A Multiscale Study of CFRP Based on Asymptotic Homogenization with Application to Mechanical Analysis of Composite Pressure Vessels.

The application of composites is increasingly extensive due to their advanced properties while the analysis still remains complex on different scales. In this article, carbon fiber reinforced polymer (CFRP) is modeled via asymptotic homogenization employing a representative volume element (RVE) with periodic boundary conditions. A multiscale mechanical model of CFRP is established to bridge the microscopic model, mesoscopic model, and macroscopic model. According to asymptotic homogenization, the coefficients of the material constitutive equation are calculated with volume-averaged stress and strain. Using the homogenized materials properties of CFRP, the tensile experiments of composite layers with the layout of [(0∘/60∘/0∘/-60∘)4] are carried out to validate asymptotic homogenization method. The results indicated that the asymptotic homogenization approach can be used to calculate the homogenized elastic moduli and Poisson's ratio of the whole structure, where the numerical results are basically consistent with test data. The sequent homogenized CFRP laminate model is applied to the mechanical analysis of type III composite pressure vessels, whereby burst pressure is accurately predicted. This work might shed some light on multiscale analysis of composite pressure vessels.

[Mongolian medicine three acupoints balance needling improves depressive behavior by regulating p11/tPA/BDNF pathway and miRNA-16 of hippocampus and middle raphe nucleus in depression model rats].

OBJECTIVE: To observe the effect of Mongolian medicine three-acupoints balance needling on the expression of p11/tPA/BDNF pathway and miRNA-16 in the hippocampus and middle raphe nucleus (MRN) in chronic stress depression model rats, so as to explore its mechanisms underlying improvement of depression. METHODS: Male SD rats were randomly divided into blank control, model, medication and Mongolian medicine acupuncture (acupuncture) groups, with 12 rats in each group. The depression model was established by using chronic unpredictable mild stress method. The rats in the medication group received gavage of prozac (2 mg/kg, diluted with normal saline, 1 mg/mL) 1 h after stress stimulation, once per day for 28 days, and those in the acupuncture group received three-acupoints (Heyi, Badagan and Xin) needling, once a day for 28 days. The behavioral changes were detected by using open field test and sugar consumption test before modeling and after the intervention. The immunoactivity of p11 and tPA proteins in the MRN, and their expression levels in both the MRN and hippocampus were detected by using immunofluorescence histochemistry and Western blot, separately, and the expression levels of miRNA-16 and BDNF mRNA in the hippocampus and MRN detected by using real-time quantitative PCR. RESULTS: After modeling, the crossing and rearing scores of open field tests and the relative consumption of sucrose in the model group were apparently lower than those of the blank control group (P<0.05), the expression levels of p11 and tPA in the MRN, and those of p11 and tPA proteins and BDNF mRNA in the MRN and hippocampus were significantly down-regulated (P<0.05), while those of miRNA-16 in the hippocampus and MRN were significantly up-regulated (P<0.05). Compared with the model group, the crossing and rearing scores of open field tests and glucose consumption, as well as the expression levels of p11 and tPA proteins and BDNF mRNA in the hippocampus and MRN were obviously increased in both the medication and acupuncture groups (P<0.05), while the expression of miRNA-16 in hippocampus was markedly down-regulated in both the medication and acupuncture groups (P<0.05). No significant differences were found between the acupuncture and medication groups in all the indexes mentioned above (P>0.05). CONCLUSION: Mongolian medicine three-acupoints balance needling can improve the depressive state in depression rats, which may be associated with its effects in up-regulating the expression of p11 and tPA proteins and BDNF mRNA in the hippocampus and MRN and in down-regulating miRNA-16 in the hippocampus, suggesting an involvement of miRNA-16 controlled p11/tPA/BDNF signaling pathway in the antidepressant effect of acupuncture.

Self-Healable Conductive Nanocellulose Nanocomposites for Biocompatible Electronic Skin Sensor Systems.

Electronic skins are developed for applications such as biomedical sensors, robotic prosthetics, and human-machine interactions, which raise the interest in composite materials that possess both flexibility and sensing properties. Polypyrrole-coated cellulose nanocrystals and cellulose nanofibers were prepared using iron(III) chloride (FeCl3) oxidant, which were used to reinforce polyvinyl alcohol (PVA). The combination of weak H-bonds and iron coordination bonds and the synergistic effect of these components yielded self-healing nanocomposite films with robust mechanical strength (409% increase compared to pure PVA and high toughness up to 407.1%) and excellent adhesion (9670 times greater than its own weight) to various substrates in air and water. When damaged, the nanocomposite films displayed good mechanical (72.0-76.3%) and conductive (54.9-91.2%) recovery after a healing time of 30 min. More importantly, the flexible nanocomposites possessed high strain sensitivity under subtle strains (<48.5%) with a gauge factor (GF) of 2.52, which was relatively larger than the GF of ionic hydrogel-based skin sensors. These nanocomposite films possessed superior sensing performance for real-time monitoring of large and subtle human motions (finger bending motions, swallowing, and wrist pulse); thus, they have great potentials in health monitoring, smart flexible skin sensors. and wearable electronic devices.

