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

Abstract

Silk and cellulose are biopolymers that show strong potential as future sustainable materials. They also have complementary properties, suitable for combination in composite materials where cellulose would form the reinforcing component and silk the tough matrix. A major challenge concerns balancing structure and functional properties in the assembly process. We used recombinant proteins with triblock architecture, combining structurally modified spider silk with terminal cellulose affinity modules. Flow alignment of cellulose nanofibrils and triblock protein allowed continuous fiber production. Protein assembly involved phase separation into concentrated coacervates, with subsequent conformational switching from disordered structures into β sheets. This process gave the matrix a tough adhesiveness, forming a new composite material with high strength and stiffness combined with increased toughness. We show that versatile design possibilities in protein engineering enable new fully biological materials and emphasize the key role of controlled assembly at multiple length scales for realization.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

“…On the other hand, reports show that highly aligned nanofibers can be achieved when assembling them into fibers. [ 326–328 ] The results highlight the role of alignment for achieving good fibril contacts and hence properties (Figure 14b). [ 329 ]…”

“…Reproduced with permission. [ 328 ] Copyright 2019 The Authors, published by AAAS. Reproduced/adapted from ref.…”

“…In another study, recombinantly produced and engineered silk proteins containing cellulose adhesive proteins were combined with cellulose fibrils having nonmodified native surfaces to show toughening and strengthening of aligned nanocellulose fibrils (Figure 14c). [ 328 ]…”

Bioinspired functionally graded composite assembled using cellulose nanocrystals and genetically engineered proteins with controlled biomineralization

“…First, we set out to explore the use of reinforcing structural proteins to produce a tough fracture energy-dissipating matrix (Figure 2d and Figure S1). [20][21][22][23] We hypothesized that such proteins would enable bridging interactions between the stiff long-range chiral nematic helicoidal CNC scaffold, thus acting as a molecular binder. Second, our earlier reports demonstrate that to use these proteins as a binding matrix for biocomposites, it is crucial to initially induce their phase separation and condensation into highly concentrated assemblies, often described as coacervates (Figure 2e-f and S2-S6).…”

“…[24][25][26][27] Key advantages of concentrated coacervates include increased intermolecular interactions, low viscosity and interfacial tension, all of which greatly facilitate wetting and in ltration through the CNC network to result in strong binding to the reinforcing phase and, in turn, to high adhesive properties that could not be achieved in the absence of coacervation (Figure 2h). [20][21][22][23] Furthermore, we have recently found that CMP-1 in the club of the peacock mantis shrimp has a 3-block primary structure (Figure 2d) 14 that may result in all three of the characteristics required to act as a matrix of a tough biocomposite. First, it has a conserved mid-block carbohydrate-binding module that is likely used as an anchor to chitin brils in the club.…”