A nanometre-scale resolution interference-based probe of interfacial phenomena between microscopic objects and surfaces

Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces. But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach. Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object’s contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus. The unique view-from-below perspective of reflection interference contrast microscopy also reveals previously unseen deformations and allows the first direct observation of femtolitre-scale capillary condensation dynamics underneath micron-sized particles. Our implementation of reflection interference contrast microscopy provides a generally applicable nanometre-scale resolution tool that can be potentially exploited to dynamically probe ensembles of objects near surfaces so that statistical/probabilistic behaviour can be realistically captured

Embedding Synthetic Microvascular Networks in Poly(Lactic Acid) Substrates with Rounded Cross-Sections for Cell Culture Applications

Synthetic microvascular networks are essential to enable in vitro studies of cell biology, biophysics, hemodynamics, and drug discovery, as well as in applications involving tissue engineering and artificial vasculature. But current limitations make it challenging to construct networks incorporating a hierarchy of microchannel diameters that possess cell-favored circular cross-sectional topographies. We report a new approach that overcomes these limitations by employing pressure-assisted expansion of biocompatible degradable poly(lactic acid) (PLA) substrates. This single-step process is straightforward and highly controllable, making it possible to simultaneously shape the interior topology of branched 3D and pseudo-3D microchannel networks across wide range of diameters. We further demonstrate in vitro culture of confluent endothelial cell monolayers in microchannel networks treated by this process, suggesting potential as a tool to help generate bio-mimicking vascular-like environments

BioMEMS and Electrophoresis in 2006: Review of the 23rd Annual Meeting of the American Electrophoresis Society

The 23rd Annual Meeting of the American Electrophoresis Society (AES) was held at the San Francisco Hilton in San Francisco, California on 12–17 November 2006. This year’s meeting featured a look toward the future, with an emphasis on theoretical and experimental advances in miniaturization of BioMEMS, electrokinetics, and proteomics technologies. A total of 13 sessions accommodating 71 presentations and 18 posters were held in conjunction with the Annual Meeting of the American Institute of Chemical Engineers (AIChE). This review and corresponding special issue of Biomicrofluidics provide a sampling of some of the exciting research presented at the conference

Vortex-assisted DNA delivery

Electroporation is one of the most widely used methods to deliver exogenous DNA payloads into cells, but a major limitation is that only a small fraction of the total membrane surface is permeabilized. Here we show how this barrier can be easily overcome by harnessing hydrodynamic effects associated with Dean flows that occur along curved paths. Under these conditions, cells are subjected to a combination of transverse vortex motion and rotation that enables the entire membrane surface to become uniformly permeabilized. Greatly improved transfection efficiencies are achievable with only a simple modification to the design of existing continuous flow electroporation systems

Enlargement and circularization of PLA microchannels by pressure-assisted expansion.

<p>(a) Microchannels with initially rectangular cross-sectional profiles are molded in PLA using a PDMS master. (b–d) Pressurized air is injected upon heating the PLA into the rubbery state (i.e., above the glass transition temperature and below the melting temperature) causing the interior air pressure force to exceed the wall resistance. The initially rectangular channels eventually attain circular cross-sections. (e–g) Corresponding images of cross-sectional profiles obtained at different times during the expansion process (<i>w₀</i> = 81 µm, <i>h₀</i> = 31 µm) (e) before expansion; (f) 80°C, 15 psi for 15 min; and (g) 80°C, 15 psi for 25 min (expansion ratio = 5; bars, 50 µm). (h) Comparison between experimental results (symbols) and model predictions (lines) capture the expansion of initially rectangular microchannels as a function of time under different processing conditions (<i>w₀</i> = <i>h₀</i> = 31 µm). Microchannel size is expressed in terms of the instantaneous width (<i>w</i>). (i) Circular cross-sectional profiles are obtained regardless of initial rectangular channel aspect ratio (<i>h₀</i>/<i>w₀</i>; 80°C at 15 psi). (j) Cross-sectional images of channels before and after expansion under the same conditions as (i) with initial aspect ratios of 2.23 (<i>w₀</i> = 16 µm, <i>h₀</i> = 35 µm), 1.00 (<i>w₀</i> = <i>h₀</i> = 31 µm), 0.38 (<i>w₀</i> = 81 µm, <i>h₀</i> = 31 µm), and 0.07 (<i>w₀</i> = 498 µm, <i>h₀</i> = 33 µm) (white bar, 100 µm; black bar, 1000 µm). All experiment data are mean ± sd of 3 independent experiments.</p

Seeding and culture of bovine aortic endothelial cells (BAECs) throughout PLA microchannel networks.

<p>(a) Confocal microscopy shows that the interior walls of a 200 µm diameter straight circularized microchannel can be uniformly seeded with endothelial cells that subsequently are confluently cultured in a monolayer lining the channel wall. (b) Fluorescent images show BAECs survive and maintain their morphology after 5 days in the straight circularized microchannel (bar, 50 µm). (c) BAECs seeded in four generations of branched microchannel network with diameters extending below 50 µm uniformly cover all channel walls and maintain viability after 3 days of culture (bar, 50 µm).</p