High Mechanical Modulus Research Articles

Stepwise Cross-Linking of Fibroin and Hyaluronic for 3D Printing Flexible Scaffolds with Tunable Mechanical Properties.

The development of 3D printing techniques has provided a promising platform to study tissue engineering and mechanobiology; however, the pursuit of printability limits the possibility of tailoring scaffolds' mechanical properties. The brittleness of those scaffolds also hinders potential clinical application. To overcome these drawbacks, a double-network ink composed of only natural biomaterials is developed. A shear-thinning hydrogel made of silk fibroin (SF) and methacrylated hyaluronic acid (MAHA) presents a high mechanical modulus with a low concentration of macromers. The physical cross-linking due to protein folding further increases the strength of the scaffolds. The proposed SF/MAHA scaffold exhibits a storage modulus 10 times greater than that of methacrylated gelatin scaffold, along with better flexibility and biodegradation. The synergistic effect between fibroin and hyaluronic allows us to tailor the mechanical strength of scaffolds without compromising their printability. The hierarchy porous structure of the SF/MAHA scaffolds offers a better spatial microenvironment for the migration and proliferation of cells compared to gelatin scaffolds. For the first time, this strategy achieves 3D printing of natural biomaterials with controlled mechanical characteristics by manipulating the cross-linking of peptide chains. The design of such ductile scaffolds with hydrolysis resistance provides a new platform for the mechanobiology research. It also shows promise in the tissue engineering of musculoskeletal system where structural strength is needed.

Double-cross-linked aerogels towards ultrahigh mechanical properties and thermal insulation at extreme environment

Aerogels with low density and excellent thermal insulation are seriously plagued by poor mechanical properties with low compressive moduli in the kPa range, especially in extreme conditions such as high temperatures and fires. In this work, a new double chemical cross-linking and physical cross-linking strategy is developed to synthesize ultrahigh-modulus aerogels with extreme-condition resistance from low-cost polyvinyl alcohol (PVA), bio-based phytic acid (PA) and montmorillonite (MMT). The resultant aerogels consist of interpenetrating networks with chemically cross-linked domains between PVA and PA and physically cross-linked domains among PVA, PA and MMT, leading to an ultrahigh compressive modulus of 41.9 MPa and a specific modulus of 455.4 MPa·cm3·g−1, which can even withstand a car crush. Benefitting from the formation of ultra-strong network backbones containing phosphorus and clay, the aerogels amazingly show excellent fire resistance and high-temperature thermal insulation features. This robust porous material can maintain its structural integrity and high modulus (~2 MPa) after exposure to extremely high-temperature flame (~1300 °C), and also exhibits high mechanical modulus of ~4 MPa after heating treatment at 900 °C. These special characteristics make the aerogel a promising insulation candidate in the fields of aviation, aerospace and other applications.

Dynamic Capillary-Driven Additive Manufacturing of Continuous Carbon Fiber Composite

Summary Additive manufacturing (AM) of lightweight and energy-efficient composites using continuous carbon fibers and thermosetting polymers offers great opportunities for advancing composite manufacturing with design flexibility, reliability, and repeatability. However, to date there have been few AM techniques reported to process continuous fiber-reinforced thermosetting composites. Here, we report a dynamic capillary-driven AM approach with a controllable viscosity and degree of curing of polymer to enable its fast and near-simultaneous infusion and curing to implement in situ solidification of composites into arbitrary shapes. Using the technique, we developed a robotic system consisting of a uniquely designed printing head and an automated robot arm, yielding a 3D printer that enables us to print a composite on 2D and 3D substrates or in free space. The printed composite had high fiber volume fraction (58.6%) and degree of curing (95%) with high mechanical strength (810 MPa) and modulus (108 GPa).

