Abstract
3D printing can be used for the regeneration of complex tissues with intricate 3D microarchitecture. Trabecular bone is a complex and porous structure with a high degree of anisotropy. Changes in bone microarchitecture are associated with pathologies such as osteoporosis [1]. The objective of this study is to determine the viability of using 3D printing to replicate trabecular bone structures with a good control over the microarchitecture and mechanical properties.
Cylindrical samples of bovine trabecular bone were used in this study. Micro-computed tomography (microCT) was carried out and an isotropic voxel size of 22 µm was obtained (Xradia Versa 520, Zeiss, USA). After 3D reconstruction the main microstructure characteristics were analysed using ImageJ (NIH, US).
The 3D printed bone replicas were created by segmenting the microCT imaged bone tissue and then converted into a STL file using Avizo (FEI, US). The 3D printer used for this study was the ProJet 5500X (3D Systems, US), which allows a number of different materials to be printed in the same built with a resolution of 25 µm. Preliminary results were obtained using one single material (VisiJet CR-WT, Tensile Modulus: 1–1.6 GPa, Tensile Strength: 37–47 MPa). The 3D printed bone replicas followed a critical cleaning step to remove any remaining support material in the pores. MicroCT was then carried out for the bone replicas obtaining the same isotropic voxel size as for their biological counterparts. ImageJ was used to obtain the main microstructure characteristics.
The values of bone volume fraction (BV/TV), mean trabecular thickness (Tb.Th), mean trabecular spacing (Tb.Sp), and degree of anisotropy (DA) were measured for bone samples and their 3D printed replicas [2].
Preliminary results on the first bone sample with its 3D printed replica showed similar apparent trabecular structures. Their respective BV/TV was found to be 0.24 (bone) and 0.43 (replica). The Tb.Th and Tb.Sp were 0.222 mm and 0.750 mm respectively for the bone and 0.376 mm and 0.575 mm for the replica. Finally, their respective DA was found to be 0.68 (bone) and 0.66 (replica).
The main microstructure characteristics analyzed showed some differences between the bone sample and the 3D printed replica. In particular, the 3D microstructures resulted over-dimensioned mainly due to factors such as microCT voxel size, resolution of the 3D printer and supporting material removal. However this is a preliminary investigation. Further analysis will focus on optimizing the microCT imaging as well as the 3D printing process to achieve more accurate bone replicas. In addition, multi-material printing will be employed to optimize some of the mechanical properties obtained through in situ microCT testing and FE subject-specific modelling.
