| research Biocompatibility of CAD/CAM biomaterials for bone tissue engineering application Dr Katharina Pippich, Katharina Hast, Adem Aksu, Stefanie Grom, Dr Tobias Wolfram, Frank Reinauer, Dr Dr Andreas Fichter, Dr Dr Achim von Bomhard, Germany Large bone defects have so far mainly been treated with autogenous bone grafts. Owing to limited availability and donor site morbidity, research is ongoing into the devel- opment of various bone replacement materials. An advan- tage of CAD/CAM implants is the possibility of patient- specific engineering. Ceramics and polymers have been extensively investigated, but not all materials can be pro- duced in a standardised and patient-specific way yet. In this study, a wide range of materials were investigated, all of which can be CAD/CAM manufactured and individually dimensioned in the clean room with standardised tech- niques using digital light processing, selective laser sinter- ing and fused deposition modelling. The novelty of the ma- terials is the compounding of these, including the special processing by 3D printing. Eight polymer and ceramic CAD/ CAM materials—poly-L-lactic acid and calcium carbonate, poly-L-lactic acid and tricalcium phosphate, poly-L-lactic acid and polyglycolic acid and calcium carbonate, poly-D, 1a 1c 1b 1d Fig. 1: Scaffold construction (sizes in mm). Scale bars = 1 mm. 3D view (a), top view (b), side view (c), Cross section (d). 24 4 2023 L-lactic acid and magnesium, poly-D, L-lactic acid, beta- tricalcium phosphate (β-TCP) and hydroxyapatite, β-TCP and β-TCP'—were tested to evaluate the cytotoxic effects on human osteoblasts. Biocompatibility was tested using a proliferation assay, a cytotoxicity assay, an apoptosis assay and fluorescence microscopy. The ceramic-based scaffolds, in particular β-TCP, showed very high cell counts in the proliferation assay as well as rapidly falling apopto- sis rates and offer significant potential for use for patient- specific bone replacement implants. Introduction Bone defects often occur in the context of tumour resec- tion, bone inflammation, malformation or trauma.1 Autoge- nous bone transplantation continues to be the gold stan- dard for the reconstruction of such defects. However, bone availability is limited in this case, and not inconsid- erable donor site morbidity, including impaired wound healing, functional limitations, scarring and necrosis, can occur.2 Research in the field of bone regeneration is steadily growing.3 Of great interest are biomaterials, which being bone replacement materials, avoid the creation of donor sites and the associated complications and which, owing to their osteoconductive properties and suitable architecture, represent a viable alternative to autogenous bone transplantation.4–6 In addition, materials that can be additively manufactured offer the advantage of being able to be individually dimensioned according to the defect. The growing demand requires bone replacement materi- als to possess improved mechanical and biological prop- erties. An ideal biomaterial is characterised by biocom- patibility and is replaced by regenerated new bone after the healing period. In terms of chemical composition and architecture, it should mimic the extracellular bone matrix so that cells can adhere, multiply and differentiate.7, 8 Bio- materials that are very frequently used include ceramics such as beta-tricalcium phosphate (β-TCP) and hydroxy- apatite (HA). Owing to their osteoconductivity and similar composition to that of bone, they play a crucial role in tis- sue engineering. In particular, β-TCP has a high degree