Développement et applications des biocéramiques

In this study, the osteogenic differentiation of murine pre-osteoblasts cultured on patterned silicon was investigated. Specifically, micropatterns were fabricated in <100> orientation silicon wafers to create linear gratings with a width of either 2 μm (2 μm depth, 10 μm pitch) or 20 μm (2 μm depth, 30 μm pitch). Two subclones (4, 24) of the MC3T3-E1 osteoblast-like cell line were seeded on the micropatterns and cultured in osteogenic induction medium for 28 days. Cells cultured on planar silicon served as the controls. Apatite formation was examined using synchrotron X-ray diffraction. Deposition of [002] and [211]/[112] apatite-like material was clearly observed in subclone 4 (strongly mineralizing) osteoblasts cultured on both micro patterns.

Developing multimodal contrast agents is an upcoming area and hydroxyapatite nanoparticles substituted with various elements like gadolinium, eurobium etc., seems to be a promising contrast agent, especially for multimodal imaging of bone-tissue interface. A bimodal contrast agent using silver (Ag+) and gadolinium (Gd3+) ions co-substituted hydroxyapatite nanoparticles has been developed for X-ray and magnetic resonance imaging. Ag+ and Gd3+ ions were co-substituted into hydroxyapatite at various atomic percentages (Ag:Gd=0.25:0.25, 0.25:0.5, 0.25:0.75) using microwave accelerated wet chemical synthesis. Pure as well as Ag+ and Gd3+ ions substituted hydroxyapatite samples were also synthesized for comparison. All samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy etc., and found to be monophasic, nanocrystalline with the substituted ions. These co-substituted hydroxyapatite samples were then tested in different diagnostic modalities such as X-ray, computed tomography imaging and magnetic resonance imaging. Appreciable variation in contrast was observed with different amount of substitutions. All the Ag+ and Gd3+ ions co-substituted hydroxyapatite nanoparticles showed higher contrast in all imaging modalities compared to those substituted with either Ag+ or Gd3+ ions only. Hydroxyapatite sample co-substituted with 0.25Ag and 0.75Gd at. % substitution showed the best bimodal CT-MRI contrast.

The present work reports an initial engineering approach for fabricating lysozyme-bound regenerated cellulose fiber and film. Glycine-esterified cotton was dissolved in an ionic liquid solvent 1–Butyl–3–methylimidazolium Chloride (BMIMCl) in which lysozyme was activated and covalently attached to cotton cellulose through an enzymatic conjugation between its carboxyl groups and glycine cellulose’s amino groups. The resulting solution was extruded for fiber/film formation in a water bath. After performing a bicinchoninic acid (BCA) protein assay, quantity of attached lysozyme to cellulose fiber/film was evaluated. The study exhibited that a synthesis of lysozyme conjugation on cellulose in BMIMCl could be completed in a control manor, resulting in a cellulose solution suitable for fiber/film production. It was also found that lysozyme could be successfully immobilized onto the cellulose fiber and film regenerated from solution spinning with a reasonable amount ranging from 197.6 to 343.7 μg/mL.mg.

Tricalcium silicate-based materials are growing in popularity for dental procedures. This study reports the physical properties of two experimental tricalcium silicate-based Generex A and B materials. Generex A is designed for vital dental pulp therapy, the repair of root perforations, or to seal a resected root apex. Generex B is designed for nonsurgical root canal procedures as a sealant. ADA 57 and ISO 9917 methods were used for testing in vitro properties of flow, working and setting times, film thickness, dimensional stability, solubility, radiopacity, compressive strength, and freedom from lead and arsenic. In vitro tests of fluid flow were conducted to compare microleakage. Generex A met the ADA 57 and ISO 9917 requirements as they apply for the intended use of this material; Generex B met the ADA 57 requirements for a root canal sealer. Both materials had lower film thickness and higher radiopacity, than ProRoot® MTA. The setting times of the Generex materials were no shorter than MTA, but the handling was very much improved over MTA. Furthermore, these materials sealed as well as the standard ProRoot MTA material. These new materials are suitable for testing in animal models for their intended use.

