Scaffolds are bioactive substrates that play vital role in tissue repair and regeneration since they could mimic components and structural perspectives of extracellular matrix (ECM) [1–3]. Scaffolds should not only possess suitable mechanical properties, but also need to imitate the structural aspects of natural ECM to create an ideal support for cell seeding, adhesion, proliferation as well as differentiation with least inflammatory and toxic reactions [1–5]. Natural ECM consists of diverse interwoven protein fibers with nanometer diameters and nanoscale structure [1, 2, 5, 6]. These nanoscale structures can support cell functions and direct cell fate [1, 2, 5]. In this regard, fabricating scaffolds with the same architecture of native tissues is one of the main challenges in this field [1, 2, 5, 6]. Production of nanoscale scaffolds as ECM substitutes have been well developed in various methods including phase separation, self-assembly, synthetic molding and electrospinning [1, 2, 5]. Among these, the electrospinning process has recently gained considerable attention because of its high degrees of processability, diverse applicability of biopolymers over other methods and capacity in mimicking extracellular matrix (ECM) structure with adjustable porosity and pore size distribution of fibers [1, 2, 5, 7]. Furthermore, the large surface area of electrospun fibers and porous structure can extensively enhance cell viability and functionality [1, 2, 5, 8, 9]. Until now, the wide range of polymers are capable of being electrospun which shows flexibility in designing fibrous scaffolds from pure or blended of natural and synthetic polymers [1, 2, 5, 6, 8–10]. Natural polymers include collagen, fibrin, silk, carboxymethyl cellulose (CMC), hyaluronic acid (HA) and chitosan (Ch) which are actively interacted with cells through cell surface receptor ligands and in following cell-signaling pathways resulting in the regulation of normal cell behavior [1, 10–13]. Because of their bioactive properties and biodegradability, they are more likely to interact with cells, but they are expensive, not easy accessible and have poor mechanical properties. By contrast, synthetic polymers provide great applicability by chemical or physical modifications and their excellent processability [1, 5, 13, 14]. However, these polymers lack bioactivity and special care needs to be taken to ensure that newly synthesized polymers are biocompatible [1, 5, 13, 14]. Poly vinyl alcohol (PVA) is food and drug administration (FDA) approved polymer for clinical use due to its degradability, cytocompatibility and processability as well as excellent strength and elongation properties [1, 4–6, 15]. Nevertheless, single-component biopolymer is generally insufficient for good physical and biochemical fiber specifications [2, 11, 13, 16–18]. To overcome these limitations, recent effort has been given to takes advantage of the physical properties of the synthetic polymers and the bioactivity of the natural polymers while minimizing disadvantages of both combine for the preparation of electrospun fibers [2, 11, 13, 16–18].
Silk protein generated from silk cocoons has been extensively used for the medical applications including wound healing, tissue regeneration and drug delivery [4, 7, 19]. Besides, Ch derivative as a biomimetic polymer has antibacterial effects on wound healing and skin tissue regeneration [4, 5, 16]. Cell adhesion to Ch hydrogels and their degradation can be controlled by N-acetylation. The N-acetylglucosamine moiety in Ch is a structural feature also found in glycosaminoglycan (GAG), a component of native ECM. Since the properties of GAG include specific interactions with bioactive components and cells, this suggests that the analogous structure of Ch may mimic these bioactivities. It is expected that with combination of synthetic PVA and natural derived polymers including Ch and silk could provide proper microenvironment for cell proliferation and differentiation in skin regeneration.
In this study we have fabricated hybrid Ch-PVA + Silk fibrous mat in uniform size and desirable porosity, degradability and mechanical properties through co-electrospinning process for wound healing application in a full-thickness excisional animal model. The physical and chemical characteristics of Ch-PVA + Silk fibrous mat including pore size, porosity, tensile strength, degradability and hydrophilic properties were evaluated in vitro. The cellular attachment, morphology and proliferation on fabricated fibers were investigated during extended time of incubation. The differentiation potential of mesenchymal stem cell to keratinocyte performed using defined conditional media. The wound healing test involved using Ch-PVA + Silk fibrous mat seeded with MSC-derived keratinocytes was performed in rat animal models (an overview of this study is shown in Fig. 1).