Novel calcium-alginate capsules with aqueous core and thermo-responsive membrane

Novel calcium-alginate (Ca-alginate) capsules with aqueous core and thermo-responsive membrane are successfully prepared by introducing a co-extrusion minifluidic approach, and the thermo-responsive gating characteristics of Ca-alginate capsule membranes embedded with poly(N-isopropylacrylamide) (PNIPAM) microspheres are investigated systematically. The experimental results show that the prepared Ca-alginate capsules are highly monodisperse, and the average diameter and membrane thickness of Ca-alginate capsules are about 2.96 mm and 0.11 mm respectively. The Ca-alginate capsule membranes exhibit desired thermo-responsive gating property. With increasing the content of PNIPAM microspheres embedded in the Ca-alginate capsule membranes, the thermo-responsive gating coefficient of the capsule membranes increases simply. When solute molecules diffuse through the capsule membrane, the thermo-responsive gating coefficient is significantly affected by the molecular weight of solute molecules.     

Thermo-responsive Hercosett/Poly(N-isopropylacrylamide) films: a new, fast, optically responsive coating

Poly(N-isopropylacrylamide) (PNIPAM) is a common thermo-responsive, water-soluble polymer, while Hercosett is a cationic resin commonly employed in the paper industry. In this paper, Hercosett? and poly(N-isopropylacrylamide) (PNIPAM) nanoparticles were used to prepare composite films that show thermo-responsive behavior and swelling–shrinking properties in water. First, size-controlled PNIPAM hydrogel nanoparticles were synthesized. These were then embedded within a matrix of the cationic resin Kymene 577H by film casting. The distribution of nanoparticles in the resin film was investigated. The thermo-responsive properties of the as-synthesized PNIPAM hydrogel nanoparticles and of the composite films were characterized together with the repeatability of the swelling–shrinking cycles. The presence of nanoparticles endowed the film with highly enhanced water retention (in comparison with resin-only films) and, most importantly, thermo-responsiveness. A very fast optical and morphological response was in fact observed. Due to the dual (optical and morphological) response, this new system is suitable for applications in optical or morphological actuation and gating.     

Effect of freeze-drying and rehydrating treatment on the thermo-responsive characteristics of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) microspheres

Investigations on the effect of freeze-drying and rehydrating treatment on equilibrium volume changes and on the thermo-response rate of poly(N-isopropylacrylamide) (PNIPAM) microspheres were carried out. The experimental results showed that freeze-drying and rehydrating treatment had nearly no effect on the low critical solution temperature and equilibrium volume changes of PNIPAM microspheres. Furthermore, when the PNIPAM microspheres were frozen in only liquid nitrogen through rapid cooling, the response rate of PNIPAM microspheres to environmental temperature change was nearly not affected by the treatment, which was surprisingly different from the macroscopic hydrogel. The dimension effect was responsible for this phenomenon. The micron-sized PNIPAM microsphere itself has a much quicker response rate compared with the bulky hydrogel because the characteristic time of gel deswelling is proportional to the square of a linear dimension of the hydrogel.     

Fabrication of novel thermo-responsive electrospun nanofibrous mats and their application in bioseparation

To fulfill the development of biotechnology and biomedicine, environmental-responsive polymer materials are wanted for isolation and purification of biomolecules. Herein, a novel thermo-responsive poly(methyl methacrylate) (PMMA)/poly(N-isopropylacrylamide) (PNIPAM) blend nanofibrous mat was developed, which can adsorb and release a model solute, bovine serum albumin (BSA), through the way of hydrophilicity–hydrophobicity transition behavior of PNIPAM. The uniform bead-free electrospun nanofibers were obtained from the homogeneous PMMA solution in the presence of different amount of PNIPAM. Scanning electron microscopy (SEM) analysis showed that the electrospinnability of PMMA was improved by the addition of PNIPAM, and the diameter of resultant nanofibers could be modulated by controlling the amount of PNIPAM. The thermo-responsive swelling behavior of the blend nanofibrous mats was reversible and reproducible by changing environmental temperature across the lower critical solution temperature (LCST) of PNIPAM. Moreover, the separation property of the blend nanofibrous mats was found to be related to the amount of PNIPAM as well as the concentration of BSA. As for a better separation effect, the nanofibers with higher content of PNIPAM were favorable.     

