Active membranes with switchable pores that are based on hydrogels can be used to measure the cell size distribution in blood samples. The system investigated in the present research is based on a polyethylene terephthalate (PET) membrane that is surface polymerized with poly(N-isopropyl acrylamide) (PNiPAAm) to form active pores of arbitrary geometry. The PET membrane provides the functionality of a backbone for mechanical rigidity, while the soft PNiPAAm hydrogel forms the active pores. Modeling and simulation of the active hydrogel behavior proved to adequately predict the opening and closing of the pores under application of an activating stimulus, e.g. temperature. The applied model is called Temperature-Expansion-Model and uses the analogy of thermal expansion to model the volume swelling of hydrogels. The Normalized Extended Temperature-Expansion-Model can englobe arbitrary hydrogels and large geometric displacements. Studies of pore opening – performed by using commercial finite element tools – show good agreement of the experimentally measured shape change of active pores. Based on these studies, the particulate fluid flow through the switchable pores is analyzed. Through application of a membrane process, i.e. a given variation of applied pressure and switching stimulus for the hydrogel, the size profile of the blocking particles can be measured directly using the flux difference under constant pressure. This allows the measurement of the cell size distribution in blood samples, e.g. to detect circulating tumor cells or anomalies in the distribution that hint to anemia.
Adrian Ehrenhofer and Thomas Wallmersperger, "Active hydrogel composite membranes for the analysis of cell size distributions," Proc. SPIE 10968, Behavior and Mechanics of Multifunctional Materials XIII, 1096815 (Presented at SPIE Smart Structures + Nondestructive Evaluation: March 07, 2019; Published: 29 March 2019); https://doi.org/10.1117/12.2513199.
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