Silicon nanoporous membranes as a rigorous platform for validation of biomolecular transport models

Abstract

Microelectromechanical systems (MEMS), a technology that resulted from significant innovation in semiconductor fabrication, have recently been applied to the development of silicon nanopore membranes (SNM). In contrast to membranes fabricated from polymeric materials, SNM exhibit slit-shaped pores, monodisperse pore size, constant surface porosity, zero pore overlap, and sub-micron thickness. This development in membrane fabrication is applied herein for the validation of the XDLVO (extended Derjaguin, Landau, Verwey, and Overbeek) theory of membrane transport within the context of hemofiltration. In this work, the XDLVO model has been derived for the unique slit pore structure of SNM. Beta-2-microglobulin (B2M), a clinically relevant “middle molecular weight” solute in kidney disease, is highlighted in this study as the solute of interest. In order to determine interaction parameters within the XDLVO model for B2M and SNM, goniometric measurements were conducted, yielding a Hamaker constant of 4.61× 10−21 J and an acid-base Gibbs free energy at contact of 41 mJ/m2. The XDLVO model was combined with existing models for membrane sieving, with predictions of the refined model in good agreement with experimental data. Furthermore, the results show a significant difference between the XDLVO model and the simpler steric predictions typically applied in membrane transport. The refined model can be used as a tool to tailor membrane chemistry and maximize sieving or rejection of different biomolecules.

Slit pores preferred over cylindrical pores for high selectivity in biomolecular filtration

“…The output is shown for LW, AB (with D = 0.11 nm and D = 0.6 nm) and EL interactions. Values for the acid-base decay constant can vary significantly, with D = 0.11 nm taken from our previous study [5] and D = 0.6 nm appearing elsewhere in the literature [10]. It is clear from the model calculations that XDLVO interactions can both increase (attractive forces) and decrease (repulsive forces) the partition coefficient compared to the purely steric case.…”

“…The potential function can be represented by a Boltzmann distribution through g ( ρ ) = exp(− E ( ρ )/ kT ), where E ( ρ ) is the energy at a given non-dimensional pore position ρ , k is the Boltzmann constant, and T is temperature [10]. The osmotic reflection coefficient, which was also calculated in our previous work [5], is neglected here for the sake of simplification. This omission is justified due to the much larger impact of the partition coefficient on solute sieving.…”

“…The surface element integration approach has been applied to determine the interaction energy between the solute and membrane surface [5]. This method has been applied previously for cylindrical pores [10][12][13] and has been recently developed for slit pores by our research group [5].…”

“…This method has been applied previously for cylindrical pores [10][12][13] and has been recently developed for slit pores by our research group [5]. The expression for the energy of a sphere at a given pore position is…”

“…We recently published a comprehensive transport model for the unique slit pore structure of SNM that includes, for the first time, a consideration of intermolecular interactions between the membrane and solute in the unique slit pore geometry. These interactions, which include van der Waals (LW), acid-base (AB), and electrostatic (EL) forces, can have a significant impact on the transport of solutes through the membrane [5]. Collectively, these forces comprise the extended Derjaguin, Landau, Verwey, and Overbeek (XDLVO) theory.…”