Extrusion freeformed integrated synthetic bone graft and fracture fixation system

Vaezi, Mohammad, Yang, Shoufeng, Black, Cameron, Gibbs, David and Oreffo, Richard O.C. (2014) Extrusion freeformed integrated synthetic bone graft and fracture fixation system. International Conference on Progress in Additive Manufacturing (Pro-AM 2014), Singapore, Singapore. 25 - 27 May 2014.

Abstract

Synthetic bone graft is commonly used in trauma and reconstructive surgery to facilitate anatomic restoration of bone fragments including joint surfaces. Migration of the synthetic or human derived bone graft material from the desired location is a frequently encountered clinical complication contributing to surgery failure. The purpose of this research work is to develop a 3D printed bone graft which integrates directly with a locking plate fracture fixation system, as such the graft is rigidly held and able to resist applied forces and thus not migrate. Furthermore the fabrication technique allows precise control of porosity which is known to be critical in cellular migration and resorption. Whilst additive manufacturing (AM) processes are well known for reproducing the shape of a biomaterial from, for example, CT data they are less well known for their ability to reproduce compositional and potentially microstructural design from a computer file. Extrusion freeforming was used in this project to make synthetic bone grafts with multi-scale porosity and fixation feature.

An extrusion-based three dimensional (3D) printer was designed and established which produces a graft, enabling direct integration with a fracture fixation/stabilisation system via a customised region in the synthetic bone graft. The developed 3D printer has proven highly reliable in the generation of latticed 3D structures and can process a wide range of biomaterials with reproducibility, flexibility at low cost. In this fabrication process, a continuous flow of materials in the form of biomaterial paste is dispensed sequentially using a 3D motion system incorporated with the extrusion nozzle to form a 3D complex object. The additive nature of the developed 3D printer ensures minimal waste of bio-material and provides a platform for mass production of biomedical lattice structures. The main feature and focus of the developed 3D bio-printer is the ability to generate porous bioactive 3D structures containing highly uniform interconnected pores with precise control of porosity and filament size. Optimal porosity and filament size have been identified through in-vitro investigation alongside positive results showing cell adhesion, proliferation and viability. An optimized 3D printed integrated bone graft was placed within a chick femoral defect and implanted subcutaneously in a mouse to evaluate efficiency of the proposed approach for bone fixation. Following 28 days implantation the mouse was euthanized and the device retrieved. Macro photographic and micro computed tomographic (µCT) analyses demonstrate integration between fixation system and excellent localisation of graft within the defect site with no migration

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Contributors

Author: Shoufeng Yang

Author: Richard O.C. Oreffo

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