Optimized hybrid dielectrophoretic microchip for separation of bioparticles.

Point-of-care diagnostics requires a smart separation of particles and/or cells. In this work, the multiorifice fluid fractionation as a passive method and dielectrophoresis-based actuator as an active tool are combined to offer a new device for size-based particle separation. The main objective of the combination of these two well-established techniques is to improve the performance of the multiorifice fluid fractionation by taking advantage of dielectrophoresis-based actuator for separating particles. Initially, by using numerical simulations, the effect of using dielectrophoresis-based actuator in multiorifice fluid fractionation on the separation of particles was investigated, and the size of the device was optimized by 25% compared to a device without dielectrophoresis-based actuator. Also, adding dielectrophoresis-based actuator to multiorifice fluid fractionation can extend the range of flow rates needed for separation. In the absence of dielectrophoresis-based actuator, the separation took place only when the flow rate is 100 µL/min, in the presence of dielectrophoresis-based actuator (20 Vp-p), the separation happened in flow rates ranging from 70 to 120 µL/min.

Inkjet Printing of Curing Agent on Thin PDMS for Local Tailoring of Mechanical Properties.

Rapid prototyping of thin, stretchable substrates with engineered stiffness gradients at desired locations has potential impact in the robustness of skin-wearable electronics, as the gradients can inhibit cracking of interconnect and delamination of embedded electronic chips. Drop-on-demand inkjetting of thinned polydimethylsiloxane (PDMS) curing agent onto a spin-cast 80 µm-thick 20:1 (base: curing agent) PDMS substrate sets the elastic modulus of the subsequently cured film with sub-millimeter accuracy. The inkjet process creates digitally defined stiffness gradient spans as small as 100 µm for single droplets. Varying the drop density results in differences in elastic modulus of up to 80%. In jetting tests of curing agent into pure base PDMS, a continuous droplet spacing of 100 µm results in smooth lines with total widths of 1 mm and a curing agent gradient span of ≈300 µm. Release of freeform mesh elastomer microstructures by removing the uncured base after selective jetting of curing agent into pure base PDMS results in structural line width resolution down to 500 µm.

Material Gradients in Stretchable Substrates toward Integrated Electronic Functionality.

The approach toward a stretchable electronic substrate employs multiple soft polymer layers patterned around silicon chips, which act as surrogates for conventional electronics chips, to create a controllable stiffness gradient. Adding just one intermediate polymer layer results in a six-fold increase in the strain failure threshold enabling the substrate to be stretched to over twice its length before delamination occurs.