Regeneration of skin appendages and nerves: current status and further challenges

Tailoring bioinks of extrusion-based bioprinting for cutaneous wound healing

Extrusion-based bioprinting (EBB) holds potential for regenerative medicine. However, the widely-used bioinks of EBB exhibit some limitations for skin regeneration, such as unsatisfactory bio-physical (i.e., mechanical, structural, biodegradable) properties and compromised cellular compatibilities, and the EBB-based bioinks with therapeutic effects targeting cutaneous wounds still remain largely undiscussed. In this review, the printability considerations for skin bioprinting were discussed. Then, current strategies for improving the physical properties of bioinks and for reinforcing bioinks in EBB approaches were introduced, respectively. Notably, we highlighted the applications and effects of current EBB-based bioinks on wound healing, wound scar formation, vascularization and the regeneration of skin appendages (i.e., sweat glands and hair follicles) and discussed the challenges and future perspectives. This review aims to provide an overall view of the applications, challenges and promising solutions about the EBB-based bioinks for cutaneous wound healing and skin regeneration.

Biofabrication of Human Skin with Its Appendages

Much effort has been made to generate human skin organ in the laboratory. Yet, the current models are limited due to the lack of many critical biological and structural features of the skin. Importantly, these in vitro models lack appendages and fail to recapitulate the whole human skin construction. Thus, engineering a human skin with the capacity to generate all components, including appendages, is a major challenge. This review intends to provide an update on the recent efforts underway to regenerate appendage-bearing skin organs based on scaffold-free and scaffold-based bioengineering approaches. Although the mouse skin equivalents containing hair follicles, sebaceous glands, and sweat glands have been established in vitro, there has been limited success in humans. A combination of biofabricated matrices and cell aggregates, such as organoids, can pave the way for generating skin substitutes with human-like biological, structural, and physical features. Accordingly, the formation of human skin organoids and reconstruction of vascularized skin equipped with immune cells prompt calls for more scientific research. The generation of appendage-bearing skin substitutes can be applied in practice for wound healing, hair restoration, and scar treatment.

Efficacy and safety of small extracellular vesicle interventions in wound healing and skin regeneration: A systematic review and meta-analysis of animal studies

Small extracellular vesicles (sEVs) have been proposed as a possible solution to the current lack of therapeutic interventions for endogenous skin regeneration. We conducted a systematic review of the available evidence to assess sEV therapeutic efficacy and safety in wound healing and skin regeneration in animal models. 68 studies were identified in Web of Science, Scopus, and PubMed that satisfied a set of prespecified inclusion criteria. We critically analyzed the quality of studies that satisfied our inclusion criteria, with an emphasis on methodology, reporting, and adherence to relevant guidelines (including MISEV2018 and ISCT criteria). Overall, our systematic review and meta-analysis indicated that sEV interventions promoted skin regeneration in diabetic and non-diabetic animal models and influenced various facets of the healing process regardless of cell source, production protocol and disease model. The EV source, isolation methods, dosing regimen, and wound size varied among the studies. Modification of sEVs was achieved mainly by manipulating source cells via preconditioning, nanoparticle loading, genetic manipulation, and biomaterial incorporation to enhance sEV therapeutic potential. Evaluation of potential adverse effects received only minimal attention, although none of the studies reported harmful events. Risk of bias as assessed by the SYRCLE's ROB tool was uncertain for most studies due to insufficient reporting, and adherence to guidelines was limited. In summary, sEV therapy has enormous potential for wound healing and skin regeneration. However, reproducibility and comprehensive evaluation of evidence are challenged by a general lack of transparency in reporting and adherence to guidelines. Methodological rigor, standardization, and risk analysis at all stages of research are needed to promote translation to clinical practice.

Differential distribution and genetic determination of eccrine sweat glands and hair follicles in the volar skin of C57BL/6 mice and SD rats

BACKGROUND

Eccrine sweat glands (ESGs) and hair follicles (HFs) are the prominent skin appendages regulating human body temperature. C57BL/6 mice and Sprague-Dawley (SD) rats are the most commonly used model animals for studying ESGs and HFs. Previous studies have shown the distribution of ESGs and HFs in volar hindfeet of C57BL/6 mice, but there are few or no reports on the distribution of ESGs and HFs in volar forefeet of C57BL/6 mice and volar feet of SD rats. Here, we investigated the differential distribution and genetic determination of ESGs and HFs in the volar skin of C57BL/6 mice and SD rats through gross observation, iodine-starch sweat test, double staining with Nile Blue A and Oil Red O, hematoxylin and eosin (HE) staining, double immunofluorescence staining of LIM Homeobox 2 (LHX2)/Na⁺-K⁺-ATPase α1(NKA) or LHX2/Na⁺-K⁺-2Cl^－ cotransporter 1 (NKCC1), and qRT-PCR detection of ESG-related gene Engrailed 1 (En1) and HF-related gene LHX2.

RESULTS

The results showed ESGs but no HFs in the footpads of C57BL/6 mice and SD rats, both ESGs and HFs in the inter-footpads (IFPs) of C57BL/6 mice, and neither ESGs nor HFs in the IFPs of SD rats. The relative quantitative change in En1 was consistent with the differential distribution of ESGs, and the relative quantitative change of LHX2 was consistent with the differential distribution of HFs.

CONCLUSION

C57BL/6 mice and SD rats had their own characteristics in the distribution of ESGs and HFs in the volar skin, and researchers should choose mice or rats, and even forefeet or hindfeet as their research object according to different purposes. The study provides a basis for selection of optimal animal models to study development, wound healing and regeneration of skin appendages.

