Papers by Author: Kārlis A. Gross

Abstract: Splitting problems at HA-coated implants are generally due to biological reasons. Bond-coatings were used to prevent the splitting problem of zirconia ceramics; this method can be widely seen in industrial applications. Two main groups were used; the first group consisted of spraying a bond layer of titania onto commercially pure titanium. This followed by a spray of HA with 5, 10 and 15 % zirconia (8 % yttria doped) as main layer onto the first bond-coating. For the second group, the samples were coated without bond-coating. Firstly, X-ray diffraction patterns of the starting powders were taken. Then x-ray diffraction patterns of the plasma sprayed samples were taken. In literature, it was seen that 20 % zirconia was sufficient for the transformation into a monoclinic structure for the bond-coated samples. For this study it was found that 10 % zirconia was sufficient to transform to the same structure of the desired crystalline phase transformation. The coating kept its crystal structure and relatively small amount of amorphous transformation was detected. A similar structure was produced using less zirconia. It was thought that the use of titanium-oxide bond-coating layer would play an important role as a third variable in the results. To further investigate these phenomena, more detailed researches must be conducted with using titanium-oxide yittria stabilized zirconia (8 wt %) hydroxyapatite bond-coatings with HA main coatings.

Abstract: Bisphosphonates (BP) are drugs currently administered orally to treat diseases characterised by an excessive bone resorption. Alternative and more efficient delivery routes and more potent compounds are being investigated. Three implantable delivery systems, which allow the controlled release of therapeutic agents from the device core, are examined in this paper. (4- (aminomethyl) benzene) bisphosphonic acid (ABBP) was incorporated on Ca8.8Na0.8(PO4)4.8(CO3)1.2(OH)0.4F1.6 particles by refluxing the powder in a 60 mmol suspension in acetone at 60°C for 5 hours. 4-aminophenyl acetic bisphosphonate monosodium salt (APBP) and 1- H-indole-3-acetic bisphosphonate monosodium (IBP) were loaded on Ca10(PO4)6(OH)1F1 ceramic bodies by stirring the ceramic bodies in 0.04M BP solutions. Injectable acrylic cements based on self-curing formulations of methyl methacrylate (MMA) and vitamin E were loaded with APBP and IBP. The incorporation of ABBP was confirmed by MAS-NMR spectroscopy. Modified powder shows two different phosphorous environments, the first one at 2.91 ppm can be assigned to the apatite base and the second one at 18.0 ppm has to be attributed to the phosphonic group of the ABBP. The IBP addition on ceramic surfaces did not decrease the number of osteoclast colonies and appeared to improve the performance of the HA as a surface for osteoblast culture. A therapeutic dosage of APBP and IBP can be achieved from acrylic cements that showed lack of toxicity and an increased cellular activity and proliferation.

Abstract: The biomaterial surface represents the first contact point for proteins and cells and is thus critical to optimise the features to transmit the best signals for tissue and organ regeneration. Both chemistry and topography are surface characteristics that can be modified by the manufacturing process and provide signals to cells. While chemistry and crystallinity have received attention for thermally sprayed hydroxyapatite coatings, the control of the surface microtopography has not been addressed. This study collected a range of implants with a coating and assessed the topography on dental implants, orthopaedic screws and hip prostheses. The surface was found to be composed of large topographic features (angular particulate and smooth areas) and micron sized aspects (fine grains, cracks and ridges). Thermal spray experiments were designed to determine the influence of processing conditions on droplet spreading. This knowledge was then applied to see the effect of different parameters on the final coating topography. The parameters investigated for their influence on the surface topography included substrate roughness, substrate temperature, spray distance and particle size. The particle size showed the largest influence on altering the roughness, Ra of the coating. A two-fold increase in particle size doubled the roughness from Ra of 4.8 µm when the powder was sprayed under the same conditions.

Abstract: In order to overcome the fragility and to improve the physical stability of hydroxyapatite (HA) on the implant, 5, 10, and 15 % yttria stabilized zirconia (YTZP) was added to the starting plasma spraying HA powder Metco XPT-D-703. From the recent literature it is already known that HA coatings tend to dissolve in body fluid environment. To decrease the dissolution effect many additives like zirconia (Zr) could be added to HA powder. In this study, prepared HA composite powders were sprayed onto titanium (Ti) surfaces with a Metco plasma gun. As a control group, pure HA powder was sprayed onto other Ti samples. All samples were subjected to tensile tests according to the ASTM C-633-79. SEM images were taken using back-scattering from prepared cross-sections. X-ray diffraction images were taken from the surface. It was seen that with the increase of the Zr content, the tensile test values increased. Pure HA showed also that the addition of Zr had improved the tensile bond strenght (TBS) values.

Abstract: Bisphosphonates (BPs) may play an important role in minimizing osteolysis. In this work two new bisphosphonates pertaining to second and third generations respectively, have been synthesized and incorporated onto a chemically enriched hydroxyapatite. BP synthesis has been performed by adding H3PO3, PCl3 and methanesulfonic acid over 4-aminophenyl acetic acid (APBP) and 1-H-indole-3-acetic acid (IBP) respectively at 65°C in a N2 atmosphere. These compounds bear a primary amine group bonded to an aromatic ring, and a secondary amine group within a heterocyclic ring respectively. A chemically enriched hydroxyapatite with a chemical content corresponding to a 50% fluorided hydroxyapatite has been synthesized. Ceramic bodies manufactured by uniaxial pressure followed by cold isostatic press have a 97% density and submicron grain size. The BP was adsorbed onto the surface by immersion in a stirred solution at 37°C for 48 hours. A 10-fold decrease of the surface energy was observed for bodies modified with the APBP whereas only a 25 % decrease is obtained for bodies loaded with the bisphosphonate loaded with the IBP.