As microfluidic systems transition from research tools to disposable clinical-diagnostic devices, new substrate materials are needed to meet both the regulatory requirement as well as the economics of disposable devices. This paper introduces a UV-curable polyurethane-methacrylate (PUMA) substrate that has been qualified for medical use and meets all of the challenges of manufacturing microfluidic devices. PUMA is optically transparent, biocompatible, and exhibits high electroosmotic mobility without surface modification. We report two production processes that are compatible with the existing methods of rapid prototyping and present characterizations of the resultant PUMA microfluidic devices.

This paper describes a sample digitization method that generates tens of thousands of nanoliter-sized droplets in a high-density array in a matter of minutes. We show that the sample digitization depends on both the geometric design of the microfluidic device and the viscoelastic forces between the aqueous sample and a continuous oil phase. Our design avoids sample loss: Samples are split into tens of thousands of discreet volumes with close to 100% efficiency without the need for any expensive valving or pumping systems. We envision this technology will have broad applications that require simple sample digitization within minutes, such as digital polymerase chain reactions and single-cell studies.

We present a method to determine the concentration of nucleic acids in a sample by partitioning it into droplets with a non-uniform volume distribution. This digital PCR method requires no special equipment for partitioning, unlike other methods that require nearly identical volumes. Droplets are generated by vortexing a sample in an immiscible oil to create an emulsion. PCR is performed and droplets in the emulsion are imaged. Droplets with one or more copies of a nucleic acid are identified and the nucleic acid concentration of the sample is determined. Numerical simulations of droplet distributions were used to estimate measurement error and dynamic range, and to examine the effects of the total volume of droplets imaged and the shape of the droplet size distribution on measurement accuracy. The ability of the method to resolve 1.5-and 3-fold differences in concentration was assessed by using simulations of statistical power. The method was validated experimentally; droplet shrinkage and fusion during amplification were also assessed experimentally and showed negligible effects on measured concentration.

We recently reported a new UV-curable polyurethane-methacrylate (PUMA) resin that has excellent qualities as a disposable microfluidic substrate for clinical diagnostic applications. This article discusses strategies to improve the production yield of PUMA chips that contain dense and high-aspect-ratio features, which presents unique challenges in demolding and bonding steps. These fabrication improvements were deployed to produce a microfiltration device that contained closely spaced and high-aspect-ratio columns, suitable for retaining and concentrating cells or beads from a highly diluted suspension.

The design and fabrication of a self-digitization dielectrophoretic (SD-DEP) chip with simple components for single-cell manipulation and downstream nucleic acid analysis is presented. The device employed the traditional DEP and insulator DEP to create the local electric field that is tailored to approximately the size of single cells, enabling highly efficient single-cell capture. The multistep procedures of cell manipulation, compartmentalization, lysis, and analysis were performed in the integrated microdevice, consuming minimal reagents, minimizing contamination, decreasing lysate dilution, and increasing assay sensitivity. The platform developed here could be a promising and powerful tool in single-cell research for precise medicine.