Silk Fibroin-Based Bioengineered Scaffold for Enabling Hemostasis and Skin Regeneration of Critical-Size Full-Thickness Heat-Induced Burn Wounds

Millions of people around the globe are affected by full-thickness skin injuries. A delay in the healing of such injuries can lead to the formation of chronic wounds, posing several clinical and economic challenges. Current strategies for wound care aim for skin regeneration and not merely skin repair or faster wound closure. The present study aimed to develop a bioactive wound-healing matrix comprising natural biomaterial silk fibroin (SF), clinical-grade human fibrin (FIB), and human hyaluronic acid (HA), resulting in SFFIBHA for regeneration of full-thickness burn wounds. A porous, hemostatic, self-adhesive, moisture-retentive, and biomimetic scaffold that promotes healing was the expected outcome. The study validated a terminal sterilization method, suggesting the stability and translational potential of the novel scaffold. Also, the study demonstrated the regenerative abilities of scaffolds using in vitro cell culture experiments and in vivo full-thickness burn wounds of critical size (4 cm × 4 cm) in a rabbit model. Under in vitro conditions, the scaffold enhanced primary dermal fibroblast adhesion and cell proliferation with regulated extracellular matrix (ECM) synthesis. In vivo, the scaffolds promoted healing with mature epithelium coverage involving intact basal cells, superficial keratinocytes, multilayers of keratohyalin, dermal regeneration with angiogenesis, and deposition of remodeled ECM in 28 days. The relative gene expression of the IL6 marker indicated transitions from inflammation to proliferation stage. In addition, we observed skin appendages and rete peg development in the SFFIBHA-treated wound tissues. Although wound closure was observed, neither negative (untreated/sham) nor positive (commercially available product; NeuSkin) control wounds developed skin appendages/rete pegs or native skin architecture. After 56 days, healing with organized ECM production enabled the recovery of mechanical properties of skin with higher tissue maturity in SFFIBHA-treated wounds. Thus, in a single application, the SFFIBHA scaffold proved to be an efficient biomimetic matrix that can guide burn wound regeneration. The developed matrix is a suture-less, hemostatic, off-the-shelf product for potential wound regenerative applications.

Novel 3D-Printed Cell Culture Inserts for Air-Liquid Interface Cell Culture

In skin research, widely used in vitro 2D monolayer models do not sufficiently mimic physiological properties. To replace, reduce, and refine animal experimentation in the spirit of '3Rs', new approaches such as 3D skin equivalents (SE) are needed to close the in vitro/in vivo gap. Cell culture inserts to culture SE are commercially available, however, these inserts are expensive and of limited versatility regarding experimental settings. This study aimed to design novel cell culture inserts fabricated on commercially available 3D printers for the generation of full-thickness SE. A computer-aided design model was realized by extrusion-based 3D printing of polylactic acid filaments (PLA). Improvements in the design of the inserts for easier and more efficient handling were confirmed in cell culture experiments. Cytotoxic effects of the final product were excluded by testing the inserts in accordance with ISO-norm procedures. The final versions of the inserts were tested to generate skin-like 3D scaffolds cultured at an air-liquid interface. Stratification of the epidermal component was demonstrated by histological analyses. In conclusion, here we demonstrate a fast and cost-effective method for 3D-printed inserts suitable for the generation of 3D cell cultures. The system can be set-up with common 3D printers and allows high flexibility for generating customer-tailored cell culture plastics.

Multi-functional wound dressings based on silicate bioactive materials

Most traditional wound dressings passively offer a protective barrier for the wounds, which lacks the initiative in stimulating tissue regeneration. In addition, cutaneous wound healing is usually accompanied by various complicated conditions, including bacterial infection, skin cancer, and damaged skin appendages, bringing further challenges for wound management in clinic. Therefore, an ideal wound dressing should not only actively stimulate wound healing but also hold multi-functions for solving problems associated with different specific wound conditions. Recent studies have demonstrated that silicate bioceramics and bioglasses are one type of promising materials for the development of wound dressings, as they can actively accelerate wound healing by regulating endothelial cells, dermal fibroblasts, macrophages, and epidermal cells. In particular, silicate-based biomaterials can be further functionalized by specific structural design or doping with functional components, which endow materials with enhanced bioactivities or expanded physicochemical properties such as photothermal, photodynamic, chemodynamic, or imaging properties. The functionalized materials can be used to address wound healing with different demands including but not limited to antibacterial, anticancer, skin appendages regeneration, and wound monitoring. In this review, we summarized the current research on the development of silicate-based multi-functional wound dressings and prospected the development of advanced wound dressings in the future.

Stem Cell-Based Tissue Engineering for the Treatment of Burn Wounds: A Systematic Review of Preclinical Studies

Burn wounds are a devastating type of skin injury leading to severe impacts on both patients and the healthcare system. Current treatment methods are far from ideal, driving the need for tissue engineered solutions. Among various approaches, stem cell-based strategies are promising candidates for improving the treatment of burn wounds. A thorough search of the Embase, Medline, Scopus, and Web of Science databases was conducted to retrieve original research studies on stem cell-based tissue engineering treatments tested in preclinical models of burn wounds, published between January 2009 and June 2021. Of the 347 articles retrieved from the initial database search, 33 were eligible for inclusion in this review. The majority of studies used murine models with a xenogeneic graft, while a few used the porcine model. Thermal burn was the most commonly induced injury type, followed by surgical wound, and less commonly radiation burn. Most studies applied stem cell treatment immediately post-burn, with final endpoints ranging from 7 to 90 days. Mesenchymal stromal cells (MSCs) were the most common stem cell type used in the included studies. Stem cells from a variety of sources were used, most commonly from adipose tissue, bone marrow or umbilical cord, in conjunction with an extensive range of biomaterial scaffolds to treat the skin wounds. Overall, the studies showed favourable results of skin wound repair in animal models when stem cell-based tissue engineering treatments were applied, suggesting that such strategies hold promise as an improved therapy for burn wounds.

