Biomimetic MXene membranes with negatively thermo-responsive switchable 2D nanochannels for graded molecular sieving

Negatively thermo-responsive 2D membranes,which mimic the stomatal opening/closing of plants,have drawn substantial interest for tunable molecular separation processes.However,these membranes are still restricted significantly on account of low water permeability and poor dynamic tunability of 2D nanochannels under temperature stimulation.Here,we present a biomimetic negatively thermo-responsive MXene membrane by covalently grafting poly(N-isopropylacrylamide)(PNIPAm)onto MXene nanosheets.The uniformly grafted PNIPAm polymer chains can enlarge the interlayer spacings for increasing water permeability while also allowing more tunability of 2D nanochannels for enhancing the capability of gradually separating multiple molecules of different sizes.As expected,the constructed membrane exhibits ultrahigh water permeance of 95.6 L m^(-2) h^(-1) bar^(-1) at 25℃,which is eight-fold higher than the state-of-the-art negatively thermoresponsive 2D membranes.Moreover,the highly temperature-tunable 2D nanochannels enable the constructed membrane to perform excellent graded molecular sieving for dye-and antibiotic-based ternary mixtures.This strategy provides new perspectives in engineering smart 2D membrane and expands the scope of temperature-responsive membranes,showing promising applications in micro/nanofluidics and molecular separation.

Preparation and Thermo-Responsive Properties of Poly(Oligo(Ethylene Glycol)Methacrylate)Copolymers with Hydroxy-Terminated Side Chain

Thermo-responsive random copolymers,poly(2-(2-methoxyethoxy)ethoxyethyl methacrylate-co-(ethylene glycol)methyl ether methacrylate)(P(EO_(2)-co-EO_(4/5)))and poly(2-(2-methoxyethoxy)ethoxyethyl methacrylate-co-ethylene glycol methacrylate(P(EO2-co-EG4/5))are synthesized via atom transfer radical polymerization(ATRP).The successful synthesis and the narrow polydispersity index(PDI)of two copolymers are indicated by 1H nuclear magnetic resonance(1H-NMR)and gel permeation chromatography(GPC)analyses.The transition behaviors of polymers in the aqueous solution are demonstrated by changes in turbidity and particle sizes.The transition behavior of P(EO2-co-EG4/5)is found to be milder than that of P(EO2-co-EO4/5).Moreover,the presence of hydrogen bonds without thermo-responsive properties established by hydroxyl groups in the end-side chain of P(EO_(2)-co-EG_(4/5))hinders the dehydration at the transition temperature(TT).Attenuated total reflection Fourier transform infrared spectrometry(ATR-FTIR)analysis along with contact angle measurements reveals that both P(EO_(2)-co-EO_(4/5))and P(EO_(2)-co-EG_(4/5))films undergo phase transitions from hydrophilicity to hydrophobicity above TT.By examining the swelling and collapse behaviors of the polymer films during phase transitions,it can be concluded that the end hydroxyl groups may establish hydrogen bonds with neighboring ether groups within the films,which remain intact throughout the phase transition process due to their strong bonding interactions.This leads to an increase in steric hindrance within swollen films thereby impeding dehydration processes and inducing hysteresis during phase transitions.

A novel responsive stabilizing Janus nanosilica as a nanoplugging agent in water-based drilling fluids for exploiting hostile shale environments

