Preparation and Characterization of Porous Collagen Membranes on Silicon
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AA8.17.1
Preparation and Characterization of Porous Collagen Membranes on Silicon Lori A. Lepak1, Troy Richards2, Nancy Guillen3, Michelle Caggana4, James N. Turner4, and Michael G. Spencer2 1 Cornell University, Dept. of Chemistry and Chemical Biology, Ithaca NY 14853 2 Cornell University, Dept. of Electrical and Computer Engineering 3 Research Experience for Undergraduates (REU) Program 4 Wadsworth Center, Empire State Plaza, Albany NY 12201 ABSTRACT 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 (~ 400 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 µm 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. INTRODUCTION The techniques of selective filtration and equilibrium dialysis are often used to expedite the analysis of complex mixtures of cellular products and smaller molecules in solution. For example, the development of a porous material for an efficient separation of hemoglobin from DNA could greatly simplify the genetic testing of blood samples. Nanometer-scale pores would be required to achieve a sized-based separation of DNA (2 nm) from hemoglobin (5.5 nm). To fully integrate the membrane system with analytical microdevices, photolithographic patternability of the membrane material is essential. In some applications, the ability to implant a device without immunogenic reactions will be a critical requirement. Thus, the goal of this project is to develop membrane systems which meet the concurrent requirements of biocompatibility, nanometer-scale pore sizes, and integrability with Si devices. Our initial investigations have utilized type I collagen as the membrane material. Collagen possesses the advantage of biocompatibility, and membranes fabricated from monomeric collagen appear to have average pore sizes of less than 100 nm. Under certain conditions, it appears to be possible to eliminate through-membrane pores altogether. Furthermore, we have demonstrated techniques for lithographically patterning collagen at 25 micron and above length scales.
AA8.17.2
EXPERIMENT Diffu
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