Microfluidic device for droplet-based protein microencapsulation using peptide hydrogel

Abstract

This paper presents a method to encapsulate protein in hydrogel beads using micro-droplet generating and merging technology. Encapsulation of biomaterials in gel is known to increase stability of the encapsulated materials and broaden the range of biological applications from diagnostic devices to the artificial organs. By using the aqueous two-phase droplet generation system described in this report, simple, in-situ formation and manipulation of protein-encapsulated hydrogel beads in a PDMS microfluidic channel is possible. Peptide hydrogel, $PuraMatrix^{TM}$, is used as the gel material, which self-assembles from the sol-state into the nanofiber networks in the presence of salt concentrations. After the sol-state hydrogel droplets of picoliter to nanoliter volume are generated in the focusing channel, they immediately merge with protein solution for gelation and encapsulation. For merging, the microchannel integrates double-T junction, in which the hydrogel droplets pass through the middle channel as in plug shapes, and other solutions flow through the symmetric side branches. This design increases the coalescence frequency and the contact time of the solution with hydrogel droplets, which are the key parameters for merging of dispersed phase liquids in oil phase. The efficiency of encapsulation in hydrogel droplets was up to 100% at various flow rate conditions. To demonstrate the possible applications of the device, the enzyme glucose oxidase is encapsulated in hydrogel and further mixed with the substrate, glucose solution, at the second double-T junction. The enzyme-substrate containing hydrogel beads are monitored by the fluorescence intensity of by-products of the reaction. This device shows the possibility of various biological assay applications, such as protein-protein interaction.