## 1 Introduction  
Electrospinning is a widely used technique based on a starting polymeric solution and high electric field between two electrodes to fabricate nano- and micro- fibers for biomedical applications. Nanosized fibers mimicking the original structure of extracellular matrix (ECM) [1] can be fabricated by electrospinninging technique. The features of samples are affected by (i) solution parameters (i.e., rheological properties, type of solvent(s), etc. ), (ii) process parameters, and (iii) environmental parameters [1; 2; 3; 4]. Among them, the selection of a proper solvent system plays a crucial role on the features of samples [5; 6]. Recently, the standard solvents used for the electrospinning process, which are toxic, such as chloroform, dichloromethane, hexafluoro-2-propanol, dimethylformamide, methanol, or a mixture of them, have been increasingly substituted by less harmful solvents such as acetic acid, formic acid or acetone [7; 8; 9], which have been defined as benign solvents [10], highlighting the important properties related to prevention of biopolymer denaturation and presence of traces of toxic solvents on the fibers, as well as having a positive environmental impact. Poly(\(\varepsilon\)-caprolactone) (PCL) has been widely used in combination with benign solvents (acetic acid or formic acid or acetone) to develop the starting polymeric solution for the production of electrospun mats [7; 8; 9; 10]. PCL is widely investigated for biomedical applications because of its biocompatibilityand biodegradationability [11; 12; 13] and is approved by the Food and Drug Administration (FDA) for clinical use. However, PCL bioactivity can be enhanced by the addition of bioactive biomaterials such as bioactive glasses (BGs). Generally, bioactive glasses have shown high bioactivity and high interaction with hard and soft tissues [14; 15]. In this work, 45S5 BG (composition 45 wt% SiO\({}_{2}\), 24.5 wt% CaO, 24.5 wt% Na\({}_{2}\)O, and 6.0 wt% P\({}_{2}\)O\({}_{5}\)) [16], Sr- and Mg-substituted bioactive glass (BGMS10 [17; 18; 19; 20; 21; 22; 23]), and Zn-substituted bioactive glass (BGMS_2 Zn [24]) were incorporated in PCL fibers by electrospinningning technique. BGMS10 was designed starting from the composition of 45S5 by adding SrO and MgO; subsequently, ZnO was added to the BGMS10 composition to produce a Zn-substituted bioactive glass labelled as BGMS_2 Zn [24]. The incorporation of different ions into bioactive glass compositions aims to impart specific biological functionalities and to enhance the therapeutic behavior [25; 26; 27; 28]. In particular, Sr has been shown to enhance osteogenic differentiation, to stimulate osteoblast differentiation [29] and bone formation [30; 31; 32; 33] as well as angiogenesis and cell proliferation [34; 35; 36]. Furthermore, Sr, because of its anabolic and anti-resorptive effect on bone, is already in use as strontium ranelate in the treatment of osteoporosis [37]. Mg, which is the 4 th most abundant cation in the human body, not only stimulates stem cells proliferation and differentiation but it plays a pivotal role in bone metabolism by enhancing ALP activity [38]. Furthermore, Mg can be useful for bone regeneration [39; 40]. Therefore, it is expected that PCL fibers containing BGMS10 and BGMS_2 Zn particles will release Sr and Mg showing enhanced cell adhesion and proliferation in in vitro tests. In addition, it is expected that PCL fibers containing BGMS_2 Zn particles will also release Zn ions. Zn is not only essential for cell growth and proliferation, but it also takes part in enzyme production, replication of DNA, and growth factors (GFs) [41; 42; 43]. Furthermore, Zn ions have shown antimicrobial properties [44; 45; 46]. Therefore, the incorporation in PCL fibers of such ion-doped BGs aims to enhance bioactivity, cell proliferation, and angiogenesis as well [47; 48; 49; 50].