BIOACTIVE GLASS 13-93 FIBERS Elemental analysis of bioactive glass 13-93 fiber The flexural strength of glass fibers decreased slightly after 24 hours of immersion in SBF after immersion in sbf. but it further increased from the nitial strength value after 1 week of immersion. As brittle materials,glass fibers are very sensitive to the presence of 0600 microscopic imperfections, or flaws, which behave as stress concentrators. As the si-gel forms on the bioactive glass surface, it overcomes the microscopic imperfections or flaw in the surface and the strength of the fibers is increased. this can also be detected from the Weibull modulus value that is 2 for nonimmersed fibers, but increases up to 3.6 for im- Distance from fiber surface/um mersed fibers, onto which a Si-rich layer has been formed. Figure 3. The EDXA analysis result of bioactive glass 13-93 fiber After I week immersion time, the flexural strength starts to surface after 24 h of immersion in SBF. Distance from the fiber surface decrease and this is probably due to increasing thickness of measured toward the centre of the fiber the CaP-layer. This layer forms a brittle core and decrease the overall strength of the fibers. from 5 to 40 weeks. the further decrease in strength is rather low, and this may be analysis data, it can be noticed that after 24 h the Na+, K+. explained by the fact that the CaP-layer reaches sufficient and Ca2+have started to diffuse out from the glass surface, thickness and slows down the further degradation and leach- and there is an increase in the amount of silicon in the glass ing of ions from the glass. The flexural modulus starts to surface. The transformed layer has a thickness varying from decrease steadily after 1 week of immersion. This is most 2 to 3 um after 24 h of immersion probably due to the transfer of the stiff glass phase to the low In the compositional analysis for fibers immersed for 5 modulus Si-gel layer. The high standard deviation in modulus weeks into SBE, there is a clear Ca-and P-rich layer on the values after 2 weeks immersion is probably due to the inho fiber surface and a Si-rich layer beneath the CaP-rich layer en in Figures 4 and 5. The Cap-rich layer has uniform The change in mass in vitro correlates closely to the thickness of-2 um all over the fiber surface. The thickness surface area of the glass samples, as the samples with uniform of the Si-rich layer is variable over the fiber surface, and as surface areas, but variable initial masses, had a uniform shown in Figure 6, the thickness of the Si-rich layer is -5-30 change in overall mass, and so the change in mass was um after 5 weeks of immersion in SBF. From Figure 6, it can proportional to the surface area of the samples, rather than the be noticed that the remnants of an additional CaP-rich layer total volume of the samples. The initial leaching of ions can can be detected on top of the continuous CaP-rich layer. be detected as a loss of mass. Later in the experiment, the During sample preparation, it was noticed that as the samples mass of the samples increased, which is caused by the con- were dried, the CaP-rich surface became very brittle and tinuous increase in thickness of the CaP-layer. The diffusion some of the outer layer detached from the fiber surface of the elements from the surface rules the degradation of structures manufactured from bioactive glass. The total deg radation of the bioactive glass structures can be adjusted by controlling the surface/volume ratio. Thin fibers are expected DISCUSSION to resorb and transform to calcium phosphate faster than thicker fibers The formation of a hydroxycarbonate apatite layer on top of From the compositional analysis, on the reacted surfaces, the bioactive glass is a result of the following steps: (1) the dissolution of ions was clearly observed. A Si-rich layer leaching and formation of silanols (SiOH); (2) loss of soluble silica and formation of silanols; (3) polycondensation of Elemental analysis of bioactive glass 13-93 fiber silanols to form a hydrated silica gel; (4)formation of an after 5 weeks immersion in SBF amorphous calcium phosphate layer; and(5)crystallization of a hydroxycarbonate apatite layer. The formation of the Si nd CaP-rich layers in glass surfaces are usually analyzed be 25 by techniques such as X-ray diffraction(XRD), Fourier trans form infrared(FTIR)spectroscopy, or SEM. 6 The effect of formation of Si-and CaP-rich layers to the mechanical prop- $150 erties of the glasses has not been studied earlier. When 8 100 bioactive glass is drawn to fibers, very uniform test speci mens are achieved from which, for example, mechanical properties can be measured. In this study, the formation of 4 6 8 reactive layers on top of the surface of bioactive glass 13-93 Distance from fiber surface / um fibers was investigated, and its effect to mechanical proper- Figure 4. The result of EDXA analysis of bioactive glass 13-93 fiber ties and mass have been analyzed surface after 5 weeks of immersion in SBfanalysis data, it can be noticed that after 24 h the Na, K, and Ca2 have started to diffuse out from the glass surface, and there is an increase in the amount of silicon in the glass surface. The transformed layer has a thickness varying from 2 to 3
