Impact of Calcium Phosphate Particle Morphology on Osteoconduction: an in vivo study

Apatite/β−TCP particles exhibiting non-conventional urchin-like morphology were prepared by hydrothermal synthesis. Their implantation in the rat calvarium was followed during 60 days. A total absence of osteoconduction was observed despite a favorable chemical composition, stressing the fundamental role of particle morphology on bone regeneration. Results are discussed in relation with other literature data. Possible explanations include the disfavored accumulation of biological mediators due to the acicular shape of the particles and/or a limited accessibility for cells

New calcium carbonate-based cements for bone reconstruction

The feasibility of calcium carbonate-based cements involving the re-crystallization of metastable calcium carbonate varieties has been demonstrated. Two cement compositions were obtained by mixing either calcium carbonate phases (cement A) or a calcium carbonate and a calcium phosphate phase (cement B) with an aqueous media. These cements set and hardened after 30 minutes and 90 minutes respectively. The final composition of cement A was calcite and aragonite whereas cement B lead to a carbonated apatite analogous to bone mineral. Despite poor mechanical properties the presence of a high carbonate content in the final phase might be of interest to increase the cement resorption rate and to favour its replacement by bone tissue. First assays of implantation performed on fresh anatomical pieces (fresh cadavers) at 37°C revealed important advantages of such cement compositions: easiness of use, rapid setting, good adhesion to bone, very good homogeneity and stability of the cement

Bioceramics: spark plasma sintering (SPS) of calcium phosphates

Calcium phosphates (Ca-P) are major constituents of calcified tissues, and are also extensively used for the elaboration of biomaterials. However, the usual high-temperature sintering processes generally lead to strong alterations of their chemical, physical and biological properties. Spark plasma sintering (SPS) is a non-conventional sintering technique based on the use of pulsed current, enabling fast heating and cooling rates, and lower sintering temperatures are often observed. The sintering of several orthophosphates (DCPD, amorphous TCP, beta-TCP, OCP, HA and biomimetic nanocrystalline apatites) by SPS was investigated in order to track potential advantages of this technique over usual Ca-P sintering methods. Special attention was given to the SPS consolidation of highly bioactive nanocrystalline apatites

Production, by co-grinding in a media mill, of porous biodegradable polylactic acid-apatite composite materials for bone tissue engineering

This paper presents the results of a study of the production of porous biodegradable composite materials by co-grinding, followed by scaffolding. Dry powders of polylactic acid and nanocrystalline carbonated apatite, analogous to bone mineral were co-ground in a tumbling ball mill in order to disperse the mineral filler within the polymer. Porous scaffolds were then made by hot moulding the mixture of the two components along with a pore-forming agent which was subsequently eliminated by washing. The mechanical resistance of the scaffolds was evaluated in order to determine the best operating conditions to produce implants offering optimised properties for use as bone substitutes. It was shown that 30 wt.% of filler and 70 wt.% of pore-forming agent produce scaffolds which are sufficiently porous and resistan

Nanocrystalline apatites: From powders to biomaterials

Non-stoichiometric nanocrystalline apatite powders are used to elaborate highly-bioactive biomaterials. Their exceptional surface reactivity arises from a structured but rather unstable hydrated layer involving ions in nonapatitic chemical environments, like in bone mineral. The initial powder characteristics can be tailored through precipitation parameters (pH, temperature, maturation time in solution). The drying of nanocrystalline apatite suspensions at very low temperature (4 °C) leads to ceramic-like materials exhibiting average mechanical properties (compressive strength 54 MPa) and a high porosity which could be exploited to entrap active organic compounds (e.g. growth factors). The consolidation at 150–200 °C of nanocrystalline apatite powders has also been studied using uni-axial pressing and spark plasma sintering (SPS). The results indicate only a limited alteration of the initial nanocrystals, and the bioceramics obtained show mechanical properties close to those reached with sintered stoichiometric HA. The high ion mobility in the hydrated layer of the nanocrystals can lead to “crystal fusion” processes. This capability to favor crystal–crystal interactions at low temperature, while preserving the non-stoichiometry and nanometer dimensions of apatite crystals, opens interesting perspectives for the elaboration of new resorbable and highly-bioactive bioceramics

Mechanical properties of self-setting composites: influence of the carboxymethylcellulose content and hydration state

The impact of the carboxymethylcellulose (CMC) content on the mechanical properties of calcium phosphate–calcium carbonate–CMC composite cements for bone substitution was investigated. The relevance of the compressive test conditions (wet or dried composite cements) is discussed and models are proposed to better understand the mechanisms involved in the mechanical properties of the composite materials. Based on a modellisation using the Voigt model for dried composite cements, we show that a minimum of CMC content of around 10–20 % is needed to enhance the mechanical properties of the dried composite materials (up to 86 MPa for the composite including 50 wt% CMC) through the formation of a mineral–organic entangled network. The compressive strength of the wet samples is low (\3 MPa) but the gain observed in the dried composites is encouraging and might be extrapolated to wet conditions if we were to use a less hydrophilic polysaccharid

