ARTICLE IN PRESS O. Roualdes et al. Biomaterials xxx(2009)1-12 3.5 3.0 50 2.5 2.0 e1.0 0.5 Synovial lining cells Subsynovial tissue Fig 8. Comparison of the ng cell and sub-synovial tissue for alumina( group B, n= 12) and zirconia ( group C. n=12) Values are ed as mean+ SEM, *p<0.001 compared to the sar material in the sub-synovial compartment bALA to the sintering process itself. Thus, even if the material used in this study cannot be characterized as a nano-phase ceramic, it is a good picture of the new generation of alumina-zirconia composites currently developed and used in arthroplasty [10, 16, 18 Although their superiority in terms of mechanical strength and aging resis- tance has been clearly demonstrated [16, 46], there is lack of careful biological evaluation. This work tries to respond to this need in two parts. At first, we focalized on the in vitro cytocompatibility of the alumina-zirconia sintered ceramic assessment Then we evaluated the in vitro and in vivo biological influence of it alumina and zirconia constitutive powders as a model of wear debris. When osteoblasts were cultured upon a nano-structured sin- tered alumina ceramic, Webster et al. showed that cell adhesion and proliferation increased compared with conventional ceramics. However, it was the opposite for fibroblasts [22-24. If osteoblasts are bone forming cells, fibroblasts can be considered as cells that contribute to fibrous encapsulation and callus formation, events that may lead to loosening failure. These results and this theory may explain the good osteointegrative potential of the material. In Fig. 7. Histological es(stained with Goldner the present study, we only used micron-structured sintered synovial lining cell alumina-zirconia ceramic. Then we were not comparing the nano (c)represent section of animals that were injected three time respectively with and conventional structure of ceramics on cell comportment but lumina or zirconia particles and showed a slight reaction of the synovial lining cell rather to observing the difference between the response of osteo- layer and macrophage infiltration. blasts and fibroblasts, depending on the surface of ceramics. After cell seeding on the material, the adhesion of cells were indirectly Discussion nvestigated by comparing the cell proliferation upon and beside the discs by mrt assay which is representative of the proportion of The present study consisted of the evaluation of the biological cells that have not been fixed ompatibility of an alumina-zirconia composite. If the cyto- studies, we did not observe any modification or difference of the compatibility of conventional ceramics (micro-structured and adhesion for both fibroblasts and osteoblasts(data not shown). The monolithic composed) has been clearly demonstrated there is less micro-structured ceramic discs, with polished or rough surface. information about their nano-structured and or composite version. appear as surfaces adapted for cell promoting Here, we investigated on an alumina-zirconia ceramic processed In fact, this composite only slightly reduced cell proliferation of om nano-powders. Although starting from nano-phases powders both osteoblasts and fibroblasts, even if it was statistically significan (40 and 350 nm for zirconia and alumina respectively). sintering for osteoblasts but not for fibroblasts. The cell functions, represented mechanisms leaded to a sub-micron microstructure(600 nm to by CIH and fn productions appeared also accurate for both cell types I um for zirconia and alumina respectively ) which is obvious due In the conditions of our study, this material showed a satisfactory Please cite this article in press as: Roualdes 0, et al, In vitro and in vivo evaluation of an, Biomaterials(2009). doi: 10.1016/ j biomaterials 2009. 11.1074. Discussion The present study consisted of the evaluation of the biological compatibility of an alumina–zirconia composite. If the cyto￾compatibility of conventional ceramics (micro-structured and monolithic composed) has been clearly demonstrated, there is less information about their nano-structured and/or composite version. Here, we investigated on an alumina–zirconia ceramic processed from nano-powders. Although starting from nano-phases powders (40 and 350 nm for zirconia and alumina respectively), sintering mechanisms leaded to a sub-micron microstructure (600 nm to 1 mm for zirconia and alumina respectively), which is obvious due to the sintering process itself. Thus, even if the material used in this study cannot be characterized as a nano-phase ceramic, it is a good picture of the new generation of alumina–zirconia composites currently developed and used in arthroplasty [10,16,18]. Although their superiority in terms of mechanical strength and aging resis￾tance has been clearly demonstrated [16,46], there is lack of careful biological evaluation. This work tries to respond to this need in two parts. At first, we focalized on the in vitro cytocompatibility of the alumina–zirconia sintered ceramic assessment. Then, we evaluated the in vitro and in vivo biological influence of it alumina and zirconia constitutive powders as a model of wear debris. When osteoblasts were cultured upon a nano-structured sin￾tered alumina ceramic, Webster et al. showed that cell adhesion and proliferation increased compared with conventional ceramics. However, it was the opposite for fibroblasts [22–24]. If osteoblasts are bone forming cells, fibroblasts can be considered as cells that contribute to fibrous encapsulation and callus formation, events that may lead to loosening failure. These results and this theory may explain the good osteointegrative potential of the material. In the present study, we only used micron-structured sintered alumina–zirconia ceramic. Then we were not comparing the nano and conventional structure of ceramics on cell comportment but rather to observing the difference between the response of osteo￾blasts and fibroblasts, depending on the surface of ceramics. After cell seeding on the material, the adhesion of cells were indirectly investigated by comparing the cell proliferation upon and beside the discs by MTT assay which is representative of the proportion of cells that have not been fixed on the material. Contrary to Webster studies, we did not observe any modification or difference of the adhesion for both fibroblasts and osteoblasts (data not shown). The micro-structured ceramic discs, with polished or rough surface, appear as surfaces adapted for cell promoting. In fact, this composite only slightly reduced cell proliferation of both osteoblasts and fibroblasts, even if it was statistically significant for osteoblasts but not for fibroblasts. The cell functions, represented by CIH and FN productions appeared also accurate for both cell types. In the conditions of our study, this material showed a satisfactory Fig. 7. Histological appearances of rat synovial membranes (stained with Goldner trichrome, magnification 40). (a) The control section showed a synovial lining cell layer composed by one layer of flat synoviocytes and no sign of inflammation. (b) and (c) represent section of animals that were injected three time respectively with alumina or zirconia particles and showed a slight reaction of the synovial lining cell layer and macrophage infiltration. Synovial lining cells Score of total particles amount Sub-synovial tissue 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 +++ +++ Fig. 8. Comparison of the scores of total particle amount between synovial lining cell and sub-synovial tissue for alumina ( , group B, n ¼ 12) and zirconia ( , group C, n ¼ 12). Values are expressed as mean  SEM, þþþp < 0.001 compared to the same material in the sub-synovial compartment. O. Roualdes et al. / Biomaterials xxx (2009) 1–12 9 ARTICLE IN PRESS Please cite this article in press as: Roualdes O, et al., In vitro and in vivo evaluation of an..., Biomaterials (2009), doi:10.1016/ j.biomaterials.2009.11.107