BIOACTIVE GLASS 13-93 FIBERS TABLE I. The Results of the Elemental Analyses solid glass block was successfully drawn to fibers. Glass Glass Glass Theoretical particles were used in early tests, but it was soon noticed that Sample Fibers Remnants their surfaces started to crystallize at the melt spinning tem- Na.o 5.93 6 perature. Some crystallites were transferred to the fibers as 11 well. When a solid block of glass was used, the homogeneous Moo 4.83 fibers were successfully manufactured and only the upper surface of the glass crystallized. Using this manufacturin P,O 4 method, -50% of the weight of the initial glass block wa 53.0 53.0 successfully drawn to fibers in each case All values are given in weight percentage. Elemental Analyses The results of the elemental analyses are shown in Table L. average sample sizes were as follows: 27 mg for 38 um The compositions are given in weight percentage. As seen in fibers, 67 mg for 100 um fibers, and 137 mg for 210 um Table I, there are no significant compositional changes in the fibers. The initial weight of the sample as well as the weight glass during the fiber manufacturing process. The manufac after immersion was measured with accuracy of 0.01 mg. tured glass fibers as well as the remnants of the glass(partly There were two parallel samples tested for each series at each crystallized) possessed an identical compositional structure time point, and the average of these two measurements is It can also be noticed that with this manufacturing method, reported in this study homogeneous glass batches can be achieved with only minor variation in compositions compared with the theoretically SEM and Compositional Analysis. For the SEM analy- calculated values techniques. The fibers were placed in\s a specimen hols a sis, test specimens were first prepared using hot mount Tensile Testing perpendicular to the surface prior to mounting so as to hieve a cross-sectional view of the fiber. After casting, the All the fibers exhibited a brittle failure and a linear force- specimens were ground and finally polished using No. 4000 deflection response to the point of failure Sic-paper. A SEM Model XL30(Philips, The Netherlands) As seen in tensile test results in Table I, there is a large equipped with an energy dispersive spectrometer(EDS) variation in tensile strength results of bioactive glass 13-93 fibers. The thinner fibers possess higher mechanical strength positional analysis. The analysis was performed by scanning values compared with the thicker fibers, but also the Weibull over the formed surface layers to achieve a compositional modulus (1.8)is the lowest for the thin fibers. The Weibull nalysis for each layer For each sample, two or three parallel modulus is higher(3. 1)for fibers with the largest diameter runs were performed. The analysis data were transferred to When all the tested fibers are considered as one lot, the Excel where, using the initial images, the distances could be Weibull modulus value is 2.1 calibrated. The compositional analysis data presented in this study are taken from samples that have been immersed in Flexural Strength Retention In Vitro SBF for 24 h and 5 weeks The results of the three-point bending tests after variou immersion times are shown in Table ll. The flexural strength RESULTS of fibers first started to decrease when immersed in Sbf. but the strength was recovered after immersion in Sbf between Processing of the Fibers 2 days and I week. After I week immersion, the flexural strength started to decrease again, and after 7 weeks, the During melt spinning, the upper surface(the one in contact flexural strength was less than 15%o of the initial strength. The with the air)of the glass block crystallized slightly. Only a decrease in strength was reasonably low from 7 to 40 weeks TABLE IL. The Effect of the Fiber Diameter on the values of Median Tensile Strength, Average Tensile Strength, and Weibull Modulus of the bioactive glass 13-93 Fibers Fiber Number Median Lowest-Highest Standard Strength (MPa) Modulus 25-33 910.10 65.3-1693.9 861.80 35742 176 34-47 809.85 147.8-1918.6 795.69 31945 2.20 93-160 424.75 150.2-725.7 15122average sample sizes were as follows; 27 mg for 38
m fibers, 67 mg for 100
m fibers, and 137 mg for 210
