For fabricating three-dimensional, functionalized microstructures for cell culture applications, we have developed a new multistep process, called Substrate Modification And Replication by Thermoforming or SMART. Unlike to other microreplication processes, such as micro injection moulding, its central microtechnical thermoforming process provides the specific feature of forming thin polymer films not in a molten but only in a softened state. Due to the permanent material coherence of the film during forming, modifications previously created on the planar film are maintained and they are even available on perpendicular sidewalls or even in undercut regions of the three-dimensionally shaped microstructure. For instance, a cell adhesion pattern previously created on a planar polymer film by a mask based UV modification process is maintained (high lateral resolution) during thermoforming and is still recognized by cells cultured within these microcavities. Furthermore, surface topographies and bulk modifications are maintained as well (please see Figure). The latter can be used e.g. to produce highly porous, thin-walled micro-container arrays (r-3D-KITChip) by a combination with ion track technology. This multistep procedure SMART enables the fabrication of thin-walled, flexible microstructures whose material properties and size and shape are highly adaptable. Thus, SMART-processed cell culture substrates can be specifically customized to various requirements not only in the field of advanced cell culture technology.
Examples for film-based microstructures produced by the SMART process:
- Combination with ion track technology to fabricate highly porous, thin-walled structures (first picture, coop. with C. Trautmann, GSI, Germany).
- Creation of cell adhesion patterns on strongly curved surfaces by the combination of thermoforming and a mask based UV irradiation of a previously planar cell repellent polymer film (second picture).
- Integration of nanotopographies by the combination with a previously, on the planar polymer film performed nanoimprint process (third picture, coop. with R. Truckenmüller, UTwente, The Netherlands, A. Schleunitz, PSI, Switzerland).
- Fabrication of thin film electrodes in thermoformed microstructures by depositing a pattern of catalytic seeds onto the planar film before thermoforming and, starting from these seeds, the formation of a closed electrical conducting layer by electroless plating after thermoforming (fourth picture).
