Tissue engineering of skin and regenerative medicine for wound care

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.

A regenerative approach to the pharmacological management of hard-to-heal wounds

A wound is considered hard-to-heal when, despite the appropriate clinical analysis and intervention, the wound area reduces by less than a third at four weeks and complete healing fails to occur within 12 weeks. The most prevalent hard-to-heal wounds are associated with underlying metabolic diseases or vascular insufficiency and include arterial, venous, pressure and diabetic foot ulcers. Their common features include an abnormal immune response and extended inflammatory phase, a subdued proliferation phase due to cellular insufficiencies and finally an almost non-existent remodeling phase. Advances in wound care technology, tested in both pre-clinical models and clinical trials, have paved the way for improved treatment options, focused on regeneration. These interventions have been shown to limit the extent of ongoing inflammatory damage, decrease bacterial load, promote angiogenesis and deposition of granulation tissue, and stimulate keratinocyte migration thereby promoting re-epithelialization in these wounds. The current review discusses these hard-to-heal wounds in the context of their underlying pathology and potential of advanced treatment options, which if applied promptly as a standard of care, could reduce morbidity, promote quality of life, and alleviate the burden on a strained health system.

Cell secretomes for wound healing and tissue regeneration: Next generation acellular based tissue engineered products

Wound represents a significant socioeconomic burden for both affected individuals and as a whole healthcare system. Accordingly, stem cells have garnered attention due to their differentiation capacity and ability to aid tissue regeneration by releasing biologically active molecules, found in the cells' cultivated medium which known as conditioned medium (CM) or secretomes. This acellular approach provides a huge advantage over conventional treatment options, which are mainly used cellular treatment at wound closure. Interestingly, the secretomes contained the cell-secreted proteins such as growth factors, cytokines, chemokines, extracellular matrix (ECM), and small molecules including metabolites, microvesicles, and exosomes. This review aims to provide a general view on secretomes and how it is proven to have great potential in accelerating wound healing. Utilizing the use of secretomes with its secreted proteins and suitable biomaterials for fabrications of acellular skin substitutes can be promising in treating skin loss and accelerate the healing process.

Wound healing properties of a fibrin-based dermal replacement scaffold

When serious cutaneous injury occurs, the innate wound healing process attempts to restore the skin's appearance and function. Wound healing outcome is affected by factors such as contraction, revascularisation, regeneration versus fibrosis and re-epithelialisation and is also strongly influenced by the pattern and extent of damage to the dermal layer. Dermal replacement scaffolds have been designed to substitute for lost tissue, provide a structure to promote dermal regeneration, and aid skin grafting, resulting in a superior healing outcome. In this study the wound healing properties of a novel fibrin-alginate dermal scaffold were assessed in the porcine wound healing model and also compared to two widely used dermal scaffolds and grafting alone. The fibrin-alginate scaffold, unlike the other scaffolds tested, is not used in combination with an overlying skin graft. Fibrin scaffold treated wounds showed increased, sustained superficial blood flow and reduced contraction during early healing while showing comparable wound closure, re-epithelialisation and final wound outcome to other treatments. The increase in early wound vascularisation coupled with a decrease in contraction and no requirement for a skin graft suggest that the fibrin-based scaffold could provide an effective, distinctive treatment option to improve healing outcomes in human patients.

Design of Asymmetric Nanofibers-Membranes Based on Polyvinyl Alcohol and Wool-Keratin for Wound Healing Applications

The development of asymmetric membranes—i.e., matching two fibrous layers with selected composition and morphological properties to mimic both the epidermis and dermis—currently represents one of the most promising strategies to support skin regeneration during the wound healing process. Herein, a new asymmetric platform fabricated by a sequential electrospinning process was investigated. The top layer comprises cross-linked polyvinylalcohol (PVA) nanofibers (NFs)—from water solution—to replicate the epidermis’s chemical stability and wettability features. Otherwise, the bottom layer is fabricated by integrating PVA with wool-keratin extracted via sulfitolysis. This protein is a biocompatibility polymer with excellent properties for dermis-like structures. Morphological characterization via SEM supported by image analysis showed that the asymmetric membrane exhibited average fiber size—max frequency diameter 450 nm, range 1.40 μm—and porosity suitable for the healing process. FTIR-spectrums confirmed the presence of keratin in the bottom layer and variations of keratin-secondary structures. Compared with pure PVA-NFs, keratin/PVA-NFs showed a significant improvement in cell adhesion in in vitro tests. In perspective, these asymmetric membranes could be promisingly used to confine active species (i.e., antioxidants, antimicrobials) to the bottom layer to support specific cell activities (i.e., proliferation, differentiation) in wound healing applications.

The promising rise of bioprinting in revolutionalizing medical science: Advances and possibilities

Bioprinting is a relatively new yet evolving technique predominantly used in regenerative medicine and tissue engineering. 3D bioprinting techniques combine the advantages of creating Extracellular Matrix (ECM)like environments for cells and computer-aided tailoring of predetermined tissue shapes and structures. The essential application of bioprinting is for the regeneration or restoration of damaged and injured tissues by producing implantable tissues and organs. The capability of bioprinting is yet to be fully scrutinized in sectors like the patient-specific spatial distribution of cells, bio-robotics, etc. In this review, currently developed experimental systems and strategies for the bioprinting of different types of tissues as well as for drug delivery and cancer research are explored for potential applications. This review also digs into the most recent opportunities and future possibilities for the efficient implementation of bioprinting to restructure medical and technological practices.

An overview on the manufacturing of functional and mature cellular skin substitutes

There are different types of skin diseases due to chronic injuries that impede the natural healing process of the skin. Tissue engineering (TE) has focused on the development of bioengineered skin or skin substitutes that cover the wound, providing the necessary care to restore the functionality of injured skin. There are two types of substitutes: acellular skin substitutes (ASSs), which offer a low response of the body, and cellular skin substitutes (CSSs), which incorporate living cells and appear as a great alternative in the treatment of skin injuries due to them presenting a greater interaction and integration with the rest of the body. For the development of a CSS, it is necessary to select the most suitable biomaterials, cell components, and methodology of biofabrication for the wound to be treated. Moreover, these CSSs are immature substitutes that must undergo a maturing process in specific bioreactors, guaranteeing their functionality. The bioreactor simulates the natural state of maturation of the skin by controlling parameters such as temperature, pressure, or humidity, allowing a homogeneous maturation of the CSSs in an aseptic environment. The use of bioreactors not only contributes to the maturation of the CSSs, but also offers a new way of obtaining large sections of skin substitutes or natural skin from small portions acquired from the patient, donor, or substitute. Based on the innovation of this technology and the need to develop efficient CSSs, this work offers an update on bioreactor technology in the field of skin regeneration.

