Fabrication of biopolymer-based staple electrospun fibres for nanocomposite applications by particle-assisted low temperature ultrasonication Elias Mulky a,b , Gökçe Yazgan b,c , Katharina Maniura-Weber b , Reto Luginbuehl a , Giuseppino Fortunato c, ⁎, Ana-Maria Bühlmann-Popa c a RMS Foundation, Chemistry & Biology, Bischmattstrasse 12, Bettlach, Switzerland b Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Materials–Biology Interactions, Lerchenfeldstrasse 5, 9014 St Gallen, Switzerland c Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Protection and Physiology, Lerchenfeldstrasse 5, 9014 St Gallen, Switzerland abstract article info Article history: Received 24 March 2014 Received in revised form 18 August 2014 Accepted 10 September 2014 Available online 16 September 2014 Keywords: PLLA Staple fibres Fibre reinforced composite Nanoparticles Ultrasonication We demonstrate the fabrication of staple polymer-based fibres by the ultrasound-assisted processing of electrospun meshes. Bioabsorbable Poly-L-Lactic Acid (PLLA) was electrospun from organic solvent mixtures, yielding continuous fibres with diameters in the range of 244 ± 78 nm. Subsequently, the obtained fibres were sonicated at low temperatures in the presence of nanoparticles in order to obtain fibres with small aspect ratios. The influence of the dispersion medium, the sonication process parameters (temperature and time) and the dimensions of the particles used on the respective length distribution of the obtained nanofibres was inves- tigated. Hexane was identified as an optimal dispersion medium for the system studied in this work. When a cooling bath temperature of 0 °C was used, a slight increase in the obtained fibres' average length and distribu- tion was observed as compared to cooling at -80 °C (54 ± 43 μm vs 44 ± 31 μm). Moreover, in the presence of hydroxyapatite and hydrophilic and hydrophobic TiO 2 nanoparticles in the dispersion medium longer fibres were obtained (44 ± 31 μm, 63 ± 47 μm, and 51 ± 52 μm). Finally, the application of the obtained PLLA- fibre–hydroxyapatite (HA) nanoparticle precursors for the fabrication of a fibre-reinforced Brushite-based ce- ment with high compressive strength is shown. This method of obtaining nanoscaled fibre-reinforced materials opens up a wide range of perspectives for the fabrication of composites for tissue engineering applications. © 2014 Published by Elsevier B.V. 1. Introduction Dispersed short discontinuous fibres, also known as staple fibres, are widely used as additives in polymeric materials and cement-based matrices to engineer fibre reinforced composites (FRCs) [1–3]. With the increasing interest in micro- and nano-scale composites – especially in the field of bone and tissue engineering – the required raw materials and resulting structures are fabricated in micrometre to nanometre scale to improve mechanical properties or to mimic biological features and elicit specific biological reactions [4–6]. Electrospinning is a very versatile method to produce nano- to micron-sized fibres from a wide range of polymeric and inorganic materials [7–10]. This process typical- ly yields oriented or random non-woven fibre mats [7,11,12]. Electrospinning is used in many applications [13], including tissue engi- neering [14–17], drug delivery [8], or high performance membranes and textiles [18–21]. The process typically does not yield staple fibres, but it generates meshes and spindles with endless, partially fused fibres [22]. Therefore, subsequent processing steps are required to cut and unbun- dle into staple fibres of desired length, which can be further dispersed into relevant polymer or inorganic matrices. Different processes for the production of staple fibres with diameters down to 5 μm have been described; however few investigations on the scission of submi- cron sized fibres have been conducted. Stoiljkovic and co-workers proc- essed electrospun microfibres from polystyrene-co-butadiene containing n-butyl methacrylate and Coumarin as a photocrosslinker. By irradiating the resultant fibre meshes with UV light under a mask the dissolution of non-irradiated areas in THF could be achieved, generating staple fibres of 20 to 150 μm in length dependent on the photomask used [23]. This process is thus suitable only for fibres containing photosensitive groups. Poly-L-Lactic Acid-co-polyethylene oxide staple fibres in the range of 10 μm were obtained by freezing the nanofibre meshes in ethanol using liquid nitrogen, followed by mechanical cutting using a motor driven blade [24]. High shear homogenization was applied for the milling of high molecular weight styrene-co-4-vinylbenzyl 2-brompropionate nanofibre meshes [25]. Greenfeld and collaborators observed the appearance of discrete short fibres up to a length of 1 mm when electrospinning low molecular weight polymethyl-methacrylate (PMMA) (15 kDa) [26]. In a recent work, Sawawi and co-workers Materials Science and Engineering C 45 (2014) 277–286 ⁎ Corresponding author. E-mail addresses: reto.luginbuehl@rms-foundation.ch (R. Luginbuehl), giuseppino.fortunato@empa.ch (G. Fortunato). http://dx.doi.org/10.1016/j.msec.2014.09.009 0928-4931/© 2014 Published by Elsevier B.V. Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec