The project focuses on experimental and theoretical research of reaction-transport phenomena in microfluidic devices with integrated semipermeable membranes for the efficient synthesis and separation of products of enzyme reaction. The devices employ free enzymes (e.g. thermolysin, L-threonine aldolase, lipase) to prepare chemical precursors important in the synthesis of drugs, pesticides or dietary supplements. Enzyme reactions forming optical isomers are investigated. Membranes specifically synthesized for this purpose provide the separation of one optical form of the product with high selectivity while preventing the permeation of the enzyme catalyst. For reactions in the aqueous phase, the electric charge of the products-ampholytes is set by pH value so that the DC electric field imposed perpendicular to the membrane surface accelerates the transport of the reaction products to the permeate. The retentate stream of the microfluidic devices is recycled to reduce the consumption of enzyme catalyst and to increase the yield of an enzyme reaction.
The proposed experimental project aims at thorough understanding of processes and phenomena that may occur in desalination chambers of electrodialysis units. We exploit the power of microfluidics as an enabling technology to (i) construct a simple electrodialysis unit consisting of one desalination channel and (ii) equip this channel with sampling ports and electric potential measuring spots. This milifluidic electrodialysis unit allows us to reconstruct
the concentration, pH and electric potential profiles developed in the desalination channel under various desalination conditions in 2 dimensions. On top of that, this unit also enables direct observation of electrokinetics that is responsible for the occurrence of the overlimiting current. Overlimiting current is today considered as a means of process intensification. The goal of the submitted proposal is to produce high-quality experimental data that can be analyzed from the perspective of underlying electrodialysis principles. Our work should thus contribute to the future design of large electrodialysis units.
Heterogeneous ion-exchange membranes are recognized as inherent functional components of large electroseparation units used for electrodialysis or electrodeionization. In this proposal, we set out to study interactions of aforementioned membranes with large charged polymeric molecules not capable of passing through the membranes for steric reasons. These interactions mostly arising from electrostatic repulsions or attractions between the charge borne by the molecules and the charge fixed in the membranes can result in profound qualitative and quantitative changes in the behavior of the ion-exchange membranes. The proposal aims to describe the qualitative and quantitative changes as functions of (i) the size of the molecules and (ii) the charge they bear. Successful solution of this project can significantly contribute to the optimization of electrodialysis units intended for processing of complex samples often of biological origin.
Reaction-transport phenomena affected by an external electric field were investigated in integrated microfluidic and millifluidic devices for an enzyme catalyzed synthesis of antibiotics. Mild reaction conditions were provided by aqueous two-phase systems (ATPS) consisting of polyethylene glycol, inorganic salt, and water. The use of ATPS allowed for an enzyme catalyzed synthesis in one aqueous phase coupled with continuous delivery and /or removal of reaction substrates and/or reaction products to/from another aqueous phase. Reaction-transport processes in two types of integrated devices were investigated. One of them provided stable counter-current flow of ATPS. The transport of ionic reaction components was enhanced by an electric field imposed perpendicularly to the interface. The other device intensified the interfacial mass transport using extremely fine droplet flow with consequent phase separation by an imposed electric field. Scaling rules characterizing the combined reaction-transport process were identified with the help of a mathematical model.
The project studied the principal reaction-transport phenomena occurring at heterogeneous ion-exchange membranes under DC electrical field. The primary goal of the project was to find links between surface heterogeneities of such membranes and the exhibited behavior. We used two approaches for solving this project. In the first one called bottom-up approach, we made artificial membranes with designed spatial distribution of conductive ion exchange resin particles embedded in a nonconductive polymeric resin and characterized these membranes with standard electrochemical experiments and fluorescent imaging microscopy. In the second approach called top-down approach, we scrutinized small pieces of commercially available heterogeneous membranes by using cutting-edge analytical tools such as microcomputed tomography, standard electrochemical measurements and fluorescent imaging.
The project deals with fluid mechanics phenomena in smart microfluidic systems driven by external electric fields. Experimental glass and plexiglass microfluidic chips with embedded microelectrodes were fabricated. One liquid was dispersed in another immiscible liquid in the form of regular droplets. Oil in water (O/W), water in oil (W/O), and leaky dielectric fluid in leaky dielectric fluid (L/L) droplets were formed. The following experiments were carried out. O/W and L/L droplets were electrically charged, addressed, merged and separated above microelectrodes by means of electrokinetic phenomena. Faradaic interactions were partially avoided with the use of conductive separating membranes. Passive charging of W/O droplets due to the dissolution of base metals was tested. Poisson-Nernst-Planck-Navier-Stokes mathematical models of the droplet handling was developed. Effects of the Maxwell stress and Faradaic interactions on the behavior and addressing performance of the microsystems was quantified.