Target Receptors of Regenerating Nerves: Neuroma Formation and Current Treatment Options

Neuromas form as a result of disorganized sensory axonal regeneration following nerve injury. Painful neuromas lead to poor quality of life for patients and place a burden on healthcare systems. Modern surgical interventions for neuromas entail guided regeneration of sensory nerve fibers into muscle tissue leading to muscle innervation and neuroma treatment or prevention. However, it is unclear how innervating denervated muscle targets prevents painful neuroma formation, as little is known about the fate of sensory fibers, and more specifically pain fiber, as they regenerate into muscle. Golgi tendon organs and muscle spindles have been proposed as possible receptor targets for the regenerating sensory fibers; however, these receptors are not typically innervated by pain fibers, as these free nerve endings do not synapse on receptors. The mechanisms by which pain fibers are signaled to cease regeneration therefore remain unknown. In this article, we review the physiology underlying nerve regeneration, the guiding molecular signals, and the target receptor specificity of regenerating sensory axons as it pertains to the development and prevention of painful neuroma formation while highlighting gaps in literature. We discuss management options for painful neuromas and the current supporting evidence for the various interventions.

Exosomes Derived From Umbilical Cord Mesenchymal Stem Cells Treat Cutaneous Nerve Damage and Promote Wound Healing

Wound repair is a key step in the treatment of skin injury caused by burn, surgery, and trauma. Various stem cells have been proven to promote wound healing and skin regeneration as candidate seed cells. Therefore, exosomes derived from stem cells are emerging as a promising method for wound repair. However, the mechanism by which exosomes promote wound repair is still unclear. In this study, we reported that exosomes derived from umbilical cord mesenchymal stem cells (UC-MSCs) promote wound healing and skin regeneration by treating cutaneous nerve damage. The results revealed that UC-MSCs exosomes (UC-MSC-Exo) promote the growth and migration of dermal fibroblast cells. In in vitro culture, dermal fibroblasts could promote to nerve cells and secrete nerve growth factors when stimulated by exosomes. During the repair process UC-MSC-Exo accelerated the recruitment of fibroblasts at the site of trauma and significantly enhanced cutaneous nerve regeneration in vivo. Interestingly, it was found that UC-MSC-Exo could promote wound healing and skin regeneration by recruiting fibroblasts, stimulating them to secrete nerve growth factors (NGFs) and promoting skin nerve regeneration. Therefore, we concluded that UC-MSC-Exo promote cutaneous nerve repair, which may play an important role in wound repair and skin regeneration.

Research progress of natural tissue-derived hydrogels for tissue repair and reconstruction

There are many different grafts to repair damaged tissue. Various types of biological scaffolds, including films, fibers, microspheres, and hydrogels, can be used for tissue repair. A hydrogel, which is composed a natural or synthetic polymer network with high water absorption capacity, can provide a microenvironment closely resembling the extracellular matrix (ECM) of natural tissues to stimulate cell adhesion, proliferation, and differentiation. It has been shown to have great application potential in the field of tissue repair and regeneration. Hydrogels derived from natural tissues retain a variety of proteins and growth factors in optimal proportions, which is beneficial for the regeneration of specific tissues. This article reviews the latest research advances in the field of hydrogels from a variety of natural tissue sources, including bone tissue, blood vessels, nerve tissue, adipose tissue, skin tissue, and muscle tissue, including preparation methods, advantages, and applications in tissue engineering and regenerative medicine. Finally, it summarizes and discusses the challenges faced by natural tissue-derived hydrogels used in tissue repair, as well as future research and application directions.

Reciprocal blood exchange in heterochronic parabionts has a deleterious effect on the lifespan of young animals without a positive effect for old animals

Our previous study showed that the exchange of blood between heterochronic parabionts for 3 months did not rejuvenate the immune system of the old partners. Moreover, the young immune system became more aged and began to function according to the "old" principle. Does this "forced aging" affect all organism's systems in this model? We checked the levels of corticosterone, testosterone, IGF-1, insulin, thyroxine in the blood of heterochronic parabionts but did not find significant changes compared to the age-related controls. Since numerous data support the possibility of rejuvenation of the brain, muscles, and other tissues using the model of heterochronic parabiosis, as well as opposite data, we planned to assess the overall effect of this long-term blood exchange on the rate of organism aging. We measured the lifespan of animals that exchanged with blood for 3 months and then were disconnected. Median and maximum life expectancy decreased in young heterochronic parabionts compared with the isochronic control. Old heterochronic parabionts showed only a small trend towards an increase in the median lifespan but it was not statistically significant, and the maximum lifespan did not change compared to the isochronic parabionts. These data support our assumption that old blood contains factors capable of inducing aging in young animals. Finding and selective suppression of aging factor production in the organism could be the key research field for life extension.

Reprograming the immune niche for skin tissue regeneration - From cellular mechanisms to biomaterials applications

Despite the rapid development of therapeutic approaches for skin repair, chronic wounds such as diabetic foot ulcers remain an unaddressed problem that affects millions of people worldwide. Increasing evidence has revealed the crucial and diverse roles of the immune cells in the development and repair of the skin tissue, prompting new research to focus on further understanding and modulating the local immune niche for comprehensive, 'perfect' regeneration. In this review, we first introduce how different immunocytes and certain stromal cells involved in innate and adaptive immunity coordinate to maintain the immune niche and tissue homeostasis, with emphasis on their specific roles in normal and pathological wound healing. We then discuss novel engineering approaches - particularly biomaterials systems and cellular therapies - to target different players of the immune niche, with three major aims to i) overcome 'under-healing', ii) avoid 'over-healing', and iii) promote functional restoration, including appendage development. Finally, we highlight how these strategies strive to manage chronic wounds and achieve full structural and functional skin recovery by creating desirable 'soil' through modulating the immune microenvironment.