Chemical cross-linked polyvinyl alcohol/cellulose nanocrystal composite films with high structural stability by spraying Fenton reagent as initiator.

Cross-linked polyvinyl alcohol (PVA) composite films with high structural stability were prepared by free radical copolymerization between cellulose nanocrystal (CNC) and maleic anhydride (MAH) modified PVA through spraying Fenton free radical as initiator. The influence of chemical cross-linked and physical network structure on mechanical, thermal and water absorption properties of the composite films were investigated. Compared to PVA and PVA/CNC composite film, significant improvements in the mechanical, thermal and water uptake properties of the cross-linked composite film were found. The tensile strength of the cross-linked composite film was enhanced from 23.1MPa (neat PVA film) and 32.6MPa (PVA/CNC-10%) to 42.5MPa, and the maximum thermal degradation temperature was increased from 266.8°C and 281.2°C to 366.7°C (cross-linked composite film). Besides, the water absorption was reduced from 385.9% and 220.6% to 175.7% for cross-linked composite film. It indicates that compared with physical network structure in PVA/CNC composite film, the multiple cross-linked networks showed excellent thermal stability, resistance of water swelling and structural stability at the same CNC loading level. Thus, the PVA/CNC composite film with the multiple cross-linked network shows greater property reinforcements.

In vitro degradation and possible hydrolytic mechanism of PHBV nanocomposites by incorporating cellulose nanocrystal-ZnO nanohybrids.

Fabrication and characterization of bbiodegradable nanocomposites based on poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) matrix reinforced with cellulose nanocrystal (CNC)-ZnO nanohybrids via simple solution casting for possible use as antibacterial biomedical materials is reported. The obtained nanocomposites exhibited an excellent antibacterial ratio of 95.2-100% for both types of bacteria namely S. aureus and E. coli and showed 9-15% degradation after one week. The addition of CNC-ZnO showed a positive effect on hydrophilicity and barrier properties. More significantly, the nanocomposites with 10wt% CNC-ZnO showed enhancement in tensile strength (140.2%), Young's modulus (183.1%), and the maximum decomposition temperature (Tmax) value increased by 26.1°C. Moreover, this study has provided a possible mechanism for using such nanofillers on the hydrolytic degradation of PHBV, which was beneficial to obtain the high-performance nanocomposites with modulated degradation rate for antibacterial biomaterials.

From Cellulose Nanospheres, Nanorods to Nanofibers: Various Aspect Ratio Induced Nucleation/Reinforcing Effects on Polylactic Acid for Robust-Barrier Food Packaging.

The traditional approach toward improving the crystallization rate as well as the mechanical and barrier properties of poly(lactic acid) (PLA) is the incorporation of nanocelluloses (NCs). Unfortunately, little study has been focused on the influence of the differences in NC morphology and dimensions on the PLA property enhancement. Here, by HCOOH/HCl hydrolysis of lyocell fibers, microcrystalline cellulose (MCC), and ginger fibers, we unveil the preparation of cellulose nanospheres (CNS), rod-like cellulose nanocrystals (CNC), and cellulose nanofibers (CNF) with different aspect ratios, respectively. All the NC surfaces were chemically modified by Fischer esterification with hydrophobic formate groups to improve the NC dispersion in the PLA matrix. This study systematically compared CNS, CNC, and CNF as reinforcing agents to induce different kinds of heterogeneous nucleation and reinforce the effects on the properties of PLA. The incorporation of three NCs can greatly improve the PLA crystallization ability, thermal stability, and mechanical strength of nanocomposites. At the same NC loading level, the PLA/CNS showed the highest crystallinity (19.8 ± 0.4%) with a smaller spherulite size (33 ± 1.5 µm), indicating that CNS, with its high specific surface area, can induce a stronger heterogeneous nucleation effect on the PLA crystallization than CNC or CNF. Instead, compared to PLA, the PLA/CNF nanocomposites gave the largest Young's modulus increase of 350 %, due to the larger aspect ratio/rigidity of CNF and their interlocking or percolation network caused by filler-matrix interfacial bonds. Furthermore, taking these factors of hydrogen bonding interaction, increased crystallinity, and interfacial tortuosity into account, the PLA/CNC nanocomposite films showed the best barrier property against water vapor and lowest migration levels in two liquid food simulates (well below 60 mg kg-1 for required overall migration in packaging) than CNS- and CNF-based films. This comparative study was very beneficial for selecting reasonable nanocelluloses as nucleation/reinforcing agents in robust-barrier packaging biomaterials with outstanding mechanical and thermal performance.