Dual-responsive shape memory hydrogels with novel thermoplasticity based on a hydrophobically modified polyampholyte

Abstract

Shape memory hydrogels offer the ability to recover their permanent shape from temporarily trapped shapes without application of external forces. Here, we report a novel dual-responsive shape memory hydrogel with characteristic thermoplasticity. The water-insoluble hydrogel is prepared by simple ternary copolymerization of acrylamide (AM) and acrylic acid (AA) with low amounts of a cationic surfmer, in the absence of organic crosslinkers. Through either ionic/complex binding of carboxyl groups via trivalent cations or salt-dependent hydrophobic association, the hydrogel can memorize a temporary shape successfully, which recovers its permanent form in the presence of a reducing agent or deionized water. Besides, the unique thermoplasticity of the hydrophobic polyampholyte hydrogel allows the change of its permanent shape upon heating and the fixation after cooling, which is in strong contrast to the conventional chemically cross-linked shape memory hydrogels. This fascinating feature undoubtedly enriches the shape memory hydrogel systems. Thus, we believe that the facile strategy could provide new opportunities with regard to the design and practical application of stimulus-responsive hydrogel systems.

Trends in polymeric shape memory hydrogels and hydrogel actuators

“…A hydrophobic polyampholyte SMH reported by Yang et al possesses a unique thermoplasticity, which can change its permanent shape upon heating. 52 Through either ligand-ion bindings or salt-dependent hydrophobic association, temporary shapes can be memorized. Recently, a novel dual crosslinked single-network hydrogel has been fabricated through copolymerization of acrylamide (AAm) and AAc with n-octadecyl acrylate.…”

Thermal/Light Dual-Activated Shape Memory Hydrogels Composed of an Agarose/Poly(acrylamide-co-acrylic acid) Interpenetrating Network

“…This enhancement demonstrated that physical crosslinkers were formed to provide sufficient strength for the gel locking a temporary shape. [38] After exposure to simulated sunlight irradiation in the presence of reductive citric acid for 2 h (the photoreduction of Fe(III) to Fe(II) ions was demonstrated in Figure S5, Supporting Information), the storage modulus G′ and loss modulus G″ recovered to the original values, indicative of the disassociation of acrylic acid-Fe(III) complexes. [37]…”

A review of shape memory polymers bearing reversible binding groups

“…The ability to instill shape memory characteristics using ionic interactions is not limited to hydrophobic polymers as evidenced by recent reports of ion containing shape memory hydrogels (SMH). [114][115][116][117] For example, a dual-responsive SMH based on acrylamide (AM), acrylic acid (AA), and a low concentration (1.5 mol %) of cationic surfmer (Dimethylhexadecyl[2(dimethylamino)ethylmethacrylate]ammonium bromide) (C16DMAEMA) was recently reported. 116 Physical crosslinks used for temporary shape programming could be accomplished either through ion/complex associations between Fe 31 and carboxyl groups or salt-strengthened hydrophobic interactions.…”

“…[114][115][116][117] For example, a dual-responsive SMH based on acrylamide (AM), acrylic acid (AA), and a low concentration (1.5 mol %) of cationic surfmer (Dimethylhexadecyl[2(dimethylamino)ethylmethacrylate]ammonium bromide) (C16DMAEMA) was recently reported. 116 Physical crosslinks used for temporary shape programming could be accomplished either through ion/complex associations between Fe 31 and carboxyl groups or salt-strengthened hydrophobic interactions. Shape recovery is triggered for ion complexes by introducing a reducing agent (ascorbic acid), whereas shape recovery of the hydrophobic domain is induced by deionized water.…”