Silver oxide nanoparticles embedded silk fibroin spuns: Microwave mediated preparation, characterization and their synergistic wound healing and anti-bacterial activity

Abstract

The synergistic wound healing and antibacterial activity of silver oxide nanoparticles embedded silk fibroin (Ag₂O-SF) spuns is reported here. UV–Vis spectro photometric analysis of these spuns showed the surface plasmon resonance (SPR) confirming the formation of the silver oxide nanoparticles (Ag₂O NPs) on the surface of the silk fibroin (SF). Scanning electron microscope (SEM) and Differential scanning calorimetry (DSC) also confirmed the presence of Ag₂O NPs on surface of SF. X-ray diffraction (XRD) analysis revealed the crystalline nature of both SF and Ag₂O-SF. Fourier transform infrared spectroscopy (FT-IR) results showed the different forms of silk (I and II) and their corresponding protein (amide I, II, III) confirmations. Biodegradation study revealed insignificant changes in the morphology of Ag₂O-SF spuns even after 14 days of immersion in phosphate buffered saline (PBS). Ag₂O-SF spuns showed excellent antibacterial activity against both pathogen (S. aureus and M. tuberculosis) and non-pathogen (E. coli) bacteria. More importantly, In vitro wound healing (scratch assay) assay revealed fast migration of the T3T fibroblast cells through the scratch area treated with extract of Ag₂O-SF spuns and the area was completely covered within 24 h. Cytotoxicity assay confirmed the biocompatible nature of the Ag₂O-SF spuns, thus suggesting an ideal material for wound healing and anti-bacterial applications.

Introduction

Generally, skin wounds are disruption of normal skin physiology. The moment wound is created, the healing process is initiated with a specific mechanism by which the body tends to re-establish the skin continuity [1]. This is a complex process and involves the interactions between cells, extracellular matrix components and growth factors [2]. However, there are many external biocompatible wound dressing materials which can promote and aid the wound healing quickly when compared to allowing the wound to heal through the natural process. The ideal wound dressing material should have unique qualities includes providing thermal insulation, mechanical protections, prevent bacterial contamination, allow gaseous and fluid exchange, be non-adherent to the wound, easily removable without irritation, nontoxic, non-allergic, promote moist environment in the wound, enhance water and vapor permeation, absorb excess exudates from the wound and promote epithelialization by releasing biological agents to the wound [3]. There are different natural materials in the form of film, gel, sponges, and electrospunmats of chitosan, fibrin, elastin, gelatin, and hyaluronic acid which can be used as wound dressing materials [4].

Wound infections happens immediately when bacteria adheres to the wound interface [5], [6]. To overcome this problem antibiotics, antimicrobial agents such as metallic nanoparticles have been utilized for wound healing. Electrospun nanofibers with incorporated antibacterial agents such as chitosan [7], [8], silver nanoparticles [9], [10], zinc oxide [11], [12] and chlorhexidine [13], [14] have also demonstrated their potential use in wound healing applications. However, recent studies revealed that the antibiotic resistant bacterial infections have considerably increased in such cases. For example, the methicillin-resistant Staphylococcus aureus (MRSA) accounts for a considerable part of the reported cases of S. aureus infections all over the world [15]. Therefore, researchers have focused on polymers, lipids and peptides as new anti-microbial agents. However, those methods always need complex and tedious procedures, and face the problems of high product cost, low availability and poor biocompatibility. Therefore, there is a growing need to develop biocompatible materials which are cost effective, facile and eco-friendly.

Here, we report the design of a novel, biocompatible and eco-friendly material using silk fibroin (SF) embedded with silver oxide nanoparticles (Ag₂O-SF) for wound healing applications. Silk from the B. mori cocoons, is a structural polymer which contains two proteins namely silk fibroin (SF) and a glue-like protein called sericin. Sericin is detected by T-cells as an antigenic factor; therefore, sericin is to be removed from the cocoon fibers by a process called degumming. The fibrous product obtained after the degumming is SF and is one of the most invaluable material in the field of biomedical engineering [16], [17]. We have chosen this material due to its unique properties including good biocompatibility, permeability, biodegradability, morphologic flexibility, proper mechanical properties and importantly it promotes collagen synthesis and re-epithelialization [18], [19]. Furthermore, it is considered to be proper material for the fabrication into different forms of biomedical products including blended fibers, films, gels, and three-dimensional scaffolds because of its minimal adverse effects on the immune system [16], [17], [20].

In recent years, silver (Ag) and silver oxide (Ag₂O) nanoparticles (NPs) have gained much importance amongst metallic nanoparticles in the field of wound dressings and other biomedical applications because of their broad spectrum antimicrobial properties [21]. Here, we prepared different Ag₂O-SF spuns using microwave irradiations (MI). The individual anti-microbial and wound healing activity of Ag₂O and SF and their synergistic interaction in both activities are studied.