Basic Quality Controls Used in Skin Tissue Engineering

Reconstruction of skin defects is often a challenging effort due to the currently limited reconstructive options. In this sense, tissue engineering has emerged as a possible alternative to replace or repair diseased or damaged tissues from the patient's own cells. A substantial number of tissue-engineered skin substitutes (TESSs) have been conceived and evaluated in vitro and in vivo showing promising results in the preclinical stage. However, only a few constructs have been used in the clinic. The lack of standardization in evaluation methods employed may in part be responsible for this discrepancy. This review covers the most well-known and up-to-date methods for evaluating the optimization of new TESSs and orientative guidelines for the evaluation of TESSs are proposed.

A three-dimensional bioprinting technique, based on a gelatin/alginate hydrogel, for the tissue engineering of hair follicle reconstruction

Hair loss remains a challenging clinical problem that influences the quality of life. Three-dimensional (3D) bioprinting has become a valuable tool for fabricating tissue constructs for transplantation and other biomedical applications. Although some simple organs, such as skin and cartilage, have been successfully simulated, it remains challenging to make hair follicles (HFs), which are highly complex organs. The tissue engineering of human HFs has been a long-standing challenge, and progress with this has lagged behind that with other lab-grown tissues. This is principally due to a lack of availability of a platform that can successfully recapitulate the microenvironmental cues required to maintain the requisite cellular interactions for hair neogenesis. In this study, we used a 3D bioprinting technique based on a gelatin/alginate hydrogel to construct a multilayer 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. In conclusion, our 3D-bioprinted multilayer composite scaffold prepared using a gelatin/alginate hydrogel provides a suitable 3D microenvironment for DPCs to induce HF formation. The ability to regenerate entire HFs should have a significant impact on the medical management of hair loss. This method may also have critical applications for skin tissue engineering, with its appendages, for other purposes.

Effect of Bone Marrow Mesenchymal Stem Cell Sheets on Skin Capillary Parameters in a diabetic wound model: A Novel Preliminary Study

Background

Treatment with BMMSCs has anti-inflammatory, tissue regenerative, angiogenic, and immune-stimulating effects. When using as sheets or accumulate, BMMSCs causes the development of neoangiogenesis in damaged skin tissue. Diabetes, a metabolic disorder, can negatively affect many physiological functions, including the process of skin injury repair. This adverse impact may increase the risk of skin surgery. RSF is commonly used in reconstructive surgery. The terminal part of the RSF is often affected by necrosis because of impaired blood flow, which is exacerbated in diabetes. This study investigated the effect of stem cells, applied as accumulated or cell sheets, along with RSF surgery on skin capillaries in STZ-induced diabetic rats.

Methods

Thirty male Wistar rats were divided into three groups (n = 10): diabetes-RSF control, diabetes-RSF local applied stem cells (loc-BMMSCs), diabetes-RSF applied stem cells as accumulated or cell sheets (ac-BMMSCs). Two weeks after the STZ injection, RSF surgery and stem cell therapy (6 × 109) were carried out (day zero). Furthermore, stereological methods were used to investigate the capillary patterns among the groups. Anti-CD31/PCAM1 immunohistochemistry was also used for further confirmation of changes in capillary parameters.

Results

The results demonstrated that capillaries were protected by MSC sheets in the flap tissue, and the thickness of the epidermal layer was improved, indicationg the possible beneficial effects of MSC sheets on diabetic wound treatment.

Conclusion

Stem cells, as ac-BMMSCs, may decrease the levels of wound healing complications in diabetes and can be considered as a cell therapy option in such conditions.

Advances in Skin Tissue Bioengineering and the Challenges of Clinical Translation

Skin tissue bioengineering is an emerging field that brings together interdisciplinary teams to promote successful translation to clinical care. Extensive deep tissue injuries, such as large burns and other major skin loss conditions, are medical indications where bioengineered skin substitutes (that restore both dermal and epidermal tissues) are being studied as alternatives. These may not only reduce mortality but also lessen morbidity to improve quality of life and functional outcome compared with the current standards of care. A common objective of dermal-epidermal therapies is to reduce the time required to accomplish stable closure of wounds with minimal scar in patients with insufficient donor sites for autologous split-thickness skin grafts. However, no commercially-available product has yet fully satisfied this objective. Tissue engineered skin may include cells, biopolymer scaffolds and drugs, and requires regulatory review to demonstrate safety and efficacy. They must be scalable for manufacturing and distribution. The advancement of technology and the introduction of bioreactors and bio-printing for skin tissue engineering may facilitate clinical products' availability. This mini-review elucidates the reasons for the few available commercial skin substitutes. In addition, it provides insights into the challenges faced by surgeons and scientists to develop new therapies and deliver the results of translational research to improve patient care.

Microwave Enabled Physically Cross Linked Sodium Alginate and Pectin Film and Their Application in Combination with Modified Chitosan-Curcumin Nanoparticles. A Novel Strategy for 2nd Degree Burns Wound Healing in Animals

This study reports microwave assisted physically cross-linked sodium alginate and pectin film and their testing in combination with modified chitosan-curcumin nanoparticles for skin tissue regeneration following 2nd degree burn wound. Film was formulated by solution casting method and physically cross-linked using microwave irradiation at frequency of 2450 MHz, power 750 Watt for different time intervals for optimization. The optimized formulation was analyzed for various physiochemical attributes. Afterwards, the optimized film and optimized modified chitosan-curcumin nanoparticles were tested in combination for skin regeneration potential following burn wound in vivo and skin samples extracted and tested for different attributes. The results indicated that the optimized film formulation (5 min microwave treatment) physicochemical attributes significantly enhanced addressing the properties required of a wound healing platform. The vibrational analysis indicated that the optimized film experienced significant rigidification of hydrophilic domains while the hydrophobic domains underwent significant fluidization which also resulted in significant increase in the transition temperatures and system enthalpies of both polymer moieties with microwave treatment. The combined film and nanoparticles application significantly increased protein content in the wounds which were evident from higher absorbance ratios of amide-I and amide-II (2.15 ± 0.001), significantly higher melting transition temperature and enthalpy (∆T = 167.2 ± 15.4 °C, ∆H = 510.7 ± 20.1 J/g) and higher tensile strength (14.65 ± 0.8 MPa) with significantly enhanced percent re-epithelization (99.9934 ± 2.56) in comparison to other treatments. The combined application of film and nanoparticles may prove to be a new novel treatment strategy for 2nd degree burn wound healing.

