Abstract
Despite the enormous potential in bioinspired fabrication of high-strength structure by mimicking the spinning process of spider silk, currently accessible routes (e.g., microfluidic and electrospinning approaches) still have substantial function gaps in providing precision control over the nanofibrillar superstructure, crystalline morphology or molecular orientation. Here the concept of biomimetic nanofibrillation, by copying the spiders’ spinning principles, was conceived to build silk-mimicking hierarchies in two-phase biodegradable blends, strategically involving the stepwise integration of elongational shear and high-pressure shear. Phase separation confined on nanoscale, together with deformation of discrete phases and pre-alignment of polymer chains, was triggered in the elongational shear, conferring the readiness for direct nanofibrillation in the latter shearing stage. The orderly aligned nanofibrils, featuring an ultralow diameter of around 100 nm and the “rigid−soft” system crosslinked by nanocrystal domains like silk protein dopes, were secreted by fine nanochannels. The incorporation of multiscale silk-mimicking structures afforded exceptional combination of strength, ductility and toughness for the nanofibrillar polymer composites. The proposed spider spinning-mimicking strategy, offering the biomimetic function integration unattainable with current approaches, may prompt materials scientists to pursue biopolymer mimics of silk with high performance yet light weight.
Highlights
The peptide chains connected by intersheet hydrophobic interactions and hydrogen bonds, and glycine-rich amorphous matrix conserved in the bulkier amino acid residues[26,27]
By direct scanning electron microscopy (SEM) observation, Fig. 1c suggests that the biomimetic strategy exerted profound structural regularization for the phase morphology and fibrillar texture in the poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) blends with varied weight proportions ranging from 90/10 to 40/60
It is worth stressing that the density of nanofibrils showed little variability with blend constituents, which suggested the flexibility of nanofibrillation for both PLA and PBS phases
Summary
The peptide chains connected by intersheet hydrophobic interactions and hydrogen bonds, and glycine-rich amorphous matrix conserved in the bulkier amino acid residues[26,27]. The protein molecules mainly fall into two interacting function categories: “rigid” building blocks—a small proportion around 15%28, which are oriented β-crystals serving as molecule crosslinks and key contributors to the high strength and stiffness of silk thread, and “soft” phase, which is composed of weakly oriented and less orderly amorphous sections that render silk threads superb elasticity[29]. Based on this semi-crystalline network model, theoretical simulations have been revealed to directly reproduce the stress−strain curves with high accuracy compared to those acquired from experimental measurements[26,30]. Following the structure-by-processing principles, the biomimetic strategy may function analogously in enabling the well-defined control over self-assembly, phase separation and confinement of polymer blends, triggering the alignment of polymer chains into fibrillar threads[39]
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