Quadruple-responsive nanocomposite based on dextran-PMAA-PNIPAM, iron oxide nanoparticles, and gold nanorods.

A quadruple-responsive nanocomposite that responds to temperature, pH, magnetic field, and NIR is obtained by incorporating superparamagnetic iron oxide nanoparticles (SPIONs) and gold nanorods (AuNRs) into a dextran-based smart copolymer network. The dual-sensitive copolymer is prepared by sequential RAFT polymerization of methacrylic acid and N-isopropylacrylamide from trithiocarbonate groups linked to dextran in one pot. These functionalized nanocomposites with superior stability can respond to the four stimuli mentioned above well. As evidenced by UV-vis and TEM measurements, the temperature-induced unusual blue-shift in the longitudinal plasmon band is possibly due to the side-to-side assembly of AuNRs.

Silicene/poly(N-isopropylacrylamide) smart hydrogels as remote light-controlled switches.

Smart hydrogels with good flexibility and biocompatibility have been widely used. The common near-infrared (NIR) photothermal agents are facing a trade-off between good photothermal-conversion efficiency and high biocompatibility. Therefore, developing new metal-free photothermal agents with low cost, high biocompatibility and excellent phase stability is still in urgent need. In this study, we successfully combined poly(N-isopropylacrylamide) (PNIPAM) with the two-dimensional (2D) silicene nanosheets via the in situ polymerization method. Attributed to the thermal-responsive nature of PNIPAM and the excellent photothermal properties of 2D silicene, the obtained silicene/PNIPAM composite hydrogels exhibited dual thermal and NIR responsive properties. This smart hydrogel showed rapid, reversible and repeatable NIR light-responsive behaviors. The volume of this smart hydrogels can shrink significantly under NIR irradiation and recover to its original size without the NIR irradiation. Remote near-infrared light-controlled microfluidic pipelines and electronic switches based on obtained silicene/PNIPAM composite hydrogels were also demonstrated. This work significantly broadens the application prospects of silicene-based hydrogels in remote light-controlled devices.

Temperature- and redox-directed multiple self assembly of poly(N-isopropylacrylamide) grafted dextran nanogels.

Poly(N-isopropylacrylamide) (PNIPAAm) grafted dextran nanogels with dodecyl and thiol end groups have been synthesized by RAFT process. Dodecyl-terminated polymers (DexPNI) can be readily dissolved in water and further self assemble into ordered stable nanostructures through direct noncovalent interactions at room temperature. SEM, AFM and DLS measurements confirm the formation of spherical nanogels at hundred-nanometer scales. The elevation of environment temperature will indirectly result in the formation of collapsed nanostructures due to the LCST phase transition of PNIPAAm side chains. Turbidimetry results show that the phase transition behaviors of DexPNI are greatly dependent on PNIPAAm chain length and polymer concentration: increasing PNIPAAm chain length and polymer concentration both lead to lower LCSTs and sharper phase transitions. Moreover, the dodecyl-terminated polymers can transform into thiol-terminated versions by aminolysis of trithiocarbonate groups, and further into chemical (disulfide) cross-linked versions (SS-DexPNI) by oxidation. SS-DexPNI nanogels have "doubled" chain length of PNIPAAm, and hence sharper phase transitions. In situ DLS measurements of the evolution of hydrodynamic radius attest that the self assembly of SS-DexPNI nanogels can be selectively directed by the change in either external temperature or redox potential. These nanogels thus are promising candidates for triggered intracellular delivery of encapsulated cargo. We can also expect that the polymer can be noncovalently (by dodecyl end groups) or covalently (by thiol end groups) coated on a series of nanomaterials (e.g., carbon nanotubes, graphene, gold nanomaterials) to build a variety of novel smart, and robust nanomaterials.

Ultralow fouling zwitterionic polymers grafted from surfaces covered with an initiator via an adhesive mussel mimetic linkage.

In this work, nonfouling zwitterionic polymers were grafted via surface-initiated atom transfer radical polymerization (ATRP) from surfaces covered with an adhesive catechol initiator. The catechol initiator was attached to both bare gold and amino-functionalized surfaces, and the nonfouling performances of the resulting polymer brushes were compared. Under optimal conditions, ultralow protein adsorption from both single-protein solutions of fibrinogen and lysozyme and complex media of 10% blood serum and 100% blood plasma/serum was achieved. Furthermore, the 3-day accumulation of Pseudomonas aeruginosa on the treated glass surfaces was studied in situ using a laminar flow chamber. The results showed that these zwitterionic coatings dramatically reduced the biofilm formation of P. aeruginosa as compared to the reference bare glass.

Variation analysis of affinity-membrane model based on Freundlich adsorption.

