Method of Fabrication of Self-enclosed Microchannels and/or Chambers with or Without Integrated Interconnects and Electrodes
Background: Conventional methods that create fluidic channels using photopolymers create channels and chambers by-coating, patterning, and developing each layer sequentially. These conventional methods of fabricating microchannels also involve using molds or patterning channels onto a flat substrate. In the latter method, the flat substrate acts as the bottom support for the microchannel or chamber. Microneedles have been fabricated using a variety of methods including molding and micromachining. The disadvantages of these methods are that: 1) If a substrate is used as part of the microfluidic channel or chamber, the device cannot be released from the substrate. 2) In multiple layer fabrication methods, material is wasted in the coating process. 3) Different materials compose the inner surface of the microchannels making the device leakage prone and making fluidic control using electrokinetic methods difficult (because there are more variables). 4) Integration of electrodes is only possible for methods where the device is adhered to a support surface. 5) The support substrates usually used in micromachining are not very flexible. Thus, the device is usually not flexible. Technology: Researchers at the University of California, Irvine have developed a method of fabrication of self-enclosed microchannels and/or chamber with or without integrated interconnects and electrodes. The UC method allows reduction in costs and time because only a single development step is required to define all the walls of the microfluidic device. This allows for reduction of photopolymer that is wasted during the application step (usually a spin-on process). This method also allows for reduction of masks and alignment steps, especially if a gray tone mask is used. All surfaces of the device can be made of one material (the photopolymer), this reduces the parameters involved in electrokinetic or mechanical pumping and allows better control of surface effects because there is only one material to deal with. Other advantages include: 1) The method of fabricating electrodes and interconnects allows microneedles to be made where the interconnects are insulated from the fluid environment and the fluid within. 2) Electrodes could be used for a plurality of purposes including actuating the medium (electrokinetic or by electrolysis), DNA hybridization and detection, and sensing of various parameters. 3) Since a support substrate is not needed for the bottom or top surface, the whole device can be released from the transparent substrate. This reduces the cost of the substrate and allows for fabrication of long or even flexible completely enclosed microchannels. 4) There is no need for bonding or sealing of any surfaces for the fabrication of devices using this method. The whole device is essentially made from a single photopolymer layer. Because the interface between the walls of the device created-is mechanically strong, leakage can be avoided and the device can withstand much higher pumping pressures and stresses (such as bending a flexible conduit). Application: This method can be used to fabricate a microfluidic channels and chambers for use in a plurality of devices including catheters, microneedles, electrokinetic capillaries, inkjet nozzles, micro PCR (Polymerase Chain Reaction) chambers, and flexible fluid conduits.
Example 1: Micro Drug Delivery Device or Inkjet Nozzle where a chamber with two electrodes and a microfluidic channel connected to it is patterned using this method. The device is released from the transparent substrate allowing the microfluidic channel to become a microneedle (or inkjet nozzle). The chamber is filled with a drug (or ink). The drug (or ink) is delivered by expulsion due to electrolysis at the electrodes when a voltage is applied to the electrodes.
Example 2: Micro PCR Chamber where a micro PCR chamber is constructed. Embedded interconnects act as heating elements, and PCR would be performed on small fluid samples.
Example 3: Catheters, Microneedles, Electrokinetic Capillaries, Flexible Fluid Conduits, Long microchannels. They would be created by fabricating and releasing a microchannel. Flexible catheters can be fabricated using this method by using a flexible photopolymer and releasing the whole structure from the transparent substrate.
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