Strong, tough and bio-degradable polymer-based 3D-ink for fused filament fabrication (FFF) using WS2 nanotubes

Abstract

WS 2 inorganic nanotubes (WS 2-NT) have been incorporated into Polylactic Acid (PLA) by melt mixing to create a biodegradable , mechanically reinforced nanocomposite filament. The filament was then processed by Fused Filament Fabrication (FFF) 3D-printer, and the morphology and characteristics before and after printing were compared. We found that addition of WS 2-NT to PLA by extrusion mixing increases the elastic modulus, yield strength and strain-at-failure by 20%, 23% and 35%, respectively. Moreover, we found that the printing process itself improves the dispersion of WS 2-NT within the PLA filament, and does not require changing of the printing parameters compared to pure PLA. The results demonstrate the advantage of WS 2-NT as reinforcement specifically in 3D-printable polymers, over more traditional nano-reinforcements such as graphene and carbon nanotubes. WS 2-nt based 3D-printable nanocomposites can be used for variety of applications from custom-made biodegradable scaffold of soft implants such as cartilage-based organs and biodegradable soft stents to the more general easy-to-apply nano-reinforced polymers. Advanced manufacturing, and especially 3D printing, has attracted a lot of attention in the last decades, mostly due to its high versatility in materials and designs-including topographies that cannot be produced in traditional subtractive manufacturing, and the ease of custom-tailoring products. The latter has enormous advantage in the medical fields-especially orthopedic, dental and plastic medicine, as it allows precise anatomical design of the printed device-be it an implant, a surgical tool or a support model-to the specific patient 1,2. The most widely used printing technique is the Fused Filament Fabrication (FFF) used to fabricate thermoplastics such as Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS) and Polycarbonate (PC). In FFF, a thermoplastic filament is extruded through a heated nozzle onto a build platform as layer by layer are infused together to a final solid shape. The temperature of the extruding nozzle and build platform, as well as layer thickness, orientation, and printing speed can be tailored to control the properties of the final product. The use of thermoplastic polymers allows for fast, low-cost and relatively simple fabrication of lightweight structures, but the final product will be mechanically weak. Moreover, as the demand for multifunctional materials increases, the need for complex designs to optimize the use of such materials also rises 3-5. Polymer matrix composites, and especially nanocomposites, propose an elegant solution: the micro-and nano-additives will provide improved mechanical 6 , electrical 7 , and other desired properties, while the polymer matrix maintains ease of fabrication and lightweight structure. The choice of nanofillers and thus of properties is vast 4,8 , but the transition from a pure polymer to polymer nanocomposite is far from trivial. Issues such as adhesion, orientation and dispersion of the nanofillers within the final prod...

Interaction of Poly L-Lactide and Tungsten Disulfide Nanotubes Studied by In Situ X-ray Scattering during Expansion of PLLA/WS2NT Nanocomposite Tubes

“…WS 2 NTs are a promising choice of nanofiller because of their established synthesis methods [51,52], high aspect ratio, excellent mechanical properties [53], and lack of known cytotoxicity [54][55][56]. Moreover, recent studies on PLA/WS 2 NT nanocomposites blended by melt mixing showed the capacity of WS 2 NTs to easily disperse in the polymer matrix, promote PLA crystallization, and reinforce PLA at low loading (0.5 wt%) [57][58][59][60]. As an additional advantage, WS 2 could confer enhanced radiopacity to a PLLA-based BVS [61] due to the higher atomic number of tungsten (compared to the carbon and oxygen atoms of the PLLA), which would enable X-ray imaging of the BVS during implantation and follow-up treatment.…”

Tungsten disulfide nanotubes enhance flow-induced crystallization and radio-opacity of polylactide without adversely affecting in vitro toxicity

“…WS 2 nanoparticles possess beneficial physical and mechanical properties [44,74] and have recently been studied for various biomedical applications such as friction-reducing agents in nickeltitanium alloys [75] and for reinforcing orthopedic implants [53]. The first step in the use of these nanomaterials for any medical application is to assess their biocompatibility in vitro.…”

“…Despite the fact that medical implants made of pure tungsten release tungsten into the blood stream as they corrode [34,35], studies on patients who received implanted tungsten embolization coils have revealed no toxicity in adult and pediatric patients [34,[36][37][38][39]. The literature lead us to the mineral tungstenite (tungsten disulfide, WS 2 ) for four reasons: methods to create high aspect ratio particles are well established (WS 2 nanotubes, WSNT) [40,41], WSNT disperse readily in PLA (among other polymers) without any surface modification [42,43], 0.5 wt% of WSNT increases the elastic modulus, yield strength and strain at failure of extruded PLA by 20%, 23% and 35%, respectively [44] and WS 2 nanoparticles show promising biocompatibility in vitro [45][46][47]. The high-aspect ratio (30-150 nm diameter, 1-20 µm length, [44]) of WSNT is expected to favor preferential orientation along the hoopdirection of the BVS during tube expansion, the first step of BVS processing where a nearly radial deformation is applied to an extruded PLA tube.…”

“…The literature lead us to the mineral tungstenite (tungsten disulfide, WS 2 ) for four reasons: methods to create high aspect ratio particles are well established (WS 2 nanotubes, WSNT) [40,41], WSNT disperse readily in PLA (among other polymers) without any surface modification [42,43], 0.5 wt% of WSNT increases the elastic modulus, yield strength and strain at failure of extruded PLA by 20%, 23% and 35%, respectively [44] and WS 2 nanoparticles show promising biocompatibility in vitro [45][46][47]. The high-aspect ratio (30-150 nm diameter, 1-20 µm length, [44]) of WSNT is expected to favor preferential orientation along the hoopdirection of the BVS during tube expansion, the first step of BVS processing where a nearly radial deformation is applied to an extruded PLA tube. Surprisingly, we found that the WSNT remain mainly oriented along the axial direction of the initial extruded tube while PLA crystals orient along the hoop direction (as neat PLA) [48].…”

Poly(L-lactic acid) Reinforced with Hydroxyapatite and Tungsten Disulfide Nanotubes

“…The presence of minute amounts of solvent adversely affected the nanotube-PLLA interaction and consequently the mechanical properties of the film. In the future, solvent-free processing of the film can be envisaged, like hot-pressing, or extrusion, and subsequent 3D printing [74].…”