Serum-derived exosomes accelerate scald wound healing in mice by optimizing cellular functions and promoting Akt phosphorylation

Wound exudate holds great clinical and research potential in wound repair via paracrine signaling. In essence, exudate is modified serum that contains a high concentration of exosomes. The aim of this study was to investigate the role of serum-derived exosomes in scald wound healing of NIH mice skin and to explore the underlying mechanisms. Hence, we constructed a deep second-degree scald model in NIH mice, testing the benefits of exosomes in the scald wound healing. The scratch wound assay, apoptosis assay and MTT assay were conducted to assess the effects of serum-derived exosomes on migration, apoptosis and proliferation of HaCaT cells and fibroblasts. Our results showed that serum-derived exosomes injected subcutaneously entered cells and effectively accelerated wound healing processes in mice. Additionally, serum-derived exosomes optimized functions of cells related to skin injury repair by stimulating fibroblast proliferation, promoting HaCaT cell migration, and suppressing apoptosis of HaCaT cells induced by heat stress. Further study revealed that serum-derived exosomes enhanced phosphorylation of the serine-threonine kinase Akt in scalded skin tissue. These results suggest a potential clinical use of serum-derived exosomes for treating skin scald.

Effect of 3D-Fibroblast Dermis Constructed by Layer-by-Layer Cell Coating Technique on Tight Junction Formation and Function in Full-Thickness Skin Equivalent

Human skin equivalents (HSEs) consisting of an epidermis and dermis have been used as promising tools for drug evaluation and for clinical applications in regenerative medicine. Normal human dermal fibroblasts (NHDFs) are essential for the fabrication of HSEs because they play an important role in the maturation of the epidermis. Recently, epidermal tight junctions (TJs), which are complex cell-cell junctions, have attracted much attention as a second barrier and regulator for other barrier functions. In a previous study, we revealed the expression of TJ-related proteins and the time course of formation of TJ structure in the HSE (layer-by-layer (LbL)-three-dimensional (3D) Skin) constructed by layer-by-layer (LbL) cell coating technique that have a unique dermis consisting of NHDFs only (3D-fibroblast dermis). However, the effect of the 3D-fibroblast dermis on the formation of functional epidermal TJs is unknown. In this study, we investigated the effect of the 3D-fibroblast dermis on the expression of TJ-related proteins and TJ function in LbL-3D Skin. We demonstrated that the 3D-fibroblast dermis affects the long-term expression of TJ-related proteins and the formation of TJ with barrier function in the epidermis. These results show that the 3D-fibroblast dermis in LbL-3D Skin contributes to the formation and maintenance of functional TJs as in native human skin by direct contact with KCs.

Cellular human tissue-engineered skin substitutes investigated for deep and difficult to heal injuries

Wound healing is an important function of skin; however, after significant skin injury (burns) or in certain dermatological pathologies (chronic wounds), this important process can be deregulated or lost, resulting in severe complications. To avoid these, studies have focused on developing tissue-engineered skin substitutes (TESSs), which attempt to replace and regenerate the damaged skin. Autologous cultured epithelial substitutes (CESs) constituted of keratinocytes, allogeneic cultured dermal substitutes (CDSs) composed of biomaterials and fibroblasts and autologous composite skin substitutes (CSSs) comprised of biomaterials, keratinocytes and fibroblasts, have been the most studied clinical TESSs, reporting positive results for different pathological conditions. However, researchers' purpose is to develop TESSs that resemble in a better way the human skin and its wound healing process. For this reason, they have also evaluated at preclinical level the incorporation of other human cell types such as melanocytes, Merkel and Langerhans cells, skin stem cells (SSCs), induced pluripotent stem cells (iPSCs) or mesenchymal stem cells (MSCs). Among these, MSCs have been also reported in clinical studies with hopeful results. Future perspectives in the field of human-TESSs are focused on improving in vivo animal models, incorporating immune cells, designing specific niches inside the biomaterials to increase stem cell potential and developing three-dimensional bioprinting strategies, with the final purpose of increasing patient's health care. In this review we summarize the use of different human cell populations for preclinical and clinical TESSs under research, remarking their strengths and limitations and discuss the future perspectives, which could be useful for wound healing purposes.

Peel Test to Assess the Adhesion Strength of the Dermal-Epidermal Junction in Tissue-Engineered Skin

Innovative therapies combining gene-corrected stem cells and the production of bioengineered tissues to treat epidermolysis bullosa are emerging. However, quantitative tests to measure the adhesion forces between two highly viscoelastic substrates such as those found in bilayered bioengineered skin are needed and are still lacking. The objective of this study was to develop a mechanical test to measure the dermal-epidermal adhesion strength of our bilayered tissue-engineered skin substitute (TES) produced with the self-assembly method. We developed a peel test, which allows the displacement of both skin layers in a T configuration, based on the ASTM International standard. A MATLAB program was written to process and analyze raw data. The experimental setup was tested by measuring the dermal-epidermal adhesion strength in TESs produced with normal or collagen VII-deficient cells. Our peel testing method allowed us to detect the impact of the absence of collagen VII in the dermal-epidermal adhesion strength of TESs and also to examine the progression of the dermal-epidermal adhesion strength in relation to culture time in normal TES. Impact statement This study describes a method for assessing the adhesion strength at the dermal-epidermal junction of individual tissue-engineered skin substitute (TES). An ASTM standardized protocol of peel testing was designed to measure this important mechanical property. Our innovative approach will serve as a quality control in the production, improvement, and application of TESs for the treatment of pathologies affecting the dermal-epidermal adhesion such as epidermolysis bullosa. Data presented contribute to research on the interfaces between biological substrates and provide a reference factor for the characterization of products derived from tissue engineering.

Hair follicle stem cells as a skin-organizing signaling center during adult homeostasis

Stem cells are the essential source of building blocks for tissue homeostasis and regeneration. Their behavior is dictated by both cell-intrinsic cues and extrinsic cues from the microenvironment, known as the stem cell niche. Interestingly, recent work began to demonstrate that hair follicle stem cells (HFSCs) are not only passive recipients of signals from the surroundings, but also actively send out signals to modulate the organization and function of their own niches. Here, we discuss recent findings, and briefly refer to the old, on the interaction of HFSCs and their niches with the emphasis on the outwards signals from HFSCs toward their niches. We also highlight recent technology advancements that further promote our understanding of HFSC niches. Taken together, the HFSCs emerge as a skin-organizing center rich in signaling output for niche remodeling during various stages of adult skin homeostasis. The intricate crosstalk between HFSCs and their niches adds important insight to skin biology that will inform clinical and bioengineering fields aiming to build complete and functional 3D organotypic cultures for skin replacement therapies.

Recent trends on burn wound care: hydrogel dressings and scaffolds

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

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.

Chronic Leg Ulcers: Are Tissue Engineering and Biomaterials Science the Solution?

