Papers by Author: Laurent Gremillard

Abstract: In the last years, bioactive glasses and glass-ceramics drew the attention for their application in the production of implants. Among them, Bioglass^® 45S5 is the most commonly used in terms of bioactivity, but its sintering behavior and the related glass-ceramics strongly depend on the followed synthesis process. For these reasons, this paper reports a comparison of the properties and the thermal behavior of bioactive 45S5 glasses produced by a conventional melting process starting from suitable solid precursors or an innovative sol-gel procedure.

Abstract: In this study we show that mechanical properties of bioceramic scaffolds can be significantly improved by repeated infiltration with a low-viscosity polycaprolactone solution. Biphasic calcium phosphate (BCP: 70% hydroxyapatite, 30% β-tricalcium phosphate) scaffolds characterized by a bimodal pore size distribution and a global porosity of 70% have been chosen as starting materials. Polymer content in the ceramic scaffold was varied so that an inorganic/organic ratio close to that of bone may be achieved. Work of fracture at maximum stress was 36 J/m2 for the ceramic scaffold alone and reached 127 J/m2 for the 8-times infiltrated samples. These results are superior to the ones previously obtained with polycaprolactone infiltrated alumina due to higher micropore content. We show that during bending tests, polycaprolactone phase formed fibrils while the crack propagated. Crack bridging by polycaprolactone ensured the integrity of the composite once the ceramic scaffold was broken and directly involved in the composite toughening. Because of its composition, microstructure and mechanical behavior of this kind composite can be an interesting candidate for bone substitution.

Abstract: The aim of this study was to evaluate the cytocompatibility, cell ingrowth and extracellular matrix deposition of a newly developed porous bioactive glass as a bone substitute. Two types of bioactive glass, different in their pore size (75 and 20 ppi, resp. ~350 and ~1200 $m), were used in this study. The materials were seeded with human osteoblastic (MG63) and fibroblastic (M-228 F01 and M-191 F01) cell lines. The cells were visualized by two techniques, scanning electron microscopy and confocal microscopy. For confocal microscopy cell nuclei were labeled with propidium iodide (IP) and the extracellular matrix components (type I collagen and osteocalcin) by specific antibodies. Cells and matrix were visualized by fluorescence. The bioactive glass used in this study was shown to be non cytotoxic. Cell growth and colonization at the surface and in the depth of the material were observed. Extracellular matrix deposition was also demonstrated which proved the proper biofunctionality of the biomaterial. Scanning electron microscope allowed us to visualize cells at a high magnification at the surface of the bioglass and evidenced that the biomaterials were covered by a sheet of cells with their matrix; on the other hand, confocal microscopy permitted us to observe cell ingrowth and matrix deposition within the depth of the substitute. We showed that extracellular matrix was synthesized mainly in the upper levels where the cell population was the most confluent. In summary, this porous bioglass appears promising for bone substitution.

Abstract: Ceramics have been increasingly used in orthopaedics during the last 30 years. Their biological inertness, high hardness and good mechanical strength make them excellent candidates for components such as femoral heads and acetabular cup in Total Hip Replacement prostheses. Currently used bio-inert ceramics – alumina and zirconia – give good clinical results, especially compared to metal – polymer couplings. However, they are subjected to severe biological, tribological and mechanical solicitations during more than fifteen years for the most successful prostheses. They answer these solicitations by presenting specific degradation mechanisms. We will thus examine the phenomena that can account for the long-term behaviour of zirconia components (heads and cups) in THR prostheses.

Abstract: In this study, we report on the effect of Bioglass® structural transformations on its sintering behaviour. In a previous paper, we showed that while heating up to 1000°C, five successive transformations occur: glassy transition, phase separation, two crystallization processes and a second glassy transition. The sintering of the material exhibits two main shrinkage stages associated to the two glassy transitions at 550°C and 850°C. At 580°C, the glass-in-glass phase separation induces a decrease of the sintering rate immediately followed by the crystallisation of the major phase Na2CaSi2O6 between 600 and 700°C, from the surface to the bulk of the particles. A completed inhibition of sintering takes place followed by a minor shrinkage due to volume crystallization. A plateau is observed until the second glassy transition.