Search

Hydroxyapatite (HA) porous ceramics are increasingly used in biomedical applications. Their physical characteristics, such as porous volume, require perfect control of the pore shape, as well as the number and the size of their interconnections. The aim of our study was to evaluate a new HA ceramic using polymethylmethacrylate microbeads (PMMA) as the porous agent. Four interconnection sizes (30, 60, 100 and 130 microm) with a 175-260 microm pore size and three pore sizes (175-260, 260-350 and 350-435 microm) for a 130 microm interconnection size were tested. Various HA implants were appraised by microscopic evaluation in a 4.6 x 10 mm rabbit femur cancellous bone defect 12 weeks after implantation. The best osteoconduction result was obtained in the center of the ceramic by means of a 130 microm interconnection size and a 175-260 microm mean pore size. Bone formation obtained within the pores was double that obtained in our previous study where naphtalen microbeads were used as the porous agents., (Copyright 2001 Kluwer Academic Publishers)

The osteogenic potential of an association of two kinds of hydroxyapatite (HA) porous ceramics with autologous bone marrow cells cultured with or without dexamethasone (10(-8)M) addition in the culture medium and non-cultured rabbit marrow stromal stem cells (MSCs) was tested after 4 weeks of implantation in the dorsal muscles of spine in rabbit. A significantly higher number of rabbits with implants containing bone tissue inside pores were obtained with 10(7) cells ml(-1) cultured treated with Dex. In the HA porous ceramic using naphtalen as porogen agent, the bone recolonization remains only at the periphery of implants and in the second row of pores, while in the HA porous ceramic using polymethacrylate (PMMA) microbeads as porogen agent, the bone recolonization is observed in the depth of implants. In the PMMA HA group, the Krüskal-Wallis variance analysis between the rabbits is significantly different with the percentage of number of occupied pores and occupied pores with bone tissue is different (p<0.05)., (Copyright 1999 Kluwer Academic Publishers)

The interconnections in a porous biomaterial are the pathways between the pores. They conduct cells and vessels between pores. Thus they favour bone ingrowth inside ceramics. The aim of our study was to determine the effect on bone ingrowth of interconnections in two ceramics: hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) with the same porosity of about 50% and a mean pores size of 100-300 microm and a mean interconnection size of 30-100 microm. In vitro, four discs for osteoblast culture were studied after 14 and 28 days of incubation. The results show that human osteoblasts can penetrate interconnections over 20 microm in size, and colonize and proliferate inside macropores, but the most favourable size is over 40 microm. In vivo, eight cylinders were implanted in the middle shaft of both rabbit femurs for 12 or 24 weeks. The histomorphometric results show that interconnections in porous ceramics favour bone ingrowth inside the macropores. In the HA group the rate of calcification and bone ingrowth do not differ, and chondroid tissue is observed inside pores. But in beta-TCP, the calcification rate and the bone ingrowth increased significantly. At week 12 significant correlation between new bone ingrowth and the size of the interconnections is observed between new bone ingrowth and the density of pores. In conclusion we notice that in vivo a 20 microm interconnection size only allows cell penetration and chondroid tissue formation; however the size of the interconnections must be over 50 microm to favour new bone ingrowth inside the pores. We propose the concept of "interconnection density" which expresses the quantity of links between pores of porous materials. It assures cell proliferation and differentiation with blood circulation and extracellular liquid exchange. In resorbable materials, pore density and interconnection density are more important than their size, contrary to unresorbable materials in which the sizes and the densities are equally important., (Copyright 1999 Kluwer Academic Publishers)

Interventional radiology is beginning to be used in bone pathology. An injectable biomaterial Ethibloc*, composed of alcohol and a vegetal protein (zein), has been successfully used for percutaneous treatment of benign bone lesions. The reasons for this success remained unknown and needed to be understood. In this study, using a rabbit model, an evaluation was made of bone formation and tissue reaction during the first weeks after the injection of this biomaterial. Ethibloc* was injected percutaneously into bone defects in rabbit distal femurs. Three time intervals were studied: 2, 4 and 8 wks. The three control groups constituted unfilled, polymethylmethacrylate (PMMA), and alcohol. Undecalcified bone technique was used for a qualitative analysis and histomorphometric evaluation. A low bone formation was found which was less than in the control groups (PMMA and unfilled). The "Ethibloc group" was characterized by an early inflammatory reaction. Good clinical results obtained with Ethibloc* probably arose, after an initial vascular thrombosis, from a secondary bone reaction and spontaneous osteogenesis obtained after the disappearance of vascular or hyperpression reaction., (Copyright 1998 Chapman & Hall)