Effect of grain orientation and magnesium doping on β-tricalcium phosphate resorption behavior

The efficiency of calcium phosphate (CaP) bone substitutes can be improved by tuning their resorption rate. The influence of both crystal orientation and ion doping on resorption is here investigated for beta-tricalcium phosphate (β-TCP). Non-doped and Mg-doped (1 and 6 mol%) sintered β-TCP samples were immersed in acidic solution (pH 4.4) to mimic the environmental conditions found underneath active osteoclasts. The surfaces of β-TCP samples were observed after acid-etching and compared to surfaces after osteoclastic resorption assays. β-TCP grains exhibited similar patterns with characteristic intra-crystalline pillars after acid-etching and after cell-mediated resorption. Electron BackScatter Diffraction analyses, coupled with Scanning Electron Microscopy, Inductively Coupled Plasma–Mass Spectrometry and X-Ray Diffraction, demonstrated the influence of both grain orientation and doping on the process and kinetics of resorption. Grains with c-axis nearly perpendicular to the surface were preferentially etched in non-doped β-TCP samples, whereas all grains with simple axis (a, b or c) nearly normal to the surface were etched in 6 mol% Mg-doped samples. In addition, both the dissolution rate and the percentage of etched surface were lower in Mg-doped specimens. Finally, the alignment direction of the intra-crystalline pillars was correlated with the preferential direction for dissolution. Statement of significance: The present work focuses on the resorption behavior of calcium phosphate bioceramics. A simple and cost-effective alternative to osteoclast culture was implemented to identify which material features drive resorption. For the first time, it was demonstrated that crystal orientation, measured by Electron Backscatter Diffraction, is the discriminating factor between grains, which resorbed first, and grains, which resorbed slower. It also elucidated how resorption kinetics can be tuned by doping β-tricalcium phosphate with ions of interest. Doping with magnesium impacted lattice parameters. Therefore, the crystal orientations, which preferentially resorbed, changed, explaining the solubility decrease. These important findings pave the way for the design of optimized bone graft substitutes with tailored resorption kinetics

Infrared mapping of inorganic materials: a supervised method to select relevant spectra

cited By 0Spectroscopic imaging is expanding thanks to new instrumental concepts, technological developments, easier use and lower costs. This leads to collect and to handle huge hyperspectral databases. Among data providing useful information, there may also be unwanted information (i.e., either biased or irrelevant with respect to the information one wants to retrieve from the analysis). The classical approach aims at building a spectra library, which contains both informative spectra and outliers, so as to train learning algorithms. However, reference spectra cannot always be acquired, especially for samples prone to ageing or changes when exposed to humidity, temperature… Thus, building a library with reference spectra is not always possible. To handle this issue, a new supervised method (SSMS for Supervised Selective Method based on SIMPLISMA) has been designed and is described in this article, to identify and exclude unwanted spectra from the resolution process when no library is available. SSMS relies on a supervised exclusion of the unwanted spectra. It ensures both a quick treatment and an accurate analysis of the data (reduced number of representative spectra to supervise). This new method is applicable to any type of hyperspectral database. In this work, its efficiency is demonstrated on a database acquired using a FT-IR microscope. To avoid issues arising from the acquisition of maps with classic ATR crystals (cross-contamination and successive residual imprints on the material), the use of a new set-up called static-ATR is explored. In addition, the combined use of SSMS and of a physical model permits to identify the origins of the outlier spectra. Thus, it becomes possible to improve the experimental method (sample preparation, acquisition parameters…). Finally, with a constrained Alternating Least Squares method (ALS), relevant chemical information is obtained. The robust method developed here permits to achieve chemical maps at the micron scale for inorganic materials. © 2019 Elsevier B.V

Spherical instrumented indentation as a tool to characterize porous bioceramics and their resorption

Resorbable ceramics used as porous bone substitutes are designed to favor bone in-growth and to be gradually replaced by natural tissues after in vivo resorption. However, a lack of experimental techniques to quantitatively monitor the evolution of their mechanical properties during resorption is noted. In this paper, we propose to use spherical instrumented indentation to follow-up the resorption of microporous resorbable ceramics at a local scale. Tests were performed at the core and at the surface of samples immersed for different durations in model fluids. Instrumented indentation was found to be an efficient technique to characterize and to follow-up the resorption of microporous ceramics, in excellent agreement with microstructural changes observed with X-ray diffraction and X-ray tomography. Instrumented indentation has the ability to capture the presence of gradients in the samples, enables the direct testing of wet samples and appears as a superior technique to compression tests mostly used in the literature