Progress in hydrogels for skin wound repair

As the first defensive line between the human body and the outside world, the skin is vulnerable to damage from the external environment. Skin wounds can be divided into acute wounds (mechanical injuries, chemical injuries and surgical wounds, etc.) and chronic wounds (burns, infections, diabetes, etc.). In order to manage skin wound, a variety of wound dressings have been developed, including gauze, films, foams, nanofibers, hydrocolloids and hydrogels. Recently, hydrogels have received much attention because of their natural extracellular matrix (ECM)-mimik structure, tunable mechanical properties, and facile bioactive substance delivery capability. They show great potential application in skin wound repair. This paper first introduces the anatomy and function of the skin, the process of wound healing and conventional wound dressings, and then introduces the composition and construction methods of hydrogels. Next, this paper introduces the necessary properties of hydrogels in skin wound repair and the latest research progress of hydrogel dressings for skin wound repair. Finally, the future development goals of hydrogel materials in the field of wound healing are proposed. This article is protected by copyright. All rights reserved.

Applications of tetrahedral DNA nanostructures in wound repair and tissue regeneration

Tetrahedral DNA nanostructures (TDNs) are molecules with a pyramidal structure formed by folding four single strands of DNA based on the principle of base pairing. Although DNA has polyanionic properties, the special spatial structure of TDNs allows them to penetrate the cell membrane without the aid of transfection agents in a caveolin-dependent manner and enables them to participate in the regulation of cellular processes without obvious toxic side effects. Because of their stable spatial structure, TDNs resist the limitations imposed by nuclease activity and innate immune responses to DNA. In addition, TDNs have good editability and biocompatibility, giving them great advantages for biomedical applications. Previous studies have found that TDNs have a variety of biological properties, including promoting cell migration, proliferation and differentiation, as well as having anti-inflammatory, antioxidant, anti-infective and immune regulation capabilities. Moreover, we confirmed that TDNs can promote the regeneration and repair of skin, blood vessels, muscles and bone tissues. Based on these findings, we believe that TDNs have broad prospects for application in wound repair and regeneration. This article reviews recent progress in TDN research and its applications.

A new susceptibility index to predict the risk of severe herpes zoster-associated pain: A Japanese regional population-based cohort study, the Shizuoka study

BACKGROUND

Approximately 7-20% of patients with herpes zoster (HZ) develop zoster-associated pain (ZAP). ZAP not only impairs quality of life and psychological well-being, but also can reduce work effectiveness, which has negative economic effects. Reports of ZAP risk factors are inconsistent.

OBJECTIVE

To confirm risk factors for the development of severe ZAP in HZ patients in Japan using a large-scale database, the Shizuoka Kokuho Database.

METHODS

A population-based cohort study using the Shizuoka Kokuho Database was conducted. Of 792,647 patients, 7491 (0.95%) experienced "severe ZAP" (as defined in this study). We developed a ZAP risk prediction scoring system by identifying risk factors using logistic regression analysis of several candidate risk factors for severe ZAP: age, sex, seasonality, and presence of comorbidities (using the Charlson comorbidity index), excluding HIV/AIDS.

RESULTS

We identified peripheral vascular disease and the onset from October to December as novel risk factors for severe ZAP, in addition to the previously reported risk factors of age and comorbidities (cerebral vascular disease, chronic pulmonary disease, rheumatic disease, peptic ulcer, liver disease, diabetes, and malignant neoplasms with/without metastasis). In contrast, dementia was found to reduce ZAP risk. We developed a susceptibility index to predict the risk of ZAP.

CONCLUSION

We newly demonstrated that peripheral vascular disease and the onset from October to December are ZAP risk factors. Our comorbidity findings support previous observations. The susceptibility index proposed here provides a new approach to the prevention of ZAP using early intervention for high-risk patients.

A Comparative Study of Breast Sensibility and Patient Satisfaction After Breast Reconstruction: Autologous, 2-Stage Implant-Based, and Prepectoral Direct-to-Implant Reconstruction

BACKGROUND

Currently, a variety of treatment modalities are implemented for breast reconstruction. However, clinical prognosis regarding sensory regeneration of the breast and patient-reported satisfaction remains underexamined. In this study, we aimed to compare breast sensibility after various reconstruction.

METHODS

We conducted a retrospective comparative study of all patients who underwent breast reconstruction between August 2016 and October 2019 at our institution. Acellular dermal matrixes were used to cover the implant inferolaterally in a dual-plane subpectoral approach and to wrap the implant in prepectoral direct to implant (DTI). The cutaneous tactile pressure threshold and patient satisfaction outcome were tested.

RESULTS

A total of 105 breasts were assessed, 30 breasts reconstructed with deep inferior epigastric perforator (DIEP) flap, 40 breasts reconstructed with 2-stage subpectoral implant, and 35 breasts reconstructed with prepectoral DTI. In the specific group-to-group analysis, DIEP and implant groups showed significant differences in sensory recovery, mainly in lateral areas of the reconstructed breast. In 2-stage reconstruction and DTI groups, there were no statistically significant differences. When comparing patient groups using only patients with follow-up lengths of more than 12 months, the difference was more clearly indicated (P = 0.049). Better sensory recovery predicted high satisfaction scores in patient-reported outcomes (P = 0.007).

CONCLUSIONS

We found that subpectoral implant reconstruction and DTI show no statistically significant differences in sensory recovery, and autologous DIEP flap reconstruction results in a better prognosis than prosthesis implant reconstruction. Furthermore, the clarity of the differences increased when the follow-up length was longer than 12 months. Better patient-reported satisfaction was associated with good breast sensibility.

