Experimental studies of silk and silk composites for biomedical application

• Main Author: Plowright, Robyn
• Published: Nottingham Trent University 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.740760

Genetic engineering has been utilised to produce a range of silk based biomaterials capable of promoting mineralisation to aid bone regeneration via biomimetic routes. Silk fusion proteins, where the silk domain is a derivative of the major ampullate dragline Spidroin 1 from Nephila Clavipes, consisting of a 15mer repeat of a 33-amino acid consensus sequence (SGRGGLGGQG AGAAAAAGGA GQGGYGGLGSQGT)15, were designed to bind to target minerals, silica and hydroxyapatite, through the incorporation of specific binding peptides. The R5 silicifying peptide (SSKKSGSYSGSKGSKRRIL) found in diatoms, was selected for silk-silica composites, the location of the R5, N vs C terminal on the silk repeating unit, was assessed with respect to silicifying capabilities. The VTK peptide (VTKHLNQISQSY), identified via phage display was selected for hydroxyapatite binding, samples compared had the VTK peptide attached to the N, C and both termini of the silk repeating unit. Location and number of binding peptides was evaluated for mineralising capabilities. Samples were primarily studied as films, it was shown that the naturally occurring beneficial physical properties of silk, high tensile strength and versatility, were not affected by the addition of binding peptides for both R5 and VTK containing samples. Further, we could manipulate the mechanical properties of the films by annealing them in the presence of methanol to increase the crystalline beta content, modifying their; hydrophobicity, stiffness and resistance to degradation. After mineralisation studies were completed, chimeric samples were implemented as coatings on both silk and titanium scaffolds. The R5 domain silicifying capabilities were proven to be effective at silicification on the silk scaffold, however comparison to the titanium scaffold showed a more than 10-fold reduction in silica presence, a likely cause being the inert nature of the titanium being exhibited.