Étude de nouveaux matériaux polymères pour membranes de séparation et actionneurs contrôlés par stimuli

Stimuli-responsive materials have exhibited a wide range of applications, because the necessity of designing novel “smart” systems usually requires materials that can change their chemical and/or physical properties upon exposure to changed environmental conditions. Two representative applications are stimuli-responsive porous membranes and polymer actuators which are subjects of this thesis. On one hand, stimuli-responsive porous membranes are a class of membranes that can adjust their mass transfer and interfacial properties to manipulate permeability and selectivity in response to changing environmental conditions, such as pH, light, temperature, redox, and so on. There has been a rapid development in this field over the past decades or so. However, there are some limitations for these stimuli-responsive porous membranes. For example, for pH-responsive porous membranes, addition of acids and bases into the solution results in salt accumulation that can contaminate the system and diminish the switchability, while temperature or light responsive porous membranes may be damaged by the stimuli to a certain extent. Therefore, it is still urgent to develop environmentally friendly and cost-effective stimulation modes for stimuli-responsive porous membranes. On the other hand, polymer actuators have aroused scientists’ extensive research interest because of their potential applications in biomedicine, artificial muscles and soft robots. Instead of utilizing mechanical force to achieve motion or deformation, polymer actuators can move or deform under thermal, optical or electrical stimulation. Among them, photo-thermal-responsive polymer actuators based on liquid crystal polymer networks (LCNs) have emerged as a particularly promising materials system. For this kind of actuator, the photothermal agents are needed to convert optical energy into thermal energy to induce the LC-to-isotropic phase transition that drives the actuator to deform macroscopically. However, the photothermal reagents often have poor compatibility with organic polymeric matrices, resulting in a dilemma that reducing the doping percentages of photothermal reagents would weaken the photo-actuation speeds of the LCN actuators, whereas increasing the doping percentages would lead to serious phase segregations, and then sacrifice the mechanical properties of the LCN actuators. Moreover,fabricating photothermal-responsive LCN actuators that can perform light-driven caterpillar-type motion on untreated surfaces is also challenging. The main topic of this thesis is to learn from nature to design and fabricate the stimuli-responsive porous membranes for the size separation and nanofiltration and the stimuli-responsive polymer actuators based on LCN for remotely controlled motion. We introduce the CO2-responsive polymers into membrane separation, in a bid to develop a new external stimulus that can reversibly “open” and “close” the membrane pore sizes and further impact the size selectivity of the membrane. Compared with other stimuli, using CO2 as trigger has several merits, such as environmental friendliness, easy operation, excellent repeatabil-ity without any damage and contamination and good depth inside the membranes. Moreover, we designed a photothermal-responsive LCN-based trilayer actuator that can perform near-infrared (NIR) light -guided bending, moving waves and motion on un-treated, either horizontal or inclined surface. The research works in this thesis mainly contain above-mentioned two topics, presented in three chapters. In the first work, we proposed a novel concept that gas-tunable pore sizes as well as gas-controlled separation of species can be successfully realized by using CO2/Ar as trigger. In this work, a CO2-responsvie polymer, poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA), was grafted to the polydopamine (PDA) modified polyvinylidene fluoride (PVDF) membrane to undergo reversible contraction/extension in response to CO2/Ar, resulting in the corresponding opening and closure of membrane pore. The reversible rejection of gold nanoparticles (AuNPs) with the diameter of 50 nm can be realized by alternating CO2/Ar bubbling time. This novel modality that integrates CO2-responsive polymers, tunable membrane pore size and membrane separation shows the great potential of developing smart membranes for applications requiring or involving tunable, size-selective separation of molecular species or nanoparticles. On the basis of the first work, in order to improve the separation capability of CO2-responsive polymer membranes, we developed a CO2-responsive nanofiltration mem-brane based on pyrene modified PDEAEMA (Py-PDEAEMA) and graphene oxide (GO) for water purification. This composite nanofiltration membrane had a number of attrib-utes potentially appealing for water treatment, such as the reversible, gas-tunable water permeability, both high water permeability and rejection of organic dye molecules and gas-tunable changes of the charge sign. To our knowledge, this is the first report about CO2-responsive nanofiltration membrane. This work combines the advantages of a CO2-responsive polymers and GO-based nanofiltration membrane, demonstrating new perspectives in developing smart stimuli-responsive nanofiltration membranes for water purification. In the third work, we designed a LCN-based actuator that performed NIR light-guided locomotion. The actuator had a trilayer structure, including a thin reduced graphene oxide (RGO) top layer, an inactive polymer middle layer and an active LCN bottom layer. When exposing the RGO side to a moving NIR laser, a moving wave along the strip actuator is generated, which makes the strip an effective caterpillar walker that could move on untreated, either horizontal or inclined surface under the guide of NIR laser. Moreover, while known actuators using photothermal effect are usually fabricated by mixing the nanofiller as NIR light heater with the polymer, which may weak the reversible deformation degree and raise the compatibility concern, the easy trilayer fabrication method laminates directly a “sheet” of RGO on thick polymer layers, which circumvents the potential problems

