Immune Cells in Cutaneous Wound Healing: A Review of Functional Data from Animal Models

The healing of skin wounds involves the activation and recruitment of various immune cell types, many of which are believed to contribute significantly to different aspects of the repair process. Roles for immune cells have been described in practically all stages of wound healing, including hemostasis, inflammation, proliferation and scar formation/remodeling. Over the last decade, tools to deplete immune cell populations in animal models have become more advanced, leading to a surge in the number of studies examining the function of specific immune cell types in skin repair. In this review, we will summarize what is known about distinct immune cell types in cutaneous wound healing, with an emphasis on data from animal studies in which specific cell types have been targeted.     

Tissue Sheet Engineered Using Human Umbilical Cord-Derived Mesenchymal Stem Cells Improves Diabetic Wound Healing

Diabetic foot ulceration is a common chronic diabetic complication. Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) have been widely used in regenerative medicine owing to their multipotency and easy availability. We developed poly(lactic-co-glycolic acid) (PLGA)-based scaffold to create hUC-MSC tissue sheets. In vitro immunostaining showed that hUC-MSC tissue sheets formed thick and solid tissue sheets with an abundance of extracellular matrix (ECM). Diabetic wounds in mice treated with or without either the hUC-MSC tissue sheet, hUC-MSC injection, or fiber only revealed that hUC-MSC tissue sheet transplantation promoted diabetic wound healing with improved re-epithelialization, collagen deposition, blood vessel formation and maturation, and alleviated inflammation compared to that observed in other groups. Taken collectively, our findings suggest that hUC-MSCs cultured on PLGA scaffolds improve diabetic wound healing, collagen deposition, and angiogenesis, and provide a novel and effective method for cell transplantation, and a promising alternative for diabetic skin wound treatment.     

Exosomes Derived from Human Umbilical Cord Mesenchymal Stem Cells Accelerate Diabetic Wound Healing via Promoting M2 Macrophage Polarization,Angiogenesis, and Collagen Deposition

Some scholars have suggested that the clinical application of exosomes derived from human umbilical cord mesenchymal stem cells (hucMSCs-exo) might represent a novel strategy to improve diabetic wound healing. However, the mechanisms underlying the effects of hucMSCs-exo on wound healing remain poorly understood. This study aimed to identify the mechanism of hucMSCs-exo in treating diabetic wounds. HucMSCs-exo were isolated from human umbilical cord mesenchymal stem cells (hucMSCs) and subcutaneously injected into full-thickness wounds in diabetic rats. Wound healing closure rates and histological analysis were performed. The levels of tumor necrosis factor-α (TNF-α), macrophage mannose receptor (MMR/CD206), platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), and vascular endothelial growth factor (VEGF) were detected by immunohistochemistry. The degree of collagen deposition was examined using Masson’s trichrome staining. Gross evaluation of wound healing was carried out from day 0 to 14 post-surgery, and the wound site was harvested for histology on days 3, 7, and 14 post-wounding. HucMSCs-exo transplantation increased diabetic wound healing. In vitro, hucMSCs-exo promoted the proliferation of human umbilical vein endothelial cells (HUVECs) and NIH-3T3 cells. In vivo, hucMSCs-exo reduced wound area and inflammatory infiltration and increased collagen fibers. In addition, wound tissues in the hucMSCs-exo group had higher CD206, CD31, and VEGF expressions and lower TNF-α levels than those in the control group on day 14. Our results demonstrated that hucMSCs-exo facilitated diabetic wound repair by inducing anti-inflammatory macrophages and promoting angiogenesis and collagen deposition.     

