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1.
Zhiqiang Li Jianfeng Shen Hongwei Ma Xin Lu Min Shi Na Li Mingxin Ye 《Materials science & engineering. C, Materials for biological applications》2013,33(4):1951-1957
A methodology is described for the preparation of pH- and temperature-responsive double network (DN) hydrogels with poly(N-isopropylacrylamide) (PNIPAM) as a tightly crosslinked 1st network, polyacrylic acid (PAA) as a loosely crosslinked 2nd network and graphene oxide (GO) as an additive. GO sheets were first prepared via an oxidation reaction and then dispersed in NIPAM aqueous solution via silanization. Free-radical polymerization of NIPAM was carried out at 20 °C in a water bath, and then subjected to UV light, leading to the formation of pH- and temperature-responsive PNIPAM/AA/GO DN hydrogels. The effects of GO sheets and AA contents on various physical properties were investigated. Results show that PNIPAM/AA/GO hydrogels undergo a large volumetric change in response to temperature. It also exhibits significantly fast swelling/deswelling compared with conventional PNIPAM hydrogel. Moreover, the PNIPAM/AA/GO hydrogels have a much better mechanical property than the conventional PNIPAM hydrogels. 相似文献
2.
Qingsong Zhang Li Chen Youyu Dong Si Lu 《Materials science & engineering. C, Materials for biological applications》2013,33(3):1616-1622
The structure, morphology, thermal behaviors and cytotoxicity of novel hydrogels, composed of poly(N-isopropylacrylamide)(PNIPAM) and biodegradable polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) under nanoclay hectorite “Laponite XLG” severed as physical cross-linker, were characterized by X-ray diffraction, scanning electron microscopy, gravimetric method, differential scanning calorimetry, and cell culture experiments. It was found that, due to the introduction of hydrophobic PHBV, the homogeneity of interior pore in the pure PNIPAM nanocomposite hydrogel was disrupted, the transparency and swelling degree gradually decreased. Although the weight ratio between PHBV and NIPAM increased from 5 to 40 wt.%, the volume phase transition temperature (VPTTs) of hydrogel were not altered compared with the pure PNIPAM nanocomposite hydrogel. No matter what PHBV content, the PHBV/PNIPAM/Hectorite hydrogels always exhibit good stimuli-responsibility. In addition, human hepatoma cells(HepG2) adhesion and spreading on the surface of PHBV-based hydrogels was greatly improved than that of pure PNIPAM nanocomposite hydrogel at 37 °C due to the introduction of PHBV. 相似文献
3.
以异丙基丙烯酰胺(NIPAM)为单体、N,N’-亚甲基双丙烯酰胺(MBA)为交联剂、过硫酸钾(KPS)为引发剂,采用无皂乳液聚合法制备聚N-异丙基丙烯酰胺(PNIPAM),考察了聚合时间、温度、浓度、pH值、共存NaCl和MgCl2浓度对PNIPAM热致聚集行为的影响,并通过扫描电镜(SEM)、红外光谱(FTIR)等手段对PNIPAM的形貌和分子结构进行了表征。结果表明:线型PNIPAM更易在水中稳定存在,采用无皂乳液聚合技术制备PNIPAM过程简单、易操作,产物温敏效应明显。PNIPAM的热致聚集行为随聚合时间的延长、PNIPAM悬浊液浓度的增加、pH值的减小、共存盐浓度的增大而更为显著。 相似文献
4.
