound. However, some of the biomaterials raise questions when applied on a wide scale because of their scarcity, high transportation costs and processing challenges. Therefore, even if a biomaterial has good wound healing qualities, it may be technically unsuitable for use in actual medical scenarios. All of these restrictions have been examined closely in this review.

Rapid culture of human keratinocytes in an autologous, feeder-free system with a novel growth medium

BACKGROUND AIMS

The ability to culture human keratinocytes is beneficial in the treatment of skin injury and disease, as well as for testing chemicals in vitro as a substitute for animal testing.

RESULTS

We have identified a novel culture medium for the rapid growth of keratinocytes from human skin. "Kelch's medium" supports keratinocyte growth that is as rapid as in the classical Rheinwald and Green method, but without the need for cholera toxin or xenogeneic feeder cells. It enables keratinocytes to out-compete co-cultured autologous fibroblasts so that separation of the epidermis from the dermis is no longer required before keratinocyte culture. Enzymatic digests of whole human skin can therefore be used to generate parallel cultures of autologous keratinocytes, fibroblasts and melanocytes simply by using different cell culture media.

CONCLUSIONS

This new keratinocyte medium and the simplified manufacturing procedures it enables are likely to be beneficial in skin engineering, especially for clinical applications.

Understanding the mechanisms of spontaneous and skin-grafted wound repair: the path to engineered skin grafts

Spontaneous wound repair is a complex process that involves overlapping phases of inflammation, proliferation and remodelling, co-ordinated by growth factors and proteases. In extensive wounds such as burns, the repair process would not be achieved in a timely fashion unless grafted. Although spontaneous wound repair has been extensively described, the processes by which wound repair mechanisms mediate graft take are yet to be fully explored. This review describes engraftment stages and summarises current understanding of molecular mechanisms which regulate autologous skin graft healing, with the goal of directing innovation in permanent wound closure with skin substitutes. Graftability and vascularisation of various skin substitutes that are either in the market or in development phase are discussed. In doing so, we cast a spotlight on the paucity of scientific information available as to how skin grafts (both autologous and engineered) heal a wound bed. Better understanding of these processes may assist in developing novel methods of wound management and treatments.

Composition and Performance of Autologous Engineered Skin Substitutes for Repair or Regeneration of Excised, Full-Thickness Burns

Prompt and permanent wound closure after burn injuries remains a requirement for patient recovery. Historically, split-thickness skin autograft (STAG) has served as the prevailing standard of care for closure of extensive, deep burns. Because STAG availability may be insufficient in life-threatening burns, alternatives have been evaluated for safety and efficacy of wound closure. Since the 1970s, alternatives consisting of cultured epidermal keratinocytes, and/or acellular dermal substitutes were studied and translated into services and devices that facilitated wound closure, survival, and recovery after major burns. Cultured epithelial autografts (CEA) promoted epidermal closure of wounds but were not stable during long-term recovery. An acellular dermal substitute consisting of collagen and glycosaminoglycans (C-GAG) provided more uniform dermal repair, and reduced needs for epidermal harvesting but was subject to loss from microbial contamination. More recently, an autologous engineered skin substitute (ESS) has been reported and includes a C-GAG polymer populated with fibroblasts and keratinocytes which form basement membrane. ESS can be applied clinically over a vascularized dermal substitute and generates stable wound closure that is smooth, soft, and strong. Despite these advances, no current alternatives for permanent wound closure restore the anatomy and physiology of uninjured skin. Current alternatives act by mechanisms of wound healing, not by developmental biology by which skin forms in utero with pigment, hair, sweat and sebaceous glands, microvasculature, and nerve. Until full-thickness burns are restored with all of the normal structures and functions of uninjured skin, regenerative medicine of skin will remain an ambitious aspiration for future researchers and engineers to achieve.

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.

