Papers by Author: Ute Ploska

Abstract: The thrust of the investigations presented here is to point out the degradation behaviour in vitro and the ingrowth behaviour in vivo of four different calcium alkaline phosphate cements. Two of the figuline and mouldable composites consist of the crystalline phase Ca₂KNa(PO₄)₂ and two of the crystalline phase Ca₁₀[K/Na](PO₄)₂ each containing 2wt% medium gel strength porcine gelatin. Furthermore Α-TCP was added to both Ca₁₀[K/Na](PO₄)₂ cements as a hardening supporting reactant. The testing material groups differ in small amorphous portions containing either silica phosphate (GB9), magnesium potassium phosphate (GB14) or diphosphates (401545 and 401545(70)). The respective composites show a monomodal particle size distribution (d₅₀~7µm; span~4) and an average total porosity around 28vol%.For the solubility studies cylindrical samples (d=6mm; h=12mm) were stored in a 0.1mol TRIS buffer solution and incubated at 37°C for maximum 50 weeks. The storage solution was analysed and renewed every week. The results are plotted cumulative. For the in vivo studies critical size defects were dissected to mandibles in a sheep model in which a 1cm³ area of the bottom of the mandibles was surgically resected and replaced with the figuline cements whereas the mouldability allows the reconstruction of the original outer contour without draining off even when replacing upside down.

Abstract: The paper presented here deals with rheological and hardening properties during the setting reaction, and density and compressive strength after the final setting of a figuline composite consisting of Ca₂KNa(PO₄)₂ and 2wt% medium gel strength gelatin. Compared to the composite with monomodal particle size distribution (d₅₀=7.18µm; span=3.9) and its properties during and after setting reaction, the goal of this work is to increase the resulting product compressive strength by mixing different particle sizes in order to obtain bi- and trimodal distributions. For the bimodal powder mixtures the ratio in diameter (d_course/d_small) was chosen with 7/1 and volume ratio d_course/d_small was 70/30%. For the trimodal powder mixtures the ratio in diameter (d_course/d_medium/d_small) was chosen with 70/7/1 and volume ratio d_course/d_medium/d_small was set to 44/28/28%.After establishing an adequate crushing and sieving process the tap density and powder density of each fraction was determined. Subsequently, the different particle sizes were mixed and the densities and the Hausner ratio were determined again. The mixtures show an increase in both densities especially the tap density increased significantly. Rheological investigations show that the graphs of storage and loss moduli of the multimodal powder mixtures respectively are similar. The characteristic setting times show a slight decrease compared with the monomodal composite but not significantly different data. When comparing the resulting compressive strength of cylindrical samples, which were stored direct after reaching the initial setting time under physiological conditions, the studies illustrated in all cases for the multimodal mixtures a significant increase in compressive strength and a higher density.

Abstract: This study describes the preparation of a composite material [1] from synthetic nano-scaled hydroxyapatite (nHA) and a gelatin matrix (80% nHA, 20% gelatin). This composite material is intended to extend the range of biological hydroxyapatite-based defect-filling materials for bone replacement. Ostim® (aqueous suspension of nHA having a crystallite size of about 20nm) was used as the inorganic component whereas porcine gelatin (type A, 180 Bloom) composed the organic part. Both components were homogenized during a spray-drying process. Cylindrical samples of the spray-dried granulate (HG 80/20) produced by pressing had adequate mechanical stability for storage, transport and handling in the surgery. The flexural strengths for the samples were determined on dry samples as well as after storing in media (distilled water, SBF solution) for 60 minutes. After staying 30 minutes in a SBF solution or in water, flexural strength dropped off about 30% while the shape of the sample was retained. Temperature treatments of both granulate and pressed samples resulted in reduction of the sample swelling from 70vol-% to 50vol-%. The sample produced by pressing can be machined (turned, drilled, milled).

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: 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: The influence of several sinter additives (three glasses, magnesium acetate, bismuth trioxide) on the compressive strength and also on the solubility of a sintered ceramics, which is composed of 57.6Mol% CaO, 26.2Mol% P2O5, 10.4Mol% ZrO2 and 5.8Mol% CaF2 was tested. The amount of sinter additives, pre-mixing of the powders, pressure power, sintering temperature and sintering time were varied. The most dense samples were produced with the finest powders (D50 ~ 1/m) and the highest sintering temperatures (1200°C). The mechanical stability of the samples was more influenced by the particle size of the powders than by the kind of binder as well as the pressure power. The compressive strength of the sintered samples ranged between 180MPa (D50 of the powder = 2.4/m) and 530MPa (D50 of the powder < 1/m). Storing of the samples in simulated body fluid for 4 weeks at a temperature of 37°C did not influence the compressive strength significantly. The sintered ceramics can be finished, for instance by grinding or polishing.

Abstract: To guarantee of the security of ceramic medical products the identification and quantification of the current degradation products is required by the ISO 10993-14 standard. Two methods - the gravimetrical registration of the mass loss and the quantitative determination of the leached ions by spectrometric methods - are planned. When checking the application of the ISO standard to calcium phosphate ceramics that can be used as implant materials a considerable difference in the results obtained with both methods was observed. It seems to be that precipitation reactions are responsible for that situation. To clear up the influence of precipitation reactions on the results the working procedure of the ISO standard was slightly modified. A first interpretation of the results is tried.