Thermo-responsive nanocomposites have recently emerged as potential nanoplugging agents for shale stabilization in high-temperature water-based drilling fluids(WBDFs). However, their inhibitory properties have not been very effective in high-temperature drilling operations. Thermo-responsive Janus nanocomposites are expected to strongly interact with clay particles from the inward hemisphere of nanomaterials, which drive the establishment of a tighter hydrophobic membrane over the shale surface at the outward hemisphere under geothermal conditions for shale stabilization. This work combines the synergistic benefits of thermo-responsive and zwitterionic nanomaterials to synchronously enhance the chemical inhibitions and plugging performances in shale under harsh conditions. A novel thermoresponsive Janus nanosilica(TRJS) exhibiting zwitterionic character was synthesized, characterized,and assessed as shale stabilizer for WBDFs at high temperatures. Compared to pristine nanosilica(Si NP)and symmetrical thermo-responsive nanosilica(TRS), TRJS exhibited anti-polyelectrolyte behaviour, in which electrolyte ions screened the electrostatic attraction between the charged particles, potentially stabilizing nanomaterial in hostile shaly environments(i.e., up to saturated brine or API brine). Macroscopically, TRJS exhibited higher chemical inhibition than Si NP and TRS in brine, prompting a better capability to control pressure penetration. TRJS adsorbed onto the clay surface via chemisorption and hydrogen bonding, and the interactions became substantial in brine, according to the results of electrophoretic mobility, surface wettability, and X-ray diffraction. Thus, contributing to the firm trapping of TRJS into the nanopore structure of the shale, triggering the formation of a tight hydrophobic membrane over the shale surface from the outward hemisphere. The addition of TRJS into WBDF had no deleterious effect on fluid properties after hot-treatment at 190℃, implying that TRJS could find potential use as a shale stabilizer in WBDFs in hostile environments.

Effect of Graft Yield on the Thermo-Responsive Permeability Through Porous Membranes with Plasma-Grafted Poly(N-isopropylacrylamide)Gates

The effect of graft yield on both the thermo-responsive hydraulicpermeability and the therrno-responsive diffusional permeability through porous membranes withplasma-grafted poly(N-isopropylacrylamide) (PNIPAM) gates was investigated. Both thermo-responsiveflat membranes and core-shell microcapsule membranes with a wide range of graft yield of PNIPAM wereprepared using a plasma-graft pore-filling polymerization method. The grafted PNIPAM was formedhomogeneously throughout the entire thickness of both the flat polyethylene membranes and themicrocapsule polyamide membranes. Both the hydraulic permeability and the diffusional permeabilitywere heavily dependent on the PNIPAM graft yield. With increasing the graft yield, the hydraulicpermeability (water flux) decreases rapidly at 25℃ because of the decrease of the pore size;however, the water flux at 40℃ increases firstly to a peak because of the increase ofhydrophobicity of the pore surface, and then decreases and finally tends to zero because of the poresize becoming smaller and smaller. For the diffusional permeability, the temperature showsdifferent effects on the diffusional permeability coefficients of solutes across the membranes. Whenthe graft yield was low, the diffusional coefficient of solute across the membrane was higher attemperature above the lower critical solution temperature (LCST) than that below the LCST; however,when the graft yield was high, the diffusional coefficient was lower at temperature above the LCSTthan that below the LCST. It is very important to choose or design a proper graft yield of PNIPAMfor obtaining a desired thermo-responsive 'on/off' hydraulic or diffusional permeability.

Halloysite Nanotube Composited Thermo-responsive Hydrogel System for Controlled-release

Halloysite nanotube-composited thermo-responsive hydrogel system has been successfully developed for controlled drug release by copolymerization of N-isopropylacrylamide （NIPAM） with silane-modified halloysite nanotubes （HNT） through thermally initiated free-radical polymerization. With methylene blue as a model drug, thermo-responsive drug release results demonstrate that the drug release from the nanotubes in the composited hy-drogel can^be well controlled by manipulating the environmental temperature. When the hydrogel network is swol- len at temperature below the lower critical solution temperature （LCST）, drug releases steadily from lumens of the embedded nanotubes, whereas the drug release stops when hydrogel shrinks at temperature above the LCST. The release of model drug from the HNT-composited hydrogel matches well with its thermo-responsive volume phasetransition, and shows characteristics of well controlled release. The design strategy and release results of the pro- posed novel HNT-composited thermo-responsive hydrogel system provide valuable guidance for designing respon- s_i_ve nanocomposites for controlled-release of active agents.

