Development of polymer wicks for the fabrication of bio-medical sensors

Polymer based wicking structures were fabricated by sintering powders of polycarbonate (PC), ultra-high molecular weight polyethylene and polyamide 12, aiming at selecting a suitable material for an innovative electroencephalography (EEG) bio-electrode. Preliminary experiments showed that PC based wicks displayed the best mechanical properties, therefore more detailed studies were carried out with PC to evaluate the influence of powder granulometry and processing parameters (pressure, temperature and time) on the mechanical properties, porosity, mean pore radius and permeability of the wicks. It was concluded that the mechanical properties are significantly enhanced by increasing the processing time and pressure, although at the expense of a significant decrease of porosity and mean pore diameter (and thus permeability), particularly for the highest applied pressures (74kPa). However, a good compromise between porosity/permeability and mechanical properties could be obtained by sintering PC powders of particle sizes below 500μm at 165°C for 5min, upon an applied pressure of 56kPa. Moreover, PC proved to be chemically stable in contact with an EEG common used disinfectant. Thus, wicking structures with appropriate properties for the fabrication of reusable bio-electrodes could be fabricated from the sintering of PC powders.

The authors gratefully acknowledge the Fundacão para a Ciência e Tecnologia, FCT (COMPETE Program) under the project FCOMP-01-0124 – FEDER-010190 (Ref. PTDC/SAU-ENB/116850/2010), FEDER, via FCT, under PEst-C/CTM/LA0025/2013 and PEst-C/EME/UI0285/2013 and MatePro Project, NORTE-07-0124-FEDER000039, supported by the Programa Operacional Regional do Norte (ON.2). C.F. acknowledges discussions with M. Oliveira and the revision of the document performed by P. Fiedler