Recent Applications of Electrospun Nanofibrous Scaffold in Tissue Engineering

Tissue engineering is a relatively new area of research that combines medical, biological, and engineering fundamentals to create tissue-engineered constructs that regenerate, preserve, or slightly increase the functions of tissues. To create mature tissue, the extracellular matrix should be imitated by engineered structures, allow for oxygen and nutrient transmission, and release toxins during tissue repair. Numerous recent studies have been devoted to developing three-dimensional nanostructures for tissue engineering. One of the most effective of these methods is electrospinning. Numerous nanofibrous scaffolds have been constructed over the last few decades for tissue repair and restoration. The current review gives an overview of attempts to construct nanofibrous meshes as tissue-engineered scaffolds for various tissues such as bone, cartilage, cardiovascular, and skin tissues. Also, the current article addresses the recent improvements and difficulties in tissue regeneration using electrospinning.

Cell-Biomaterial Constructs for Wound Healing and Skin Regeneration

Over the years, conventional skin grafts, such as full-thickness, split-thickness, and pre-sterilized grafts from human or animal sources, have been at the forefront of skin wound care. However, these conventional grafts are associated with major challenges, including supply shortage, rejection by the immune system, and disease transmission following transplantation. Due to recent progress in nanotechnology and material sciences, advanced artificial skin grafts-based on the fundamental concepts of tissue engineering-are quickly evolving for wound healing and regeneration applications, mainly because they can be uniquely tailored to meet the requirements of specific injuries. Despite tremendous progress in tissue engineering, many challenges and uncertainties still face skin grafts in vivo, such as how to effectively coordinate the interaction between engineered biomaterials and the immune system to prevent graft rejection. Furthermore, in-depth studies on skin regeneration at the molecular level are lacking; as a consequence, the development of novel biomaterial-based systems that interact with the skin at the core level has also been slow. This review will discuss 1) the biological aspects of wound healing and skin regeneration, 2) important characteristics and functions of biomaterials for skin regeneration applications, and 3) synthesis and applications of common biomaterials for skin regeneration. Finally, the current challenges and future directions of biomaterial-based skin regeneration will be addressed.

The role of mineralocorticoids and glucocorticoids under the impact of 11β-hydroxysteroid dehydrogenase in human breast lesions

We attempted to explore the possible involvement of the in situ availability of mineralocorticoids and mineralocorticoid receptor (MR) in the pathogenesis of mammary ductal carcinoma. We also explored their individual profiles among different subtypes of invasive ductal carcinomas of no special type (IDC-NST) by evaluating the status of MR, Glucocorticoid receptor (GR), and 11β hydroxysteroid dehydrogenase (HSD) 1/2 at each stage of the putative cascade of the mammary ductal proliferative disorders. In this study, IDC-NST, ductal carcinoma in situ (DCIS), atypical ductal hyperplasia (ADH), and non-pathological breast tissues were all evaluated by immunohistochemistry. MR was significantly lower in ADH than in DCIS or IDC-NST. 11βHSD2 was significantly lower in ADH than normal breast tissue and 11βHSD1 was significantly higher in DCIS than normal, ADH, or IDC-NST. MR in progesterone receptor (PR)-positive IDC-NST cases tended to be associated with the Ki-67 labeling index. Results of the present study demonstrated that the status of MR and GR in conjunction with the 11βHSDs was correlated with the development of low-grade proliferative disorders in mammary glands. In addition, the potential crosstalk between MR and PR could also influence cell proliferation of breast carcinoma cells but further investigations are required for clarification.

Engineered Pullulan-Collagen-Gold Nano Composite Improves Mesenchymal Stem Cells Neural Differentiation and Inflammatory Regulation

Tissue repair engineering supported by nanoparticles and stem cells has been demonstrated as being an efficient strategy for promoting the healing potential during the regeneration of damaged tissues. In the current study, we prepared various nanomaterials including pure Pul, pure Col, Pul–Col, Pul–Au, Pul–Col–Au, and Col–Au to investigate their physicochemical properties, biocompatibility, biological functions, differentiation capacities, and anti-inflammatory abilities through in vitro and in vivo assessments. The physicochemical properties were characterized by SEM, DLS assay, contact angle measurements, UV-Vis spectra, FTIR spectra, SERS, and XPS analysis. The biocompatibility results demonstrated Pul–Col–Au enhanced cell viability, promoted anti-oxidative ability for MSCs and HSFs, and inhibited monocyte and platelet activation. Pul–Col–Au also induced the lowest cell apoptosis and facilitated the MMP activities. Moreover, we evaluated the efficacy of Pul–Col–Au in the enhancement of neuronal differentiation capacities for MSCs. Our animal models elucidated better biocompatibility, as well as the promotion of endothelialization after implanting Pul–Col–Au for a period of one month. The above evidence indicates the excellent biocompatibility, enhancement of neuronal differentiation, and anti-inflammatory capacities, suggesting that the combination of pullulan, collagen, and Au nanoparticles can be potential nanocomposites for neuronal repair, as well as skin tissue regeneration in any further clinical treatments.

