Ya. Yu. Filippov

Modifying brushite-containing phosphate cements by complexing additives

The use of citric acid, sodium pyrophosphate, and sodium tri- and hexametaphosphates is studied as additives intended to retard the curing of brushite cements for convenience of their osteoplastic use. The effects of these additives on the curing rates, microstructures, and mechanical properties of these cements are studied.

Carbonate substituted hydroxyapatite (CHA) powder consolidated at 450°C

CHA powder was consolidated without noticeable changing of its carbonate content using low-melting Na-Ca phosphate glass with the composition referred to 54% Na4CaP6O18 and 46% Na2CaP2O7 as a binder. A temperature window suitable for obtaining the composite was assessed as 450 – 475°C. The composites obtained at 450°C and 400 MPa for 1 hr demonstrate compressive strength up to 25 MPa.

Porous Ceramic Based on Calcium Pyrophosphate

Porous ceramic, whose composition is mainly represented by calcium β-pyrophosphate β-Ca2P2O7, is prepared from a porous mixture containing synthetic calcium γ-pyrophosphate γ-Ca2P2O7 and milled 1-aqueous sodium dihydrophosphate in an amount from 2.5 to 40 wt.%. Ceramic sintering proceeds by a liquid-phase sintering mechanism due to melt formation in the system Na2O–CaO–P2O5. Ceramic microstructure after firing in the range 800 – 1000°C makes it possible to consider sodium polyphosphate not only as a component facilitating sintering by a liquid-phase mechanism, but also as an inorganic pore-forming agent.

Reaction-Associated Resorbable Phosphate Materials: Production and Testing in Vitro

The properties of reaction-associated calcium-phosphate materials obtained by pressing paste based on α-tricalcium phosphate with subsequent holding in different solutions are presented. The phase composition, solubility and mechanical characteristics of the materials obtained are studied and biological tests in vitro are performed.

Ceramics Based on Brushite Powder Synthesized from Calcium Nitrate and Disodium and Dipotassium Hydrogen Phosphates

Brushite (CaHPO4 · 2H2O) powder has been synthesized in aqueous 1.0 M solutions of calcium nitrate dipotassium hydrogen phosphate, and disodium hydrogen phosphate at a Ca/P ratio of unity, without adjusting the pH of the reaction. After synthesis and drying, the fraction of a reaction by-product (NaNO3, KNO3, or their mixture) in the powder was about 20 wt %. After firing at temperatures from 800 to 1000°C, the ceramics prepared using the powder synthesized from Ca(NO3)2 and Na2HPO4 consisted of β-Ca2P2O7 and β-NaCaPO4. After firing at temperatures from 900 to 1100°C, the ceramics prepared using the powder synthesized from Ca(NO3)2 and K2HPO4 consisted of Са10К(РО4)7 and СаК2Р2О7. The ceramic composites produced in this study can be recommended as materials for resorbable bone implants.

Iron-substituted tricalcium phosphate ceramics

Porous iron-substituted tricalcium phosphate (FeTCP) ceramics with a Fe content of 0.49 and 1.09% has been developed. The hydrostatically estimated ceramics porosity is 40–45%. The solubility of ceramics in an isotonic solution has been studied. The solubility rate of FeTCP ceramics is slightly higher as compared with iron-free ceramics. Based on the results of in vitro tests of FeTCP ceramics on cultured fibroblasts, these materials are believed to be biocompatible. The developed materials can be recommended for use in medicine in the treatment of diseases associated with bone lesions.

Copper-substituted tricalcium phosphates

Copper-substituted tricalcium phosphates (CuTCP) with different copper contents were developed using precipitation of copper-containing amorphous calcium phosphates (ACP) from salt solutions followed by heat treatment. Porous CuTCP ceramic was obtained using negative replicas. Using a set of investigation methods (powder X-ray diffraction, IR spectroscopy, ESR spectroscopy, and scanning electron microscopy), all copper-substituted tricalcium phosphates were found to have the whitlockite structure with copper incorporated in TCP in the 2+ oxidation state. The resulting material is promising for the use in regenerative medicine owing to higher solubility in body fluids compared with TCP and combination of bactericidal properties and the lack of cytotoxicity.

Powder Mixtures Based on Calcium Hydroxyapatite and Sodium Salts

Powder mixtures based on calcium hydroxyapatite (HAP) and sodium salts in the amount corresponding to 25 mol % of Na2O in the Na2O–CaO–P2O5 system were studied by isothermal exposures in the range of 600—1200°C. According to XRD data, the phase composition of the samples of HAP/Na2CO3 after calcination included HAP, β-CaNaPO4, and CaO. The phase composition of the ceramic samples from the HAP/Na2HPO4 powder mixture after calcination contained the phases of β-CaNaPO4 and Na4P2O7. The phase composition of the ceramic samples from the powder mixture of HAP/NaH2PO4 after calcination contained Ca2P2O7, Ca10Na(PO4)7, β-CaNaPO4, CaNa2P2O7, and Na4P2O7. The presence of sodium salts in the amount corresponding to 25 mol % of Na2O in the Na2O–CaO–P2O5 system provided the occurrence of liquid- phase sintering in compact preforms from the studied powder mixtures. However, the presence of the water-soluble salt Na4P2O7 in ceramic samples of HAP/Na2HPO4 and HAP/NaH2PO4 after calcination imposes a restriction on the use of such materials in contact with an aqueous medium. And the presence of CaO in the HAP/Na2CO3 samples excludes the use of such materials as bone implants.

Reinforcement of Brushite Cement Based on α-TCP by Rigid Polylactide Framework

Brushite cement obtained from α-Ca3(PO4)2 and orthophosphoric acid in the presence of Mg(H2PO4)2 with compressive strength of 18 MPa was armored with a framework with the Kelvin architecture made of polylactide by thermoextrusion 3D printing. It is shown that armoring of cement with polylactide framework allows one not only to increase the compressive strength of such a structure (up to 35 MPa) but also to significantly improve its deformability (up to 15%).

Preparation of β-Ca 3 (PO 4 ) 2 /Poly(D,L-lactide) and β-Ca 3 (PO 4 ) 2 /Poly(ε-caprolactone) Biocomposite Implants for Bone Substitution

Highly permeable macroporous implants of various architectures for bone grafting have been fabricated by thermal extrusion 3D printing using highly filled β-Ca3(PO4)2/poly(D,L-lactide) (degree of filling up to 70 wt %) and β-Ca3(PO4)2/poly(ε-caprolactone) (degree of filling up to 70 wt %) composite filaments. To modify the surface of the composite macroporous implants with the aim of improving their wettability by saline solutions, we have proposed exposing them to a cathode discharge plasma (2.5 W, air as plasma gas) in combination with subsequent etching in a 0.5 M citric acid solution. It has been shown that the main contribution to changes in the wettability (contact angle) of the composites is made by the changes produced in their surface morphology by etching in a low-temperature plasma and citric acid. An alternative approach to surface modification of the composites is to produce a carbonate hydroxyapatite layer via precipitation from a simulated body fluid solution a factor of 5 supersaturated relative to its natural analog (5xSBF).