Biomedical subjects

Sylvain Deville

Publications and source records attributed to Sylvain Deville.

5 recordsLinked to original sources

PubMed2006

Freeze casting of hydroxyapatite scaffolds for bone tissue engineering.

Although extensive efforts have been put into the development of porous scaffolds for bone regeneration, with encouraging results, all porous materials have a common limitation: the inherent lack of strength associated with porosity. Hence, the development of porous hydroxyapatite scaffolds has been hindered to non-load bearing applications. We report here how freeze casting can be applied to synthesize porous scaffolds exhibiting unusually high compressive strength, e.g. up to 145 MPa for 47% porosity and 65 MPa for 56% porosity. The materials are characterized by well-defined pore connectivity along with directional and completely open porosity. Various parameters affecting the porosity and compressive strength have been investigated, including initial slurry concentration, freezing rate, and sintering conditions. The implications and potential application as bone substitute are discussed. These results might open the way for hydroxyapatite-based materials designed for load-bearing applications. The biological response of these materials is yet to be tested.

Bone and Bones↗

PubMed2006

Freezing as a path to build complex composites.

Materials that are strong, ultralightweight, and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to the nanometer scale. Nacre, a structure found in many molluscan shells, and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic-metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those of materials currently used for implantation.

Biocompatible Materials↗

PubMed2005

Influence of surface finish and residual stresses on the ageing sensitivity of biomedical grade zirconia.

We demonstrate in this paper the influence of surface finish on the ageing kinetics of biomedical grade zirconia. The critical influence of polishing has been systematically investigated by optical microscopy, atomic force microscopy and X-ray diffraction. The stress state around polishing scratches gives rise to preferential transformation in the zone of the induced scratches and consequently to accelerated ageing. The influence of residual stresses is analyzed semi-quantitatively by preparing samples with various surface finish, thus with various stress states. Rough polishing produces a compressive surface stress layer beneficial for the ageing resistance, while smooth polishing produces preferential transformation nucleation around scratches. When a thermal treatment of 2h at 1200 degrees C is applied to relax the residual stresses, all the surfaces states exhibit the same sensitivity to ageing. These results demonstrate that roughness alone cannot be used for ensuring a long-term stability. The variation of ageing sensitivity is indeed related indirectly to the surface roughness via the induced surface stress state. The current ISO standards are not able to take these effects into account. Indeed, great variations in ageing kinetics were observed for samples with different surface states, although all well below the ISO requirements.

Biocompatible Materials↗

PubMed2005

A critical comparison of methods for the determination of the aging sensitivity in biomedical grade yttria-stabilized zirconia.

Since the recent failure events of two particular series of zirconia femoral heads for total hip replacement prosthesis, a large decrease in the use of zirconia ceramics for orthopaedic implants has been observed. In spite of the biomedical success of this material during the last 10 years, this decrease in use was required for safety reasons, until the cause of the failures is known. It has been shown that these failures were related to the low temperature hydrothermal degradation (also known as aging). Thus, it is crucial to better understand the aging behavior, in order to be able to assess its importance and then control it if required. In this study, various techniques relevant to assess the hydrothermal degradation sensitivity of biomedical grade yttria-stabilized zirconia are discussed and compared. The expected outputs of conventional methods, that is, X-ray diffraction and scanning electron microscopy are examined. More recent methods like optical interferometry and atomic force microscopy are presented, with their respective benefits and drawbacks. An up-to-date comparison of these different techniques is provided, and their use for ensuring the long-term reliability of a particular batch of zirconia in terms of aging degradation is demonstrated.

Biodegradation, Environmental↗

PubMed2004

Critical effect of cubic phase on aging in 3mol% yttria-stabilized zirconia ceramics for hip replacement prosthesis.

The isothermal tetragonal-to-monoclinic transformation of 3Y-TZP ceramics sintered at two different temperatures (1450 degrees C and 1550 degrees C) and duration (2 and 5h) is investigated at 134 degrees C in steam. Particular attention is paid to the presence of a cubic phase and its effect on isothermal aging. Sintering at 1550 degrees C can result in a significant amount of large cubic grains in the specimens, that have a detrimental impact on aging resistance, especially for the first stage of the aging process. Cubic grains appear to be enriched in yttrium, which in turn leads to a depletion of yttrium in the neighboring tetragonal grains. These grains will act as nucleation sites for tetragonal-to-monoclinic transformation. Even for specimens sintered at lower temperature, i.e. 1450 degrees C, the presence of a cubic phase is expected from the phase diagram, leading to a significant effect on aging sensitivity.

Ceramics↗