Fine Regulation during Wound Healing by Mast Cells,a Physiological Role Not Yet Clarified

Mast cells (MCs) are bone marrow-derived cells capable of secreting many active molecules, ranging from the mediators stored in specific granules, some of which have been known about for several decades (histamine, heparin), to small molecules produced immediately upon stimulation (membrane lipid derivatives, nitric oxide), to a host of constitutively secreted, multifunctional cytokines. With the aid of a wide array of mediators, the activated MCs control the key events of inflammation and therefore participate in the regulation of local immune response. On the basis of the structure, origin, principal subtypes, localization and function of these cells, their involvement in injury repair is therefore to be considered in acute and chronic conditions, respectively. The importance of MCs in regulating the healing processes is underscored by the proposed roles of a surplus or a deficit of their mediators in the formation of exuberant granulation tissue (such as keloids and hypertrophic scars), the delayed closure or dehiscence of wounds and the transition of acute to chronic inflammation.     

TRPV1: Role in Skin and Skin Diseases and Potential Target for Improving Wound Healing

Skin is innervated by a multitude of sensory nerves that are important to the function of this barrier tissue in homeostasis and injury. The role of innervation and neuromediators has been previously reviewed so here we focus on the role of the transient receptor potential cation channel, subfamily V member 1 (TRPV1) in wound healing, with the intent of targeting it in treatment of non-healing wounds. TRPV1 structure and function as well as the outcomes of TRPV1-targeted therapies utilized in several diseases and tissues are summarized. In skin, keratinocytes, sebocytes, nociceptors, and several immune cells express TRPV1, making it an attractive focus area for treating wounds. Many intrinsic and extrinsic factors confound the function and targeting of TRPV1 and may lead to adverse or off-target effects. Therefore, a better understanding of what is known about the role of TRPV1 in skin and wound healing will inform future therapies to treat impaired and chronic wounds to improve healing.     

Impact of Exosomes Released by Different Corneal Cell Types on the Wound Healing Properties of Human Corneal Epithelial Cells

Corneal wound healing involves communication between the different cell types that constitute the three cellular layers of the cornea (epithelium, stroma and endothelium), a process ensured in part by a category of extracellular vesicles called exosomes. In the present study, we isolated exosomes released by primary cultured human corneal epithelial cells (hCECs), corneal fibroblasts (hCFs) and corneal endothelial cells (hCEnCs) and determined whether they have wound healing characteristics of their own and to which point they modify the genetic and proteomic pattern of these cell types. Exosomes released by all three cell types significantly accelerated wound closure of scratch-wounded hCECs in vitro compared to controls (without exosomes). Profiling of activated kinases revealed that exosomes from human corneal cells caused the activation of signal transduction mediators that belong to the HSP27, STAT, β-catenin, GSK-3β and p38 pathways. Most of all, data from gene profiling analyses indicated that exosomes, irrespective of their cellular origin, alter a restricted subset of genes that are completely different between each targeted cell type (hCECs, hCFS, hCEnCs). Analysis of the genes specifically differentially regulated for a given cell-type in the microarray data using the Ingenuity Pathway Analysis (IPA) software revealed that the mean gene expression profile of hCECs cultured in the presence of exosomes would likely promote cell proliferation and migration whereas it would reduce differentiation when compared to control cells. Collectively, our findings represent a conceptual advance in understanding the mechanisms of corneal wound repair that may ultimately open new avenues for the development of novel therapeutic approaches to improve closure of corneal wounds.     

Stem Cells-Derived Extracellular Vesicles: Potential Therapeutics for Wound Healing in Chronic Inflammatory Skin Diseases

Endosome-derived small extracellular vesicles (EVs), often referred to as exosomes, are produced by almost all, if not all, cell types, and are critical for intercellular communication. They are composed of a lipid bilayer associated with membrane proteins and contain a payload of lipids, proteins and regulatory RNAs that depends on the parental cell physiological condition. By transferring their “cargo”, exosomes can modulate the phenotype of neighboring and distant cells. Stem cells (SC) were widely studied for therapeutic applications regarding their regenerative/reparative potential as well as their immunomodulatory properties. Whether from autologous or allogeneic source, SC beneficial effects in terms of repair and regeneration are largely attributed to their paracrine signaling notably through secreted EVs. Subsequently, SC-derived EVs have been investigated for the treatment of various diseases, including inflammatory skin disorders, and are today fast-track cell-free tools for regenerative/reparative strategies. Yet, their clinical application is still facing considerable challenges, including production and isolation procedures, and optimal cell source. Within the emerging concept of “allogeneic-driven benefit” for SC-based therapies, the use of EVs from allogeneic sources becomes the pragmatic choice although a universal allogeneic cell source is still needed. As a unique temporary organ that ensures the mutual coexistence of two allogeneic organisms, mother and fetus, the human placenta offers a persuasive allogeneic stem cell source for development of therapeutic EVs. Advancing cell-free therapeutics nurtures great hope and provides new perspectives for the development of safe and effective treatment in regenerative/reparative medicine and beyond. We will outline the current state of the art in regard of EVs, summarize their therapeutic potential in the context of skin inflammatory disorders, and discuss their translational advantages and hurdles.     