3D spheroids of human placenta-derived mesenchymal stem cells attenuate spinal cord injury in mice

Mesenchymal stem cell (MSC) is an absorbing candidate for cell therapy in treating spinal cord injury (SCI) due to its great potential for multiple cell differentiation, mighty paracrine secretion as well as vigorous immunomodulatory effect, of which are beneficial to the improvement of functional recovery post SCI. However, the therapeutic effects of MSC on SCI have been limited because of the gradual loss of MSC stemness in the process of expanding culture. Therefore, in this study, we aimed to maintain those beneficial properties of MSC via three-dimensional spheroid cell culture and then compared them with conventionally-cultured MSCs in the treatment of SCI both in vitro and in vivo with the aid of two-photon microscope. We found that 3D human placenta-derived MSCs (3D-HPMSCs) demonstrated a significant increase in secretion of anti-inflammatory factors and trophic factors like VEGF, PDGF, FGF via QPCR and Bio-Plex assays, and showed great potentials on angiogenesis and neurite morphogenesis when co-cultured with HUVECs or DRGs in vitro. After transplantation into the injured spinal cord, 3D-HPMSCs managed to survive for the entire experiment and retained their advantageous properties in secretion, and exhibited remarkable effects on neuroprotection by minimizing the lesion cavity, inhibiting the inflammation and astrogliosis, and promoting angiogenesis. Further investigation of axonal dieback via two-photon microscope indicated that 3D-HPMSCs could effectively alleviate axonal dieback post injury. Further, mice only treated with 3D-HPMSCs obtained substantial improvement of functional recovery on electrophysiology, BMS score, and Catwalk analysis. RNA sequencing suggested that the 3D-HPMSCs structure organization-related gene was significantly changed, which was likely to potentiate the angiogenesis and inflammation regulation after SCI. These results suggest that 3D-HPMSCs may hold great potential for the treatment of SCI.

Generation of Skin Organoids: Potential Opportunities and Challenges

Although several types of human skin substitutes are currently available, they usually do not include important skin appendages such as hair follicles and sweat glands, or various skin-related cells, such as dermal adipocytes and sensory neurons. This highlights the need to improve the in vitro human skin generation model for use as a tool for investigating skin diseases and as a source of cells or tissues for skin regeneration. Skin organoids are generated from stem cells and are expected to possess the complexity and function of natural skin. Here, we summarize the current literatures relating to the "niches" of the local skin stem cell microenvironment and the formation of skin organoids, and then discuss the opportunities and challenges associated with multifunctional skin organoids.

Prognostic value of neutrophil-to-lymphocyte ratio in COVID-19 patients: A systematic review and meta-analysis

BACKGROUND

Neutrophil-to-lymphocyte ratio (NLR) is an accessible and widely used biomarker. NLR may be used as an early marker of poor prognosis in patients with COVID-19.

OBJECTIVE

To evaluate the prognostic value of the NLR in patients diagnosed with COVID-19.

METHODS

We conducted a systematic review and meta-analysis. Observational studies that reported the association between baseline NLR values (ie, at hospital admission) and severity or all-cause mortality in COVID-19 patients were included. The quality of the studies was assessed using the Newcastle-Ottawa Scale (NOS). Random effects models and inverse variance method were used for meta-analyses. The effects were expressed as odds ratios (ORs) and their 95% confidence intervals (CIs). Small study effects were assessed with the Egger's test.

RESULTS

We analysed 61 studies (n = 15 522 patients), 58 cohorts, and 3 case-control studies. An increase of one unit of NLR was associated with higher odds of severity (OR 6.22; 95%CI 4.93 to 7.84; P < .001) and higher odds of all-cause mortality (OR 12.6; 95%CI 6.88 to 23.06; P < .001). In our sensitivity analysis, we found that 41 studies with low risk of bias and moderate heterogeneity (I2  = 53% and 58%) maintained strong association between NLR values and both outcomes (severity: OR 5.36; 95% CI 4.45 to 6.45; P < .001; mortality: OR 10.42 95% CI 7.73 to 14.06; P = .005).

CONCLUSIONS

Higher values of NLR were associated with severity and all-cause mortality in hospitalised COVID-19 patients.

The Roles of Non-coding RNA in the Development and Regeneration of Hair Follicles: Current Status and Further Perspectives

Alopecia is a common problem that affects almost every age group and is considered to be an issue for cosmetic or psychiatric reasons. The loss of hair follicles (HFs) and hair caused by alopecia impairs self-esteem, thermoregulation, tactile sensation and protection from ultraviolet light. One strategy to solve this problem is HF regeneration. Many signalling pathways and molecules participate in the morphology and regeneration of HF, such as Wnt/β-catenin, Sonic hedgehog, bone morphogenetic protein and Notch. Non-coding RNAs (ncRNAs), especially microRNAs and long ncRNAs, have significant modulatory roles in HF development and regeneration via regulation of these signalling pathways. This review provides a comprehensive overview of the status and future prospects of ncRNAs in HF regeneration and could prompt novel ncRNA-based therapeutic strategies.

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.

[Research advances on skin tissue regeneration in wound repair]

Wound repair is one of the common clinical problems faced by burn, plastic, and reconstructive surgeons. Current wound repair strategies applied in clinical settings can only achieve pathological repair instead of physiological regeneration. To 'perfectly' repair the defective tissue is the long-time goal of researchers working in this field for a long time. This review introduces the research updates of skin tissue regeneration in wound repair, focusing on the new concept of tissue regeneration technique with stem cells as the core and the construction of scaffold materials for tissue-engineered skin. In summary, making cells proliferate and differentiate into functional skin organ according to the needs of wound healing, regulating the precise location of different cells in the process of wound healing, and reconstructing the normal structure of skin remain the problems needing future explorations.

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.

Engineering immune-responsive biomaterials for skin regeneration

The progress of biomaterials and tissue engineering has led to significant advances in wound healing, but the clinical therapy to regenerate perfect skin remains a great challenge. The implantation of biomaterial scaffolds to heal wounds inevitably leads to a host immune response. Many recent studies revealed that the immune system plays a significant role in both the healing process and the outcome. Immunomodulation or immuno-engineering has thus become a promising approach to develop pro-regenerative scaffolds for perfect skin regeneration. In this paper, we will review recent advancements in immunomodulating biomaterials in the field of skin repair and regeneration, and discuss strategies to modulate the immune response by tailoring the chemical, physical and biological properties of the biomaterials. Understanding the important role of immune responses and manipulating the inherent properties of biomaterials to regulate the immune reaction are approaches to overcome the current bottleneck of skin repair and regeneration.

