Designing, fabrication and characterization of nanostructured functionally graded HAp/BCP ceramics

Abstract

Nanostructured calcium phosphate functionally graded materials (FGMs) with simultaneous gradients of density, phase composition, and mechanical properties were fabricated by consecutive uniaxial pressing of stoichiometric (SHAp) and calcium deficient (CDHAp) hydroxyapatite powders in multilayered samples and reaction sintering. During sintering procedure SHAp composition remained stable (HAp) while CDHAp was phase transformed in biphasic calcium phosphate (BCP, i.e. HAp þβ-TCP) yielding HAp/BCP FGMs. To reduce mismatch stress between adjacent layers, generated during sintering, gradient of phase composition was optimized by introducing intermediate layer(s) made from a mixture of SHAp and CDHAp in an appropriate mass ratio. Optimal processing conditions for preparation of nanostructured ceramics were provided via two-step sintering. High-quality FGMs structure, without delamination, cracks and micro-structural damages was observed by an SEM technique; moreover, a detailed examination by FE-SEM established the unidirectional (perpendicular with respect to the layers) gradual change of microstructure, from fully dense to $40% of porosity. Detailed micro-Raman and FTIR spectroscopy studies showed an increase of β-TCP amount along the FGMs height, confirming gradient of phase composition. Mechanical properties measured by microindentation revealed gradual change of microhardness from 650 to 115 HV, with simultaneous change of Young's modulus from 92 to 24 GPa.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

“…Based on in vitro tests, cellular activity reached a maximum in the case of LENS™-PS HAp coating. Marković et al [ 564 ] fabricated nanostructured functionally graded HAp/Hap + β-TCP(BCP) by sintering. Farnoush et al [ 565 ] formed functionally graded HAp-TiO 2 nanostructured composite coating on Ti–6Al–4V substrate via electrophoretic deposition.…”

Chitosan-PLGA polymer blends as coatings for hydroxyapatite nanoparticles and their effect on antimicrobial properties, osteoconductivity and regeneration of osseous tissues

“…The room for such improvements is apparently limitless. As for the control of microstructure, it is known that parameters such as morphology [6], crystallinity [7], grain [8] and particle size [9,10], topography [11], porosity [12] or compositional gradient [13] have an immense effect on the physical properties and bioactivity of HAp. As for doping HAp, each of its three constitutive ions — calcium, phosphate and hydroxyl — can be substituted with other ions and dozens of chemically different forms of HAp are known so far [14].…”

In vitro bioactivity study of TiCaPCO(N) and Ag‐doped TiCaPCO(N) films in simulated body fluid

“…Figure compares the Raman shift spectra of the PED films with those of the Biogran control and HA powder. HA is characterized by the typical apatite phosphate ( ) mode at 963 cm −1 (P–O symmetric stretching mode, ν1) and the vibration bands at 429 cm −1 (ν2) and 450 cm −1 (ν2) which are attributed to the OPO bending modes . It can be seen that in the case of the Biograin sample, a strong Raman peak at 963 cm −1 appeared after as long as 7 days of exposure to SBF whereas 28 days were needed to form a CaP‐based phase on the surface of the PED TiCaPCO film.…”