Key Engineering Materials Vols. 284-286

Abstract: A new type of ceramic-polymer biomaterial having excellent apatite-forming ability in simulated body fluid (SBF) was prepared by hot-pressing a mixture consisting of poly(-L-lactic acid)(PLA) and calcium carbonate (vaterite). The composite containing 30% vaterite showed no brittle fracture behavior and comparably high bending strength of ~50 MPa. Apatite layer of several micrometers in thickness formed on its surface after soaking in SBF at 37°C only for 1 day. Osteoclast culture tests showed that the composite coated with apatite has excellent bioresorbability. After incubation of human osteoblasts, mineralized bone nodule formation was seen on the surface.

Abstract: A bioactive polyethylene polymer substrate can be produced by incorporation of sulfonic functional groups (-SO3H ) on its surface. Variation of the surface potential of the polyethylene modified with -SO3H groups with soaking in SBF were investigated using a laser electrophoresis zeta-potential analyzer. To complement the study using the laser electrophoresis, the surface was examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with an attached energy dispersive electron probe X-ray analyser (FE-SEM/EDS). It was found that the surface potential of the polyethylene was highly negative charged after soaking in SBF for 0.5 h, increased for higher soaking times (up to 48 h), and then decreased. The negative charge of the polymer at soaking time of 0.5 h is attributed to the presence of –SO3H groups on the surface. The initial increase in the surface potential was attributed to the incorporation of positively charged calcium ions to form a calcium sulphate, and then the subsequent decrease was assigned to the incorporation of negatively charged phosphate ions to form an amorphous calcium phosphate, which eventually transformed into apatite.

Abstract: This paper describes the use of confocal microscopy as a new method for in situ analysis of the apatite layer which forms on bioactive substrates after immersion in a simulated body fluid (SBF). Conventional methods such as secondary electron microscopy (SEM) require drying and coating of the samples. This approach causes damage to the structure of the apatite layer of which a common example is surface cracking. With confocal microscopy samples are examined in situ and build a unique optical sectioning of the samples. As shown in this paper, using these sections, a clear image can be constructed of the reactive layer which forms on a sample both in horizontal and vertical cross-sections.

Abstract: The adhesion of bovine collagen type I, bovine serum albumin, bovine IgG, 1 % and 10 % (v/v) human serum to hydroxyapatite (HA), silicon-substituted hydroxyapatite (Si-HA) and tissue culture plastic were studied. The materials were incubated at 37 °C for 30 minutes, after which the protein solution was removed and analyzed. The adsorbed protein was evaluated by electrophoresis and immunoassay after extraction from the materials. The degree of adhesion was higher for collagen, followed by IgG and albumin on all materials. However there was no difference in the amount of collagen adsorbed onto the surface of each material and this was also the finding with albumin and IgG. These results suggest that the increased bioactivity seen with Si-HA is not due to the degree of protein adhesion, but may possibly be due to changes in the conformation of the bound proteins.

Abstract: The structure of silica-based glasses consists on a disrupted network of SiO4 tetrahedra where network modifiers generate non-bridging oxygen groups (NBO), that play an important role at the initial steps of the bioactive process. Infrared spectroscopy is a sensitive technique to the presence of NBO groups and glass local structure modifications. The infrared study has been complemented with a theoretical approach using the Y Stevels parameter. Moreover, the in vitro bioactivity of the glasses as a function of Y Stevels paremeter has been studied, which can be a finding of a predictive tool for bioactivity of glasses.

Abstract: Organic polymers with ability of apatite formation in body environment are expected as novel bone substitutes having not only bone-bonding ability, i.e. bioactivity, but also mechanical performance analogous to natural bone. Several metal oxides have been found to be effective for the apatite deposition in body environment. In addition, release of calcium ions from the materials significantly enhances it. In this study, we attempted to synthesize bioactive organic-inorganic hybrids from Poly(vinyl alcohol) (PVA) by incorporation of various metal oxides and calcium salt. Silica and molybdenum oxides were selected as metal oxides. Ability of apatite formation on the hybrids was examined in vitro using simulated body fluid (SBF, Kokubo solution). Apatite deposition were observed to occur on the surfaces of PVA/silica and PVA/molybdenum oxide hybrids in SBF, when their compositions were appropriately controlled.

Abstract: The coatings formed on the H2O2-treated titanium substrate by electrodeposition were used in order to evaluate the difference of transformations in the simulated body fluid (SBF) and the culture medium with MG63 cells. A porous hydroxyapatite (HA) coating with relatively low crystallinity and large crystallites was formed on the H2O2-treated titanium substrate by electrodeposition. HA coating transformed for 5 days in the SBF consisted of densely-packed rod-shaped crystallites with various differentiated grains. Octacalcium phosphate (OCP) and HA coating transformed for 5 days in the culture medium consisted of both flake-shaped and rod-shaped crystallites with indistinct grains. MG-63 cells were well attached and proliferated during the transformation into this flaked-shaped OCP. This difference between transformations of the HA coatings in the acellular SBF and in the culture medium with MG63 cells is due to different ion composition in each solution and proteins in culture medium.

Abstract: Dense hydroxyapatite (HA) and hydroxyapatite/tricalcium (HA/TCP) were immersed in Fast calcified solution (FCS) at 37°C in constant temperature culture box for 7 days. It was observed that the phase components of dense ceramics affected the composition, crystallinity and phase components of formed apatites on the surface of ceramics. It is a mixture of hydroxyapatite with a strong preferential crystallographic direction of 002 and octacalcium phosphate (OCP) on the surface of HA/TCP ceramics, whereas only an HA phase was detected on the surface of HA ceramics.

Abstract: In vitro behavior of 30 new glasses in the system Na2O-K2O-MgO-CaO-B2O3 -P2O5-SiO2 was investigated by immersing them into a simulated body fluid for 4 to168 hours. This study involved the observation of both the changes in the properties of the immersion solution and on the glasses surface after immersion. In vitro reactivity was different for each experimental glass depending on its chemical composition. By comparing these glasses to four established bioactive glasses showing different in vivo bioactivity, a fast estimation of the bioactivity of glasses can be done; thereby the optimization of bioactive glasses for various clinical applications can be developed.

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.