Silicon micromachining provides the precise control of nanoscale features that can be fundamentally enabling for miniaturized, implantable medical devices. Concerns have been raised regarding blood biocompatibility of silicon-based materials and their application to hemodialysis and hemofiltration. A high-performance ultrathin hemofiltration membrane with monodisperse slit-shaped pores was fabricated using a sacrificial oxide technique and then surface-modified with poly(ethylene glycol) (PEG). Fluid and macromolecular transport matched model predictions well. Protein adsorption, fouling, and thrombosis were significantly inhibited by the PEG. The membrane retained hydraulic permeability and molecular selectivity during a 90 hour hemofiltration experiment with anticoagulated bovine whole blood. This is the first report of successful prolonged hemofiltration with a silicon nanopore membrane. The results demonstrate feasibility of renal replacement devices based on these membranes and materials.

Polydisperse Ficoll mixtures have been used to explore glomerular sieving. Ficoll appears to be neither absorbed nor secreted by the renal tubule, and so urinary Ficoll concentrations reflect only the glomerular filtration barrier. The literature is contradictory regarding Ficoll's behavior as an idealized spherical solute. Further definition of Ficoll transport will inform interpretation of in vivo results. Flat-sheet membranes comprising a uniform array of slit pores measuring 8 nm by 45 mum were perfused with FITC-labeled Ficoll 70 and BSA. Ficoll and BSA concentrations were quantified by gel-permeation chromatography and Bradford assay, respectively. BSA and Ficoll molecules with diameters equal to approximately half of the slit pore width displayed hindered transport in agreement with modeled rigid sphere transport through slit-shaped pores. Ficoll molecules larger than approximately 0.65 slit width displayed transport rates in excess of predictions. Ficoll molecules with Stokes-Einstein diameters greater than the pore dimension were observed in permeate samples. We present data for Ficoll filtration through a novel array of well-defined pores, which illustrate that Ficoll is well modeled as an ideal sphere in one size domain, but the model breaks down as molecular diameter approaches pore size. These data inform the present debate regarding glomerular filtration and affect conclusions drawn from the use of Ficoll as a tracer molecule. The apparent hyperpermeability of Ficoll through slit-shaped pores suggests that further modeling incorporating deformation of the molecule is necessary when using Ficoll solutions to characterize membranes.

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This paper details the development of amorphous hydrogenated silicon carbide (a-SiC:H) films as structural material that is resistant to biofouling. The a-SiC:H films were deposited by PECVD and evaluated for their mechanical and anti-biofouling properties. It was found that the as-deposited films exhibited compressive residual stresses that could be converted to moderate tensile stresses upon a post deposition anneal. The amorphous films exhibited a much lower Young’s modulus but similar burst stress when compared to polycrystalline 3C-SiC films of like thickness. The as-deposited a-SiC:H films were more resistant to biofouling than silicon and silicon dioxide surfaces. Coating the a-SiC:H films with polyethylene glycol (PEG) significantly improved the anti-fouling characteristics for extended periods.

A Poly (ethylene glycol) (PEG) self-assembled monolayer was solution phase coupled to common MEMS (microelectromechanical systems) substrates through a one step procedure in order to investigate the potential anti-fouling properties of the polymer for implantable biomedical MEMS applications.