Journal of Materials Science: Materials in Medicine

Anderheiden, D.; Klee, D.; Höcker, H.; Heller, B.; Kirkpatrick, C.; Mittermayer, C.

doi: 10.1007/BF00702936pmid: N/A

An OH-functionalized poly(carbonate urethane) (PCU) is used for developing a new antithrombogenic surface. Biomolecules like glycine or the fibronectin fragment Gly-Arg-Gly-Asp-Ser (GRGDS) are covalently bound to the PCU surface by succinyl dichloride coupling. The modification steps are controlled by infrared spectroscopy and amino acid analysis. Successfully modified films are tested under stationary cell culture conditions.

Labeque, R.; Clark, B.; Ferreira, J.; Langer, R.; Mullon, C.; Lees, R.

doi: 10.1007/BF00702937pmid: N/A

Phospholipase A2 (PLA2) hydrolyses certain phospholipids of low density lipoproteins. PLA2-treated LDL is known to be rapidly cleared from plasma. A prototype plasma filter containing immobilizedCrotalus atrox PLA2 on agarose beads was developed. After a 90 min treatment with the extracorporeal device, plasma cholesterol concentration in cholesterol-fed NZW rabbits decreased by 32%. The decrease was dependent on the enzymatic activity in the plasma filter. The decrease in plasma cholesterol of hypercholesterolemic rabbits that were treated with control reactors (agarose beads only) was 5%. White and red blood cell counts and platelets remained unchanged during the treatment. Plasma cholesterol reduction (25–40%) was also obtained following intravenous injection of active PLA2 to modify plasma lipoproteins. PLA2 infusion created a radical change in biliary composition. Bile phospholipid composition was 90–95% lysophosphatidylcholine as compared with more than 95% before injection of active PLA2. Phospholipid and bile salts total mass increased by 10%. While biliary secretion rate of protein increased by 10%, biliary secretion rate of cholesterol remained unchanged. This technique is specific for lipoproteins, does not require any fluid replacement of sorbent regeneration, and offers a potential new approach for lowering serum cholesterol and LDL levels.

Cadic, Ch.; Dupuy, B.; Vitiello, S.

doi: 10.1007/BF00702938pmid: N/A

One of the implantation problems in immunoprotected living cells is the appearance of local inflammatory phenomena around microcapsules. Some of the mediators released in such pathophysiological conditions were tested. A toxic action of compounds such as elastase, collagenase, free radicals and lysozyme was evidenced. Interleukins 1 and 2 revealed no cytotoxicity within the test limits on the experimental cellular model chosen. These results underline the importance of inflammatory mediators released by adjacent, or even resident, cells in the implant.

Muller, D.; Zhou, F.; Khamlichi, S.; Jozefonvicz, J.

doi: 10.1007/BF00702939pmid: N/A

Dextran-coated silica supports are potentially excellent stationary phases for high-performance liquid chromatography of proteins. These supports combined the advantages of polysaccharide phases with the excellent mechanical characteristics of silica. The passivation of the inorganic phase was obtained by a coating with dextran or agarose substituted with a calculated amount of positively charged diethylaminoethyl (DEAE) functions. The passivation of the silica beads can be improved by a second coating with native polysaccharide. The supports presented minimal non-specific adsorption as tested by high-performance size-exclusion chromatography. Because of their polysaccharidic overlayer, these phases were easily grafted with active ligands like anticoagulant compounds (heparin or functional dextrans) or amidine derivatives and used in high-performance affinity chromatography. The affinity of these active supports for thrombin in solution was evaluated and their performances in affinity chromatography were determined. On these supports, the non-specific interactions were minimized and the importance of the specific binding between the active ligand and thrombin in the overall interaction mechanism was enhanced.

Vaidyanathan, J.; Vaidyanathan, T.

doi: 10.1007/BF00702940pmid: N/A

The interactive effects of ambient temperature of cure and resin composition on the extent of cure are evaluated by the measurement of percentage conversion of double bonds, heat of cure and microhardness of visible light cure dental resin systems. Three bonding agents, including two BisGMA-based resins (Command Bond, Pentron Bond) and one urethane-dimethacrylate-based resin (Coe Bond), were evaluated. The results indicate a significant effect of ambient temperature of cure and resin composition on percentage conversion, molar heat of cure and microhardness. In the temperature range of 25–60 °C, thermal activation appears to be a promising approach to improve conversion and crosslinking in dental resins. At lower ambient temperatures of cure (25 °C), urethane dimethacrylate resin undergoes higher levels of conversion than BisGMA-based resins. At higher temperatures, the percentage conversion increases with temperature in all resins. However, the molar heat of cure and hardness values show a significant increase with temperature only in BisGMA-based resins, but not in the urethane dimethacrylate resin. The difference in percentage conversion and heat of cure variation with temperature and the similarity of the latter variation with that of microhardness, probably indicates that the heat of cure is a better predictor of the extent of cure in these thermoset resins. It appears that enhanced crosslinking due to thermal activation may significantly influence the extent of cure at higher ambient temperatures.

