Estimation Of The Porosity Of The Microfabricated Chitosan-carbon Nanoparticle Membrane:a Solute Transport-based Study

In recent years, the rapid development of microfluidic technique has not only promoted the upgrade of biochemical analysis instruments but also made it possible to miniaturize blood purification devices, such as artificial livers and kidneys. Semi-permeable membrane is the core of blood purification devices. Thus, the key to the miniaturization of these devices is the integration of the high performance semi-permeable membrane into devices. Today, the laminar flow-based interfacial reaction technology has been applied to fabricate membranes on chips. However, due to the very tiny size of this type of interfacial membrane, so far, there has not been a feasible method to determine porosity (a key performance parameter of membranes). In this study, a solute transport-based method was proposed to estimate the porosity of membranes fabricated on chips. First, an H-shaped microchannel (-5 mm length,～500μm width and～85μm height) was fabricated with polydimethylsiloxane (PDMS) using lithography technique, and a chitosan-carbon nanoparticle membrane was formed in the microchannel using the acidic chitosan solution (pH=5) and the basic buffer solution (pH=10) with carbon nanoparticles. The thickness characteristics (the change in thickness along the flow direction of reagents) of membranes fabricated in 15,20 and 25 minutes were analyzed using the software Matlab. Then, a porosity-related mass transfer model was developed to theoretically simulate the solute transport across the membrane under the assumption that the porosity of the fabricated membrane linearly increases along the flow direction of reagents according to the experimental phenomena in the literature. Next, the urea microdialysis experiment was performed using a counter-current microdialysis mode. The fluxes of solutions at two outlets were measured and the urea concentrations in solutions collected from two outlets were detected using a biochemical analyzer. With the help of the software COMSOL, the theoretical solution fluxes and urea concentrations at both outlets under various porosity distributions were simulated by changing the parameters of the porosity distribution, and then the fitted parameters of the porosity distribution were obtained under the minimum difference between theoretical and experimental values. The results show that the average porosities of membranes formed at 15,20 and 25 minutes are 0.356±0.050,0.242±0.018 and 0.235±0.009, respectively. Finally, the estimated membrane porosity was validated using the creatinine microdialysis experiment. This work provides a feasible method to characterize the porosity of on-chip fabricated membranes.