Manufacturing Tailored Medical Implants with Evolving Stiffness

Millions of bone fractures occur worldwide of which a significant number are treated operatively. Despite advancements in the fields of biomechanics and production technology, the plates and screws used for operative fixation have barely changed since the 1960s. Using these devices, surgeons unfortunately tend to create overly stiff fixations that can lead to impaired healing. Additionally, although patients have different fracture morphologies, perform different activities of daily living, and have different muscle capacities, they are all treated with the same generic plates with fixed stiffness. Ideally, plates are adapted to patient-specific needs throughout the healing process. Stiffness-tailored bioresorbable plates and screws can be used to overcome the disadvantages of current bone plates. In the Flexible Sheet Metal Working group of the Mechanical Engineering Department of KU Leuven, processes and procedures have been developed to manufacture thin shell implants, using Incremental Sheet Forming (ISF). The implants are tailored to and optimized for a good geometric fit for individual patients. In this Ph.D., the ultimate goal is to manufacture a biocompatible and biodegradable implant that guarantees the required stiffness to ensure fracture healing. Production of biomechanically optimized designs using ISF with relevant materials and variable part thicknesses is the main manufacturing objective in optimizing implant characteristics. In addition, combining ISF with Additive Manufacturing (AM) will be investigated to influence the stiffness of such implants as a function of time. Using the required stiffness in space and time as an input, combinations of relevant materials and variable part thicknesses according to the provided biomechanically optimized designs will be studied. Monitoring the initial and time-dependent stiffness through mechanical loading and analysing resorption rates will allow to validate the different manufacturing methods and implant designs. This opens the potential to identify suitable control variables required to tailor resorption rates for the envisaged implants.