Dynamic Capillary-Driven Additive Manufacturing of Continuous Carbon Fiber Composite

Additive manufacturing (AM) of lightweight and energy-efficient composites using continuous carbon fibers and thermosetting polymers offers great opportunities for advancing composite manufacturing with design flexibility, low cost, reliability and repeatability, with potential use in a wide range of applications. However, to date there has been no AM technique reported to process continuous carbon fibers and thermosetting polymers for direct 3D printing. The temperature-dependent viscosity of thermosetting polymers suffers a significant decrease before the composite suddenly turns into a solid, making it difficult to infuse the polymer into the fiber structure and quickly cure the composite into a solid while retaining the desirable pattern during the additive manufacturing process. Here, we overcome these difficulties and report a dynamic capillary-driven AM approach, called localized in-plane thermal assisted (LITA) 3D printing, with a controllable viscosity and degree of curing of polymer to enable its fast and near-simultaneous infusion and curing to implement in situ solidification of composites into arbitrary shapes. Using the LITA technique, we developed a robotic system consisting of a uniquely designed printing head and an automated robot arm, yielding a 3D printer that enables us to print a composite on 2D and 3D substrates or in free space. The printed composite had high fiber volume fraction (60%) and degree of curing (95%) with high mechanical strength (810 MPa) and modulus (108 GPa).

Mechanical properties, hemocompatibility, cytotoxicity and systemic toxicity of carbon fibers/poly(ether-ether-ketone) composites with different fiber lengths as orthopedic implants

Poly(ether-ether-ketone) (PEEK) has attracted more and more attention due to its chemical resistance, biocompatibility and other properties. Furthermore, carbon fibers-PEEK composite (CF-PEEK) has been considered as a novel implant because of its high mechanical strength and elastic modulus that matching with human bones. However, the length of CF has a great influence on mechanical strength and elastic modulus of the randomly distributed chopped CF-PEEK composites. In this work, CF-PEEK composites with more than 10 times length difference of fibers (length of short CF: 150–200 μm and length of long CF: 2–3 mm) were studied. As the results shown, the mechanical strength (including tensile strength, bending strength and compressive strength) of long CF-PEEK composites were more than two times of that of short CF-PEEK composites. Meanwhile, tensile modulus and bending modulus of the two kinds of composites matched well with the modulus of human cortical bone. In addition, according to the results of cytotoxicity test and hemocompatibility assessment, it indicated that the two kinds of CF-PEEK composites showed mild toxicity and no hemolytic reaction. And the histopathological section of systemic toxicity test showed that the CF-PEEK composites had no obvious acute toxicity to organisms.

A dual-layered artificial solid electrolyte interphase formed by controlled electrochemical reduction of LiTFSI/DME-LiNO3 for dendrite-free lithium metal anode

Dendrite growth and low coulombic efficiency (CE) are the key issues to hinder the lithium (Li) metal anode in practical battery application. Naturally formed fragile and unstable solid electrolyte interphase (SEI) film between Li anode and electrolyte is one of the main reasons for them. Here we create a dual-layered artificial SEI (ASEI) film by controlled electrochemical method, which can simultaneously suppress dendrite formation and improve electrochemical performance of Li metal anode. The ASEI film with an average thickness of 40 nm shows a dual-layered structure with organic species (−(CH2CH2O)n− and lithium alkylcarbonate) in the outer layer and abundant inorganic species (LiF, Li2O, Li3N and Li2S) in the inner layer, providing enough flexibility, high mechanical modulus, high kinetic and thermodynamic stability. The ASEI film demonstrates extremely superior Li+ ion conductivity and low interface impedance, enabling a compact and dendrite-free Li deposition during cycling, and remarkably improving the CE to an average value of 97.5% for over 350 cycles. The superior electrochemical performance of lithium−sulfur (Li−S) full cells with the protection of ASEI film on Li anode further proves that the ASEI film has optimistic potential in Li metal batteries. This work provides a simple and feasible strategy for preparing ASEI film for dendrite-free Li metal anode, which has great prospects in high specific energy Li metal batteries.

