Meta-Isobutoxy Phenylboronic Acid for Nanoscale Multi-Stimuli-Responsive Low-Molecular-Weight Hydrogelator

Abstract

Hydrogelators generate hydrogels when dissolved in water, forming a network of interlocking chains on the nanoscale level. For their unique viscoelastic, mechanical, and swelling properties, these hydrogels have found various applications, such as water absorbent, biocompatible, and biodegradable scaffolds in tissue engineering and nanocarriers in drug delivery. When measuring the solubility of p-, m-, and o-isobutoxy derivatives of phenylboronic acid, we identified m-isobutoxyphenylboronic acid (PBA) as a low-molecular-weight hydrogelator, the first of which solely based on phenylboronic acid. At low concentrations, PBA gelated water into a network of cross-linked nanofibers combining amorphous and crystalline phases, as shown by electron and optical microscopy, rheometry, and differential scanning calorimetry and confirmed by small-and wide-angle X-ray scattering. By increasing the PBA concentration, we were able to tailor the elastic modulus (G′) of PBA hydrogels across 2 orders of magnitude, from 2.5 to 103 kPa. In turn, at a specific PBA concentration, we tuned their viscoelastic properties by adding urea, thereby adjusting the gelation temperature between 62 and 56 °C and G′ at body temperature between 63.4 and 30.4 kPa. Moreover, PBA hydrogels dissolved in response to various triggers (pH increase, H 2 O 2 and cyclodextrin addition) and selectively absorbed dyes for liquid mixture separation. These findings demonstrate that PBA has a high potential as a biodegradable, multistimuli-responsive, low-molecular-weight hydrogelator for bioapplications.