Preparation and characterization of dual stimuli-responsive microcapsules with a superparamagnetic porous membrane and thermo-responsive gates

A novel dual stimuli-responsive microcapsule with a superparamagnetic porous membrane and linear-grafted poly(N-isopropylacrylamide) (PNIPAM) gates in the membrane pores is successfully prepared and characterized. Oleic acid (OA)-modified Fe₃O₄ nanoparticles are embedded into the polyamide microcapsule membrane during interfacial polymerization process, and then plasma-induced grafting polymerization is used to graft PNIPAM into the pores of microcapsule membranes. The prepared microcapsule membranes exhibit time-independent superparamagnetic property with good magnetic-responsive ability, and satisfactory thermo-responsive controlled-release property due to the thermo-responsive swollen/shrunken property of PNIPAM gates grafted on the inner pore surface of the microcapsule membranes.     

Interactions between temperature-sensitive hydrogel microspheres and granulocytes

Poly(N-isopropylacrylamide) (PNIPAM) has a low critical solution temperature (LCST) at 32°C in water and the hydrophilicity changes through the LCST. The microspheres whose surface was composed of PNIPAM exhibited phase transition behavior around 32°C. Therefore, the interactions between PNIPAM micropheres and granulocytes depended on the temperature. That is, the oxygen consumption and active oxygen production by cells in contact with PNIPAM-containing microspheres and adhesion of the microspheres to the cell surface were more enhanced above the LCST of PNIPAM than below it, whereas no significant temperature dependence of cell–microspheres interaction was observed in nonthermosensitive microsphere systems. It was suggested that the function of cells could be controlled with temperature using the temperature-sensitive microspheres.     

可自去除模板法制备环境响应性PNIPAM空心微球

本文采用可自去除模板法制备了单分散的聚（N-异丙基丙烯酰胺） （PNIPAM）空心微球, 用透射电子显微镜（TEM）研究了不同工艺条件对微球尺寸和形貌的影响机制. 结果表明, 酸性单体甲基丙烯酸（MAA）的加入量决定了PNIPAM微球空腔的形成速度; 而MAA及表面活性剂十二烷基硫酸钠（SDS）的加入量对空心微球的粒径及空腔大小亦有明显影响. 具体地讲, 当MAA的浓度从1.06 mmol/L增加到4.24 mmol/L时, 空心微球的平均粒径从250 nm左右增加到约450 nm, 内部空腔尺寸从40 nm增加到270 nm; 而当SDS的浓度从0增加到0.62 mmol/L时, 空心微球的平均粒径及内部空腔尺寸分别从450和270 nm降低到320和130 nm. 紫外分光光度计和动态光散射的检测结果显示, 所得PNIPAM空心微球具有受pH控制的温度敏感性.     

Preparation of Hollow Silica Microspheres via Poly(N-isopropylacrylamide)

Core-shell structured SiO₂/poly(N-isopropylacrylamide) (SiO₂/PNIPAM) microspheres were successfully fabricated through hydrolysis and condensation reaction of tertraethyl or-thosilicate (TEOS) on the surface of PNIPAM template at 50 oC. The PNIPAM template can be easily removed by water at room temperature so that SiO₂ hollow microspheres were finally obtained. The transmission electron microscope and scanning electron microscope observations indicated that SiO₂ hollow microspheres with an average diameter of 150 nm can be formed only if there are enough concentration of PNIPAM and TEOS, and the hy-drolysis time of TEOS. FTIR analysis showed that part of PNIPAM remained on the wall of SiO₂ because of the strong interaction between PNIPAM and silica. This work provides a clean and efficient way to prepare hollow microspheres.     