Chronic leg ulcers (CLUs) are full thickness wounds that usually occur between the ankle and knee, fail to heal after 3 months of standard treatment, or are not entirely healed at 12 months. CLUs present a considerable burden on patients, subjecting them to severe pain and distress, while healthcare systems suffer immense costs and loss of resources. The poor healing outcome of the standard treatment of CLUs generates an urgent clinical need to find effective solutions for these wounds. Tissue Engineering and Biomaterials Science offer exciting prospects for the treatment of CLUs, using a broad range of skin substitutes or scaffolds, and dressings. In this review, we summarize and discuss the various types of scaffolds used clinically in the treatment of CLUs. Their structure and therapeutic effects are described, and for each scaffold type representative examples are discussed, supported by clinical trials. Silver dressings are also reviewed due to their reported benefits in the healing of leg ulcers, as well as recent studies on new dermal scaffolds, reporting on clinical results where available. We conclude by arguing there is a further need for tissue-engineered products specifically designed and bioengineered to treat these wounds and we propose a series of properties that a biomaterial for CLUs should possess, with the intention of focusing efforts on finding an effective treatment.

Growth factor mimetics for skin regeneration: In vitro profiling of primary human fibroblasts and keratinocytes

Small molecules have gained considerable interest in regenerative medicine, as they can effectively modulate cell fates in a spatiotemporal controllable fashion. A continuous challenge in the field represents genuine mimicry or activation of growth factor signaling with small molecules. Here, we selected and profiled three compounds for their capacity to directly or indirectly activate endogenous FGF-2, VEGF, or SHH signaling events in the context of skin regeneration. Phenotypic and functional analysis of primary skin fibroblasts and keratinocytes revealed unique, cell-specific activity profiles for the FGF-2 mimetic SUN11602 and the putative VEGF mimetic ONO-1301. Whereas SUN11602 exclusively stimulated keratinocyte differentiation, ONO-1301 mainly affected the proliferation and migration behavior of fibroblasts. In each skin cell type, both compounds selectively enhanced the expression of MMP1 and VEGFA. A combined small molecule FGF-2/VEGF mimicry may not only improve angiogenesis-related microcirculation but also reduce early fibrosis while facilitating wound remodeling at later stages. SUN11602 and ONO-1301 represent valuable tools for improving the management of difficult-to-heal wounds, particularly for the design and development of small molecule-functionalized, next-generation, engineered skin substitutes.

Design and characterization of 3D printed, neomycin-eluting poly-L-lactide mats for wound-healing applications

This study evaluates the suitability of 3D printed biodegradable mats to load and deliver the topical antibiotic, neomycin, for up to 3 weeks in vitro. A 3D printer equipped with a hot melt extruder was used to print bandage-like wound coverings with porous sizes appropriate for cellular attachment and viability. The semicrystalline polyester, poly-l-lactic acid (PLLA) was used as the base polymer, coated (post-printing) with polyethylene glycols (PEGs) of MWs 400 Da, 6 kDa, or 20 kDa to enable manipulation of physicochemical and biological properties to suit intended applications. The mats were further loaded with a topical antibiotic (neomycin sulfate), and cumulative drug-release monitored for 3 weeks in vitro. Microscopic imaging as well as Scanning Electron Microscopy (SEM) studies showed pore dimensions of 100 × 400 µm. These pore dimensions were achieved without compromising mechanical strength; because of the "tough" individual fibers constituting the mat (Young's Moduli of 50 ± 20 MPa and Elastic Elongation of 10 ± 5%). The in vitro dissolution study showed first-order release kinetics for neomycin during the first 20 h, followed by diffusion-controlled (Fickian) release for the remaining duration of the study. The release of neomycin suggested that the ability to load neomycin on to PLLA mats increases threefold, as the MW of the applied PEG coating is lowered from 20 kDa to 400 Da. Overall, this study demonstrates a successful approach to using a 3D printer to prepare porous degradable mats for antibiotic delivery with potential applications to dermal regeneration and tissue engineering. Illustration of the process used to create and characterize 3D printed PLLA mats.

Targeted regulation of lymphocytic ER stress response with an overall immunosuppression to alleviate allograft rejection

Transplantation is the most effective, and sometimes the only resort for end-stage organ failure. However, allogeneic graft suffers greatly from lymphocyte-mediated immunorejection, which bears close relationship with a hyperactivation of endoplasmic reticulum (ER) stress response in host lymphocytes, especially in CD8⁺ T cells (T-8). Therefore, regulating lymphocytic ER unfolded protein response (UPR) might be a potential therapeutic breakthrough in alleviating graft rejection. Here, ER-targetable liposome is prepared via the surface modification of ER-targeting peptide (Pardaxin), which efficiently loads and directly delivers small molecule inhibitor of UPR sensor IRE1α into the ER of lymphocytes, inducing a systemic immunosuppression that facilitates tumorigenesis and metastasis in the tumor inoculation challenge in vivo. And in vitro, a stage-differential dependency of IRE1α in the phase transition of T-8 is identified. Specifically, inhibiting IRE1α at the early responding stages of T-8, especially at the activation phase, results in a shrunk proliferation, impaired effector function, and limited memory commitment, which might contribute centrally to the induced overall immunosuppression. Based on this, a classical acute rejection model, murine full-thickness trunk skin allograft that primary arises from the hyperactivity of T-lymphocyte, is used. Results suggest that lymphocytic IRE1α inactivation attenuates transplant rejection and prolongs graft survival, with a limited effector function and memory commitment of host T-8. Moreover, an even higher immunosuppressive effect is obtained when IRE1α inhibition is used in combination with immunosuppressant tacrolimus (FK506), which might owe to a synergistic regulation of inflammatory transcription factors. These findings provide a deeper insight into the biological polarization and stress response of lymphocytes, which might guide the future development of allogeneic transplantation.

A Short History of Skin Grafting in Burns: From the Gold Standard of Autologous Skin Grafting to the Possibilities of Allogeneic Skin Grafting with Immunomodulatory Approaches

Due to groundbreaking and pioneering developments in the last century, significant improvements in the care of burn patients have been achieved. In addition to the still valid therapeutic standard of autologous split-thickness skin grafting, various commercially available skin substitutes are currently available. Significant progress in the field of tissue engineering has led to the development of promising therapeutic approaches. However, scientific advances in the field of allografting and transplant immunology are of great importance. The achievement of various milestones over the past decades has provided thought-provoking impulses in the field of skin allotransplantation. Thus, biologically viable skin allotransplantation is still not a part of the clinical routine. The purpose of this article is to review the achievements in burn surgery with regards to skin allotransplantation in recent years.