Role of small intestinal submucosa extracellular matrix in advanced regenerative wound therapy

Advanced regenerative therapies using cellular and tissue-based products (CTPs) can play an important role in effective management of hard-to-heal wounds. CTPs derived from allogenic or xenogenic tissues use an extracellular matrix (ECM) to provide a therapeutic ECM scaffold in the wound bed to facilitate tissue regeneration. One such example is OASIS Extracellular Matrix (Cook Biotech Incorporated), a porcine small intestinal submucosa extracellular matrix (SIS-ECM) that preclinical and clinical data have shown to be tolerable and effective in promoting tissue regeneration in hard-to-heal wounds.

Role of small intestinal submucosa extracellular matrix in advanced regenerative wound therapy

Advanced regenerative therapies using cellular and tissue-based products (CTPs) can play an important role in effective management of hard-to-heal wounds. CTPs derived from allogenic or xenogenic tissues use an extracellular matrix (ECM) to provide a therapeutic ECM scaffold in the wound bed to facilitate tissue regeneration. One such example is OASIS Extracellular Matrix (Cook Biotech Incorporated), a porcine small intestinal submucosa extracellular matrix (SIS-ECM) that preclinical and clinical data have shown to be tolerable and effective in promoting tissue regeneration in hard-to-heal wounds.

Skin substitutes for the management of mohs micrographic surgery wounds: a systematic review

The data on skin substitute usage for managing Mohs micrographic surgery (MMS) wounds remain limited. This systematic review aimed to provide an overview of skin substitutes employed for MMS reconstruction, summarize clinical characteristics of patients undergoing skin substitute-based repair after MMS, and identify advantages and limitations of skin substitute implementation. A systematic review of Ovid MEDLINE, EMBASE, Cochrane Library, and Web of Science databases, from inception to April 7, 2021, identified all cases of MMS defects repaired using skin substitutes. A total of 687 patients were included. The mean patient age was 70 years (range: 6-98 years). Commonly used skin substitutes were porcine collagen (n = 397), bovine collagen (n = 78), Integra (n = 53), Hyalofill (n = 43), amnion/chorion-derived grafts (n = 40), and allogeneic epidermal-dermal composite grafts (n = 35). Common factors influencing skin substitute selection were cost, healing efficacy, cosmetic outcome, patient comfort, and ease of use. Some articles did not specify patient and wound characteristics. Skin substitute usage in MMS reconstruction is not well-guided. Blinded randomized control trials comparing the efficacy of skin substitutes and traditional repair methods are imperative for establishing evidence-based guidelines on skin substitute usage following MMS.

A critical review on starch-based electrospun nanofibrous scaffolds for wound healing application

Starch-based nanofibrous scaffolds exhibit a potential wound healing processes as they are cost-effective, flexible, and biocompatible. Recently, natural polymers have received greater importance in regenerative medicine, mainly in the process of healing wounds and burns due to their unique properties which also include safety, biocompatibility, and biodegradability. In this respect, starch is considered to be one of the reliable natural polymers to promote the process of wound healing at a significantly faster rate. Starch and starch-based electrospun nanofibrous scaffolds have been used for the wound healing process which includes the process of adhesion, proliferation, differentiation, and regeneration of cells. It also possesses significant activity to encapsulate and deliver biomaterials at a specific site which persuades the wound healing process at an increased rate. As the aforementioned scaffolds mimic the native extracellular matrix more closely, may help in the acceleration of wound closure, which in turn may lead to the promotion of tissue reorganization and remodeling. In-depth knowledge in understanding the properties of nanofibrous scaffolds paves a way to unfold novel methods and therapies, also to overcome challenges associated with wound healing. This review is intended to provide comprehensive information and recent advances in starch-based electrospun nanofibrous scaffolds for wound healing.

Continuous tension reduction technique in facial scar management: A comparison of W-plasty and straight-line closure on aesthetic effects in Asian patients

W-plasty is a very popular scar excisional revision technique. The core of the technique is to break up the scar margins into small triangular components, so as to cause light scattering and make the scar less noticeable. However, due to skin tension, facial incision scars tend to spread. Applying W-plasty alone cannot achieve the ideal repair effect of facial scars. In this study, we proposed a scar revision technique combined W-plasty with continuous tension-reduction (CTR) technique to improve the appearance of facial scars. Sixty patients with facial scar were comprised in this retrospective study. Scars were assessed independently using the scar scale before and at 12-month follow-up. Clinical results showed a significant difference in scar appearance between different groups at 12-month follow-up. Vancouver scar scale (VSS), visual analogue scale (VAS) scores, and patient satisfaction were significant better in W-plasty and CTR than other groups at 12-month follow-up. No severe complications were reported. The application of the tension offloading device provides an environment where the tension is continuously reduced, which could greatly decrease tension on the surgical incision. Combined with W-plasty, this technique could significantly improve the scar's aesthetic appearance.