Supramolecular Assembly of a Molecularly Engineered Protein and Polymer

Programmable assembly of biomolecules is a fast growing research area that aims to emulate nature's elegance in creating numerous hierarchical self-assembled structures, which are responsible for unimaginably difficult biological functions. Protein assembly is a particularly challenging task, owing to their structural diversity, conformational heterogeneity, and high molecular weight. This article reveals the ability of a supramolecular structure-directing unit (SSDU) to regulate the entropically favourable supramolecular assembly of a covalently conjugated protein (bovine serum albumin (BSA)) to produce well-defined protein-decorated micelles with remarkably high thermal stability, suppression of the thermal denaturation of the protein, and retention of enzymatic activity. Furthermore, a SSDU-appended thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) co-assembles with the SSDU–BSA conjugate because, in both cases, assembly was primarily driven by specific molecular recognition between the SSDUs. However, the resulting supramolecular protein–polymer conjugate exhibits distinctly different polymersome structure to that of the micellar particle produced by the protein-SSDU conjugate. In this case, the enzymatic activity can be significantly suppressed above the lower critical solution temperature of supramolecularly conjugated PNIPAM, possibly due to collapse of the de-solvated polymer chains on the protein surface.     

Poly (N-isopropylacrylamide)/poly (ethylene oxide) blend nanofibrous scaffolds: thermo-responsive carrier for controlled drug release

A facile electrospinning method has been utilized to fabricate poly (N-isopropylacrylamide) (PNIPAM)/poly (ethylene oxide) (PEO) blend nanofibers having the mean fiber diameters from approximately 250 to 380 nm. Scanning electron microscopy (SEM) images showed that the morphology and diameter distribution of the nanofibrous scaffolds can be easily modulated by changing the weight ratio of PNIPAM/PEO in electrospinning solution. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) demonstrated that there were interactions between the molecules of PNIPAM and PEO. Vitamin B12 was chosen as a hydrophilic model drug for in situ encapsulation in PNIPAM/PEO blend nanofibrous scaffolds. The rate of drug release can be controlled by adjusting the weight ratio of PNIPAM/PEO, the temperature of release medium and the drug loading amount. It is suggested that the blend nanofibrous scaffold could be used as a new thermo-responsive matrix for the entrapment and controlled release of drugs.     

Temperature-Responsive Polyoxometalate Catalysts for DBT Desulfurization in One-Pot Oxidation Combined with Extraction

Intelligent thermo-responsive catalysts [C₁₆H₃₃N(CH₃)₃]₃[PO₄{MO(O₂)₂}₄]/poly(N-isopropylacrylamide) (M = Mo and W, abbreviated as C₁₆PM(O₂)₂/PNIPAM) have been prepared using thermo-responsive polymer PNIPAM as a support. The thermo-responsive hybrids exhibit novel switchable property based on the change of temperature, while its solubility in organic solvent is reversibly controllable through an external temperature stimulus linking the gap between heterogeneous catalysis and homogeneous one. Moreover, non-polar organic substrates are accumulated around the catalytic sites by two synergistic effects of amphiphilic POM molecules and the existence of PNIPAM. Therefore, this solid hybrid has been successfully used in catalyzing the oxidation of refractory sulfur-containing compound dibenzothiophene into its corresponding sulfone with high selectivity in the presence of H₂O₂. Application of this catalyst brings about an efficient, useful and green process in desulfurization through extraction and oxidation simultaneously.     

Controlled Self-assembly of Thermo-responsive Amphiphilic H-shaped Polymer for Adjustable Drug Release

Despite the fact that some progress has been made in the self-assembly of H-shaped polymers,the corresponding self-assemblies that respond to external stimulus and are further utilized to adjust the release of drugs are still deficient.The stimuli-responsive segments with amphiphilic H-shaped structure are generally expected to enhance the controllability of self-assembly process.The synthesis and self-assembly behavior of thermo-responsive amphiphilic H-shaped polymers with poly(ethylene glycol) (PEG),polytetrahydrofuran (PTHF) and poly(N-isopropyl acrylamide) (PNIPAM) as building blocks are reported in this paper.The inner architecture structure and size of complex micelles formed by H-shaped self-assemblies were effectively adjusted when the solution temperature was increased above the lower critical solution temperature of PNIPAM segments.Furthermore,it was found that the architecture of self-assemblies underwent a transition from the complex micelles based on primary micelles with hybrid PEG/PNIPAM shells to large complex micelles based on primary micelles with hybrid PTHF/PNIPAM cores and PEG shells during the thermal-induced self-assembly process.The adjustable release rate of doxorubicin (DOX) from the DOX-loaded complex micelles and basic cell experiments further proved the feasibility of these self-assemblies as the thermal-responsive drug delivery system.     