Translational stem cell therapy: vascularized skin grafts in skin repair and regeneration

The skin is made up of a plethora of cells arranged in multiple layers with complex and intricate vascular networks, creating a dynamic microenvironment of cells-to-matrix interactions. With limited donor sites, engineered skin substitute has been in high demand for many therapeutic purposes. Over the years, remarkable progress has occurred in the skin tissue-engineering field to develop skin grafts highly similar to native tissue. However, the major hurdle to successful engraftment is the incorporation of functional vasculature to provide essential nutrients and oxygen supply to the embedded cells. Limitations of traditional tissue engineering have driven the rapid development of vascularized skin tissue production, leading to new technologies such as 3D bioprinting, nano-fabrication and micro-patterning using hydrogel based-scaffold. In particular, the key hope to bioprinting would be the generation of interconnected functional vessels, coupled with the addition of specific cell types to mimic the biological and architectural complexity of the native skin environment. Additionally, stem cells have been gaining interest due to their highly regenerative potential and participation in wound healing. This review briefly summarizes the current cell therapies used in skin regeneration with a focus on the importance of vascularization and recent progress in 3D fabrication approaches to generate vascularized network in the skin tissue graft.

Evaluation of the efficiency and safety of botulinum toxin A injection on improving facial scars: A protocol for systematic review and meta-analysis

BACKGROUND

Botulinum toxin A injection is an established method of treatment. Clinical practitioners use it widely in their practice to prevent the occurrence of facial scars. However, the effectiveness and safeness of has not been comprehensively established. The objective of the current systematic review is to evaluate the efficacy and safety of using botulinum toxin A injection to improve facial scars.

METHODS AND ANALYSIS

This systematic review involves browsing a number of electronic databases to search for related articles. The search will include databases in both English (PubMed, EMBASE, Web of Science, Spocus, and Cochrane Central Register of Controlled Trials) and Chinese (WanFang database, China Nation Knowledge Infrastructure, and VIP database), the periods of searching will be from inception till the 15th of September 2020. Completing the search in databases allows to consider randomized controlled studies that compares botulinum toxin A interventions to any comparison interventions in those who have facial scars. The review will be inclusive of papers in both languages, English and Chinese. The independent screening of studies for eligibility is conducted by 2 independent authors. Discussion was used to resolve discrepancies between the authors. The Cochrane Risk of Bias Tool V.2.0 is adopted for evaluating the methodological quality of each study. Data extraction was performed by 2 independent authors. For dichotomous outcomes, the were expressed as relative risk (RR) with 95% confidence intervals (CI). For continuous outcomes the results were expressed as the mean difference (MD) or standardized mean difference (SMD) with 95% CI. The statistical analysis of the present study is carried out in RevMan 5.3 software.

RESULTS

This study will output a comprehensive synthesis of existing evidence in relation to botulinum toxin A. Moreover, the results will also provide an interpretation of the effectiveness and safety of botulinum toxin A.

CONCLUSION

The present review contributes to the existing body of knowledge by adding more evidence to evaluate if botulinum toxin A is effective and safe to be used as an intervention for improving facial scars.

OSF REGISTRATION NUMBER

DOI 10.17605/OSF.IO/94TXP (https://osf.io/94TXP/).

Human primary epidermal organoids enable modeling of dermatophyte infections

Technology of generating human epidermal derivatives with physiological relevance to in vivo epidermis is continuously investigated for improving their effects on modeling of human natural dermatological status in basic and clinical studies. Here, we report a method of robust establishment and expansion of human primary epidermal organoids (hPEOs) under a chemically defined condition. hPEOs reconstruct morphological, molecular, and functional features of human epidermis and can expand for 6 weeks. Remarkably, hPEOs are permissive for dermatophyte infections caused by Trichophyton Rubrum (T. rubrum). The T. rubrum infections on hPEOs reflect many aspects of known clinical pathological reactions and reveal that the repression on IL-1 signaling may contribute to chronic and recurrent infections with the slight inflammation caused by T. rubrum in human skin. Thus, our present study provides a new insight into the pathogenesis of T. rubrum infections and indicates that hPEOs are a potential ex vivo model for both basic studies of skin diseases and clinical studies of testing potential antifungal drugs.

Electrospun PCL/PLA Scaffolds Are More Suitable Carriers of Placental Mesenchymal Stromal Cells Than Collagen/Elastin Scaffolds and Prevent Wound Contraction in a Mouse Model of Wound Healing

Mesenchymal stem/stromal cells (MSCs) exert beneficial effects during wound healing, and cell-seeded scaffolds are a promising method of application. Here, we compared the suitability of a clinically used collagen/elastin scaffold (Matriderm) with an electrospun Poly(ε-caprolactone)/poly(l-lactide) (PCL/PLA) scaffold as carriers for human amnion-derived MSCs (hAMSCs). We created an epidermal-like PCL/PLA scaffold and evaluated its microstructural, mechanical, and functional properties. Sequential spinning of different PCL/PLA concentrations resulted in a wide-meshed layer designed for cell-seeding and a dense-meshed layer for apical protection. The Matriderm and PCL/PLA scaffolds then were seeded with hAMSCs, with or without Matrigel coating. The quantity and quality of the adherent cells were evaluated in vitro. The results showed that hAMSCs adhered to and infiltrated both scaffold types but on day 3, more cells were observed on PCL/PLA than on Matriderm. Apoptosis and proliferation rates were similar for all carriers except the coated Matriderm, where apoptotic cells were significantly enhanced. On day 8, the number of cells decreased on all carrier types except the coated Matriderm, which had consistently low cell numbers. Uncoated Matriderm had the highest percentage of proliferative cells and lowest apoptosis rate of all carrier types. Each carrier also was topically applied to skin wound sites in a mouse model and analyzed in vivo over 14 days via optical imaging and histological methods, which showed detectable hAMSCs on all carrier types on day 8. On day 14, all wounds exhibited newly formed epidermis, and all carriers were well-integrated into the underlying dermis and showing signs of degradation. However, only wounds treated with uncoated PCL/PLA maintained a round appearance with minimal contraction. Overall, the results support a 3-day in vitro culture of scaffolds with hAMSCs before wound application. The PCL/PLA scaffold showed higher cell adherence than Matriderm, and the effect of the Matrigel coating was negligible, as all carrier types maintained sufficient numbers of transplanted cells in the wound area. The anti-contractive effects of the PCL/PLA scaffold offer potential new therapeutic approaches to wound care.

Total full-thickness skin grafting for treating patients with extensive facial burn injury: A 10-year experience

INTRODUCTION

Facial burns are not only a severe burn injury, but result in psychological disturbance. The improvement of the methods of treating facial burns remains topical. The aim of the study was to evaluate the effectiveness of approach based on full-thickness skin autografting for facial burn injuries.

