Jarl B. Rosenholm

Influence of sol and surface properties on in vitro bioactivity of sol-gel-derived TiO2 and TiO2-SiO2 films deposited by dip-coating method

Different sol-gel-derived titania and titania-silica films were prepared and their properties related to in vitro bioactivity. The films were prepared by depositing the sols on the substrate surface using a dip-coating method. The sols were monitored carefully as a function of time, using rheological techniques and dynamic light scattering. The topography of the films was characterized using atomic force microscopy, and thicknesses and refractive indexes of the films were evaluated by fitting transmittance spectra measured in a wave length region of 370-1100 nm with a spectrophotometer. The in vitro bioactivity tests were performed in simulated body fluid. Surface topography was found to be of great importance with respect to the bioactivity of the studied films.

Calcium phosphate formation on porous sol-gel-derived SiO2 and CaO-P2O5-SiO2 substrates in vitro.

Sol-gel-derived SiO2 and CaO-P2O5-SiO2 have been shown to be bioactive and bone bonding. In this study bioactive sol-gel-derived SiO2 and CaO-P2O5-SiO2 systems were tested for in in vitro bioactivity. The calcined ceramic monoliths were immersed in a simulated body fluid and analyzed to follow the hydroxyapatite formation on the ceramic surface. Apatite-forming ability was investigated in terms of structural changes by changing the composition and the preparation method. The role of Ca and P dopants in the substrate structure is complicated, and careful characterization is needed. The composition and structure together determine the in vitro bioactivity. The pore structure was analyzed using N2-adsorption/desorption isotherms. The results indicate that a great mesopore volume and a wide mesopore size distribution favor hydroxycarbonate apatite nucleation and a great surface area is not needed. The performed preparation process for silica in a basic environment provides a convenient way to prepare a mesoporous material.

Synthesis and characterization of goethite and goethite-hematite composite: experimental study and literature survey

Aging of synthetic goethite at 140 degrees C overnight leads to a composite material in which hematite is detectable by Mössbauer spectroscopy, but X-ray diffraction does not reveal any hematite peaks. The pristine point of zero charge (PZC) of synthetic goethite was found at pH 9.4 as the common intersection point of potentiometric titration curves at different ionic strengths and the isoelectric point (IEP). For the goethite-hematite composite, the common intersection point (pH 9.4), and the IEP (pH 8.8) do not match. The electrokinetic potential of goethite at ionic strengths up to 1 mol dm(-3) was determined. Unlike metal oxides, for which the electrokinetic potential is reversed to positive over the entire pH range at sufficiently high ionic strength, the IEP of goethite is rather insensitive to the ionic strength. A literature survey of published PZC/IEP values of iron oxides and hydroxides indicated that the average PZC/IEP does not depend on the degree of hydration (oxide or hydroxide). Our material showed a higher PZC and IEP than most published results. The present results confirm the allegation that electroacoustic measurements produce a higher IEP than the average IEP obtained by means of classical electrokinetic methods.

Surface properties of in vitro bioactive and non-bioactive sol-gel derived materials.

The acid-base properties of several in vitro bioactive (able to form bone mineral-like calcium phosphate on their surfaces) and non-bioactive sol-gel processed oxides are studied. The amount of Lewis acid sites was calculated from the pyridine adsorption using the Langmuir adsorption model. The Henry adsorption model was used in cases where no specific affinity between the adsorbent and the probe molecule was observed. The results were used to calculate the specific amounts of acidic and basic sites on SiO2- and TiO2-based materials. The zeta potential was measured for dip-coated TiO2 films, calcium- and phosphate-doped TiO2 films and for a non-bioactive Al2O3 film. Also, the calcium phosphate formation in simulated body fluid on in vitro bioactive TiO2 film was studied with zeta potential measurements. The results showed dependence on the negative surface charge and the important role of calcium adsorption in the beginning of the calcium phosphate formation. Surface topography of the films was investigated with atomic force microscopy, including a detailed analysis of the peak heights and distribution over cross sections. It was observed that in vitro bioactivity was strongly dependent on the nanoscale dimensions. Consequently, the in vitro calcium phosphate formation seems to be due to both the chemical interactions and the surface structure.

