Gelatin-chondroitin-6-sulfate-hyaluronic acid scaffold seeded with vascular endothelial growth factor 165 modified hair follicle stem cells as a three-dimensional skin substitute

A review of glycosaminoglycan-modified electrically conductive polymers for biomedical applications

The application areas of electrically conductive polymers have been steadily growing since their discovery in the late 1970s. Recently, electrically conductive polymers have found their way into biomedicine, allowing the realization of many relevant applications ranging from bioelectronics to scaffolds for tissue engineering. Extracellular matrix components, such as glycosaminoglycans, build an important class of biomaterials that are heavily researched for biomedical applications due to their favorable properties. Due to their highly anionic character and the presence of sulfate groups in glycosaminoglycans, these biomolecules can be employed to functionalize conductive polymers, which enables the tailorability and improvement of cell-material interactions of conductive polymers. This review paper gives an overview of recent research on glycosaminoglycan-modified conductive polymers intended for biomedical applications and discusses the effect of different biological dopants on material characteristics, such as surface roughness, stiffness, and electrochemical properties. Moreover, the key findings of the biological characterization in vitro and in vivo are summarized, and remaining challenges in the field, particularly related to the modification of electrically conductive polymers with glycosaminoglycans to achieve improved functional and biological outcomes, are discussed. STATEMENT OF SIGNIFICANCE: The development of functional biomaterials based on electrically conductive polymers (CPs) for various biomedical applications, such as neural regeneration, drug delivery, or bioelectronics, has been increasingly investigated over the last decades. Recent literature has shown that changes in the synthesis procedure or the chosen dopant could adjust the resulting material characteristics. Hence, an interesting approach lies in using natural biomolecules as dopants for CPs to tailor the biological outcome. This review comprehensively summarizes the state of the art in the field of glycosaminoglycan-modified electrically conductive polymers for the first time, particularly highlighting the effect of the chosen dopant on material characteristics, such as surface morphology or stiffness, electrochemical properties, and consequently, cell-material interactions.

LSD1 interacting with HSP90 promotes skin wound healing by inducing metabolic reprogramming of hair follicle stem cells through the c-MYC/LDHA axis

It has been demonstrated that hair follicle stem cells (HFSCs) can contribute to wound closure and repair. However, the specific mechanism remains unclear due to the complexity of the wound repair process. Lysine-specific demethylase 1 (LSD1), an important gene for the regulation of stem cell differentiation, has been reported to participate in wound healing regulation. Heat shock protein 90 (HSP90), a chaperone protein, is recently discovered to be a driver gene for wound healing. This study explored the molecular mechanisms by which the binding between LSD1 and HSP90 affects the role of HFSCs during skin wound healing. Following bioinformatics analysis, the key genes acting on HFSCs were identified. The expression of LSD1, HSP90, and c-MYC was found to be upregulated in differentiated HFSCs. Analysis of their binding affinity revealed that LSD1 interacted with HSP90 to enhance the stability of the transcription factor c-MYC. Lactate dehydrogenase A (LDHA) has been documented to be essential for HFSC activation. Therefore, we speculate that LDHA may induce the differentiation of HFSCs through glucose metabolism reprogramming. The results showed that c-MYC activated LDHA activity to promote glycolytic metabolism, proliferation, and differentiation of HFSCs. Finally, in vivo animal experiments further confirmed that LSD1 induced skin wound healing in mice via the HSP90/c-MYC/LDHA axis. From our data, we conclude that LSD1 interacting with HSP90 accelerates skin wound healing by inducing HFSC glycolytic metabolism, proliferation, and differentiation via c-MYC/LDHA axis.

[Progress on three-dimensional cell culture technology and their application]

Three-dimensional (3D) cell culture model is a system that co-culture carriers with 3D structural materials and different types of cells in vitro to simulate the microenvironment in vivo. This novel cell culture model has been proved to be close to the natural system in vivo. In the process of cell attachment, migration, mitosis and apoptosis, it could produce biological reactions different from that of monolayer cell culture. Therefore, it can be used as an ideal model to evaluate the dynamic pharmacological effects of active substances and the metastasis process of cancer cells. This paper compared and analyzed the different characteristics of cell growth and development under two-dimensional (2D) and 3D model culture and introduced the establishment method of 3D cell model. The application progress of 3D cell culture technology in tumor model and intestinal absorption model was summarized. Finally, the application prospect of 3D cell model in the evaluation and screening of active substance was revealed. This review is expected to provide reference for the development and application of new 3D cell culture models.

Effects of Hair Follicle Stem Cells Coupled With Polycaprolactone Scaffold on Cutaneous Wound Healing in Diabetic Male Rats

INTRODUCTION

Chronic wounds are debilitating complications of diabetes mellitus. The present study was conducted to investigate the effect of the hair follicle stem cells (HFSCs) by polycaprolactone scaffold on the healing of incisional cutaneous wounds on streptozotocin-induced diabetic male rats.

