Arnold Chen

Reversible deactivation of higher-order posterior parietal areas. I. Alterations of receptive field characteristics in early stages of neocortical processing

Somatosensory processing in the anesthetized macaque monkey was examined by reversibly deactivating posterior parietal areas 5L and 7b and motor/premotor cortex (M1/PM) with microfluidic thermal regulators developed by our laboratories. We examined changes in receptive field size and configuration for neurons in areas 1 and 2 that occurred during and after cooling deactivation. Together the deactivated fields and areas 1 and 2 form part of a network for reaching and grasping in human and nonhuman primates. Cooling area 7b had a dramatic effect on receptive field size for neurons in areas 1 and 2, while cooling area 5 had moderate effects and cooling M1/PM had little effect. Specifically, cooling discrete locations in 7b resulted in expansions of the receptive fields for neurons in areas 1 and 2 that were greater in magnitude and occurred in a higher proportion of sites than similar changes evoked by cooling the other fields. At some sites, the neural receptive field returned to the precooling configuration within 5-22 min of rewarming, but at other sites changes in receptive fields persisted. These results indicate that there are profound top-down influences on sensory processing of early cortical areas in the somatosensory cortex.

Reconfigurable microfluidics combined with antibody microarrays for enhanced detection of T-cell secreted cytokines.

Cytokines are small proteins secreted by leukocytes in blood in response to infections, thus offering valuable diagnostic information. Given that the same cytokines may be produced by different leukocyte subsets in blood, it is beneficial to connect production of cytokines to specific cell types. In this paper, we describe integration of antibody (Ab) microarrays into a microfluidic device to enable enhanced cytokine detection. The Ab arrays contain spots specific to cell-surface antigens as well as anti-cytokine detection spots. Infusion of blood into a microfluidic device results in the capture of specific leukocytes (CD4 T-cells) and is followed by detection of secreted cytokines on the neighboring Ab spots using sandwich immunoassay. The enhancement of cytokine signal comes from leveraging the concept of reconfigurable microfluidics. A three layer polydimethylsiloxane microfluidic device is fabricated so as to contain six microchambers (1 mm × 1 mm × 30 μm) in the ceiling of the device. Once the T-cell capture is complete, the device is reconfigured by withdrawing liquid from the channel, causing the chambers to collapse onto Ab arrays and enclose cell/anti-cytokine spots within a 30 nl volume. In a set of proof-of-concept experiments, we demonstrate that ∼90% pure CD4 T-cells can be captured inside the device and that signals for three important T-cell secreted cytokines, tissue necrosis factor-alpha, interferon-gamma, and interleukin-2, may be enhanced by 2 to 3 folds through the use of reconfigurable microfluidics.

Three-dimensional fit-to-flow microfluidic assembly

Three-dimensional microfluidics holds great promise for large-scale integration of versatile, digitalized, and multitasking fluidic manipulations for biological and clinical applications. Successful translation of microfluidic toolsets to these purposes faces persistent technical challenges, such as reliable system-level packaging, device assembly and alignment, and world-to-chip interface. In this paper, we extended our previously established fit-to-flow (F2F) world-to-chip interconnection scheme to a complete system-level assembly strategy that addresses the three-dimensional microfluidic integration on demand. The modular F2F assembly consists of an interfacial chip, pluggable alignment modules, and multiple monolithic layers of microfluidic channels, through which convoluted three-dimensional microfluidic networks can be easily assembled and readily sealed with the capability of reconfigurable fluid flow. The monolithic laser-micromachining process simplifies and standardizes the fabrication of single-layer pluggable polymeric modules, which can be mass-produced as the renowned Lego(®) building blocks. In addition, interlocking features are implemented between the plug-and-play microfluidic chips and the complementary alignment modules through the F2F assembly, resulting in facile and secure alignment with average misalignment of 45 μm. Importantly, the 3D multilayer microfluidic assembly has a comparable sealing performance as the conventional single-layer devices, providing an average leakage pressure of 38.47 kPa. The modular reconfigurability of the system-level reversible packaging concept has been demonstrated by re-routing microfluidic flows through interchangeable modular microchannel layers.

Stereomask lithography for multi-protein patterning.

The advances of biologically-friendly micropatterning technologies have benefited many areas of biological and medical research, including quantitative biochemical assay, point-of-care devices, biosensing and regenerative medicine. Conventional micropatterning techniques, for example, photolithography and soft lithography, have seen encouraging adaptation to creating biological micropatterns in the last decades. However, they still have not completely addressed the major needs of constructing multi-object biological microarrays with single-cell resolution without requiring cleanroom access. In this chapter, we present a novel versatile biological lithography technique to achieve integrated multi-object patterning with high feature resolution and high adaptability to various biomaterials, referred to as stereomask lithography (SML). A novel three-dimensional stereomask has been developed for successive patterning of multiple objects. The stereomask consists of both patterned through holes, which layout new micropatterns and non-through recesses, which protect pre-existing features on the substrate. Furthermore, high-precision reversible alignment among multiple bio-objects is achieved by adopting a peg-in-hole design between the substrate and stereomasks. As demonstration, we have successfully used the SML technique to construct complex biological microenvironment with various bio-functional components at single-cell resolution.

Universal adhesive-free Fit-to-Flow microfluidic connections

World-to-chip (macro-to-micro) interface continues to be one of the most complicated, ineffective, and unreliable components in the development of emerging μTAS involving integrated microfluidic operations. In this paper, we present standardized adhesive-free microfluidic interfaces, referred to as Fit-to-Flow (F2F) connections, using two physical mechanisms to achieve hermetic seal performance (up to 336 kPa), high-density 2D tube-packaging (1 tube/mm2), self-aligned plug-in (10.7 µm), and applicability to broad fluidic chip platforms. A 3D microfluidic mixer and a 6-level chemical gradient generator have been devised to illustrate the applicability of the universal fluidic connections to classic microfluidic operations.

On-chip control of pneumatic-based bistable valve switch

Bistable valves are of particular interest due to its capability of remaining in open or closed states without energy consumption. This aspect is appealing for microfluidics transferring from benchside to bedside as input access and controls are limited. In this paper, we present pneumatic-based, bistable valve (BSV) switches for immediate on-chip fluid-flow manipulation without the requirement of external microcontroller circuitries. The applicability of the on-chip controller is demonstrated in a 4-to-1 microfluidic multiplexor. Furthermore, clinical relevance of on-chip BSV switches is displayed in point-of-care ABO blood-typing diagnostic chips.

Stereomask Lithography for multi-object bio-patterning

The advent of biological micro-patterning techniques has given new impetus to many areas of biological research, including quantitative biochemical analysis, biosensing, and regenerative medicine. Conventional micropatterning techniques (e.g. photolithography and soft lithography) although have seen encouraging adaptation to biological applications, still have not completely addressed the needs of constructing multi-object biological microarrays with single cell resolution without requiring cleanroom access. In this abstract, we present a novel versatile biological lithography technique to achieve integrated multi-object patterning with high resolution and high adaptability to various biomaterials, referred to as the Stereomask Lithography (SML). It is based on serial placement of multiple biological objects using a novel three dimensional shadow mask with protection for previously patterned materials and a peg-in-hole interlayer alignment scheme.