Mechanical behavior study of plasma sprayed hydroxyapatite coatings onto Ti6Al4V substrates using scratch test

Mechanical behavior and fracture mechanisms of plasma sprayed hydroxyapatite coatings on Ti-6Al-4V substrate were assessed taking into consideration two variables: the coating thickness and the substrate roughness. The results show that the specimens having a substrate arithmetic average roughness parameter Ra = 2.29 μm is favorable with respect to Ra = 1.23 μm. For coating thickness above 105 μm, cracks can be observed in the coating/substrate interface and the higher critical load Pc2 (used generally in comparative evaluation of adherence) decreases. A 90 μm coating thickness sprayed on a substrate having an arithmetic average roughness parameter Ra equal to 2.29 μm seems to be the best compromise between microstructure, mechanical resistance (high critical loads and fairly good contact quality) and long term stability in the physiological medium (low dissolution rate) for an orthopedic application

Polyurethane/fluor-hydroxyapatite nanocomposite scaffolds for bone tissue engineering. Part I: morphological, physical, and mechanical characterization

In this study, new nano-fluor-hydroxyapatite (nFHA)/polyurethane composite scaffolds were fabricated for potential use in bone tissue engineering. Polyester urethane samples were synthesized from polycaprolactone, hexamethylene diisocyanate, and 1,4-butanediol as chain extender. Nano fluor-hydroxyapatite (nFHA) was successfully synthesized by sol-gel method. The solid–liquid phase separation and solvent sublimation methods were used for preparation of the porous composites. Mechanical properties, chemical structure, and morphological characteristics of the samples were investigated by compressive test, Fourier transform infrared, and scanning electron microscopy (SEM) techniques, respectively. The effect of nFHA powder content on porosity and pore morphology was investigated. SEM images demonstrated that the scaffolds were constituted of interconnected and homogeneously distributed pores. The pore size of the scaffolds was in the range 50–250 μm. The result obtained in this research revealed that the porosity and pore average size decreased and compressive modulus increased with nFHA percentage. Considering morphological, physical, and mechanical properties, the scaffold with a higher ratio of nFHA has suitable potential use in tissue regeneration

MESURE DE LA TENACITE DE L’HYDROXYAPATITE PAR INDENTATION

L’objectif de cette étude est de caractériser le comportement fragile de l’hydroxyapatite (HAP) par évaluation de sa ténacité. Cette ténacité a été estimée pour des d’échantillons sous forme massive et pour des revêtements par indentation Vickers. Pour les échantillons d’HAP sous forme massive, des fissures de type Médian sont visibles à chaque coin des empreintes pour des charges ≥ 200g. Un phénomène de fissuration latérale pouvant conduire à un écaillage est observé pour les charges testées les plus élevées. La mesure de la longueur des fissures, couplée à l’utilisation de la formule analytique d’Evans et Charles, permet de calculer une valeur de ténacité qui est inférieure au MPa.m1/2. Pour les revêtements d’HAP, l’indentation latérale produit des empreintes qui sont accompagnées d’un phénomène de multi-fissuration. En intégrant ce phénomène de multi-fissuration, la valeur de la ténacité estimée pour les revêtements d’HAP est du même ordre de grandeur que celle des échantillons sous forme massive

MESURE DE LA TENACITE DE L’HYDROXYAPATITE PAR INDENTATION

L’objectif de cette étude est de caractériser le comportement fragile de l’hydroxyapatite (HAP) par évaluation de sa ténacité. Cette ténacité a été estimée pour des d’échantillons sous forme massive et pour des revêtements par indentation Vickers. Pour les échantillons d’HAP sous forme massive, des fissures de type Médian sont visibles à chaque coin des empreintes pour des charges ≥ 200g. Un phénomène de fissuration latérale pouvant conduire à un écaillage est observé pour les charges testées les plus élevées. La mesure de la longueur des fissures, couplée à l’utilisation de la formule analytique d’Evans et Charles, permet de calculer une valeur de ténacité qui est inférieure au MPa.m1/2. Pour les revêtements d’HAP, l’indentation latérale produit des empreintes qui sont accompagnées d’un phénomène de multi-fissuration. En intégrant ce phénomène de multi-fissuration, la valeur de la ténacité estimée pour les revêtements d’HAP est du même ordre de grandeur que celle des échantillons sous forme massive

Mechanical behavior study of plasma sprayed hydroxyapatite coatings onto Ti6Al4V substrates using scratch test

Mechanical behavior and fracture mechanisms of plasma sprayed hydroxyapatite coatings on Ti-6Al-4V substrate were assessed taking into consideration two variables: the coating thickness and the substrate roughness. The results show that the specimens having a substrate arithmetic average roughness parameter Ra = 2.29 μm is favorable with respect to Ra = 1.23 μm. For coating thickness above 105 μm, cracks can be observed in the coating/substrate interface and the higher critical load Pc2 (used generally in comparative evaluation of adherence) decreases. A 90 μm coating thickness sprayed on a substrate having an arithmetic average roughness parameter Ra equal to 2.29 μm seems to be the best compromise between microstructure, mechanical resistance (high critical loads and fairly good contact quality) and long term stability in the physiological medium (low dissolution rate) for an orthopedic application