On the natural frequency and vibration mode of composite beam with non-uniform cross-section

In this paper, the vibratory properties and expression of natural modes of laminated composite beam with variable cross-section ratios of elastic modulus and density along the axis of the beam have been investigated via theoretical analysis. Based on the generalized Hamilton principle, the longitudinal and transverse vibration equations have been deduced by the means of variational method. Then, the natural frequencies of longitudinal and transverse vibration modes have been obtained using the method of power series, which agree well with finite element simulations. The first-order natural frequencies of longitudinal and transverse of composite beams are plotted as a function of the elastic modulus or densities difference of two components. With distinct material characteristics, the effect of shape factor on the first and second order lateral modes of composite beam is also revealed. In addition, the study shows that the boundary conditions impose a strong effect on the shape factor. The method presented in this paper is not only suitable for the laminated composite beam with variable cross-section, but will also be applicable to more general cases of composite beams of complex geometry and component in vibration mechanics. This controllable vibration performance achieved in this paper may shed some light on and stimulate new architectural design of composite engineering structures

Optimization of Protein-Protein Interaction Measurements for Drug Discovery Using AFM Force Spectroscopy

Increasingly targeted in drug discovery, protein-protein interactions challenge current high throughput screening technologies in the pharmaceutical industry. Developing an effective and efficient method for screening small molecules or compounds is critical to accelerate the discovery of ligands for enzymes, receptors and other pharmaceutical targets. Here, we report developments of methods to increase the signal-to-noise ratio (SNR) for screening protein-protein interactions using atomic force microscopy (AFM) force spectroscopy. We have demonstrated the effectiveness of these developments on detecting the binding process between focal adhesion kinases (FAK) with protein kinase B (Akt1), which is a target for potential cancer drugs. These developments include optimized probe and substrate functionalization processes and redesigned probe-substrate contact regimes. Furthermore, a statistical-based data processing method was developed to enhance the contrast of the experimental data. Collectively, these results demonstrate the potential of the AFM force spectroscopy in automating drug screening with high throughput

Shoshonitic enclaves in the high Sr/Y Nyemo pluton, southern Tibet: Implications for Oligocene magma mixing and the onset of extension of the southern Lhasa terrane

Post-collisional potassic and high Sr/Y magmatism in the Lhasa terrane provides critical constraints on the timing and mechanism of subduction of Indian lithosphere and its role in the uplift of the Tibetan Plateau. Here, we report whole-rock geochemistry, mineral geochemistry, zircon U Pb ages, and in situ zircon Hf isotope ratios for the Nyemo pluton, a representative example of such magmatism. The Nyemo pluton is composed of high Sr/Y host rocks and coeval shoshonitic mafic microgranular enclaves (MMEs). Whole-rock compositions of the host rocks and MMEs form linear trends in Harker diagrams, consistent with modification of both end-members by magma mixing. Although the main high Sr/Y phase of the pluton formed by partial melting of the lower crust of the thickened Lhasa terrane, the MMEs display abnormally enriched light rare earth elements, low whole-rock ε_(Nd)(t) and low zircon ε_(Hf)(t) that suggest derivation from low degree melting of hydrous and enriched mantle. Based on the occurrence of shoshonitic magma and high La/Yb and high Sr/Y with adakitic affinity host rocks around 30 Ma, the Nyemo pluton is best explained as a record of onset of extension that resulted from convective removal of the mantle lithosphere beneath Tibet in the Oligocene

