Contact-free determination of material characteristics using a newly developed pressure-operated strain-applying...

Experimental mechanostimulation of biologic samples serves to understand fundamental processes in mechanobiology. Unfortunately, present techniques do not allow contact-free investigation of material characteristics. We developed a mechanostimulator that functions under the assumption that the counterforce generated by a biologic sample placed on a carrier membrane (test-on-carrier) is extractable from the total signal. As material characteristics of biologic samples are poorly defined, we substituted them by polyurethane and latex membranes. Based on the knowledge of the previously measured carrier membrane's compliance, we calculated the test membrane's compliance from the pressure-volume relationship inside the bioreactor. We hypothesized that knowing the carrier membranes' compliance allows calculation of the sample's compliance. Compliances of latex membranes were larger than those of polyurethane ones (p < 0.05). The average differences between calculated and directly determined compliances were 3.9% +/- 2.7% and 6.7% +/- 4.8% (mean +/- SD) under static and dynamic mechanostimulation, respectively (p > 0.05). The variability of compliance values was several fold larger (p < 0.01) for latex-on-polyurethane compared to polyurethane-on-latex combinations. There was high correlation between Young's modulus as determined from static compliance estimation and by uniaxial stretching in a tension-testing machine (r(2) = 0.987, p < 0.001). In conclusion, our mechanostimulator allowed reliable contact-free determination of material characteristics and may thus be suitable for contact-free assessment of biologic samples. The compliance of the carrier membrane should be at least two times larger than the compliance of the tested material.