(378f) Development of Slug-Flow Microfluidic Devices for Lipase Catalyzed Reactions

Enzyme lipase catalyzes reactions such as hydrolysis, glycerolysis or transesterifications of oils on the hydrophilic-hydrophobic interface. These two-phase enzyme reactions are typically carried out in well mixed batch systems. Slug-flow microfluidic systems offer a new alternative. The interfacial area between two immiscible liquids in a slug flow is large and the diffusion distance between the interfacial surface and the slug core is short. Moreover, internal circulation within the slugs further increases intensity of the interfacial mass and heat transport and thus accelerates transport-limited chemical reactions. Because both liquid phases move in capillaries or microchannels with precisely defined flow rate, the residence time of all droplets is almost equal. Products with a required composition can be obtained. In this study, we deal with a microcapillary/microchannel reaction system for enzyme hydrolysis of triglycerides. The microdevices were fabricated by a combination of traditional techniques ? UV photolithography, micromachining, hot assembling, casting and prepolymerization. The water-oil emulsion was generated in a plexiglass microchip with a T microchannel crossing. Both the oil and water were pumped into the microchip by a precise syringe pumps. The oil-water emulsion was formed in the T crossing in certain intervals of the oil and water flow rates. A map of slug-flow character was studied in the parameter plane formed by the flow rates. Similarly, dependence of the interfacial surface density was obtained. The generated water-oil dispersion left the microchip into a microcapillary of a chosen length. The capillary connected the microchip for generation of the slug flow and another microchip for separation of the liquid phases. We used two types of microfluidic separators. The first one consisted of a central channel and an array of small side channels. Due to hydrophobicity of the PDMS substrate, the oil phase preferably entered the side channels. The separation efficiency of this microchip was significantly improved when another syringe pump drew the oil phase from the separator. As the latter possibility, we used a simple plexiglas gravitational separator that was fabricated by micromachining and gluing. In the experiments, we used water solutions of enzyme Lipolase 100L EX (Novozyme) and unrefined soybean oil. The flow rates and the length of the connecting capillary define the residence time of the reaction mixture within the microfluidic system. Effects of the residence time on the triglyceride conversion are being studied. The results will be compared with those given by batch experiments and discussed with respect to capabilities of the proposed microfluidic system to serve as a microreactor for lipase catalyzed reactions with regeneration of free enzyme directly in the microchip.