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Skin Tissue Engineering

An electrospun NF has contributed to the development of innovative grafting scaffolds for skin. For instance, high porosity of electrospun NFs could provide larger structural space of accommodation for the grafted cells. It also facilitates migration, cell proliferation, oxygen exchange, and nutrient delivery in wound healing. The small pore size of nanofibrous scaffolds provides dehydration and limits the wound infection. The tunable mechanical properties ofelectrospun NFs also prevent wound contraction during implantation. Various natural polymers such as collagen, gelatin, silk, chitosan, and fibrinogen have been fabricated into NFs for wound healing. Cell culture suggests that NFs favored the attachment and proliferation of keratinocytes or fibroblasts. Vatankhah et al. developed cellulose acetate/gelatin electrospun NFs to mimic dermis ECM (a complex combination of proteins and polysaccharides). Electrospun cellulose acetate/gelatin 25:75 NFs represent distinct adherence features and high proliferation of human dermal fibroblasts based on data [53]. In another study, animal data suggest that early-state healing in the collagen NF was promoted with the absence ofsurface tissue debris, and prominent capillary and fibroblast proliferation. However, limitation of natural polymer includes low resistance to enzymatic degradation and weak mechanical properties. In contrast, biodegradable synthetic polymers, such as poly(glycolic acid) (PGA), poly(lactic acid) (PLA), PCL, and their copolymers, are commonly used for skin and other tissue engineering (TE) due to their favorable mechanical properties. To investigate the relationship between the degradation properties of NFs and their efficacy for dermal regeneration, PLA and PLGA with different lactide/glycolide mole fractions (85:15, 75:25, and 50:50) were mixed and electrospun into NFs. In vivo studies showed that poly-L-lactic acid (PLLA) NFs remained stable after 12 months ofimplantation, whereas NFs of PLGA 85:15, 75:25 lost 50% of their original masses after 4 and 3 months, respectively. PLGA (85:15, 75:25) NFs appears to generate favorable biodegradable scaffolds for dermal replacement supporting the growth of keratinocyte, fibroblast, and endothelial cells [54]. The degradation rate can match the healing rate in defected tissue. Similarly, other degradable composite NFs, such as PLGA/dextran, PCL/gelatin, poly(lactic acid-co-caprolactone) (PLCL)/fibrinogen have been fabricated for skin tissue engineering, and promising results were obtained [55].

Wound dressing protects the wound from microorganisms. It absorbs exudates and accelerates the healing process. In cases of burns, diabetic ulcers, and split-skingraft- donor sites the wound healing process is prolonged. Electrospun NFs can efficiently absorb exudates and adjust the wound moisture [56]. The high porosity of nanofibrous membranes contributes to air permeability required for cell respiration. The relatively small pore size of NFs can preserve the wound from bacterial infections. Several advantages such as enhanced homeostasis, flexibility in dressing, mechanical strength, and functionalization with various bioactive molecules are offered by the NF dressings. A NF also possesses the advantage of scar-free regeneration by conducting the normal skin cell proliferation. Electrospun NFs of polyvinyl alcohol (PVA), poly(vinyl acetate), and a blend loaded with ciprofloxacin hydrochloride were studied as wound dressings. Addition of poly (vinyl acetate) to PVA NFs muted drug release at earlier stages, prolonging drug release [57]. In another study, dynamic interactions of fusidic acid—loaded electrospun PLGA NFs with wound bacteria have been explored [58]. In vitro microbiological tests showed bacterial colonization of fibers forming a thick layer of biofilm. Interestingly, the preexposure of membrane to wound bacteria causes significant improvement in drug release rate, which was the consequence of the changes in fiber morphology as well as the reduction in pH of the incubation medium. However, loading of adequate concentrations of fusidic acid into the NFs can remarkably prohibit bacterial biofilm formation [58]. Epidermal growth factor—loaded silk NFs can also accelerate the healing process by compressing the time of wound closure [59].

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