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Calcium phosphate cements are able to set in situ when injected into bone tissue. We evaluated the tissue reaction occurring when a DCPD-based calcium phosphate cement was either set within the bone or implanted when already set. The samples were implanted in rabbit condyles and examined histologically after 8 and 16 weeks. The relative bone surface, the fibrous capsule around the implants and the implant section surface were measured. Solid material seemed to be better tolerated than paste implants. More bone was found at the solid implant contact whatever the implantation time and the solid material degraded much less rapidly. In conclusion, the physico-chemical modification of the biological environment occurring during setting increases the foreign body reaction against the material.

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The resistance of macroporous calcium phosphate ceramics to compressive strength generally is low and depends on, among other factors, porosity percentage and pore size. A compromise always is adopted between high porosity, required for a good integration, and mechanical strength, which increases with material density. We improved the strength of macroporous calcium phosphate ceramics of interconnected porosity by filling the pores with a highly soluble, selfsetting calcium phosphate cement made of TCP and DCPD. Cylinders of the resulting material were implanted in sheep condyles and subjected to histological analysis after 20, 60, and 120 days. Microradiographs were made of the histological sections. The control material consisted of ceramic that had not been loaded with cement. Progressive ingrowth of bone into the ceramic pores occurred as the cement was degraded during the first implantation period. Marked degradation of the cement was apparent after 2 months, with fragmentation of the cement in most of the pores and the presence of bone tissue between the fragments. All the cement had been replaced by bone after 4 months. Some fragments of cement still were embedded in the newly formed bone. There was no significant difference between the integration of loaded and nonloaded ceramics. Filling the macroporous ceramic pores with a calcium phosphate cement significantly improved the mechanical strength of these ceramics without modifying their integration in the healing bone. © 2000 John Wiley & Sons, Inc. J Biomed Mater Res, 50, 125–130, 2000.

Plasma-sprayed alumina (Al2O3) coatings on metal stems of hip prostheses are used to favour bone apposition on the stem without fibrous interposition. We tested both in vitro and in vivo in rabbits, alumina coatings in order to evaluate the biological effect of this material on bone. Mice fibroblasts were grown on Al2O3-coated discs and time course of aluminium concentration was recorded in two phosphate and citrate buffers (pH 4 and 7) bathing the alumina coated discs. Alumina-coated cylinders were implanted into femur condyles of ten rabbits for periods of time from 1–6 months. Then, they were histologically analysed using light and scanning electron microscopy, and X-ray microanalysis. Cell proliferation was not affected on alumina coatings compared to controls. In pH 4 buffer, aluminium was released from the coatings. From a period of implantation of 4–6 months an increasing demineralization process took place in the bone at the coating contact. Aurine staining showed the presence of aluminium at the interface between the non-mineralized and the mineralized bone. These results suggest that aluminium is released from alumina coatings and leads to bone demineralization at the coating contact.

Plasma-sprayed HA-coatings used for orthopaedic surgery can contain different percentages of crystalline phase. The influence of the amount of crystalline and amorphous phase on the biological properties of coatings is not known. The aim of this study is to determine the effect of this coating characteristic on mammalian cell functions in vitro. It appears that 100% crystalline coatings have an inhibiting effect on cell proliferation and on alkaline phosphatase activity. A direct contact of the cells with the material is necessary to obtain this effect. The material evolves during the period of culture. Poorly crystalline coatings dissolve during the period of culture and the roughness parameters change during the same period.

HA-ceramics used in human surgery as osteoconductive surfaces show a great variety of characteristics. Certain characteristics such as grain size, porosity, and surface area, are controlled by the sintering temperature of the slurry. We grew L-929 fibroblast cells on HA-ceramic disks that had been sintered at different temperatures ranging from 850°–1350°C. The cell line growth rate was lower on ceramic disks than on the culture-grade polystyrene used as a negative control. Cell growth correlated with the ceramic sintering temperature although no significant difference in the cell adhesion to the different ceramics was shown. Growth rate on ceramics sintered at low temperatures (850° and 950°C) was negative whereas it was positive on disks sintered at higher temperatures. When the cells were separated from the disks by a polycarbonate membrane, the growth rate was negative on those membranes in contact with low-temperature sintered disks and positive on the high-temperature sintered disks. The calcium and phosphorus concentration in the culture medium in contact with ceramics sintered below 1050°C decreased during the culture period. Ceramics sintered between 1100° and 1250°C brought about an increase in Ca and P concentrations while ceramics sintered at higher temperatures did not induce any changes. SEM examination of the 850° and 1200°C sintered ceramics showed that the 850°C sintered ceramics consisted of small grains with pores between them and the 1200°C sintered ceramics were made of larger grains without any visible pores, thereby decreasing the surface of material in contact with the culture medium. This difference in surface area was confirmed by the fact that the amount of albumin adsorbed onto the ceramic was dependent on the sintering temperature. In conclusion, the modification of the culture medium brought about by high-surfaced ceramics could influence the growth of cells with which such ceramics come in contact. © 1997 John Wiley & Sons, Inc.

Cancellous bone cells were isolated from adult dogs, introduced into cell culture, subcultured and grown on hydroxylapatite granules. Cells immobilized on these granules were used to make bioreactors which were implanted in dog ulna diaphyse to fill osseous defects. The bioreactor implantation constituted a bone cell autograft and showed bone formation in a reactor containing cultured cells but not in the control reactor containing hydroxylapatite granules without cells. These results indicate that hydroxylapatite material can be used in bioartificial organs. The properties of hydroxylapatite used in bone reconstruction are due to the cells and extra-cellular matrix immobilized on its surface.

It is very likely that the need for bone substitutes will increase in the next decade. The present substitutes are generally bioactive and osteoconductive. Glassy or ceramic materials have been used up to now to act as a guide for bone healing tissue and were shown to admit bone apposition at their surface, probably due to the epitaxial growth of carbonated apatite crystals on it. Different forms of bone substitutes have been developed which do not show exactly the same properties. The reaction of bone tissue against bioactive material debris shows major differences from that of polymers or metals.In vitromodels were developed to study the interface between bone cells and extracellular matrix, and the surface of bioactive material. Biotechnology makes available some morphogenetic proteins or growth factors in large quantities for combination with osteoconductive material which then can become osteoinductive. Bioartificial bone tissue constituted by a primary osteogenic cell line immobilised at the surface of osteoconductive materials made it possible to obtain osteogenic materials. The ideal bone biomaterial is still to be engineered. The combination of material sciences and molecular biology will help to optimise the next generation of material surfaces.