Dual-Action Icariin-Containing Thermosensitive Hydrogel for Wound Macrophage Polarization and Hair-Follicle Neogenesis

Bone morphogenetic protein (BMP) pathway is essential for M2 macrophage polarization and hair-follicle neogenesis. Icariin, a flavonoid derived from Epimedium, is a mediator of the BMP pathway. Here, we develop a hydrogel formulation functionalized with icariin for regulation of macrophage polarization to accelerate wound healing and hair-follicle neogenesis. Compared to skin defects without icariin treatment, those treated with icariin+PEG hydrogel healed faster and had new hair follicles. Results in vivo showed that icariin+PEG hydrogel induced a higher level of M2 phenotypic transformation of macrophages. Moreover, icariin+PEG hydrogel significantly accelerated wound-repair process by reducing the invasion of inflammation, excessive deposition of collagen, immoderate activation of myofibroblasts, and increasing the regeneration of hair follicles. Furthermore, studies in vitro demonstrated that the icariin+PEG hydrogel induced macrophages to polarize to the M2 phenotype and dermal papilla cell to hair follicles. Finally, molecular analysis demonstrated that the icariin+PEG hydrogel increased the expression of BMP4 and Smad1/5 phosphorylation in skin wounds. These results demonstrate the therapeutic potential of icariin-containing thermosensitive hydrogels for inducing M2 macrophage polarization to accelerate wound healing and promote hair-follicle neogenesis by regulating the BMP pathway.

Off-the-shelf acellular fetal skin scaffold as a novel alternative to buccal mucosa graft: the development and characterization of human tissue-engineered fetal matrix in rabbit model of hypospadiasis

AIM

In this study, we aimed to develop a novel alternative to buccal mucosal graft from the acellular human fetal skin to manage hypospadias in a rabbit model. We optimized the decellularization protocol to develop and characterize the human tissue-engineered fetal dermal matrix as an "off-the-shelf" natural biomaterial.

MATERIAL AND METHODS

Human fetal skin was obtained at 16-19 weeks gestational age with respect to a signed informed consent from parents under the university ethical committee approval. The dissected full-thickness fetal skin tissues were placed into SDS and Triton X-100 in different dosages to achieve the optimum decellularization protocol. Histopathology of the acellular fetal matrix was assessed by Hematoxylin & Eosin (H&E) and DAPI staining to confirm the removal of all cell materials, Masson's trichrome staining for collagen evaluation, DNA quantification for confirmation of DNA content, and scanning electron microscopy (SEM) for evaluation of scaffold microstructure. Immunohistochemistry (IHC) staining was used to detect specific dermal markers, namely vimentin, type I collagen, cytokeratin (CK)19. The prepared dermal scaffolds were then grafted on the 8 rabbit models of hypospadias. The rabbits underwent evaluations at 1, 2, 3, and 6 months postoperatively.

RESULTS

H&E, Masson's trichrome, DAPI staining, and SEM confirmed the significant removal of cells; meanwhile, the ECM was completely preserved. At the time of biopsy, after 2, 4, and 6 months, no evidence of inflammation, fibrosis, necrosis, or rejection was observed. The grafted dermal scaffolds appeared histologically and anatomically normal. It was observed that the scaffolds were recellularized by circulating CD 34 + bone marrow stem cells (BMSCs) inside the body, implicating the body as a natural bioreactor.

CONCLUSION

The application of acellular fetal skin (AFS) is a safe and feasible method that can decrease surgical time in a complex hypospadias reconstruction. Moreover, AFS demonstrated excellent angiogenesis characteristics and migration of the stem cells to the scaffold observed during the course of treatment. Novel natural AFS scaffold without cell seeding is an excellent alternative to buccal mucosal graft; hence, it can overcome the limitations concerning the graft size and prevent the creation of wounds in oral mucosal tissue.