Application of Monodisperse Thermo-Responsive Composite Microgels with Core-Shell Structure Based on Au@Ag Bimetallic Nanorod as Core in Surface Enhanced Raman Spectroscopy Substrate

The monodisperse Au@Ag bimetallic nanorod is encapsulated by crosslinked poly( N-isopropylacrylamide)( PNIPAM) to produce thermo-responsive composite microgel with well-defined core-shell structure( Au@ Ag NR@ PNIPAM microgel)by seed-precipitation polymerization method using butenoic acid modified Au @ Ag NRs as seeds. When the temperature of the aqueous medium increases from 20℃ to 50℃,the localized surface plasmon resonance( LSPR) band of the entrapped Au @ Ag NR is pronouncedly red-shifted because of the decreased spatial distances between them as a result of shrinkage of the microgels,leading to their plasmonic coupling. The temperature tunable plasmonic coupling is demonstrated by temperature dependence of the surface enhanced Raman spectroscopy( SERS) signal of 1-naphthol in aqueous solution. Different from static plasmonic coupling modes from nanostructured assembly or array system of noble metals,the proposed plasmonic coupling can be dynamically controlled by environmental temperature. Therefore, the thermo responsive hybrid microgels have potential applications in mobile LSPR or SERS microsensors for living tissues or cells.

Rheological properties of novel thermo-responsive polycarbonates aqueous solutions

Thermo-responsive multiblock polycarbonates were facilely synthesized by covalently binding poly(ethylene glycol)(PEG) and poly(propylene glycol)(PPG) blocks,using triphosgene as coupling agent and pyridine as catalyst.The aqueous solutions of thermo-responsive polycarbonates were investigated by rheological measurements.Steady-state shear measurements reveal that the polycarbonate solutions exhibit shear-thinning behavior and the hydrophilic content has a pronounced effect on the flow behavior of the polycarbonates aqueous solutions.The shear viscosity decreases with increasing poly(ethylene oxide)(PEO) composition.The increase of viscosity with increasing concentration is probably attributed to the formation of stronger network owing to interchain entanglement of PEO block at higher concentration.When the flow curves are fitted to the power law model,flow index is obtained to be less than 1,as exhibiting typical pesudoplastic fluid.The viscoelastic properties of the system also show close dependence on the composition of polycarbonates.Temperature sweep confirms that the multiblock polycarbonates exhibit thermo-responsive properties.For 7% aqueous solution of polycarbonate with composition ratio of EO to PO of 1/1,the sol-gel transition occurs at 37 ℃,which makes the system suitable as an injectable drug delivery system.

The Microstructure and Gelling Mechanism of Thermo-responsive Chitosan Hydrogel System

Thermo-respansive chitosan hydrogel system （TRCHS） was prepared and its mierostructure was investigated by scaning electron microscope （SEM） and mercury intrusion poremaster （MIP）. Based on analyzing the data, a special porosity property was reported at the first time. Its gelling mechanism was studied by a group of contrast experiments. Results may provide experimental and theoretical supports for how to apply it on tissue engineering scaffold and how to influeuee or control its essential properties.

Photoluminescence and ratiometric thermo-response of Eu^(2+)and Eu^(3+)in BaAl_(2)B_(2)O_(7):Eu^(2+),Eu^(3+)phosphor materials

A novel Eu^(2+)-Eu^(3+)co-activated ratiometric thermo-sensitive phosphor was developed and synthesized by solid-state reaction.The valence state of Eu,photoluminescence and thermo-sensitive performance of the phosphor prepared either in ambient air or carbothermally were investigated and discussed.The phosphor shows high sensitivity(Sa=0.0173 K^(-1),S_(r)=0.461%/K)and superior signal discriminability(Δν∼10380 cm^(−1)).The thermo-sensitive performance is subject to the dual effects of different thermo-responses by Eu^(2+)versus Eu^(3+)combined with energy transfer from Eu^(2+)to Eu^(3+),so that the sensitivity of the phosphor in the temperature range presents a non-monotonic trend.The development of the BaAl_(2)B_(2)O_(7):Eu^(2+),Eu^(3+)phosphor is not only expected to be relevant for application in the field of temperature sensing,but also of reference significance for improving the sensitivity by means of energy transfer between co-activator ions over a wider temperature range of Eu^(2+)-Eu^(3+)co-activated ratiometric thermo-sensitive phosphors.

