Advancements in bone tissue engineering have increased interest in 3D-printed scaffolds for bone regeneration. Polylactic acid (PLA), a biocompatible and biodegradable polyester, is a promising candidate for bone scaffold materials. Reinforcing PLA with inorganic nanotubes of tungsten disulfide (INT-WS2) offers new possibilities for scaffold design. INT-WS2 is an innovative material known for its chemical stability, non-toxicity, and favorable mechanical properties. Integrating PLA with INT-WS2 marks a pioneering development in bone scaffold technology, providing a safer, more effective alternative to other nanofillers, such as TiO₂ nanoparticles and carbon nanotubes, which face challenges related to cytotoxicity and dispersion. This study adds an important aspect to the characterization of this material by investigating the cytocompatibility and hydrolytic degradation effects on 3D-printed samples of PLA reinforced with 0.5 wt% INT-WS2. The samples are proposed as structurally suitable candidate for load-bearing 3D-printed bone scaffolds, with the femur chosen as the upper-limit mechanical benchmark. Controlled hydrolytic degradation of PLA/INT-WS2 samples was conducted over 12 weeks under human-body simulated conditions. Results demonstrated that the material underwent bulk degradation while maintaining mass and surface hardness. Although the ultimate tensile strength progressively decreased to two-thirds of its initial value, potentially allowing gradual loading of the growing bone, it remained significantly higher than the maximum stress experienced by the human femur during normal walking. Furthermore, the PLA/INT-WS2 nanocomposite exhibited non-toxic behavior, promoting cell viability and proliferation. Despite the need for a longer experiment to fully assess the degradation rate, these findings support PLA/INT-WS2 as a promising candidate for tailored 3D-printed bone scaffolds designed for individual patients.

Abstract Conductive elastomer composites can be used as flexible, lightweight, and inexpensive sensors, but they require ohmic electrical contacts to ensure readout consistency, and such contacts can suffer from hysteresis, non‐ohmic behavior, and cyclic fatigue. This work investigates a common cause of non‐ohmic conduction in such composite contacts, namely the thin insulating layer native to the surface of most silicone rubber composites that have been infused with multi‐walled carbon nanotubes for piezoresistive sensing. Voltage sweep dc measurements of individual contacts on this surface layer behave as parallel head‐to‐tail diodes with asymmetric hysteresis. Frequency sweep ac measurements quantify the insulator thickness with a leaky capacitor model to be ∼1 µm, independent of nanotube concentration, much thicker than the apparent layer thickness as imaged with scanning electron microscopy. This analysis also confirms highly anisotropic bulk conduction, circa 100 times higher in‐plane than cross‐plane. To remove the surface layer, a simple surface abrasion is shown to achieve deep ohmic electrical contact to the elastomer bulk. A three‐terminal method for verifying ohmic contacts is demonstrated and works even when all contacts are non‐ohmic. This three‐terminal method be easily applied to other conductive polymers for contact quality‐testing.

The sensitivity volume (SV) method for electrical impedance tomography allows for noninvasive, real-time electri-cal imaging using noise-robust resistance measurements. With the SV figure of merit, a set of highly sensitive measurements are optimized for the problem at hand. This method, applied to multi-walled carbon nanotube infused elastomers produces artificial skin sensors whose electrical readout is robust against wear and deformation. This work demonstrates an experimental implementation of the SV method for 2D tomography to demonstrate a 3 x 3 keypad sensor. The result exhibits high pattern fidelity, improved resolution, a minimal number of measurements, and high signal to noise.

This paper introduces a pioneering approach that combines ex situ synthesis with advanced manufacturing to develop ZIF-67-PA12 Nylon composites with mixed-matrix membranes (MMMs), with the goal of enhancing hydrogen storage systems. One method involves producing MOF-PA12 composite powders through an in situ process, which is then commonly used as a base powder for powder bed fusion (PBF) to fabricate various structures. However, developing the in situ MOF-PA12 matrix presents challenges, including limited spreadability and processability at higher MOF contents, as well as reduced porosity due to pore blockage by polymers, ultimately diminishing hydrogen storage capacity. To overcome these issues, PBF is employed to form PA12 powder into films, followed by the ex situ direct synthesis of ZIF-67 onto these substrates at loadings exceeding those typically used in conventional MMM composites. In this study, ZIF-67 mass loadings ranging from 2 to 30 wt.% were synthesized on both PA12 powder and printed film substrates, with loadings on printed PA12 films extended up to 60 wt.%. ZIF-67-PA12-60(f) demonstrated a hydrogen capacity of 0.56 wt.% and achieved 1.53 wt.% for ZIF-67-PA12-30(p); in comparison, PA12 exhibited a capacity of 0.38 wt.%. This was undertaken to explore a range of ZIF-67 Metal–organic frameworks (MOFs) to assess their impact on the properties of the composite, particularly for hydrogen storage applications. Our results demonstrate that ex situ-synthesized ZIF-67-PA12 composite MMMs, which can be used as a final product for direct application and do not require the use of in situ pre-synthesized powder for the PBF process, not only retain significant hydrogen storage capacities, but also offer advantages in terms of repeatability, cost-efficiency, and ease of production. These findings highlight the potential of this innovative composite material as a practical and efficient solution for hydrogen storage, paving the way for advancements in energy storage technologies.