脐血造血干/祖细胞与脂肪干细胞共培养的作用距离研究

设计了一种细胞间距可调的transwell共培养方法,以研究脐带血来源的造血干/祖细胞(HS/PCs)和人脂肪干细胞(human-adipose derived stem cells,h-ADSCs)体外共培养时细胞间作用距离对造血干细胞扩增能力和脂肪干细胞在共培养后干细胞特性的影响.采用不同规格的砂纸打磨孔板的上壁面...     

Hypothermia Does Not Boost the Neuroprotection Promoted by Umbilical Cord Blood Cells in a Neonatal Hypoxia-Ischemia Rat Model

Neonatal hypoxic-ischemic encephalopathy (HIE) is one of the leading causes of death and long-term disability in the perinatal period. Currently, therapeutic hypothermia is the standard of care for this condition with modest efficacy and strict enrollment criteria. Therapy with umbilical cord blood cells (UCBC) has come forward as a strong candidate for the treatment of neonatal HIE, but no preclinical studies have yet compared the action of UCBC combined with hypothermia (HT) with the action of each therapy by itself. Thus, to evaluate the potential of each therapeutic approach, a hypoxic-ischemic brain lesion was induced in postnatal day ten rat pups; two hours later, HT was applied for 4 h; and 24, 48, and 72 h post-injury, UCBC were administered intravenously. The neonatal hypoxic-ischemic injury led to a brain lesion involving about 48% of the left hemisphere that was not improved by HT (36%) or UCBC alone (28%), but only with the combined therapies (25%; p = 0.0294). Moreover, a decrease in glial reactivity and improved functional outcomes were observed in both groups treated with UCBC. Overall, these results support UCBC as a successful therapeutic approach for HIE, even when treatment with therapeutic hypothermia is not possible.     

Wound Healing Impairment in Type 2 Diabetes Model of Leptin-Deficient Mice—A Mechanistic Systematic Review

Type II diabetes mellitus (T2DM) is one of the most prevalent diseases in the world, associated with diabetic foot ulcers and impaired wound healing. There is an ongoing need for interventions effective in treating these two problems. Pre-clinical studies in this field rely on adequate animal models. However, producing such a model is near-impossible given the complex and multifactorial pathogenesis of T2DM. A leptin-deficient murine model was developed in 1959 and relies on either dysfunctional leptin (ob/ob) or a leptin receptor (db/db). Though monogenic, this model has been used in hundreds of studies, including diabetic wound healing research. In this study, we systematically summarize data from over one hundred studies, which described the mechanisms underlying wound healing impairment in this model. We briefly review the wound healing dynamics, growth factors’ dysregulation, angiogenesis, inflammation, the function of leptin and insulin, the role of advanced glycation end-products, extracellular matrix abnormalities, stem cells’ dysregulation, and the role of non-coding RNAs. Some studies investigated novel chronic diabetes wound models, based on a leptin-deficient murine model, which was also described. We also discussed the interventions studied in vivo, which passed into human clinical trials. It is our hope that this review will help plan future research.     