Thermo-Responsive MOF/Polymer Composites for Temperature-Mediated Water Capture and Release

We report an in situ polymerization strategy to incorporate a thermo-responsive polymer, poly(N-isopropylacrylamide) (PNIPAM), with controlled loadings into the cavity of a mesoporous metal–organic framework (MOF), MIL-101(Cr). The resulting MOF/polymer composites exhibit an unprecedented temperature-triggered water capture and release behavior originating from the thermo-responsive phase transition of the PNIPAM component. This result sheds light on the development of stimuli-responsive porous adsorbent materials for water capture and heat transfer applications under relatively mild operating conditions.     

分子识别与温度响应复合智能材料

研究和开发具有双重和多重刺激响应型智能高分子材料已成为一个重要的发展方向。本文详细地综述了我们近年来在基于聚(N-异丙基丙烯酰胺)(PNIPAM)和β-环糊精(β-CD)的复合智能线型高分子、复合智能微球和复合智能膜方面的研究进展。不同形式的复合智能材料均采用相同的反应机理制备。综述了制备工艺条件、共聚单体比例、接枝率、客体分子种类和浓度等因素对于不同形式复合智能材料的温度响应性和分子识别特性的影响规律,并对复合智能膜在亲合分离、控制释放和手性拆分等方面的应用进行了介绍。评述了分子识别与温度响应复合智能材料的研究意义和发展方向,并对其应用前景进行了展望。     

Photochemical switching of the phase-transition temperatures of p-NIPAM-Pt nanoparticles thermosensitive polymer composites associated with electrodes: functional electrodes for switchable electrocatalysis

The thermosensitive poly(N-isopropylacrylamide) (p-NIPAM) is electropolymerized onto Au surfaces. The incorporation of the photoisomerizable N-carboxyethyl nitrospiropyran compound into p-NIPAM allows the reversible photochemical control of the gel-to-solid phase-transition temperatures of the polymer. Whereas the gel-to-solid phase-transition temperature of the nitrospiropyran-modified p-NIPAM is 33±2 °C, the phase-transition temperature of the nitromerocyanine-functionalized p-NIPAM matrix corresponds to 38±1 °C. Upon the incorporation of Pt nanoparticles (NPs) into the photochemically controlled p-NIPAM, a hybrid photoswitchable electrocatalytic matrix is formed. At a fixed temperature corresponding to 38 °C, the effective electrocatalytic reduction of H(2)O(2), or the oxidation of ascorbic acid, proceeded in the presence of the nitromerocyanine-functionalized p-NIPAM, yet these electrocatalytic transformations were inhibited in the presence of the nitrospiropyran-modified p-NIPAM.     

Self-assembly of Hollow PNIPAM Microgels to Form Discontinuously Hollow Fibers

A new kind of hollow hydrogel microfiber with discontinuous hollow structure was prepared by an ice-segregation-induced self-assembly process. Monodisperse thermo-responsive hollow poly（N-isopropylacrylamide）（PNIPAM） microgels were first synthesized by seed precipitation polymerization using colloidal Si O2 nanoparticles as seeds, followed by removing the silica cores of the formed Si O2/PNIPAM core/shell composite microgels with hydrofluoric acid. Then, the discontinuously hollow hydrogel microfibers were produced by unidirectional freezing of 1 wt% hollow PNIPAM microgel aqueous dispersion in liquid nitrogen bath, followed by freeze-drying to remove the formed ice crystals. Many orderly arrayed dents were observed on the surfaces of the hydrogel microfibers by field-emission scanning electron microscopy, indicating that they are constructed by closely packed monodisperse hollow PNIPAM microgels. The effect of freezing method and the hollow microgel concentration in the aqueous dispersion on the morphological structure of the hollow hydrogel microfibers was investigated.     

