· New concepts in fluidics and cellular mechanics for

controlled microinjection (2008-2010)

Sponsor: NSF

Collaborator: Prof. Nejat Olgac

Student: RA position is filled

· Experimental and theoretical analysis of bacterial transport

phenomena in microbial fuel cell (2008)

Sponsor: Center for Environmental Science and Engineering, U. of Connecticut

Collaborator: Prof. Baikun Li

Students: Bin Xie, Pilar Vivar

· Quantitative analysis of molecular transport and population kinetics

of stem cell cultivation in a microfluidic system (2007-2009)

Sponsor: Connecticut Department of Public Health

Collaborators: Prof. Joanne Conover, Prof. Xudong Yao

Student: Max M. Villa

· Self diffusion of isolated and pair-interacting particles in nonadsorbing

polymer solutions (2007)

Sponsor: University of Connecticut Research Foundation

Collaborator: Dr. Remco Tuinier

Student: Bin Xie

Self diffusion plays a key role in biological functions because many biochemical reactions are regulated by the formation of activated protein complexes. For transport-limited cases, the reaction rate is often determined by the random motion, and thus the self diffusivity, of the participating proteins, and is reflected on the motility of a single protein and protein-protein interactions. This project is important for the fundamental understanding of the crowding effect on self diffusion of biomolecules or colloids in a physiological microenvironments such as biological cells or tissues, and would facilitate the development of medical diagnostic and therapeutic methods based on molecular probing techniques.

As the first step, we provided theoretical estimation of the self-similar behavior of particle retardation in dilute and semi-dilute polymer solutions. The fluid flow, with velocity vectors and streamlines shown on the left, is induced by a translating particle in a polymer solution with nonuniform polymer density and fluid viscosity. The color contours represent the total normal stress field. The exponential scaling laws shown in the middle are established for the reduced tracer diffusivity for the translation and rotation motions in semi-dilute cases. R is known as the retardation factor, determining an apparent transport property such as diffusivity or viscosity of polymer solutions compared with the pure solvent. The stretched exponential scaling factor ω measures the significance of the particle size a relative to the characteristic depletion thickness δ, and the parameter x measures the effect of the bulk polymer concentration c_b and the intrinsic viscosity [η]. The images shown on the right are calibration experiments using fluorescent recover after photobleaching (FRAP) method.

Relevant Publications:

Tuinier, R. and Fan, T.-H., Scaling of Nanoparticle Retardation in Semi-dilute Polymer Solutions, Soft Matter, 4, 254-257 (2008).

Fan, T.-H. and Tuinier, R., Asymptotic Analysis of Tracer Diffusivity in Nonadsorbing Polymer Solutions, Phys. Rev. E, 76, 051405 (2007).

Fan, T.-H., Dhont, J.K.G., and Tuinier, R., Motion of a Sphere Through a Polymer Solution, Phys. Rev. E, 75, 011803 (2007).

Tuinier, R., Dhont, J.K.G., and Fan, T.-H., How Depletion Affects Sphere Motion Through Solutions Containing Macromolecules, Europhys. Lett., 75, 929-935 (2006).