Reshaping the imprinting strategy through the thermo-responsive moiety-derived“deep eutectic solvents”effect

As a new concept having emerged in last few years,the“deep eutectic solvents”(DESs)effect integrated into the imprinting technology inevitably exposes design limitations of stimuli-responsive molecularly imprinted polymers(MIPs),as well as inadequate analysis of the adsorption performance of MIPs.Herein,a simple yet defined N-isopropylacrylamide/(3-acrylamidopropyl)trimethylammonium chloride(NIPAM/APTMAC)binary DESs system was proposed to prepare intelligent MIPs with thermo-sensitivity.Accordingly,magnetic and thermo-responsive MIPs based on functional monomers-derived DESs(TMDESs-MIPs1)were synthesized,revealing DESs effect-regulated affinity/kinetics for the enhanced adsorption capability,eco-friendly thermo-regulated elution for high release efficiency,and simple magnetic separation,along with superior selectivity to rhein(RH)and good regeneration ability.TM-DESs-MIPs1 were utilized to extract RH from Cassiae semen samples coupled with high performance liquid chromatography(HPLC),yielding satisfactory recoveries(79.47%−110.82%)and low limits of detection(LOD)(16.67μg/L).Another two kinds of MIPs adopting the thermo-responsive moiety-derived DESs effect strategy further demonstrated great applicability of such intelligent MIPs for analyses of complicated samples.

Studies on LCST of poly (N-isopropylacrylamide-co-acrylic acid-co-N-diacetone acrylamide)

Linear copolymers from N-isopropylacrylamide （NIPA）, acrylic acid （AA） and diacetone acrylamide （DAA） have been prepared. The effect of composition, ionic strength and pH on their lower critical solution temperature （LCST） has been investigated.

Thermo- and pH-Responsive Hydrogels Based on N-Isopropylacrylamide and Allylamine Copolymers

The thermo- and pH-responsive hydrogels were synthesized via copolymerization of N-isopropylacrylamide and al-lylamine hydrochloride monomers. The equilibrium swelling of the hydrogels was studied as a function of temperature and pH in aqueous solutions. It was shown that controlled alteration of the hydrogel phase transition temperature can be achieved by changing their composition and pH of the environment. Increase in content of hydrophilic allylamine from 10 to 60 wt% in monomer mixture causes a shift of the phase transition temperature from 35oC to 47oC. Hydrogels with N-isopropylacrylamide/allylamine hydrochloride mass ratio of 3:2 show the highest pH-response. Values of average molecular weight between polymer cross-links, , and Flory parameter, χ, were calculated using temperature dependences of the equilibrium swelling of the synthesized hydrogel.

A Novel Drug Delivery System for Osteosarcoma Chemotherapy

A thermo-responsive chitosan hydrogel system （TRCHS） was prepared by chitosan （ CS ） and β- glycerophosphate （ β- GP ） to deliver Adriamycin （ ADM ） locally for curing osteosarcoma. Release property was investigated by release experiments in vitro and results show that it can be applied to local drug release because it is able to release drug at high concentration for 17 days. The treatment effect was studied by injecting intratumorally to osteosarcoma tumors （ CRL- 1427） implanted sabcutaneously on Specific Pathogen-free （SPF） mice. The statistical analytical results show that TRCHS delivering ADM is more efficacioas than saline intratumoral injection, which loads the same quantity of ADM , but is less poisonous. Based on the analysis above, this novel biodegradable polymer implant is an effective and safe vehicle for sustained local delivery of ADM, and is supposed to be applied in neoadjuvant chemotherapy for osteosarcoma.

