Advancing mechanical testing of biological tissues and hydrogels: A buoy-based approach

Quantifying the material properties of tissues and hydrogels aids in the development of biomedical applications through better understanding of the mechanics and mechanobiological principles at play. This study introduces a mechanical testing platform designed to address challenges in measuring mm-scale tissue and hydrogel material properties. Using a floating buoy design, the platform enables horizontal submerged tensile testing with non-submersible load cells. Buoy drag testing without a sample attached resulted in signal noise (mean ± standard deviation) of -1.6E-4 ± 2.8E-2 mN for stationary recording and 1.3E-2 ± 6.7E-2 mN for maximum buoy displacement speed (1000 µm/s), suggesting the magnitude of drag forces from buoy movement are negligible in comparison to the minimum resolution of force measurement. Validation testing with latex orthodontic bands showed a ∼ 28 × reduction in signal noise with the buoy approach compared to a previously used approach, and similar force displacement recordings using the buoy approach with 2 separate hardware systems. Simultaneous imaging enabled geometrical and microstructural analysis of the sample. Murine bladder tissue was mechanically tested using two different hardware systems and testing protocols. The platform was able to accurately capture the nonlinear stress-stretch response, alongside expected strain-softening and preconditioning behavior. Stress-relaxation testing yielded results consistent with expected microstructural and viscoelastic responses of mouse bladder tissue. The versatility of the platform underscores the potential for it to integrate with various force measurement and actuator-based systems. In conclusion, this platform offers a new avenue for accurate measurement of tissue and hydrogel mechanics, facilitating mm-scale soft material research.