Study On Silk Fibroin-based Scaffolds For Wound Scar Inhibition

Hypertrophic traumatic scar is the outcome of abnormal healing caused by the self-repair process after skin injury.For severe skin defects,spontaneous tissue regeneration and uncontrolled collagen deposition often result in the formation of hypertrophic traumatic scar.Tissue engineering scaffolds act as templates for the extracellular matrix,by intervening in the microenvironment of wound healing and regulating collagen deposition,thus potentially inhibiting,or reducing the formation of traumatic scarring at the root.The subject hence consists of four components as follows.Skin tissue consists of the epidermis,dermis,and subcutaneous tissue.Among them,the epidermis is mainly used to block and protect the dermis.After peeling from the silk fiber,silk nanofiber(SNF)with a diameter of 100-400 nm was obtained.SNF films were collected with a uniform and controlled thickness,which were used as an epidermal layer substitute.After immersion in a crosslinker-activated 0.4 wt.%silk fibroin(SF)solution,the SNF film showed a decrease in porosity and an increase in hydrophobicity,with the contact angle increasing from79.41°±3.68°to 92.14°±2.47°,helping to hinder the loss of water from skin defects.The mechanical properties of the SNF film in the wet state were enhanced from 0 MPa to 13.26±0.80 MPa,contributing to the protection of the underlying tissue from physical abrasion,similar with the structural characteristics and physicochemical properties of the epidermis of normal skin.A silk fibroin/hyaluronic acid(SF-HA)porous scaffold was prepared by freeze-drying technique to mimic the dermis of normal skin.Among them,SF and HA mimic the protein and polysaccharide components of the extracellular matrix of skin tissue,respectively.The SNF film and the SNF-HA scaffold were adhered together by regenerated SF scaffold to form a SNF-SF-HA bilayer silk fibroin-based functional scaffold.The bilayer scaffold maintained morphological stability after prolonged immersion in PBS(>1 month),and the two layers were tightly bound to each other without separation.The SNF-SF-HA bilayer scaffold mimics the natural morphology and structure of skin tissue in terms of structure and components.Compared to the SNF film,the SNF-SF-HA scaffold has larger pores and increased hydrophilicity and swelling ratio by 31.9%and 626.8%respectively,suggesting that it may absorb tissue fluid and maintain the microenvironment moist during the pre-wound healing phase.In addition,the water vapor permeability of the bilayer scaffold is adequate for the normal function of tissue engineered skin.In vitro,human umbilical vein endothelial cells were seeded in SNF film,SNF-SF-HA scaffold,and silicone gel film.The results showed that the SNF film had the highest cell viability,the scaffold the second high and the silicone gel film the weakest.This indicated that SNF films were more conducive to cell growth,adhesion,proliferation,and migration than silicone gel films.The cell viability of the scaffold was weaker than that of the SNF films,but still met the cytocompatibility requirements of the dressing,speculated to be due to differences in structure between the two-dimensional and three-dimensional materials.The New Zealand White rabbit ear was used as a model for scar trauma,with a blank control group,SNF film group,and SNF-SF-HA scaffold group.HE staining,Masson's staining,Sirius staining and immunohistochemistry including fluorescence labeling of TGF-?1,COL-1 and?-SMA were performed at the 4^th and 6^th postsurgical weeks.The results indicated that the scar raised(lower)and morphology of the SNF-SF-HA scaffold was significantly better than the other groups;the inflammation infiltration of the scaffold was weaker and the proliferation of fibroblasts was less;the deposition of collagen fibers was thinner and the content and morphology of type III collagen were the closest to normal skin;the expression levels of TGF-?1,COL-1 and?-SMA also showed different levels of down-regulation.In summary,the SNF-SF-HA bilayer silk fibroin-based functional scaffold effectively inhibited and reduced scar hyperplasia in rabbit ears.It is speculated that it plays a templating and filling role in wound healing and tissue reconstruction by absorbing tissue fluid,creating a positive microenvironment for wound reconstruction,down-regulating inflammatory infiltration and fibroblast proliferation,regulating collagen fiber deposition and collagen type conversion,as well as down-regulating the expression levels of TGF-?1,COL-1 and?-SMA,hindering wound contraction,thus achieving the purpose of inhibiting scar formation.This silk fibroin-based scaffold has considerable prospects for application in the prevention and cure of hypertrophic traumatic scar in skin tissue engineering.