(6af) Elastohydrodynamics and Soft Matter Mechanics to Understand Biological Adhesion, Human Touch, and Optics-Free Cytometry

Research Experience: My experience and abilities lie at the interface between the mechanics of soft matter and applications in cell biology and artificial touch. In particular, I have exploited elastohydrodynamic phenomena—effects arising from the coupling of soft structures and fluid flow—to understand various observations in nature. My work has elucidated how tree frogs stick to surfaces while submerged, how fingerprints influence tactile sensation, and how the sidewalls of microfluidic channels deform during transit of biological analytes as a means of mechanical biosensing.

My graduate work with Prof. Joelle Frechette at Johns Hopkins University found how drainage channels in the toe pads of tree frogs reduced hydrodynamic resistance and promoted contact with flooded surfaces. Drainage channels, however, also reduce the adhesion of tree frogs once in contact. The improvements in making contact offset the reduced adhesion. During my postdoc in Prof. Darren Lipomi’s group at UC San Diego, I continuously measured particles and fluid velocity in a microfluidic channel by monitoring the fluid-induced (elastohydrodynamic) deformation in the sidewalls using only a voltage signal. This new microfluidic sensor circumvents the need for costly optical measurements. This was done with an ultra-sensitive palladium nanoislands on graphene strain sensor embedded in the elastic sidewalls of the microfluidic channel. I also applied soft matter mechanics to the sense of touch and found that human subjects can be sensitive to monolayer differences in surfaces, due to cues from friction, and that human subjects determine how soft a surface is by using indentation depth and contact area. We are using these findings to design devices that can generate tactile sensations. For example, we have found that deformable, patterned interfaces amplify differences in friction, which would help make two surfaces feel more different.

Selected Publications:

Dhong, C., Lipomi D., et al. “Role of fingerprint-inspired relief structures in elastomeric slabs for detecting frictional differences arising from surface monolayers.” (Submitted)

Dhong, C., Lipomi D., et al. “Optics-free, non-contact measurements of fluids, bubbles and particles in microchannels using metallic nanoislands on graphene.” (Submitted)

Carpenter, CW.^*, Dhong, C.^*, Ramachandran, V.S., Lipomi, D., et al., “Human ability to discriminate surface chemistry by touch.” Materials Horizon (2018) *Authors contributed equally to the work

Dhong, C., Frechette, J. “Peeling flexible beams in viscous fluids: Rigidity and extensional compliance.” Journal of Applied Physics (2017)

Wang, Y., Dhong, C., Frechette, J., “Out-of-contact elastohydrodynamic deformation due to lubrication forces.” Physical Review Letters (2015)

Dhong, C., Frechette, J. “Coupled effects of applied load and surface structure on the viscous forces during peeling.” Soft Matter (2015)

Future Directions: My future research will create devices that are designed using soft matter mechanics with functional materials. This enables devices with unique functionalities and allows me to probe fundamental phenomenon in soft matter and biology. For example, it is known that circulating tumor cells are three times softer than regular healthy cells and there are no current diagnostic methods that take advantage of this fact. I propose identifying circulating tumor cells without the use of antibodies or prohibitively expensive equipment by measuring the cell stiffness. Cell stiffness as a biomarker is not limited to cancer; malarial cells are also mechanically distinct from their healthy counterparts. Using the nanoisland-on-graphene strain measurements of elastohydrodynamic phenomenon, the continuous, high-throughput measurements of cell stiffness can transform medical diagnostics. Detecting diseased cells is just one aspect, fundamental biomechanical studies will investigate drug efficacy have on the endothelial tissue by monitoring the viscoelastic response of arteries in real time.

In addition, current technology has not effectively addressed the sense of touch. State-of-the-art haptic devices can still only generate a simple vibration. I look forward to combining soft matter phenomenon with functional materials to create devices that generate haptic sensations that go beyond this limitation.

Teaching Interests:

I would enjoy teaching any core chemical engineering course, especially transport. At the graduate level, I would enjoy teaching any transport phenomenon course, which would incorporate numerical methods. I would also like to teach electives in continuum mechanics topics such as adhesion, contact and fracture mechanics. I have taught fluid/transport and helped to develop and taught a master’s level lab course at Johns Hopkins University. At UC San Diego, I have also guest lectured two classes in a polymeric materials course.