Accessing the DNA in Breast Tissue: Adhesive Cell Capture from Flow onto Fibers of Cellulose Papers

The epithelial cells in human breastmilk represent an underutilized tissue source for research on human breast health or, in future applications, molecular-level-based cancer screening or individualized assessment of cancer risk. It remains a challenge to collect the targeted species from the milk of lactating women and new mothers, individuals for whom laboratories may be inaccessible or for whom cancer screening is a low priority. A compact, mailable device, for instance based on paper, that removes liquid and collects DNA and other targeted components is preferred over mailing milliliters of refrigerated liquid. After establishing that human DNA in breastmilk resides mostly in its cells, we focus on cell capture, employing MCF-7 cells expressing the green fluorescent protein (GFP-MCF-7) as a means to track cell progression through layers of papers, determine cell capture mechanisms, and evaluate device designs during cell flow and water removal. We show that, for the current cellulose papers, cell capture is largely an adhesive process rather than one of size-based filtration, with cells passing through layers of paper intact until they are captured. The numbers of tracer cells captured on different surfaces, from the device entrance to a liquid reservoir, are shown to be proportional to the human DNA retained at those locations. In a simple model for milk, in which bovine serum albumin is added to cell suspensions, 1% protein minimally interferes but 5% protein blocks cell capture, further supporting a model of adhesion as opposed to filtration (size-based) retention. Further, the staggering of paper porosity to produce slower liquid travel through the device facilitates greater cell capture in regions with large pores, likely a result of the impact of wall shear rate on cell capture. Engineering calculations for estimated wall shear rates inside the papers revealed that the flow dependence of capture in paper layers behaves similarly to established epithelial cell capture in shear flow chambers.