UC Irvine

PDMS (polydimethylsiloxane) devices are important for several complex microfluidic applications. The molds used to create these devices are commonly made with SU-8 liquid photoresists, however, dry film photoresists are increasingly gaining ground in similar applications. In this work, we present a multi-layer dry resist lamination photolithography fabrication procedure for the development of microfluidic device molds. Here, we report a method to achieve alignment within ~50-μm of error for two-layer devices using ADEX or SUEX photoresists ranging from 10um to 300-μm in thickness. This method is advantageous for not requiring a clean room setting and using standardized height dry film photoresists for easy mold replicability.Multilayer alignment typically requires the first layer to be developed before adding the second, so that first-layer features are visible to allow alignment of the second layer. This works fine with liquid resists such as SU-8, which can flow over the topography of the fully developed first layer. However, dry film resists must be laminated onto a flat surface. Here, we demonstrate that mask patterns can be revealed by an appropriately designed post-exposure bake, without using developer, leaving an intact first layer of resist that allows lamination of a second layer. 50-μm alignment accuracy was achieved between first and second layer patterns without the use of a mask aligner. This fabrication method was used to create two microfluidic devices with multi-layer architecture, a neuronal coculture chemotaxis device and a hydrophoretic cell sorting device. Cancer organoids are three-dimensional tissues that can be grown from patient biopsy material or tumor fragments that are dissociated and embedded in Matrigel or similar basement membrane extracts. Organoids can be used for rapid drug screening of patient derived cancer cells to develop cancer therapy and treatment options more efficiently for patients. Conventional organoid preparations require substantial amounts of patient-derived tissue per experimental condition, forcing months of culture expansion that can be detrimental to patients with rapidly progressing tumors. The use of a droplet generator to culture organoids into smaller Matrigel beads would increase the drug screening rate, reduce costs, and increase the accuracy of screenings. In this work, a hydrophoretic cell sorting device was developed to group cancer cells and cell clusters ranging up to 250um in diameter into similar sized categories. The grouping of cells in this manner would aid in the consistent generation of uniform cancer organoids. Here, we discuss the development and testing of the hydrophoretic cell sorting device and test a droplet generation device to encapsulate cancer cells in Matrigel which are later grown into organoids.