By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.

The mitotic spindle must function in cell types that vary greatly in size, and its dimensions scale with the rapid, reductive cell divisions that accompany early stages of development. The mechanism responsible for this scaling is unclear, because uncoupling cell size from a developmental or cellular context has proven experimentally challenging. Here we combined microfluidic technology with Xenopus egg extracts to characterize spindle assembly within discrete, geometrically defined volumes of cytoplasm. Reductions in cytoplasmic volume, rather than developmental cues or changes in cell shape, were sufficient to recapitulate spindle scaling observed in Xenopus embryos. Thus, mechanisms extrinsic to the spindle, specifically a limiting pool of cytoplasmic component(s), play a major role in determining spindle size.

Microfluidic inertial focusing has been demonstrated to be an effective method for passively positioning microparticles and cells without the assistance of sheath fluid. Because inertial focusing produces well-defined lateral equilibrium particle positions in addition to highly regulated interparticle spacing, its value in flow cytometry has been suggested. Particle focusing occurs in straight channels and can be manipulated through cross sectional channel geometry by the introduction of curvature. Here, we present a staged channel design consisting of both curved and straight sections that combine to order particles into a single streamline with longitudinal spacing. We have evaluated the performance of these staged inertial focusing channels using standard flow cytometry methods that make use of calibration microspheres. Our analysis has determined the measurement precision and resolution, as a function of flow velocity and particle concentration that is provided by these channels. These devices were found to operate with increasing effectiveness at higher flow rates and particle concentrations, within the examined ranges, which is ideal for high throughput analysis. Further, the prototype flow cytometer equipped with an inertial focusing microchannel matched the resolution provided by a commercial hydrodynamic focusing flow cytometer. Most notably, our analysis indicates that the inertial focusing channels virtually eliminated particle coincidence at the analysis point. These properties suggest a potentially significant role for inertial focusing in the development of inexpensive flow cytometry-based diagnostics and in applications requiring the analysis of high particle concentrations.

Microgel particles capable of bulk-degradation have been synthesized from a solution of diacrylated triblock copolymer composed of poly(ethylene glycol) (PEG) and poly(lactic acid) (PLA) in a microfluidic device using stop flow lithography (SFL). It has been previously demonstrated that SFL can be used to fabricate particles with precise control over particle size and shape. Here we have fabricated hydrogel particles of varying size and shape and examined their mass-loss and swelling behavior histologically and mechanically. We report that these features in addition to the degradation behavior of the hydrogel particles may be tailored with SFL. By decreasing the applied UV dose during fabrication, hydrogel particles can be made to exhibit a distinct deviation from the classical erosion profiles of bulk-degrading hydrogels. At higher UV doses, a saturation in cross-linking density occurs and bulk-degrading behavior is observed. Finally, we synthesized multifunctional composite particles, providing unique features not found in homogeneous hydrogels.