Sergio Leal Braga Juan José Milón Guzmán Hugo Guillermo Jiménez Pacheco 《International Journal of Refrigeration》2009,32(5):953-959
An experimental apparatus was developed to investigate the supercooling phenomenon of pure water inside cylindrical capsules used for cold storage process. The Phase Change Material (PCM) used was distilled water. The external coolant material was a water–alcohol mixture (50% vol.), controlled by a constant temperature bath (CTB) in four fixed values (?4 °C, ?6 °C, ?8 °C, and ?10 °C). Temperatures varying with time were measured inside and outside the capsule. Cylindrical capsules with internal diameter of 30 mm, 45 mm, and 80 mm, with 1.5 mm wall thickness were made in aluminum, bronze or acrylic materials. The Cooling Rate (CR) was investigated for different positions on the internal wall of the capsule, for different external coolant temperatures (Tc), different capsules diameters and different materials. The results showed that the cooling rate is a strong function of the angular position on the internal wall, the coolant temperature, the capsule material, and the capsule's diameter. 相似文献
5.
Rachelle M. Kleinberger Nicholas A.D. Burke Kari Dalnoki-Veress Harald D.H. Stöver 《Materials science & engineering. C, Materials for biological applications》2013,33(7):4295-4304
Micropipette aspiration and confocal fluorescence microscopy were used to study the structure and mechanical properties of calcium alginate hydrogel beads (A beads), as well as A beads that were additionally coated with poly-l-lysine (P) and sodium alginate (A) to form, respectively, AP and APA hydrogels. A beads were found to continue curing for up to 500 h during storage in saline, due to residual calcium chloride carried over from the gelling bath. In subsequent saline washes, micropipette aspiration proved to be a sensitive indicator of gel weakening and calcium loss. Aspiration tests were used to compare capsule stiffness before and after citrate extraction of calcium. They showed that the initial gel strength is largely due to the calcium alginate gel cores, while the long term strength is solely due to the poly-l-lysine–alginate polyelectrolyte complex (PEC) shells. Confocal fluorescence microscopy showed that calcium chloride exposure after PLL deposition led to PLL redistribution into the hydrogel bead, resulting in thicker but more diffuse and weaker PEC shells. Adding a final alginate coating to form APA capsules did not significantly change the PEC membrane thickness and stiffness, but did speed the loss of calcium from the bead core. 相似文献
6.
《Composites Science and Technology》2006,66(11-12):1532-1538
A series of hydroxyapatite/gelatin/alginate nanocomposites with different amount of alginate were synthesized by a co-precipitation method. With the increase of alginate amount, a cross-linked alginate/gelatin polymer network formed, which induced a gradual red shift of organic absorption peaks in FT-IR analysis. TEM images indicated that the development of HAP nanocrystals in an aqueous gelatin/alginate mixture was highly influenced by the alginate content. On increasing alginate content, the dimensions of the crystals increased and their morphology changed from needle-like to long fiber-like, and at high alginate content, the crystals tended to aggregate in separate clusters. The results of the electron diffraction strongly indicated alginate promoted the preferential alignment in c direction of HAP nanocrystals. SEM results showed that high amount of alginate led to regular shape and large size of HAP crystals after the composites were calcined for 4 h at 600 °C. 相似文献
7.
Covalent functionalization of azide-modified SiO(2) with well-defined, alkyne-terminated poly(N-isopropylacrylamide) was accomplished by the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition. The alkyne-terminated RAFT chain transfer agent was first synthesized, and then the alkyne-terminated thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) with different molecular weights were synthesized by the RAFT of NIPAM monomer. The polymerization kinetics and the evolution of number-average molecular weights (M(n)), and polydispersities (M(w)/M(n)), with monomer conversions were investigated. A copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "grafting to" method was used to attach thermoresponsive polymers onto the exterior surface of SiO(2) nanoparticles which produced relatively high grafting density. The as-synthesized hybrid nanoparticles showed thermoresponsive behavior and were characterized by FTIR, XPS, TGA, DLS, and TEM, etc. 相似文献
8.
