Material extrusion additive manufacturing of poly(lactic acid)/Ti6Al4V@calcium phosphate core-shell nanocomposite scaffolds for bone tissue applications

The use of porous scaffolds with appropriate mechanical and biological features for the host tissue is one of the challenges in repairing critical-size bone defects. With today's three-dimensional (3D) printing technology, scaffolds can be customized and personalized, thereby eliminating the problems associated with conventional methods. In this work, after preparing Ti6Al4V/Calcium phosphate (Ti64@CaP) core-shell nanocomposite via a solution-based process, by taking advantage of fused deposition modeling (FDM), porous poly(lactic acid) (PLA)-Ti64@CaP nanocomposite scaffolds were fabricated. Scanning electron microscope (SEM) showed that nanostructured calcium phosphate was distributed uniformly on the surface of Ti64 particles. Also, X-ray diffraction (XRD) indicated that calcium phosphate forms an octacalcium phosphate (OCP) phase. As a result of incorporating 6 wt% Ti64@CaP into the PLA, the compressive modulus and ultimate compressive strength values increased from 1.4 GPa and 29.5 MPa to 2.0 GPa and 53.5 MPa, respectively. Furthermore, the differential scanning calorimetry results revealed an increase in the glass transition temperature of PLA, rising from 57.0 to 62.4 °C, due to the addition of 6 wt% Ti64@CaP. However, it is worth noting that there was a moderate decrease in the crystallization and melting temperatures of the nanocomposite filament, which dropped from 97.0 to 89.5 °C and 167 to 162.9 °C, respectively. The scaffolds were seeded with human adipose tissue-derived mesenchymal stem cells (hADSCs) to investigate their biocompatibility and cell proliferation. Calcium deposition, ALP activity, and bone-related proteins and genes were also used to evaluate the bone differentiation potential of hADSCs. The obtained results showed that introducing Ti64@CaP considerably improved in vitro biocompatibility, facilitating the attachment, differentiation, and proliferation of hADSCs. Considering the findings of this study, the 3D-printed nanocomposite scaffold could be considered a promising candidate for bone tissue engineering applications.

The influence of poorly-/well-dispersed organo-montmorillonite on interfacial compatibility, fire retardancy and smoke suppression of polypropylene/intumescent flame retardant composite system

A novel linear polymeric charring agent (PEPAPC) was synthesized via the nucleophilic substitution reaction, and then embedded into polypropylene (PP) substrate to improve the fire retardancy and anti-dripping performance. Unfortunately, the opposite polarity between intumescent flame retardant (IFR) and polymer-matrix could seriously deteriorate the interfacial compatibility, harmful to the flame-retardant efficiency and smoke toxicity suppression of PP/IFR composites. For the foregoing reasons, flame retardant PP/IFR/Organo-montmorillonite (OMMT) nanocomposites with the combination of maleic anhydride-grafted PP as compatibilizer have been prepared via melt intercalation technique. When 2 wt% well-dispersed OMMT were incorporated, it showed a significant reduction in peak heat release rate and total heat release (90.5 and 62.7%) compared with pristine PP, and an achievement in limiting oxygen index value of 32% from 18.5% for pristine PP, which can be attributed to the nano-barrier and catalytic carbonization effect of well-dispersed OMMT within the polymer-matrix. More importantly, the well-dispersed OMMT displays significant smoke toxicity suppression, toughening and strengthening effect on PP/IFR system. The peak CO release and total smoke production for PP-6 were decreased by 89.8 and 64.7%, respectively. This work may provide an effective approach towards fabricating high-performance polymeric materials on organic/inorganic hybrid nanocomposites with homogenous dispersion, thereby effectively reducing the fire hazard risk.

