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The demands of modern materials are highly challenging as well as partially contradictory. For example, materials should be strong like steels but chemically inert like soft low-surface energy polymers. These conflicts can be overcome by effectively combining disparate materials in composites that allow fusing of the traditional material classes like ceramics, polymers, and metals. Such combinations require sufficient adhesion between the individual materials. If adhesion is based on mechanical interlocking, the chemistry and chemical compatibility of the individual materials play a negligible role for the adhesion, but the mechanical properties of the materials are exclusively important. This work focusses on a technologically relevant example of a micro-mechanical interlocking surface structure on grade 304 stainless steel (SST) by nanoscale sculpturing. Using a low aggressive/low toxic seawater-like and diluted HNO3-based electrolyte, the resulting structure is free from preferential grain-boundary etching. The sculptured surface is super hydrophilic with undercuts suitable for mechanical interlocking with polymers. In single-lap shear tests, different two-component adhesives failed cohesively on structured SST while showing more than a doubling of the ultimate shear strength compared to the state-of-the-art grit-blasted SST composites which only showed adhesive failure.
With the aim of optimizing the traditional construction process of a fiber-reinforced lattice structure, the present study modified a previously proposed technique called “truss stacking and node gluing.” To explicitly investigate the structural compressive properties (compressive strength and compressive modulus under the flat pressure), the geometrical parameters, material properties, and topological configuration were examined in detail. Additionally, the present study conducted the relevant theoretical analyses to predict the possible destruction modes and compressive properties. All the samples were tested with a universal testing machine at a rate of 2 mm/min using the ASTM-C365 standard. The results showed that compressive properties are positively related to the relative density and negatively related to the aspect ratio. It was also found that the compressive performance for different materials was in the following order (from good to bad): cotton-fiber reinforced epoxy composite (CREC), jute-fiber reinforced epoxy composite (JREC), and nylon-fiber reinforced epoxy composite (NREC). Furthermore, the mixed topological structure performed as well as the square structure, and they both overmatched the diamond structure. Lastly, the accuracy of the theoretical analysis was evaluated by comparing the theoretical values and the experimental values.
The thickness effect has a significant influence on the fatigue life of micro–nanometer thin films. Due to the increasing application of micro–nanometer thin films in the field of microelectronics, a suitable fatigue prediction model is urgently needed. To reveal the impact of the thickness effect on the fatigue life of a copper wire film, cyclic tension fatigue test of four groups of copper wire films were carried out. Based on the theory of continuous damage mechanics and damage homogenization method, a fatigue damage accumulation model that considered the film thickness was proposed. Based on the proposed fatigue damage prediction model, the damage evolution law and fatigue life of copper wire films with different thickness and strain range were predicted. Furthermore, the size effect of the copper films was analyzed. The results showed that the fatigue life of copper wire films will decrease with the increase of thickness and strain amplitude; the thinner the film, the more significant the thickness effect on the fatigue life is; with the increase of the film thickness, the film thickness effect will gradually decrease.
Grain refinement has been applied to enhance the materials strength for miniaturization and lightweight design of nuclear equipment. It is critically important to investigate the low-cycle fatigue (LCF) properties of grain refined 316LN austenitic stainless steels for structural design and safety assessment. In the present work, a series of fine-grained (FG) 316LN steels were produced by thermo-mechanical processes. The LCF properties were studied under a fully reversed strain-controlled mode at room temperature. Results show that FG 316LN steels demonstrate good balance of high strength and high ductility. However, a slight loss of ductility in FG 316LN steel induces a significant deterioration of LCF life. The rapid energy dissipation in FG 316LN steels leads to the reduction of their LCF life. Dislocations develop rapidly in the first stage of cycles, which induces the initial cyclic hardening. The dislocations rearrange to form dislocations cell structure resulting in cyclic softening in the subsequent cyclic deformation. Strain-induced martensite transformation appears in FG 316LN stainless steels at high strain amplitude (Δε/2 = 0.8%), which leads to the secondary cyclic hardening. Moreover, a modified LCF life prediction model for grain refined metals predicts the LCF life of FG 316LN steels well.
Austenitic stainless steel is used in several industrial branches due to its mechanical and thermal properties, and to its good corrosion resistance. With low cost and biocompatibility, it is used to manufacture prostheses and devices for bone fixation. However, direct contact with body fluids may cause corrosion. Thin films of FeAlCr intermetallic alloy can be used to increase service life of prostheses and avoid replacement surgeries. The aim of this work was to cover the austenitic stainless steel to study the effect of target–substrate distance on the film characteristics. Coatings were performed using the magnetron sputtering technique with the substrate positioned at different distances from the target. The influence on film thickness, morphology, roughness, and adhesion to the substrate was investigated. The thin films of FeAlCr (160 nm thick deposited at 100 mm far from the substrate) were formed by smaller particles (11.2 nm long), densely packed (551,000 particles/mm2), with flat and regular appearance, and greater adherence to the substrate.
