Cross-flow Microfiltration for Lab-on-chip Defatting of Human Breast Milk

Determining the lactose concentration in human breast milk (HBM) via standard assay techniques requires fat removal from the milk (defatting), followed by lactose detection in the remaining skim milk. This work focuses on methods of defatting which can be subsequently integrated in the same Lab-on-Chip (LOC) as the lactose measurement. One method under study for defatting HBM is the use of a cross-flow microfiltration structure. This kind of microfiltration prevents clogging and separates the large fat globules from the smaller nutrition constituents of milk, of which lactose is amongst the smallest. To test if large fat globules may clog the channel or not, the biocompatibility of PMMA and HBM was studied. The weight of absorbed fat on the surface of PMMA was found to be 3-orders of magnitude lower than that of the total fat in HBM. Photolithgraphy using SU-8 was applied for mold fabrication; however, hot-embossing using SU-8 mold has not been successful due to the high stress resulting in the demolding process. To improve mold strength, nickel molds were fabricated by electroplating using different current densities. As expected, the deposition rates were found to have a linear relationship with applied current density, while the smaller features have a higher deposition rate than larger features.