Novel Hydrogel Actuator Based on Biomimetic Chemistry

Abstract

Hydrogel actuators were prepared by combining ionoprinting technique with reversible metal ion coordination chemistry found in mussel adhesive proteins. Hydrogels were formulated with biomimetic dopamine moiety, which contains a catechol side chain that is capable of forming mono-, bis-, and tris-complexes with ferric (Fe 3+ ) ions with increasing pH. CatecholFe 3+ complexation increased local crosslinking density, which induced hydrogel bending at the site of Fe 3+ ionoprinting. The effect of pH on the dynamic response of hydrogel actuation was tracked by following the radius of curvature at the ionoprinting site. Both the rate of change and the maximum radius of curvature increased when the pH with increasing pH (2.5-9.5), indicating that pH can be used to modulate hydrogel actuation. Additionally, hydrogels containing Fe 3+ demonstrated higher extent of deswelling when equilibrated at a basic pH. Similarly, dynamic mechanical analysis in the compression mode revealed that both the storage and loss modulus values for Fe 3+ -containing hydrogels increased with increasing pH. These results indicated that bis-and tris-complexes formed at an elevated pH level contributed to a faster rate of actuation and a more condensed network architecture. Hydrogel actuation and deswelling were also observed at pH of 3.5 although to a lesser degree, potentially due to a stronger affinity between network-bound catechol and Fe 3+ ions as compared to complexes formed in a dilute solution.

Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein

“…The ability for catechol to transition reversibly between metal ion complexes [Fig. (D)] of different stoichiometry (i.e., mono‐ vs. tris‐catecholate complexes) in response to pH was exploited to create a pH‐responsive actuator . DMA‐containing hydrogel was locally ionoprinted with ferric ions (Fe +3 ), which increased local crosslinking density at the ionoprinting site and resulted in the sharp bending of the hydrogel .…”

Effect of pH on the Rate of Curing and Bioadhesive Properties of Dopamine Functionalized Poly(ethylene glycol) Hydrogels

“…The interfacial binding energy measured between the protein and titanium surfaces was the highest under acidic conditions (pH = 3). Catechol and metal ions also form strong complexes with stoichiometry and stability that are pH-dependent. − However, the effect of pH on its adhesion to biological substrates has yet to be determined. Catechol forms reversible coordination bonds with metal oxides and ions, which differ from the oxidation-mediated covalent bonds that catechol forms with nucleophiles (e.g., −NH 2 , −SH) found on biological substrates. , Additionally, there is a need to understand the effects of pH on the rate of intermolecular cross-linking of catechol, which affects the rate of curing and the bulk cohesive properties of catechol-containing adhesives.…”

Polymeric Hydrogels—A Promising Platform in Enhancing Water Security for a Sustainable Future

“…[26][27][28][29][30] Apart from these permanently cross-linked hydrogels, biomimetic chemistry and supramolecular assembly approaches can be utilized to prepare hydrogels with reversible chemical interactions. For example, mussel-inspired coordination chemistry can be employed to fabricate hydrogels with biomimetic dopamine groups containing catechols side chains that can reversibly complex ferric ions by tuning the pH, [31] while supramolecular hydrogels can be cross-linked by reversible noncovalent interactions, such as hydrogen-bond, metal-ligand coordination, electrostatic, hydrophobic, or host-guest interactions. [32][33][34] Alternatively, hydrogels can be fabricated as coatings or grafts on substrates to impart complementary properties such as improved strength and resistance to humid or harsh environments.…”