The thermal expansion coefficient (CTE) is a vital design parameter for reducing the thermal-stress-induced structural failure of electronic chips/devices. At the micro- and nano-scale, the typical size range of the components in chips/devices, the CTEs are probably different from that of the bulk materials, but an easy and accurate measurement method is still lacking. In this paper, we present a simple but effective method for determining linear CTEs of micro-scale materials only using the prevalent nanoindentation system equipped with a heating stage for precise temperature control. By holding a constant force on the sample surface, while heating the sample at a constant rate, we measure two height–temperature curves at two positions, respectively, which are close to each other but at different heights. The linear CTE is obtained by analyzing the difference of height change during heating. This method can be applied to study the size effect or surface effect of CTE of embedded micro-scale structures, aiding the failure analysis and structural design in the semiconductor industry.
A simple and effective strategy is proposed for fabricating honeycomb-patterned ethyl cellulose (EC) films via a combination of the dip-coating and breath figure methods under a wide humidity range (40–90%). A mixture of toluene and methanol as a volatile solvent/nonsolvent pair was used to effectively control the surface morphology. Additionally, honeycomb patterns were successfully formed via dip-coating under a low humidity (relative humidity less than 40%), when water was directly added into the mixed solution. The important factors that influenced the morphology of EC honeycomb-patterned films were investigated, such as the humidity, solution concentration, and the withdrawal speed during dip-coating. The pore sizes could be controlled by changing the film-formation conditions. Water contact angle enables a transition from hydrophilic to hydrophobic. The possible mechanisms of honeycomb pattern formation are discussed. The fabrication of an ordered honeycomb-patterned film in a cost-effective and convenient manner will have broad application potential in the future.
Additive manufacturing (AM) has made long strides in the recent past and rapidly evolved into a promising alternative in specific applications. The aircraft industry is not an exception to this. The true just-intime production possibility is critical for the aircraft maintenance industries, though the lack of material freedom is a major hurdle. Several fire-retardant materials were investigated for AM in the aerospace context, but mainly for fused deposition modeling (FDM). The material consolidation constraints in FDM led to the expansion to the use of selective laser sintering (SLS) to some extent. Nevertheless, the material options are still limited, proprietary, and lack scientific insights into the material consolidation mechanics. Attempts are made in this paper to fill this gap, evaluating a new fire-retardant material for processing by SLS. Experiments conducted to ascertain the material, process, structure, and consolidation relationships indicated energy density levels 0.062–0.070 J/mm2 with laser power 13 W and scan speed varied slightly around 390 mm/s to give the best laser sintering and mechanical property results in polyetherimide powders.
A triazine-based graphite carbon nitride (tri-C3N4) was successfully prepared using a solid and mild method, and modified through concentrated acid and the hydrothermal method. Interestingly, the modified tri-C3N4 (tri-HC3N4) showed good water stability and excellent fluorescence property. Meanwhile, tri-HC3N4 was successfully used to construct a high-sensitive and selective fluorescence sensor to Ag+. The as-prepared fluorescence sensor showed a fast response and a low detection limit as 0.4046 μM. Moreover, the possible quenching mechanisms were discussed based on the photoinduced electron transfer and the formation of new complex between tri-HC3N4 and Ag+ with the help of the related characterizations. This study does not only provide a new tri-HC3N4 for a high efficiency fluorescence sensor, but also show the potential application in biological sciences.
Continuous hBN films have been grown by means of a radio-frequency-sputtering technology, and their material properties have been investigated. The prepared hBN films can achieve good smoothness in a large area. The surface morphologies and compositions of the hBN films on Si substrate and Al film have been characterized, indicating that there is no difference. The 101-phase peak of hBN film is the strongest, and the optical band gap of the fabricated film is 5.84 eV. An attempt on the fabrication of the hBN based resistive switching (RS) device has been made by using an Ag/hBN/Al structure, leading to the observation of a clear and stable RS behavior. The device exhibits a resistance window (high-resistivity state/low-resistivity state) of around 102, and the RS behaviors of hBN film prepared by sputtering were first observed. It has been found that the opening voltage for the device is changed when a different cycle voltage is applied because of the built-in electric field increasing with the increase of applied cycle voltage. The mechanism of the RS behavior has been analyzed, which lay a foundation for the application of hBN as RS material in resistive random access memory to improve the storage density.
Biomedical Materials, Regenerative Medicine and Drug Delivery
The recent scientific progress has shown the promising effect of the vaccine in immunotherapy of cancer, which relies on the antigen processing/presentation capability of dendritic cells (DCs). As a result, cancer vaccines targeting DC, which also named as DC vaccine, was a hot-spot in vaccine development. Herein, a nanostructured lipid carrier (NLC) was employed to load chlorin e6 (Ce6) to serve as a potential in situ DC vaccine (NLC/Ce6) for effective immunotherapy of gastric cancer. Taking advantage of the photodynamic effect of Ce6 to generate reactive oxygen species (ROS) under laser irradiation, the NLC/Ce6 was able to trigger cell death and expose tumor-associated antigen (TAA). Moreover, mimicking the natural inflammatory response, the ROS can also recruit the DC for the effective processing/presentation of the in situ exposed TAA. As expected, we observed strong capability DC vaccination efficacy of this platform to effectively inhibit the growth of both primary and distant gastric tumors.