METHODS

The wound model was obtained by a biopsy punch of the skin of the animals' back. The animals were randomly divided into five groups as follows: (1) Sham (nondiabetic, not treated), (2) Control (diabetic, not treated), (3) Scaffold (diabetic, treated with polycaprolactone nanofiber scaffold), (4) HFSCs (diabetic, treated with HFSCs), and (5) Scaffold + HFSCs (diabetic, treated with combination of Scaffold and HFSCs). The wounds were photographed in the course of the treatment and their healing rate was assessed. The samples were collected from the wound sites 7, 14, and 28 d after their development. Angiogenesis was surveyed by examining messenger RNA expression and the protein synthesis levels of vascular endothelial growth factor receptor 2 (VEGFR2) and platelet/endothelial cell adhesion molecule-1/cluster of differentiation 31. The histological changes were investigated using hematoxylin and eosin and Masson's trichrome staining. Furthermore, the wound breaking strength was measured on the 28th day by tensiometry.

RESULTS

The application of the VEGFR2 as a substrate promotes the expression of CD31 in HFSCs and Scaffold + HFSCs groups compared to controls (P < 0.0001). HFSCs and scaffold also rescue the diabetes-induced dysfunction as assessed based on the parameters, such as viability, proliferation, colony formation, cellular adhesion, and chemotactic migration. HFSCs augment the levels of VEGFR2 and promote the restoration of the wound healing in diabetic groups. Furthermore, the maximum biomechanical stress significantly increased in the experimental diabetic groups (Scaffold: 1.38 ± 0.09, HFSCs: 2.13 ± 0.8, Scaffold + HFSCs: 2.38 ± 0.11) compared to the diabetes control group (1.16 ± 0.12). Using of HFSCs and scaffold on diabetic wounds leads to an accelerated wound closure, notably.

CONCLUSIONS

Thus, the current data showed that HFSCs and scaffold form excellent biomaterial in the treatment of diabetic wounds.

Preparation and characterization of antibacterial and anti-inflammatory hyaluronic acid-chitosan-dexamethasone hydrogels for peri-implantitis repair

Numerous treatment methods for peri-implantitis have been widely used including oral cleaning, traditional metal scraping means, or local antibiotic application. However, to continuously release antibacterial and anti-inflammatory drug in location in situ for effective peri-implantitis repair is still challenging. Herein, an anti-inflammatory drug dexamethasone (DE)-incorporated hyaluronic acid (HA)-chitosan (CT) composite hydrogels system was developed to repair peri-implantitis. The physicochemical characterization and biocompatibility of the hydrogel were evaluated in vitro. The in vivo hydrogels degradation and peri-implantitis repair were assessed in mice. The results showed that the prepared multifunctional hydrogels achieved sustained release, with an equilibrium swelling of 18, and promoted the growth against NIH-3T3 fibroblast cells. The in vitro antibacterial tests showed HA-CT-DE hydrogels can inhibit methicillin-resistant Staphylococcus aureus and Escherichia coli. It down-regulated the expression levels of inflammation factor IL-1β, IL-6 and, TNF-α in peri-implantitis. The prepared HA-CT-DE composite hydrogels with integrated function is promising for the treatment of peri-implantitis.

Hyaluronan in skin wound healing: therapeutic applications

Hyaluronan is a vital constituent in effective skin wound healing. This polysaccharide is ubiquitous throughout the human body and has functional significance for tissue repair and remodelling. The importance of hyaluronan in the proliferative phase of healing is diverse, impacting on cell migration, proliferation, modification of the inflammatory response and on angiogenesis. As such, it holds therapeutic potential for a variety of clinical applications that range from facilitating effective wound healing to burns management and scarring. This overview of the multifaceted roles of hyaluronan considers its current applications to clinical practice in plastic surgery as well as the latest advances in research.

Vascularization strategies for tissue engineering for tracheal reconstruction

Tissue engineering technology provides effective alternative treatments for tracheal reconstruction. The formation of a functional microvascular network is essential to support cell metabolism and ensure the long-term survival of grafts. Although several tracheal replacement therapy strategies have been developed in the past, the critical significance of the formation of microvascular networks in 3D scaffolds has not attracted sufficient attention. Here, we review key technologies and related factors of microvascular network construction in tissue-engineered trachea and explore optimized preparation processes of vascularized functional tissues for clinical applications.

In Vitro and In Vivo Evaluation of Carboxymethyl Cellulose Scaffolds for Bone Tissue Engineering Applications

The present study involves the development of citric acid-cross-linked carboxymethyl cellulose (C3CA) scaffolds by a freeze-drying process. Scaffolds were fabricated at different freezing temperatures of -20, -40, or -80 °C to investigate the influence of scaffold pore size on bone regeneration. All three scaffolds were porous in structure, and the pore size was measured to be 74 ± 4, 55 ± 6, and 46 ± 5 μm for -20, -40, and -80 °C scaffolds. The pores were larger in scaffolds processed at -20 °C compared to -40 and -80 °C, indicating the reduction in pore size of the scaffolds with a decrease in freezing temperature. The cytocompatibility, cell proliferation, and differentiation in C3CA scaffolds were assessed with the Saos-2 osteoblast cell line. These scaffolds supported the proliferation and differentiation of Saos-2 cells with significant matrix mineralization in scaffolds processed at -40 °C. Subcutaneous implantation of C3CA scaffolds in the rat model was investigated for its ability of vascularization and new matrix tissue formation. The matrix formation was observed at the earliest of 14 days in the scaffolds when processed at -40 °C while it was observed only after 28 days of implantation with the scaffolds processed at -20 and -80 °C. These results suggest that the citric acid-cross-linked CMC scaffolds processed at -40 °C can be promising for bone tissue engineering application.