Co-culture of ASCs/EPCs and dermal extracellular matrix hydrogel enhances the repair of full-thickness skin wound by promoting angiogenesis

Background

The repair of large-scale full-thickness skin defects represents a challenging obstacle in skin tissue engineering. To address the most important problem in skin defect repair, namely insufficient blood supply, this study aimed to find a method that could promote the formation of vascularized skin tissue.

Method

The phenotypes of ASCs and EPCs were identified respectively, and ASCs/EPCs were co-cultured in vitro to detect the expression of dermal and angiogenic genes. Furthermore, the co-culture system combined with dermal extracellular matrix hydrogel was used to repair the full-scale skin defects in rats.

Result

The co-culture of ASCs/EPCs could increase skin- and angiogenesis-related gene expression in vitro. The results of in vivo animal experiments demonstrated that the ASCs/EPCs group could significantly accelerate the repair of skin defects by promoting the regeneration of vascularized skin.

Conclusion

It is feasible to replace traditional single-seed cells with the ASC/EPC co-culture system for vascularized skin regeneration. This system could ultimately enable clinicians to better repair the full-thickness skin defects and avoid donor site morbidity.

3D bioprinting for skin tissue engineering: Current status and perspectives

Skin and skin appendages are vulnerable to injury, requiring rapidly reliable regeneration methods. In recent years, 3D bioprinting has shown potential for wound repair and regeneration. 3D bioprinting can be customized for skin shape with cells and other materials distributed precisely, achieving rapid and reliable production of bionic skin substitutes, therefore, meeting clinical and industrial requirements. Additionally, it has excellent performance with high resolution, flexibility, reproducibility, and high throughput, showing great potential for the fabrication of tissue-engineered skin. This review introduces the common techniques of 3D bioprinting and their application in skin tissue engineering, focusing on the latest research progress in skin appendages (hair follicles and sweat glands) and vascularization, and summarizes current challenges and future development of 3D skin printing.

Extracellular vesicles derived from fibroblasts promote wound healing by optimizing fibroblast and endothelial cellular functions

Extracellular vesicles (EVs) have been exhibited as promising candidates for delivering endogenous therapeutic cargos for regenerative therapies. Fibroblasts could be candidate source cells for EVs, to investigate their therapeutic effects in wound healing. Here we demonstrated the isolation and characterization of fibroblast-derived (L929 cell line) EVs (L929-EVs). Furthermore, L929-EVs treatment showed pro-wound healing effects in vitro by enhancing proliferation, migration, and scarless wound healing related genes in fibroblast cells. L929-EVs treatment also enhanced the migration and tube formation of endothelial cells. The combination of L929-EVs with fibrin glue accelerated wound healing in the mouse skin wound model by enhancing collagen formation, collagen maturation, and blood vessels in the wounded skin. The role of fibroblast-derived EVs in wound healing could be an important phenomenon, and fibroblast-derived EVs could be harnessed for wound healing therapies.

Circ6401, a novel circular RNA, is implicated in repair of the damaged endometrium by Wharton's jelly-derived mesenchymal stem cells through regulation of the miR-29b-1-5p/RAP1B axis

Background

Accumulating evidence indicates that mesenchymal stem cells (MSCs) exert tissue repair effects and therapeutic angiogenesis through their noncoding RNAs (ncRNAs). Our previous studies showed that MSCs derived from Wharton’s jelly (WJ-MSCs) can ameliorate damaged human endometrium by promoting angiogenesis. There is limited information on the functions and mechanism of ncRNAs in MSC-induced endometrial repair, and additional studies are needed for more insights.

Methods

Here, WJ-MSCs were cocultured with or without endometrial stromal cells (ESCs) damaged by mifepristone (cocultured group versus non-cocultured group). TUNEL staining assays, EdU proliferation assays, flow cytometry apoptosis assays, and western blot assays were performed to observe the reparative effect of WJ-MSCs on damaged ESCs. Subsequently, circular RNA (circRNA) and microRNA microarrays were performed between the two groups. A subset of top upregulated circRNAs was validated by qRT-PCR. The functions of circ6401 (hsa_circ_0006401) in WJ-MSCs were investigated using lentivirus-mediated circRNA overexpression assays. The subcellular localization of circ6401 and miR-29b-1-5p in WJ-MSCs was identified by double RNA fluorescence in situ hybridization. Dual-luciferase reporter assays and western blot assays were performed to elucidate the regulatory mechanisms among circ6401, miR-29b-1-5p, and RAP1B.

Results

WJ-MSCs significantly improved ESC proliferation and upregulated the expression of vascular angiogenesis markers. Circ6401 was upregulated in WJ-MSCs cocultured with damaged ESCs, while miR-29b-1-5p was significantly downregulated. Furthermore, circ6401 was found to bind to miR-29b-1-5p and prevent it from decreasing the level of RAP1B, a crucial protein involved in the VEGF signaling pathway, which promoted angiogenesis and stimulated the proliferation of ESCs.

Conclusions

Our results showed the abundance and regulation profiles of ncRNAs of WJ-MSCs during repair of damaged ESCs and, for the first time, clarified the underlying mechanism by which circ6401 promotes endometrial repair by WJ-MSCs; thus, demonstrating that circ6401 may serve as a potential therapeutic target.

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.

Platelet-rich plasma accelerates skin wound healing by promoting re-epithelialization

BACKGROUND

Autologous platelet-rich plasma (PRP) has been suggested to be effective for wound healing. However, evidence for its use in patients with acute and chronic wounds remains insufficient. The aims of this study were to comprehensively examine the effectiveness, synergy and possible mechanism of PRP-mediated improvement of acute skin wound repair.

