Low Force Dynamic and Fatigue Testing of Orthopaedic Micro-Implants for Fracture Fixation

Orthopaedic micro-implants are used in Medicine and Dentistry to treat bone disease and fractures, and soft tissue injuries. It is crucial that the implants are robust and secure enough to maintain structural rigidity and alignment of bone or soft tissue during the healing process. During normal patient activity, implants can be subjected to high in vivo loading, which may result in catastrophic failure. Therefore, tests simulating loading conditions are critical to assess the expected performance over a specific period time or loading profile typically following ASTM, ISO, and FDA guidelines.

Cyclic fatigue tests have been successfully carried out on titanium finger micro-implants using our ElectroPuls™ E1000 and E3000 systems. We performed fatigue tests with a low-capacity Dynacell load cell mounted to the upper actuator with a small bolt and nut assembly used as the loading head. We used a metallice vice for the lower fixture.

We first performed the test in Digital Position Control to ensure stability. We then ran the tests in load control at 5, 10, 15 and 20Hz. We found that the control was very stable and peaks were well controlled with an accuracy of ±0.1N.

All of the testing was performed using the default loop control gains derived from the standard stiffness tuning. Using a combination of this tuning and Amplitude Control, the response was reasonable to achieve the amplitudes demanded and maintain the control stability.Within the ElectroPuls controller, it is possible to further adjust the control loop to improve turn-around and response. The optimization involves adjusting a single proportional term, Gain Factor, to add more loop gain.

In summary, the ElectroPuls dynamic systems achieve exceptional response and accuracy across a wide frequency range and are ideal for durability testing of implants. Using hardware features, such as inertia compensation from the Dynacell load cell, you can optimize the system response in or out of an environmental bath. These characteristics allow laboratories to investigate a comprehensive range of implant characteristics and performance.