Soft, bio-inspired chitin/protein nanocomposites - mechanical behavior and interface interactions between recombinant...

The rubber-like cuticle of arthropods is a complex nanocomposite of chitin and resilin. High-quality chitin nanofibrils (ChNFs) were combined with recombinant resilin-like proteins (RLPs) to study the mechanical properties of hydrated nanocomposites and ChNF/resilin interactions. Constructs from the resilin gene CG15920 found in Drosophila melanogaster were cloned. These constructs contained exon I (comprising 18 N-terminal elastic repeats), either with or without exon II (a chitin-binding domain (ChBD)). The encoded proteins were then expressed as soluble products in Escherichia coli. The RLPs were purified using immobilized metal affinity chromatography. Their adsorption to chitin was studied in a water suspension of ChNFs by centrifugation and on the model surface of ChNFs by a quartz crystal microbalance. RLP with ChBD interacted strongly with the ChNF, which demonstrates the role of ChBD. ChNF suspensions were mixed with resilin solutions, followed by casting and ruthenium (II)-mediated photo-crosslinking. Tensile properties of hydrated ChNF/resilin nanocomposites were measured in water. The addition of 70 % ChNF resulted in nanocomposites with 30 times higher strength, of 9 MPa compared with the neat ResChBD RLP of 0.3 MPa, at 80 % hydration state, clarifying the reinforcement function of chitin in arthropod cuticles and demonstrating that resilin-like hydrogels showed a strength of 0.2-0.3 MPa and a strain to failure of 167-214 % at an 80 % water content.