Composite sponges from sheep decellularized small intestinal submucosa for treatment of diabetic wounds

Despite the fast development of technology in the world, diabetic foot wounds cause deaths and massive economical losses. Diabetes comes first among the reasons of non traumatic foot amputations. To reduce the healing time of these fast progressing wounds, effective wound dressings are in high demand. In our study, sheep small intestinal submucosa (SIS) based biocompatible sponges were prepared after SIS decellularization and their wound healing potential was investigated on full thickness skin defects in a diabetic rat model. The decellularized SIS membranes had no cytotoxic effects on human fibroblasts and supported capillary formation by HUVECs in a fibroblast-HUVEC co-culture. Glutaraldehyde crosslinked sponges of three different compositions were prepared to test in a diabetic rat model: gelatin (GS), gelatin: hyaluronic acid (GS:HA) and gelatin: hyaluronic acid: SIS (GS:HA:SIS). The GS:HA:SIS sponges underwent a 24.8 ± 5.4% weight loss in a 7-day in vitro erosion test. All sponges had a similar Young's modulus under compression but GS:HA:SIS had the highest (5.00 ± 0.04 kPa). Statistical analyses of histopathological results of a 12-day in vivo experiment revealed no significant difference among the control, GS, GS:HA, and GS:HA:SIS transplanted groups in terms of granulation tissue thickness, collagen deposition, capillary vessel formation, and foreign body reaction (P > 0.05). On the other hand, in the GS:HA:SIS transplanted group 80% of the animals had a complete epidermal regeneration and this was significantly different than the control group (30%, P < 0.05). Preclinical studies revealed that the ECM of sheep small intestinal submucosa can be used as an effective biomaterial in diabetic wound healing.

Hybrid Sponge-Like Scaffolds Based on Ulvan and Gelatin: Design, Characterization and Evaluation of Their Potential Use in Bone Tissue Engineering

Ulvan, a bioactive natural sulfated polysaccharide, and gelatin, a collagen-derived biopolymer, have attracted interest for the preparation of biomaterials for different biomedical applications, due to their demonstrated compatibility for cell attachment and proliferation. Both ulvan and gelatin have exhibited osteoinductive potential, either alone or in combination with other materials. In the current work, a series of novel hybrid scaffolds based on crosslinked ulvan and gelatin was designed, prepared and characterized. Their mechanical performance, thermal stability, porosity, water-uptake and in vitro degradation ability were assessed, while their morphology was analyzed through scanning electron microscopy. The prepared hybrid ulvan/gelatin scaffolds were characterized by a highly porous and interconnected structure. Human adipose-derived mesenchymal stem cells (hADMSCs) were seeded in selected ulvan/gelatin hybrid scaffolds and their adhesion, survival, proliferation, and osteogenic differentiation efficiency was evaluated. Overall, it was found that the prepared hybrid sponge-like scaffolds could efficiently support mesenchymal stem cells' adhesion and proliferation, suggesting that such scaffolds could have potential uses in bone tissue engineering.

Hair follicle stem cells combined with human allogeneic acellular amniotic membrane for repair of full thickness skin defects in nude mice

Repair of large skin defects caused by burns, trauma, or tumor operations is a clinical challenge. Hair follicle stem cells (HFSCs) are involved in epithelialization of wounds, formation of new hair follicles and promote vascularization in the newly formed skin, and human acellular amniotic membrane (hAAM) is a promising scaffold for skin substitute. Here, we investigated the ability of rat HFSCs (rHFSCs) combined with an hAAM to repair full thickness skin defects in nude mice. The effect of the rHFSC-hAAM composite on the repair of skin defects in nude mice was assessed by hematoxylin and eosin staining, immunohistochemistry, and EdU-labeled cell tracking. Isolated and cultured rHFSCs had strong cloning and proliferation potentials. Immunofluorescence staining and flow cytometry assays showed that rHFSCs expressed high levels of integrin α6, CK15, p63, and Sox9. Cells cultured in hAAM showed flaky and cluster-like morphology and were able to adhere and grow effectively. After transplantation, the rHFSC-hAAM composite promoted wound healing in nude mice. Moreover, cells in the rHFSC-hAAM composite were directly involved in hair follicle formation and angiogenesis of tissue around the hair follicle. These results provide an experimental and theoretical basis for the clinical application of HFSCs in repair of human skin defects and a new approach for skin tissue engineering.

