Sinikka Veittola

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.

Adjustable biodegradation for ceramic fibres derived from silica sols

Biodegradable silica fibres were prepared from TEOS-derived silica sols by dry spinning. The spinnability of the sols and its influence on the green state fibre structure were investigated. The same sols can be used to prepare diAerent fibre structures depending on the process stage, temperature and viscosity. The spinning moment was found to be important in order to control the biodegradation. Influence of catalysts (HNO3 and/or NH3) as well as evaporation of the liquid on the process were investigated. They did not have an influence on the spinnability, but they reduced the overall reaction time. The prepared green state fibres were aged for 1 and 3 months indicating stable structure as a function of ageing time according to the biodegradation experiments, except in the case of high catalyst concentration. A porous structure was revealed using transmission electron microscopy. Heat-treatment of the fibres induced remarkable diAerences in the fibre bulk structure according to FT‐IR measurements. # 2000 Elsevier Science Ltd. All rights reserved.

In vitro bioactivity and structural features of mildly heat-treated sol-gel-derived silica fibers.

The ability of sol-gel-derived silica fibers heat treated at a low temperature to induce formation of bone-like calcium phosphate (HCA) on their surfaces provides alternatives for the design of novel biomaterials, for example as implants used in tissue guiding or bone repairs. In this study, dry spinning was used to prepare the sol-gel fibers, which were heat-treated at 175 degrees and 250 degrees C. In addition, the differences in the surface topography (in a nanometer scale) of different fibers with respect to their in vitro bioactivity were studied. The structure of the fibers was varied using three different factors: (1) spinnable sols having varying structures and sizes of silica polymers to establish varying viscosity levels; (2) aging of green-state fibers; and (3) heat treatment of fibers. The in vitro bioactivity and solubility tests were done in simulated body fluid (SBF). To monitor surface topography and roughness of the heat-treated silica fibers, a scanning probe microscopy (SPM) with tapping mode AFM was used. Different fibers obtained clearly different properties. The fibers spun at about eta > 3.0 Pas had the best properties with respect to bioactivity, especially when they were heat-treated at 175 degrees C. It was found that surface structure in a nanometer scale was the most important factor controlling the in vitro bioactivity of heat-treated silica fibers. The correct proportions between the peaks and peak distances at the surfaces are suggested to be important with respect to in vitro bioactivity. The results indicate that peak distance distribution between 5-50 nm, especially between 5-20 nm, together with a peak height > or = 1 nm is most favorable for calcium phosphate formation.

Self-reinforcement and hydrolytic degradation of amorphous lactic acid based poly(ester-amide), and of its composite with sol-gel derived fibers.

The self-reinforcing and hydrolytic degradation of an amorphous poly(ester-amide) (PEA) based on lactic acid have been studied and compared with those of poly-L-lactide (PLLA). The studied PEA-rods were self-reinforced (SR) by solid-state die drawing resulting double shear strength. The hydrolytic degradation of PEA was studied during exposure to phosphate buffered saline at pH 7.4 and at 37 °C for 18 weeks. The degradation and mechanical properties of PEA were also followed in a self-reinforced composite structure consisting of PEA and sol-gel derived SiO2-fibers (SGF, 8 wt %). The hydrolytic degradation of the SR-PEA-rods with and without SG-fibers was significantly faster than that of SR-PLLA-rods. The weight average molecular weight (Mw) of PEA decreased by 90% from the initial Mw during the first 6 weeks in hydrolysis, when the Mw of the PLLA decreased by 10%.