Spherical instrumented indentation as a tool to characterize porous bioceramics and their resorption

cited By 0Resorbable ceramics used as porous bone substitutes are designed to favor bone in-growth and to be gradually replaced by natural tissues after in vivo resorption. However, a lack of experimental techniques to quantitatively monitor the evolution of their mechanical properties during resorption is noted. In this paper, we propose to use spherical instrumented indentation to follow-up the resorption of microporous resorbable ceramics at a local scale. Tests were performed at the core and at the surface of samples immersed for different durations in model fluids. Instrumented indentation was found to be an efficient technique to characterize and to follow-up the resorption of microporous ceramics, in excellent agreement with microstructural changes observed with X-ray diffraction and X-ray tomography. Instrumented indentation has the ability to capture the presence of gradients in the samples, enables the direct testing of wet samples and appears as a superior technique to compression tests mostly used in the literature. © 2019 Elsevier Lt

The in vitro evolution of resorbable brushite cements: A physico-chemical, micro-structural and mechanical study

The mechanisms by which calcium phosphate bone substitutes evolve and are resorbed in vivo are not yet fully known. In particular, the formation of intermediate phases during resorption and evolution of the mechanical properties may be of crucial interest for their clinical efficiency. The in vitro tests proposed here are the first steps toward understanding these phenomena. Microporous Dicalcium Phosphate Dihydrate (DCPD) samples were immersed in tris(hydroxymethyl)aminomethane (TRIS) and Phosphate Buffered Saline (PBS) solutions, with or without daily refresh of the medium, for time-points up to 14 days. Before and after immersion, samples were extensively characterised in terms of morphology, chemistry (XRD coupled with Rietveld analysis), microstructure (X-ray tomography, SEM observations) and local mechanical properties (instrumented micro-indentation). The composition of the immersion solutions was monitored in parallel (pH, elemental analysis). The results show the influence and importance of the experimental set-up and protocol on the formation of apatite and octacalcium phosphate concurrently to DCPD dissolution; moreover, strong inter-correlations between physico-chemistry, microstructure and mechanics are demonstrated. Statement of Significance Ideally, the resorption kinetics of biodegradable bone substitutes should be controlled to favor the healing processes of bone. Although biodegradable bone grafts are already used in surgeries, their resorption process is still partially unknown. The present work studies these resorption phenomena, their kinetics and mechanisms and their consequences on the properties of a calcium phosphate resorbable material. The original in vitro approach developed in this work couples for the first time physico-chemical, micro-structural and mechanical assessments. The dissolution of the CaP phase in body fluids and the reprecipitation of more stable phases are studied on a local scale, which has permitted to evidence and monitor the development of a gradient of properties between the surface and the core of the samples

4D in situ monitoring of the setting of alpha plaster using synchrotron X-ray tomography with high spatial and temporal resolution

International audienceThis paper is dedicated to the in situ follow up of the setting of an α plaster using synchrotron X-ray tomography, with a high spatial resolution, down to 0.3 µm (0.16 µm voxel size), and a high time resolution with a scan every 30 s. This combination of spatial and time resolution is amongst the best reported in the literature so far and is of particular interest for the study of moderately rapid transformation of the microstructure at a small scale. It enables to characterize both the dissolution of hemihydrate particles and the precipitation of gypsum crystals. A dissolution rate for the hemihydrate particles is determined, in good coherence with previous work on β plaster using lab X-ray tomograph. A thickening of gypsum crystals with hydration time is also noted. A quantitative analysis of hydration is performed through the calculation of a microstructural degree of reaction from the X-ray tomography volumes, after peak deconvolution of the gray value histogram at different hydration times

3-D printing of chitosan-calcium phosphate inks: rheology, interactions and characterization

Bone substitute fabrication is of interest to meet the worldwide incidence of bone disorders. Physical chitosan hydrogels with intertwined apatite particles were chosen to meet the bio-physical and mechanical properties required by a potential bone substitute. A set up for 3-D printing by robocasting was found adequate to fabricate scaffolds. Inks consisted of suspensions of calcium phosphate particles in chitosan acidic aqueous solution. The inks are shear-thinning and consist of a suspension of dispersed platelet aggregates of dicalcium phosphate dihydrate in a continuous chitosan phase. The rheological properties of the inks were studied, including their shear-thinning characteristics and yield stress. Scaffolds were printed in basic water/ethanol baths to induce transformation of chitosan-calcium phosphates suspension into physical hydrogel of chitosan mineralized with apatite. Scaffolds consisted of a chitosan polymeric matrix intertwined with poorly crystalline apatite particles. Results indicate that ink rheological properties could be tuned by controlling ink composition: in particular, more printable inks are obtained with higher chitosan concentration (0.19 mol·L−1)