Piezoresistive sensors for force mapping of hip-prostheses

Abstract

The success of artificial prosthetic replacements depends on the fixation of the artificial prosthetic component after being implanted in the thighbone. This work shows a smart prosthesis based on highly sensitive silicon thin-film piezoresistive sensors attached to a hip prosthesis. The performance of the sensors for this application is studied and compared to commercial strain gauge sensors. Mechanical stress-strain experiments were performed in compressive mode, during 10,000 cycles and data was acquired at mechanical vibration frequencies of 0.5 Hz, 1 Hz and 5 Hz, and sent to a computer by means of a wireless link. The results show that there is a decrease in sensitivity of the thin-film silicon piezoresistive (n-type nanocrystalline Si) sensors when they are attached to the prosthesis, however this decrease does not compromise its monitoring performance. The sensitivity, compared to that of commercial strain gauges, is much larger due to their higher gauge factor (-23.5), when compared to the gage factor of commercial sensors (2).This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011 and by projects NANO/NMed-SD/0156/2007 and PTDC/CTM-NAN/112574/2009. The authors also thank support from the COST Action MP1003, 2010 ‘European Scientific Network for Artificial Muscles’. VS, VC and MSM thank the FCT for the SFRH/BPD/63148/2009, SFRH/BD/48708/2008 and SFRH/BD/60713/2009 grants, respectively. CR thanks the IINL for a financial support via a PhD