Influence of sol and stage of spinnability on in vitro bioactivity and dissolution of sol-gel-derived SiO2 fibers.

The ability of the sol-gel-derived green state silica fibers to induce the formation of bone-like calcium phosphate (HCA) on their surfaces has not been studied earlier. Bioactive silica fibers provide alternatives for the design of novel products, e.g., as implants used in tissue guiding or bone repairs. In this study, dry spinning was used to prepare the sol-gel fibers. Different fibers with different bulk structures were prepared by changing the composition and controlling the stage of spinnability. Additionally, the influence of the aging time of the fibers on the bulk structure of the samples was investigated. Furthermore, the ability to form calcium phosphate was investigated in vitro in the simulated body fluid (SBF). Transmission electron microscopy was used to illustrate the bulk structure of the green state fibers and scanning electron microscopy to illustrate the formed calcium phosphate layer on the fibers. The fibers were additionally characterized by measuring the dissolution of the silica in the SBF. In vitro bioactive silica fibers were successfully prepared. The calcium phosphate layer was formed within 1-5 days in the best case. The structural stability and the in vitro bioactivity varied with the aging time expect in one case where practically stable fibers could be prepared. The concentration of silica released in the SBF had no direct connection with the HCA formation. The silica-rich gel layer was not observed on the fibers, but the structure of the fibers was suggested to have an important role in the HCA formation.

In vitro bioactivity of aerosol-gel deposited TiO(2) thin coatings.

Bioactive, pure, and Ca- or P-doped TiO(2) thin coatings on Ti metal and Si wafers were prepared by the aerosol-gel technique. The coatings were characterized by X-ray photoelectron spectroscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. Bioactivity was determined in vitro in a simulated body fluid and was shown to be fully comparable to sol gel-derived TiO(2) coatings prepared by dip-coating. However, the formation rate of carbonate containing apatite decreased with increasing dopant concentration, which was related to changes in chemical composition and topology of the coatings.

Effect of aging time of sol on structure and in vitro calcium phosphate formation of sol-gel-derived titania films.

Titanium and its alloys have been used successfully in the manufacture of orthopedic and dental implants to replace damaged bone tissue. In this study, different sol-gel-derived TiO(2) coatings were produced on titanium substrates using different aging times (5, 10, 24, or 48 h) of the sol before dipping the coatings and varying numbers (one, three, or five) of coating layers. The influence of the aging time of the sol on the structure of the titania coatings with respect to in vitro bioactivity was investigated. The in vitro bioactivity tests were done in a simulated body fluid (SBF). The sol properties were monitored using a capillary viscometer and dynamic light scattering to determine the viscosity and particle size, respectively. The topography of the films was characterized using atomic force microscopy. The various sol aging times and numbers of layers produced differences in the topography of the titania films. For the coatings with one and three layers, the aging of the sols had an influence on the height of the peaks (lower with longer aging times) although the peak distance was about the same. The number of coating layers had a stronger influence. The distribution of the peak distances became narrower with an increasing number of coating layers. The coating with three layers (top coating prepared after 24 h of sol aging) and the coatings with five layers had a similar distribution of peak distances (15-50 nm), which was favorable for calcium phosphate formation. On these substrates, calcium phosphate formation started within 3-6 days of immersion in SBF. The aging time of the titania sol and the number of coating layers were found to have a strong influence on the surface topography in the nanometer scale of the titania films. The results indicate that the topography of the outermost surface is of importance for in vitro bioactivity.

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.

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.

Evaluation of the Structure and Acid-Base Properties of Bulk Wood by FT-Raman Spectroscopy.

The structure of pine wood (Pinus silvestris L.) has been analyzed by FT-Raman spectroscopy, taking birch wood and the wood components cellulose, hemicellulose (xylan), and lignin as well as previously characterized wood resins as references. The acid-base properties of bulk pine wood were evaluated by comparing the spectra recorded before and after the treatment with various solvents. After the treatment with the probe liquids having only a Lifshitz-van der Waals (LW) component, it was found that the LW interactions in pine wood take place without changing the main structure. After treatment with Lewis acid-base active probe liquids, the spectra indicate that, e.g., the intense peak located at approximately 2936 cm-1 (CH2 stretch) seems to disappear, suggesting that this peak may be related to Lewis acidity. In addition, after treatment with a Lewis acid, it was found that the intense peak located at approximately 1657 cm-1 (C&dbond;C) is shifted, relating to Lewis basicity. With the ratio approximately 2936/ approximately 1657 cm-1 as a measure of the acid-base properties of bulk wood, a value of about 2.00 indicates that the bulk pine wood is largely acidic. The pH determined supports the evaluation made by FT-Raman spectroscopy. Copyright 1998 Academic Press.

Calcium phosphate induction by sol-gel-derived titania coatings on titanium substrates in vitro.

Titanium and its alloys are used widely in the manufacture of orthopedic and dental implants. Sol-gel-prepared titania is able to stimulate bone-like apatite formation in in vitro and in vivo cultures. These materials can be used, for example, as coatings on dental and orthopedic implants. However, the processes that lead to apatite formation are not fully understood. In this study different kinds of titania coatings on commercially pure titanium (c.p. Ti) were tested for apatite-forming ability. The rate of apatite formation is considered to be descriptive of a material's bioactive (bone-bonding) potential. Apatite-forming tests were done in simulated body fluid (SBF). Apatite-forming ability was highest with the addition of valeric acid to sol (600 degrees C) or with sintering sol-gel coatings at 450 degrees-550 degrees C. At that temperature range calcium phosphate forms on the coatings in 1 week. Calcium phosphate forming is observed in 1 day on standard coatings sintered at 500 degrees C.