The influence of pH and NaCl on the zeta potential and rheology of anatase dispersions

Abstract The rheological behaviour of anatase dispersions was compared with the ζ potential, when the pH (from 3 to 10) and sodium chloride concentration (from 0 to 1 mol dm−3) was varied over a wide range. The isoelectric point, pHiep, is shifted to higher values with increasing salt concentration until a charge reversal was no longer observed at a concentration of 1 mol dm−3 NaCl. The rheological properties were analyzed in the form of the critical yield stress and the shear stress and viscosity at arbitrarily selected high and low shear rates, respectively. The maximum of the rheological properties was found to correlate with to the pHiep. The electrokinetic and rheological features of the system were related to a recent theory of Hunter et al. [J. Colloid Int. Sci. 28 (1968) 250] by plotting the yield stress against the square of the ζ potential for each salt concentration. The acidic branch, i.e. when pH pHiep), however, the curves did not show the expected linear behaviour. Also when comparing the influence of pH and sodium chloride concentration on the rheology, it was found that on the acidic yield stress branch the dependency of pH and salt concentration was very different from the one on the alkaline branch. On the acidic branch, low ionic strengths shared a common straight line. On the contrary, the alkaline branch had separate linear dependencies for each salt concentration. Moreover, the lines on the alkaline side seemed to be quite parallel for medium salt concentrations.

Comparison of different commercial pretreatment methods for hot-dip galvanized and Galfan coated steel

Abstract The performance of different pretreatment methods for hot-dip galvanized (HDG) and Galfan coated steel has been studied by treating both substrates with three different commercial pretreatment systems. Conventional chromate based pretreatment, zinc phosphating pretreatment and zirconium based pretreatment systems were studied. The chemically pretreated substrates were characterized by using electron spectroscopy for chemical analysis (ESCA), glow discharge optical emission spectroscopy (GD-OES) and atomic force microscopy. The pretreated surfaces were coated with a polyurethane clear coat and the corrosion resistance of the coated panels was tested by a prohesion test. ESCA results show that chromium from the chromate final rinses in the conventional chromate based and the zinc phosphating pretreatment is adsorbed of equal amount. ESCA results also show that there is a difference in surface composition of the zirconic acid rinsed samples prepared with two different techniques. According to the GD-OES results the galvanized steel strip materials react to a different degree in the chromate and zirconium based pretreatments. According to the prohesion test results of the clear coated pretreated HDG samples the zirconic acid rinse pretreatment is similar in corrosion performance to the two other pretreatments studied. The prohesion test result also show that the untreated Galfan coated steel strip has better corrosion resistance than the untreated HDG steel strip.

Microbe repelling coated stainless steel analysed by field emission scanning electron microscopy and physicochemical methods

Coating of stainless steel with diamond-like carbon or certain fluoropolymers reduced or almost eliminated adhesion and biofilm growth of Staphylococcus epidermidis, Deinococcus geothermalis, Meiothermus silvanus and Pseudoxanthomonas taiwanensis. These species are known to be pertinent biofilm formers on medical implants or in the wet-end of paper machines. Field emission scanning electron microscopic analysis showed that Staph. epidermidis, D. geothermalis and M. silvanus grew on stainless steel using thread-like organelles for adhesion and biofilm formation. The adhesion threads were fewer in number on fluoropolymer-coated steel than on plain steel and absent when the same strains were grown in liquid culture. Psx. taiwanensis adhered to the same surfaces by a mechanism involving cell ghosts on which the biofilm of live cells grew. Hydrophilic (diamond-like carbon) or hydrophobic (fluoropolymer) coatings reduced the adherence of the four test bacteria on different steels. Selected topographic parameters, including root-mean-square roughness (Sq), skewness (Ssk) and surface kurtosis (Sku), were analysed by atomic force microscopy. The surfaces that best repelled microbial adhesion of the tested bacteria had higher skewness values than those only slightly repelling. Water contact angle, measured (θm) or roughness corrected (θy), affected the tendency for biofilm growth in a different manner for the four test bacteria.

Electrostatic and electrosteric stabilization of aqueous slips of 3Y-ZrO2 powder

Abstract Yttria-doped zirconia powder (3Y-ZrO2) was characterized and dispersed in distilled water. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the slip. Zeta potential, apparent viscosity and the mean particle size as a function of pH indicated the pH range of electrostatic stabilization. These results showed that electrostatic stabilization of the slip can be accomplished in low acidic and high basic range of pH. Dissolution of yttria from the powder surface in acidic pH was found to be high and fast, risky to the stability of the slip as well as the microstructure of the sintered body. Electrosteric stabilisation by addition of an anionic polyelectrolyte (PMAA-NH3) shifted the isoelectric point (IEP) to lower pH. The state of dispersion was further investigated by particle size measurements of the solid phase in the slip. The optimum amount of dispersant is discussed in terms of zeta potential and viscosity. The adsorption of polyelectrolyte is considered at pH 4, native pH of suspension and at pH 10, below and above the IEP of powder and correlated with the dissociation rate of polymer and the net surface charge of particles at given pH. Higher adsorption of dissociated polymer to the positively charged surfaces justifies the higher optimum amount of polyelectrolyte at pH 4.

Optimization of commercial zirconic acid based pretreatment on hot-dip galvanized and Galfan coated steel

Abstract The influence of a commercial zirconic acid based pretreatment has been investigated on hot-dip galvanized and Galfan coated steel. The studied pretreatment system includes two alkaline cleaning steps, an alkaline oxidation and a zirconic acid based after rinse. The optimum conditions for the after rinse were tested by varying the rinse parameters such as treatment time, temperature, solution concentration and pre- and postdrying of panels. The pretreated panels were characterized by using electron spectroscopy for chemical analysis (ESCA), glow discharge optical emission spectroscopy (GD-OES) and contact angle measurements. Pretreated panels were also clear coated and corrosion resistance of the coated panels was tested. The results show that, for the two lowest solution concentrations, time and temperature are the most important treatment parameters. They affect the amount of zirconium adsorbed in the conversion coating, but are less important for the highest solution concentration. The highest level of zirconium on the samples is obtained with the intermediate concentration, in combination with the longest treatment time and highest temperature. According to peak positions in the ESCA spectra, the Zr adsorbed is mainly in the form of ZrO2. GD-OES depth profiles show that the zirconic acid based pretreatment has reacted to different depths in the studied zinc coated steel strip materials. The trend in the corrosion resistance is similar for both substrates. According to contact angle measurements the initial pretreated surface is wetting and hydrophilic in nature. The pretreated surface was also found to age rapidly.

NMR studies of counterion binding in the water—sodium octanoate-pentanol system

Abstract The nuclear magnetic relaxation rate and quadrupole splitting of 23 Na + counterions have been studied as a function of temperature and composition for all the different phases of the three-component system sodium octanoate pentanol-water. For isotropic aqueous sodium octanoate solutions the effect on 23 Na relaxation of adding decanol, N,N -dimethylaniline, p -xylene, cyclohexane, and sodium chloride was investigated. The results are used to obtain information on the ionic interactions in the solutions. For aqueous sodium octanoate solutions a strengthened interaction of the micellarly bound counterions is observed as the amphiphile concentration is increased and addition of sodium chloride is found to lead in general to a change, not only in the fraction of bound counterions, but also in the interactions of these ions. Solubilization of pentanol and decanol in octanoate micelles leads to an enforced counterion relaxation. For the sodium octanoate-pentanol-water system, counterion binding appears to be mainly determined by the ratio of octanoate to water while the effects of phase structure (normal and reversed micellar solutions and hexagonal and lamellar liquid crystals) as well as of pentanol concentration are small. Very rapid 23 Na relaxation is observed for the highest alcohol contents of the alcohol-rich solution phases of the sodium octanoate-decanol-water and sodium octanoate-pentanol-water systems. This is ascribed to a partial dehydration of the sodium ions due to a dissociation of the reversed micelles and a formation of ion-pairs. The activation energies of the relaxation process support the conclusions drawn from the relaxation rates as do the quadrupole splittings. The latter permit some insight into the geometrical arrangement of counterions and amphiphile polar end-groups at the micellar surface. This is achieved by using the temperature dependence to deduce the sign of the order parameter. Both the relaxation rates and the quadrupole splittings indicate a considerable specificity of the ionic interactions and, over a wide concentration region in the lamellar phase, the quadrupole splittings suggest some penetration of the counterions between the polar end-groups. At the highest and lowest water contents the counterions appear to take up positions in which the ion-ion vectors are more nearly perpendicular to the lamellae.