Thermo-responsive stick-slip behavior of advancing water contact angle on the surfaces of poly(N-isopropylacrylamide)-grafted polypropylene membranes

Wettability of a solid surface is highly important to its practical application,especially for the surface that shows thermoresponsive properties.In this paper,we describe a thermo-responsive stick-slip behavior of water droplets on the surfaces of poly(N-isopropylacrylamide)(PNIPAM)-grafted polypropylene membranes.Field emission scanning electron microscope(FESEM) images elucidate that the morphology of PNIPAM-grafted membrane surface is thermo-responsive,i.e.,the surface becomes rougher above the lower cr...     

Preparation of biodegradable polymeric hollow microspheres using O/O/W emulsion stabilized by Labrafil

Biodegradable hollow microspheres were prepared by double oil and water emulsion using a lipophilic surfactant, Labrafil M 1944 CS. Olive oil was emulsified in biodegradable polymer-dissolved dichloromethane mixed with Labrafil by vigorous sonication. This oil-in-oil emulsion was directly re-emulsified in 0.1% poly(vinyl alcohol) solution, subsequently solidified by evaporating dichloromethane. Olive oil and Labrafil were extracted from the microspheres by using hexane. After vigorous washing with n-hexane, the hollow microsphere was freeze-dried and examined under scanning electron microscopy, confirming the morphology of hollow microspheres with thin walls and huge blank cores inside. The concentration of poly(l-lactide) in dichloromethane affected the size of hollow microspheres while the volume of olive oil or dichloromethane did not. This hollow microsphere is expected to be employed as an imaging contrast agent and a novel drug delivery vehicle.     

温敏梳状嵌段共聚物对PS微球阻抗蛋白吸附作用的研究

采用可逆加成断裂链转移聚合(RAFT)方法和大分子单体技术,制备了温敏性聚N-异丙基丙烯酰胺(PNIPAM)-聚乙烯基吡咯烷酮(PVP)与PNIPAM-聚氧化乙烯(PEO)梳状嵌段共聚物,这些共聚物具有PVP或PEO支链.以溶菌酶为蛋白模型研究了所得共聚物对聚苯乙烯(PS)微球表面蛋白吸附的抑制作用.通过絮凝实验、激光散射法表观粒径测定、电泳迁移率测定及蛋白吸附量的定量数据比较了不同梳状结构的抗蛋白吸附效果.结果表明,预吸附梳状嵌段共聚物可有效阻抗蛋白吸附,亲水支链增加阻抗性能提高,即使环境温度高于PNIPAM的相转变温度也能阻抗蛋白吸附.透射电镜和共聚物胶体粒径测试表明,梳状嵌段共聚物阻抗蛋白吸附的机制是预吸附后PVP或PEO亲水支链在微球表面形成了阻隔层.通过PS微球的变温絮凝实验可评价预吸附聚合物的抗蛋白吸附性能,快速获得定性结果.     

Adsorption of poly(N-isopropylacrylamide-co-4-vinylpyridine) onto core-shell poly(styrene-co-methylacrylic acid) microspheres

Adsorption of the thermoresponsive copolymer of poly(N-isopropylacrylamide-co-4-vinylpyridine) (PNIPAM-co-P4VP) onto the core-shell microspheres of poly(styrene-co-methylacrylic acid) (PS-co-PMAA) is studied. The core-shell PS-co-PMAA microspheres are synthesized by one-stage soap-free polymerization in water. The copolymer of PNIPAM-co-P4VP is synthesized by free radical polymerization of N-isopropylacrylamide and 4-vinylpyridine in the mixture of DMF and water using K₂S₂O₈ as initiator. Adsorption of PNIPAM-co-P4VP onto the core-shell PS-co-PMAA microspheres results in formation of the composite microspheres of PS/PMAA-P4VP/PNIPAM. The driven force to adsorb the copolymer of P4VP-co-PNIPAM onto the core-shell PS-co-PMAA microspheres is ascribed to hydrogen-bonding and electrostatic affinity between the P4VP and PMAA segments. The resultant composite microspheres of PS/PMAA-P4VP/PNIPAM with surface chains of PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 33 °C.