Freeze casting is a fabrication method that allows producing near‐net‐shaped ceramics with variable porosity. Hydroxyapatite (HA) was modified by the addition of different amounts of SiO2 nanoparticles during freeze cast preparation. The addition of SiO2 introduced a partial phase transformation of HA to β‐tricalcium phosphate and improved the form stability due to less shrinkage after sintering. The impact of surface roughness of pure HA ceramics and the influence of SiO2 introduction during freeze casting on adhesion, proliferation, and differentiation of human osteoblast‐like cells (MG‐63) was investigated. While both cell attachment and proliferation of smooth pressed HA was significantly enhanced compared to rough freeze cast HA, the addition of SiO2 improved the cell numbers of the latter. The expression of cell differentiation markers osteocalcin and collagen I was found to be supported by rough surfaces (Ra = 5–6 µm) in particular on ceramics containing SiO2

Ceramics based on calcium phosphates is known to be a prospective material for biomedical applications. Noticeable attention is paid to hydroxyapatite Ca10(PO4)6(OH)2 (HAp) due to its affinity to a bone mineral. It was recognized recently that Si‐doped HAp is a highly promising material in sense of bioactivity improvement. In the frame of distinct research activity structured around this subject, some special problems are to be solved: (1) solubility of Si in the bulk of HAp lattice (and its limit) vs. segregation of Si to free surfaces and grain boundaries, (2) rationalization of Si effect on sintering of HAp ceramics, (3) charge compensation over aliovalent doping of HAp with Si and its interplay with thermal stability of HAp phase.The work was focused on a fabrication of Si‐HAp with Ca10(Po4)6‐x(SiO4)x(OH)2‐x (x=0..1) nominal composition and evaluation the effect of Si on sintering of HAp ceramics. The limit of Si solubility in HAp lattice was estimated to be not higher than x=0.1 in the formula above (at 1000 °C, according to XRD and SEM/EDX). The essence of the silicon influence consists in significant suppression of grain growth during the initial stage of sintering. Silicon doping reduces grain boundary mobility (increasing activation energy of lattice diffusion) along with the increase of pore mobility (in fact, increasing grain boundary diffusion). We believe that the effect of Si on sintering behaviour can be treated in terms of its segregation to grain boundaries, the phenomenon arising from a lattice instability of Si‐HAp due to the charge compensation in the course of aliovalent doping.

No abstract

Calcium phosphate ceramics have a high potential for biomedical applications. In this work Si-modified calcium phosphate ceramics were prepared from the silica-containing hydroxylapatite (HAp) suspensions using the freeze gelation technique, an environment-friendly low-cost method for the near-net-shape fabrication of ceramic components. Sintering behavior, phase composition, and microstructural characteristics of HAp with varying silica content were studied using dilatometry, thermogravimetry, XRD, REM, and Hg-intrusion. It was shown that the addition of silica has an essential effect on the sintering behavior and the phase composition of the samples and allows the in situ control over the HAp/Si-HAp to tricalcium phosphate (TCP)/Si-TCP ratio.

No abstract