Papers by Author: Pierre Millet

Abstract: The properties of the interface between biomaterials and the host tissue play an important role for the process of successful adaptation of implants. Extensive research has focused on shortening the time of osseointegration by modifying the surface in adding a coating such as hydroxyapatite (HAp). We have developed a new type of biocompatible nanohydroxyapatite (n-HAp) coatings, which are characterized before and after deposit on a Ti-6Al-4V substrate using neutron diffraction and scanning electron microscopy. Three months after the implantation in the sheep tibias, high-energy synchrotron radiation (ID15B, ESRF, Grenoble, France) diffraction studies of the cortical bone identify that the c-axes of HAp are preferentially oriented in the direction of the stresses that bone usually withstands. This non destructive analysis of the bone-implant interface proves that bone maturation is achieved successfully with this novel n-HAp coating and demonstrates that the mineralization is completed without spatial organization. None of these findings are obtained with uncoated titanium alloys. The presence of this n-HAp coating on Ti-6Al-4V substrate is decisive in obtaining this mature bone at the interface.

Abstract: The aim of this work was to study the implant-bone interface by synchrotron radiation in order to show the evolution of the crystallites of hydroxyapatite (Hap) reconstituted at the interface with the implant. The implant used an orthopaedic surgery is the Titanium alloy (Ti-6Al-4V), the implants are currently coated with (HAp), Ca₁₀ (PO₄)₆ (OH)₂, in order to obtain a stable and functional direct connection between the bone and the implant. In this work, two implants have been used, the first one coated with HAp and the second uncoated. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the crytallinity index and texture of the new bone crystals reconstituted at the interface using synchrotron radiation on ID15 at ESRF in Grenoble, France.

Abstract: The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the residuals stresses and texture of the new bone crystals reconstituted at the interface using synchrotron radiation on ID15 at ESRF in Grenoble, France.

Abstract: The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca₁₀ (PO₄)₆ (OH)₂, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the texture of the reconstituted bone crystals at the interface applying non destructive x-ray diffraction. The required high spatial resolution was achieved utilizing high-energy synchrotron radiation on ID15 at ESRF in Grenoble, France.

Abstract: Technology developments of implant composition and manufacture have been used in the medical field. Several different implants have been developed with varying degrees of commercial success. As a long-term establishment is a measure of the therapeutic success, it is necessary to use biocompatible implants in order to have good mechanical and fracture resistance of new bone reconstructed at the interface with the implant. Titanium (Ti-Al-4V) implants coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2 are widely used in orthopedic applications in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface the new bone reconstituted after implantation must have the same orientation as the natural bone in order to accept the implant. Therefore we studied the texture and the crystallinity of the new bone crystals reconstituted at the interface applying by high-energy synchrotron radiation on beamline ID15 at ESRF in Grenoble, France.

Abstract: The quantitative evaluation of the preferential orientation of crystallites by the synchrotron and neutron diffraction techniques during regeneration at the interface with implant gives a good prediction of the mechanical properties of the bone. During the process of bone healing after implantation, the speed and quality of regeneration is affected by the nature of the implant surface. Titanium alloy (Ti-Al-4V) is currently coating with the hydroxyapatite (HAp), Ca10(PO4)6 (OH)2, in order to obtain a stable and functional direct connection between bone and implant. At the interface implant-bone, the new bone reconstituted after implantation must have the same mechanical properties of bone in order to accept the implant. Therefore, it is necessary to study by means of two non destructive techniques: neutron diffraction and synchrotron radiation, the crystal growth and texture of this new bone crystals reconstituted at the interface.

Abstract: In recent years, nanostructured coatings by Plasma Thermal Spraying (PTS) attracted intense interest due to their enhanced mechanical properties as hardness, strength and ductility. The aim of this study was to evaluate the influence of coating the implant by nanohydroxyaptite, n-HAp, Ca10 (PO4)6(OH)2. The results obtained with n-HAp will also compared with the implant coated with HAp. Bone is a composite material in which are associated a mineral phase in the form of crystals of HAp and an organic matrix constituted by collagen. The c-axes of HAp and the collagen fibers are preferentially oriented in the direction of the stresses that the bones need to withstand. At the interface implant-bone, the new bone reconstituted after implantation must have the same proprieties of the original bone in order to have good fixation with the implant. Therefore, it is necessary to study the mechanical properties of this new bone crystals reconstituted at the interface with the implants coated with n-HAp and HAp by neutrons diffraction on D20 at ILL.

Abstract: A full review for technological processes used today, in dental prostheses industry for titanium casting, both in Europe and in United States, reveal that, there is no equipment available on the market able to cast small titanium parts in secondary inert vacuum by induction melting and centrifugal casting. All these advanced processes together contribute to an original concept of the Denticast System. The computer controlled cast sequence is another important factor contributing to a robust system, able to reproduce the achieved technological quality in a reliable manner. Mechanical testing (tensile and hardness) shows that the different alloys used in Denticast project and cast using the prototype, are in most of the results superior to those obtained with two different commercial systems (pressure-vacuum and centrifugal systems). The samples are usable for dental prosthesis without any risk for the patient health.

Abstract: The aim of this study was to create a nano-structured coating using Plasma Thermal Spraying (PTS). This process consists in introducing pre-agglomerated nanosized particles in a high-temperature and high-velocity gas jet and projected them onto the substrate to form, layer by layer, a nanostructured coating. In order to retain nanometer grain sizes in the deposited coating through specific PTS technologies, a thermal field and velocity distribution in the plasma jet are analytically calculated. A finite element analysis is employed to calculate the thermal field evolution inside the agglomerated particles and the thermal induced internal stress distribution is determined. The parameters determined by the theoretical analysis are used for experimental coatings. The average crystallite size of nano-hydroxyapatite powder was 90nm. After deposit via Plasma Thermal Spraying (PTS) process and followed by a 2 hours heat treatment to reduce amorphous fraction, the experimental deposited coating shows that it retains the nanometer crystallite sizes. The substructure of nanocrystals was evaluated at about 120nm in size. Such a nanocoating may play the role of nucleation site to bone, allowing a faster stabilization of the implant.

Abstract: The basic principles behind human tissue response to artificial surface implantation may be developed under its biological aspect, it is necessary for a medical use to study the mechanical limits of every biomaterials to predict the tissue and the body's response according to the composition, the structure and the design of a biomedical material. To promote a stable and functional direct connection between bone and implant, titanium implants can be coated with materials based on calcium phosphate ceramics such as hydroxyapatite (HAp)(Ca10(P04)6(OH)2). The preferred orientation of HAp crystallites at the interface bone-implant in sheep tibia bones has been measured with the neutron 2-axis diffractometer D20 at the Institut Max von Laue-Paul Langevin (ILL), extracted 60 days after implantation. The implant has two faces, one coated and one non-coated with plasma-sprayed HAp (80 .m). We probed the samples with a spatial resolution of 0.5 mm started from the interface in order to inspect the reorganisation of the HAp crystallite’s distribution after implantation.