Regenerative effect of combined laser and human stem cell-conditioned medium therapy on hypertrophic burn scar

PURPOSE

This study aimed to determine the effect of combined treatment with non-ablative laser and human stem cell-conditioned medium (HSCM) on tissue regeneration after burn-induced hypertrophic scar (HTS) formation.

METHODS

Fourteen patients with HTSs on both sides of the same body part were subjected to three sessions of non-ablative laser treatment, with an interval of four weeks between each treatment. Following laser treatment, HSCM and normal saline were applied to the HTSs of the right (experimental) and left side (control), respectively. Over the next 6 days, HSCM and moisturizer were applied to experimental scars, while only moisturizer was applied to control scars. Skin characteristics were evaluated before laser treatment and on the seventh day after the third laser treatment.

RESULTS

No significant intergroup differences were noted in the initial evaluation (P > 0.05). We found significant differences between the pre- and post-treatment measurements of erythema (P < 0.001), trans-epidermal water loss (TEWL; P < 0.001), and Cutometer® parameters (all parameters; P <0^.05) of experimental scars. Control scars also showed significant differences between pre- and post-treatment measurements of thickness (P = 0.01), erythema (P < 0.001), TEWL (P < 0.001), and Cutometer® parameters (all parameters; P < 0.05). Changes (pre- to post-treatment) in scar thickness between the experimental (-0.003 ± 0.09) and control scars (0.04 ± 0.12) were significant (P = 0.01).

CONCLUSION

These results suggest that HSCM has a positive effect on short-term results when applied after laser treatment of hypertrophic scars.

Role of Cultured Skin Fibroblasts in Regenerative Dermatology

The skin, as the largest organ, covers the entire outer part of the body, and since this organ is directly exposed to microbial, thermal, mechanical and chemical damage, it may be destroyed by factors such as acute trauma, chronic wounds or even surgical interventions. Cell therapy is one of the most important procedures to treat skin lesions. Fibroblasts are cells that are responsible for the synthesis of collagen, elastin, and the organization of extracellular matrix (ECM) components and have many vital functions in wound healing processes. Today, cultured autologous fibroblasts are used to treat wrinkles, scars, wounds and subcutaneous atrophy. The results of many studies have shown that fibroblasts can be effective and beneficial in the treatment of skin lesions. On the other hand, skin substitutes are used as a regenerative model to improve and regenerate the skin. The use of these alternatives, restorative medicine and therapeutic cells such as fibroblasts has tremendous potential in the treatment of skin diseases and can be a new window for the treatment of diseases with no definitive treatment. NO LEVEL ASSIGNED: This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description ofthese Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Highlights on Advancing Frontiers in Tissue Engineering

The field of tissue engineering continues to advance, sometimes in exponential leaps forward, but also sometimes at a rate that does not fulfill the promise that the field imagined a few decades ago. This review is in part a catalog of success in an effort to inform the process of innovation. Tissue engineering has recruited new technologies and developed new methods for engineering tissue constructs that can be used to mitigate or model disease states for study. Key to this antecedent statement is that the scientific effort must be anchored in the needs of a disease state and be working toward a functional product in regenerative medicine. It is this focus on the wildly important ideas coupled with partnered research efforts within both academia and industry that have shown most translational potential. The field continues to thrive and among the most important recent developments are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies that warrant special attention. Developments in the aforementioned areas as well as future directions are highlighted in this article. Although several early efforts have not come to fruition, there are good examples of commercial profitability that merit continued investment in tissue engineering. Impact statement Tissue engineering led to the development of new methods for regenerative medicine and disease models. Among the most important recent developments in tissue engineering are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies. These technologies and an understanding of them will have impact on the success of tissue engineering and its translation to regenerative medicine. Continued investment in tissue engineering will yield products and therapeutics, with both commercial importance and simultaneous disease mitigation.