This work investigates the mechanical deformation and fracture characteristics of pristine bundles of vertically aligned multi-walled carbon nanotubes (MWCNTs) subjected to axial compressionin situtransmission electron microscope (TEM). Accurate measurements of force-displacement data were collected simultaneously with real-time TEM videos of the deformation process. Two distinct regimes were observed in the force-displacement curve: (1) an initial elastic section with a linear slope, followed by (2) a transition to a force plateau at a critical buckling force. Morphological data revealed coordinated buckling of the pristine bundle, indicating strong van der Waals (VdW) forces between the nanotubes. The experimental setup measured an effective modulus of 83.9 GPa for an MWCNT bundle, which was in agreement with finite element analysis (FEA) simulations. FEA also highlighted the significant role of VdW forces in the bundle mechanical reactions. Furthermore, we identified nickel nanoparticles as key players in the fracture behavior of the bundles, acting as nucleation sites for defects. The direct mechanical measurements of MWCNT bundles provide valuable insights into their mechanical deformation and fracture behavior, while correlating it to the morphology of the bundle. Understanding these interactions at the bundle level is crucial for improving the reliability and durability of VACNTs-based components.

Carbon nanotubes (CNTs) are extremely conductive and flexible, making them ideal for applications such as flexible electronics and nanoelectromechanical systems. However, in order to properly apply them in such devices, their long-term durability must be assessed. In the present study, we demonstrate cyclic loading of a thick MWCNT (175 nm) under axial compression, observed in situ under a transmission electron microscope (TEM). The force was applied via controlled displacement, while real-time TEM videos of the deformation process were gathered to produce the morphological data. The in situ observations combined with force–displacement curves revealed the onset of buckling instabilities, and the elastic limits of the tube were assessed. The MWCNT retained its original structure even after 68 loading–unloading cycles, despite observed clues for structural distortions. The stiffness of the tube, calculated after each loading cycle, was in a 0.15 to 0.28 TPa range—comparable to the literature, which further validates the measurement set-up. These in situ tests demonstrate the resilience of CNTs to fatigue which can be correlated with the CNTs’ structure. Such correlations can help tailoring CNTs’ properties to specific applications.

In this study, a reactive adsorbent filler was integrated into a polymeric matrix as a novel reactive protective barrier without undermining its mechanical, thermal, and chemical properties. For this purpose, newly synthesized TiO2/MCM/polydimethylsiloxane (PDMS) composites were prepared, and their various properties were thoroughly studied. The filler, TiO2/MCM, is based on a (45 wt%) TiO2 nanoparticle catalyst inside the pores of ordered mesoporous silica, MCM-41, which combines a high adsorption capacity and catalytic capability. This study shows that the incorporation of TiO2/MCM significantly enhances the composite's Young's modulus in terms of tensile strength, as an optimal measurement of 1.6 MPa was obtained, compared with that of 0.8 MPa of pristine PDMS. The composites also showed a higher thermal stability, a reduction in the coefficient of thermal expansion (from 290 to 110 ppm/°C), a 25% reduction in the change in the normalized specific heat capacity, and an increase in the thermal degradation temperatures. The chemical stability in organic environments was improved, as toluene swelling decreased by 40% and the contact angle increased by ~15°. The enhanced properties of the novel synthesized TiO2/MCM/PDMS composite can be used in various applications where a high adsorption capacity and catalytic/photocatalytic activity are required, such as in protective equipment, microfluidic applications, and chemical sensor devices.