The variation analysis of membrane properties including membrane thickness and pore-size was carried out theoretically by using affinity-membrane model based upon the Freundlich adsorption equation. As the percentage variation of membrane thickness and distribution of pore-size increase, we find that (1) the time of total saturation is delayed; (2) the loading capacity at the point of breakthrough are decreased; (3) solute recovery efficiency and ligand utilization efficiency is decreased; (4) the thickness of unused membrane is increased. The results show that even small variations of thickness and distribution of pore size may severely degrade the membrane performance.

Mathematical analysis of affinity membrane chromatography.

A mathematical model including convection, diffusion and Freundlich adsorption is developed. To examine the validity of the model, the affinity membranes were prepared by coating chitosan on the nylon membranes, a ligand of poly-L-lysine was bound to the chitoan-coating membranes, and the adsorption behavior of bilirubin through the stacked affinity membranes was investigated. The agreements between the theoretical and experimental results are exceptional. Using our new model, we show that: (1) As Pe increases, the breakthrough curves become sharper. For Pe greater than 30, the effect of axial diffusion is insignificant; (2) As m increases, the time of total saturation is delayed and the loading capacity at the point of breakthrough is increased; (3) As n decreases, the time of total saturation is delayed and the loading capacity at the point of breakthrough is increased; (4) As r increases, both the time of total saturation and the loading capacity at the point of breakthrough are increased; (5) adsorption rate influences the time of total saturation strongly but contributes little to the loading capacity.

Adsorption of bilirubin with polylysine carrying chitosan-coated nylon affinity membranes.

Microporous polyamide membranes were activated by bisoxirane and subsequently bound with chitosan (CS) to amplify reactive groups. Then polylysine (PLL) as ligand was immobilized onto the CS-coated nylon membranes. The contents of CS and PLL of PLL-attached membranes were 93.2 and 90.4 mg/g nylon membrane, respectively. Such PLL-attached membranes were used to adsorb bilirubin from the bilirubin-phosphate solution and bilirubin-albumin solution. The adsorption mechanism of bilirubin and the effects of temperature, initial concentration of bilirubin, albumin concentration and ionic strength on adsorption were investigated by batch experiments. The results showed that the adsorption capacity increased with increasing the temperature while decreased with increasing the NaCl concentration and albumin concentration, and the adsorption isotherm fitted the Freundlich model well. The result of dynamic experiment showed PLL-attached membranes can well remove the bilirubin from the bilirubin-albumin solution.

Nanoporous Ni(OH)2 thin film on 3D Ultrathin-graphite foam for asymmetric supercapacitor.

Nanoporous nickel hydroxide (Ni(OH)2) thin film was grown on the surface of ultrathin-graphite foam (UGF) via a hydrothermal reaction. The resulting free-standing Ni(OH)2/UGF composite was used as the electrode in a supercapacitor without the need for addition of either binder or metal-based current collector. The highly conductive 3D UGF network facilitates electron transport and the porous Ni(OH)2 thin film structure shortens ion diffusion paths and facilitates the rapid migration of electrolyte ions. An asymmetric supercapacitor was also made and studied with Ni(OH)2/UGF as the positive electrode and activated microwave exfoliated graphite oxide ('a-MEGO') as the negative electrode. The highest power density of the fully packaged asymmetric cell (44.0 kW/kg) was much higher (2-27 times higher), while the energy density was comparable to or higher, than high-end commercially available supercapacitors. This asymmetric supercapacitor had a capacitance retention of 63.2% after 10,000 cycles.

Functionalizable and ultra-low fouling zwitterionic surfaces via adhesive mussel mimetic linkages.

In this work, a biomimetic polymer (pCB(2)-catechol(2)), with two zwitterionic poly(carboxybetaine) (pCB) arms for ultra-low fouling and two adhesive catechol groups for surface anchoring, was developed. Two pCB arms were grown from an initiator with two catechol groups via atom transfer radical polymerization (ATRP). Binding tests of pCB(2)-catechol(2) were performed on a gold surface under a range of conditions such as pH values and solvents. Protein adsorption from single protein solutions of fibrinogen and lysozyme, and complex media of 100% blood plasma and serum was evaluated using a surface plasmon resonance (SPR) sensor. Results are compared with those from two other polymers (i.e., one polymer with one pCB chain and one catechol group, termed as pCB-catechol, and another polymer with one pCB chain and two catechol groups, termed as pCB-catechol(2)). Furthermore, the direct immobilization of anti-activated leukocyte cell adhesion molecule (anti-ALCAM) was carried out on the pCB(2)-catechol(2) modified surface. Results showed that the antibody-immobilized surface maintained its excellent ultra-low fouling properties. The detection of activated leukocyte cell adhesion molecule (ALCAM) in 100% blood plasma with high sensitivity and specificity was achieved. This work demonstrates an effective and convenient strategy to obtain functionalizable and ultra-low fouling surfaces.