In vitro bioactivity and gene expression by cells cultured on titanium dioxide doped phosphate-based glasses

Retention of mechanical properties and cytocompatibility of a phosphate-based glass fiber/polylactic acid composite

Polymers prepared from polylactic acid (PLA) have found a multitude of uses as medical devices. The main advantage of having a material that degrades is so that an implant would not necessitate a second surgical event for removal. In addition, the biodegradation may offer other advantages. In this study, fibers produced from a quaternary phosphate-based glass (PBG) in the system 50P(2)O(5)-40CaO-5Na(2)O-5Fe(2)O(3) (nontreated and heat-treated) were used to reinforce the biodegradable polymer, PLA. Fiber properties were investigated, along with the mechanical and degradation properties and cytocompatibility of the composites produced. Retention of mechanical properties overtime was also evaluated. The mean fiber strength for the phosphate glass fibers was 456 MPa with a modulus value of 51.5 GPa. Weibull analysis revealed a shape and scale parameter value of 3.37 and 508, respectively. The flexural strength of the composites matched that for cortical bone; however, the modulus values were lower than those required for cortical bone. After 6 weeks of degradation in deionized water, 50% of the strength values obtained was maintained. The composite degradation properties revealed a 14% mass loss for the nontreated and a 10% mass loss for the heat-treated fiber composites. It was also seen that by heat-treating the fibers, chemical and physical degradation occurred much slower. The pH profiles also revealed that nontreated fibers degraded quicker, thus correlating well with the degradation profiles. The in vitro cell culture experiments revealed both PLA (alone) and the heat-treated fiber composites maintained higher cell viability as compared to the nontreated fiber composites. This was attributed to the slower degradation release profiles of the heat-treated composites as compared to the nontreated fiber composites. SEM analyses revealed a porous structure after degradation, and it is clear that there are possibilities here to tailor the distribution of porosity within polymer matrices.

Effect of surface treatment on the bioactivity of nickel-titanium

In this paper, the bioactive properties of Ni-Ti alloy after different surface treatments were evaluated in different media (Hanks' balanced salt solution, Dulbecco's modified Eagle's medium and osteogenic). Evaluation was performed on the basis of X-ray photoelectron spectroscopy and atomic force microscopy studies after immersing samples for up to 24h in the relevant media. This allowed assessment of the kinetics of Ca(2+) and P(5+) precipitation and early interaction of the media with surfaces. In addition, the surface free energy was measured and the influence of heat treatment on phase transformation temperatures and rate of nickel and titanium ion release was investigated. The most favourable bioactive properties were observed for simply ground Ni-Ti samples when evaluated in HBSS, which showed similar properties to reference positive samples (BioactiveTi). On the other hand, samples heat-treated at 600 degrees C showed very low levels of precipitation of Ca and P. Most interestingly, evaluation in the media containing organic components (protein, vitamins, antibiotics and drugs) revealed that bioactivity for all the samples was at the same level (except for the reference negative) irrespective of the surface preparation method. It demonstrated that organic components interact with the surface rapidly, forming a thin protein layer, and this altered the surface properties of the samples, making them bioactive. No significant difference in kinetics of the Ca(2+) and P(5+) precipitation were observed. Nevertheless, further ion release and chemical composition evaluation revealed that alkali treatment and spark oxidation cannot be considered as a useful for biomedical application due to very high levels of Ni in the top layer (alkali-treated) and high rate of Ni release (spark-oxidized and alkali-treated).