Double helical conformation and extreme rigidity in a rodlike polyelectrolyte

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While double and multiple helix structures appear widely in nature, only rarely are these found in synthetic non-chiral macromolecules. Here we report a double helical conformation in the densely charged aromatic polyamide poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT. This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). We present X-ray diffraction, NMR spectroscopy, and molecular dynamics (MD) simulations that reveal and confirm the double helical conformation. The discovery of this extreme rigidity in combination with high charge density gives insight into the self-assembly of molecular ionic composites with high mechanical modulus (~ 1 GPa) yet with liquid-like ion motions inside, and provides fodder for formation of other 1D-reinforced composites.

Influence of heating rate and aging temperature on omega and alpha phase precipitation in Ti[sbnd]35Nb alloy

Metastable β Ti alloys based on Nb exhibit features that make them suitable for load-bearing biomedical applications, so it is crucial to evaluate their phase transformation and properties. This paper discusses the effects of aging heat treatments on the microstructure, phase transformation and mechanical behavior of Ti35Nb alloy. Samples were solution heat treated in the β field, quenched and aged under different conditions of heating rates, isothermal aging temperature and isothermal aging time. To enhance the alloy's mechanical behavior, thermal analysis and high temperature X-ray diffraction experiments coupled with Vickers hardness tests were employed to determine the temperature range of isothermal ω phase precipitation, as well as α phase precipitation temperature, thereby providing information to optimize aging heat treatment conditions. Results indicate that Ti35Nb alloy subjected to a heating rate of 30 °C/min and an isothermal aging temperature of 500 °C applied for 4 h would ensure high mechanical strength and low elastic modulus. The application of these aging conditions led to a microstructure consisting of very refined α phase precipitates homogeneously dispersed in the β phase matrix, presenting an ultimate tensile strength of 972 MPa, elongation of 7.5% and elastic modulus of 78 GPa, making this aged alloy a promising candidate for biomedical applications. These results shed light on the correlations between phase transformations, microstructure and mechanical behavior in high solute content TiNb alloys for biomedical applications.

Extremely Stretchable, Self-Healable Elastomers with Tunable Mechanical Properties: Synthesis and Applications

Stretchable and autonomously self-healable elastomers with wide-ranging tunable mechanical properties have attracted increasing attention in various industries. To date, it continues to be a huge challenge to synthesize self-healing elastomers integrating extreme stretchability, relatively high mechanical modulus, and autonomous and rapid self-healing capability. Herein, we propose a novel covalent/supramolecular hybrid construction strategy, in which the covalent cross-links are responsible for providing high modulus and elasticity, while supramolecular cross-links realize extreme stretchability and rapid self-healing under room temperature depending on the ultrafast exchange kinetics of metal–ligand motifs and multicoordination modes. The representative polyurea hybrid elastomer, CSH-PPG-Zn-0.25, can be stretched more than 180× its original length with the highest Young’s modulus (1.78 ± 0.08 MPa) among reported ultrastretchable materials. CSH-PPG-Zn-0.25 can fully restore mechanical properties of compl...

Silicone hydrogel properties based upon effective silicone chemistry

Purpose: The silicone component of silicone hydrogels is the major contributor to oxygen permeability. However, silicone is hydrophobic and tends to impart properties to the contact lens which may challenge comfort; such as lower water content, lower surface wettability and higher mechanical modulus. The typeof silicone chemistry used in a silicone hydrogel has a significant impact on the overall contact lens properties and performance. Effective Silicone Index (ESI) is a material property that describes the efficiency with which different contact lens materials utilize silicon content to contribute to Dk.

Mechanical Properties of a Newly Additive Manufactured Implant Material Based on Ti-42Nb.

