Considerations for Biotribometers: Cells, Gels, and Tissues

Tribological evaluation of biological materials, such as cells and tissues, present both opportunities and challenges to experimentalists. When working with living materials, maintaining homeostasis during testing in vitro or in vivo often requires appropriate control of the environment, selection of the testing time and duration, applied loads, and shear stresses. This manuscript provides much of the background and design information used in the development of a microtribometer that has been modified to perform biotribology measurements in vitro. The focus of this manuscript is on mammalian cells in monolayer, and a series of order-of-magnitude calculations are used to inform future instrument designs and considerations, including: sliding speed ranges from 10 nm/s to 100 mm/s, contact pressures less than 6 kPa, temperature ~ 37 °C, and contact areas on the order of 1,000’s of µm². The design and development of these biotribology instruments enable in situ fluorescence microscopy and allow for statistically significant gene expression analyses such as quantitative reverse-transcription polymerase chain-reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA).