Effect of the reduced graphene oxide (rGO) compaction degree and concentration on rGO-polymer composite printability and cell interactions

Graphene derivatives combined with polymers have attracted enormous attention for bone tissue engineering applications. Among others, reduced graphene oxide (rGO) is one of the preferred graphene-based fillers for the preparation of composites via melt compounding, and their further processing into 3D scaffolds, due to its established large-scale production method, thermal stability, and electrical conductivity. In this study, rGO (low bulk density 10 g L-1) was compacted by densification using a solvent (either acetone or water) prior to melt compounding, to simplify its handling and dosing into a twin-screw extrusion system. The effects of rGO bulk density (medium and high), densification solvent, and rGO concentration (3, 10 and 15% in weight) on rGO dispersion within the composite, electrical conductivity, printability and cell-material interactions were studied. High bulk density rGO (90 g L-1) occupied a low volume fraction within polymer composites, offering poor electrical properties but a reproducible printability up to 15 wt% rGO. On the other hand, the volume fraction within the composites of medium bulk density rGO (50 g L-1) was higher for a given concentration, enhancing rGO particle interactions and leading to enhanced electrical conductivity, but compromising the printability window. For a given bulk density (50 g L-1), rGO densified in water was more compacted and offered poorer dispersability within the polymer than rGO densified in acetone, and resulted in scaffolds with poor layer bonding or even lack of printability at high rGO percentages. A balance in printability and electrical properties was obtained for composites with medium bulk density achieved with rGO densified in acetone. Here, increasing rGO concentration led to more hydrophilic composites with a noticeable increase in protein adsorption. Moreover, scaffolds prepared with such composites presented antimicrobial properties even at low rGO contents (3 wt%). In addition, the viability and proliferation of human mesenchymal stromal cells (hMSCs) were maintained on scaffolds with up to 15% rGO and with enhanced osteogenic differentiation on 3% rGO scaffolds

Valorization of seashell waste in polypropylene composites: An accessible solution to overcome marine landfilling

Waste mussel (Mytilus galloprovencis) and clam (Ruditapes philippinarum) shells can be used as a bio-filler in polymeric composites. In this work, powdered shell wastes were incorporated into a polypropylene (PP) matrix. The powdered shell wastes were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy equipped with an energy dispersive spectrometer (SEM-EDS). DSC analysis of the PP composites indicates that both fillers did not act as nucleating agents but partially interfere with the formation of the crystalline phase of the polymer matrix. Moreover, by increasing the filler content, the elastic modulus of PP enhanced from ∼450 to ∼510 MPa. Finally, it was evidenced that mussels and clams shell powders enhanced the solar reflectance features of PP

Study of the compounding process parameters for morphology control of LDPE/layered silicate nanocomposites

A careful insight into melt compounding procedure is proposed in order to achieve a better understanding and control of the dispersion and orientation mechanisms of organo-clay platelets into LDPE nanocomposites. The method involved is the preparation of a maleic anhydride grafted polyethylene master-batch containing 10 wt% organo-clay via twin-screw extrusion. A substantial nano-dispersion and orientation of clay platelets was obtained as observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Moreover, the nanocomposites prepared by diluting the master-batch through the blend mixing with additional LDPE preserved or improved the exfoliation and lamellae orientation. Finally, the thermo-gravimetric analysis (TGA) showed a significant improvement of the thermal stability while both differential scanning calorimetry (DSC) and XRD evidenced a slight increase of the LDPE crystallinity degree with respect to neat polymer matrices thus suggesting the occurrence of orientation also for the polymer

Study of the compounding process parameters for morphology control of LDPE/layered silicate nanocomposites

A careful insight into melt compounding procedure is proposed in order to achieve a better understanding and control of the dispersion and orientation mechanisms of organo-clay platelets into LDPE nanocomposites. The method involved is the preparation of a maleic anhydride grafted polyethylene master-batch containing 10 wt% organo-clay via twin-screw extrusion. A substantial nano-dispersion and orientation of clay platelets was obtained as observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Moreover, the nanocomposites prepared by diluting the master-batch through the blend mixing with additional LDPE preserved or improved the exfoliation and lamellae orientation. Finally, the thermo-gravimetric analysis (TGA) showed a significant improvement of the thermal stability while both differential scanning calorimetry (DSC) and XRD evidenced a slight increase of the LDPE crystallinity degree with respect to neat polymer matrices thus suggesting the occurrence of orientation also for the polymer

In situ Rheo-SALS experiments on LDPE nanocomposites: A preliminary study

A preliminary study of Flow Induced Crystallization In LDPE nanocomposites containing a layered silicate nanofiller has been carried out by means of In situ Rheo-SALS technique. A good degree of exfoliation of the nanoclay into the polymer matrix was observed by TEM analysis. The first Rheo-SALS results clearly Indicate that the application of mild flow conditions strongly enhances the crystallization kinetics, both In nanocomposite and reference LDPE samples. Moreover, in the sheared nanocomposite the polymer crystals are highly oriented, much more than in the reference sample, thus suggesting that the presence of small amounts of exfoliated nanoclay favours the orientation of chain segments along the flow direction. The analysis of the Hv scattering patterns allowed extracting basic quantitative information on crystallization kinetics and spherulitlc morphology

Flow induced crystallization of LDPE nanocomposites. A rheological and morphological characterization

AbstractThe flow induced crystallization behaviour of a LDPE:PE-g-MA:D72T 90:9:1 nanocomposite has been investigated by in-situ Rheo-SALS technique and data have been compared with those obtained from a reference LDPE:PE-g-MA 90:9 sample. Rheo SALS results, confirming thermal analysis findings, indicate that under mild shear flow fields the organoclay exhibits a negligible nucleating effect. Both nucleation density and, as a consequence, crystallization rate, are not appreciably affected by the application of external flow field for both the examined systems, revealing that no evident synergic effects between the organoclay and the shear flow are present. On the other hand, Rheo SALS analysis indicates that the nanocomposite submitted to flow exhibits a higher level of crystal orientation. TEM morphological analyses support this observation suggesting that the orientation of the nanofiller along the flow direction templates the growth of oriented crystals

Shape fidelity and sterility assessment of 3D printed polycaprolactone and hydroxyapatite scaffolds

Polycaprolactone (PCL) and hydroxyapatite (HA) composite are widely used in tissue engineering (TE). They are fit to being processed with three-dimensional (3D) printing technique to create scaffolds with verifiable porosity. The current challenge is to guarantee the reliability and reproducibility of 3D printed scaffolds and to create sterile scaffolds which can be used for in vitro cell cultures. In this context it is important for successful cell culture, to have a protocol in order to evaluate the sterility of the printed scaffolds. We proposed a systematic approach to sterilise 90%PCL-10%HA pellets using a 3D bioprinter before starting the printing process. We evaluated the printability of PCL-HA composite and the shape fidelity of scaffolds printed with and without sterilised pellets varying infill pattern, and the sterility of 3D printed scaffolds following the method established by the United States Pharmacopoeia. Finally, the thermal analyses supported by the Fourier Transform Infrared Spectroscopy were useful to verify the stability of the sterilisation process in the PCL solid state with and without HA. The results show that the use of the 3D printer, according to the proposed protocol, allows to obtain sterile 3D PCL-HA scaffolds suitable for TE applications such as bone or cartilage repair