Synthesis of Bioactive Microcapsules Using a Microfluidic Device

Abstract

Bioactive microcapsules containing<em> Bacillus thuringiensis</em> (<em>BT</em>) spores were generated by a combination of a hydro gel, microfluidic device and chemical polymerization method. As a proof-of-principle, we used <em>BT</em> spores displaying enhanced green fluorescent protein (EGFP) on the spore surface to spatially direct the EGFP-presenting spores within microcapsules. <em>BT</em> spore-encapsulated microdroplets of uniform size and shape are prepared through a flow-focusing method in a microfluidic device and converted into microcapsules through hydrogel polymerization. The size of microdroplets can be controlled by changing both the dispersion and continuous flow rate. Poly(<em>N</em>-isoproplyacrylamide) (PNIPAM), known as a hydrogel material, was employed as a biocompatible material for the encapsulation of <em>BT</em> spores and long-term storage and outstanding stability. Due to these unique properties of PNIPAM, the nutrients from Luria-Bertani complex medium diffused into the microcapsules and the microencapsulated spores germinated into vegetative cells under adequate environmental conditions. These results suggest that there is no limitation of transferring low-molecular-weight-substrates through the PNIPAM structures, and the viability of microencapsulated spores was confirmed by the culture of vegetative cells after the germinations. This microfluidic-based microencapsulation methodology provides a unique way of synthesizing bioactive microcapsules in a one-step process. This microfluidic-based strategy would be potentially suitable to produce microcapsules of various microbial spores for on-site biosensor analysis.

Keywords

• microcapsulation
• NIPAM
• hydrogel
• microfluidic device
• spore