Preparation and characterization of porous collagen membranes on silicon

Advances in biotechnology in the past decade have raised the possibility of fabricating biocompatible, porous membranes for molecular sieving and dialysis separations of particles sized 20-50 nm or less. As a prerequisite for-such applications, we demonstrate that thin films (similar to400 nm) of monomeric bovine dermal collagen spin-deposited on a silicon substrate are patternable using standard semiconductor microlithographic processing techniques. Patterning via liftoff has reliably produced square features as small as 10-25 mum laterally, and 50 nm thick, in initial experiments. HVEM (high vacuum electron microscope) images of these collagen membranes have revealed typical pore sizes ranging from 1-100 nm. Through-membrane diffusion of chromophores spanning this size range was quantified via UV/vis spectrometry. These studies revealed that a 400 nm thick collagen membrane crosslinked with 0.02% glutaraldehyde rejected detectable quantities of methyl orange dye (MW 327) for at least 48 hours, while a 100 nm thick layer admitted methyl orange in under 30 minutes. DNA has been demonstrated to pass through a 100 nm thick collagen layer more slowly than through a bare through-etched control wafer.