Modification of Nanoporous Silicon Nitride with Stable and Functional Organic Monolayers

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

Conventional hemodialysis (HD) uses floor-standing instruments and bulky dialysis cartridges containing ≈2 m2 of 10 micrometer thick, tortuous-path membranes. Portable and wearable HD systems can improve outcomes for patients with end-stage renal disease by facilitating more frequent, longer dialysis at home, providing more physiological toxin clearance. Developing devices with these benefits requires highly efficient membranes to clear clinically relevant toxins in small formats. Here, the ability of ultrathin (<100 nm) silicon-nitride-based membranes to reduce the membrane area required to clear toxins by orders of magnitude is shown. Advanced fabrication methods are introduced that produce nanoporous silicon nitride membranes (NPN-O) that are two times stronger than the original nanoporous nitride materials (NPN) and feature pore sizes appropriate for middle-weight serum toxin removal. Single-pass benchtop studies with NPN-O (1.4 mm2 ) demonstrate the extraordinary clearance potential of these membranes (105 mL min-1 m-2 ), and their intrinsic hemocompatibility. Results of benchtop studies with nanomembranes, and 4 h dialysis of uremic rats, indicate that NPN-O can reduce the membrane area required for hemodialysis by two orders of magnitude, suggesting the performance and robustness needed to enable small-format hemodialysis, a milestone in the development of small-format hemodialysis systems.

An in vitro platform for elucidating the molecular genetics of S. aureus invasion of the osteocyte lacuno-canalicular network during chronic osteomyelitis

Staphylococcus aureus osteomyelitis is a devasting disease that often leads to amputation. Recent findings have shown that S. aureus is capable of invading the osteocyte lacuno-canalicular network (OLCN) of cortical bone during chronic osteomyelitis. Normally a 1 μm non-motile cocci, S. aureus deforms smaller than 0.5 μm in the sub-micron channels of the OLCN. Here we present the μSiM-CA (Microfluidic - Silicon Membrane - Canalicular Array) as an in vitro screening platform for the genetic mechanisms of S. aureus invasion. The μSiM-CA platform features an ultrathin silicon membrane with defined pores that mimic the openings of canaliculi. While we anticipated that S. aureus lacking the accessory gene regulator (agr) quorum-sensing system would not be capable of invading the OLCN, we found no differences in propagation compared to wild type in the μSiM-CA. However the μSiM-CA proved predictive as we also found that the agr mutant strain invaded the OLCN of murine tibiae.

Protein Separation and Hemocompatibility of Nitride Membranes in Microfluidic Filtration Systems

Improving the health outcomes for end-stage renal Disease (ESRD) patients on hemodialysis (HD) requires new technologies for wearable HD such as a highly efficient membrane that can achieve standard toxic clearance rates in small device footprints. Our group has developed nanoporous silicon nitride (NPN) membranes which are 100 to 1000 times thinner than conventional membranes and are orders-ofmagnitude more efficient for dialysis. Counter flow dialysis separation experiments were performed to measure urea clearance while microdialysis experiments were performed in a stirred beaker to measure the separation of cytochrome-c and albumin. Hemodialysis experiments testing for platelet activation as well as protein adhesion were performed. Devices for the counter flow experiments were constructed with polydimethylsiloxane (PDMS) and a NPN membrane chip. The counter flow devices reduced the urea by as much as 20%. The microdialysis experiments showed a diffusion of ~ 60% for the cytochrome-c while clearing ~ 20% of the Albumin. Initial hemocompatibility studies show that the NPN membrane surface is less prone to both protein adhesion and platelet activation when compared to positive control (glass).