Aline Nicolau Rúbia Martignago Mariath Emilse Agostini Martini Denise dos Santos Martini Dimitrios Samios 《Materials science & engineering. C, Materials for biological applications》2010,30(7):951-962
Oligo and polyesters were prepared from epoxidized oleic acid (EOA) and methyl oleate (EMO) in polymerization reaction with cis-1,2-cyclohexanedicarboxylic anhydride (CH) and triethylamine (TEA) as the initiator at 165 °C for 3 h. In order to increase the molecular weight of the products, a small amount of butanodiol diglycidil ether (BDGE) was added. The different steps of the reactions were elucidated by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). These same techniques as well as size exclusion chromatography (SEC), thermogravimetric analysis (TGA) and electric impedance spectroscopy (EIS) were used to characterize the products of the EMO/CH/TEA, EMO/CH/BDGE/TEA, EOA/CH/TEA and EOA/CH/BDGE/TEA reaction systems. The formation of internal ester groups was confirmed by NMR and FTIR. The Mw products are between 2500 g/mol and 85000 g/mol. The ΔΗ values are 44.6 KJ/ee and 42.7 KJ/ee for the EOA and EMO systems, respectively. The thermal degradations of the products start at temperatures higher than 180 °C. All of the products reveal glass transitions between ? 57 °C and ? 14 °C, while the EMO ones also present crystallization-like behavior at ? 7 °C and 3 °C. The dielectric properties of the products include very high resistivity and low capacitance. 相似文献
9.
Up to now, glass capsules, which cannot resist the mixing process of concrete, have been mostly used in lab-scale proof-of-concept to encapsulate polymeric agents in self-healing concrete. This study presents the design of polymeric capsules which are able to resist the concrete mixing process and which can break when cracks appear. Three different polymers with a low glass transition temperature Tg have been extruded: Poly(lactic acid) (PLA) (Tg = 59 °C), Polystyrene (PS) (Tg = 102 °C) and Poly(methyl methacrylate/n-butyl methacrylate) (P(MMA/n-BMA)) (Tg = 59 °C). After heating the capsules prior to mixing with other components of the mix, to shift from a brittle state to a rubbery state, their survival ratio considerably increased. Moreover, a part of the capsules, which previously survived the concrete mixing process, broke with crack appearance. Although some optimization is still necessary concerning functional life of encapsulated adhesives, this seems to be a promising route. 相似文献
10.
《Advanced Powder Technology》2014,25(5):1520-1526
Maghemite nanoparticles (MNPs) with a thin layer of polyrhodanine (PRd) at the surface were synthesized via chemical oxidative polymerization of rhodanine monomer at the MNPs surface in the presence of ferric chloride as oxidant. X-ray diffraction (XRD) pattern gave direct evidence that the synthesized nanoparticles are crystalline maghemite of about 8 nm in size. Magnetization of the particles versus an applied magnetic field exhibited no hysteresis loop, indicated superparamagnetic behavior in the particles. Transmission electron microscopy (TEM) together with Fourier-transform infrared (FT-IR) spectroscopy were used to determine the morphology and the chemical structure of the magnetic core and the polymeric shell. Through the microscopy analysis the shell thickness was estimated to be about 1.5 nm, whereas through thermogravimetric analysis (TGA) it was estimated to be about 0.6 nm. Moreover inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements revealed that the oxidant residue in the polymer backbone is ca. 4 wt.%. 相似文献
11.
