Preparation And Properties Of GdPO₄ Dopedhydroxyapatite Bioceramic Materials

Bioceramic refers to a type of material with a specific biological or physiological function,which is mainly used for the repairation and reconstruction of human bone tissue.Hydroxyapatite（HA）commonly used for hard tissue repairation,however,is difficult to be processed due to its relatively poor toughness.For practical applications in clinical medicine,it cannot meet the repairing requirements of bone defects with different shapes.Therefore,it is gently necessary to improve the mechanical properties.In this paper,the preparation and properties of GdPO₄ doped HA bioceramics（HA-GP）are investigated.A modified sol-gel method was employed to produce HA-GP.The phase compositions,microstructure and mechanical properties of the ceramics were studied.The composition with the best properties was chosen for evaluating its magnetic resonance imaging performance.This paper provides a new scheme for the application of the modified hydroxyapatite in the field of clinical medicine.The synthesized process of the powders by a sol-gel method was investigated.Based on the experimental results,the effects of reactant concentration,dropping rate,pH value of reaction solution,stirring,drying and sintering on the synthetic powders were clear.The modified sol-gel method process was described as follows:Ca（NO₃）₂?4H₂O,C₆H₈O₇?H₂O and（NH₄）₂HPO₄ were dissolved in deionized water in turn.The pH value of the reaction solution was adjusted to 2.5.The solution was slowly stirred by magnetic force,and then dried under the air blast.After sintering at 650°C for 2 h and 900°C for 4 h,the HA powders with excellent crystalline can be obtained.HA-GP bioceramics were synthesized by the modified sol-gel method,and their phase composition,microstructure and mechanical properties were investigated.The as-fabricated HA-GP consisted of Ca₁₀（PO₄）₆（OH）₂ andβ-Ca₃（PO₄）₂.The content of theβ-Ca₃（PO₄）₂ had a decrease trend initially,followed by a significant increase with the doping of GdPO₄.With the addition of GdPO₄,the sinterability of HA-GP was enhanced,and the grains were refined.However,when the doping amount is excessive,the porosity and grain size of HA-GP had a significant increase.The mechanical properties can be improved significantly by doping GdPO₄.Compared with HA,the hardness of HA-GP was enhanced nearly 3 times,and its fracture toughness gained an increase nearly 44%.7.5 mol%GdPO₄ doped HA（HA-GP7.5）had the best comprehensive properties.It only had a pure Ca₁₀（PO₄）₆（OH）₂,and the hardness and fracture toughness were 4.5GPa and 1.44 MPa?m^1/2,respectively.The magnetic resonance imaging performance of HA-GP7.5 solutions was investigated.The longitudinal relaxation（T₁）weighted imaging brightened gradually with increasing the concentration of ceramic powders aqueous solution,while the transverse relaxation（T₂）weighted imaging darkened gradually with the concentration increasing,indicating that the contrast and resolution of magnetic resonance imaging was enhanced significantly.