A robust platform for functional microgels via thiol-ene achemistry with reactive polyether-based nanoparticles

Abstract

We herein report the development of crosslinked polyether particles as a reactive platform for the preparation of functional microgels. Thiol-ene crosslinking of poly(allyl glycidyl ether) in miniemulsion droplets - stabilized by a surface active, bio-compatible polyethylene glycol block copolymer - resulted in colloidal gels with a PEG corona and an inner polymeric network containing reactive allyl units. The stability of the allyl groups allows the microgels to be purified and stored before a second, subsequent thiol-ene functionalization step allows a wide variety of pH- and chemically-responsive groups to be introduced into the nanoparticles. The facile nature of this synthetic platform enables the preparation of microgel libraries that are responsive to different triggers but are characterized by the same size distribution, surface functionality, and crosslinking density. In addition, the utilization of a crosslinker containing cleavable ester groups renders the resulting hydrogel particles degradable at elevated pH or in the presence of esterase under physiological conditions.

Fig. 1

Representative SEM image of precursor microgels MG-A24.

Fig. 2

Swelling degree of microgels MG-A4, -A6, -A8, -A10, and -A24 in THF calculated from the hydrodynamic diameters determined by DLS.

Fig. 3

Influence of crosslinker feed ratio on the swelling ratios of MG-A8 precursor microgels from 8 hours irradiation time in THF and methanol.

Fig. 4

Characterization of the pH-dependent swelling profiles of functionalized microgels MG-C8.

Fig. 5

Characterization of zwitterionic microgels from the modification with histamine and acetic acid moieties: pH dependent swelling degrees of MG-A8-His+MAA and schematic illustration of the charge distribution in the bifunctional microgels at different pH values.

Fig. 6

Degradation experiments of MG-A10-MAA in Milli-Q water with pH 10 at room temperature, in PBS buffer with pH 7.4 in the presence of porcine liver esterase at 37 °C and in pure Milli-Q water (control). The hydrodynamic diameters (≥90 % by number) were followed over time.

Scheme 1

Microgel formation via crosslinking of PAGE and PAGE-b-PEO using light induced thiol-ene reaction with PTMP in dispersed droplets.

Scheme 2

Preparation of pH responsive microgels through the network functionalization of precursor particles via thiol-ene click reaction