Use of sandwich structures in biomedical applications: an innovative design for external ring fixators

Sandwich structures are known for their excellent strength-to-weight ratio and are being increasingly used in the automotive, aerospace, marine, and construction sectors. These structures may also offer promising designs for other fields such as biomedical fixation devices, in which the combination of lightness and stiffness is of paramount importance. This study investigated the potential of fabricating orthopedic external ring fixators from sandwich panels to develop innovative designs and broaden the scope of sandwich-structure applications. Semicircular and circular rings were fabricated from sandwich panels composed of carbon fiber composite face sheets and a polyvinyl chloride (PVC) foam core. It is evident from the available literature that epoxy/carbon fiber-reinforced composite and PVC materials with appropriate biocompatibility are used in a large number of medical devices. Layered carbon fiber composites and aluminum rings were also tested to provide a point of comparison. The mechanical results demonstrated that the sandwich rings exhibited a load-carrying capacity comparable to that of aluminum rings typically utilized in surgical procedures while exhibiting a weight reduction of approximately 60%. They provide approximately four times the mechanical advantage for specific stiffness and strength. They weigh approximately half as much as layered composite rings and are more cost-effective owing to the reduced use of carbon fibers. Furthermore, the innovative sandwich design exhibited significantly superior radiolucency compared to other rings, thus reducing the risk of confusion between the fixator and bone during stabilization and surgical operations. In summary, the sandwich rings exhibited notable improvements in load capacity, lightness, mechanical advantage, radiolucency, and cost. The proposed design has the potential to expand the applications of sandwich structures considerably, offering a cost-effective and commercially viable solution for biomedical fixators.