Extensive studies have been conducted on utilising natural fibres as reinforcement in composite production. All-polymer composites have attracted much attention because of their high strength, enhanced interfacial bonding and recyclability. Silks, as a group of natural animal fibres, possess superior properties, including biocompatibility, tunability and biodegradability. However, few review articles are found on all-silk composites, and they often lack comments on the tailoring of properties through controlling the volume fraction of the matrix. To better understand the fundamental basis of the formation of silk-based composites, this review will discuss the structure and properties of silk-based composites with a focus on employing the time–temperature superposition principle to reveal the corresponding kinetic requirements of the formation process. Additionally, a variety of applications derived from silk-based composites will be explored. The benefits and constraints of each application will be presented and discussed. This review paper will provide a useful overview of research on silk-based biomaterials.

This paper investigates the dissolution of two biopolymers, cellulose and silk fibroin, in a mixture of 1-ethyl-3-methylimidazolium acetate (EmimAc) and dimethyl sulphoxide (DMSO). EmimAc is a promising environmentally friendly solvent currently in wide use but can be limited by its high viscosity, which inhibits the speed of dissolution. To mediate this, DMSO has been used as a cosolvent and has been shown to significantly lower the solution viscosity and aid mass transport. Dissolution experiments are carried out separately for both cellulose and silk fibrion with a range of EmimAc:DMSO ratios from 100 wt% EmimAc to 100 wt% DMSO. Interestingly, the optimal EmimAc:DMSO ratio (in terms of dissolution speed) is found to be very different for the two biopolymers. For cellulose, a mixture of 20 wt% EmimAc with 80 wt% DMSO is found to have the fastest dissolution speed, while for silk fibroin, a ratio of 80 wt% EmimAc with 20 wt% DMSO proves the fastest. These dissolution trials are complemented by rheological and nuclear magnetic resonance experiments to provide further insight into the underlying mechanisms. Finally, we produce hybrid biopolymer films from a solution to show how this work provides a foundation for future effective dissolution and the preparation of hybrid biopolymer films and hybrid biocomposites.

Hybrid biomaterials of silk fibroin and cellulose offer improvements over single-component alternatives in the pursuit of optimised and sustainable materials: showing superior strength, biocompatibility, and flexibility. We investigate the behaviours of fully dissolved and coagulated hybrid films at various compositions and characterise the system with X-ray diffraction, dynamic mechanical thermal, thermogravimetric, and mechanical analyses. We confirm a system optimum in modulus, maximum strength, and maximum strain at failure (2.2 GPa, 28 MPa, and 3.3% respectively) at 85%-95% cellulose and 5%-15% silk fibroin hybrid composition. Thermogravimetric analysis indicates this is due to increasing interaction density in hybrid compositions correlated with the formation of a hybrid mixed phase up to 4 wt%. We recreate conflicting trends in literature showing sample flexibility improving and reducing with addition of silk fibroin and indicate this is due to variations in sample creep and strain rate. We report a slow stress relaxation and time-dependent viscoelasticity causing this, using comparative mechanical tests at different rates of deformation. We propose a slipping mechanism for stress relaxation similar to those seen in other biopolymer-based biological systems, for example actin filaments in cytoskeletons.