The application of Ti-6Al-4V alloy or commercially pure titanium for additive manufacturing enables the fabrication of complex structural implants and patient-specific implant geometries. However, the difference in Young’s modulus of α + β-phase Ti alloys compared to the human bone promotes stress-shielding effects in the implant–bone interphase. The aim of the present study is the mechanical characterization of a new pre-alloyed β-phase Ti-42Nb alloy for application in additive manufacturing. The present investigation focuses on the mechanical properties of SLM-printed Ti-42Nb alloy in tensile and compression tests. In addition, the raw Ti-42Nb powder, the microstructure of the specimens prior to and after compression tests, as well as the fracture occurring in tensile tests are characterized by means of the SEM/EDX analysis. The Ti-42Nb raw powder exhibits a dendrite-like Ti-structure, which is melted layer-by-layer into a microstructure with a very homogeneous distribution of Nb and Ti during the SLM process. Tensile tests display Young’s modulus of 60.51 ± 3.92 GPa and an ultimate tensile strength of 683.17 ± 16.67 MPa, whereas, under a compressive load, a compressive strength of 1330.74 ± 53.45 MPa is observed. The combination of high mechanical strength and low elastic modulus makes Ti-42Nb an interesting material for orthopedic and dental implants. The spherical shape of the pre-alloyed material additionally allows for application in metal 3D printing, enabling the fabrication of patient-specific structural implants.

Enhancing the properties of some inverse opal metamaterials by the stopband control

The inverse opal structures present very good mechanical and optical properties, like high mechanical strength and Young modulus, important photoluminescence and stimulated Brillouin scattering. Enhancement of the optical properties of the metamaterials based on different types of inverse opal can be obtained by controlling the stopband of the 3D periodic structure. SiO2, TiO2 and CeO2 photonic crystals with inverse opal structures have been studied, presenting voids of 100 – 280 nm. The stopband dependence on the physical and geometrical parameters of the matrix has been analyzed (ions nature, voids diameter, photoelastic constant). The study was performed by structural simulation methods, using the HFSS program. The test configuration was set for the visible light domain. The effective refraction index n and the stimulated Brillouin scattering coefficient gP have been determined and represented on parametrical graphs. Results were compared with the theoretic calculated values. By varying different structural parameters and the stopband control, superior values of the optical parameters have been obtained, in comparison with the data given in literature. We report an increasing of the photoluminescence with about 7%, respectively and enhancement of the stimulated Brillouin scattering coefficient of 11 % when parameters are correlated.

Radiation shielding property of structural polymer composite: Continuous basalt fiber reinforced epoxy matrix composite containing erbium oxide

For protecting human body and equipment against radiation in nuclear power industry, radiation medicine and aerospace exploration, advanced materials possessing good shielding capability, low density and high mechanical strength and modulus are in urgent demand. In this study, radiation protective basalt fiber (BF) reinforced epoxy matrix composite containing erbium oxide (Er2O3) particles was fabricated by prepreg-autoclave process, in order to make a novel mechanical/radiation shielding composite. For prepared unidirectional and quasi-isotropic BF/Er2O3 composite laminates, basalt fibers and Er2O3 particles distributed uniformly, and no obvious agglomeration of particles and defects were found. NaI(Tl) detector was used to test mass attenuation coefficient for evaluating X and gamma rays shielding performance at different photon energies ranging from 31 keV to 662 keV. The experimental results indicate that BF/Er2O3 composite shows good X and gamma rays shielding performance, and mass attenuation coefficient of BF/Er2O3 composite is much larger than that of aluminum in relatively low energy from 31 keV to 80 keV. The effect of prepreg stacking consequence on shielding performance was also discussed. In addition, to verify the applicability of classic “mixture role” on mass attenuation coefficient of anisotropic composites, theoretical mass attenuation coefficient at different photon energies was calculated using XCOM software based on the weight fraction and mass attenuation coefficient of each constituent element among BF/Er2O3 composite. It is found that there is maximum deviation of 10.3% between experimental and theoretical results. Thus, it is believed that the method is suitable for predicting shielding performance of continuous fiber reinforced composite materials. Considering the advantages in light weight and high mechanical property, the studied three-phase composite is promising for using in radiation shielding structure application.

Epidermal radio frequency electronics for wireless power transfer.