Structure and properties of strontium-doped phosphate-based glasses

Owing to similarity in both ionic size and polarity, strontium (Sr2+) is known to behave in a comparable way to calcium (Ca2+), and its role in bone metabolism has been well documented as both anti-resorptive and bone forming. In this study, novel quaternary strontium-doped phosphate-based glasses, containing 1, 3 and 5 mol% SrO, were synthesized and characterized. (31)P magic angle spinning (MAS) nuclear magnetic resonance results showed that, as the Sr2+ content is increased in the glasses, there is a slight increase in disproportionation of Q2 phosphorus environments into Q(1) and Q3 environments. Moreover, shortening and strengthening of the phosphorus to bridging oxygen distance occurred as obtained from FTIR. The general broadening of the spectral features with Sr2+ content is most probably due to the increased variation of the phosphate-cation bonding interactions caused by the introduction of the third cation. This increased disorder may be the cause of the increased degradation of the Sr-containing glasses relative to the Sr-free glass. As confirmed from elemental analysis, all Sr-containing glasses showed higher Na2O than expected and this also could be accounted for by the higher degradation of these glasses compared with Sr-free glasses. Measurements of surface free energy (SFE) showed that incorporation of strontium had no effect on SFE, and samples had relatively higher fractional polarity, which is not expected to promote high cell activity. From viability studies, however, the incorporation of Sr2+ showed better cellular response than Sr(2+)-free glasses, but still lower than the positive control. This unfavourable cellular response could be due to the high degradation nature of these glasses and not due to the presence of Sr2+.

Incorporation of vitamin E in poly(3hydroxybutyrate)/Bioglass composite films: effect on surface properties and cell attachment

This study investigated the possibility of incorporating alpha-tocopherol (vitamin E) into poly(3hydroxybutyrate) (P(3HB))/Bioglass composites, which are being developed for bone tissue engineering matrices. P(3HB) films with 20 wt% Bioglass and 10 wt% vitamin E were prepared using the solvent casting technique. Addition of vitamin E significantly improved the hydrophilicity of the composites along with increasing the total protein adsorption. The presence of protein adsorbed on the composite surface was further confirmed using X-ray photoelectron spectroscopy analysis. Preliminary cell culture studies using MG-63 human osteoblasts showed that the addition of vitamin E in the P(3HB)/20 wt% Bioglass films significantly increased cell proliferation. The results achieved in this study confirmed the possibility of incorporating vitamin E as a suitable additive in P(3HB)/Bioglass composites to engineer the surface of the composites by promoting higher protein adsorption and increasing the hydrophilicity.

Effect of increasing titanium dioxide content on bulk and surface properties of phosphate-based glasses

There is an ingoing need for more effective and less costly bone substitute materials. In a previous study, addition of titanium dioxide (TiO2) up to 5 mol.% was shown to be effective in controlling glass degradation, and this was reflected in enhanced gene expression and bone-forming capacity of phosphate-based glasses. In the current study, incorporation of the maximum possible amount of TiO2 has been attempted in order to further improve the biological response of these glasses. This report describes the physical, surface properties and short-term response of an osteoblast cell line (MG63) on phosphate glasses doped with the maximum possible TiO2 content. The results showed that a maximum of 15 mol.% TiO2 can be incorporated into the ternary formulations while maintaining their amorphous nature; such incorporation was associated with a significant increase in density and glass transition temperature. On crystallization, X-ray diffraction analysis showed the presence of TiP2O7 and NaCa(PO3)3 as the main phases for all TiO2-containing glasses, while beta-(CaP2O6) was only detected for 10 and 15 mol.% TiO2 glasses. The degradation rate, however, was significantly reduced by an order of magnitude with incorporation of 10 and 15 mol.% TiO2, and this was reflected in the released ions. This change in the bulk properties, produced with TiO2 incorporation, was also associated with a significant change in the hydrophilicity and surface reactivity of these glasses. Even though the addition of TiO2 reduced the hydrophilicity and the surface free energy of these glasses compared to TiO2 free composition, TiO2-containing glasses still have a significantly reactive surface layer compared to Thermanox. Generally glasses with 5-15 mol.% TiO2 supported MG63 cell growth and maintained high cell viability for up to 7 days culture, which is comparable to Thermanox. Based on the results obtained from this study, TiO2-containing phosphate glasses are promising substrates for bone tissue engineering applications.