METHODS

Full-thickness wounds were made on the back of C57/BL6 mice. PRP or saline solution as a control was administered to the wound area. Wound healing rate, local inflammation, angiogenesis, re-epithelialization and collagen deposition were measured at days 3, 5, 7 and 14 after skin injury. The biological character of epidermal stem cells (ESCs), which reflect the potential for re-epithelialization, was further evaluated in vitro and in vivo.

RESULTS

PRP strongly improved skin wound healing, which was associated with regulation of local inflammation, enhancement of angiogenesis and re-epithelialization. PRP treatment significantly reduced the production of inflammatory cytokines interleukin-17A and interleukin-1β. An increase in the local vessel intensity and enhancement of re-epithelialization were also observed in animals with PRP administration and were associated with enhanced secretion of growth factors such as vascular endothelial growth factor and insulin-like growth factor-1. Moreover, PRP treatment ameliorated the survival and activated the migration and proliferation of primary cultured ESCs, and these effects were accompanied by the differentiation of ESCs into adult cells following the changes of CD49f and keratin 10 and keratin 14.

CONCLUSION

PRP improved skin wound healing by modulating inflammation and increasing angiogenesis and re-epithelialization. However, the underlying regulatory mechanism needs to be investigated in the future. Our data provide a preliminary theoretical foundation for the clinical administration of PRP in wound healing and skin regeneration.

Bovine Meniscus Middle Zone Tissue: Measurement of Collagen Fibril Behavior During Compression

BACKGROUND

Type I collagen is the major component of the extracellular matrix of the knee's meniscus and plays a central role in that joint's biomechanical properties. Repair and reconstruction of tissue damage often requires a scaffold to assist the body to rebuild. The middle zone of bovine meniscus is a material that may be useful for the preparation of extracellular matrix scaffolds.

METHODS

Here, synchrotron-based small-angle X-ray scattering (SAXS) patterns of bovine meniscus were collected during unconfined compression. Collagen fibril orientation, D-spacing, compression distance and force were measured.

RESULTS

The collagen fibrils in middle zone meniscal fibrocartilage become more highly oriented perpendicular to the direction of compression. The D-spacing also increases, from 65.0 to 66.3 nm with compression up to 0.43 MPa, representing a 1.8% elongation of collagen fibrils perpendicular to the compression.

CONCLUSION

The elasticity of the collagen fibrils under tension along their length when the meniscus is compressed, therefore, contributes to the overall elastic response of the meniscus only under loads that exceed those likely to be experienced physiologically.

Multifunctional Alginate Hydrogel Protects and Heals Skin Defects in Complex Clinical Situations

Skin defects, soft tissue damage, and fractures often occur simultaneously in severe trauma. Under current medical technology, fractures can be quickly fixed by internal or external repair techniques, and early functional exercises can be performed. However, skin defects heal over a long time and can even be difficult to heal. Functional exercise may cause cutting of fresh granulation to break and impair wound healing. Functional exercise and wound healing seem to contradict each other. In this study, an alginate hydrogel was developed. With self-healing characteristics, the hydrogel tightly adhered to the wound and could self-heal breaks in the gel caused by functional exercises. These characteristics enable this hydrogel to be used in complex clinical situations to solve sports rehabilitation and skin defect repair problems. In addition, this hydrogel can slowly release strontium ions, promote angiogenesis and collagen deposition in the wound, and quickly heal the wound.

A Concise Review on Tissue Engineered Artificial Skin Grafts for Chronic Wound Treatment: Can We Reconstruct Functional Skin Tissue In Vitro?

Chronic wounds occur as a consequence of a prolonged inflammatory phase during the healing process, which precludes skin regeneration. Typical treatment for chronic wounds includes application of autografts, allografts collected from cadaver, and topical delivery of antioxidant, anti-inflammatory, and antibacterial agents. Nevertheless, the mentioned therapies are not sufficient for extensive or deep wounds. Moreover, application of allogeneic skin grafts carries high risk of rejection and treatment failure. Advanced therapies for chronic wounds involve application of bioengineered artificial skin substitutes to overcome graft rejection as well as topical delivery of mesenchymal stem cells to reduce inflammation and accelerate the healing process. This review focuses on the concept of skin tissue engineering, which is a modern approach to chronic wound treatment. The aim of the article is to summarize common therapies for chronic wounds and recent achievements in the development of bioengineered artificial skin constructs, including analysis of biomaterials and cells widely used for skin graft production. This review also presents attempts to reconstruct nerves, pigmentation, and skin appendages (hair follicles, sweat glands) using artificial skin grafts as well as recent trends in the engineering of biomaterials, aiming to produce nanocomposite skin substitutes (nanofilled polymer composites) with controlled antibacterial activity. Finally, the article describes the composition, advantages, and limitations of both newly developed and commercially available bioengineered skin substitutes.

Proteins and Peptides as Important Modifiers of the Polymer Scaffolds for Tissue Engineering Applications-A Review

Polymer scaffolds constitute a very interesting strategy for tissue engineering. Even though they are generally non-toxic, in some cases, they may not provide suitable support for cell adhesion, proliferation, and differentiation, which decelerates tissue regeneration. To improve biological properties, scaffolds are frequently enriched with bioactive molecules, inter alia extracellular matrix proteins, adhesive peptides, growth factors, hormones, and cytokines. Although there are many papers describing synthesis and properties of polymer scaffolds enriched with proteins or peptides, few reviews comprehensively summarize these bioactive molecules. Thus, this review presents the current knowledge about the most important proteins and peptides used for modification of polymer scaffolds for tissue engineering. This paper also describes the influence of addition of proteins and peptides on physicochemical, mechanical, and biological properties of polymer scaffolds. Moreover, this article sums up the major applications of some biodegradable natural and synthetic polymer scaffolds modified with proteins and peptides, which have been developed within the past five years.