Sub-100 nm Nanoparticle Upconcentration in Flow by Dielectrophoretic Forces.

This paper presents a novel microfluidic chip for upconcentration of sub-100 nm nanoparticles in a flow using electrical forces generated by a DC or AC field. Two electrode designs were optimized using COMSOL Multiphysics and tested using particles with sizes as low as 47 nm. We show how inclined electrodes with a zig-zag three-tooth configuration in a channel of 20 µm width are the ones generating the highest gradient and therefore the largest force. The design, based on AC dielectrophoresis, was shown to upconcentrate sub-100 nm particles by a factor of 11 using a flow rate of 2-25 µL/h. We present theoretical and experimental results and discuss how the chip design can easily be massively parallelized in order to increase throughput by a factor of at least 1250.

Hydrosilane-Modified Poly(2-Hydroxyethyl Methacrylate) Brush as a Nanoadhesive for Efficient Silicone Bonding.

Leaching of chemicals from adhesion promoters is, in particular, problematic for the food, water, pharmaceutical, and MedTech industries where any chemical contamination is unacceptable. A solution to this issue is to employ covalently attached nanoscale polymer brushes as adhesive layers for plastics. One of the industrially most relevant adhesion targets in that respect is poly(dimethylsiloxane) (PDMS), being used for many high-end applications such as catheters and breast implants. In this work, we have synthesized a novel surface-immobilized poly(2-hydroxyethyl methacrylate)-based brush adhesive containing reactive hydrosilane groups that can bond directly to PDMS. Two different medical grades of addition-cured PDMS were molded on top of titanium substrates already coated with the polymer brush. Titanium plates were used for the chemical analysis, and titanium rods were used for adhesion testing. Adhesion testing revealed a high adhesive force, in which cohesive failure was observed in the bulk PDMS. The necessity of the hydrosilane group in the polymer brush adhesive layer was demonstrated in comparative studies using similar brushes lacking this functionality.

Correction to "Hydrosilane Modified Poly(2-Hydroxyethyl Methacrylate) Brush as a Nanoadhesive for Efficient Silicone Bonding".

[This corrects the article DOI: 10.1021/acsomega.9b01282.].

Confinement dependent chemotaxis in two-photon polymerized linear migration constructs with highly definable concentration gradients.

Dendritic cell chemotaxis is known to follow chemoattractant concentration gradients through tissue of heterogeneous pore sizes, but the dependence of migration velocity on pore size and gradient steepness is not fully understood. We enabled chemotaxis studies for at least 42 hours at confinements relevant to tissue models by two-photon polymerization of linear channel constructs with cross-sections from 10 × 10 µm(2) to 20 × 20 µm(2) inside commercially available chemotaxis analysis chips. Faster directed migration was observed with decreasing channel dimensions despite substantial cell deformation in the narrower channels. Finite element modeling of a cell either partly or fully obstructing chemokine diffusion in the narrow channels revealed strong local accentuation of the chemokine concentration gradients. The modeled concentration differences across a cell correlated well with the observed velocity dependence on channel cross-section. However, added effects due to spatial confinement could not be excluded. The design freedom offered by two-photon polymerization was exploited to minimize the accentuated concentration gradients in cell-blocked channels by introducing "venting slits" to the surrounding medium at a length scale too small (≤500 nm) for the cells to explore, thereby decoupling effects of concentration gradients and spatial confinement. Studies in slitted 10 × 10 µm(2) channels showed significantly reduced migration speeds indistinguishable from speeds observed in unslitted 20 × 20 µm(2) channel. This result agrees with model predictions of very small concentration gradient variations in slitted channels, thus indicating a strong influence of the concentration gradient steepness, not the channel size, on the directed migration velocity.

In-chip fabrication of free-form 3D constructs for directed cell migration analysis.

Free-form constructs with three-dimensional (3D) microporosity were fabricated by two-photon polymerization inside the closed microchannel of an injection-molded, commercially available polymer chip for analysis of directed cell migration. Acrylate constructs were produced as woodpile topologies with a range of pore sizes from 5 × 5 µm to 15 × 15 µm and prefilled with fibrillar collagen. Dendritic cells seeded into the polymer chip in a concentration gradient of the chemoattractant CCL21 efficiently negotiated the microporous maze structure for pore sizes of 8 × 8 µm or larger. The cells migrating through smaller pore sizes made significantly more turns than those through larger pores. The introduction of additional defined barriers in the microporous structure resulted in dendritic cells making more turns while still being able to follow the chemoattractant concentration gradient.

Fabrication and characterization of 3D micro- and nanoelectrodes for neuron recordings.

In this paper we discuss the fabrication and characterization of three dimensional (3D) micro- and nanoelectrodes with the goal of using them for extra- and intracellular studies. Two different types of electrodes will be described: high aspect ratio microelectrodes for studying the communication between cells and ultimately for brain slice recordings and small nanoelectrodes for highly localized measurements and ultimately for intracellular studies. Electrical and electrochemical characterization of these electrodes as well as the results of PC12 cell differentiation on chip will be presented and discussed.