Our testing results are from testing our first generation prototype, Fluffy.
Finite Element Analysis
Finite element analysis (FEA) is an excellent computer-based tool to simulate the operation of our device and observe a millisecond-by-millisecond record of the forces encountered in our device. Using a simplified model, we attached the Osteonexus to a piece of bone with a fracture site. This fracture site had half of the strength of the original bone, which has been shown to be the strength of the callus formed during the first four weeks of healing. We loaded them under 1 mm active dynamization and compared that to static fixation, where the weight of a 70 kg (155 lb) man was loaded on a statically fixed device.
Our results show that the Osteonexus Active Dynamizer generates therapeutic stresses at the fracture site for improved healing response. The stresses, noted at 1.3 MPa, have been correlated to osteocyte differentiation endochondral ossification. In comparison, the statically fixed device shows significantly less stress at the fracture site.
Power Feedback Testing
The design of the Osteonexus allows for us to monitor the progress of a fracture as it heals. The idea is that as a fracture heals, the force required to operate the Osteonexus and induce active dynamization increases. Thus, the power required to operate the motor similarly increases. We monitored power drain and compared it to the strength of the material being compressed.
To test the power drain, we used springs (since we can't test in vivo) and placed them between the two halves of Fluffy. These springs had different spring constants, and we characterized these springs using an Instron 5565 in our facilities. We developed methods to record power consumption via our own National Instruments LabView VI and ELVIS data acquisition board.
Our results show that as the spring constant increases, the power consumption of the motor increases in a linear relationship. We are working on developing a precise model to correlate how hard the Osteonexus is working to the strength of the fracture site. This model will allow the flight physician to monitor progress and provide realtime feedback to a patient regarding the fracture healing process.