Thickness measurement of soft tissue biomaterials: A comparison of five methods

Thickness measurement in soft connective tissues is a continuing problem due to the apparent compression of the tissue by micrometer-type gauges. We have compared five methods for the measurement of thickness: (1) a Mitutoyo non-rotating thickness gauge; (2) a custom-built, instrumented thickness gauge which was strain-gauged to measure contact force; (3) a commercial Hall effect probe (Panametrics Magna-Mike); (4) a custom-built electrical resistance probe; and (5) measurement of fresh frozen histological sections under polarized light. Using bovine pericardium as a test material, all the methods examined were adequate to assess sample-to-sample and location-to-location differences in thickness. The resistance gauge gave significantly greater thicknesses than did the other methods, with little or no compression; indeed, extrapolation to zero load of thickness readings from the instrumented gauge yielded identical thickness. Thicknesses measured by frozen sections were indistinguishable from those measured with the non-rotating gauge, the instrumented gauge under 0.5-1.2 g compressive load, or the Hall effect probe. With the correct technique, the simple and inexpensive non-rotating gauge remains a pragmatic choice for thickness measurement in planar soft tissue.