Grafting of CNTs onto the surface of PBO fibers at high-density for enhancing interfacial adhesion, mechanical properties and stability of composites

To improve the interfacial adhesion and mechanical performance of PBO fiber composites, CNTs were uniformly grafted onto them at a high-density. The grafting of CNTs with massive reactive groups can improve the surface wettability and interfacial interaction of PBO fibers with epoxy resin. The IFSS and ILSS values of themodified composites (PBO-CNT-3) increased by 103.09 and 62.73%, respectively. As CNTs can strengthen interfacial regions of the composites, the mechanical properties (hardness and modulus) of the interphase were enhanced significantly. This led to the effective transfer of interfacial load, elimination of stress concentration, and improvement in the structural stability of the composites. As a result, the impact strength of the modified composites (PBO-CNT-3) was up to 103.76 kJ/m² (an increase of 56.24%) compared to the original composites. The surface morphology and deformation behavior of the fractured composites indicate that the interfacial failure mode of the composites grafted with CNTs changes from adhesive failure to both cohesive and substrate failure. This strategy of grafting CNTs at a high-density opens a new avenue for the interfacial regulation of structural composites, ultra-capacitor, sensor, and catalytic materials.

Electrospun polyurethane/carbon nanotube composites with different amounts of carbon nanotubes and almost the same fiber diameter for biomedical applications

The aim of this study was to investigate the net effect of raw carbon nanotube (CNTs) on the final properties of polyurethane (PU)/CNT composites considering their biomedical applications. So, neat PU and PU/CNT composites containing different amounts of CNTs (0.05%, 0.1%, 0.5%, and 1%) were prepared by electrospinning. Electrospinning parameters optimized to have a bead-free structure with no significant difference between their mean fiber diameter and porosity percentage. The results showed adding CNTs caused an increase in crystallinity percentage, water absorption ratio, young modulus, toughness, conductivity, degradation time in an accelerated medium, clotting time, and human umbilical vein endothelial cells adhesion. But a direct relationship between CNT percentage and the calcium adsorption was not detected. Moreover, no significant cytotoxicity was observed for 7-day extracts of all samples. These nanocomposites have a vast range of properties which make them a good candidate as neural, cardiovascular, osseous biomaterials or tendon, and ligament substitute.

Guided Wave-based System for Real-time Cure Monitoring of Composites using Piezoelectric Discs and Phase-shifted Fiber Bragg Gratings

A real-time, in-process cure monitoring system employing a guided wave-based concept for carbon fiber reinforced polymer (CFRP) composites was developed. The system included a single piezoelectric disc that was bonded to the surface of the composite for excitation, and an embedded phase-shifted fiber Bragg grating (PS-FBG) for sensing. The PS-FBG almost simultaneously measured both quasi-static strain and the ultrasonic guided wave-based signals throughout the cure cycle. A traditional FBG was also used as a base for evaluating the high sensitivity of the PS-FBG sensor. Composite physical properties (degree of cure and glass transition temperature) were correlated to the amplitude and time of arrival of the guided wave-based measurements during the cure cycle. In addition, key state transitions (gelation and vitrification) were identified from the experimental data. The physical properties and state transitions were validated using cure process modeling software (e.g., RAVEN®). This system demonstrated the capability of using an embedded PS-FBG to sense a wide bandwidth of signals during cure. The distinct advantages of a fiber optic-based system include multiplexing of multiple gratings along a single optical fiber, small size compared to piezoelectric sensors, ability to embed or surface mount, utilization in harsh environments, electrically passive operation, and electromagnetic interference (EMI) immunity. The embedded PS-FBG fiber optic sensor can monitor the entire life-cycle of the composite structure from curing, post-cure/assembly, and in-service creating "smart structures".

A multimodal data-set of a unidirectional glass fibre reinforced polymer composite

A unidirectional (UD) glass fibre reinforced polymer (GFRP) composite was scanned at varying resolutions in the micro-scale with several imaging modalities. All six scans capture the same region of the sample, containing well-aligned fibres inside a UD load-carrying bundle. Two scans of the cross-sectional surface of the bundle were acquired at a high resolution, by means of scanning electron microscopy (SEM) and optical microscopy (OM), and four volumetric scans were acquired through X-ray computed tomography (CT) at different resolutions. Individual fibres can be resolved from these scans to investigate the micro-structure of the UD bundle. The data is hosted at https://doi.org/10.5281/zenodo.1195879 and it was used in Emerson et al. (2018) [1] to demonstrate that precise and representative characterisations of fibre geometry are possible with relatively low X-ray CT resolutions if the analysis method is robust to image quality.