Bianco, P.; Ducheyne, P.; Bonnell, D.

doi: 10.1007/BF00702941pmid: N/A

In an effort to understand thein vivo interactions of titanium and its alloys with a biological environment, surface science methods have been used on specimens retrieved fromin vitro andin vivo experiments. A relatively new technique that has the potential to further our knowledge of the oxide-solution interface is scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (TS). This work documents the use of STM/TS in the study of titanium thin films before and after immersion in anin vitro solution. Titanium thin films were fabricated using a procedure which produced an oxide that had minimal contaminants. Half of the thin films were immersed in an electrolyte. STM/TS was performed immediately after the immersion period. Constant current images were obtained. Current-voltage characteristics were recorded at regions of interest. The topography of the nonimmersed films revealed that the surface was qualitatively the same as other sputter deposited metal films. I–V curves showed little spatial variation. The topography of the immersed film showed little change from the nonimmersed ones. However, significant spatial variation of the local electronic structure was noted. This indicates that titanium surface-fluid interactions do not occur uniformly on the film.

Radin, S.; Ducheyne, P.

doi: 10.1007/BF00702942pmid: N/A

Plasma spraying is a commonly used technique to apply thin calcium phosphate ceramic coatings. Special consideration is given to retaining the original structure of CPC particles. However, changes are possible. Thus this study focused on plasma spraying induced changes in material characteristics of commercial coatings and their influence onin vitro dissolution. All analysed coatings were found to undergo significant plasma spraying induced changes in phase composition, crystal structure, and specific surface area. The phase transformations depended on the starting particle characteristics. Specifically, β-TCP transformed to α-TCP. HA was dehydroxylated and transformed to oxyhydroxyapatite (OHA), and partly decomposed to α-TCP and tetra calcium phosphate. These transformations lead to a considerable increase ofin vitro dissolution rates at physiological pH.

Majola, A.; Vainionpää, S.; Rokkanen, P.; Mikkola, H.; Törmälä, P.

doi: 10.1007/BF00702943pmid: N/A

The strength and strength retention of self-reinforced (SR) absorbable polylactic acid composite rods were evaluated after intramedullary and subcutaneous implantation in rabbits. Rods made of poly-l-lactic acid (SR-PLLA) and of poly-dl-lactic acid + poly-l-lactic acid composite (SR-PDLLA/PLLA) were used. The molecular mass (M v) of PLLA was 260.000 and that of PDLLA 100.000. The bending and shear strengths were measured after a follow-up of 1–48 weeks. The initial bending strength of the SR-PLLA rods was 250–271 MPa and the shear strength was 94 98 MPa. After intramedullary and subcutaneous implantation of 12 weeks the bending strength of the SR-PLLA implants was 100 MPa. At 36 weeks the bending strength had decreased to the level of the strength of cancellous bone (10–20 MPa). There were no changes in the shear strength during 12 weeks hydrolysis. The initial bending strength of SR-PDLLA/PLLA implants was 209 MPa and during the follow-up the implants lost their bending and shear strength faster than the SR-PLLA implants. The present investigation gave us the impetus to continue the studies with the fixation of experimental cortical bone osteotomies with SR-PLLA intramedullary rods.

Tanahashi, Masami; Kamiya, Kanichi; Suzuki, Tohru; Nasu, Hiroyuki

doi: 10.1007/BF00702944pmid: N/A

In the preparation of fibrous hydroxyapatite (HAp), using the gel system consisting of agar gel containing calcium nitrate and over-layered (NH4)2HPO4 solution, the pH of the solution was found to greatly influence the growth rate and morphology of the resultant products. In particular, a pH value of about 9–10 produced straight fibrous HAp in the shortest time. Also, the Ca/P molar ratio of the product increased with the pH value of the starting solution. The growth rate and morphology of the product were correlated to the ion species present in the solution at different pHs.

Hisatsune, K.; Tanaka, Y.; Tani, T.; Udoh, K.; Yasuda, K.

doi: 10.1007/BF00702945pmid: N/A

The phase transformation associated with hardening in a low carat gold alloy for porcelain bonding during continuous heating was studied by resistivity measurements, hardness tests, X-ray diffraction and scanning and transmission electron microscopies. A short-range order structure, based on Au-Pd, was produced at a lower temperature. At an elevated temperature, two types of precipitation were observed. One is a nodular reaction consisting of an L12 ordered structure based on Pd3Sn and a disordered FCC structure at grain boundary. The other is a formation of spherical L12 ordered precipitates based on Pd3Sn within the grain followed by Ostwald ripening. A fine dispersed precipitate of the latter contributed to the remarkable hardening.