Microelectrical impedance tomography for biophysical characterization of thin film biomaterials

We present a new method for measuring the electrical resistivities of a stratified sample of thin biomaterials or tissue layers. The presented technique makes use of impedance measurements between 11 pairs of electrodes separated by varying distances. The electrodes are made of gold stripes, 20-500 /spl mu/m wide and 8 mm long. We used hydrogels of poly-hydroxyethyl methacrylate (pHEMA) as a model material for our measurements. By changing the concentration of cross-linker we were able to tune the resistivity of the hydrogel between 1,000 /spl Omega/m and 17,000 /spl Omega/m. Using these hydrogels we were able to detect a change in resistivity of a 120 /spl mu/m layer lying 250 /spl mu/m into the sample.