Enzymatic catalysis has been attracting increasing interest in the design and synthesis of functional polymers and hydrogels in a mild, efficient, and environmentally friendly fashion compared to conventional techniques including photo-irradiation and redox initiation. A well-established method of generating hydrogels involves the use of hydrogen peroxidase (H2O2) and β-diketone (e.g., acetylacetone (ACAC), 1,3-cyclopentadione) in the presence of horseradish peroxidase enzyme (HRP) to generate carbon-centered radicals that can initiate chain polymerization to create three-dimensional, cross-linked hydrogels. However, ACAC has relatively high toxicity and may cause an irreproducible induction period, calling for the need for a safer and more efficient system of hydrogel generation. It remains challenging to demonstrate an HRP-mediated initiating system without β-diketones.<br/>Here, we report a novel ternary radical initiating system containing HRP, H2O2, and N-hydroxy-5-norbornene-2,3-dicarboxylic acid imide (HONB). This initiating system readily generates a nitroxide radical to trigger polymerization and hydrogelation at room temperature (approx. 22 °C) in aqueous media with oxygen tolerance and works with a variety of monomers and crosslinkers of various concentrations, and nanoparticles of various sizes. Furthermore, the gelation time can be controlled by easily adjusting the pH value of reaction media ranging from 2.3 to 7.5 or varying the molar ratio of the individual components of the ternary initiating system. This technology can be used in various biological and industrial applications and bring forth the advancement of polymer chemistry.

Novel enzyme mediated ternary radical initiating system for producing hydrogels

ACS Fall 2021

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