MiR-101-3p targets KPNA2 to inhibit the progression of lung squamous cell carcinoma cell lines

We herein discuss the impacts of miR-101-3p on the tumorigenesis-related cell behaviors in lung squamous cell carcinoma (LUSC) by repressing KPNA2. TCGA database was utilized to measure miR101-3p and KPNA2 levels in LUSC tissues and cells. The interaction of miR-101-3p and KPNA2-3’UTR was determined by dual luciferase assay. Western blot evaluated the protein level of KPNA2. MiR-101-3p was under-expressed in LUSC cells while KPNA2 was overexpressed. Western blot confirmed the impact of KPNA2 expression on cancer cell progression. The negative regulatory impact of miR-101-3p on KPNA2 was also verified. In vitro cell function assays revealed the suppressing effect of high miR-101-3p expression on cell invasion, migration and viability, as well as its promoting effect on apoptosis. Up-regulated miR-101-3p weakened the promoting effect of overexpressed KPNA2 on LUSC malignant progression. To conclude, miR-101-3p repressed viability, invasion, and migration, and facilitated cell apoptosis in LUSC by suppressing KPNA2

Ubiquitylation activates a peptidase that promotes cleavage and destabilization of its activating E3 ligases and diverse growth regulatory proteins to limit cell proliferation in Arabidopsis

The characteristic shapes and sizes of organs are established by cell proliferation patterns and final cell sizes, but the underlying molecular mechanisms coordinating these are poorly understood. Here we characterize a ubiquitin-activated peptidase called DA1 that limits the duration of cell proliferation during organ growth in Arabidopsis thaliana. The peptidase is activated by two RING E3 ligases, Big Brother (BB) and DA2, which are subsequently cleaved by the activated peptidase and destabilized. In the case of BB, cleavage leads to destabilization by the RING E3 ligase PROTEOLYSIS 1 (PRT1) of the N-end rule pathway. DA1 peptidase activity also cleaves the deubiquitylase UBP15, which promotes cell proliferation, and the transcription factors TEOSINTE BRANCED 1/ CYCLOIDEA/PCF 15 (TCP15) and TCP22, which promote cell proliferation and repress endoreduplication. We propose that DA1 peptidase activity regulates the duration of cell proliferation and the transition to endoreduplication and differentiation during organ formation in plants by coordinating the destabilization of regulatory proteins

A novel and high-efficient method for the preparation of heat-stable antifungal factor from Lysobacter enzymogenes by high-speed counter-current chromatography

Heat-stable antifungal factor (HSAF) produced by the biocontrol bacterium Lysobacter enzymogenes shows considerable antifungal activity and has broad application potential in the agricultural and medical fields. There is a great demand for pure HSAF compounds in academic or industrial studies. However, an efficient preparation method that produces a high yield and high purity of HSAF is lacking, limiting the development of HSAF as a new drug. In the present study, high-speed counter-current chromatography (HSCCC) combined with column chromatography was successfully developed for the separation and preparation of HSAF from the crude extract of L. enzymogenes OH11. The crude extract was obtained by macroporous resin adsorption and desorption, and the main impurities were partly removed by ultraviolet light (254 nm) and gel filtration (Sephadex LH-20). In the HSCCC procedure, the selected suitable two-phase solvent system (n-hexane/ethyl acetate/methanol/water = 3:5:4:5, v/v, the lower phase added with 0.1% TFA) with a flow rate of 2.0 mL/min and a sample loading size of 100 mg was optimized for the separation. As a result, a total of 42 mg HSAF with a purity of 97.6% and recovery of 91.7% was yielded in one separation. The structure elucidation based on HR-TOF-MS, 1H and 13C NMR, and antifungal activities revealed that the isolated compound was unambiguously identified as HSAF. These results are helpful for separating and producing HSAF at an industrial scale, and they further demonstrate that HSCCC is a useful tool for isolating bioactive constituents from beneficial microorganisms