Up-regulated lncRNA5322 elevates MAPK1 to enhance proliferation of hair follicle stem cells as a ceRNA of microRNA-19b-3p

Hair follicle stem cells (HFSCs), located in the bulge region of the follicle, maintain hair follicle growth and cycling. Long non-coding RNAs (lncRNAs), non-protein coding transcripts, are widely known to play critical roles in differentiation and proliferation of stem cells. Therefore, the current study aimed to explore the regulatory roles of lncRNA5322 in HFSCs proliferation and the underlying regulatory mechanisms. Initially, the expression patterns of lncRNA5322 and microRNA-19b-3p (miR-19b-3p) in HFSCs were detected. Subsequently, gain-and loss-of-functions analyses were conducted to explore the roles of lncRNA5322, miR-19b-3p and mitogen-activated protein kinase 1 (MAPK1) in cell proliferation, colony formation and apoptosis of HFSCs, with the expression of cyclin-dependent kinase (CDK)1 and CDK2 examined. Also, the interaction relationships among lncRNA5322, miR-19b-3p and MAPK1 were explored. Furthermore, a mouse model was established to detect the roles of lncRNA5322, miR-19b-3p, and MAPK1 in wound contraction and epidermal regeneration. Over-expressed lncRNA5322 was found to promote proliferation, colony formation ability but inhibit apoptosis of HFSCs, in addition to up-regulation of the expression of CDK1 and CDK2. LncRNA5322 was found to act as a ceRNA of miR-19b-3p which directly targeted MAPK1. Furthermore, up-regulation of lncRNA5322 enhanced wound contraction and epidermal regeneration in vivo by increasing the expression of MAPK1 through functioning as a ceRNA of miR-19b-3p. In summary, the results in this study suggested that lncRNA5322 serves as a ceRNA of miR-19b-3p to elevate the expression of MAPK1, ultimately promoting HFSCs proliferation, wound contraction and epidermal regeneration of mouse model.

Feasibility of repairing full-thickness skin defects by iPSC-derived epithelial stem cells seeded on a human acellular amniotic membrane

Background

Induced pluripotent stem cells (iPSCs) can generate epithelial stem cells (EpSCs) as seed cells for skin substitutes to repair skin defects. Here, we investigated the effects of a human acellular amniotic membrane (hAAM) combined with iPSC-derived CD200⁺/ITGA6⁺ EpSCs as a skin substitute on repairing skin defects in nude mice.

Methods

Human urinary cells isolated from a healthy donor were reprogrammed into iPSCs and then induced into CD200⁺/ITGA6⁺ epithelial stem cells. Immunocytochemistry and RT-PCR were used to examine the characteristics of the induced epithelial stem cells. iPSC-derived EpSCs were cultured on a hAAM, and cytocompatibility of the composite was analyzed by CCK8 assays and scanning electron microscopy. Then, hAAMs combined with iPSC-derived EpSCs were transplanted onto skin defects of mice. The effects of this composite on skin repair were evaluated by immunohistochemistry.

Results

The results showed that CD200⁺/ITGA6⁺ epithelial stem cells induced from iPSCs displayed the phenotypes of hair follicle stem cells. After seeding on the hAAM, iPSC-derived epithelial stem cells had the ability to proliferate. After transplantation, CD200⁺/ITGA6⁺ epithelial stem cells on the hAAM promoted the construction of hair follicles and interfollicular epidermis.

Conclusions

These results indicated that transplantation of a hAAM combined with iPS-derived EpSCs is feasible to reconstruct skin and skin appendages, and may be a substantial reference for iPSC-based therapy for skin defects.

Preparation and properties of cellulose nanocrystals, gelatin, hyaluronic acid composite hydrogel as wound dressing

Gelatin (GA), hyaluronic acid (HA) and cellulose nanocrystals (CNC) are promising materials for skin wound care. In this study the GA-HA-CNC hydrogels were prepared by cross-linking and freeze-drying. The composition and mechanism of GA-HA-CNC hydrogels were confirmed by FTIR. The morphology and pore size were obtained by SEM. We accessed the physical property from rheological results and swelling ratio. NIH-3T3 cells were inoculated into the hydrogels and cultured for different days, then we analyzed the cytotoxicity of the prepared hydrogels by CCK-8 methods and live/dead pictorial diagram using staining kits. FTIR revealed the combination between GA, HA and CNC was attributed to the amide bond and hydrogen bonding. SEM results showed that the drying GA-HA-CNC hydrogels were spongy, with the pore diameter about 80-120 µm. CNC significantly enhanced the property of the hydrogels and play a vital role according to the rheology and swelling results. The cells culture results showed that NIH-3T3 cells can attached to, grow, and proliferate well on the GA-HA-CNC hydrogels. In conclusion, the natural GA-HA-CNC hydrogel has great potential for the skin wound repair.

Are hair follicle stem cells promising candidates for wound healing?

INTRODUCTION

With the continued focus on in-depth investigations of hair follicle stem cells (HFSCs), the role of HFSCs in wound healing has attracted increasing attention from researchers. This review may afford meaningful implications for HFSC treatment of wounds.

AREAS COVERED

We present the properties of HFSCs, analyze the possibility of HFSCs in wound healing, and sum up the recent studies into wound repair with HFSCs. The details of HFSCs in wound healing have been discussed. The possible mechanisms of wound healing with HFSCs have been elaborated. Additionally, the factors that influence HFSCs in wound healing are also summarized.

EXPERT OPINION

Hair follicle stem cells are promising sources for wound healing. However, a further understanding of human HFSCs and the safety use of HFSCs in clinical practice still remain in relative infancy.

