Photonic and microfluidic strategies for bioanalysis applications

A problem presented at the UK MMSG Southampton 2007.

Presented by:
Dr Tracy Melvin (Optoelectronics Research Centre, University of Southampton)
Participants:
S Brooks, D Friedrich, M Gratton, M Jones, J King, T Melvin, J Oliver, R Repetto, SL Waters, T Witelski

Problem Description

Integrated microfluidic/optical devices provide an ideal platform for examining the response of mammalian cells to the environment i.e. to biochemical and mechanical stimuli. We are interested in designing and fabricating fluidic devices for controlled mixing and delivery of various solutions to cultured cells on the base of shallow wide channel structures; the cells are to be interrogated optically from below. Designing such a device is complicated by the need to create a well controlled environment for the study.

Questions to be addressed by the study group include

  1. How deformed are the cells in the channel due to the flow and how is the flow profile and mixing of fluids by transverse molecular diffusion influenced by the presence of the cells.
  2. What is the distribution of chemical species within any channel as it is taken-up by the cells.
  3. What distribution and patterns of cells should be put on the lower layer, what is the ideal shape of the channel and what flux of fluid should be put through it.

Study Group Report

We analysed the underlying equations for the micro mixer on the various length scales. In the bends and junctions we have to consider the full 3D Navier-Stokes equations because we cannot neglect inertia effects. This leads to secondary flow profiles in the bends which mix the two concentrations. Because the flow is reversible this advective mixing is undone in the next bend. To design an effective serpentine mixer we have to vary the bend configuration: change the curvature or channel shape. In the channels between the bends the flow is unidirectional. The residence time in this channels has to be long enough to smooth the high concentration gradients that result from the stiring in the bends.

In the interrogator region, the evaluation of diffusion shows that the suggested flow velocity of U = 10–5 ms−1 is a good choice. It is slow enough so that the diffusion time over the height of the channel is of the same size as the convection time over a single cell spot. On the other hand the flow speed still fast enough so that the diffusion across concentration lanes is negligible. A drawback of the choosen flow speed is the fact that divots created through the uptake over on cell spot cannot be compensated over the length of the interrogation region.

Download the full report

Follow-Up Activities

The following student projects have been inspired by this problem:

Fluid flow and analyte diffusion in microfluidic devices
Modelling Project, ECMI Modelling Workshop, August 2008.
Supervised by RJ Whittaker.