Enzyme‐catalysed polymer cross‐linking: Biocatalytic tools for chemical biology, materials science and beyond

Abstract

Intermolecular cross-linking is one of the most important techniques that can be used to fundamentally alter the material properties of a polymer. The introduction of covalent bonds between individual polymer chains creates 3D macromolecular assemblies with enhanced mechanical properties and greater chemical or thermal tolerances. In contrast to many chemical cross-linking reactions, which are the basis of thermoset plastics, enzyme catalysed processes offer a complimentary paradigm for the assembly of cross-linked polymer networks through their predictability and high levels of control. Additionally, enzyme catalysed reactions offer an inherently 'greener' and more biocompatible approach to covalent bond formation, which could include the use of aqueous solvents, ambient temperatures, and heavy metal-free reagents. Here, we review recent progress in the development of biocatalytic methods for polymer cross-linking, with a specific focus on the most promising candidate enzyme classes and their underlying catalytic mechanisms. We also provide exemplars of the use of enzyme catalysed cross-linking reactions in industrially relevant applications, noting the limitations of these approaches and outlining strategies to mitigate reported deficiencies.

Transglutaminase-Catalyzed Bottom-Up Synthesis of Polymer Hydrogel

“…Transglutaminase (TGase) is an acyltransferase, which catalyzes the amide-transferase reaction between the γ-amyl group of glutamine residue and the ε-amino group of lysine in protein, resulting in form the ε- (γ-glutamine) -lysine heteromorphic peptide bond ( Fisher et al, 2017 ). It can also make polymers containing amino and glutamate functional groups undergo cross-linking reactions ( Maddock et al, 2020 ). TGase is widely distributed in nature and can be isolated and extracted from animals, plants and microorganisms.…”

Crosslinking Strategies for the Microfluidic Production of Microgels

“…The alginate-tyramine conjugates can be crosslinked via horseradish peroxidase (HRP)-catalyzed oxidative coupling of phenol moieties in the presence of hydrogen peroxide (H 2 O 2 ). Gel networks composed of covalently crosslinked polymer chains have better mechanical properties and greater chemical and thermal stability compared with ionically crosslinked polymer networks [ 72 ]. In addition, enzymatic crosslinking offers high reaction rates under physiological conditions and a “green” approach to hydrogel synthesis, including the mildness of the reaction and biocompatible catalysts [ 72 ].…”

“…Gel networks composed of covalently crosslinked polymer chains have better mechanical properties and greater chemical and thermal stability compared with ionically crosslinked polymer networks [ 72 ]. In addition, enzymatic crosslinking offers high reaction rates under physiological conditions and a “green” approach to hydrogel synthesis, including the mildness of the reaction and biocompatible catalysts [ 72 ]. Typical microgels prepared by enzymatic crosslinking of modified polysaccharides in microfluidic chips are shown in Table S5 in the supplementary material .…”

Crosslinking Strategies for Microfluidic Production of Microgels

“…The alginate-tyramine conjugates can be crosslinked via horseradish peroxidase (HRP)-catalyzed oxidative coupling of phenol moieties in the presence of hydrogen peroxide (H2O2). Gel networks composed of covalently crosslinked polymer chains have better mechanical properties and greater chemical and thermal stability compared to ionically crosslinked polymer networks [67]. In addition, enzymatic crosslinking offers high reaction rates under physiological conditions and a 'green' approach to hydrogel synthesis, including the mildness of the reaction and biocompatible catalysts [67].…”

“…Gel networks composed of covalently crosslinked polymer chains have better mechanical properties and greater chemical and thermal stability compared to ionically crosslinked polymer networks [67]. In addition, enzymatic crosslinking offers high reaction rates under physiological conditions and a 'green' approach to hydrogel synthesis, including the mildness of the reaction and biocompatible catalysts [67]. Typical microgels prepared by enzymatic crosslinking of modified polysaccharides in microfluidic chips are shown in Table S5.…”