The fibrous scaffolds for bone tissue engineering that mimic the extracellular matrix with bioactive and bactericidal properties could provide adequate conditions for regeneration of damaged bone. Electrospun ultrathin fiber covered with nano-hydroxyapatite is a favorable fibrous scaffold design. We developed a fast and reproducible strategy to produce polyvinylidene fluoride (PVDF)/nano-hydroxyapatite (nHAp) nanofibrous scaffolds with bactericidal and bioactive properties. Fibrous PVDF scaffolds were obtained first by the electrospinning method. Then, their surfaces were modified using oxygen plasma treatment followed by electrodeposition of nHAp. This process formed nanofibrous and superhydrophilic PVDF fibers (133.6 nm, fiber average diameter) covered with homogeneous nHAp (202.6 nm, average particle diameter) crystals. Energy-dispersive X-ray spectrometry demonstrated the presence of calcium phosphate, indicating a Ca/P molar ratio of approximately 1.64. X-ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy spectra identified β-phase of nHAp. Thermal analysis indicated a slight reduction in stability after nHAp electrodeposition. Bactericidal assays showed that nHAp exhibited 99.8% efficiency against Pseudomonas aeruginosa bacteria. The PVDF/Plasma and PVDF/nHAp groups had the highest cell viability, total protein, and alkaline phosphatase activity by 7 days after exposure of the scaffolds to MG63 cell culture. Therefore, the developed scaffolds are an exciting alternative for application in bone regeneration.
Interactions between smooth muscle cells (SMCs) and biomaterials must not result in phenotype changes as this may generate uncontrolled multiplication processes and occlusions in vascular grafts. The aim of this study was to relate the hydrolytic stability and biocompatibility of polyurethanes (PUs) on SMCs. A higher polycaprolactone (PCL) concentration was found to improve the hydrolytic stability of the material and the adhesion of SMCs. A material with 5% polyethylene glycol, 90% PCL, and 5% pentaerythritol presented high cell viability and adhesion, suggesting a contractile phenotype in SMCs depending on the morphology. Nevertheless, all PUs retained their elastic modulus over 120 days, similar to the collagen of native arteries (~10 MPa). Furthermore, aortic SMCs did not present toxicity (viability over 80%) and demonstrated adherence without any abnormal cell multiplication processes, which is ideal for the function to be fulfiled in situ in the vascular grafts.
Nowadays, theranostics drug delivery systems (DDSs) with imaging and therapy bi-functions have been regarded as a future orientation for imaging-guided cancer therapy. To achieve high imaging quality, a donor–acceptor (D–A)/Förster resonance energy transfer (FRET) bi-adjustment strategy is carried out for designing dual-colored DDSs with amplified aggregation-induced emission (AIE) behavior for imaging-guided cocktail cancer therapy in this study. In detail, four AIE-active conjugated polymers P-1 to P-4 are synthesized via the Suzuki reaction. Noteworthily, the D–A-type structure is applied in tuning the fluorescence color from orange (P-1) to far-red/near-infrared (P-2), while the intramolecular FRET process further enhanced the fluorescence signal for six times (P-3). Afterwards, P-3-based amphipathic polymer P-4 further acts as a drug carrier in preparing doxorubicin (Dox)- and curcumin (Cur)-loaded polymer dots (Pdots) (Dox-loaded Pdots as PDox and Cur-loaded Pdots as PCur). PDox + PCur DDS is successfully applied in imaging-guided cocktail cancer therapy to give obviously higher in vivo anticancer efficacy compared with single PDox or PCur. In addition, the drug-loaded Pdots also exhibit higher biocompatibility compared with free drugs. This work provides a novel D–A/FRET bi-adjustment strategy for developing high efficiency imaging-guided cocktail DDSs in cancer therapy.
The negative regulation effect of tumor microenvironment (TME) greatly compromised the efficacy of various cancer treatments, especially cancer immunotherapy. As a result, it is generally recognized that remodeling of TME along with the treatment is a promising way to realize satisfactory cancer therapy. Here, in our study, a drug delivery system (DDS) composed cancer cell membrane (CCM) vehicle loaded mitoxantrone (Mit) and sorafenib (Sfn) was proposed with the aim to combine TME regulation and chemotherapy-induced immunotherapy in one platform. Our results confirmed that after treating with this DDS, the Mit induced immunogenic cell death (ICD) could be augmented by Sfn-based TME regulation to realize effective cancer immunotherapy. The Sfn was shown to downregulate of the regulatory T cells (Treg) level while activating the effector T cells of TME. The synergetic TME regulation along with cancer immunotherapy might be a promising way for advanced cancer treatment.