Nataporn Sowasod Kyuya Nakagawa Wiwut Tanthapanichakoon Tawatchai Charinpanitkul 《Materials science & engineering. C, Materials for biological applications》2012,32(4):790-798
Cryogel based encapsulation of curcumin, an herbal extract, was successfully carried out with a ternary system of colloidal chitosan, κ-carrageenan, and carboxymethylcellulose sodium salt. The effects of chitosan concentration, κ-carrageenan/CMC ratio of the polymer suspension and molecular weight of chitosan on the sol–gel formation were investigated. The effects of cooling rate during freeze-drying and oil phase composition on the encapsulation yield and the release behavior of curcumin from the hydrogel were determined. And so were the effects of pH of the phosphate-buffered media and oil phase composition on the swelling of the specimens. The microstructure of the resulting specimens revealed core-shell nanoparticles (i.e. oil droplet for core and cryogel membrane for shell) entrapped in the cryogel matrix. The encapsulation yield for two types of suspensions was in a range of 83.9 to 99.6% when a high-MW chitosan was used. Controlled release of the encapsulated curcumin in an aqueous system could be maintained for 4 days, and the releasable amount of curcumin was in a range of 41.1 to 59.9%. The encapsulation yield as well as the released pattern and releasable amount of curcumin were significantly influenced by the cooling protocol used during freezing. Irrespective of the introduced oil phase composition, controlled release of curcumin was achievable when the cooling rate was sufficiently high at ? 2.0 °C/min and, interestingly, either a burst release or a first order release could simply be achieved by changing the freezing condition. 相似文献
12.
Chih-Wei Peng Hsin-Yi Lin Hsin-Wei Wang Wei-Wen Wu 《Materials science & engineering. C, Materials for biological applications》2012,32(8):2491-2500
Three-dimensional plotting was used to manufacture fibrous alginate hydrogel wound dressings. Samples manufactured using varied operating parameters (increased air pressure, nozzle diameter, and layer increment or decreased calcium concentration, alginate concentration, and speed of the nozzle in the x and y directions) were compared to the control samples. The changes in the fiber size, porosity, tensile properties, degradation, swelling ratio, tetracycline release efficacy, water vapor transmission rate (WVTR), and bacterial inhibition potential due to alterations of the operating parameters were measured. The samples manufactured using altered operating parameters had larger fiber sizes and were less porous than the controls (p < 0.05). A significantly higher Young's modulus, a larger ultimate tensile strength, less degradation, and lower swelling ratios were also found among some of the altered samples (p < 0.05). The tetracycline release efficacies and bacterial inhibition potentials of the altered samples were not found to be significantly different from those of the controls. The WVTRs of most samples were slightly lower than those of common commercial dressings. When compared to films, the fibrous samples were able to absorb liquid faster and were less stiff, allowing for better conformation to the contours of the wounds. The fibrous samples also provided more sustained tetracycline release. 相似文献
13.
A versatile route applied to the synthesis of thermoresponsive magnetite nanoparticles involved the formation of nanoparticles by coprecipitation of Fe2+/Fe3+ in the presence of an alkaline solution, followed by attachment of the reversible addition-fragmentation transfer (RAFT) agents onto the surface of the Fe3O4 nanoparticles via the electrostatic interactions, subsequent grafting from polymerization of N-isopropylacrylamide (NIPAM) through surface-initiated RAFT polymerization. The surface-initiated RAFT polymerization can be conducted in a well-controlled manner, as revealed by the linear kinetic plot, linear evolution of number-average molecular weights (M n ) versus monomer conversions, and the relatively narrow molecular weight distributions (M w /M n ?1.5) of the grafted PNIPAM chains. The as-synthesized hybrid nanoparticles showed thermoresponsive behavior and were characterized by FTIR, XPS, TGA, VSM, DLS, and TEM, etc. 相似文献
14.