Polymerizable Skin Hydrogel for Full Thickness Wound Healing

The skin is the largest organ in the human body, comprising the main barrier against the environment. When the skin loses its integrity, it is critical to replace it to prevent water loss and the proliferation of opportunistic infections. For more than 40 years, tissue-engineered skin grafts have been based on the in vitro culture of keratinocytes over different scaffolds, requiring between 3 to 4 weeks of tissue culture before being used clinically. In this study, we describe the development of a polymerizable skin hydrogel consisting of keratinocytes and fibroblast entrapped within a fibrin scaffold. We histologically characterized the construct and evaluated its use on an in vivo wound healing model of skin damage. Our results indicate that the proposed methodology can be used to effectively regenerate skin wounds, avoiding the secondary in vitro culture steps and thus, shortening the time needed until transplantation in comparison with other bilayer skin models. This is achievable due to the instant polymerization of the keratinocytes and fibroblast combination that allows a direct application on the wound. We suggest that the polymerizable skin hydrogel is an inexpensive, easy and rapid treatment that could be transferred into clinical practice in order to improve the treatment of skin wounds.

3D bioprinting of a gelatin-alginate hydrogel for tissue-engineered hair follicle regeneration

Hair follicle (HF) regeneration remains challenging, principally due to the absence of a platform that can successfully generate the microenvironmental cues of hair neogenesis. Here, we demonstrate a 3D bioprinting technique based on a gelatin/alginate hydrogel (GAH) to construct a multilayer composite scaffold simulating the HF microenvironment in vivo. Fibroblasts (FBs), human umbilical vein endothelial cells (HUVECs), dermal papilla cells (DPCs), and epidermal cells (EPCs) were encapsulated in GAH (prepared from a mixture of gelatin and alginate) and respectively 3D-bioprinted into the different layers of a composite scaffold. The bioprinted scaffold with epidermis- and dermis-like structure was subsequently transplanted into full-thickness wounds in nude mice. The multilayer scaffold demonstrated suitable cytocompatibility and increased the proliferation ability of DPCs (1.2-fold; P < 0.05). It also facilitated the formation of self-aggregating DPC spheroids and restored DPC genes associated with hair induction (ALP, β-catenin, and α-SMA). The dermal and epidermal cells self-assembled successfully into immature HFs in vitro. HFs were regenerated in the appropriate orientation in vivo, which can mainly be attributed to the hierarchical grid structure of the scaffold and the dot bioprinting of DPCs. Our 3D printed scaffolds provide a suitable microenvironment for DPCs to regenerate entire HFs and could make a significant contribution in the medical management of hair loss. This method may also have broader applications in skin tissue (and appendage) engineering. STATEMENT OF SIGNIFICANCE: Hair loss remains a challenging clinical problem that influences quality of life. Three-dimensional (3D) bioprinting has become a useful tool for the fabrication of tissue constructs for transplantation and other biomedical applications. In this study, we used a 3D bioprinting technique based on a gelatin/alginate hydrogel to construct a multi-layer composite scaffold with cuticular and corium layers to simulate the microenvironment of dermal papilla cells (DPCs) in the human body. This new approach permits the controllable formation of self-aggregating spheroids of DPCs in a physiologically relevant extracellular matrix and the initiation of epidermal-mesenchymal interactions, which results in HF formation in vivo. The ability to regenerate entire HFs should have a significant impact on the medical management of hair loss.

Strategies to Induce Blood Vessel Ingrowth into Skin Grafts and Tissue-Engineered Substitutes

Skin is a multilayer organ consisting of several tissues and appendages residing in a complex niche. Adequate and physiologically regulated vascularization is an absolute requirement for skin homeostasis, regeneration, and wound healing. The lack of vascular networks and ischemia results in delayed wound closure. In addition, vascularization is critical for the prolonged function and survival of skin grafts and tissue-engineered skin substitutes. This study highlights the clinical challenges associated with the limited vascularization in the cutaneous wounds. Then, we highlight the novel approaches for the development of vascular networks in the skin autografts, allografts, and artificial substitutes. Also, the future directions to overcome the existing vascularization complications in skin grafting and synthetic skin substitutes are presented. Statement of Significance Delayed closure of large dermal wounds, such as burn injuries, results from the lack of vascular networks and ischemia. The amount of blood supply in the skin graft is the primary factor determining the quality of the transplanted grafts. The current skin grafts and their fabrication methods lack the appropriate features that contribute to the vascularization and integration of the wound bed and graft and adherence to the skin layers. Therefore, the new generation of skin grafts should consider advanced technologies to induce vascularization and overcome current challenges.

