Design, construction and validation of a computer controlled system for functional loading of soft tissue

Osteoarthritis is a chronic degenerative disease affecting body joints. Abnormal mechanical loading could be an initiating factor of cartilage damage, by influencing chondrocytes activity. To date, devices performing mechanical studies of viable tissues are mostly uniaxial. In this work, we developed and validated a multi-axial device for static and dynamic mechanical testing of viable soft tissues. The system, named RPETS, is composed of a motor driven indenter, moving vertically and horizontally along the bottom of a tank containing tissue samples and it can apply combined compression, sliding, and rolling on viable samples. Validation studies were performed with standard rubber and bovine nasal cartilage tissue. Static tests demonstrated that the system is comparable to existing uniaxial devices, with a maximum force control error smaller than 0.5 N and a positioning resolution of 5 μm. Dynamic tests performed with different motion profiles showed that the system can exert a load of 100 N with a maximum velocity of 100 mm/s maintaining the force control error within 10% of the desired value. Sinusoidal motion frequency can vary between 0.05 and 0.5 Hz. In practical tests, viability staining of dynamically loaded cartilage slices showed extents of cell death to depend on the indenter velocity.