Hybrid cellulose nanocrystal/alginate/gelatin scaffold with improved mechanical properties and guided wound healing

Nature derived biopolymers such as polysaccharides and collagen have attracted considerable attention in biomedical applications. Despite excellent biocompatibility and bioactivity, their poor mechanical properties could not meet the requirement for skin regeneration. In this study, cellulose nanocrystal (CNC) was incorporated into the calcium cross-linked sodium alginate/gelatin (SA/Ge) scaffold to reinforce its physicochemical properties. A novel sodium alginate/gelatin/cellulose nanocrystal (SA/Ge/CNC) scaffold was successfully prepared through electrostatic interaction of sodium alginate and gelatin, ionic cross-linking of calcium ions with sodium alginate, and incorporation of CNC. Afterwards, the SA/Ge and SA/Ge/CNC scaffolds were fully characterized and compared with scanning electron microscopy images, swelling behaviors, tensile strengths and contact angles. The involvement of CNC produces a hybrid SA/Ge/CNC scaffold with desired porous network, moderate swelling behavior, and superior mechanical strength (from 18 MPa to 45 MPa). Furthermore, in vitro cytotoxicity and cell growth assay using mouse embryonic fibroblast cells validated that SA/Ge/CNC scaffold was non-toxic and can prompt cell adhesion and proliferation. The in vivo skin regeneration experiments using the SA/Ge/CNC scaffold group showed an improved skin wound healing process with accelerated re-epithelialization, increased collagen deposition and faster extracellular matrix remodeling. Overall, the results suggested that the SA/Ge/CNC hybrid scaffold with enhanced mechanical performance and wound healing efficacy was a promising biomaterial for skin defect regeneration.

Cellulose nanocrystal (CNC) is incorporated into Ca²⁺ cross-linked alginate/gelatin (SA/Ge) scaffold to improve physical, chemical and biological aspects. The SA/Ge/CNC scaffold with enhanced wound healing efficacy is a promising biomaterial for skin defect regeneration.

Gelatin-polysaccharide composite scaffolds for 3D cell culture and tissue engineering: Towards natural therapeutics

Gelatin is a promising material as scaffold with therapeutic and regenerative characteristics due to its chemical similarities to the extracellular matrix (ECM) in the native tissues, biocompatibility, biodegradability, low antigenicity, cost-effectiveness, abundance, and accessible functional groups that allow facile chemical modifications with other biomaterials or biomolecules. Despite the advantages of gelatin, poor mechanical properties, sensitivity to enzymatic degradation, high viscosity, and reduced solubility in concentrated aqueous media have limited its applications and encouraged the development of gelatin-based composite hydrogels. The drawbacks of gelatin may be surmounted by synergistically combining it with a wide range of polysaccharides. The addition of polysaccharides to gelatin is advantageous in mimicking the ECM, which largely contains proteoglycans or glycoproteins. Moreover, gelatin-polysaccharide biomaterials benefit from mechanical resilience, high stability, low thermal expansion, improved hydrophilicity, biocompatibility, antimicrobial and anti-inflammatory properties, and wound healing potential. Here, we discuss how combining gelatin and polysaccharides provides a promising approach for developing superior therapeutic biomaterials. We review gelatin-polysaccharides scaffolds and their applications in cell culture and tissue engineering, providing an outlook for the future of this family of biomaterials as advanced natural therapeutics.

Microfibrous scaffolds from poly(l-lactide-co-ε-caprolactone) blended with xeno-free collagen/hyaluronic acid for improvement of vascularization in tissue engineering applications

Success of 3D tissue substitutes in clinical applications depends on the presence of vascular networks in their structure. Accordingly, research in tissue engineering is focused on the stimulation of angiogenesis or generation of a vascular network in the scaffolds prior to implantation. A novel, xeno-free, collagen/hyaluronic acid-based poly(l-lactide-co-ε-caprolactone) (PLC/COL/HA) (20/9.5/0.5 w/w/w) microfibrous scaffold was produced by electrospinning. Collagen types I and III, and hyaluronic acid were isolated from human umbilical cords and blended with the GMP grade PLC. When compared with PLC scaffolds the PLC/COL/HA had higher water uptake capacity (103% vs 66%) which may have contributed to the decrease in its Young's Modulus (from 1.31 to 0.89 MPa). The PLC/COL/HA better supported adipose tissue-derived mesenchymal stem cell (AT MSC) adhesion; within 24 h the cell number on the PLC/COL/HA scaffolds was 3 fold higher. Co-culture of human umbilical vein endothelial cells and AT MSCs induced capillary formation on both scaffold types, but the PLC/COL/HA led to formation of interconnected vessels whose total length was 1.6 fold of the total vessel length on PLC. Clinical use of this scaffold would eliminate the immune response triggered by xenogeneic collagen and transmission of animal-borne diseases while promoting a better vascular network formation.

