Vanadyl–Catecholamine Hydrogels Inspired by Ascidians and Mussels

Abstract

In general, mechanical properties and gelation kinetics exhibit a positive correlation with the amount of gelation reagents used. Similarly, for catechol-containing hydrogels, which have attracted significant attention, because of their unique dual properties of cohesion and adhesion, increased amounts of cross-linking agents, such as organic oxidants and/or transition metals (Fe3+), result in enhanced mechanical strength and more rapid gelation kinetics. Here, we report a new metal–ligand cross-linking chemistry, inspired by mussels and ascidians, that defies the aforementioned conventional stoichiometric concept. When a small amount of vanadium is present in the catechol-functionalized polymer solution (i.e., [V] ≪ [catechol]), organic radicals are rapidly generated that trigger the gelation reaction. However, when a large amount of the ion is added to the same solution (i.e., [V] ≫ [catechol]), the catechol remains chemically intact by coordination that inhibits gelation. Thus, a large amount of cross-linking agent is not necessary to prepare mechanically strong, biocompatible hydrogels using this system. This new chemistry may provide insight into the biological roles of vanadium and its interaction with catechol-containing molecules (i.e., determination of the liquid state versus the solid state). Excess amounts of vanadium ([V] ≫ [catechol]) coordinate with catechol, which may result in a liquid state for ascidian blood, whereas excess amounts of catechol ([V] ≪ [catechol]) generate an organic radical-mediated chemical reaction, which may result in solid-state conversion of the mussel byssal threads.

Mussel‐Inspired Materials: Self‐Healing through Coordination Chemistry

“…The balance between the redox and coordination abilities of the metal has been put to functional use by Park et al [84] They drew inspiration from the fact that ascidians (sessile marine animals) contain catechols and vanadiumw ithal ow metal/catechol ratio while the blue mussel locally has ah igher one approaching the 1:3F e/catechol region. The latter gives ah igh degree of coordination cross-linking, but requiresh igh amountso fi ron, whichi nt urn can lead to cytotoxicity.H owever,i na scidians vanadium is used as the cross-linking metal in trace amounts ( Figure 9A).…”

“…A) The catechol molecules used by ascidians( left) and blue mussels (right). B) Colorimetric study based on vandadium concentrationsf rom the ascidian(low metal to catechol) to the mussel (high metal to catechol) regime.T he figurewas adapted from reference [84]. worm jaws.…”

Polydopamine Inter‐Fiber Networks: New Strategy for Producing Rigid, Sticky, 3D Fluffy Electrospun Fibrous Polycaprolactone Sponges

“…Inter‐molecular crosslinking properties of pDA allowed to form inter‐fiber networks within the PCL fibrous sponges. As previously described, a stoichiometric excess of dopamine monomers to Fe 3+ ions can facilitate the sequential oxidation of dopamine monomers to initiate dopamine polymerization . The irreversible chemical reaction rather than the reversible metal coordination, which can be occurred at the excess amount of Fe 3+ ions, was employed as a core technology to reinforce the rigidity of 3D‐PCL fibrous sponges.…”

Microwave‐Accelerated Rapid, Chemical Oxidant‐Free, Material‐Independent Surface Chemistry of Poly(dopamine)

“…For example, when vanadyl chloride was added to dopamine solution, the formation of pDA fi lms exhibiting an approximately sevenfold increase in thickness was observed (≈10 vs 70 nm). [ 14 ] In addition, iron ions formed by the dissolution of K 3 [Fe(CN) 6 ] were reported to show enhanced kinetics in dopamine oxidation, yielding rapid formation of polydopamine. [ 15 ] However, when forming pDA, unavoidable surface contamination of the transition metal oxidants bound to the pDA fi lm occurs.…”

“…Radical formation in catechol is another important factor to form pDA. [ 14,[40][41][42][43] We investigated the involvement of radicals in the accelerated pDA coating because microwave energy generates free radicals particularly when strong microwave energy-absorbing materials exist in a solution. The microwave-absorbing materials can effectively induce local area superheating in the solution, which results in free radical generation by sudden breakage of covalent bonds.…”