Effect of Baicalin on Wound Healing in a Mouse Model of Pressure Ulcers

One of the most frequent comorbidities that develop in chronically ill or immobilized patients is pressure ulcers, also known as bed sores. Despite ischemia-reperfusion (I/R)-induced skin lesion having been identified as a primary cause of pressure ulcers, wound management efforts have so far failed to significantly improve outcomes. Baicalin, or 5,6,7-trihydroxyflavone, is a type of flavonoid which has been shown to possess a variety of biological characteristics, including antioxidative and anti-inflammatory effects and protection of I/R injury. In vitro wound scratch assay was first used to assess the function of baicalin in wound healing. We established a mouse model of advanced stage pressure ulcers with repeated cycles of I/R pressure load. In this model, topically applied baicalin (100 mg/mL) induced a significant increase in the wound healing process measured by wound area. Histological examination of the pressure ulcer mouse model showed faster granulation tissue formation and re-epithelization in the baicalin-treated group. Next, baicalin downregulated pro-inflammatory cytokines (IL-6 and IL-1β), while upregulating the anti-inflammatory IL-10. Additionally, baicalin induced an increase in several growth factors (VEGF, FGF-2, PDGF-β, and CTGF), promoting the wound healing process. Our results suggest that baicalin could serve as a promising agent for the treatment of pressures ulcers.     

人脐血造血干/祖细胞对裸鼠的致突变作用

目的研究人脐血造血干/祖细胞(HS/PCs-HUCB)对裸鼠的致突变作用。方法取雄性BALB/c裸鼠,随机分为5组:HS/PCs-HUCB高、中、低剂量组及阴性、阳性对照组,HS/PCs-HUCB高、中、低剂量组分别经尾静脉注射1.25×109、3.75×108和1.25×108个细胞/kg,阴性对照组经尾静脉注射含1%人血白蛋白的0.9%NaCl注射液,50ml/kg,阳性对照组经腹腔注射环磷酰胺,50mg/kg,每d给药1次。微核试验连续给药2d,末次给药24h后取骨髓细胞涂片,Giemsa染色,每组裸鼠计数12000个骨髓嗜多染红细胞(PCE)中微核细胞数;精子畸形试验连续给药5d,首次给药后第35天取附睾,精子滴片,伊红染色,每组裸鼠计数1500个精子的形态。结果HS/PCs-HUCB各剂量组裸鼠的微核率和精子畸形率与阴性对照组比较,差异均无统计学意义,各组间精子畸形类型构成比差异无统计学意义,畸形精子以无定形为主,其次为无钩、双头、双尾、双体、胖头等;而阳性对照组的微核率和精子畸形率均显著高于阴性对照组。结论HS/PCs-HUCB对裸鼠无致突变作用。     

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

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

Optimization of an Ex-Vivo Human Skin/Vein Model for Long-Term Wound Healing Studies: Ground Preparatory Activities for the ‘Suture in Space’ Experiment Onboard the International Space Station

This study is preliminary to an experiment to be performed onboard the International Space Station (ISS) and on Earth to investigate how low gravity influences the healing of sutured human skin and vein wounds. Its objective was to ascertain whether these tissue explants could be maintained to be viable ex vivo for long periods of time, mimicking the experimental conditions onboard the ISS. We developed an automated tissue culture chamber, reproducing and monitoring the physiological tensile forces over time, and a culture medium enriched with serelaxin (60 ng/mL) and (Zn(PipNONO)Cl) (28 ng/mL), known to extend viability of explanted organs for transplantation. The results show that the human skin and vein specimens remained viable for more than 4 weeks, with no substantial signs of damage in their tissues and cells. As a further clue about cell viability, some typical events associated with wound repair were observed in the tissue areas close to the wound, namely remodeling of collagen fibers in the papillary dermis and of elastic fibers in the vein wall, proliferation of keratinocyte stem cells, and expression of the endothelial functional markers eNOS and FGF-2. These findings validate the suitability of this new ex vivo organ culture system for wound healing studies, not only for the scheduled space experiment but also for applications on Earth, such as drug discovery purposes.     

