Research On The Theory And Fabrication Of Thermoplastic Micrfluidic Device With Three-dimensional Microstructures

In this study, we call microfluidic devices which have three-dimensional channels or multilayer structures as "three-dimensional microfluidic devices". Among which, three-dimensional channels mean certain inner microstructures exist in the channels, and multilayer structures mean the device composes by more than two layers.In planar microchip, when the chip is used for cells filtration and trapping, especial electric or magnetic fields are required. However, three-dimensional devices can do these only by using the microstructures fabricated in microchannels, which is simple and quick. The development of three-dimensional microfluidic devices have become a hot topic.Sample operation is achieved only in a planar channel for double layer microfluidic chip, which is one of the bottlenecks slowing the realization of trueμTAS platforms. An approach to overcome this problem is the fabrication of multilayer microfluidic systems, in which each layer can achieve a function. The development of multilayer microfluidic devices have become a forefront topic.Hot embossing and thermal bonding, which are significant approaches to fabricate thermoplastic planar microfluidic device, have difficulties in the fabrication of multilayer microfluidic devices:(1) the replication precision is not acceptable, and the replication defects can easily generate; (2) channel deformation can destroy the in-channel structures; (3) multilayer bonding is affected by reservoir diameter, channel width and substrate thickness.The work is supported by National Basic Research Program of China (2007CB714502) and Major Program of National Natural Science Foundation of China (20890024). It emphasizes on the theory and fabrication of three-dimensional microfluidic devices with hot embossing and thermal bonding, the research works can be summarized as follows:(1) The filling and deformation behavior of glassy or hyperelastic thermoplastics is studied. This work lays a foundation for the embossing of three-dimensional microstructures.The filling and deformation behavior during hot embossing is studied based on theoretical analysis, finite element simulation, synchronous recording and asynchronous analysis. We present the conception of "lack-filling region", and study its formation and elimination. The relationship between lack-filling area and heating rate, applying pressure rate and remaining temperature and pressure time has been established.The study of filling and deformation behavior of glassy or hyperelastic thermoplastics during hot embossing with male die have not been reported. (2) The fracture mechanism of metal electrodes integrated on thermoplastic electrophoresis microchips is studied. Fabrication approach for a new kind of PET electrophoresis microchip is developed.The relationship between electrode stress and bonding parameters, thermal stress and the length of electrode in reservoir is studied base on fracture theory and visco-elastic theory. Bonding experiments and finite element analysis are conducted to verify the theoretical results. Fabrication approach of PET microchips is developed, and the fabrication of reservoir, the hot embossing of microchannels, the alignment of electrode, surface modification and thermal bonding process are studied.In this section, the studies of electrode fracture mechanism and fabrication approach for PET electrophoresis microchips are innovative.(3) The deformation mechanism of microchannel during thermal bonding is studied. An approach, named pre-compensation, is presented to minimize the effects of channel deformation on in-channel microstructures. Fabrication approach of PMMA blood cells filtration device with in-channel microweirs is developed.Based on thermal visco-elastic theory, the channel deformation during thermal bonding is studied by theory and simulation. The theoretical results are verified by experiments. Pre-compensation approach is presented to minimize the effects of channel deformation. Fabrication approach of blood cells filtration device with in-channel microweirs is developed. The compensation value, channel network design, silicon mold fabrication, three-dimensional channel embossing and chip bonding are investigated.In this section, the studies of channel deformation model, channel pre-compensation and fabrication approach for PMMA blood cells filtration are innovative.(4) An approach for the fabrication of multilayer three-dimensional thermoplastic microfluidic device is presented.Relationship between reservoir diameter, channel width, substrate thickness and multilayer bonding is established through finite element simulation and multilayer bonding experiments. A new approach for multilayer thermoplastic microdevices bonding is presented. The processes included in MTBP, such as DTSLB, EBAB, MSB, TP-SM and LEW are studied. Three multilayer PMMA microfluidic devices are fabricated using MTBP.In this section, EBAB, MSB, DTSLB and LEW approaches are all presented for the first time. TP-SM is an improved approach.