METHODS

During 2000-2019, ninety seven patients with the facial burn were treated in Burn Center. All patient were divided into two groups. The comparative analysis between groups was done.

RESULTS

Group A was treated with full-thickness skin grafts (42 patients - 43.3%). Since 2010, total full-thickness skin graft was used in 11 patients from Group A. In group B, 55 patients (56.7%) were treated with split-thickness skin grafts, including 9 patients (16.4%) with total split-thickness skin graft transplantation. Total full-thickness skin graft was performed in case of a deep and extensive facial burn and cicatricial deformities. During the long-term period, a positive cosmetic result and the absence of indications for reconstructive operations were noted.

CONCLUSION

The approach of facial burn treatment based on total full-thickness skin graft allows conditions for engraftment and adaptation of autograft, reduces the risk of scar developing and achieves maximum cosmetic results of treatment.

Early-stage bilayer tissue-engineered skin substitute formed by adult skin progenitor cells produces an improved skin structure in vivo

BACKGROUND

In recent years, significant progress has been made in developing highly complex tissue-engineered skin substitutes (TESSs) for wound healing. However, the lack of skin appendages, such as hair follicles and sweat glands, and the time required, are two major limitations that hinder its broad application in the clinic. Therefore, it is necessary to develop a competent TESS in a short time to meet the needs for clinical applications.

METHODS

Adult scalp dermal progenitor cells and epidermal stem cells together with type I collagen as a scaffold material were used to reconstitute bilayer TESSs in vitro. TESSs at 4 different culture times (5, 9, 14, and 21 days) were collected and then grafted onto full-thickness wounds created in the dorsal skin of athymic nude/nude mice. The skin specimens formed from grafted TESSs were collected 4 and 8 weeks later and then evaluated for their structure, cell organization, differentiation status, vascularization, and formation of appendages by histological analysis, immunohistochemistry, and immunofluorescent staining.

RESULTS

Early-stage bilayer TESSs after transplantation had a better efficiency of grafting. A normal structure of stratified epidermis containing multiple differentiated layers of keratinocytes was formed in all grafts from both early-stage and late-stage TESSs, but higher levels of the proliferation marker Ki-67 and the epidermal progenitor marker p63 were found in the epidermis formed from early-stage TESSs. Interestingly, the transplantation of early-stage TESSs produced a thicker dermis that contained more vimentin- and CD31-positive cells, and importantly, hair follicle formation was only observed in the skin grafted from early-stage TESSs. Finally, early-stage TESSs expressed high levels of p63 but had low expression levels of genes involved in the activation of the apoptotic pathway compared to the late-stage TESSs in vitro.

CONCLUSIONS

Early-stage bilayer TESSs reconstituted from skin progenitor cells contained more competent cells with less activation of the apoptotic pathway and produced a better skin structure, including hair follicles associated with sebaceous glands, after transplantation, which should potentially provide better wound healing when applied in the clinic in the future.

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

The morbidity, mortality, and burden of burn victims and patients with severe diabetic wounds are still high, which leads to an extensively growing demand for novel treatments with high clinical efficacy. Biomaterial-based wound treatment approaches have progressed over time from simple cotton wool dressings to advanced skin substitutes containing cells and growth factors; however, no wound care approach is yet completely satisfying. Bioactive glasses are materials with potential in many areas that exhibit unique features in biomedical applications. Today, bioactive glasses are not only amorphous solid structures that can be used as a substitute in hard tissue but also are promising materials for soft tissue regeneration and wound healing applications. Biologically active elements such as Ag, B, Ca, Ce, Co, Cu, Ga, Mg, Se, Sr, and Zn can be incorporated in glass networks; hence, the superiority of these multifunctional materials over current materials results from their ability to release multiple therapeutic ions in the wound environment, which target different stages of the wound healing process. Bioactive glasses and their dissolution products have high potency for inducing angiogenesis and exerting several biological impacts on cell functions, which are involved in wound healing and some other features that are valuable in wound healing applications, namely hemostatic and antibacterial properties. In this review, we focus on skin structure, the dynamic process of wound healing in injured skin, and existing wound care approaches. The basic concepts of bioactive glasses are reviewed to better understand the relationship between glass structure and its properties. We illustrate the active role of bioactive glasses in wound repair and regeneration. Finally, research studies that have used bioactive glasses in wound healing applications are summarized and the future trends in this field are elaborated.

Skin Wound Healing Process and New Emerging Technologies for Skin Wound Care and Regeneration

Skin wound healing shows an extraordinary cellular function mechanism, unique in nature and involving the interaction of several cells, growth factors and cytokines. Physiological wound healing restores tissue integrity, but in many cases the process is limited to wound repair. Ongoing studies aim to obtain more effective wound therapies with the intention of reducing inpatient costs, providing long-term relief and effective scar healing. The main goal of this comprehensive review is to focus on the progress in wound medication and how it has evolved over the years. The main complications related to the healing process and the clinical management of chronic wounds are described in the review. Moreover, advanced treatment strategies for skin regeneration and experimental techniques for cellular engineering and skin tissue engineering are addressed. Emerging skin regeneration techniques involving scaffolds activated with growth factors, bioactive molecules and genetically modified cells are exploited to overcome wound healing technology limitations and to implement personalized therapy design.

Homogenization of initial cell distribution by secondary flow of medium improves cell culture efficiency

Homogenization of the initial cell distribution is essential for effective cell development. However, there are few previous reports on efficient cell seeding methods, even though the initial cell distribution has a large effect on cell proliferation. Dense cell regions have an inverse impact on cell development, known as contact inhibition. In this study, we developed a method to homogenize the cell seeding density using secondary flow, or Ekman transportation, induced by orbital movement of the culture dish. We developed an orbital shaker device that can stir the medium in a 35-mm culture dish by shaking the dish along a circular orbit with 2 mm of eccentricity. The distribution of cells in the culture dish can be controlled by the rotational speed of the orbital shaker, enabling dispersion of the initial cell distribution. The experimental results indicated that the cell density became most homogeneous at 61 rpm. We further evaluated the cell proliferation after homogenization of the initial cell density at 61 rpm. The results revealed 36% higher proliferation for the stirred samples compared with the non-stirred control samples. The present findings indicate that homogenization of the initial cell density by Ekman transportation contributes to the achievement of higher cell proliferation.

