Development of a cost-effective torsional unit for rodent long bone assessment

Thorough mechanical testing of rodent bones requires an understanding of bone behavior in a variety of loading modes including tension, compression, bending and shear. While these tests are easily conducted with single axis mechanical testing machines, it may also be desirable to determine torsional properties of bone. Although higher-end materials testing machines will enable torsional and/or rotational testing, simpler, less expensive systems rarely offer these capabilities. In this work, we illustrate the development of a torsional system that uses a simple rack and pinion concept to deliver a rotary motion to bones given the linear motion of a testing machine. As the bone field becomes increasingly interdisciplinary, more biologists and non-test engineers need cost-effective mechanical testing capabilities and the torsional system described here has proven to be more than adequate for standard biomechanical testing requirements. Furthermore, given the small-scale size of rodent long bones, a series of potting/testing fixtures were developed that enabled preparation and handling of the specimens without incurring damage to the bone shafts. Once fabricated the system was used to destructively load mice humeri and femurs and quantify torsional properties.