Papers by Author: Georg Berger

Abstract: The setting behaviour, the compressive strength and the porosity of four calcium alkali orthophosphate cements were examined under laboratory conditions (dry) and under conditions similar to those during clinical application (37°C, contact with body fluid). The results showed an increase of the setting times when specimens were covered with simulated body fluid. Especially, the final setting time (FHZ) was significantly higher for three of the four cements. Furthermore, when specimens were stored in SBF for 16h, an extensive decrease of the compressive strength was noted. The porosity was more than twice as high after 16h in SBF and this may be the cause for the great decrease of the compressive strength.

Abstract: Bioactive ceramics such as β-tricalcium phosphate (β-TCP) promote and enhance biological fixation. Ceramics with a porous interconnected structure are suited for facilitation of bony ingrowth. An interconnected pore system with pore diameters in excess of 100 µm is required for cell penetration, tissue ingrowth, vascularization and nutrient delivery to the centre of the regenerating tissue. Human osteoblasts were cultured on the surface of a ceramic. In an in-vivo study, β-TCP samples with a porous interconnected structure were implanted into the femur of sheep and then investigated 6 weeks after operation. Histological analysis was performed on the area surrounding the implant. An indentation test was performed to complete failure of the bone/ceramic compound. Linear load, peak load and stiffness were recorded. All cylinders were found to be biocompatible and osteoconductive. Bone was more abundant in the outer ring than in the rest of the cylinder. The ceramic/bone compound was of low mechanical grade.

Abstract: Discs of TiAl6V4 were cleaned and stored in calcium containing salt melt. The characterization of the reaction layer was realized by TF-XRD, SEM, SIMS, AES, and eddy current. The release of Ca ions was determined after storing the samples in TRIS-HCl buffer solution under physiological conditions for at least 16 weeks. The thickness of the generated calcium titanate layer varied in dependence on salt melt composition, temperature, and storing time in the range of 0.4-0.9.m. The Ca content of the layer depends on melt composition, temperature and storing time and was in the range from 5-42.g●cm-2 in correlation with the thickness. The morphology of the layers also changed in dependence on the salt melt composition and the storing time and temperature.

Abstract: Bioactive ceramics such as hydroxypatite (HA) promote and enhance biological fixation. There is still a discussion on the desired longevity of the coating. Stable coatings require an optimum between resorption rate, flexural strength and adhesive strength of the coating. Ceramic coatings containing fluorapatite (FA, Ca5(PO4)3F) and calcium zirconium phosphate (CZP, CaZr4(PO4)6) promise lower resorption rates than conventional HA coatings in the biological milieu. It is hoped that they can improve the long-term stability of implants by eliminating the detrimental resorption of coating material. For the in vivo studies plasma sprayed coatings were generated. The materials were implanted into the distal femur epiphysis of rabbits and investigated after 2, 4, 6, 12, and 24 weeks postoperatively. Histological analysis was preformed on the areas surrounding the implant. The amount of osseointegration was determined by using the automatically image analysis. The bonding strengths were compared with HA coating and uncoated titanium alloy. According to available data, there is inhibition of mineralization of bone at the interface of calcium zirconium phosphate ceramics of the described composition.

Abstract: Commercially available calcium phosphate cements set by precipitation of nanoapatite or brushite. The goal of this study was to elucidate the most suitable conditions for forming cements from calcium potassium sodium phosphate. Furthermore, the behaviour of these cements after immersion in SBF and/or TRIS solution was investigated. Using varying additives resulted in differences in solubility kinetics. The XRD spectra of all investigated cement compositions displayed Ca2KNa(PO4)2 after setting. However, the various cement compositions differed with respect to apatite formation when immersed in TRIS buffer in and/or SBF solution. Therefore, when investigating calcium phosphate cements we consider it necessary to clearly differentiate between the phases which form after completion of the final setting time when these materials set in air, and the phases which form in a time dependant manner after immersion in different biological fluids.

Abstract: The reactivity of CaTi4(PO4)6 (CTP) with alumina and yttria-stabilized zirconia (Y-TZP) ceramics was studied. CTP powder was synthesized and composites with commercial alumina or zirconia matrices containing 10 wt% of CTP were prepared. They were sintered at different temperatures and characterized using XRD, SEM, and EDX analyses. The results showed that the alumina/CTP and Y-TZP/CTP composites start to react below 1000 °C. In the alumina/CTP composite the first reaction product, detected at 970 °C, was AlPO4. At temperatures above 1280 °C TiO2 and CaTiO3 were also formed and no CTP peaks could be detected using XRD analysis. The composite sintered at 1500 °C consisted of Al2O3 matrix, AlPO4, TiO2, CaTiO3 and Al2TiO5. The reaction products formed in the Y-TZP/CTP composite at 970 °C were TiO2 and Ca2Zr7O16. At higher sintering temperatures, 1280 °C and above, CTP was no longer present, Ca2Zr7O16 decomposed, forming CaO2 and ZrO2, and Y2O3 was consumed to form YPO4. Consequently, upon cooling to room temperature the matrix phase transformed to monoclinic ZrO2. Based on these results it can be concluded that CTP is not a suitable bioactive second phase for the fabrication of CTP composites with alumina or zirconia matrices.

Abstract: A long-term stable material, which has two main crystalline phases – fluorapatite (FA) and calcium zirconium phosphate (CZP) [1, 2] and could be processed to dense sintered samples was tested related to the use with two application forms – spongiosa-like specimen and foils. The suitability of various sintering additives was investigated alone and in diverse combinations. During sintering of the spongiosa-like samples volume shrinkage of about 50% was observed whereas the shrinkage in x,y plane was about twice of the shrinkage in z direction. The cuboid form was not affected by the shrinkage. The compression strength of the spongiosa-like materials was in the range of 1MPa up to 1.6MPa. A ceramic foil was generated via foil slip casting of a slip containing about 38vol% of FA-CZP. Temperature programs were created for debindering and sintering of the green foil and the four-fold laminate, respectively.

Abstract: This paper presents equipment for the measurement of initial as well as final setting times of calcium phosphate cements containing alkali to achieve higher solubility. Until now, the selfsetting process of cements also if alkali is integrated has been tested by using the “standard test method for time of setting of hydraulic-cement paste by Gillmore needles” in accordance to ASTM C 266 – 99. This procedure needs high man power and, furthermore, the results have been markedly influenced by individual experiences that are incorporated in the criterion “without appreciable indentation”.