# Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications
## 1 Introduction
This is applied for the production of so-called Vycor-brand glass, in which porous glass with a high SiO2 content is produced by extracting a borate segregation phase [6]. An exceptional variety of applications is offered by bioactive glasses, which are also classified as hydrolvtically active. Searching for a material that could form a direct contact with the bone without being encapsulated in fibrous tissue, the first bioactive glass was discovered by [PERSON] in 1969. The hypothesis underlying his work involved the fact that a material capable of forming a bone-like hydroxyapatite (HAp) layer on its surface should not be rejected by the body, as HAp is the main mineral phase of natural bone tissue. The glass composition 45 SiO2-24.5 Na2O-24.5 CaO-6P2O5 (wt%) is referred to as 45S5 and it was trademarked under the name Bioglass(r) by the University of Florida [7]. Since the discovery of 45S5 glass, many other bioactive glass (BG) compositions have been developed. These are not silicate glasses alone, but also borate glasses, which, as already mentioned, exhibit particularly high dissolution rates and, in addition, the ability to form apatite, as well as phosphate glasses, which exhibit less pronounced bioactivity but high solubility as soon as they come into contact with biological fluids. Alongside their ability to form hydroxyapatite-like surface layers after being put in contact with biological fluids, BG are also osteoinductive, i.e., they are able to stimulate bone cells, thus significantly accelerating tissue healing for both, hard and soft tissue, stimulate angiogenesis and inhibit bacterial growth [7; 8; 9; 10]. In the vast majority of applications, medical products made of and containing bioactive glass are offered as powders or granules. Products with short, randomly oriented fibres that can be loaded with antibacterial agents and growth factors are serving as wound dressings [10]. Despite the success of commercially available, granular bioactive glasses used as bone substitute, they suffer from a few drawbacks as a defined and enclosed cavity is always required for the application. Otherwise, migration of the material into the surrounding tissue will occur [11; 12]. Easier to handle than particles are 3D porous scaffolds [13], composite materials in which the glass particles [14; 15] or short fibres [16] are embedded in biocompatible polymers [17], scaffolds with disordered fibre orientation created by electrospinning [10] or melt-derived microfibres [18]. Continuous fibres made from bioactive glasses that can be processed into textiles would be very attractive for numerous medical applications. For example, they might serve as reinforcing fibres in resorbable polymers, which could offer exciting prospects for load-bearing implants, as studied by [PERSON] et al. [19]. Moreover, textiles made of BG would also be a promising option for wound closure and may additionally be loaded with ions to specifically promote tissue regeneration. Furthermore, flexible, porous and customised scaffolds for tissue engineering could be produced from fibres. Textile glass fibres can be made from strong viscous melts with melt spinning by downdrawing from bushing tips (Figure 1). Glass fibre formation involves a combination of extrusion and attenuation. During extrusion, the molten glass exits through a bushing made of an erosion-resistant platinum/rhodium alloy with very fine orifices. The winders apply tension to the glass, drawing it out into thin filaments. These are cooled by water spray, coated with a sizing and gathered together to form a strand. The most important melt properties are: the fibre-forming viscosity (\(\eta\)) that is quoted between \(10^{1.8}\) to \(10^{2.5}\) Pa-s and its corresponding temperature, the liquidus temperature at which crystals can form within hours and remain in equilibrium in melt and the processing temperature range, that is the difference between fibre-forming and liquidus temperature.