Designs
Design 1
The plan for Design 1 was to "sandwich" a biodegradable material in between two metal plates so that as the material degraded, the metal plates would get closer and closer over time. This would cause a decrease in the moment of inertia due to the decrease in the cross-sectional area of the fixation device, thus ultimately changing the stiffness of the device over time. However, this design was far too oversimplified and did not have a compressive mechanism. The overall mechanism was also found to be too thick and the difficulty of controlling the degredation rate of the biodegradable material was far too imprecise.
Design 2
Design 2 utilized the same "sandwich" technique as Design 1, except that instead of a degradable material, an electrically controlled elongation material was used to decrease the cross-sectional area of the implant. However, this design was also oversimplified and had similar issues as Design 1, such as the thickness and lack of a compressive mechanism. This new material also had the added possibility of illiciting an immune response from the body.
Design 3
Design 3 utilized a two plate system with uniformally spaced pillars of biodegradable material that would seperate the two plates. As the material degraded, microspings that connect the two plates would pull the outer plate closer to the inner plate over time, decreasing the cross-sectional area. However, this design turned out to be too thick, high cost, and unnecessarily complicated.
Design 4
Design 4 used only a one plate system with a Shape Memory Polymer (SMP) in between the plate and the bone. This material would be inductively heated during the healing process to alter its shape and change the stiffness during the healing prcoess. As the material was further researched it was deemed that microsprings would not be necessary for the impant. The change in material shape would pull the plate downward and decrease the cross-sectional area. The plate would be guided by partially threaded screws.
Pro/Engineer Model of Fixation Devcie on Humerus |
Exploded view of Pro/Engineer Model of Fixation Device |