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BACKGROUND: In applications on dental/orthopedic implants and bone regeneration, biomaterials contained magnesium have been widely used. However, the mechanism underlying the biologic effects is still largely unknown. In addition, previous reports of osteogenic effect of magnesium mainly relied on studies using ATCC osteosarcoma cell lines but not normal human osteoblasts. OBJECTIVE: This study was designed to test the effect of magnesium on osteogenic phenotypic behaviors of normal human osteoblasts. METHODS: Normal human osteoblasts derived from human alveolar bone were cultured in triplicate in growth media with varies concentrations of supplemental magnesium: 0.5mM, 1mM, 2mM, 4mM, 8mM and 16mM as the study groups and 0mM as a control group for the time intervals of 7 days, 10 days, 14 days and 21days. Cell proliferation was measured by crystal violet dye staining. Expression of osteocalcin was measured by Quantikine Elisa and mineralization of cultures was measured by Alizarin Red staining. The data were normalized per cell basis. Statistical analysis was done using ANOVA and Student’s t test. Results: Osteocalcin expression was upregulated in groups with supplemented magnesium at 0.5mM (1.16folds, p<0.01 ), 1.0mM (1.22folds, p<0.01 ), 2.0mM (1.37folds, p<0.01 ) at day 21 compared to control, while at 4mM ( p<0.01 ) and above showed down-regulation. Alizarin Red stained cultures showed higher degree of mineralization at 1mM ( p=0.0228 ) and 2mM ( p=0.0142) compared to control. Groups with 4mM and above showed less calcium deposition. Similar results have been gained also on day 10 and day 14 for both assays. CONCLUSION: Osteogenesis of normal human osteoblasts could be significantly upregulated by 2mM supplemental magnesium. These data are important for manufacturing magnesium-containing biomaterials for bone tissue regeneration and implants.

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Cette thèse porte sur l'évaluation de la réponse cellulaire in vitro vis-à-vis de différentes stratégies de modification de surface pour améliorer la capacité d’ostéointégration de céramiques bioinertes pour implants orthopédiques et dentaires. Premièrement des surfaces l'alumine-zircone avec différentes micro-rugosités obtenues par moulage par injection ont été étudiées. Le comportement d'ostéoblastes primaires humains (obtenus à partir de têtes de fémurs soumis à arthroplastie) a été étudié sur les surfaces telles quelles ou modifiées par traitement avec acide hydrofluorique. La micro-rugosité a eu seulement un effet mineur sur la réponse ostéoblastique tandis que la combinaison de micro- et nano-rugosité a eu un effet synergique sur la maturation ostéoblastique. Cette stratégie de modification de surface ouvre la voie vers des cupules acétabulaires céramiques monoblocs directement ostéo-intégrées. Deuxièmement, le robocasting (une technique d’impression 3D) a été exploré pour la production de structures macroporeuses en alumine-zircone avec une haute reproductibilité et contrôle architectural. Les structures imprimées ont présentées une topographie aux multiples niveaux grâce au design et les conditions de frittage. Les ostéoblastes ont pu s'attacher sur les structures 3D mais la préservation des cellules à l’intérieur des scaffolds sur le long terme reste à améliorer. Des techniques de sélection rapide de modifications de surface ont fait l'objet de la dernière partie de cette thèse. Deux différentes stratégies ont été utilisées sur la zircone: laser femtoseconde pour la production de multiples motifs sur un échantillon unique et échantillons avec un gradient de rugosité via le contrôle du temps d’attaque chimique. La morphologie des cellules souches humaines a permis d'avoir un indicateur précoce de la lignée de différentiation cellulaire. En conclusion, les différentes techniques de modification de surface de zircone et alumine-zircone utilisées à travers la thèse peuvent moduler l’interaction cellule-matériau en stimulant la différentiation ostéoblastique de cellules souches et la maturation des ostéoblastes. / The focus of this PhD thesis is the in vitro evaluation of cell-material interactions on bioinert ceramics with novel surface modifications for enhanced osseointegration of orthopaedic and dental implants. Firstly, alumina-zirconia surfaces with different micro-roughnesses obtained by injection moulding were studied. The behaviour of human primary osteoblasts (hObs) obtained from patients undergoing total hip replacements was studied on the different micro-rough ZTA surfaces and on combined micro-/nano-rough surfaces modified by hydrofluoric acid treatment. Micro-roughness alone had minor effects on hOb response while the combination micro-/nano-roughness induced a synergic effect on hOb maturation. This latter surface modification technique opens the way to the fabrication of ceramic acetabular cups with direct implantation capabilities. Secondly, robocasting (a 3D printing technique) was explored for the fabrication of a alumina-zirconia macroporous structures with high reproducibility and control of the architecture. Roughness at different scales was observed for the 3D structures due to the scaffold design and to the low temperature sintering conditions. Osteoblasts were able to attach on the 3D structures but cell retention at long term needs further optimization. Rapid screening of cell-material interactions was the subject of the last part of the thesis. Two different strategies were tested on zirconia: femtosecond laser to produce multiple patterns on a single sample and samples with a roughness gradient by the control of chemical etching time. Stem cell morphology was used as an early marker of cell differentiation lineage. In conclusion, the different surface modification techniques of zirconia and alumina-zirconia surfaces used in the thesis allow the modulation of cell-material interactions by stimulating stem cells osteogenesis and osteoblast maturation.

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