Surface Cracking and Degradation of Dense Hydroxyapatite through Vickers Microindentation Testing

Surface degradation and cracking of dense hydroxyapatite were evaluated through Vickers micro indentation using indentation loads ranged from 25 gf to 2000 gf. Crack lengths, imprint diameters and the number of lateral cracks and chips were measured using SEM. The crack length-indentation load data were analyzed with regard to the specific relations of Palmqvist and fully developed radial cracks. Crack type transition load from Palmqvist to median crack was experimentally assessed through serial sectioning technique. The analytical estimated transition load, based on the theoretical relation of the indentation load and crack lengths showed a good agreement with one obtained from experimental itinerary. Palmqvist and median cracks were identified in low and medium indentation loads, respectively. High indentation load could also lead to the formation of lateral cracks and chips. The tendency for lateral cracking was evaluated taking into account the number of lateral cracks and chips. The chips were found to be appeared just after test in higher indentation load, whereas in medium loads they could be detectable only after several weeks

Bone Tissue Response to Plasma Sprayed Hydroxyapatite Coatings: An In Vivo Study on Rabbit Femoral Condyles

In this study, hydroxyapatite was coated on titanium substrates by plasma spraying process. A well-known porous and lamellar microstructure was found in the lateral and outer surface of coating. The phase composition was studied by XRD and the morphological and the microstructural aspects were investigated by scanning electron and optical microscopy. The hardness of coatings and substrates was measured by Vickers indentation method. For in vivo study, rabbit condyles were exposed to two groups of coated and uncoated samples. Radiographyically, different parameters such as bone lysis, sclerosis, displacement of samples and bone resorption were taken into consideration and no statistically differences between the two groups, with no sign of infection on the edges of each hole were found. Histopathological interpretation of all coated samples indicated that the extent of callus and thickness of speculae were quite distinct from that of uncoated group. In this group, the space between implant and canal was filled up with matured connective tissues and plenty of bone speculae of woven bone in nature. However, these speculaes were thinner and immature as compared to coated samples

Design and Manufacture of Bone Cements Based on Calcium Sulfate Hemihydrate and Mg, Sr-Doped Bioactive Glass

In the present study, a novel composite bone cement based on calcium sulfate hemihydrate (CSH) and Mg, Sr-containing bioactive glass (BG) as solid phase, and solution of chitosan as liquid phase were developed. The phase composition, morphology, setting time, injectability, viscosity, and cellular responses of the composites with various contents of BG (0, 10, 20, and 30 wt.%) were investigated. The pure calcium sulfate cement was set at approximately 180 min, whereas the setting time was drastically decreased to 6 min by replacing 30 wt.% glass powder for CSH in the cement solid phase. BG changed the microscopic morphology of the set cement and decreased the size and compaction of the precipitated gypsum phase. Replacing the CSH phase with BG increased injection force of the produced cement; however, all the cements were injected at a nearly constant force, lower than 20 N. The viscosity measurements in oscillatory mode determined the shear-thinning behavior of the pastes. Although the viscosity of the pastes increased with increasing BG content, it was influenced by the frequency extent. Pure calcium sulfate cement exhibited some transient cytotoxicity on human-derived bone mesenchymal stem cells and it was compensated by introducing BG phase. Moreover, BG improved the cell proliferation and mineralization of extracellular matrix as shown by calcein measurements. The results indicate the injectable composite cement comprising 70 wt.% CSH and 30 wt.% Mg, Sr-doped BG has better setting, mechanical and cellular behaviors and hence, is a potential candidate for bone repair, however more animal and human clinical evaluations are essential.The present work was financially supported by Materials and Energy Research Center (MERC, Karaj, Iran) through grant No. 781399055. The APC was funded by Alireza Dolatshahi-Pirouz

Bone Tissue Response to Plasma Sprayed Hydroxyapatite Coatings: An In Vivo Study on Rabbit Femoral Condyles

In this study, hydroxyapatite was coated on titanium substrates by plasma spraying process. A well-known porous and lamellar microstructure was found in the lateral and outer surface of coating. The phase composition was studied by XRD and the morphological and the microstructural aspects were investigated by scanning electron and optical microscopy. The hardness of coatings and substrates was measured by Vickers indentation method. For in vivo study, rabbit condyles were exposed to two groups of coated and uncoated samples. Radiographyically, different parameters such as bone lysis, sclerosis, displacement of samples and bone resorption were taken into consideration and no statistically differences between the two groups, with no sign of infection on the edges of each hole were found. Histopathological interpretation of all coated samples indicated that the extent of callus and thickness of speculae were quite distinct from that of uncoated group. In this group, the space between implant and canal was filled up with matured connective tissues and plenty of bone speculae of woven bone in nature. However, these speculaes were thinner and immature as compared to coated samples