Effect of Polymeric Nanoparticles with Entrapped Fish Oil or Mupirocin on Skin Wound Healing Using a Porcine Model

The utilization of poly(lactic-co-glycolic) acid (PLGA) nanoparticles (NPs) with entrapped fish oil (FO) loaded in collagen-based scaffolds for cutaneous wound healing using a porcine model is unique for the present study. Full-depth cutaneous excisions (5 × 5 cm) on the pig dorsa were treated with pure collagen scaffold (control, C), empty PLGA NPs (NP), FO, mupirocin (MUP), PLGA NPs with entrapped FO (NP/FO) and PLGA NPs with entrapped MUP (NP/MUP). The following markers were evaluated on days 0, 3, 7, 14 and 21 post-excision: collagen, hydroxyproline (HP), angiogenesis and expressions of the COX2, EGF, COL1A1, COL1A3, TGFB1, VEGFA, CCL5 and CCR5 genes. The hypothesis that NP/FO treatment is superior to FO alone and that it is comparable to NP/MUP was tested. NP/FO treatment increased HP in comparison with both FO alone and NP/MUP (day 14) but decreased (p < 0.05) angiogenesis in comparison with FO alone (day 3). NP/FO increased (p < 0.05) the expression of the CCR5 gene (day 3) and tended (p > 0.05) to increase the expressions of the EGF (day 7, day 14), TGFB1 (day 21) and CCL5 (day 7, day 21) genes as compared with NP/MUP. NP/FO can be suggested as a suitable alternative to NP/MUP in cutaneous wound treatment.     

Borrowing the Features of Biopolymers for Emerging Wound Healing Dressings: A Review

Wound dressing design is a dynamic and rapidly growing field of the medical wound-care market worldwide. Advances in technology have resulted in the development of a wide range of wound dressings that treat different types of wounds by targeting the four phases of healing. The ideal wound dressing should perform rapid healing; preserve the body’s water content; be oxygen permeable, non-adherent on the wound and hypoallergenic; and provide a barrier against external contaminants—at a reasonable cost and with minimal inconvenience to the patient. Therefore, choosing the best dressing should be based on what the wound needs and what the dressing does to achieve complete regeneration and restoration of the skin’s structure and function. Biopolymers, such as alginate (ALG), chitosan (Cs), collagen (Col), hyaluronic acid (HA) and silk fibroin (SF), are extensively used in wound management due to their biocompatibility, biodegradability and similarity to macromolecules recognized by the human body. However, most of the formulations based on biopolymers still show various issues; thus, strategies to combine them with molecular biology approaches represent the future of wound healing. Therefore, this article provides an overview of biopolymers’ roles in wound physiology as a perspective on the development of a new generation of enhanced, naturally inspired, smart wound dressings based on blood products, stem cells and growth factors.     

Evaluation of a Gel Containing a Propionibacterium Extract in an In Vivo Model of Wound Healing

Inappropriate wound healing (WH) management can cause significant comorbidities, especially in patients affected by chronic and metabolic diseases, such as diabetes. WH involves several different, partially overlapping processes, including hemostasis, inflammation, cell proliferation, and remodeling. Oxidative stress in WH contributes to WH impairment because of the overexpression of radical oxygen species (ROS) and nitrogen species (RNS). This study aimed to evaluate the in vitro antioxidative action of a gel containing a Propionibacterium extract (Emorsan^® Gel) and assess its skin re-epithelialization properties in a mouse model of WH. The scavenging effects of the bacterial extract were assessed in vitro through the ABTS and DPPH assays and in L-929 murine fibroblasts. The effects of the Emorsan^® Gel were studied in vivo in a murine model of WH. After WH induction, mice were treated daily with vehicle or Emorsan^® Gel for 6 or 12 days. According to the in vitro tests, the Propionibacterium extract exerted an inhibitory effect on ROS and RNS, consequently leading to the reduction in malondialdehyde (MDA) and nitrite levels. Before proceeding with the in vivo study, the Emorsan^® Gel was verified to be unabsorbed. Therefore, the observed effects could be ascribed to a local action. The results obtained in vivo showed that through local reduction of oxidative stress and inflammation (IL-1β, TNF-α), the Emorsan^® Gel significantly reduced the infiltration of mast cells into the injured wound, leading to the amelioration of symptoms such as itch and skin irritation. Therefore, the Emorsan^® Gel improved the speed and percentage of wound area closure by improving the tissue remodeling process, prompting vascular–endothelial growth factor (VEGF) and transforming growth factor (TGF)- β production and reducing the expression of adhesion molecules. Emorsan^® Gel, by its ability to inhibit free radicals, could reduce local inflammation and oxidative stress, thus enhancing the speed of wound healing.     