Tissue engineering in dermatology - from lab to market

Tissue Engineering is a branch of regenerative medical technology which helps replace damaged tissue using appropriate scaffolding, living cells, and growth factors. Using tissue engineering products can be a promising method for treating skin lesions such as wounds and deep burns. The interaction and interconnection of cells within the bio-culture medium or within a three-dimensional scaffold provides the conditions for tissue regeneration and subsequent healing of skin wounds. Tissue engineering in the field of dermatology has evolved over time from a single application of skin cells or biopolymer scaffolds to the use of cell and scaffold combinations for the treatment, repair, and closure of acute and chronic skin wounds. It has evolved. This technology has reached a point where most products are accepted, and the body rejects a small number, which strengthens the tissue engineering market. In this article, we aimed to review and study the market of this field by reviewing various articles on tissue engineering in the field of dermatology. Tissue-engineered skin substitutes are future options for wound healing and tissue regeneration strategies.

An Up-to-Date Review of Biomaterials Application in Wound Management

Whether they are caused by trauma, illness, or surgery, wounds may occur throughout anyone's life. Some injuries' complexity and healing difficulty pose important challenges in the medical field, demanding novel approaches in wound management. A highly researched possibility is applying biomaterials in various forms, ranging from thin protective films, foams, and hydrogels to scaffolds and textiles enriched with drugs and nanoparticles. The synergy of biocompatibility and cell proliferative effects of these materials is reflected in a more rapid wound healing rate and improved structural and functional properties of the newly grown tissue. This paper aims to present the biomaterial dressings and scaffolds suitable for wound management application, reviewing the most recent studies in the field.

Large full-thickness wounded skin regeneration using 3D-printed elastic scaffold with minimal functional unit of skin

Traditional tissue engineering skin are composed of living cells and natural or synthetic scaffold. Besize the time delay and the risk of contamination involved with cell culture, the lack of autologous cell source and the persistence of allogeneic cells in heterologous grafts have limited its application. This study shows a novel tissue engineering functional skin by carrying minimal functional unit of skin (MFUS) in 3D-printed polylactide-co-caprolactone (PLCL) scaffold and collagen gel (PLCL + Col + MFUS). MFUS is full-layer micro skin harvested from rat autologous tail skin. 3D-printed PLCL elastic scaffold has the similar mechanical properties with rat skin which provides a suitable environment for MFUS growing and enhances the skin wound healing. Four large full-thickness skin defects with 30 mm diameter of each wound are created in rat dorsal skin, and treated either with tissue engineering functional skin (PLCL + Col + MFUS), or with 3D-printed PLCL scaffold and collagen gel (PLCL + Col), or with micro skin islands only (Micro skin), or without treatment (Normal healing). The wound treated with PLCL + Col + MFUS heales much faster than the other three groups as evidenced by the fibroblasts migration from fascia to the gap between the MFUS dermis layer, and functional skin with hair follicles and sebaceous gland has been regenerated. The PLCL + Col treated wound heals faster than normal healing wound, but no skin appendages formed in PLCL + Col-treated wound. The wound treated with micro skin islands heals slower than the wounds treated either with tissue engineering skin (PLCL + Col + MFUS) or with PLCL + Col gel. Our results provide a new strategy to use autologous MFUS instead "seed cells" as the bio-resource of engineering skin for large full-thickness skin wound healing.

