Lipid-Filled Mesoporous Silica As a Platform for Biomimetic Membranes

The ability of biological membranes to selectively transport ions or hydrophilic molecules using carrier proteins has inspired the design of lipid bilayer supported thin film membranes. In this work, hydrophobic carrier molecules embedded in the bilayer are used to provide selective transport of aqueous solutes across the synthetic membrane platform. Thin film mesoporous silica, which provides for tunable pore morphology, chemical and thermal stability and ease of organic functionalization, is an ideal support for lipid bilayers. Lipid bilayers are traditionally prepared in the form of pore enveloping (covering the surface of the thin film), but we have recently demonstrated the use of pore filling to provide an effective barrier to aqueous solutes. Combining selective permeable lipid bilayers with high surface area silica materials suggests many potential applications for efficient, selective dilute aqueous solute separations.

In this study, the separation of dilute aqueous saccharides, representing the recovery of dilute carbohydrates from the depolymerization of biomass, is investigated using a carbohydrate carrier (hydrophobic boronic acid) immobilized in the lipid bilayer. Lipid filled membranes (in the absence of boronic acid) reduce the flux of glucose by around a factor of 15 in comparison to bare silica and lipid enveloped membranes, demonstrating the ability of the former to act as effective barriers to aqueous sugars. Transport of glucose and other saccharides through the lipid-filled pores facilitated using boronic acid carriers is demonstrated. Factors such as pH gradients and temperature have been examined to determine the selectivity of sugars. An alkaline pH on the donor side and an acidic pH on the receptor side of the membrane was found to increase the selectivity of glucose over cellobiose by around 12.5%, whereas the selectivity of the same at a pH of 7.4 on both sides of the membrane and a temperature of 45 C was reduced by 25% in comparison to pH of 7.4 and room temperature. The design of the lipid bilayer assembly based on boronic acid composition is currently being investigated to enhance sugar selectivity. This ongoing work measures the effect of boronic acid concentrations on the structural integrity of lipid bilayers using Differential Scanning Calorimetry (DSC).