Reversible Programing of Soft Matter with Reconfigurable Mechanical Properties

Abstract

able to create a beak that possesses steep mechanical gradients with stiffness differences of two orders of magnitude occurring over centimeter-length scales. [1,2] Further, the mantis shrimp saddle is spatially organized with a highly mineralized outer layer that imparts stiffness, and a chitin-protein inner layer that confers flexibility. [3,4] In addition to synthesizing static structures, biology is also capable of creating the dynamic material systems that are needed for living systems to reconfigure during complex developmental programs (insect metamorphosis) [5] ; remodel for wound healing [6,7] ; and match properties to disparate functional needs (e.g., the lubricating and shock-absorbing properties of synovial fluid). [8] In many cases, biology creates such dynamic material systems using polymeric networks that are cross-linked through reversible physical interactions that can respond to local stimuli, [9] heal, [10][11][12] and balance the needs for strength and plasticity. [1,2,13,14] For instance, the electrostatic interactions between Ca 2+ and collagen act as sacrificial bonds to prevent brittle fracture in bone, [13,14] while domains in the titin protein that can reversibly unfold may allow muscles to withstand large deformations. [9] This emerging understanding of biological materials is also inspiring the development of high-performance technological materials. For instance, the mussel byssus illustrates the importance of coupling cross-linking mechanisms, as it uses covalent cross-links to confer strength and structural memory (i.e., elasticity) and reversible metal coordination bonds to confer the toughness and self-healing capabilities required to withstand what would seem to be nonrecoverable deformations. [10][11][12] There is growing interest in applying such a dual cross-linking strategy to fabricate high-toughness materials. A common technological approach is to use two interpenetrating polymeric networks that are individually cross-linked through separate mechanisms. [15][16][17][18][19][20][21][22][23] One network is cross-linked through strong (often covalent) bonds that confer elasticity, while the second network is cross-linked through weaker (often physical) interactions that can be broken and reformed in ways that dissipate mechanical energy to confer toughness to the dual polymeric network. [18,24] Alternative technological approaches to introduce energy-dissipating capabilities to materials include the use of nanocomposites [25][26][27] and phase-separated gels, [28] as well as topological gels (e.g., double networks, [16,29] slide-ring gels, [30] Biology uses various cross-linking mechanisms to tailor material properties, and this is inspiring technological efforts to couple independent crosslinking mechanisms to create hydrogels with complex mechanical properties. Here, it is reported that a hydrogel formed from a single polysaccharide can be triggered to reversibly switch cross-linking mechanisms and switch between elastic and viscoelastic properties. Specifically, the pH-resp...

Electrical Writing onto a Dynamically Responsive Polysaccharide Medium: Patterning Structure and Function into a Reconfigurable Medium

“…To illustrate that writing can confer anisotropic properties, we wrote three parallel lines (seven strokes) of cross stripe and vertical stripe and grid patterns onto a film and preformed tensile testing. Figure e shows that the film's mechanical properties varied depending on the written pattern and whether the stress was applied longitudinally or transversely relative to the written lines …”

Dextran‐based hydrogel with enhanced mechanical performance via covalent and non‐covalent cross‐linking units carrying adipose‐derived stem cells toward vascularized bone tissue engineering

“…In vitro and in vivo degradation of Dex-g-PCL hydrogel For in vitro degradation, the Dex-g-PCL hydrogels were immersed in Tris-HCl buffer solution (0.1 M, pH 7.4) at 37 C. The Tris-HCl buffer solution was changed every day. Samples that collected at 8,9,10,11,12,13, and 14 weeks were lyophilized and weighted. The weight remaining (%) = W o /W x × 100% (W o was the weights of the scaffolds before degradation; W x was the weights of the samples after degradation).…”

“…Thus, the fracture energy reduces for the reason that fewer chains are needed to be broken in order for the crack to propagate . Since the high water content is one reason of inherent poor mechanical behavior, introduction of restriction network to limit the swollen hydrophilic network will be an effective way to promote the mechanical performance of hydrogel . Introduction of hydrophobic polymers, such as PCL was an effective approach to improve the mechanical performance of hydrogel .…”

“…[8][9][10] Since the high water content is one reason of inherent poor mechanical behavior, introduction of restriction network to limit the swollen hydrophilic network will be an effective way to promote the mechanical performance of hydrogel. 11,12 Introduction of hydrophobic polymers, such as PCL was an effective approach to improve the mechanical performance of hydrogel. 13 In some cases, the hydrophobic interactions were reported to be strong enough to attribute to the unique mechanical properties of hydrogels.…”

Smooth waves and shocks of finite amplitude in soft materials

“…Recent technological advances have promoted the development of soft materials with reconfigurable properties, capable of undergoing reversible finite deformations (Bandyopadhyay et al, 2015, Truby and Lewis, 2016, He et al, 2017, Kim et al, 2017. The nonlinearities associated with these materials give rise to unique transport properties, that can be exploited for tunable dynamic response, energy trapping, shock mitigation and wave focusing (Nadkarni et al, 2014, Shmuel and Band, 2016, Lints et al, 2017, Lustig and Shmuel, 2018, Giammarinaro et al, 2018.…”