Die schaltbare Filtration mithilfe von Hydrogel'=Verbundmembranen zeigt großes Potential zur Lösung einer der grundlegenden Aufgaben in der Humanmedizin: der unkomplizierten und schnellen Analyse von Blutproben zur Erkennung von Unregelmäßigkeiten, wie zum Beispiel zirkulierenden Tumorzellen. In der vorliegenden Arbeit wird ein solches System diskutiert und mithilfe von Methoden des Maschinenwesens -- Modellierung und Simulation -- untersucht. Das betrachtete System besteht aus einer aktiven Hydrogelschicht, welche auf einer passiven Polymerschicht aufgebracht ist und damit eine schaltbare Verbundmembran bildet. Die Arbeit folgt zwei Hauptpfaden: Im festkörpermechanischen Teil werden die mechanischen Aspekte von Verbundmembranen dargestellt, während im fluidmechanischen Teil die Permittivität und Selektivität von Membranen näher beleuchtet werden. Im Folgenden werden Modelle zur Schaltbarkeit ausgehend von aus der Literatur bekannten Ansätzen entwickelt. Diese werden dann im Rahmen von Simulationen -- sowohl im kommerziellen Finite-Elemente-Programm Abaqus, als auch in selbst geschriebenen Matlab-Codes -- umgesetzt. Die vorliegende Arbeit zeigt, dass ein schaltbares System zur Analyse von Zellgrößenprofilen realisierbar und durch Modellierung und Simulation in einem Maß beschreibbar ist, sodass der experimentellen Realisierung nichts mehr im Wege steht. / Switchable filtration with hydrogel composite membranes shows great potential to solve one of the basic challenges in life sciences: the fast and easy analysis of blood samples to detect abnormal cells like e.g. circulating tumor cells. In the present work, a system providing these features is discussed using tools provided by engineering: modeling and simulation. The system consists of an active hydrogel composite membrane in combination with a passive polymeric membrane that provides mechanical stability. This forms a switchable composite membrane. The work follows two main paths: In the solid mechanics path, the composition of membranes and their mechanical aspects are discussed. The fluid mechanics path focuses on permittivity and selectivity for particle flows. Originating from the basic concepts of membrane permeation in literature, models for switchability are developed and simulations -- both in the commercial finite-element tool Abaqus and in Matlab scripts -- are performed. The present work proves that the concept of cell-size detection with switchable membranes is suitable for the task. Through the performed simulations, the corresponding processes can be described and designed so that the microfluidic analysis system can be experimentally realized.

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Membranes act as smart structures in respect to their permeation abilities. Control of particle and fluid permeation through a synthetic membrane can be achieved by using different effects like size-exclusion or electromagnetic interactions that occur between the particles and membrane pores. The simulation of controlled permeability provides an insight into the smart behavior of membranes for chemical signal processing, sensing interfaces or lab-on-a-chip devices. In the current work, we model the underlying physical processes on a microfluidic level using the engineer’s approach of laminar flow through pipes. Different pore geometries inside a composite membrane system consisting of a polyethylene terephthalate support membrane and a poly(N-isopropylacrylamide) hydrogel-layer are investigated. Simulations for different states of thermally induced pore opening are performed for free and blocked states. From the results we derive paradigms for the design of a membrane system for microfluidic cell-size profiling considering stimulus-range, pore shape and measurement setup.

Membranes separate uid compartments and can comprise transport structures for selective permeation. In biology, channel proteins are specialized in their atomic structure to allow transport of specific compounds (selectivity). Conformational changes in protein structure allow the control of the permeation abilities by outer stimuli (gating). In polymeric membranes, the selectivity is due to electrostatic or size-exclusion. It can thus be controlled by size variation or electric charges. Controllable permeation can be useful to determine particle-size distributions in continuous ow, e.g. in micro uidics and biomedicine to gain cell diameter profiles in blood. The present approach uses patterned polyethylene terephthalate (PET) membranes with hydrogel surface coating for permeation control by size-exclusion. The thermosensitive hydrogel poly(N-isopropylacrylamide) (PNIPAAm) is structured with a cross-shaped pore geometry. A change in the temperature of the water ow through the membrane leads to a pore shape variation. The temperature dependent behavior of PNIPAAm can be numerically modeled with a temperature expansion model, where the swelling and deswelling is depicted by temperature dependent expansion coefficients. In the present study, the free swelling behavior was implemented to the Finite Element tool ABAQUS for the complex composite structure of the permeation control membrane. Experimental values of the geometry characteristics were derived from microscopy images with the tool ImageJ and compared to simulation results. Numerical simulations using the derived thermomechanical model for different pore geometries (circular, rectangle, cross and triangle) were performed. With this study, we show that the temperature expansion model with values from the free swelling behavior can be used to adequately predict the deformation behavior of the complex membrane system. The predictions can be used to optimize the behavior of the membrane pores and the overall performance of the smart membrane.