m after 24 h of immersion. In the compositional analysis for fibers immersed for 5 weeks into SBF, there is a clear Ca- and P-rich layer on the fiber surface and a Si-rich layer beneath the CaP-rich layer as seen in Figures 4 and 5. The CaP-rich layer has uniform thickness of
2
m all over the fiber surface. The thickness of the Si-rich layer is variable over the fiber surface, and as shown in Figure 6, the thickness of the Si-rich layer is
5–30
m after 5 weeks of immersion in SBF. From Figure 6, it can be noticed that the remnants of an additional CaP-rich layer can be detected on top of the continuous CaP-rich layer. During sample preparation, it was noticed that as the samples were dried, the CaP-rich surface became very brittle and some of the outer layer detached from the fiber surface. DISCUSSION The formation of a hydroxycarbonate apatite layer on top of the bioactive glass is a result of the following steps: (1) leaching and formation of silanols (SiOH); (2) loss of soluble silica and formation of silanols; (3) polycondensation of silanols to form a hydrated silica gel; (4) formation of an amorphous calcium phosphate layer; and (5) crystallization of a hydroxycarbonate apatite layer.15 The formation of the Si￾and CaP-rich layers in glass surfaces are usually analyzed be by techniques such as X-ray diffraction (XRD), Fourier trans￾form infrared (FTIR) spectroscopy, or SEM.16 The effect of formation of Si- and CaP-rich layers to the mechanical prop￾erties of the glasses has not been studied earlier. When bioactive glass is drawn to fibers, very uniform test speci￾mens are achieved from which, for example, mechanical properties can be measured. In this study, the formation of reactive layers on top of the surface of bioactive glass 13–93 fibers was investigated, and its effect to mechanical proper￾ties and mass have been analyzed. The flexural strength of glass fibers decreased slightly after immersion in SBF, but it further increased from the initial strength value after 1 week of immersion. As brittle materials, glass fibers are very sensitive to the presence of microscopic imperfections, or flaws, which behave as stress concentrators. As the Si-gel forms on the bioactive glass surface, it overcomes the microscopic imperfections or flaws in the surface and the strength of the fibers is increased. This can also be detected from the Weibull modulus value that is 2 for nonimmersed fibers, but increases up to 3.6 for im￾mersed fibers, onto which a Si-rich layer has been formed. After 1 week immersion time, the flexural strength starts to decrease and this is probably due to increasing thickness of the CaP-layer. This layer forms a brittle core and decreases the overall strength of the fibers. From 5 to 40 weeks, the further decrease in strength is rather low, and this may be explained by the fact that the CaP-layer reaches sufficient thickness and slows down the further degradation and leach￾ing of ions from the glass. The flexural modulus starts to decrease steadily after 1 week of immersion. This is most probably due to the transfer of the stiff glass phase to the low modulus Si-gel layer. The high standard deviation in modulus values after 2 weeks immersion is probably due to the inho￾mogenity of the Si-gel and CaP layers. The change in mass in vitro correlates closely to the surface area of the glass samples, as the samples with uniform surface areas, but variable initial masses, had a uniform change in overall mass, and so the change in mass was proportional to the surface area of the samples, rather than the total volume of the samples. The initial leaching of ions can be detected as a loss of mass. Later in the experiment, the mass of the samples increased, which is caused by the con￾tinuous increase in thickness of the CaP-layer. The diffusion of the elements from the surface rules the degradation of structures manufactured from bioactive glass. The total deg￾radation of the bioactive glass structures can be adjusted by controlling the surface/volume ratio. Thin fibers are expected to resorb and transform to calcium phosphate faster than thicker fibers. From the compositional analysis, on the reacted surfaces, the dissolution of ions was clearly observed. A Si-rich layer Figure 4. The result of EDXA analysis of bioactive glass 13–93 fiber surface after 5 weeks of immersion in SBF. Figure 3. The EDXA analysis result of bioactive glass 13–93 fiber surface after 24 h of immersion in SBF. Distance from the fiber surface measured toward the centre of the fiber. BIOACTIVE GLASS 13–93 FIBERS 231