Modification of Nanoporous Silicon Nitride with Stable and Functional Organic Monolayers

Abstract

This study describes the formation of functional organic monolayers on thin, nanoporous silicon nitride membranes. We demonstrate that the vapor-phase carbene insertion into the surface C–H bonds can be used to form sub-5 nm molecular coatings on nanoporous materials, which can be further modified with monolayers of polyethylene glycol (PEG) molecules. We investigate composition, thickness, and stability of the functionalized monolayers and the changes in the membrane permeability and pore size distribution. We show that, due to the low coating thickness (~7 nm), the functionalized membrane retains 80% of the original gas permeance and 40% of the original hydraulic permeability. We also show that the carbene/PEG functionalization is hydrolytically stable for up to 48 h of exposure to water and that it can suppress nonspecific adsorption of the proteins BSA and IgG. Our results suggest that the vapor-phase carbenylation can be used as a complementary technology to the traditional self-assembly and polymer brush chemistries in chemical functionalization of nanoporous materials, which are limited in their ability to serve as stable coatings that do not occlude nanomembrane pores.

Second Generation Nanoporous Silicon Nitride Membranes for High Toxin Clearance and Small Format Hemodialysis

“…We hypothesized that PEG‐coating would improve discrimination and possibly block albumin transmission completely. We previously showed that NPN functionalization with PEG1000 created a conformal ≈7 nm coating, which shrank pores by ≈14 nm in sieving tests . Because our sieving curves for 75 nm NPN‐O begin to show hindrance of solute transport at ≈20 nm, we reasoned that PEG‐coating would significantly hinder the transport of molecules starting at ≈6 nm, which is roughly the hydrodynamic diameter of albumin but >1.5 times larger than the hydrodynamic diameter of cytochrome c (3.6 nm) .…”

“…Paired t ‐tests ( n = 3) determined there was no significant difference ( p > 0.05) between urea fractional losses at 3, 4, and 5 h and one‐way analysis of variance (ANOVA) showed there was no significant difference ( p > 0.05) between PEG and non‐PEG membranes regarding urea clearance. This result suggests that while native NPN‐O likely adsorbs some protein from the solution, this does not hinder small molecule passage. This result is also in agreement with a 23% reduction predicted by a computational model of the system at these flow rates (Figure b; see Supporting Information).…”

“…We looked for evidence of membrane fouling by studying the time course of urea reduction in the presence of 100% serum ( Figure a). After a 2 h transient period in which samples were only partially dialyzed, the single‐pass urea clearance stabilized at ≈20%, independent of the use of a conformal PEG coating . Paired t ‐tests ( n = 3) determined there was no significant difference ( p > 0.05) between urea fractional losses at 3, 4, and 5 h and one‐way analysis of variance (ANOVA) showed there was no significant difference ( p > 0.05) between PEG and non‐PEG membranes regarding urea clearance.…”

“…We have also developed a simulation for continuous hemodialysis that predicts ultrathin membranes can maintain toxins at homeostatic levels in human blood with as little as 81 cm 2 of area . In related work, we developed a stable, conformal ≈7 nm polyethylene glycol (PEG) coating for NPN that blocks protein binding without occluding pores . Here, we build on these foundational studies by directly testing the hypothesis that nanomembranes can significantly reduce the amount of membrane area required for hemodialysis compared to conventional dialysis membranes.…”

Protein Separation and Hemocompatibility of Nitride Membranes in Microfluidic Filtration Systems

“…pore size, porosity, membrane thickness). The presence of protein adsorption and platelet activation, even though less than the positive control, points to the need for more careful design of the fluid flow in future experiments, as well as the need for surface functionalization, which our group has developed for nitride surfaces [19]. …”