A facile and effective catalyst deposition process for carbon nanotube (CNT) array growth via chemical vapor deposition using a resistively heated thermal evaporation technique to sublimate FeCl 3 onto the substrate is demonstrated. The catalytic activity of the sublimated FeCl 3 catalyst precursor is shown to be comparable to the well-studied e-beam evaporated Fe catalyst, and the resulting vertically aligned CNTs (VA-CNTs) have a similar diameter, walls, and defects, as well as improved bulk electrical conductivity. In contrast to standard e-beam-deposited Fe, which yields base-growth CNTs, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy characterizations reveal a tip-growth mechanism for the FeCl 3 -derived VA-CNT arrays/forests. The FeCl 3 -derived forests have a lower (∼1/3 less) longitudinal indentation modulus, but higher longitudinal electrical conductivity (greater than twice) than that of the e-beam Fe-grown CNT arrays. The sublimation process to grow high-quality VA-CNTs is a highly facile and scalable process (extensive substrate shape and size, and moderate vacuum and temperatures) that provides a new route to synthesizing aligned CNT forests for numerous applications.

Additive Manufacturing (AM), commonly known as “3D printing”, is rapidly integrated into many various fields, from everyday commercial to high-end medical and aerospace. Its production flexibility in small-scale and complex shapes is a significant advantage over conventional methods. However, inferior physical properties of parts manufactured by AM in general, and by material extrusion in particular, compared to traditional fabrication methods, inhibit its full assimilation. Specifically, the mechanical properties of printed parts are not high enough and, more importantly, not consistent enough. Optimization of the many various printing parameters is therefore required. This work reviews the influence of material selection, printing parameters such as path (e.g., layer thickness and raster angle), build (e.g., infill and building orientation) and temperature parameters (e.g., nozzle or platform temperature) on mechanical properties. Moreover, this work focuses on the interactions between the printing parameters, their mechanisms, and the statistical methods required to identify such interactions. Choosing the right parameters can increase mechanical properties by up to 60% (raster angle and orientation build), or render other parameters insignificant (material selection), while specific settings of certain parameters can completely inverse the influence trend of other parameters. Finally, trends for future research are suggested.

Optimizing conductive ink for Direct-Write Additive Manufacturing, this work explores the effect of carboxylic functionalization of multi-walled carbon nanotubes on their affinity to silver nanoparticles deposited on them. We show a correlation between functionalization and the size of the resulted NPs: the diameter of the silver NPs deposited on pristine CNTs (∼5 nm diameter) is third of that of NPs deposited on functionalized CNTs (∼15 nm). Electrical characterization of the silver-decorated CNT-based ink shows a more significant improvement in conductivity of the functionalized CNTs-decorated with silver compared to the pristine one (maximal ∼40 and ∼20% increase in conductivity over their undecorated counterpart, respectively). However, CNT functionalization severely damages the conductivity of the CNTs themselves, resulting in a much lower conductivity. This “double-edged sword” effect of functionalization results in the highest absolute specific conductivity (3.79 × 103 S/m) achieved by decorating pristine CNTs with 25 wt% of silver. Nevertheless, the observed enhanced conductivity and the ability to control the composite’s morphology by functionalization allow fine-tuning of morphology-based properties, such as surface enhanced Raman scattering and optimization of the ink for sensing applications.

The attractive properties of single-wall carbon nanotubes (SWCNT) such as mechanical strength and high electrical and thermal conductivity are often undercut by their agglomeration and re-agglomeration tendencies. As a result, the application of SWCNT as additives in advanced composite materials remain far from their potential, with proper dispersion being the major inhibitor. This work presents a dispersion quality control approach for water-based SWCNT dispersions (dispersed by a unique combination of physical and chemical methods), using complementary and easily scalable, characterization methods. UV-Vis spectroscopy, rheological measurements, and precipitant sheet resistance were used to understand the properties of the initial solution through processing and application. From an industrial perspective, these methods are fast and easy to measure while giving a repetitive and quick indication of dispersion quality and stability. The methods were correlated with microscopy and Raman spectroscopy to validate dispersion and SWCNT quality under various dispersing energies. The protocol was then applied to estimate the stability of SWCNT solutions, as well as the effectiveness of different surfactants in aiding dispersion. The simple, fast, and scalable combination of different characterizations provides good SWCNT dispersion and can be used as a quality control system for industrial production and usage.