Asymmetric Membranes: A Potential Scaffold for Wound Healing Applications

Currently, due to uprising concerns about wound infections, healing agents have been regarded as one of the major solutions in the treatment of different skin lesions. The usage of temporary barriers can be an effective way to protect wounds or ulcers from dangerous agents and, using these carriers can not only improve the healing process but also they can minimize the scarring and the pain suffered by the human. To cope with this demand, researchers struggled to develop wound dressing agents that could mimic the structural and properties of native skin with the capability to inhibit bacterial growth. Hence, asymmetric membranes that can impair bacterial penetration and avoid exudate accumulation as well as wound dehydration have been introduced. In general, synthetic implants and tissue grafts are expensive, hard to handle (due to their fragile nature and poor mechanical properties) and their production process is very time consuming, while the asymmetric membranes are affordable and their production process is easier than previous epidermal substitutes. Motivated by this, here we will cover different topics, first, the comprehensive research developments of asymmetric membranes are reviewed and second, general properties and different preparation methods of asymmetric membranes are summarized. In the two last parts, the role of chitosan based-asymmetric membranes and electrospun asymmetric membranes in hastening the healing process are mentioned respectively. The aforementioned membranes are inexpensive and possess high antibacterial and satisfactory mechanical properties. It is concluded that, despite the promising current investigations, much effort is still required to be done in asymmetric membranes.

Autologous Matrix of Platelet-Rich Fibrin in Wound Care Settings: A Systematic Review of Randomized Clinical Trials

Platelet-rich fibrin (PRF) consists of a matrix that provides the necessary elements for wound healing, acting as a biodegradable scaffold for cell migration, proliferation, and differentiation, in addition to the delivery of growth factors and angiogenesis. This study aims to determine the effectiveness of the autologous PRF in the treatment of wounds of different etiologies. We carried out a systematic review of randomized clinical trials, guided by the recommendations of the Cochrane Collaboration using the following databases: Pubmed/MEDLINE, EMBASE, Web of Science, and CENTRAL. The search strategy resulted in the inclusion of ten studies that evaluated the use of PRF dressings for the healing of acute or chronic wounds of multiple etiologies. Among the 172 participants treated with PRF in wounds of varying etiologies and different segment times, 130 presented favorable events with the use of the intervention. Among the 10 studies included, only two of them did not demonstrate better results than the control group. The studies showed clinical heterogeneity, making it impossible to perform a meta-analysis. The findings do not provide enough evidence to support the routine use of PRF dressings as the first line of treatment for the healing of acute or chronic wounds of different etiologies. There was great variability in the application of the various protocols and the ways to prepare the PRF, resulting in clinical heterogeneity. Therefore, it makes it impossible to synthesize and to collect evidence from different types of studies in the meta-analysis, which affects the results and their proper discussion.

Reconstructed human skin shows epidermal invagination towards integrated neopapillae indicating early hair follicle formation in vitro

Application of reconstructed human Skin (RhS) is a promising approach for the treatment of extensive wounds and for drug efficacy and safety testing. However, incorporating appendages, such as hair follicles, into RhS still remains a challenge. The hair follicle plays a critical role in thermal regulation, dispersion of sweat and sebum, sensory and tactile functions, skin regeneration, and repigmentation. The aim of this study was to determine whether human neopapilla could be incorporated into RhS (differentiated epidermis on fibroblast and endothelial cell populated dermis) and whether the neopapillae maintain their inductive follicular properties in vitro. Neopapillae spheroids, constructed from expanded and self‐aggregating dermal papilla cells, synthesized extracellular matrix typically found in follicular papillae. Compared with dermal fibroblasts, neopapillae showed increased expression of multiple genes (Wnt5a, Wnt10b, and LEF1) known to regulate hair development and also increased secretion of CXCL1, which is a strong keratinocyte chemoattractant. When neopapillae were incorporated into the dermis of RhS, they stimulated epidermal down‐growth resulting in engulfment of the neopapillae sphere. Similar to the native hair follicle, the differentiated invaginating epidermis inner side was keratin 10 positive and the undifferentiated outer side keratin 10 negative. The outer side was keratin 15 positive confirming the undifferentiated nature of these keratinocytes aligning a newly formed collagen IV, laminin V positive basement membrane within the hydrogel. In conclusion, we describe a RhS model containing neopapillae with hair follicle‐inductive properties. Importantly, epidermal invagination occurred to engulf the neopapillae, thus demonstrating in vitro the first steps towards hair follicle morphogenesis in RhS.

Hydrogel membranes: A review

Hydrogel membranes (HMs) are defined and applied as hydrated porous media constructed of hydrophilic polymers for a broad range of applications. Fascinating physiochemical properties, unique porous architecture, water-swollen features, biocompatibility, and special water content dependent transport phenomena in semi-permeable HMs make them appealing constructs for various applications from wastewater treatment to biomedical fields. Water absorption, mechanical properties, and viscoelastic features of three-dimensional (3D) HM networks evoke the extracellular matrix (ECM). On the other hand, the porous structure with controlled/uniform pore-size distribution, permeability/selectivity features, and structural/chemical tunability of HMs recall membrane separation processes such as desalination, wastewater treatment, and gas separation. Furthermore, supreme physiochemical stability and high ion conductivity make them promising to be utilised in the structure of accumulators such as batteries and supercapacitors. In this review, after summarising the general concepts and production processes for HMs, a comprehensive overview of their applications in medicine, environmental engineering, sensing usage, and energy storage/conservation is well-featured. The present review concludes with existing restrictions, possible potentials, and future directions of HMs.

Enhanced biological properties of collagen/chitosan-coated poly(ε-caprolactone) scaffold by surface modification with GHK-Cu peptide and 58S bioglass

Bioactive glasses and peptides have shown promising results in improving wound healing and skin repair. The present study explores the effectiveness of surface modification of collagen/chitosan-coated electrospun poly(ε-caprolactone) scaffold with 58S bioactive glass or GHK-Cu peptide. To coat scaffolds with the bioactive glass, we prepared suspensions of silanized bioactive glass powder with three different concentrations and the scaffolds were pipetted with suspensions. Similarly, GHK-Cu-coated scaffolds were prepared by pipetting adequate amount of 1-mM solution of peptide (in milli-Q) on the surface of scaffolds. ATR-FTIR spectroscopy indicated the successful modification of collagen/chitosan-coated electrospun poly(ε-caprolactone) scaffold with bioactive glass and GHK-Cu. Microstructural investigations and in vitro studies such as cell adhesion, cell viability and antibacterial assay were performed. All samples demonstrated desirable cell attachment. Compared to poly(ε-caprolactone)/collagen/chitosan, the cell proliferation of GHK-Cu and bioactive glass-coated (concentrations of 0.01 and 0.1) scaffolds increased significantly at days 3 and 7, respectively. Poly(ε-caprolactone)/collagen/chitosan-uncoated scaffold and scaffolds coated with GHK-Cu and bioactive glass revealed desirable antibacterial properties but the antibacterial activity of GHK-Cu-coated sample turned out to be superior. These findings indicated that biological properties of collagen/chitosan-coated synthetic polymer could be improved by GHK-Cu and bioactive glass.