Assessment of nanoscopic dynamic mechanical properties and B-C-N triad effect on MWCNT/h-BNNP nanofillers reinforced HDPE hybrid composite using oscillatory nanoindentation: An insight into medical applications

A thrust on improvement of different properties of polymer has taken a contemporary route with advent of nanofillers. Although several nanofillers are existent; MultiWalled Carbon Nanotubes- (MWCNTs) and h-Boron Nitride nanoplatelets-(h-BNNPs) unique combination of 1D and 2D dimensional geometry aids an advantage of B-C-N triad elemental effects on properties of tested samples. The current study aims to investigate the effects of MWCNT and h-BNNP reinforcement in High Density Polyethylene (HDPE) for high load bearing areas of medical applications requiring both elastic and viscous behavior. The results were analyzed keeping a view of its application in areas like HDPE based fracture fixation plates, acetabular cups and others. The composite and hybrid samples with different loadings were prepared after surface modification of nanofillers by mechanical mixing and molding technique. The dynamic nano-mechanical properties like storage modulus, loss modulus and tan delta were assessed for each sample during frequency swept from 10 to 220 Hz. The viscoelastic properties like h_c/h_m, H/E, elastic-plastic deformation were investigated and evaluated. At a frequency of 10 Hz, the storage and loss modulus of 0.1 CNT increased by 37.56% and decreased by 23.52% respectively on comparison with pure HDPE. This infers a good elastic as well as viscous behavior. Overall elastic behavior of 0.1 CNT was confirmed from tan delta evaluation. The interaction between B-C-N elemental triad had significant effect on creep strength, visco-damping property (h_c/h_m and H/E), elastic plastic displacement and pile-up and sink-in behavior. Highest creep strength and visco-damping property was exhibited by 0.25 CNT/0.15 BNNP hybrid. The elastic-plastic displacement of hybrid composite was noted as least, which decreased by 30% on comparison with pure HDPE. It can be inferred that presence of 1D-MWCNT and 2D-h-BNNP had significant effect on important dynamic viscoelastic and creep properties of HDPE based hybrid composites.

Green Composites Based on Blends of Polypropylene with Liquid Wood Reinforced with Hemp Fibers: Thermomechanical Properties and the Effect of Recycling Cycles

Green composites from polypropylene and lignin-based natural material were manufactured using a melt extrusion process. The lignin-based material used was the so called “liquid wood”. The PP/“Liquid Wood” blends were extruded with “liquid wood” content varying from 20 wt % to 80 wt %. The blends were thoroughly characterized by flexural, impact, and dynamic mechanical testing. The addition of the Liquid Wood resulted in a great improvement in terms of both the flexural modulus and strength but, on the other hand, a reduction of the impact strength was observed. For one blend composition, the composites reinforced with hemp fibers were also studied. The addition of hemp allowed us to further improve the mechanical properties. The composite with 20 wt % of hemp, subjected to up to three recycling cycles, showed good mechanical property retention and thermal stability after recycling.

Study of Crystal Formation and Nitric Oxide (NO) Release Mechanism from S-Nitroso-N-acetylpenicillamine (SNAP)-Doped CarboSil Polymer Composites for Potential Antimicrobial Applications

Stable and long-term nitric oxide (NO) releasing polymeric materials have many potential biomedical applications. Herein, we report the real-time observation of the crystallization process of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), within a thermoplastic silicone-polycarbonate-urethane biomedical polymer, CarboSil 20 80A. It is demonstrated that the NO release rate from this composite material is directly correlated with the surface area that the CarboSil polymer film is exposed to when in contact with aqueous solution. The decomposition of SNAP in solution (e.g. PBS, ethanol, THF, etc.) is a pseudo-first-order reaction proportional to the SNAP concentration. Further, catheters fabricated with this novel NO releasing composite material are shown to exhibit significant effects on preventing biofilm formation on catheter surface by Pseudomonas aeruginosa and Proteus mirabilis grown in CDC bioreactor over 14 days, with a 2 and 3 log-unit reduction in number of live bacteria on their surfaces, respectively. Therefore, the SNAP-CarboSil composite is a promising new material to develop antimicrobial catheters, as well as other biomedical devices.