Epidermal electronic systems feature physical properties that approximate those of the skin, to enable intimate, long-lived skin interfaces for physiological measurements, human–machine interfaces and other applications that cannot be addressed by wearable hardware that is commercially available today. A primary challenge is power supply; the physical bulk, large mass and high mechanical modulus associated with conventional battery technologies can hinder efforts to achieve epidermal characteristics, and near-field power transfer schemes offer only a limited operating distance. Here we introduce an epidermal, far-field radio frequency (RF) power harvester built using a modularized collection of ultrathin antennas, rectifiers and voltage doublers. These components, separately fabricated and tested, can be integrated together via methods involving soft contact lamination. Systematic studies of the individual components and the overall performance in various dielectric environments highlight the key operational features of these systems and strategies for their optimization. The results suggest robust capabilities for battery-free RF power, with relevance to many emerging epidermal technologies.

Facile development of high performance QCM humidity sensor based on protonated polyethylenimine-graphene oxide nanocomposite thin film

In this paper, a protonated polyethylenimine (P-PEI)-graphene oxide (GO) nanocomposite thin film, referred as P-PEI-GO, was deposited on the quartz crystal microbalance (QCM) by a facile dipping process for the development of high performance humidity sensors. The morphological and structural characteristics of P-PEI-GO thin film were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscope. The humidity-sensing properties, such as response and recovery, sensitivity, repeatability, selectivity, humidity hysteresis and long-term stability, were investigated in a wide range of working humidity (11–97% RH). The resultant P-PEI-GO nanocomposite thin film possesses much larger specific surface area and richer hydrophilic groups than pure P-PEI film, leading to higher sensitivities and shorter response/recovery times of the sensor. Especially, the sensor preserves excellent durability, small hysteresis, good selectivity and stability compared with individual P-PEI or GO film sensor, which could be ascribed to the high mechanical modulus of GO and weak interaction between P-PEI and GO. Finally, the humidity sensing mechanism of proposed sensor was discussed in details. This research provides a feasible and effective approach to construct high performance humidity sensor operated at room temperature based on GO nanocomposites.

Structure analyses of polybutadiene rubber crosslinked with unsaturated carboxylate using contrast variation small-angle neutron scattering

We studied the structure of polybutadiene rubber (BR) crosslinked with zinc diacrylate (ZDA) to elucidate the structure of the high crosslink density BR using a contrast variation small-angle neutron scattering (CV-SANS) method. SPP(q), SZZ(q) and SPZ(q), which correspond to the partial scattering functions of the self-correlation of BR, the self-correlation of ZDA aggregates and the cross-correlation between BR and ZDA aggregates, respectively, were successfully evaluated using CV-SANS. A model function assuming a hierarchical structure consisting of spheres with broad size distributions was used to describe the SZZ(q), and the careful analysis of SPZ(q) revealed the existence of a HC-BR layer around the ZDA aggregates owing to an inhomogeneous crosslinked structure in the BR matrix. This is the first time quantitative structural analysis of the HC-BR layer in this rubber material has been performed. In addition, the network structure of the HC-BR layer in the rubber matrix is responsible for the high mechanical modulus of the rubber. We studied the structure of polybutadiene rubber (BR) crosslinked with zinc diacrylate (ZDA) to elucidate the structure of the high crosslink density BR (HC-BR) using a contrast variation small-angle neutron scattering (CV-SANS) method. The careful analysis revealed the existence of a HC-BR layer around the ZDA aggregates. This is the first time quantitative structural analysis of the HC-BR layer in this rubber material has been performed. In addition, the network structure of the HC-BR layer in the rubber matrix is responsible for the high mechanical modulus of the rubber.

