Toughening elastomers via microstructured thermoplastic fibers with sacrificial bonds and hidden lengths

Abstract

Soft materials capable of large inelastic deformation play an essential role in highperformance nacre-inspired architectured materials with a combination of stiffness, strength and toughness. The rigid "building blocks" made from glass or ceramic in these architectured materials lack inelastic deformation capabilities and thus rely on the soft interface material that bonds together these building blocks to achieve large deformation and high toughness. Here, we demonstrate the concept of achieving large inelastic deformation and high energy dissipation in soft materials by embedding microstructured thermoplastic fibers with sacrificial bonds and hidden lengths in a widely used elastomer. The microstructured fibers are fabricated by harnessing the fluid-mechanical instability of a molten polycarbonate (PC) thread on a commercial 3D printer. Polydimethylsiloxane (PDMS) resin is infiltrated around the fibers, creating a soft composite after curing. The failure mechanism and damage tolerance of the composite are analyzed through fracture tests. The high energy dissipation is found to be related to the multiple fracture events of both the sacrificial bonds and elastomer matrix. Combining the microstructured fibers and straight fibers in the elastomer composite results in a ~ 17 times increase in stiffness and a ~ 7 times increase in total energy to failure compared to the neat elastomer. Our findings in applying the

Optimal Sacrificial Domains in Mechanical Polyproteins: S. epidermidis Adhesins Are Tuned for Work Dissipation

“…Mechanical force can regulate protein structure and function in diverse ways. − Protein unfolding releases hidden biopolymer contour length that requires the input of mechanical work to extend, and this effect can act as a shock dissipator in biomaterials under tension (Figure ). − This concept of sacrificial bonds in biomaterials is well established, with strengthening effects attributed to structural changes at the protein level (e.g., unfolding) in diverse systems including bone, − muscle, , fibrin, , collagen, as well as in synthetic materials. , Here, we analyze theoretical and practical underpinnings of this behavior. We generalize the problem of mechanical work dissipation in polyproteins by considering the unfolding response of fingerprint (FP) domains (i.e., independently foldable globular domains embedded in polyproteins) using receptor–ligand (RL) complexes as pulling anchors.…”

“…13−15 This concept of sacrificial bonds in biomaterials is well established, with strengthening effects attributed to structural changes at the protein level (e.g., unfolding) in diverse systems including bone, 16−18 muscle, 19,20 fibrin, 21,22 collagen, 23 as well as in synthetic materials. 24,25 Here, we analyze theoretical and practical underpinnings of this behavior. We generalize the problem of mechanical work dissipation in polyproteins by considering the unfolding response of fingerprint (FP) domains (i.e., independently foldable globular domains embedded in polyproteins) using receptor−ligand (RL) complexes as pulling anchors.…”

Mechanically durable and damage resilient dielectric elastomer actuators

“…In addition, when these sacrificial bonds are broken, hidden lengths are released to further improve fracture toughness (Figure 2.7f). [92][93][94][95] These hidden lengths are segments constrained by sacrificial bonds that do not contribute to the end to end distance of the polymer backbone and are partially shielded from applied forces. Based on singlemolecule force spectroscopy, the release of hidden lengths increases and leads to a redistribution of load from stretched segments, enhancing fracture toughness.…”

“…Onedimensional (1D) fibers in both the macro and nano-scale have been found to enhance the crack resistance of hydrogels and elastomers significantly. [93,104,132] For instance, when the crack tip encounters a macro-fiber, the soft matrix shears to a large extent, spreading the stress along the fiber to minimize stress concentrations at the crack tip. Upon debonding of the matrix and fiber, crack deflection occurs, requiring more energy for crack propagation (Figure 2.9a).…”