ABSTRACT
The fabrication of cellulose-spider silk bio-nanocomposites comprised of cellulose nanocrystals (CNCs) and recombinant spider silk protein fused to a cellulose binding domain (CBD) is described. Silk-CBD successfully binds cellulose, and unlike recombinant silk alone, silk-CBD self-assembles into microfibrils even in the absence of CNCs. Silk-CBD-CNC composite sponges and films show changes in internal structure and CNC alignment related to the addition of silk-CBD. The silk-CBD sponges exhibit improved thermal and structural characteristics in comparison to control recombinant spider silk sponges. The glass transition temperature (Tg) of the silk-CBD sponge was higher than the control silk sponge and similar to native dragline spider silk fibers. Gel filtration analysis, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and cryo-transmission electron microscopy (TEM) indicated that silk-CBD, but not the recombinant silk control, formed a nematic liquid crystalline phase similar to that observed in native spider silk during the silk spinning process. Silk-CBD microfibrils spontaneously formed in solution upon ultrasonication. We suggest a model for silk-CBD assembly that implicates CBD in the central role of driving the dimerization of spider silk monomers, a process essential to the molecular assembly of spider-silk nanofibers and silk-CNC composites.
Subject(s)
Calcium-Binding Proteins/chemistry , Cellulose/chemistry , Nanoparticles/chemistry , Silk/chemistry , Animals , Biocompatible Materials/chemistry , Calcium-Binding Proteins/genetics , Calcium-Binding Proteins/metabolism , Calorimetry, Differential Scanning , Dynamic Light Scattering , Microscopy, Electron, Scanning , Protein Multimerization , Recombinant Proteins/biosynthesis , Recombinant Proteins/chemistry , Recombinant Proteins/isolation & purification , Scattering, Small Angle , Spiders , Transition Temperature , X-Ray DiffractionABSTRACT
Bio-inspired material systems are derived from different living organisms such as plants, arthropods, mammals and marine organisms. These biomaterial systems from nature are always present in the form of composites, with molecular-scale interactions optimized to direct functional features. With interest in replacing synthetic materials with natural materials due to biocompatibility, sustainability and green chemistry issues, it is important to understand the molecular structure and chemistry of the raw component materials to also learn from their natural engineering, interfaces and interactions leading to durable and highly functional material architectures. This review will focus on applications of biomaterials in single material forms, as well as biomimetic composites inspired by natural organizational features. Examples of different natural composite systems will be described, followed by implementation of the principles underlying their composite organization into artificial bio-inspired systems for materials with new functional features for future medicine.
Subject(s)
Biocompatible Materials/chemistry , Biomimetic Materials/chemistry , Biomimetics/methods , Animals , Humans , Nanomedicine/methods , Nanostructures/chemistry , Nanostructures/ultrastructureABSTRACT
Resilin is a polymeric rubber-like protein secreted by insects to specialized cuticle regions, in areas where high resilience and low stiffness are required. Resilin binds to the cuticle polysaccharide chitin via a chitin binding domain and is further polymerized through oxidation of the tyrosine residues resulting in the formation of dityrosine bridges and assembly of a high-performance protein--carbohydrate composite material. We describe the mechanical, structural and biochemical function of chitin binding recombinant Drosophila melanogaster resilin. Various resilin constructs were cloned including the full length gene enabling Ni-NTA purification, as well as heat and salt precipitation for rapid and efficient purification. The binding isotherms and constants (K(d), B(max)) of resilin to chitin via its chitin binding domain were determined and displayed high affinity to chitin, implying its important role in the assembly of the resilin-chitin composite. The structural and elastic properties were investigated using Fourier transform infrared spectroscopy, circular dichroism, and atomic force microscopy with peroxidase cross-linked solid resilin materials. Generally, little structural organization was found by these biophysical methods, suggesting structural order was not induced by the dityrosine cross-links. Further, the elastomeric properties found from the full length protein compared favorably with the shorter resilin generated previously from exon 1. The unusual elastomeric behavior of this protein suggests possible utility in biomaterials applications.