Magnetic properties of polymer matrix composites with embedded ferrite particles

Polymeric composite materials offer advantages for many applications because of a combination of properties, which includes high specific mechanical strength and elastic modulus and corrosion resistance. However, the non-magnetic nature of these materials impedes the use of non-destructive evaluation (NDE) techniques using magnetic sensors. In this work, glass fiber-reinforced epoxy magnetic composites were produced with the addition of 10wt% of cobalt or barium ferrite particles. Circular plates with notches of 1, 5 and 10mm in diameter were produced and characterized using magnetic flux leakage (MFL) technique. The effect of particle size on the magnetic properties of the composites was also investigated for the barium ferrite. The results indicated a good correlation between the measured magnetic signals and the presence of notches. Smaller average particle sizes hindered the identification of the smallest notch. However, it resulted in better signal-to-noise ratio for the intermediate and larger size notches.

ESCALATING APPLICATIONS OF HALLOYSITE NANOTUBES

ABSTRACT In nanotechnology different nano materials are used like carbon nanotubes, nanofluids, nanoparticles, nanoemulsions, nanocapsules, etc. Due to their toxic effects the results of these nano materials are not considered safe for humans and for the environment as well. Halloysite nanotubules (HNTs) having low cost are naturally occurring environmental friendly nanotubules. These are distinctive and handy materials formed by face weathering of aluminosilicate minerals having definite ratio of aluminum, silicon, hydrogen, and oxygen. HNTs have high mechanical strength and modulus. Due to these properties it is ideal for various applications; remediation of ecological contaminants, these are acting as a career for the delivery of drugs and various macro molecules, storage of H 2 gas, for catalytic conversions and for the processing of hydrocarbons. These are also used in anticancer therapy, sustained delivery for certain agents, as a template or nanoreactor for biocatalyst, in personal care, cosmetics and as environment caring. They are also used in the fabrication of high quality white-ware ceramics, nanotemplates and nano scale reaction bottles. Due to easy dispersability in polymer matrix, abundant availability and biocompatibility, HNTs are also used in different epoxy (EP) composites. In this review, we have tried to recap the different aspects of halloysites nanotubes for their use in different research fields.

Preparation and properties of a fullerene/polysiloxane hybrid from chemically modified fullerene and polymethoxysiloxane

An organic–inorganic hybrid was prepared by simply mixing a fullerene derivative with polymethoxysiloxane. First, C60 was subjected to a radical addition reaction with 4,4′-azobis(4-cyanovaleric acid) to provide a C60 derivative. Polymethoxysiloxane was prepared by a controlled hydrolytic condensation of tetramethoxysilane. These two compounds were mixed and heated to provide hybrid bulk body. The hybrid bulk body showed high mechanical strength and elastic modulus compared with polymethoxysiloxane or the C60/polymethoxysiloxane hybrid. The formation of a dense siloxane network was established by a homogeneous mixing of the C60 derivative with polymethoxysiloxane.

Indirect three-dimensional printing of synthetic polymer scaffold based on thermal molding process

One of the major issues in tissue engineering has been the development of three-dimensional (3D) scaffolds, which serve as a structural template for cell growth and extracellular matrix formation. In scaffold-based tissue engineering, 3D printing (3DP) technology has been successfully applied for the fabrication of complex 3D scaffolds by using both direct and indirect techniques. In principle, direct 3DP techniques rely on the straightforward utilization of the final scaffold materials during the actual scaffold fabrication process. In contrast, indirect 3DP techniques use a negative mold based on a scaffold design, to which the desired biomaterial is cast and then sacrificed to obtain the final scaffold. Such indirect 3DP techniques generally impose a solvent-based process for scaffold fabrication, resulting in a considerable increase in the fabrication time and poor mechanical properties. In addition, the internal architecture of the resulting scaffold is affected by the properties of the biomaterial solution. In this study, we propose an advanced indirect 3DP technique using projection-based micro-stereolithography and an injection molding system (IMS) in order to address these challenges. The scaffold was fabricated by a thermal molding process using IMS to overcome the limitation of the solvent-based molding process in indirect 3DP techniques. The results indicate that the thermal molding process using an IMS has achieved a substantial reduction in scaffold fabrication time and has also provided the scaffold with higher mechanical modulus and strength. In addition, cell adhesion and proliferation studies have indicated no significant difference in cell activity between the scaffolds prepared by solvent-based and thermal molding processes.