Coordinate Bond Breaking Induced by Collapse of Poly(N-isopropyl acrylamide) as Ligands of a Rare Earth Complex

A novel water-soluble luminescent complex consisting of Eu(ally-dbm)3-2Tppo and poly(N-isopropyl acrylamide)(PNIPAM)is synthesized through a series of chemical reactions.The structure of the complex is characterized by TGA,GPC,HNMR,and the thermal-responsive uorescence of the complex in aqueous solution is investigated.It is found that PNIPAM collapse above the lower critical solution temperature causes the coordination bond breaking,leading to weakening of the uorescence from Eu3+and enhancing of the uorescence from the ligands.When temperature decreases,the uorescence from Eu3+is found to boost up and the uorescence from ligands weakens accordingly.It is deduced from this phenomenon that the ligands recoordinate with europium ions again along with the temperature decreasing,which is further confirmed by IR measurements.This thermal-responsive uorescence is of reversibility,which can be used as molecular probes for biological imaging and collapse studying of PNIPAM.

Intravesical chemotherapy synergize with an immune adjuvant by a thermo-sensitive hydrogel system for bladder cancer

Surgical resection remains the prefer option for bladder cancer treatment.However,the effectiveness of surgery is usually limited for the high recurrence rate and poor prognosis.Consequently,intravesical chemotherapy synergize with immunotherapy in situ is an attractive way to improve therapeutic effect.Herein,a combined strategy based on thermo-sensitive PLEL hydrogel drug delivery system was developed.GEM loaded PLEL hydrogel was intravesical instilled to kill tumor cells directly,then PLEL hydrogel incorporated with CpG was injected into both groins subcutaneously to promote immune responses synergize with GEM.The results demonstrated that drug loaded PLEL hydrogel had a sol-gel phase transition behavior in response to physiological temperature and presented sustained drug release,and the PLEL-assisted combination therapy could have better tumor suppression effect and stronger immunostimulating effect in vivo.Hence,this combined treatment with PLEL hydrogel system has great potential and suggests a clinically-relevant and valuable option for bladder cancer.

热致硬化水凝胶驱动器用于自锁定抓手

基于水凝胶致动器的柔性抓取器由于具有刺激响应性的抓取和释放能力而受到广泛关注.然而,水凝胶抓取器力学性能通常较差,难以抓取较重的物体.本文介绍了一种具有自锁定能力的双层水凝胶抓手,它以含有微凝胶的聚N-异丙基丙烯酰胺(PNIPAm)水凝胶层为驱动层,实现抓取动作;以聚丙烯酸-醋酸钙(PAA-Ca(CH_(3)COO)_(2))水凝胶层为热致硬化层,通过提高PAA-(CH_(3)COO)_(2)层的模量来锁定抓取动作,因而水凝胶抓手可以提起自身重量500倍的重物.此外,软抓手还能在各种抓取模式下工作.本文有望为构建具有强抓取能力的软质致动器提供新的思路.

Injectable thermo-responsive nano-hydrogel loading triptolide for the anti-breast cancer enhancement via localized treatment based on “two strikes” effects

The clinical application of triptolide(TPL)in tumor therapy has been greatly limited by its toxicity and inefficient delivery.Herein,a localized and sustained-release thermo-sensitive hydrogel was developed for the intra-tumor administration of TPL.Based on the amphiphilic structure of poly(N-isopropylacrylamide-co-acrylic acid)-g-F68 copolymer,it was able to form nano-micelles to efficiently encapsulate TPL,and then turn into a hydrogel at 37C.TPL@nano-gel exhibited a sustained drug release profile in vitro and a stronger anticancer effect caused by"two strikes".The"first strike"was its enhanced cytotoxicity compared to free TPL,due to the enhanced pro-apoptosis effect observed in both MDA-MB-231 and MCF-7 cells caused by the regulation of endogenous mitochondrial pathways.Furthermore,TPL@nano-gel exhibited a"second-strike"through its anti-angiogenesis capabilities mediated through VEGFR-2 signaling inhibition.As expected,after intra-tumoral injection at a 0.45 mg/kg TPL-equivalent dose three times over 14 days in 4 T1 tumor-bearing mice,TPL@nano-gel led to lower systemic toxicity and higher antitumor efficacy compared to multiple injections of TPL.In this regard,these findings indicate that this injectable thermo-responsive hydrogel carries great potential for TPL as a safe and effective cancer therapy.