m fibers. The initial weight of the sample as well as the weight after immersion was measured with accuracy of 0.01 mg. There were two parallel samples tested for each series at each time point, and the average of these two measurements is reported in this study. SEM and Compositional Analysis. For the SEM analy￾sis, test specimens were first prepared using hot mounting techniques. The fibers were placed into a specimen holder perpendicular to the surface prior to mounting so as to achieve a cross-sectional view of the fiber. After casting, the specimens were ground and finally polished using No. 4000 SiC-paper. A SEM Model XL30 (Philips, The Netherlands) equipped with an energy dispersive spectrometer (EDS) (Model DX-4, EDAX International, USA) was used for com￾positional analysis. The analysis was performed by scanning over the formed surface layers to achieve a compositional analysis for each layer. For each sample, two or three parallel runs were performed. The analysis data were transferred to Excel where, using the initial images, the distances could be calibrated. The compositional analysis data presented in this study are taken from samples that have been immersed in SBF for 24 h and 5 weeks. RESULTS Processing of the Fibers During melt spinning, the upper surface (the one in contact with the air) of the glass block crystallized slightly. Only a solid glass block was successfully drawn to fibers. Glass particles were used in early tests, but it was soon noticed that their surfaces started to crystallize at the melt spinning tem￾perature. Some crystallites were transferred to the fibers as well. When a solid block of glass was used, the homogeneous fibers were successfully manufactured and only the upper surface of the glass crystallized. Using this manufacturing method,
50% of the weight of the initial glass block was successfully drawn to fibers in each case. Elemental Analyses The results of the elemental analyses are shown in Table I. The compositions are given in weight percentage. As seen in Table I, there are no significant compositional changes in the glass during the fiber manufacturing process. The manufac￾tured glass fibers as well as the remnants of the glass (partly crystallized) possessed an identical compositional structure. It can also be noticed that with this manufacturing method, homogeneous glass batches can be achieved with only minor variation in compositions compared with the theoretically calculated values. Tensile Testing All the fibers exhibited a brittle failure and a linear force￾deflection response to the point of failure. As seen in tensile test results in Table II, there is a large variation in tensile strength results of bioactive glass 13–93 fibers. The thinner fibers possess higher mechanical strength values compared with the thicker fibers, but also the Weibull modulus (1.8) is the lowest for the thin fibers. The Weibull modulus is higher (3.1) for fibers with the largest diameter. When all the tested fibers are considered as one lot, the Weibull modulus value is 2.1. Flexural Strength Retention In Vitro The results of the three-point bending tests after various immersion times are shown in Table III. The flexural strength of fibers first started to decrease when immersed in SBF, but the strength was recovered after immersion in SBF between 2 days and 1 week. After 1 week immersion, the flexural strength started to decrease again, and after 7 weeks, the flexural strength was less than 15% of the initial strength. The decrease in strength was reasonably low from 7 to 40 weeks. TABLE I. The Results of the Elemental Analyses Sample Glass Fibers Glass Remnants Theoretical Value Na2O 5.93 5.90 6 K2O 11.7 11.8 12 MgO 4.82 4.83 5 CaO 20.4 20.2 20 P2O5 4.05 4.05 4 SiO2 53.0 53.0 53 All values are given in weight percentage. TABLE II. The Effect of the Fiber Diameter on the Values of Median Tensile Strength, Average Tensile Strength, and Weibull Modulus of the Bioactive Glass 13–93 Fibers Fiber Diameter (m) Number of Samples Median Strength (MPa) Lowest-Highest Strength (MPa) Average Strength (MPa) Standard Deviation (MPa) Weibull Modulus 25–33 31 910.10 165.3–1693.9 861.80 357.42 1.76 34–47 30 809.85 147.8–1918.6 795.69 319.45 2.20 48–91 31 601.50 210.6–1887.5 651.48 389.09 1.99 93–160 32 424.75 150.2–725.7 440.57 151.22 3.06 BIOACTIVE GLASS 13–93 FIBERS 229