Porous materials made from calcium phosphates (Review)

Abstract

The methods of fabricating porous materials are reviewed. The optimum methods of fabricating porous materials from calcium phosphates, including materials for use as bone implants, are demonstrated.Porous materials are used for fabricating bone implants and particularly for treating nonextensive bone defects not subject to mechanical loads. The phase composition of these materials must be represented by biocompatible inorganic components with predominance of the biodegradable (resorbable) phase [1]. The pores in these materials must be permeable, and their size must be large enough, a minimum of 100 mm, to ensure penetration of physiological medium inside the material. The strength of the material must be sufficient for the physician to perform the necessary manipulations both in the stage of preparing the implant and during the surgery. When replacing a bone defect, such porous material creates conditions initially for formation of a manmade inorganic material -organic component composite, and then a regenerated hydroxyapatite carbonate -organic component composite.There are methods for fabrication of porous materials using the polymer matrix duplication method [2, 3] based on calcium phosphate powders (US Patent No. 7037869 B2) [4]; mixtures of powdered calcium phosphate and glasses from the MgO -CaO -SiO 2 -P 2 O 5 -CaF 2 or SiO 2 -Na 2 OCaO -P 2 O 5 system [5] based on powdered glass from the MgO -CaO -SiO 2 -P 2 O 5 system, whose phase composition after burning was represented by tricalcium phosphate and diopside [6]; mixtures of powdered hydroxyapatite and wollastonite [7]; mixture of hydroxyapatite and glass powder from the CaO -P 2 O 5 system [8].Polyurethane foam is primarily used as the porous polymer matrix in these methods. The method allows duplicating the pore structure of the polymer matrix. Its undoubted advantage is that production of polyurethane foam with different pore size and pore size distribution, impregnation of slips made of different materials, and drying and heat treatment that ensure production of a highly permeable ceramic, including those made of calcium phosphates, have been mastered in industry. At the same time, toxic gases are liberated when the polyurethane matrix is burned out and they must be eliminated and detoxified.This technology was used at D. I. Mendeleev Russian Chemical Engineering University to create a highly porous (up to 90% porosity) ceramic with a honeycomb structure from hydroxyapatite for use as bone implants. Several operations were performed to treat bone defects. Observations of the behavior of the implants showed that the resorption rate was approximately two times higher than with other biomaterials used for plastic bone surgery.The method of fabricating the porous materials for bone implants based on natural coral involves treating it with soluble compounds containing phosphate ions, such as phosphoric acid or ammonium hydrophosphate. During heat treatment, the coral (calcium carbonate, CaCO 3 ) reacts with H 3 PO 4 or (NH 3 ) 2 HPO 4 , forming one-(hy...

Porous Ceramic Based on Calcium Pyrophosphate

“…Ultimate strength in bending of materials based on CPP -sodium pyrophosphate powder mixes (Table 1) comprises 5 -25 MPa. The temperature for which the maximum density and strength are achieved is in good agreement with the melting temperature for sodium polyphosphate (T mNaPO 3 = 627°C). Thus, sodium polyphosphate in the form of a melt may penetrate into spaces between grains, facilitating regrouping of sodium pyrophosphate particles, sintering, and preparation of biocompatible dense materials.…”

“…Various methods are used in order to prepare porous materials [2,3]. Porous ceramic materials based on calcium phosphates for medicine are prepared by duplication with a polymer [4,5] or inorganic [6] matrix.…”