Secretome from Human Mesenchymal Stem Cells-Derived Endothelial Cells Promotes Wound Healing in a Type-2 Diabetes Mouse Model

Tissue regeneration is often impaired in patients with metabolic disorders such as diabetes mellitus and obesity, exhibiting reduced wound repair and limited regeneration capacity. We and others have demonstrated that wound healing under normal metabolic conditions is potentiated by the secretome of human endothelial cell-differentiated mesenchymal stem cells (hMSC-EC). However, it is unknown whether this effect is sustained under hyperglycemic conditions. In this study, the wound healing effect of secretomes from undifferentiated human mesenchymal stem cells (hMSC) and hMSC-EC in a type-2 diabetes mouse model was analyzed. hMSC were isolated from human Wharton’s jelly and differentiated into hMSC-EC. hMSC and hMSC-EC secretomes were analyzed and their wound healing capacity in C57Bl/6J mice fed with control (CD) or high fat diet (HFD) was evaluated. Our results showed that hMSC-EC secretome enhanced endothelial cell proliferation and wound healing in vivo when compared with hMSC secretome. Five soluble proteins (angiopoietin-1, angiopoietin-2, Factor de crecimiento fibroblástico, Matrix metallopeptidase 9, and Vascular Endothelial Growth Factor) were enriched in hMSC-EC secretome in comparison to hMSC secretome. Thus, the five recombinant proteins were mixed, and their pro-healing property was evaluated in vitro and in vivo. Functional analysis demonstrated that a cocktail of these proteins enhanced the wound healing process similar to hMSC-EC secretome in HFD mice. Overall, our results show that hMSC-EC secretome or a combination of specific proteins enriched in the hMSC-EC secretome enhanced wound healing process under hyperglycemic conditions.     

Cellular Interaction of Human Skin Cells towards Natural Bioink via 3D-Bioprinting Technologies for Chronic Wound: A Comprehensive Review

Skin substitutes can provide a temporary or permanent treatment option for chronic wounds. The selection of skin substitutes depends on several factors, including the type of wound and its severity. Full-thickness skin grafts (SGs) require a well-vascularised bed and sometimes will lead to contraction and scarring formation. Besides, donor sites for full-thickness skin grafts are very limited if the wound area is big, and it has been proven to have the lowest survival rate compared to thick- and thin-split thickness. Tissue engineering technology has introduced new advanced strategies since the last decades to fabricate the composite scaffold via the 3D-bioprinting approach as a tissue replacement strategy. Considering the current global donor shortage for autologous split-thickness skin graft (ASSG), skin 3D-bioprinting has emerged as a potential alternative to replace the ASSG treatment. The three-dimensional (3D)-bioprinting technique yields scaffold fabrication with the combination of biomaterials and cells to form bioinks. Thus, the essential key factor for success in 3D-bioprinting is selecting and developing suitable bioinks to maintain the mechanisms of cellular activity. This crucial stage is vital to mimic the native extracellular matrix (ECM) for the sustainability of cell viability before tissue regeneration. This comprehensive review outlined the application of the 3D-bioprinting technique to develop skin tissue regeneration. The cell viability of human skin cells, dermal fibroblasts (DFs), and keratinocytes (KCs) during in vitro testing has been further discussed prior to in vivo application. It is essential to ensure the printed tissue/organ constantly allows cellular activities, including cell proliferation rate and migration capacity. Therefore, 3D-bioprinting plays a vital role in developing a complex skin tissue structure for tissue replacement approach in future precision medicine.