Enhanced vascularization of PCL porous scaffolds through VEGF-Fc modification

To accelerate the vascularization of engineered tissue, an endothelial-specific fusion protein (VEGF-Fc), which consists of a human vascular endothelial growth factor (VEGF) and an immunoglobulin G Fc region, was fabricated and used to construct a bioactive interface in a porous scaffold. In this study, VEGF-Fc was immobilized on polycarprolactone (PCL) porous scaffolds by steeping, which is mediated by the hydrophobic binding of the Fc domain. The VEGF-Fc proteins were distributed stably and uniformly throughout the PCL porous scaffolds without affecting their surface morphology and mechanical properties. The immobilized VEGF-Fc activated the phosphorylation of VEGF2 receptor continuously, and further promoted the expressions of PI3K and MAPK, which effectively enhanced the adhesion and proliferation of human vascular endothelial cells (HUVECs). Furthermore, the immobilized VEGF-Fc promoted the migration of HUVECs into the scaffolds, and also enhanced the cellularization and ECM deposition in the subcutaneous implanted scaffolds in rats, which synergistically supported the vascularization of the scaffold in vivo. In view of the advantages of easy use, stability and efficiency, the VEGF-Fc fusion protein appeared to be a promising candidate for surface modification of porous scaffolds for tissue engineering.

Stem Cells and Engineered Scaffolds for Regenerative Wound Healing

The normal wound healing process involves a well-organized cascade of biological pathways and any failure in this process leads to wounds becoming chronic. Non-healing wounds are a burden on healthcare systems and set to increase with aging population and growing incidences of obesity and diabetes. Stem cell-based therapies have the potential to heal chronic wounds but have so far seen little success in the clinic. Current research has been focused on using polymeric biomaterial systems that can act as a niche for these stem cells to improve their survival and paracrine activity that would eventually promote wound healing. Furthermore, different modification strategies have been developed to improve stem cell survival and differentiation, ultimately promoting regenerative wound healing. This review focuses on advanced polymeric scaffolds that have been used to deliver stem cells and have been tested for their efficiency in preclinical animal models of wounds.

Biomaterials for Skin Substitutes

Patients with extensive burns rely on the use of tissue engineered skin due to a lack of sufficient donor tissue, but it is a challenge to identify reliable and economical scaffold materials and donor cell sources for the generation of a functional skin substitute. The current review attempts to evaluate the performance of the wide range of biomaterials available for generating skin substitutes, including both natural biopolymers and synthetic polymers, in terms of tissue response and potential for use in the operating room. Natural biopolymers display an improved cell response, while synthetic polymers provide better control over chemical composition and mechanical properties. It is suggested that not one material meets all the requirements for a skin substitute. Rather, a composite scaffold fabricated from both natural and synthetic biomaterials may allow for the generation of skin substitutes that meet all clinical requirements including a tailored wound size and type, the degree of burn, the patient age, and the available preparation technique. This review aims to be a valuable directory for researchers in the field to find the optimal material or combination of materials based on their specific application.

Vascularization of Lando® dermal scaffold in an acute full-thickness skin-defect porcine model

The Lando^® dermal scaffold is a newly developed, tissue-engineered dermal scaffold material. This study sought to observe its vascularization in an acute full-thickness skin-defect porcine model. There were eight Tibetan pigs in this research. Six 5 × 5 cm full-thickness skin-defect wounds were prepared on the dorsal area of each pig, which were divided into two groups. The experimental group wounds were covered by Lando^® dermal scaffolds, while the other received Vaseline gauzes as blank control. At day 3, 7, 14 and 21 after injury, the general condition of wounds was observed, and wound specimens were obtained for HE staining, Masson staining and the expression of CD31, α-SMA and VEGF, which were examined by immunohistochemistry. The results showed the wounds in the experimental group (Lando) were drier with a lower incidence of infection, and the granulation tissues grew better and smoother than the control group. In the experimental group, the hyperemia, edema and inflammatory reactions were milder, the fibroblasts ingrew earlier, the capillaries grew mostly parallel to the wound surface which resembled normal skin, and the collagen fibers were thicker with more regular arrangement than in the control group. The CD31 + microvessel count, α-SMA + microvessel count and VEGF expression of the experimental group were significantly higher than the control group at day 7 and 14 after injury (p < .05). In conclusion, the Lando^® dermal scaffold showed good vascularization at day 14 post grafting in an acute full-thickness skin-defect porcine model, which may be associated with increased expression of VEGF.

Harnessing chondroitin sulphate in composite scaffolds to direct progenitor and stem cell function for tissue repair

This review details the inclusion of chondroitin sulphate in bioscaffolds for superior functional properties in tissue regenerative applications.

Current Advancements and Strategies in Tissue Engineering for Wound Healing: A Comprehensive Review

Significance: With an aging population leading to an increase in diabetes and associated cutaneous wounds, there is a pressing clinical need to improve wound-healing therapies. Recent Advances: Tissue engineering approaches for wound healing and skin regeneration have been developed over the past few decades. A review of current literature has identified common themes and strategies that are proving successful within the field: The delivery of cells, mainly mesenchymal stem cells, within scaffolds of the native matrix is one such strategy. We overview these approaches and give insights into mechanisms that aid wound healing in different clinical scenarios. Critical Issues: We discuss the importance of the biomimetic niche, and how recapitulating elements of the native microenvironment of cells can help direct cell behavior and fate. Future Directions: It is crucial that during the continued development of tissue engineering in wound repair, there is close collaboration between tissue engineers and clinicians to maintain the translational efficacy of this approach.