Applications of the amniotic membrane in tissue engineering and regeneration: the hundred-year challenge

The amniotic membrane (Amnio-M) has various applications in regenerative medicine. It acts as a highly biocompatible natural scaffold and as a source of several types of stem cells and potent growth factors. It also serves as an effective nano-reservoir for drug delivery, thanks to its high entrapment properties. Over the past century, the use of the Amnio-M in the clinic has evolved from a simple sheet for topical applications for skin and corneal repair into more advanced forms, such as micronized dehydrated membrane, amniotic cytokine extract, and solubilized powder injections to regenerate muscles, cartilage, and tendons. This review highlights the development of the Amnio-M over the years and the implication of new and emerging nanotechnology to support expanding its use for tissue engineering and clinical applications.

Epidermolysis Bullosa: A Review of the Tissue-Engineered Skin Substitutes Used to Treat Wounds

Skin wound healing is a crucial process for regenerating healthy skin and avoiding the undesired consequences associated with open skin wounds. For epidermolysis bullosa (EB), a debilitating group of fragile skin disorders currently without a cure, skin blistering can often be severe and heal poorly, increasing susceptibility to life-threatening complications. To prevent these, investigational therapies have been exploring the use of tissue-engineered skin substitutes (TESSs) aimed at replacing damaged skin and promoting long-term wound closure. These products have either been developed in house or commercially sourced and are composed of allogeneic or autologous human skin cells, often with some form of bioscaffolding. They can be broadly classified based on their cellular composition: keratinocytes (epidermal substitutes), fibroblasts (dermal substitutes) or a combination of both (composite substitutes). Encouraging long-term wound healing has been achieved with epidermal substitutes. However, these substitutes have not demonstrated the same efficacy for all patients, which may be due to the molecular heterogeneity observed between EB subtypes. Autologous composite TESSs, which more closely resemble native human skin, are therefore being investigated and may hold promise for treating an extended range of patients. Additionally, future TESSs for EB are focused on using gene-corrected patient skin cells, which have already demonstrated remarkable long-term wound healing capabilities. In this review, we provide an overview of the different TESSs that have been investigated in clinical studies to treat patients with EB, as well as their long-term wound healing results. Where available, we describe the methods used to develop these products to inform future efforts in this field.

Clinical applications of acellular dermal matrices: A review

INTRODUCTION

The extracellular matrix (ECM) plays an integral role in wound healing. It provides both structure and growth factors that allow for the organised cell proliferation. Large or complex tissue defects may compromise host ECM, creating an environment that is unfavourable for the recovery of anatomical function and appearance. Acellular dermal matrices (ADMs) have been developed from a variety of sources, including human (HADM), porcine (PADM) and bovine (BADM), with multiple different processing protocols. The objective of this report is to provide an overview of current literature assessing the clinical utility of ADMs across a broad spectrum of applications.

METHODS

PubMed, MEDLINE, EMBASE, Scopus, Cochrane and Web of Science were searched using keywords 'acellular dermal matrix', 'acellular dermal matrices' and brand names for commercially available ADMs. Our search was limited to English language articles published from 1999 to 2020 and focused on clinical data.

RESULTS

A total of 2443 records underwent screening. After removing non-clinical studies and correspondence, 222 were assessed for eligibility. Of these, 170 were included in our synthesis of the literature. While the earliest ADMs were used in severe burn injuries, usage has expanded to a number of surgical subspecialties and procedures, including orthopaedic surgery (e.g. tendon and ligament reconstructions), otolaryngology, oral surgery (e.g. treating gingival recession), abdominal wall surgery (e.g. hernia repair), plastic surgery (e.g. breast reconstruction and penile augmentation), and chronic wounds (e.g. diabetic ulcers).

CONCLUSION

Our understanding of ADM's clinical utility continues to evolve. More research is needed to determine which ADM has the best outcomes for each clinical scenario.

LAY SUMMARY

Large or complex wounds present unique reconstructive and healing challenges. In normal healing, the extracellular matrix (ECM) provides both structural and growth factors that allow tissue to regenerate in an organised fashion to close the wound. In difficult or large soft-tissue defects, however, the ECM is often compromised. Acellular dermal matrix (ADM) products have been developed to mimic the benefits of host ECM, allowing for improved outcomes in a variety of clinical scenarios. This review summarises the current clinical evidence regarding commercially available ADMs in a wide variety of clinical contexts.