A microfluidic system is demonstrated here to measure the kinetic changes of cell volume under various extracellular conditions, in order to determine cell membrane transport properties. The system is comprised of microchannels, a cell immobilization chamber, an inlet and an outlet, and is made of poly(dimethylsiloxane) (PDMS) using softlithographic method. During experiments, mouse dendritic cells (mDCs), mixed with media of known concentrations, are quickly injected to the inlet of such microfluidic device, flow through a microchannel, and are then immobilized by a sieving structure, where kinetic images of cell volume response are captured by a CCD camera lively. The fluid keeps flowing due to the continuous suction from the outlet by a programmable syringe pump. Two sets of experiments have been performed: the cells are mixed with (1) solutions prepared in different concentrations of non-permeating solutes, and (2) solutions containing a permeating cryoprotective agent (CPA) plus non-permeating solute, respectively. Based on the captured images, both cell inactive volumes (Vb), permeability coefficients of water (Lp) and of CPA (Ps) through cell membranes of mDCs at different temperatures (10°C, 22°C, and 34°C) can be determined by least-squared curve fittings, respectively. A quantitative evaluation conducted using ImageJ will be performed in order to validate the microfluidic perfusion system, as well as help us understand the dynamic concentration changes around those immobilized cells. The use of this microfluidic perfusion system enables us to: 1) confine cells in a monolayer channel to prevent image ambiguity, 2) perform cell counting, 3) statistically study cell osmotic response and determine cell membrane transport properties, and (4) lower manufacturing costs.
Noninvasive Acoustic Cell Trapping in a Microfluidic Perfusion System for Online Bioassays
