Health is a leading area of innovation despite the need for a thorough understanding of the new materials and processes before their widespread use. 3D Printing is one of such innovation which is now available for some surgeons across the world, to be assisted by personalized guides and models.
     The first steps of 3D printing in the operating room took place a few decades ago as biomodels [1] and after for bone tissue engineering through plastic, metal or ceramic implant. This way of shaping is increasingly considered thanks to its gain in aesthetic [2], customization and costs [3].
      Bioceramic implants have been studied for a long time for bone repair, the first option is to find a material which is biologically and physically close. However, these two properties are difficult to achieve with synthetic materials, even though some bioceramics such as hydroxyapatite exhibit properties similar to human bones. In this aspect, 3D printing is a huge step forward. For instance, the fragility of synthetic bioceramics can be partially compensated by the 3D shaping using computerized results to achieve optimal properties through simulations.

      Here, we used a powder of Calcium Deficient HydroxyApatite (CDHA), either doped with copper (z=0.1) or not, for bone implants printing. They were synthesized respectively by brushite hydrolysis or precipitation. Cu-doping has shown promising results in antibacterial [4], angiogenic and osteogenic activities. 
                                                     Ca_10-xCu_z(PO₄)_6-x(HPO₄)_x(OH)_2-2z-x(O)_2z(V_OH)_x                                
     This powder of CDHA is known to thermally decompose into a mixture of Hydroxyapatite and Tricalcium Phosphate (HAP/TCP) according to the treatment temperature and the ratio Ca/P :    
                                                      Ca₁₀Cu_x(PO₄)₆(OH)_2-2xO_2x + Ca_3-x’Cu_x’(PO₄)₂                                                    
     To obtain a paste printable by Digital Light Processing (DLP) on Admaflex 130, the CDHA powders were grinded previously to be mixed into a photosensitive resin to obtain the best compromise between printability and mass loading. Various designs have been created, and adapted for the 3D printing, by Computed Assisted Design on Rhino 7, from simple structures like parallelepiped to Triply-Periodic Minimal Surfaces (TPMS) lattices, which appear to be promising geometries [5].
     Afterwards, these designs have been printed with different parameters to evaluate their influence on the rheological behaviour and printing parameters. After the printing, heat treatments (debinding and sintering) are required to eliminate all organic components and ensure the parts mechanical resistance. As expected, the CDHA was decomposed, at this stage, into a mixture of HAP/TCP. The phase proportions and the mechanical properties were studied and were correlated with the initial particles size. The influence of copper was evaluated and its release monitored.

References:
[1] : P. S. D'Urso et al. British Journal of Plastic Surgery (2000), 53, 200-204
[2] : J. Brie et al. Journal of Cranio-Maxillofacial Surgery. Volume 41, Issue 5 (2013) : 403-407.
[3] : H. Ballard et al. Academic radiology 27.8 (2020): 1103.
[4] : A. Jacobs et al. Materials 2021, 14, 2393.
[5] : L. Bai et al. Metals 2019, 9, 1004.