gms | German Medical Science

Objectives: The cure of critical-sizes bone defects is an huge challenge usually treated with autologous bone grafting. Especially, for long bone segmental defects > 5cm, the secured placement and retention of the autologous graft material is highly difficult while this is mandatory to ensure sufficient bone healing. Additive manufacturing (3D printing) for bone regeneration is one of the most promising applications for this technology as recently huge advantages have been made resulting in a new parametric design approach which is proposed to generate standard and patient specific implants by combining a fully resorbable autologous bone graft containment cage out of polycaprolactone/hydroxylapatite (PCL/HA) for the safe placement of graft material into the defect while this cage is capable to supply a certain primary stability to the bone in a static as well as in a dynamic setting. While this cage is already reducing the needed amount of graft material with its scaffold-like structure, after full resorption this area will probably also be replaced by healthy bone tissue resulting in superior stability.

Methods: Automated parametric computer-aided design (CAD) modeling approach is used to generate the CAD model of the cages followed by manufacturing out of PCL/HA using Fused Deposition Modeling (FDM) technique. The mechanical properties for axial compression were studied with respect to their interface to intramedullary nailing systems and dynamic compression plates for variations in length, porosity, fiber diameter, pattern on the surface, orientation of the fibers and the connection of the fibers between the external and internal surface.

Results and conclusion: Results shows that all the parameters are effective on the mechanical performance of the cages while the pattern on the surface bring fundamental changes on the compression stability. Figure 1 [Fig. 1] shows that the fatigue life of different cages, under huge axial stress, can be enhanced by changing the pattern on the surface and the diameter of the fibers. Furthermore, the results show that the cages are not only able to accept large biomechanical forces of more than 3000 N, but also, they can accept more than 10 mm axial shortening-deformation in a dynamic environment as a result of optimized design and manufacturing parameters.

Here, we present promising first-time data on the mechanical properties of a fully resorbable autologous bone graft containment cage while the data suggest optimal bio-mechanical properties for further in-vivo experiments. The cage-scaffold structure is taking loads in a controlled way which ensures that the contained graft will stay in place while also a certain primary stability is given to the segmental defect.