Hydrolysis-Driven Viscoelastic Transition in Triblock Copolyether Hydrogels with Acetal Pendants

Abstract

While the hydrolytic cleavage of ester groups is widely exploited in degradable hydrogels, the scission in the midst of chain backbones can bring dramatic changes in the mechanical properties of the hydrogels. However, the predictive design of the mechanical profile of the hydrogels is a complex task, mainly due to the randomness of the location of chain scission. To overcome this challenge, we herein present degradable ABA triblock poly(ethylene oxide)-based hydrogels containing an A-block bearing acetal pendant, which provides systematically tunable mechano-temporal properties of the hydrogels. In particular, hydrophobic endocyclic tetrahydropyranyl or exocyclic 1-(cyclohexyloxy)ethyl acetal pendants are gradually cleaved by acidic hydrolysis, leading to the gel-to-sol transition at room temperature. Most importantly, a series of dynamic mechanical analyses coupled with ex situ NMR spectroscopy revealed that the hydrolysis rate can be orthogonally and precisely tuned by changing the chemical structure and hydrophobicity of acetal pendants. This study provides a platform for the development of versatile degradable hydrogels in a highly controllable manner.

Tailoring the Interplay between Two Monomers in the Properties of Degradable Polyesters Synthesized via Ring-Opening Alternating Copolymerization

“…In this context, it is essential to develop functional monomers to tailor the characteristics of polyesters using ROAC. As a part of our ongoing effort in the development of functional epoxide monomers, − t -butyl glycidoxy acetate ( t -BGA) was designed to produce a carboxylic acid-functionalized polyether . Polymers bearing carboxylic acid groups are useful because of their versatile applications in pH-responsive drug delivery systems, hydrogels, self-healing materials, adhesives, and battery binders .…”

Precisely Programmable Degradation and Drug Release Profiles in Triblock Copolyether Hydrogels with Cleavable Acetal Pendants

“…As shown in Figure a, the degradation mechanism of the hydrogels involves the stepwise hydrolysis of the inner core-block of the A end-blocks of the triblock copolymer hydrogels, including (i) core-block swelling, (ii) acidic hydrolysis, (iii) hydrophobic-to-hydrophilic transition of the A end-block, and (iv) chain pullout to full dissolution in solution. In particular, due to the presence of two exocyclic cleavable C–O bonds in the acyclic acetal pendants in EE, rapid hydrolysis occurs first in these acyclic acetal pendants, followed by slower hydrolysis of the cyclic tetrahydropyranyl acetal pendants in TP. , From the images of the degraded hydrogels, it was obvious that the degradation kinetics of the hydrogels under mildly acidic conditions could be tuned by modulating the f TP of the A-block (Figure b). While the structure of the hydrogels persisted in the initial stage, T 0 hydrogel degraded almost completely and exhibited a liquid-like behavior after 8 days of incubation whereas T 11 hydrogel still retained its gel-like behavior.…”

“…In particular, due to the presence of two exocyclic cleavable C−O bonds in the acyclic acetal pendants in EE, rapid hydrolysis occurs first in these acyclic acetal pendants, followed by slower hydrolysis of the cyclic tetrahydropyranyl acetal pendants in TP. 27,28 From the images of the degraded hydrogels, it was obvious that the degradation kinetics of the hydrogels under mildly acidic conditions could be tuned by modulating the f TP of the A-block (Figure 3b). While the structure of the hydrogels persisted in the initial stage, T 0 hydrogel degraded almost completely and exhibited a liquid-like behavior after 8 days of incubation whereas T 11 hydrogel still retained its gel-like behavior.…”

“…In our previous work, we introduced a new strategy to precisely control the hydrogel degradation kinetics using ABAtype triblock copolymers with hydrophobic acetal pendants (Scheme 1). 27 As the hydrolysis kinetics of the acetal groups is highly affected by the structure and the conformation of the monomer, hydrogels prepared from two different acetal-based monomers also display a distinct difference in degradation behavior. 28−30 It should be noted that after the hydrolysis of all pendant moieties, the A end-block turns into the linear polyglycerol which is well known for its high biocompatibility.…”

Dual crosslinking polymer networks: correlation between polymer topologies and self-healing efficiency

“…1,2 Generally, self-healing of polymeric materials can be achieved by chemical, physical, and physicochemical approaches, 3 enabling the repetitive associ-ation and/or dissociation of polymer networks in response to stimuli, such as heat, 4 light, 5 redox response, 6 and pH changes. [7][8][9] With their environmental and economic benefits, these self-healing materials can be utilized in numerous industrial fields, including automotive coatings, adhesives, solar cells, electronic skins, sensors, and supercapacitors. 10 Over the past decade, efforts have been focused on the design of dynamic polymer networks with self-healing properties 11 utilizing Diels-Alder chemistry, 12 disulfide bonds, 13 hindered urea bonds, 14 and boron-based bonds.…”