A Biomimetic Modular Polymer with Tough and Adaptive Properties

Abstract

Natural materials employ many elegant strategies to achieve mechanical properties required for survival under varying environmental conditions. Thus these remarkable biopolymers and nanocomposites often not only have a combination of mechanical properties such as high modulus, toughness, and elasticity, but also exhibit adaptive and stimuli-responsive properties. Inspired by skeletal muscle protein titin, we have synthesized a biomimetic modular polymer that not only closely mimics the modular multi-domain structure of titin, but also manifests an exciting combination of mechanical properties, as well as adaptive properties such as self-healing and temperature-responsive shape-memory properties.Whereas man-made polymers can be prepared to meet particular parameters one at a time, it remains a challenge to design synthetic polymers with a combination of mechanical properties such as high modulus, toughness, and resilience. A further challenge is to introduce adaptive properties into polymers. In contrast, many smart strategies have evolved in nature to achieve biopolymers possessing excellent combinations of mechanical properties. 1 To survive in often variable environments, natural materials have also evolved to be adaptive, maintaining functions across a range of stress or strain, or changing properties in response to stimuli such as temperature or moisture level. 2 In recent years, the elucidation of molecular mechanisms for natural materials has prompted many biomimetic materials designs. 3 Herein, we report a Supporting Information Available: Synthesis and characterization of monomers and polymers, stress-strain, DMA, X-ray, AFM, and molecular modeling experiments. This material is available free of charge at http//:pubs.acs.org. biomimetic design of a modular polymer that has a combination of high modulus, toughness, and resilience, while possessing adaptive mechanical properties. NIH Public AccessOur biomimetic concept is based on the modular domain design observed in the skeletal muscle protein titin, which possesses a remarkable combination of strength, toughness, and elasticity. 4 The ability of titin to absorb energy by the reversible rupture of intramolecular secondary interactions, followed by re-folding induced recovery, makes it an intriguing model for the design of adaptive materials. Following titin's modular design, our group first synthesized polymers incorporating the quadruple hydrogen bonding 2-ureido-4[1H]-pyrimidone (UPy) motif 5 as the modular domain-forming mimic of the Ig domains in titin. 6 To overcome issues such as structural heterogeneity and inter-chain cross-linking, we further developed a cyclic modular polymer using a peptidomimetic β-sheet dimer. 7 Despite the well-defined single molecule unfolding properties, the synthesis of the second generation polymers is tedious, and the rupture forces of the H-bonded modules are much lower than the UPy dimer. To simplify synthesis and improve mechanical strength, the cyclic modular concept was applied to the UPy core. In our pre...

pH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli

“…(ii) Vis-à-vis other reversibly cross-linked polymer networks based on electrostatic, H-bond, or hydrophobic interactions (25)(26)(27), cross-linking based on multiple ligand-metal complexes such as metal-catecholates offers near covalent stabilities with noncovalent reformation rates and a range of possible cross-link modes from zero to three per metal ion. (iii) While the metalligand-complex theme can also be utilized to cross-link polymers in organic solvents (28) its incorporation into polymers in aqueous solvents under ambient conditions by simply increasing pH as presented here, provides a unique promising platform for environmental and physiological applications.…”

Mechanochemistry in Polymers with Supramolecular Mechanophores

“…[70,71] Interestingly, however, only few reports have described mechanically active hydrogen bonds in supramolecular polymers with unambiguous experimental evidence that show dissociation and formation of hydrogen bonds in response to mechanical stimulation. [72][73][74][75] Some of the most compelling examples of mechanoactive hydrogen bonds in polymers have been inspired by the natural protein titin. [72] Titin is a giant protein of muscle sarcomeres and has 200-300 repeating modules that are unfolded sequentially when a mechanical force is applied (Figure 13a), leading to a saw-tooth pattern in the force-extension curve.…”

“…[75] To avoid undesired hydrogen-bonding and prevent complicated folding structures, the polymer did not possess any hydrogen-bonding sites other than the UPy moieties in each module. Linear module polymer P3-4 and control polymer P3-5 were obtained by acyclic diene metathesis using corresponding monomers.…”

Supramolecular Interfacial Polymerization: A Controllable Method of Fabricating Supramolecular Polymeric Materials

“…Over the past decades, significant advances have been made in developing methods of supramolecular polymerization, from spontaneous to controllable and living supramolecular polymerization 31, 32, 33, 34, 35, 36, 37, 38. Furthermore, supramolecular polymers have displayed potential applications in many interdisciplinary fields, such as molecular muscles,39, 40, 41 self‐healing materials,42, 43, 44 self‐healing organic electronics,45, 46 heterogeneous catalysis,47 degradable drug nanocarriers,48 and stimuli‐responsive supramolecular gels 49, 50, 51…”