Scaffolds and coatings for bone regeneration

Bone tissue has an astonishing self-healing capacity yet only for non-critical size defects (<6 mm) and clinical intervention is needed for critical-size defects and beyond that along with non-union bone fractures and bone defects larger than critical size represent a major healthcare problem. Autografts are, still, being used as preferred to treat large bone defects. Mostly, due to the presence of living differentiated and progenitor cells, its osteogenic, osteoinductive and osteoconductive properties that allow osteogenesis, vascularization, and provide structural support. Bone tissue engineering strategies have been proposed to overcome the limited supply of grafts. Complete and successful bone regeneration can be influenced by several factors namely: the age of the patient, health, gender and is expected that the ideal scaffold for bone regeneration combines factors such as bioactivity and osteoinductivity. The commercially available products have as their main function the replacement of bone. Moreover, scaffolds still present limitations including poor osteointegration and limited vascularization. The introduction of pores in scaffolds are being used to promote the osteointegration as it allows cell and vessel infiltration. Moreover, combinations with growth factors or coatings have been explored as they can improve the osteoconductive and osteoinductive properties of the scaffold. This review focuses on the bone defects treatments and on the research of scaffolds for bone regeneration. Moreover, it summarizes the latest progress in the development of coatings used in bone tissue engineering. Despite the interesting advances which include the development of hybrid scaffolds, there are still important challenges that need to be addressed in order to fasten translation of scaffolds into the clinical scenario. Finally, we must reflect on the main challenges for bone tissue regeneration. There is a need to achieve a proper mechanical properties to bear the load of movements; have a scaffolds with a structure that fit the bone anatomy.

Encapsulation of troglitazone and AVE0991 by gelation microspheres promotes epithelial transformation of adipose-derived stem cells

Deformities in human soft tissue caused by trauma or burn present a difficult problem in plastic surgery. In this study, we encapsulated troglitazone and angiotensin 1-7 mimetic AVE0991 in gelation microspheres with the goal of inducing epithelial transformation for potential applications in tissue reconstruction. After troglitazone or AVE0991 were encapsulated to gelation microspheres, their release kinetics and bioactivity were examined. Surface morphology and diameter of the gelation microspheres were evaluated using light microscopy. The release of the drugs was assessed in the presence of human adipose-derived stem cells (ADSCs). Treatment with troglitazone microspheres increased cell viability and activated the β-catenin in ADSCs. Moreover, the AVE0991 microspheres also increased cell viability and C-myc expression of ADSCs. These results showed that troglitazone and AVE0991 microspheres promoted the activity of ADSCs. Furthermore, ADSCs were co-treated with troglitazone and AVE0991 microspheres. Western blot and immunofluorescent staining showed that co-treatment with troglitazone and AVE0991 microspheres elevated the expression of epithelialization associated protein CK14 in ADSCs. In conclusion, our findings indicate that microspheres with troglitazone and AVE0991 can significantly improve the viability and epithelialization of ADSCs, which provides a new approach for the construction of tissue-engineered skin.

The in vivo effect of Lacto-N-neotetraose (LNnT) on the expression of type 2 immune response involved genes in the wound healing process

Lacto-n-neotatraose (LNnT) oligosaccharide shows properties such as anti-inflammatory, type 2 immune response induction, induced angiogenesis, and anti-bacterial effects. Here, we hypothesized that the application of LnNT in the skin full-thickness wound can accelerate the healing process through its anti-inflammatory effect as well as induction of type 2 immune responses. In this study, we evaluated the cell viability of fibroblasts in the presence of LNnT. The full-thickness wound model was created by punch biopsy. The mice were treated intradermaly with LNnT at the concentrations of 100 and 200 µg or PBS as a control group. The wounds samples were compared based on the macroscopic and histological evaluations. The amount of collagen deposition and expression of genes involved in type 2 immunity were measured by the hydroxyproline assay and real time PCR method, respectively. Our results showed that LNnT had no negative effect on the cell viability of fibroblasts. LNnT increased the wound closure rate on day 7 post-wounding. H&E stain analysis revealed that mice treated with 200 µg LNnT exhibited better healing score, follicle formation, and lower epidermal thickness index. The mice treated with LNnT exhibited a lower collagen deposition on day 21 and higher collagen content on days 7 and 14 post-treatment. The LNnT groups also exhibited a lower number of neutrophils and a higher number of basal cells and fibroblasts. The expression rate of IL-10, IL-4, and IL-13 was higher in the LNnT groups. These results showed the high potential of LNnT for use in treatment of full-thickness wounds.

[Construction and preliminary study on biological characteristics of composite cell sheets of mesenchymal stem cells and endothelial progenitor cells derived from peripheral blood]

Objective

To separate peripheral blood mesenchymal stem cells (PBMSC) and peripheral blood endothelial progenitor cells (PBEPC) from peripheral blood, and investigate the biological characteristics of composite cell sheets of PBMSC and PBEPC.

Methods

The peripheral blood of healthy adult New Zealand white rabbits was extracted and PBMSC and PBEPC were separated by density gradient centrifugation. Morphological observation and identification of PBMSC and PBEPC were performed. The 3rd generation of PBMSC and PBEPC were used to construct a composite cell sheet at a ratio of 1∶1, and the 3rd generation of PBMSC was used to construct a single cell sheet as control. The distributions of cells in two kinds of cell sheets were observed by HE staining. In addition, the expression of alkaline phosphatase (ALP), osteocalcin (OCN), and vascular endothelial growth factor (VEGF) in the supernatants of cell sheets were observed by ELISA at 1, 5, and 10 days after osteogenic induction.

Results

The morphology of PBMSC was spindle-shaped or polygonal, and PBMSC had good abilities of osteogenic and adipogenic differentiation. The morphology of PBEPC was paved stone-like, and the tube-forming test of PBEPC was positive. Two kinds of cell sheets were white translucent. The results of HE staining showed that the composite cell sheet had more cell layers and higher cell density than the single cell sheet. The expressions of ALP, OCN, and VEGF in the supernatant of the two groups of cell sheets increased with the time of induction. The expression of OCN in the group of composite cell sheet was significantly higher than that in the group of single cell sheet on the 5th and 10th day, ALP on the 10th day was significantly higher than that in the group of single cell sheet, VEGF expression on the 1st, 5th, and 10th day was significantly higher than that in the group of single cell sheet, all showing significant differences ( P<0.05), and there was no significant difference between the two groups at other time points ( P>0.05).

Conclusion

PBMSC have stable differentiation ability, and they have good application prospects because of their minimally invasive access. Composite cell membranes constructed by co-culture of two kinds of cells and induction of membrane formation provides a new idea and exploration for tissue defect repair.