# Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications
## 4 Discussion  
The production of continuous fibres from medically approved bioactive glasses would be very attractive for many applications. A broad field of application would arise for resorbable materials. Currently, these materials, mostly plastics or metals, are not suitable for load-bearing implants because resorption is inherently accompanied by a loss of mechanical strength. In this regard, fibre-reinforced composites would be of great interest if the degradation of fibres and matrix could be tailored. A suggested concept for resorbable polymers reinforced with bioactive glass fibres for medical applications was presented in the publication by [PERSON] et al. [19]. In this regard, fibres made from hydrolytically active glass compositions could make an important contribution. In this study, the temperature and viscosity behaviour of the four glass compositions 1-06, 18-06, 13-93 and S53P4 were investigated with regard to the production of continuous fibres. For this purpose, glass cuboids were prepared and the analytical compositions determined. Various known compositions [31; 32] were used to select the glasses and the following considerations were made. S53P4 is a certified bioactive glass, so fibres from these glasses would be of particular interest. It is known from the literature that glass 13-93 can be drawn into fibres [29; 37]. Composition 1-06 differs only slightly from this, but in theory should dissolve more quickly because it contains B2O3. Glass 18-06 is a known experimental composition that has a higher silicate content and is therefore most likely to be processed into fibres. While glasses 13-93, 1-06 and 18-06 all showed a temperature interval for processing of more than 200 K, for glass S53P4 only a range of 25 K was determined. This is clearly below the 70 K required by [PERSON] [20] and indicates a very high tendency to crystallise, which could already be demonstrated in the hot stage microscope. It became obvious that glass S53P4 crystallised before reaching the softening temperature. In this respect, it seems almost impossible to produce fibres from this glass composition. With the help of these determined parameters, the fibres for all glass compositions except S53P4 were drawn from previously produced glass blocks using the nozzle drawing method and fibres of diameters below 15 \(\upmu\)m were obtained. These diameters correspond to technical glass fibres, for which a range of 4 to 20 \(\upmu\)m is reported [21]. The strengths of glass fibres may vary enormously, as they depend on the composition. While military fibre optics glass fibres (FOG-M) have very high tensile strengths of  
Figure 14: Representative images of the pre-osteoblast cells MC3T3-E1 adhered to the distinct bioactive glass fibres (**A–C**), depicting nuclei (blue), the structural protein actin (magenta) and the glycoprotein of the ECM fibronectin (green). (**A\({}_{1}\)–C\({}_{1}\)**) show enlarged sections of the image (magnification in the dashed orange squares). Scale bars 50 \(\upmu\)m (**upper row**) and 20 \(\upmu\)m (**lower row**). 5570 MPa, porous silica fibres produced by leaching E-glass with hydrochloric acid achieve strengths just below 400 MPa. The strengths of the produced bioactive glass fibres are in the range of about 900 to 1200 MPa and are similar to the values of sodium silicate glass fibres and phosphate glass fibres (300 to 1500 MPa) [21; 38], but are significantly below technical E-glass fibers, for which values between 2500 and 4000 MPa are reported [27; 21]. Since fibre strength is a measure of both internal structure and surface uniformity, surface defects, segregations or small crystallites appear to be more common in hydrolvically active glass fibres.