Poly(N-isopropylacrylamide)-based thermo-responsive surfaces with controllable cell adhesion

Poly(N-isopropylacrylamide)(PNIPAAm)-based thermo-responsive surfaces can switch their wettability(from wettable to non-wettable) and adhesion(from sticky to non-sticky) according to external temperature changes. These smart surfaces with switchable interfacial properties are playing increasingly important roles in a diverse range of biomedical applications; these controlling cell-adhesion behavior has shown great potential for tissue engineering and disease diagnostics. Herein we reviewed the recent progress of research on PNIPAAm-based thermo-responsive surfaces that can dynamically control cell adhesion behavior. The underlying response mechanisms and influencing factors for PNIPAAm-based surfaces to control cell adhesion are described first. Then, PNIPAAm-modified two-dimensional flat surfaces for cell-sheet engineering and PNIPAAm-modified three-dimensional nanostructured surfaces for diagnostics are summarized. We also provide a future perspective for the development of stimuli-responsive surfaces.

Interfacially stable MOF nanosheet membrane with tailored nanochannels for ultrafast and thermo-responsive nanofiltration

Two-dimensional nanosheet membranes with responsive nanochannels are appealing for controlled mass transfer/separation,but limited by everchanging thicknesses arising from unstable interfaces.Herein,an interfacially stable,thermo-responsive nanosheet membrane is assembled from twin-chain stabilized metal-organic framework(MOF)nanosheets,which function via two cyclic amide-bearing polymers,thermo-responsive poly(N-vinyl caprolactam)(PVCL)for adjusting channel size,and non-responsive polyvinylpyrrolidone for supporting constant interlayer distance.Owing to the microporosity of MOF nanosheets and controllable interface wettability,the hybrid membrane demonstrates both superior separation performance and stable thermo-responsiveness.Scattering and correlation spectroscopic analyses further corroborate the respective roles of the two polymers and reveal the microenvironment changes of nanochannels are motivated by the dehydration of PVCL chains.

Thermo-responsive and Antifouling PVDF Nanocomposited Membranes Based on PNIPAAm Modified TiO_2 Nanoparticles

A novel hydrophilic nanocomposite additive （TiO2-g-PNIPAAm） was synthesized by the surface modification of titanium dioxide （TiO2） with N-isopropylacrylamide （NIPAAm） via ＂graft-from＂ technique. And the nanocomposite membrane of poly（vinylidene fluoride） （PVDF）/TiO2-g-PNIPAAm was fabricated by wet phase inversion. The graft degree was obtained by thermo-gravimetric analysis （TGA）. Fourier transform infrared attenuated reflection spectroscopy （FTIR-ATR） and X-ray photoelectronic spectroscopy （XPS） characterization results suggested that TiO2-g-PNIPAAm nanoparticles segregated on membrane surface during the phase separation process. Scanning electron microscopy （SEM） was conducted to investigate the surface and cross-section of the modified membranes. The water contact angle measurements confirmed that TiO2-g-PNIPAAm nanoparticles endowed PVDF membranes better hydrophlilicity and thermo-responsive properties compared with those of the pristine PVDF membrane. The water contact angle decreased from 92.8~ of the PVDF membrane to 61.2~ of the nanocompostie membrane. Bovine serum albumin （BSA） static and dynamic adsorption experiments suggested that excellent antifouling properties of membranes was acquired after adding TiO2-g- PNIPAAm. The maximum BSA adsorption at 40℃ was about 3 times than that at 23 ℃. The permeation experiments indicated the water flux recover ratio and BSA rejection ratio were improved at different temperatures.