Tunable morphology and structural properties of recombinant silk-elastin biopolymers by electrospinning

Abstract

Silk-elastinlike proteins (SELPs) are a new class of bioinspired, biologically synthesized block copolymers, consisting in silk fibroin (GAGAGS) and elastin (VPGVG) repeating units. With the aim of developing new high performance protein polymers, we report the electrospinning of two new SELP copolymers based on silk fibroin crystalline blocks and elastin-like thermoplastic (VPAVG) blocks. These new copolymers, named S10E20 and S5E10, where S corresponds to the number of repetitions of the silk block and E to the number of elastin blocks, were chemically synthesized by recombinant DNA technology and biologically produced by Escherichia coli. Due to its easy implementation, electrospinning has received a lot of attention as a technique to produce nanofibers. Electrospinning of different SELPs concentrations (5, 9, 13, 17 and 21 wt%) was performed in aqueous solution or in formic acid without addition of external agents. Electrospun structures were analyzed by scanning electron microscopy and the average diameter was calculated. The effect of methanol in the electrospun mat was also evaluated, morphologically by scanning electron microscopy and structurally by analyzing the secondary structure by FTIR. By varying the concentration, the morphology and size of the electrospun structures, can be customized to tailored applications. Polymer concentration and solvent, either water or formic acid, showed to play an important and determinant role in the process of electrospinning. While low concentrations of polymer solution lead to the formation of nano-microsized structures, higher polymer concentrations produced electrospun fibers with increasing diameter and size distribution, ranging from the nano to the sub-microscale. Comparing the solvents, electrospun fibers in aqueous solution lead to the formation of fibers with higher diameter and size distribution.