BME MS Defense: Anant Agrawal

Porous Nanocrystalline Silicon Membranes as Highly Permeable and Molecularly Thin Substrates for Cell Culture

Supervised by Prof. Jim McGrath

Abstract

Porous nanocrystalline silicon (pnc-Si) is a novel silicon based material with potential uses in lab-on-a-chip devices, drug delivery, cell culture, tissue engineering and biosensing. The pnc-Si material is an ultrathin (15nm), free-standing, nanoporous membrane made with highly scalable semiconductor technology. Because pnc-Si membranes are approximately 1000 times thinner than any polymeric membrane, the permeability of pnc-Si to small solutes is orders-of-magnitude greater than conventional materials. As cell culture substrates, pnc-Si membranes could overcome the inadequacy of membrane materials used in conventional transwells and enable new types of culture devices for the precise control and manipulation of cellular microenvironments. The objective of this thesis is to investigate the feasibility of pnc-Si as a cell culture substrate by comparing cell adhesion, spreading, growth kinetics and viability on pnc-Si to conventional tissue culture substrates. By each of these metrics, the behaviors of both immortalized cells (3T3-L1 fibroblast cell line) and primary vascular endothelial cells (HUVEC) were found to be highly similar on pnc-Si, tissue culture grade polystyrene and glass.

Significantly, pnc-Si was found to degrade in cell culture media over several days without cytotoxic effects. Membrane stability could be tuned by modifying the density of a superficial native oxide layer through post production rapid thermal processing and additional surface treatment like amino-silanization. Pnc-Si was assembled in a custom designed tube to form a pnc-Si transwell device that could replace existing 24-well plate inserts. The adhesion of HUVEC to treated pnc-Si transwells was found to be comparable to commercial transwells. Collectively, the results establish pnc-Si as a viable new substrate for cell culture and a new type of degradable biomaterial. Pnc-Si membranes should find many uses in bioscience including the study of molecular transport through cell monolayers, as molecularly thin dividers for the study of cell-cell communication in co-cultures, and as biodegradable scaffolds for three-dimensional tissue constructs.