Integrated Fabrication-Conjugation Approaches for Tunable Manufacturing of Biofunctional Hydrogel Microparticles

Hydrogel microparticles with controlled structures have gained increasing attention in various applications as biosensing platforms for medical diagnostics, biological threat detection and bioprocess monitoring. However, it still remains challenging to manufacture such microparticles with tunable structures and multifunctionality and in a simple, cost-efficient and reliable manner. We present facile manufacturing methods for chemically functional and monodisperse biopolymeric–synthetic hybrid hydrogel microspheres with controlled macroporous structures that can be utilized as conjugation platforms for large biomolecules. Specifically, we exploited a simple micromolding-based approach in order to fabricate highly uniform poly(ethylene glycol) (PEG)- and poly(acrylamide) (PAAm)-based hydrogel microspheres and shape-encoded microparticles, in which a potent aminopolysaccharide chitosan providing chemically reactive and abundant amine groups is incorporated. The as-prepared microparticles showed macroporous and/or intriguing core-shell structures stemming from either spontaneous polymerization-induced phase separation or via easy porosity tuning with inert PEG porogens. Fluorescent labeling studies utilizing an amidation reaction on the chitosan’s primary amines confirmed stable incorporation of the chitosan moieties with retained chemical reactivity, showing potential of such amines as efficient conjugation handles. The utility of our hydrogel microparticles as biomolecular conjugation platforms was thoroughly examined in terms of conjugation capacity and kinetics by conjugating model biomolecules (fluorescein-labeled single-stranded DNA and red fluorescent protein R-phycoerythrin) via two high-yield bioorthogonal reactions (strain-promoted alkyne–azide cycloaddition (SPAAC) and tetrazine–trans-cyclooctene (Tz–TCO) cycloaddition). The conjugation results showed well-defined and macroporous network structures, leading to enhanced protein conjugation capacity and kinetics and allowing programmable protein conjugation. In this presentation, our recent progress on much improved macropore formation and conjugation for the PAAm-based hydrogel microparticle with acrylate functionality via EDC/NHS chemistry will also be highlighted.