Ute Ploska

Rapid resorbable, glassy crystalline materials on the basis of calcium alkali orthophosphates

Materials based on calcium orthophosphates have been developed to crystallize spontaneously and directly from the melt. The main crystalline phase consists of a new synthesized chemical of formula Ca2KNa(PO4)2. This compound crystallizes in a very wide range of chemical compositions as shown. Furthermore, the solubility was tested and compared with that of self-prepared alpha-tricalcium phosphate ceramics and commercial products of hydroxyapatite ceramics and surface-modified alpha-tricalcium phosphate ceramics. The results show that new materials containing the compound Ca2KNa(PO4)2 had the highest solubility in comparison with other tested materials.

Bone growth is enhanced by novel bioceramic coatings on Ti alloy implants

Calcium phosphate ceramics are widely used as coating materials to orthopedic implants and are found to enhance initial bony ingrowth by stimulating osseous apposition to the implant surface. In this study, two novel calcium orthophosphate materials were selected for coating onto the commonly used orthopedic implant material Ti-6Al- 4V. One was calcium alkali orthophosphate with the crystalline phase Ca10[K/Na](PO4)7 with a small addition of SiO2 (AW-Si) and the other was calcium orthophosphate composed of 70 mol % fluorapatite, Ca10(PO4)6F2 and 30 mol % CaZr4(PO4)6 (FA7Z). The coated implants were placed in cortical and cortico-cancellous bone of sheep femur for six weeks. Retrieved samples were tested for osseointegration and mechanical strength. It was found that both coatings produced enhanced bone/implant contact rate compared to the control when implanted in cortico-cancellous bone. This study demonstrates that the two coatings have the capability of encouraging bone growth, and hence the potential for being used as coating materials on Ti implants.

Solubility of compositions in the system CaTixZr4 − x(PO4)6 with X = 0–4

In vitro solubility tests of granulated materials and coatings were carried out on some compositions in the system CaTi(x)Zr4-(x)(PO4)6 with x = 0-4, in order to find a biocompatible material which is less soluble than hydroxyapatite (HA) and can also be used as bone substitution material. The granulated materials were leached out by using circulating equipment in which the solvent flows in circulation. The coatings were tested under conditions where the sample containers undergo a circular movement. The results show better chemical stability of nearly all tested compounds compared with HA for both granulated materials and coatings.

Inhibition of Mineralization by a Calcium Zirconium Phosphate Coating

Bioactive ceramics used as coating materials combine the conductive properties of a bioceramic with the mechanical stability of the metal implant. We studied a calcium zirconium phosphate-containing coating material, FA-CZP [Ca(5)(PO(4))(3)F, CaZr(4)(PO(4))(6)], that is relatively insoluble in the biological milieu. The reaction of bone to this material was investigated histologically and histomorphometrically in an animal trial. Cylindrical Ti6Al4V specimens that had been coated with FA-CZP by plasma spraying were implanted in the femoral condyles of rabbits. The implants were left in place for 2, 4, 6, 12, and 14 weeks. FA-CZP led to impaired mineralization of the newly formed bone at the interface. Noncalcified osteoid was found throughout the whole study period. The layer seemed to become thicker with time. The mineralization disorder is evidently caused by zirconium ions. The presence of zirconium in the osteoid in contact with the implant was demonstrated by means of two different staining methods.

Long-Term Stable Biomaterials Based on Apatite and Calcium Zirconium Orthophosphate

Abstract. This paper reports methods related to the synthesis of bioceram i s containing apatite and calcium zirconium orthophosphate as main crystalline phases. The phase s were identified by XRD. The chemical stability of these materials was determined b y treating crushed samples with 0.2 M TRIS-HCl buffer solution at a temperature of 37°C for 120 hrs and meas uring of the ions leached out by the ICP-OES method. The solubility of the synthesised mater ials is lower than that of hydroxyapatite especially for decreasing pH values.

Solubility and Ingrowth Behaviour of Degradable and Figuline Calcium Alkaline Phosphate Cements

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.

Do Calcium Zirconium Phosphate Ceramics Inhibit Mineralization

The solubility of a new calcium zirconium phosphate ceramics was found reduced compared to hydroxyapatite in i -vitro studies. Therefore, and for technical reasons cylinders of this new material were implanted into the distal femur epiphysis of female Chinchilla rabbits and investigated after 7, 28 and 84 days postoperatively in sawn secti ons and TEM. The cellular and tissue responses were characterized by the development of some m acrophages in the soft tissue at the interface and by primary trabecular bone approaching the interf ace and being mostly made up of osteoid, i.e. non mineralised bone matrix, in a seam up to 150 μm thick. The reason for this impaired mineralization is not yet clear. From further in vitro testing and additional transmission electron microscopy it is speculated that the inhibited development of matrix vesicles could be responsible for this process.

Investigations on Degradable and Figuline Calcium Alkaline Phosphate Cements with Multimodal Particle Size Distribution

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 (dcourse/dsmall) was chosen with 7/1 and volume ratio dcourse/dsmall was 70/30%. For the trimodal powder mixtures the ratio in diameter (dcourse/dmedium/dsmall) was chosen with 70/7/1 and volume ratio dcourse/dmedium/dsmall 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.

The Tissue Response to a Novel Calcium Zirconium Phosphate Ceramics

Abstract. The solubility of a new calcium zirconium phosphate ceramics was found reduced compared to hydroxyapatite in in vitro studies. Therefore, and for tec hnical reasons cylinders of this new material were implanted into the distal femur epiphysis of female Chinchilla rabbits and investigated after 7, 28 and 84 days postoperatively in sawn sections. T he cellular and tissue response were characterised by the development of some macrophages in th soft tissue at the interface and by primary trabecular bone approaching the interfa ce and being mostly made up of osteoid, i.e. unmineralised bone matrix, in a seam up to 150 μm thick. T e reason for this impaired mineralisation is not apparent. It is speculated from transmissi on electron microscopy of the interface that the development of matrix vesicles could be involved in this process.

A New Procedure of a Calcium-Containing Coating on Implants of Titanium Alloy

Abstract. The paper describes a new method for converting the existing o x de layer of implants of titanium and titanium alloys in calcium containing surface lay ers. The layers were generated by dipping the implants in a salt melt consisting of calcium nit rate at temperatures of 520°C until 560°C for 2 until 4 hrs. The melt reacted with the surface layer o f the implants by forming calcium titanate surface layers. Besides, the thickness of the TiO2 layer of the implants became larger. Several methods for the determination of the layer thickness w re investigated related to their suitability. The micro hardness of the layer and the tribologi cal behaviour were investigated. The presented procedure can be used for generating calci um containing surface layers on implants of titanium alloys even with complicated forms.