Ti K-edge XANES study of the local environment of titanium in bioresorbable TiO2-CaO-Na2O-P2O5 glasses

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO2-CaO-Na2O-P2O5 glasses. Both conventional melt-quenched glasses of composition (TiO2)x(CaO)0.30(Na2O)0.20-x(P2O5)0.50, where x = 0.01, 0.03 and 0.05, and sol-gel derived (TiO2)0.25(CaO)0.25(P2O5)0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO6 site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO5. The spectra from the (TiO2)0.25(CaO)0.25(P2O5)0.50 sol-gel samples reveal greater distortion in the TiO6 site in the dried gel compared to the heat-treated sol-gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.

Processing, characterisation, and biocompatibility of zinc modified metaphosphate based glasses for biomedical applications

Bulk and structural properties of zinc oxide (0 up to 20 mol%) containing phosphate glasses, developed for biomedical applications, were investigated throughout this study using differential thermal analysis (DTA), differential scanning calorimetry, X-ray powder diffraction and 31P and 23Na MAS NMR. Surface wettability and MG63 viability were also considered for surface characterisation of these glasses. The results indicated that incorporation of zinc oxide as a dopant into phosphate glasses produced a significant increase in density; however, the thermal properties presented in glass transition, and melting temperatures were reduced. NaZn(PO3)3 was detected in the X-Ray Powder Diffraction Analysis (XRD) trace of zinc containing glasses, and the proportion of this phase increased with increasing zinc oxide content. NaCa(PO3)3 as a second main phase and CaP2O6 in minor amounts were also detected. The 31P and 23Na MAS NMR results suggested that the relative abundances of the Q1 and Q2 phosphorus sites, and the local sodium environment were unaffected as CaO was replaced by ZnO in this system. The replacement of CaO with ZnO did seem to have the effect of increasing the local disorder of the Q2 metaphosphate chains, but less so for the Q1 chain-terminating sites which were already relatively disordered due to the proximity of modifying cations. Glasses with zinc oxide less than 5 mol% showed higher surface wettability, while those with 5 up to 20 mol% showed comparable wettability as zinc oxide free glasses. Regardless of the high hydrophilicity and surface reactivity of these zinc oxide containing glasses, they had lower biocompatibility, in particular 10-20 mol% ZnO, compared to both zinc free glasses and Thermanox. This may be associated with the release of significant amount of Zn2+ enough to be toxic to MG63.

Comparison of nanoscale and microscale bioactive glass on the properties of P(3HB)/Bioglass composites

This study compares the effects of introducing micro (m-BG) and nanoscale (n-BG) bioactive glass particles on the various properties (thermal, mechanical and microstructural) of poly(3hydroxybutyrate) (P(3HB))/bioactive glass composite systems. P(3HB)/bioactive glass composite films with three different concentrations of m-BG and n-BG (10, 20 and 30 wt%, respectively) were prepared by a solvent casting technique. The addition of n-BG particles had a significant stiffening effect on the composites, modulus when compared with m-BG. However, there were no significant differences in the thermal properties of the composites due to the addition of n-BG and m-BG particles. The systematic addition of n-BG particles induced a nanostructured topography on the surface of the composites, which was not visible by SEM in m-BG composites. This surface effect induced by n-BG particles considerably improved the total protein adsorption on the n-BG composites compared to the unfilled polymer and the m-BG composites. A short term in vitro degradation (30 days) study in simulated body fluid (SBF) showed a high level of bioactivity as well as higher water absorption for the P(3HB)/n-BG composites. Furthermore, a cell proliferation study using MG-63 cells demonstrated the good biocompatibility of both types of P(3HB)/bioactive glass composite systems. The results of this investigation confirm that the addition of nanosized bioactive glass particles had a more significant effect on the mechanical and structural properties of a composite system in comparison with microparticles, as well as enhancing protein adsorption, two desirable effects for the application of the composites in tissue engineering.