Spider Silk-CBD-Cellulose Nanocrystal Composites: Mechanism of Assembly

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.

Stable White Light‐Emitting Biocomposite Films

“…The SEM results indicate that the PGM complex is uniformly covering the fibrous network of the CNC host, further supporting the confocal microscopy observations. The TEM analysis also supports previous studies pointing toward the formation of a layered structure of the composites . Additionally, results indicate that multiple layers with ellipsoid components of an average size of ≈250 nm are formed in the CNC and the composite materials.…”

Biomimetic composites with enhanced toughening using silk-inspired triblock proteins and aligned nanocellulose reinforcements

“…The approach of using CBMs to bind proteins, including silk, to cellulose has been proven very efficient in previous studies. Changes in materials structures, mechanical properties, and adhesive properties are examples of the functionalities achieved ( 18 , 20 , 22 ). CBMs were initially described as parts of cellulose-degrading enzymes needed for docking the enzymes to their substrates ( 21 ), but more recently, it has been suggested that they are widespread also in biological materials, with one similar example being in the interface between carbohydrate and protein in the very tough material of squid beaks ( 17 ).…”

Biological Engineered Living Materials: Growing Functional Materials with Genetically Programmable Properties

“…One common approach to develop new BC-based materials is to blend BC with another biological macromolecule to create a composite. In fact, many biological species have been used to modify BC material properties, including spider silk 61 , gelatin 62 , zein 63 , collagen 64 , hyaluronan 65 , alginate 66 , heparin 67,68 , antimicrobial peptides 69 and growth factors 70,71 . While some of these species were incorporated into the BC matrix by non-specific interactions, others have been specifically bound by fusion to a cellulose-binding domain (CBD) protein [72][73][74] .…”