Production par co-broyage de matériaux composites poreux biodégradables à usage orthopédique

L’article présente les résultats d’une étude sur la production de matériaux composites poreux biodégradables par co-broyage suivi d’une mise en forme. De l’acide polylactique et une apatite nanocristalline carbonatée analogue au minéral osseux, sous forme de poudres, ont été cobroyés dans un broyeur à boulets afin de disperser la charge minérale dans le polymère. Des implants poreux ont ensuite été réalisés en moulant à chaud le mélange des deux constituants et un agent porogène qui a ensuite été éliminé par lessivage. La résistance mécanique des implants a enfin été caractérisée. Il a été montré que des pourcentages de 30 % de charge et 70 % d’agent porogène permettent de produire des implants suffisamment poreux et résistants

Étude par diffraction des rayons X et par spectrométrie d'absorption infrarouge des apatites carbonatées de type A phospho-calcique et arsénio-calcique «haute pression»

Phospho-calcic and arseno-calcic A type carbonated apatites evolve at 950° C when compressed at 40 kilobars. «High pressure » apatites are thermally stabler than uncompressed products. Infrared spectra of «high pressure » apatites show that carbonate ions occupy two different sites. The study of infrared spectrum evolution during the substitution of their carbonate ions by fluoride ions confirms the existence of two sites for carbonate ions. It is possible by treatment of «high pressure » arseno-calcic carbonated apatite to obtain a new apatite without decomposition. In that new apatite all carbonate ions occupy identical sites.Les apatites carbonatées de type A, arsénio-calcique et phosphocalcique comprimées sous 40 kilobars à une température de 9500 C évoluent. Les apatites obtenues sont beaucoup plus stables thermiquement que les produits non comprimés. Les spectres d'absorption infrarouge des apatites «haute pression » montrent que les ions carbonate se trouvent dans deux sites différents. L'étude de l'évolution du spectre d'absorption infrarouge, d'une part, au cours de la décomposition thermique, d'autre part, au cours de la substitution des ions carbonate par des ions fluorure confirme l'existence de deux sites pour les ions carbonate. Dans le cas de l'apatite arsénio-calcique il est possible, par traitement thermique de l'apatite «haute pression », d'obtenir sans décomposition, une apatite dont les ions carbonate occupent des sites identiques.Roux Paul, Bonel Gilbert, Dechambre Gérard. Étude par diffraction des rayons X et par spectrométrie d'absorption infrarouge des apatites carbonatées de type A phospho-calcique et arsénio-calcique «haute pression». In: Bulletin de Minéralogie, volume 101, 4, 1978. pp. 448-452

Etude à la pression ordinaire avant et après traitement sous haute pression, du système Ca3(VO4)2 - Pb3(VO4)2

Ca3(VO4)2 - Pb3(VO4)2 system has been studied at standard pressure using samples previously compressed or not. Various ranges have been determined and phases identified at atmospheric pressure and at 50 kbar. Particularly, after high pressure action, Ca3(VO4)2 gives a monoclinic phase with similar unit cell to low temperature lead vanadate ones.Après traitement sous haute pression le vanadate tricalcique donne naissance à une nouvelle phase. Afin d'identifier cette dernière le système Ca3(VO4)2 - Pb3(VO4)2 a été étudié à la pression normale et sur des échantillons préalablement traités sous pression. Les différentes phases qui apparaissent ont été caractérisées d'une part à la pression atmosphérique, d'autre part à 50 kbar. Le vanadate tricalcique haute pression cristallise dans le système monoclinique avec une maille similaire à celle de la forme très basse température du vanadate de plomb.Roux Paul, Bonel Gilbert, Dechambre Gérard. Etude à la pression ordinaire avant et après traitement sous haute pression, du système Ca3(VO4)2 - Pb3(VO4)2. In: Bulletin de Minéralogie, volume 107, 5, 1984. pp. 635-639

New calcium carbonate-based cements for bone reconstruction

Abstract The feasibility of calcium carbonate-based cements involving the re-crystallization of metastable calcium carbonate varieties has been demonstrated. Two cement compositions were obtained by mixing either calcium carbonate phases (cement A) or a calcium carbonate and a calcium phosphate phase (cement B) with an aqueous media. These cements set and hardened after 30 minutes and 90 minutes respectively. The final composition of cement A was calcite and aragonite whereas cement B lead to a carbonated apatite analogous to bone mineral. Despite poor mechanical properties the presence of a high carbonate content in the final phase might be of interest to increase the cement resorption rate and to favour its replacement by bone tissue. First assays of implantation performed on fresh anatomical pieces (fresh cadavers) at 37°C revealed important advantages of such cement compositions: easiness of use, rapid setting, good adhesion to bone, very good homogeneity and stability of the cement. Introduction Calcium phosphate (CaP) bone cements have developed considerably in the last few years essentially as bone filling and bone reinforcement biomaterial