Dongshin Kim

Selective and tunable gradient device for cell culture and chemotaxis study

This article describes a microfluidic device for cell culture and chemotaxis studies under various temporal and spatial concentration gradients of the medium or chemoattractant. Vertical membranes formed using in situ fabrication are employed to avoid fluid flow inside the cell observation chamber. Thus, the medium and chemoattractants are primarily provided by diffusion, maintaining cell-cell communication via secreted factors. Neutrophils were used to demonstrate the capability of the device for chemotaxis research. Experiments exhibited successful migration up a concentration gradient of interleukin 8.

Hydrogel-based reconfigurable components for microfluidic devices

In situ liquid-phase photopolymerization (LP(3)) has been applied to the field of microfluidics to create components within integrated systems. As an extension of LP(3) technology, we present reconfigurable components that utilize the swelling of hydrogels. These components can be conveniently used to enhance microfluidic functions and applications. In order to utilize the swelling characteristic of hydrogels to the fullest, we demonstrate strategies to increase the swelling performance temporally and spatially. To this end, two successful applications using the reconfigurable components were tested: (1) active walls to block or divert flow at different steps in the fabrication or assay process, and (2) delivery pistons to move objects to specific locations within the microchannels after device fabrication.

Development of a Tongue-Operated Switch Array as an Alternative Input Device

This article presents a tongue-operated switch array (TOSA) that provides not only an alternate input for a computer or operative system, but also an approach for silent and hands-free communication among humans or between human and machine. A TOSA has been designed and fabricated using printed circuit board technology and a membrane-switching mechanism and is integrated with a dental palate mold made from a silicone impression material. The TOSA has 5 switches (4 switches are laid out in cardinal directions and a fifth switch is located in the center). Human participant experiments have been conducted to evaluate and improve device performance. The characteristics of tactile sensation and mobility of the tongue are used to quantify the performance and optimize the geometric design of the TOSA. The results from controlled studies using repeated measures with 4 participants revealed a maximum average accuracy of 91% with SD = 5 in a switch depression task and a maximum repetition rate of 2.47 depressions/sec (SD = .21). These results indicate that operation on all switches is highly accurate and fast enough for use as an alternate input device.

Geometric optimization of a tongue-operated switch array

An oral tactile interface provides an approach for silent and hands-free communication between humans or between human and machine. An efficient tongue-operated switch array (TOSA), which provides an alternate input or manipulating method for a computer or operative system, is described. A TOSA has been designed and fabricated using printed circuit board technology and a membrane-switching mechanism, and is integrated with a dental palate mold made from a silicone impression material. The TOSA has four switches laid out in cardinal directions with a fifth switch in the center. Human subject experiments have been conducted to evaluate device performance. The characteristics of tactile sensation and mobility of the tongue are used to quantify the performance and optimize the geometric design of the TOSA. Results indicate that operation on all switches are highly accurate and fast enough for use as an alternative input method.

A Sensing Method based on Elastic Instabilities of Swelllng Hydrogels

We present a biologically inspired sensing method which can be used to detect toxins or other chemical compounds. We engineer our hydrogels in such a way that an elastic instability is triggered by a designated stimulus. Two different bi-polymer strips are fixed together. When swelling is induced, the differential response of the two gels forming the composite strip causes the strip to bend. If the bending is constrained, an explosive elastic instability can occur if either the constraint is removed or the stored elastic energy is enough to induce fracture. A judicious choice of materials (e.g., degradable adhesive materials specific to certain enzymes or chemicals) and geometric constraints allow for the tuning of the instability. The rapid geometric changes associated with the elastic instability can be easily observed