Carbon-Carbon Composites (CCC) are widely used in the aviation industry for structural applications. Their main disadvantage is their low resistance to oxidation at elevated temperatures. While the CCCs are in service they might be exposed to different fluids which contain oxidation catalysts. Therefore, this paper examined the influence of service fluids widely used in aviation industry on oxidation and mechanical properties of aircraft brake disks made of 3D CCC. Isothermal oxidation of the CCC was investigated following immersion in either hydraulic fluid MIL-PRF-83282 or cleaning agent MIL-C-87937. The brake disks were evaluated using thermogravimetric analysis revealing that MIL-C-87937 is a catalyst for oxidation of carbon while MIL-PRF-83282 is not. Further investigation was performed by exposure to 700 degrees C in a cyclic manner followed by morphological characterizations using Scanning Electron Microscope (SEM). Mechanical properties were also characterized using a Dynamic Mechanical Analyzer in a 3-point bending mode and a universal testing machine in compression mode. SEM observations showed amplified oxidation evidence on samples exposed to MIL-C-87937. The morphological changes explain the resultant mechanical degradation: increase in tan (delta) by 220% with oxidation that begins at the fiber-matrix interface and decreased compression strength by 36%. When exposed to MIL-C-87937 cleaning agent, deterioration trend of these properties seems to be accelerated.

Focused Ion Beam (FIB) is one of the most common methods for nanodevice fabrication. However, its implications on mechanical properties of polymers have only been speculated. In the current study, we demonstrated flexural bending of FIB-milled epoxy nanobeam, examined in situ under a transmission electron microscope (TEM). Controllable displacement was applied, while real-time TEM videos were gathered to produce morphological data. EDS and EELS were used to characterize the compositions of the resultant structure, and a computational model was used, together with the quantitative results of the in situ bending, to mechanically characterize the effect of Ga+ ions irradiation. The damaged layer was measured at 30 nm, with high content of gallium (40%). Examination of the fracture revealed crack propagation within the elastic region and rapid crack growth up to fracture, attesting to enhanced brittleness. Importantly, the nanoscale epoxy exhibited a robust increase in flexural strength, associated with chemical tempering and ion-induced peening effects, stiffening the outer surface. Young’s modulus of the stiffened layer was calculated via the finite element analysis (FEA) simulation, according to the measurement of 30 nm thickness in the STEM and resulted in a modulus range of 30–100 GPa. The current findings, now established in direct measurements, pave the way to improved applications of polymers in nanoscale devices to include soft materials, such as polymer-based composites and biological samples.

In this article, the limits of thin-film deposition on very rough topographies are demonstrated by depositing alumina on vertically aligned carbon nanotubes (VACNTs). Vapor deposition techniques are the enabling platforms of the thin-film industry, offering high material versatility and good coverage ability on relatively flat surfaces, leading to frequent use in a large array of applications, especially nanoscale electronic devices such as sensors and electrodes. However, when surface topography exhibits high roughness, even depositions that are not limited to line-of-sight show only partial coverage, significantly hindering performances. Our manufacturing process of VACNT/Al2O3 nanocomposites has three vaporous steps: CNT growth by chemical vapor deposition (CVD), functionalization via controlled thermal oxidation, and atomic layer deposition (ALD) of alumina. The same limited accessibility hinders each of these three steps. Morphological analyses show different CNT heights throughout the sample, with shorter CNTs in the middle, having less access to gases. As height differences between the center and peripheries escalate, sample centers may collapse under the tension. The limited accessibility of the center is manifested also in inhomogeneous oxygen contents, between sample centers and peripheries. Finally, a sharp transition in deposition quality occurs during the deposition process of Al2O3, from homogeneous to inconsistent, which is also linked to the accessibility differences between. Adjusting process parameters, we have successfully coated 1.8 mm-tall VACNT arrays with a homogeneous thin (few nm) Al2O3 layer and were able to increase the depth at which, thick (few dozens of nm) Al2O3 coating is uniform from 20 to 350 mu m. However, when VACNTs were functionalized, the penetration depth was found to correlate negatively with center oxygen content. These results, indicating diffusion as a rate-setting step in complex topography coatings, can significantly improve deposition quality and enhance the performance of thin-film applications such as membranes, sensors, and electrodes for energy harvesting and storage.

Carbon-Carbon Composites (CCC) are used as high temperature structural elements in aviation industry. Their main disadvantage is oxidation sensitivity in elevated temperatures, further enhanced when exposed to service fluids containing alkali-metals. CCC oxidation reaction and catalysts' influence on oxidation rate is widely studied, but seldom information is available on the relation between the oxidation rate, structural changes and mechanical properties of CCC. Therefore, this study examined the influence of hydraulic fluid MIL-PRF-83282 and cleaning agent MIL-C-87937, service fluids common in aviation industry, on oxidation and mechanical properties of brake disks made of 3D CCC. Results show that MIL-C-87937 (but not MIL-PRF-83282) significantly deteriorate the structure, and thus mechanical properties, of CCC.