Naturally derived proteins and glycosaminoglycan scaffolds for tissue engineering applications

Tissue engineering (TE) aims to mimic the complex environment where organogenesis takes place using advanced materials to recapitulate the tissue niche. Cells, three-dimensional scaffolds and signaling factors are the three main and essential components of TE. Over the years, materials and processes have become more and more sophisticated, allowing researchers to precisely tailor the final chemical, mechanical, structural and biological features of the designed scaffolds. In this review, we will pose the attention on two specific classes of naturally derived polymers: fibrous proteins and glycosaminoglycans (GAGs). These materials hold great promise for advances in the field of regenerative medicine as i) they generally undergo a fast remodeling in vivo favoring neovascularization and functional cells organization and ii) they elicit a negligible immune reaction preventing severe inflammatory response, both representing critical requirements for a successful integration of engineered scaffolds with the host tissue. We will discuss the recent achievements attained in the field of regenerative medicine by using proteins and GAGs, their merits and disadvantages and the ongoing challenges to move the current concepts to practical clinical application.

Functional Modification of Fibrous PCL Scaffolds with Fusion Protein VEGF-HGFI Enhanced Cellularization and Vascularization

The lack of efficient vascularization within frequently used poly(ε-caprolactone) (PCL) scaffolds has hindered their application in tissue engineering. Hydrophobin HGFI, an amphiphilic protein, can form a self-assembly layer on the surface of PCL scaffolds and convert their wettability. In this study, a fusion protein consisting of HGFI and vascular endothelial growth factor (VEGF) is prepared by Pichia pastoris expression system. Sodium dodecyl sulface-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting confirm that the VEGF-HGFI is successfully isolated and purified. Transmission electron microscope and water contact angle measurement demonstrate that VEGF-HGFI can form a self-assembly layer with about 25 nm in thickness on electrospun PCL fibers and increase their hydrophilicity. VEGF-HGFI modification can effectively enhance the adhesion, migration, and proliferation of human umbilical vein endothelial cells. Near-infrared fluorescence imaging shows that the VEGF-HGFI modification on PCL scaffolds can exist at least 21 d in vitro and at least 14 d in vivo. Bioluminescence imaging shows that VEGF-HGFI can effectively activate vascular endothelial growth factor receptor 2 receptors. Subcutaneous implantation in mice and rats reveal that cellularization and vascularization are significantly improved in VEGF-HGFI modified PCL scaffolds. These results suggest that VEGF-HGFI is a useful molecule for functional modification of scaffolds to enhance cellularization and vascularization in tissue engineering.

Current and emerging vascularization strategies in skin tissue engineering

Vascularization is a key process in skin tissue engineering, determining the biological function of artificial skin implants. Hence, efficient vascularization strategies are a major prerequisite for the safe application of these implants in clinical practice. Current approaches include (i) modification of structural and physicochemical properties of dermal scaffolds, (ii) biological scaffold activation with growth factor-releasing systems or gene vectors, and (iii) generation of prevascularized skin substitutes by seeding scaffolds with vessel-forming cells. These conventional approaches may be further supplemented by emerging strategies, such as transplantation of adipose tissue-derived microvascular fragments, 3D bioprinting and microfluidics, miRNA modulation, cell sheet engineering, and fabrication of photosynthetic scaffolds. The successful translation of these vascularization strategies from bench to bedside may pave the way for a broad clinical implementation of skin tissue engineering.

Mining for genes related to choroidal neovascularization based on the shortest path algorithm and protein interaction information

BACKGROUND

Choroidal neovascularization (CNV) is a serious eye disease that may cause visual loss, especially for older people. Many factors have been proven to induce this disease including age, gender, obesity, and so on. However, until now, we have had limited knowledge on CNV's pathogenic mechanism. Discovering the genes that underlie this disease and performing extensive studies on them can help us to understand how CNV occurs and design effective treatments.

METHODS

In this study, we designed a computational method to identify novel CNV-related genes in a large protein network constructed using the protein-protein interaction information in STRING. The candidate genes were first extracted from the shortest paths connecting any two known CNV-related genes and then filtered by a permutation test and using knowledge of their linkages to known CNV-related genes.

RESULTS

A list of putative CNV-related candidate genes was accessed by our method. These genes are deemed to have strong relationships with CNV.

CONCLUSIONS

Extensive analyses of several of the putative genes such as ANK1, ITGA4, CD44 and others indicate that they are related to specific biological processes involved in CNV, implying they may be novel CNV-related genes.

GENERAL SIGNIFICANCE

The newfound putative CNV-related genes may provide new insights into CNV and help design more effective treatments. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Sodium humate accelerates cutaneous wound healing by activating TGF-β/Smads signaling pathway in rats

Sodium humate (HA-Na) has been topically used as a wound healing and anti-inflammatory agent in folk medicine. In the present study, HA-Na was investigated for cutaneous wound healing in Sprague-Dawley rats. HA-Na solution (1.0%, w/v) was topically administered to rats undergoing excision wound models. Healing was assessed with a recombinant bovine basic fibroblast growth factor for external use as positive control. Wound healing rates were calculated on Day 3, 6, 9, 14 and 21 after injury, and tissues were also harvested after the same intervals for histological analysis. In addition, tissue hydroxyproline levels were measured. Furthermore, mRNA levels and protein expressions of transforming growth factor-β1, 2, 3 (TGF-β1, 2, 3) were determined by RT-PCR and western blot. Protein expression levels of Smad-2, -3, -4 and -7 were also detected by western blot. Our study demonstrates that HA-Na has the capacity to promote wound healing in rats via accelerated wound contraction and increased hydroxyproline content. More importantly, these wound healing effects of HA-Na might be mediated through the TGF-β/Smad signaling pathway. HA-Na may be an effective agent for enhanced wound healing.