Ying Zhang Ningjing Wu Xinyan Bai Changqi Xu Yi Liu Yong Wang 《Materials science & engineering. C, Materials for biological applications》2013,33(7):3670-3676
The objective of this study is to report for the first time the spontaneous polymerization phenomenon of self-etch dental adhesives induced by hydroxylapatite (HAp). Model self-etch adhesives were prepared by using a monomer mixture of bis[2-(methacryloyloxy)ethyl] phosphate (2MP) with 2-hydroxyethyl methacrylate (HEMA). The initiator system consisted of camphorquinone (CQ, 0.022 mmol/g) and ethyl 4-dimethylaminobenzoate (4E, 0.022–0.088 mmol/g). HAp (2–8 wt.%) was added to the neat model adhesive. In a dark environment, the polymerization was monitored in-situ using ATR/FT-IR, and the mechanical properties of the polymerized adhesives were evaluated using nanoindentation technique. Results indicated that spontaneous polymerization was not observed in the absence of HAp. However, as different amounts of HAp were incorporated into the adhesives, spontaneous polymerization was induced. Higher HAp content led to higher degree of conversion (DC), higher rate of polymerization (RP) and shorter induction period (IP). In addition, higher 4E content also elevated DC and RP and reduced IP of the adhesives. Nanoindentation result suggested that the Young's modulus of the polymerized adhesives showed similar dependence on HAp and 4E contents. In summary, interaction with HAp could induce spontaneous polymerization of the model self-etch adhesives. This result provides important information for understanding the initiation mechanism of the self-etch adhesives, and may be of clinical significance to strengthen the adhesive/dentin interface based on the finding. 相似文献
15.
Self-healing strategies are regarded as a promising solution to reduce the high maintenance and repair cost of concrete infrastructures. In the present work, a bacterial-based self-healing by use of hydrogel encapsulated bacterial spores (bio-hydrogels) was investigated. The crack closure behavior of the specimens with/without bio-hydrogels was studied quantitatively by light microscopy. To have a view of the self-healing inside the specimens, a high resolution X-ray computed microtomography (X-ray μCT) was used. The total amount and the distribution of the healing products in the whole matrix were investigated. This study indicates that the specimens incorporated with bio-hydrogels had distinct improved healing efficiency compared to the reference ones with pure hydrogel only. The healing ratios in the specimens with bio-hydrogels were in the range from 70% to 100% for the cracks smaller than 0.3 mm, which is more than 50% higher than for the ones with pure hydrogel; and the maximum crack bridging was about 0.5 mm (in 7 d), while pure hydrogels only allowed healing of cracks of about 0.18 mm. The total volume ratio of the healing product in the specimens with bio-hydrogels amounted to 2.2%, which was about 60% higher than for the ones with pure hydrogel (1.37%). 相似文献
16.
Soner Çakmak Anıl S. Çakmak Menemşe Gümüşderelioğlu 《Materials science & engineering. C, Materials for biological applications》2013,33(5):3033-3040
In this study, we developed novel thermoresponsive microcarriers as a powerful tool for cell culture and tissue engineering applications. For this purpose, two types of commercially available spherical microparticles (approximately 100 μm in diameter), dextran-based Sephadex® and vinyl acetate-based VA-OH (Biosynth®), were used and themoresponsive poly(N-isopropylacrylamide) (PNIPAAm) was grafted to the beads' surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP). Initially, hydroxyl groups of microbeads were reacted with 2-bromopropionyl bromide to form ATRP macroinitiator. Then, NIPAAm was successfully polymerized from the initiator attached microbeads by ATRP with CuBr/2,2′-dipyridyl, catalyst complex. Furthermore, grafted and ungrafted microbeads were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscope (SEM), atomic force microscopy (AFM) and electron spectroscopy for chemical analysis (ESCA). The results of characterization studies confirmed that PNIPAAm was successfully grafted onto both dextran and vinyl acetate-based beads by means of ATRP reaction and thus, grafted microbeads gained thermoresponsive characteristics which will be evaluated for cell harvesting in further studies. 相似文献
17.
《Optical Materials》2014,36(12):2250-2256
The thermo-sensitive and fluorescent complexes containing Eu(III) or Tb(III) were synthesized and characterized, in which cholesterol-g-poly(N-isopropylacrylamide) (PNIPAM) copolymer was used as a polymer ligand. The results from the experiments indicated that Eu(III) or Tb(III) was bonded to nitrogen and oxygen atoms in the polymer chain. The fluorescence lifetimes of the powdered Eu(III) and Tb(III) complexes was 11.48 ms and 10.71 ms, respectively. The maximum emission intensity of the PNIPAM–Eu(III) complex at 613 nm and the PNIPAM–Tb(III) complex at 545 nm were enhanced about 11.1 and 11.3 times compared with that of the corresponding rare earth ions, respectively. Additionally, the lower critical solution temperature (LCST) of complexes were slightly higher than those of the copolymers. 相似文献
18.
