Structural evolution of photocrosslinked silk fibroin and silk fibroin-based hybrid hydrogels: A small angle and ultra-small angle scattering investigation.

Regenerated Bombyx mori silk fibroin (RSF) is a widely recognized protein for biomedical applications; however, its hierarchical gel structure is poorly understood. In this paper, the hierarchical structure of photocrosslinked RSF and RSF-based hybrid hydrogel systems: (i) RSF/Rec1-resilin and (ii) RSF/poly(N-vinylcaprolactam (PVCL) is reported for the first time using small-angle scattering (SAS) techniques. The structure of RSF in dilute to concentrated solution to fabricated hydrogels were characterized using small angle X-ray scattering (SAXS), small angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) techniques. The RSF hydrogel exhibited three distinctive structural characteristics: (i) a Porod region in the length scale of 2 to 3nm due to hydrophobic domains (containing ß-sheets) which exhibits sharp interfaces with the amorphous matrix of the hydrogel and the solvent, (ii) a Guinier region in the length scale of 4 to 20nm due to hydrophilic domains (containing turns and random coil), and (iii) a Porod-like region in the length scale of few micrometers due to water pores/channels exhibiting fractal-like characteristics. Addition of Rec1-resilin or PVCL to RSF and subsequent crosslinking systematically increased the nanoscale size of hydrophobic and hydrophilic domains, whereas decreased the homogeneity of pore size distribution in the microscale. The presented results have implications on the fundamental understanding of the structure-property relationship of RSF-based hydrogels.

Fabrication and characterisation of an electrospun tubular 3D scaffold platform of poly(vinylidene fluoride-co-hexafluoropropylene) for small-diameter blood vessel application.

In this research, nanofibrous 3D tubular (~4-mm-diameter tube) scaffolds of poly (vinylidene fluoride-co-hexafluoropropylene) were fabricated by electrospinning. The role of surface charge in the success of these scaffolds for potential small-diameter artificial vascular grafts has been investigated using streaming potential study. Prior to endothelial cell culture, surface properties such as wettability and the surface charge of these tubular scaffolds were evaluated using unmodified and fibrinogen-adsorbed surfaces to understand their interaction with surrounding environment. The tubular scaffolds constructed using electrospinning show similar mechanical properties such as tensile strength and elastic modulus as those of native vessels. Whilst endothelial cell proliferation on unmodified tubes, as analysed by scanning electron microscopy, was found to be moderate, a simple process of dynamic fibrinogen adsorption was seen to enhance the endothelialisation of these tubular grafts. The high negative zeta potential values, high strength, robustness and structural reliability of the scaffolds represent them to be promising biomaterials for vascular graft applications.