N. D. Pinchuk

Preparation and Properties of Hydroxyapatite Strengthened with a Glass Phase

A method is described for preparing hydroxyapatite strengthened with a glass phase. The properties of the composites obtained containing both biological and synthetic hydroxyapatite are studied. Characteristics of the test materials such as pycnometric density, volumetric porosity, biological solubility, and mechanical strength are determined.

The Structure and Properties of Calcium Phosphate Ceramics Produced from Monetite and Biogenic Hydroxyapatite

It is shown that porous calcium phosphate ceramics can be produced from monetite and biogenic hydroxyapatite, the starting materials being in the ratios 25 : 75, 50 : 50, and 75 : 25 wt.%. It is established that phase transitions and solid-phase reactions take place during sintering to form polyphosphate ceramics consisting of hydroxyapatite (Ca5(PO4)3(OH)), β-pyrophosphate (β-Ca2P2O7), and β-tricalcium phosphate (β-Ca3(PO4)2), in which β-Ca2P2O7 and Ca5(PO4)3(OH) phases are predominant, depending on starting composition. When the biogenic hydroxyapatite content changes from 25 to 75 wt.%, the grain size decreases and the pore size increases. The ceramics have 40 to 42% porosity with predominant open porosity for all compositions. The ceramics show 32–55 MPa strength, which increases with the amount of biogenic hydroxyapatite in starting composition.

Synthesis and Properties of Si-Modified Biogenic Hydroxyapatite Ceramics

The paper examines the production of Si-modified biogenic hydroxyapatite ceramics. The introduction of methylsilicic acid hydrogel in amounts converted to 2 and 5 wt.% Si and subsequent sintering at 600°C increase the specific surface area by 10 times, from 6.1 to 59.8 m2/g. The porosity of ceramics increases from 43.0 to 62.3% when the modifying addition reaches up to 5 wt.%, the compressive strength being equal to 27–33 MPa. The modifying addition also influences the structure and reduces the minimum grain size of the material from 0.65 to 0.1μm

Structural and Mechanical Properties of Bioactive Glass–Ceramic Composites

Bioactive glass–ceramic composites based on biogenic hydroxyapatite or synthetic calcium phosphates mixture with addition of sodium borosilicate glass (31.5 wt.%) are prepared using onestage sintering at a temperature of ≤800°C. The comparative analysis of the structure and physical and mechanical properties of the composites produced is carried out. It is established that hydroxyapatite keeps the phase composition (Ca5(PO4)3(OH)) during sintering of the biogenic hydroxyapatite-based composites. During sintering of the composites based on a mixture of synthetic phosphates, a phase transformation and interaction of phosphates with a glass phase occur. This results in the formation of glass ceramics, which contain: calcium silicates (wollastonite CaSiO3) and sodium silicates (Na6Si2O7), sodium-calcium silicates (sodium metasilicate Na2Ca2(SiO3)3 and melilite Na2Ca6(Si2O7)(SiO4)2), sodium borate (Na3BO3), and hydroxyapatite (Ca5(PO4)3(OH). The analysis of porous structure of glass–ceramic composites showed a significant difference in the pore size distribution, depending on the material composition. The difference in the surface and fracture structure for both types of composites is established. It is shown that the mechanical properties of the composites based on biogenic hydroxyapatite are higher compared to those based on synthetic calcium phosphates at the similar total porosity value (32.5–34.5%). This may be due to the phase transformations and interaction of phosphates with glass during sintering and the formation of a complex silica structure. It is established that the strength of the composites produced is comparable to that of the native bone.

Composite Coatings from Bioactive Calcium Phosphate Ceramics on Metal Substrates

Porous bioactive membrane-type calcium phosphate coatings on metal substrates are produced. Their microstructure and physicochemical properties are studied. Titanium (including porous) and medical stainless steel are used as metal substrates. The bioactive coatings are based on biogenic hydroxyapatite or synthetic calcium phosphates (calcium phosphate content was between 68 and 85 %) and sodium borosilicate glass. To add bacteriostatic properties to the coatings, some compositions were additionally doped with cerium dioxide (5 %). The surface microstructure, some mechanical properties, and in vitro behavior of the coatings in physiological solution are examined.

STRUCTURE AND PROPERTIES OF CERAMICS BASED ON MONETITE AND NANODISPERSED SILICA

Calcium–phosphate ceramics based on monetite and nanosized silica are produced by sintering at 500°C. It is established that phase changes and solid-phase reactions occur during sintering to form ceramics that contain β-calcium pyrophosphate (Ca2P2O7), calcium silicate (wollastonite, CaSiO3), and insignificant amount of β-tricalcium phosphate (Ca3(PO4)2). It is shown that the addition of silica inhibits re-crystallization of calcium pyrophosphate into tricalcium phosphate, if compared with ceramics prepared from monetite with no silica added. It is established that increasing the silica content in the starting composition leads to a decrease in the minimum pore size from 0.83 to 0.21 μm. Highly pure nanosized silica (content of SiO2 > 99%) prepared by heat-treating of silicon carbide waste in a solar furnace is used in our research. The porosity of ceramics produced reaches 43.5–46.8% and the compressive strength is 16–24 MPa.