Toshiyuki Nomura Syota Tanii Masaya Ishikawa Hayato Tokumoto Yasuhiro Konishi 《Advanced Powder Technology》2013,24(6):1013-1016
Hollow particles have attracted considerable attention owing to their unique properties. In this work, hollow zirconia particles were synthesized using rod-shaped gram-negative bacteria, Escherichia coli, as templates. A zirconia precursor, generated by the hydrolysis of zirconium butoxide, was deposited on the surface of the bacterial cells to form the shell of the hollow particles. The as-synthesized particles had the morphology of the bacterial templates, and were about 1.7 μm long and 0.8 μm across. The bacterial templates could be removed by calcination at 800 °C. The particles shrank on calcination to a final size of about 1.0 μm long and 0.4 μm across, with a wall thickness of about 69 nm. The specific surface area and average pore diameter were 45.7 m2/g and 1.9 nm, respectively. When fixed cells without internal water were used as templates, no hollow particles were observed; this implies that the internal water inside the cells acted as the initiator for the hydrolysis of zirconium butoxide. 相似文献
19.
George V. Franks Haihong Li John-Paul O’Shea Greg G. Qiao 《Advanced Powder Technology》2009,20(3):273-279
A processing scheme which uses a single chemical that has multiple functions to achieve both efficient mineral flotation and solids dewatering is presented. Temperature sensitive polymers which display hydrophilic/hydrophobic transitions in response to changes in temperature such as poly (N-isopropyl acrylamide) (PNIPAM) have been found to be useful as such multiple function reagents. This polymer can cause the mineral particles’ surfaces to be hydrophilic at temperature below the critical solution temperature (CST = 32 °C) and hydrophobic at temperature above the CST. Therefore, both particle surface wettability and inter-particle interaction forces are reversibly controllable. When the surface is hydrophilic, particle dispersion is achieved by repulsive inter-particle forces whereas when the surface is hydrophobic, particle aggregation is induced by inter-particle hydrophobic attractive forces. In addition, the hydrophobic surface condition allows for the attachment of particles to bubbles. Flotation and solid settling tests have been conducted with silica and kaolinite suspensions treated with (PNIPAM). Both effective suspension dispersion or hydrophobic aggregation and flotation without any additional collector have been demonstrated. In solid/liquid separation, rapid settling was obtained with hydrophobic aggregation at temperature above the CST and further sediment consolidation (and water release) occurred at temperature below the CST. The approach has the potential to reduce the amount and types of reagents required for mineral processing. 相似文献
20.
Cement pastes of water to cement ratio (w/c) of 0.45 with and without nanosilica are hydrated under two conditions, room condition (20 °C with 0.1 MPa pressure) and an oil well condition (80 °C with 10 MPa pressure) for 7 days. For the cement pastes with nanosilica, 1% and 3% of cements weights were replaced by nanosilica. The composition of the hardened cement pastes is investigated using X-ray diffraction (XRD). Nuclear magnetic resonance (NMR) experiments are used to quantify the silicate polymerization in hydrated cement paste. Microstructural phases are identified according to the corresponding mechanical property using nanoindentation. The results showed that under room curing conditions, hardened cement paste with 1% nanosilica has the highest level of calcium silicate hydrate (C–S–H) polymerization. However, under high temperature and pressure curing conditions, hardened cement paste with 3% nanosilica has the highest level of C–S–H polymerization. A new relatively stiff microstructural phase is observed in cement pastes incorporating nanosilica and cured under elevated pressure and temperature conditions. The significance of curing conditions and nanosilica content on the polymerization and stiffness of hydrated cement pastes are discussed. 相似文献