Structural characterization of biomedical Co-Cr-Mo components produced by direct metal laser sintering.

Direct metal laser sintering (DMLS) is a technique to manufacture complex functional mechanical parts from a computer-aided design (CAD) model. Usually, the mechanical components produced by this procedure show higher residual porosity and poorer mechanical properties than those obtained by conventional manufacturing techniques. In this work, a Co-Cr-Mo alloy produced by DMLS with a composition suitable for biomedical applications was submitted to hardness measurements and structural characterization. The alloy showed a hardness value remarkably higher than those commonly obtained for the same cast or wrought alloys. In order to clarify the origin of this unexpected result, the sample microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX). For the first time, a homogeneous microstructure comprised of an intricate network of thin ε (hcp)-lamellae distributed inside a γ (fcc) phase was observed. The ε-lamellae grown on the {111}γ planes limit the dislocation slip inside the γ (fcc) phase, causing the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields.

Study of the interface reactions between cells and a biocompatible ceramic.

Preliminary results on the modifications induced by the growth of a Chinese Hamster Ovary (CHO) cell line on the surface of a CORD 1014 ceramic cordierite are reported. Results proved that cells strongly modify the crystallography and the chemical composition of the surface and near surface regions of the cordierite.

An experimental study in X-ray spectroscopy of the zirconium (Ca-PSZ) - bone interface. Microanalytic evaluation of the osteogenetic response.

Ultrastructural difractometric and chemical evaluations of calcium partially stabilized zirconium (Ca-PSZ) implants were performed in an in vivo study on animals in order to evaluate its biological behaviour. The chemical-morphological investigations demonstrated the presence of an osteogenetic activity at the bone-biomaterial interface. The new-osteogenesis was preceded by the formation of a loose connective tissue around the implants. This mesenchymal-type tissue without a capsular organization, allowing modulation of the mechanical forces to which the implant is subject, could be considered a positive event in the osteogenetic process and not a sign of future failure of the implant. Finally, microanalytical investigations carried out on non-implanted and implanted Ca-PSZ tools suggested that the surface of this ceramic material does not undergo modification once it has been inserted in the biological environment (12 months).

[In vitro enamel fluoridation using an ultraviolet laser]. / Fluoration de l'émail in vitro par laser à rayons ultraviolets.

28 samples of human enamel have been studied in order to measure fluoride absorption after treatment with ultraviolet radiations. Samples treated with topical application only presented limited fluoride absorption in enamel surface (up to 0.5 microns deep). The absorption rate was higher, using an U.V. lamp. In samples treated with "excimer" laser, fluoride absorption was much higher in the surface layer and occurred also deeper (3 microns).

Properties of a new carbon film for biomedical applications.

The physical and chemical properties of carbon films, about 0.5 mu thick, deposited at low temperature (40-200 degrees C) by a new physical vapour deposition technique are presented, in comparison with those of pyrolytic carbon normally used in biomedical devices. Several analytical techniques have revealed that the thin carbon films present structural properties similar to those of pyrolytic carbon. For example, similar chemical bondings of C atoms are observed in both samples. Moreover the data suggest the presence in thin C films of both tetrahedral and graphitic bondings, as in the turbostratic structure typical of pyrolytic carbon. These results confirm the similar biocompatibility properties of both types of materials already established by in vivo experiments.