Use of ionic polymer-metal composites (IPMCs) as a pressure transducer in the human spine

Currently, it is difficult to measure the pressure distribution and motion within the human spine, for both in vivo and in vitro situations. This study proposed that small thin strips of ionic polymer-metal composites (IPMC) can be used as pressure transducers for the quantification of pressure distributions within the spine. Endo-ionic motion within IPMC sensors produces an induced voltage across the thickness of these sensors when a normal or shear load is applied. A materials testing system (MTS) was used to apply consistent pure compressive loads of 200N and 350N across the surface of an IPMC 2x2cm strip. The output pressure response for the 200N load (73 psi) was 80mV in amplitude and for the 350N (127 psi) it was 108 mV. Due to their small size, IPMC sensors have the benefit of being able to fit within small gaps in the spine. These fluid-filled gaps (facet joints) range in thickness from 1-3mm, which is generally too small for typical transducers. The biocompatibility issue is also not of concern since the sensors themselves are biologically inert and, if necessary, can be coated with various flexible biocompatible materials.