Key Engineering Materials Vols. 361-363

Abstract: This paper reports on the research into multiphase bone substitutes carried out by laboratories from the ‘Pays de la Loire’ region in France. This collaborative research was funded by both the French Government and the Regional Council in the period 2000-2007. Calcium phosphate bioceramics, polymers and combinations have been developed as bone substitutes for various maxillofacial and orthopaedic applications. These bone substitutes should support and regenerate bone tissue and resorb after implantation. In the bone tissue engineering area, they have been combined with autologous bone marrow cells or bioactive factors. The bone substitutes were tested in various animal models mimicking clinical situations or under pathological conditions (osteoporosis). In order to complete our research, the multiphase materials were also evaluated in clinical trials.

Abstract: The production of nano-scale hydroxyapatite (HA) suspensions to be used for the reticulated foam method of scaffold production was investigated at temperatures of between 10 and 60OC. An increase in reaction temperature was associated with an increase in the particle size and some decrease in the aspect ratio of the particles. Pre-treatment of the polyurethane foam template using PPDS (potassium peroxodisulfate) solution resulted in a significantly improved coating of HA when compared to the untreated samples or those treated with ethanol. Initial trials coating the polyurethane with HA produced at the different reaction temperatures showed a superior coating with the suspension produced at 10OC compared to that at 60OC. A scaffold was produced using the HA suspension produced at room temperature, but further understanding of the suspension properties and the optimum conditions for coating of the PU foam are required for improved mechanical performance.

Abstract: The degradation rate of custom made calcium phosphate scaffolds, designed for bone tissue engineering applications, influences the healing process of critical size bone defects. An optimal degradation rate exists at which the neo-formed bone replaces the CaP (calcium phosphate) scaffold [1]. Consequently investigating the complex degradation behavior (dissolution, reprecipitation, osteoclast activity) of custom made CaP structures gains interest. In this work different in vitro dissolution experiments were performed to study the degradation behavior of 4 by composition different calcium phosphates. Ideally these experiments should have a predictive power regarding the in vivo degradation behavior. In vitro dissolution tests still lack standardization. Therefore this study focuses on the influence of two dissolution constraints: (i) the material’s macrostructure (porous - dense), (ii) the regenerated fluid flow (bath shaking - perfusion). From 4 different CaP compositions porous structures and as a reference dense disks were produced, using the same starting powder and heat treatment. To compare the different dissolution tests, all data was normalized to the CaP surface area. Results show that besides the structural appearances of the CaP structures, also the design of the dissolution test influences the in vitro dissolution behavior. Moreover there is a need to take the morphology of the dissolved material into account. The CaP perfusion tests show dissolution dynamics that resemble the in vivo reality more closely than the shaking bath experiments.

Abstract: This paper describes a comparative investigation into the in vitro solubility of the calcium polyphosphates, γ-Ca(PO3)2 and β-Ca(PO3)2. The differing arrangement of their polyphosphates chains appears to result in significant dissolution of γ-Ca(PO3)2 polymorph over the β-Ca(PO3)2 polymorph, which exhibits limited dissolution. These properties are discussed with respect to structure and thermodynamic stability.

Abstract: Macroporous biphasic calcium phosphate bioceramics, for use as bone substitutes, have been fabricated by cold isostatic pressing and conventional sintering, using naphthalene particles as a porogen to produce macropores. The resulting ceramics, composite materials made of hydroxyapatite and β-tricalcium phosphate containing various macroporosities and microporosities, have been submitted to compression and three-point bending tests. The mechanical tests performed on the sintered ceramics tend to validate the modelling approach and its hypothesis, i.e. the material can be considered as a microporous matrix containing isolated macropores, and the critical flaw is a macropore.

Abstract: Ceramic slips with powder loadings in the range of 80-140 wt% were used to investigate the effect of slip loading on the physical and mechanical properties of open pore HA/TCP bioceramics. The results indicated that increasing the slip loading had an effect on the properties of the samples. The average apparent density, the work of fracture and compressive strength all increased with slip loading. In contrast, the effect of increasing slip loading on the four-point bending strength was not significant.

Abstract: In the present study, Ca2P2O7-doped β-Ca3(PO4)2 bioceramics were fabricated by pressureless sintering process. The effect of Ca2P2O7 on the sintering ability, mechanical strength and degradability of the ceramics were investigated. The results showed that the Ca2P2O7 could apparently decrease the sintering ability and mechanical properties of β-Ca3(PO4)2. Moreover, the relative density and mechanical strength of the sintered samples decreased gradually with the increase of the Ca2P2O7 additive amount. However, the dissolution rate of the samples increased with the increase of the Ca2P2O7 additive amount.