Tungsten disulfide is an inorganic compound with layer structure. Nanoparticles of WS2 were found to be excellent candidates for reinforcing various polymer materials. However, long storage times in ambient conditions lead to sorption of water molecules and slow oxidation of defect sites. In the present study, the influence of various treatments on the surface composition and reactivity of several kinds of WS2 nanoparticles, were investigated. This study reveals some complex interplay between water and organic moieties desorption and the subsequent oxidation of "nascant" surfaces. Remarkably, simple immersion in HF solution seems to produce the ultimately cleanest surface of these particles.

WS 2 inorganic nanotubes (WS 2 -NT) have been incorporated into Polylactic Acid (PLA) by melt mixing to create a bio-degradable, 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.

In all prior electromagnetic modeling studies of carbon nanotube (CNT) composites, the exact three-dimensional (3D) shape and spatial distribution of the CNTs in the composite were unknown. Therefore, simplifying assumptions had to be made regarding the CNT distributions. The effect of such assumptions on the electromagnetic response of CNT composites has not been quantified. Recent advances in electron-tomography and image analysis have allowed the generation of 3D maps of multi-walled carbon nanotube (MWCNT) distributions with sub-nanometer resolution. In this work, the electromagnetic responses of experimentally mapped 3D structures of aligned-CNT polymer nanocomposites were calculated using both full-wave electromagnetic solvers and dilute-limit Effective Medium Approximations (EMA). Our results show that the electromagnetic response calculated using the full-wave solver exhibits additional resonances that are absent in the response calculated using the dilute-limit EMA. This difference is due to the strong electromagnetic coupling between adjacent MWCNTs, within five CNT radii, of each other. Using the mapped 3D MWCNTs, we also studied the anisotropy in the electromagnetic response of the composites and showed that it increases with the MWCNT volume fraction. The full-wave analysis presented in this work provides a more accurate understanding of the electromagnetic reflection and anisotropy of CNT composites.

Soft electronics based on various rubbers have lately been needed in many advanced applications such as soft robotics, wearable electronics, and remote health monitoring. The ability of a self-sensing material to be monitored in use provides a significant advantage. However, conductive fillers usually used to increase conductivity also change mechanical properties. Most importantly, the initial sought-after properties of rubber, namely softness and long elastic deformation, are usually compromised. This work presents full mechanical and electro-mechanical characterization, together with self-sensing abilities of a vinyl methyl silicone rubber (VMQ) and multi-walled carbon nanotubes (MWCNTs) composite, featuring conductivity while maintaining low hardness. The research demonstrates that MWCNT/VMQ with just 4 wt.% of MWCNT are as conductive as commercial conductive VMQ based on Carbon Black, while exhibiting lower hardness and higher elastic recovery (~20% plastic deformation, similar to pure rubber). The research also demonstrates piezo-resistivity and Raman-sensitivity, allowing for self-sensing. Using morphological data, proposed mechanisms for the superior electrical and mechanical behavior, as well as the in-situ fingerprint for the composite conditions are presented. This research novelty is in the full MWCNT/VMQ mechanical and electro-mechanical characterization, thus demonstrating its ability to serve as a sensor over large local strains, multiple straining cycles, and environmental damage.

Composites of poly(l-lactic acid) (PLLA) reinforced by adding inorganic nanotubes of tungsten disulfide (INT–WS2) were prepared by solvent casting. In addition to the pristine nanotubes, PLLA nanocomposites containing surface modified nanotubes were studied as well. Several surface-active agents, including polyethylene imine (PEI), were studied in this context. In addition, other biocompatible polymers, like poly d,l-lactic acid (PDLLA) and others were considered in combination with the INT–WS2. The nanotubes were added to the polymer in different proportions up to 3 wt %. The dispersion of the nanotubes in the nanocomposites were analyzed by several techniques, including X-ray tomography microscopy (Micro-XCT). Moreover, high-temperature rheological measurements of the molten polymer were conducted. In contrast to other nanoparticles, which lead to a considerable increase of the viscosity of the molten polymer, the WS2 nanotubes did not affect the viscosity significantly. They did not affect the complex viscosity of the molten PLLA phase, either. The mechanical and tribological properties of the nanocomposites were found to improve considerably by adding the nanotubes. A direct correlation was observed between the dispersion of the nanotubes in the polymer matrix and its mechanical properties.