To realize a robust, transparent, and easily processable polymer that is intrinsically selfhealable at room temperature, the following three material design criteria were established: (1) a readily processable and physically tunable base material, (2) a dynamic covalent bond that is operable at room temperature, and (3) optimal self-healing efficiency and mechanical properties.Thermoplastic polyurethane (TPU) is a thermoprocessable elastomer that is widely used as a protective film in the automotive and electronic industries. TPU was selected as the base material to satisfy the first criterion because its chemical structure can be fine-tuned to generate the desired transparency and mechanical properties. [4] Urethane structures containing polytetramethylene ether glycol (PTMEG) have been utilized to prepare shape memory effectassisted self-healing materials. [5] To satisfy the second criterion, an aromatic disulfide bond was selected as the chemical operator. [6] Intrinsic self-healing is chemically driven by noncovalent bonds such as hydrogen bonds, [3c-e,5c,7] metal-ligand, [8] host-guest interactions, [2e,9] or reversible (dynamic) covalent bonds [10] such as Diels-Alder, [11] radical recombination, [12] urea chemistry, [13] olefin metathesis, [14] polysiloxanes, [15] boronic esters, [16] acylhydrazones, [17] and other reactions. [18] Among these, disulfide metathesis has attracted significant attention since it can be activated at moderate temperatures (60-90 °C) and without external stimuli. [5d,19] In particular, an aromatic disulfide-based poly(urea-urethane) shows efficient room-temperature self-healing because aromatic disulfides undergo more efficient metathesis than aliphatic disulfides. [6e,f,20] The third criterion was addressed by optimizing the mechanical properties and self-healing efficiency of TPU through the design of a hard segment of the polymer containing the chemical operator, i.e., an aromatic disulfide moiety. Generally, TPUs with tightly packed hard segments have better mechanical properties but lower self-healing efficiency because the restricted chain mobility hinders disulfide metathesis. [5d,21] Loosely packed hard segments produce the opposite effect. Room-temperature self-healable cross-linked poly(urea-urethane) has an undesirable ultimate tensile strength (UTS) of ≈0.8 MPa with a toughness of ≈13 MJ m −3 . [6e] Other disulfide-containing TPUs have UTS values greater than 10 MPa, but they must be heated above 80 °C to initiate self-healing. [5d] The most important properties of self-healing polymers are efficient recovery at room temperature and prolonged durability. However, these two characteristics are contradictory, making it difficult to optimize them simultaneously. Herein, a transparent and easily processable thermoplastic polyurethane (TPU) with the highest reported tensile strength and toughness (6.8 MPa and 26.9 MJ m −3 , respectively) is prepared. This TPU is superior to reported contemporary roomtemperature self-healable materials and conveniently heals w...

Hydrogel systems based on cross-linked polymeric materials which could provide both adhesion and cohesion in wet environment have been considered as a promising formulation of tissue adhesives. Inspired by marine mussel adhesion, many researchers have tried to exploit the 3,4-dihydroxyphenylalanine (DOPA) molecule as a cross-linking mediator of synthetic polymer-based hydrogels which is known to be able to achieve cohesive hardening as well as adhesive bonding with diverse surfaces. Beside DOPA residue, composition of other amino acid residues and structure of mussel adhesive proteins (MAPs) have also been considered important elements for mussel adhesion. Herein, we represent a novel protein-based hydrogel system using DOPA-containing recombinant MAP. Gelation can be achieved using both oxdiation-induced DOPA quinone-mediated covalent and Fe(3+)-mediated coordinative noncovalent cross-linking. Fe(3+)-mediated hydrogels show deformable and self-healing viscoelastic behavior in rheological analysis, which is also well-reflected in bulk adhesion strength measurement. Quinone-mediated hydrogel has higher cohesive strength and can provide sufficient gelation time for easier handling. Collectively, our newly developed MAP hydrogel can potentially be used as tissue adhesive and sealant for future applications.

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Intrinsic self-healing polymeric materials are substances that relieve external stress and restore their original mechanical properties after extreme damage via dynamic covalent bonding in the polymeric structure or the reversible...