Preformed gelatin microcryogels as injectable cell carriers for enhanced skin wound healing

Wound dressings of cell-laden bulk hydrogel or scaffold were mainly applied for enhanced cell engraftment in contrast to free cell injection. However, dressing of cells laden in biomaterials on wound surface might not effectively and timely exert functions on deep or chronic wounds where insufficient blood supply exists. Previously, we developed injectable gelatin microcryogels (GMs) which could load cells for enhanced cell delivery and cell therapy. In this study, biological changes of human adipose-derived stem cells (hASCs) laden in GMs were compared in varied aspects with traditional two dimensional (2D) cell culture, such as cell phenotype markers, stemness genes, differentiation, secretion of growth factors, cell apoptosis and cell memory by FACS, QRT-PCR and ELISA, that demonstrated the priming effects of GMs on upregulation of stemness genes and improved secretion of growth factors of hASCs for potential augmented wound healing. In a full-thickness skin wound model in nude mice, multisite injection and dressing of hASCs-laden GMs could significantly accelerate the healing compared to free cell injection. Bioluminescence imaging and protein analysis indicated improved cell retention and secretion of multiple growth factors. Our study suggests that GMs as primed injectable 3D micro-niches represent a new cell delivery methodology for skin wound healing which could not only benefit on the recovery of wound bed but also play direct effects on wound basal layer for healing enhancement. Injectable GMs as facile multisite cell delivery approach potentially provide new minimally-invasive therapeutic strategy for refractory wounds such as diabetic ulcer or radiative skin wound.

STATEMENT OF SIGNIFICANCE

This work applied a type of elastic micro-scaffold (GMs) to load and prime hMSCs for skin wound healing. Due to the injectability of GMs, the 3D cellular micro-niches could simply realize minimally-invasive and multisite cell delivery approach for accelerating the wound healing process superior to free cell injection. The biological features of MSCs has been thoroughly characterized during 3D culture in GMs (i.e. cell proliferation, characterization of cell surface markers, stemness of MSCs in GMs, differentiation of MSCs in GMs, secretion of MSCs in GMs, induced apoptosis of MSCs in GMs). Multiple methods such as bioluminescent imaging, immunohistochemistry, immunofluorescence, qRT-PCR, ELSA and western blot were used to assess the in vivo results between groups.

Smart Dressings Based on Nanostructured Fibers Containing Natural Origin Antimicrobial, Anti-Inflammatory, and Regenerative Compounds

A fast and effective wound healing process would substantially decrease medical costs, wound care supplies, and hospitalization significantly improving the patients' quality of life. The search for effective therapeutic approaches seems to be imperative in order to avoid the aggravation of chronic wounds. In spite of all the efforts that have been made during the recent years towards the development of artificial wound dressings, none of the currently available options combine all the requirements necessary for quick and optimal cutaneous regeneration. Therefore, technological advances in the area of temporary and permanent smart dressings for wound care are required. The development of nanoscience and nanotechnology can improve the materials and designs used in topical wound care in order to efficiently release antimicrobial, anti-inflammatory and regenerative compounds speeding up the endogenous healing process. Nanostructured dressings can overcome the limitations of the current coverings and, separately, natural origin components can also overcome the drawbacks of current antibiotics and antiseptics (mainly cytotoxicity, antibiotic resistance, and allergies). The combination of natural origin components with demonstrated antibiotic, regenerative, or anti-inflammatory properties together with nanostructured materials is a promising approach to fulfil all the requirements needed for the next generation of bioactive wound dressings. Microbially compromised wounds have been treated with different essential oils, honey, cationic peptides, aloe vera, plant extracts, and other natural origin occurring antimicrobial, anti-inflammatory, and regenerative components but the available evidence is limited and insufficient to be able to draw reliable conclusions and to extrapolate those findings to the clinical practice. The evidence and some promising preliminary results indicate that future comparative studies are justified but instead of talking about the beneficial or inert effects of those natural origin occurring materials, the scientific community leads towards the identification of the main active components involved and their mechanism of action during the corresponding healing, antimicrobial, or regenerative processes and in carrying out systematic and comparative controlled tests. Once those natural origin components have been identified and their efficacy validated through solid clinical trials, their combination within nanostructured dressings can open up new avenues in the fabrication of bioactive dressings with outstanding characteristics for wound care. The motivation of this work is to analyze the state of the art in the use of different essential oils, honey, cationic peptides, aloe vera, plant extracts, and other natural origin occurring materials as antimicrobial, anti-inflammatory and regenerative components with the aim of clarifying their potential clinical use in bioactive dressings. We conclude that, for those natural occurring materials, more clinical trials are needed to reach a sufficient level of evidence as therapeutic agents for wound healing management.