Synthetic bone grafts based on hydroxyapatite–alpha tricalcium phosphate (HA/α‐TCP) biphasic system are preferred for their higher resorbability and bioactivity. In this work, a viable method is suggested to produce HA/α‐TCP systems with enhanced bioactivity and mechanical strength, through the in situ conversion of calcium‐deficient apatite precursor. A homogeneous precipitation technique was used to produce the precursor powder. It was heat‐treated to study the phase conversion using XRD and FTIR. The precursor got converted HA/β‐TCP system above 762°C, which further transformed to HA/α‐TCP system after 1165°C. The sintering temperature was optimized at 1175°C. It is the net Ca/P ratio of the precursor which decides the ratio of the phases in the final ceramic. The precursor with Ca/P = 1.585 gave a biphasic ceramic containing 47% α‐TCP. The flexural strength of this sample was more than 2.5 times higher compared to the biphasic ceramic made by sintering HA/α‐TCP powder mix. The internal microstructure of the ceramic revealed the formation of α‐TCP in sheet‐like morphology. Preferential dissolution of the α‐TCP from the sample surface in aqueous and acidic environment was confirmed quantitatively. Biomimetic growth technique in simulated body fluid has been used to assess the bioactivity in vitro.
Calcium sulfate dihydrate, constituted as uniform crystals of low dimensions, is a potential biomaterial for clinical applications like bone graft substitution and drug delivery. In this work, isopropyl alcohol has been used as a solvent to obtain low dimensional calcium sulfate dihydrate crystals from calcium nitrate ‐ sulfuric acid system. Reactants in 0.5 molar concentration at ambient conditions generated uniform rod‐shaped crystals of length 3–5 µm. Analysis using X‐ray Diffractometry and Fourier Transform Infrared Spectrometry showed the material to be well crystallized, phase‐pure calcium sulfate dihydrate.The nucleation kinetics has been studied by observing the induction time of phase formation in solutions of millimolar concentrations through turbidimetry at 300 K. The data have been analysed using classical nucleation theory to deduce parameters like interfacial tension (or surface free energy), nucleation rate and critical radius. The surface free energy obtained (5.6 mJ/m2) is comparatively lower than that reported for aqueous precipitation, which could be attributed to the presence of isopropyl alcohol. On escalating the supersaturation ratio, the nucleation rate drastically increased and the critical radius decreased exponentially. Particles formed at supersaturation 1.39 showed a monomodal distribution centered at 8.2 nm in Dynamic Light Scattering analysis. Comparable particle sizes were obtained in Transmission Electron Microscopy.
Bioactive ceramic coatings based on calcium phosphates yield better functionality in the human body for a variety of metallic implant devices including orthopaedic and dental prostheses. In the present study chemically and hence functionally gradient bioceramic coating was obtained by pulsed laser deposition method. Calcium phosphate bioactive ceramic coatings based on hydroxyapatite (HA) and tricalcium phosphate (TCP) were deposited over titanium substrate to produce gradation in physico-chemical characteristics and in vitro dissolution behaviour. Sintered targets of HA and α-TCP were deposited in a multi target laser deposition system. The obtained deposits were characterized by X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray analysis. Inductively coupled plasma spectroscopy was used to estimate the in vitro dissolution behaviour of coatings. The variation in mechanical property of the gradient layer was evaluated through scratch test and micro-indentation hardness. The bioactivity was examined in vitro with respect to the ability of HA layer to form on the surface as a result of contact with simulated body fluid. It could be inferred that chemically gradient functional bioceramic coating can be produced by laser deposition of multiple sintered targets with variable chemical composition.
The correlations of the tumor marker, tumor volume and SUV changes on PET-CT, and LDH levels themselves, and with OS, support the concept of a biological response to RMB implantation and the validity of the biological-systems approach to mCRC. A phase III clinical trial is planned.
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