A design adjustment of the inner structure minimizes the floating overhangs in the range of the flow channels. Due to this adjustment, the use of any kind of support material can be avoided. In this way it can be ensured that no residues of water soluble or non-biocompatible material remain in the system. A part from avoiding support material, the aim was to apply the cell culture reservoir on the polymer chip without the need for any adhesives. In the PF-process, polymer chips can be inserted into the build chamber and be printed directly. The deposition of the molten polymer droplets on the thermoplastic basic chips is similar to the welding process of polymers. The cell culture reservoirs have the purpose to absorb, store and pass the microfluidic into micro physiological systems. Therefore, the tightness of the whole system is crucial to ensure the functionality. The structure is generated by applying single polymer droplets, so that cavities are formed between the droplets. The optimization of the process parameters aimed to minimize the porosity of the cell culture reservoirs to ensure the fl uid tightness. The cell culture reservoirs were produced with a 0.2 mm nozzle and the layer thickness is about 0.15 mm.
By adjusting the form factor (FF), the degree of fi lling and thus the pore volume can be varied. Besides the impact of the form factor, the impact of the processing temperature (material preparation and build chamber temperature) is investigated as well. These process parameters affect the mass temperature of the molten polymer droplets. A temperature increase results in a decrease of the viscosity. Expectably, a decrease of the viscosity improves the wettability of the droplets, so that less cavities are generated. The lower viscosity, therefore, is expected to result in a reduction of the pore volume. The setting behavior of the polymer droplets immediately after the deposition is mainly affected by the temperature of the build chamber.
The figure shows the three-dimensional view of three cell culture reservoirs. The yellow colored areas mark the pores in the test samples. The integrated structures are clearly recognizable in the middle of the fi gure. It is clear to see that a low form factor and a high temperature in the build chamber result in a decrease of the pore volume.
Introduction and Objectives
The Plastic Freeforming (PF) enables the successful construction of application-specifi c reservoirs and cell culture segments directly on a universal micromachining platform (polymer chip). The cell culture reservoirs were manufactured from the copolymer ABS. The focus was on the optimization of the process parameter concerning the fluid tightness and the bonding on the polymer chip made of PC.