Hydroxyapatite (HA) is a widely studied biomaterial for bone grafting and tissue engineering applications. The crystal structure of HA lends itself to a wide variety of substitutions, which allows for tailoring of material properties. Cobalt is of interest in ion substitution in HA due to its magnetic properties. The synthesis and characterization of cobalt-substituted Hydroxyapatite (CoHA) has not been widely studied, and there is a complete lack of studies on the sintering behaviors of CoHA materials compared to pure HA. Studying the sintering behavior of a substituted apatite provides insight into which applications are appropriate for the substituted material by supplying information regarding how the substitution affects material characteristics such as stability and bulk mechanical properties. In this study both pure HA and CoHA were synthesized, pressed into pellets, and then sintered at temperatures ranging from 900- 1300°C and 700-1200°C, respectively. The study thoroughly examined the comparative sintering behaviors of the two materials. It was found that CoHA is less thermally stable than pure HA, with decomposition to TCP beginning around 1200°C for pure HA samples, while at 800°C for the CoHA. The CoHA also had a lower mechanical strength than that of the pure HA. Although the CoHA would be unsuitable for bulk applications, it is a promising material for a variety of biomedical applications including drug delivery, cancer hyperthermia, and as a MRI contrast agent.

Compared to cortical bone and polymeric bone cements, the mechanical properties of calcium phosphate cements are generally poor. This has resulted in them being used in non-load bearing clinical applications. The aim of this study was to investigate the possibility of producing a brushite cement with mechanical properties closer to those of cortical bone (i.e., >100 MPa in compression), i.e. with a potential to be used in load bearing applications. With a compressive strength of 74.4 (± 10.7) MPa, maximum at 91.8 MPa, the cement presented herein is comparable with the non degradable polymeric counterparts and the strongest hydroxyapatite cements, and is close in strength of cortical bone. Furthermore, it has a high injectability (>90%) and a setting time of approximately 17 minutes. A cement comprising these properties has great potential of changing the future clinical indications for calcium phosphate cements, and could potentially reduce the use of non-degradable polymeric cements

Different bioactive glass systems have been prepared by sol-gel. However, the production of Na2O-containing bioactive glasses by sol–gel methods has proved to be difficult as the sodium nitrate used in the preparation could be lost from the glass structure during filtration and washing. The aim of this study was to prepare the quaternary system 46S6 of bioactive glass by modified sol-gel techniques with a decrease in the time of gelation. In addition, compare the behaviour of the prepared sol-gel bioactive glass system by its corresponding prepared by melting. The obtained glasses were characterized by using several physicochemical techniques; XRD, FTIR, TEM and SEM beside the effect of the glass particles on the viability of osteoblast like cells (Saos-2). Results show that nanopowders 40-60 nm of 46S6 glass system had been prepared by modified sol-gel (acid-base reaction) method at 600°C in just three days at 600°C. Cell viability by MTT assay confirmed the effectiveness of the prepared nanobioactive glass.

Two types of polymer matrix composites were designed to use as bone replacement: PMMA+HA and PMMA+45S5® Blown Fibers. The materials were tested in vivo for 60 days and compared to two control groups: empty bone defect and porous PMMA. The histology results suggest that both materials provide a suitable scaffold for bone growth with the presence of newly formed bone tissue, blood vessels, osteocytes and osteoblasts cells. For a better understanding of the mechanical properties of scaffolds to bear physiological loads when implanted, compressive tests were carried out. The results showed difference in the compressive behaviour of the two composites, PMMA+HA specimens achieved higher values approaching 9.0 MPa of ultimate strength while PMMA+45S5® had values close to 8.0MPa. Both materials are suitable to bone replacement of small size areas.