Laterally sandwich-typed hydrogel columns with liner poly(N-isopropylacrylamide) layer: Preparation, swelling/deswelling kinetics and drug delivery characteristics

A novel thermo-responsive hydrogel column, featured with both ends of linear poly(N-isopropylacrylamide) (PNIPAM) chains being grafted onto cross-linked PNIPAM chains, was reported. The laterally sandwich-typed hydrogel columns were fabricated by radical polymerization in a three-step process using a method of ice-melting synthesis. The initiating path, morphology and thermoresponsive characteristics of the prepared hydrogel columns were experimentally studied. The results show that the hydrogel column obtained by the initiator inside part has more quick swelling and deswelling rates responsing to temperature cycling than other hydrogels owing to linear PNIPAM chains to form supermacroporous structure. The proposed hydrogel structure provide a new mode of the phase transition behavior for thermo-sensitive "smart" or "intelligent" monodisperse micro-actuators, which is highly attractive for targeting drug delivery systems, chemical separations, and sensors and so on.     

Cell growth and desorption on the surface of temperaturesensitive semi-IPNs hydrogels based on silk sericin

Semi-interpenetrating (semi-IPNs) hydrogels containing biocompatible silk sericin (SS) and poly(N-isopropylacrylamide)(PNIPAM) were prepared as novel cellular matrices. Their maximum swelling degree and basic characteristics for biomedical applications such as mouse ?broblasts (L929) cell proliferation and desorption were investigated. The results showed that the incorporation of high hydrophilic SS into PNIPAM hydrogel increased the maximum swelling degree of the semi-IPNs hydrogels, and the adhesion and growth of the L929 on semi-IPNs hydrogels were at least comparable to, or even better than, that on conventional PNIPAM hydrogel. In addition, L929 cells were found to detach from the hydrogels surface naturally by controlling environmental temperature. These results suggest great potential of semi-IPNs hydrogels in tissue engineering.     

T-shaped trifunctional crosslinker-toughening hydrogels

Currently, development of a single network hydrogel with a high fracture toughness in swelling equilibrium remains challenging.In this work, a novel T-shaped trifunctional crosslinker(T-NAGAX) with dual vinyl on the backbone and dual amide group on the side chain is synthesized by Michael addition and acylation. The T-NAGAX is used to prepare chemically crosslinked hydrogel by one-pot photo-initiated polymerization. The resulting single network hydrogels of representative polyacrylamide(PAAm), poly(N-acryloyl 2-glycine)(PACG), and poly(N-isopropyl acrylamide)(PNIPAM) crosslinked with T-NAGAX with additional hydrogen-bonds exhibit much better fracture toughness than that of the corresponding hydrogels crosslinked by N,N'-methylene bisacrylamide, a conventional crosslinker; higher mechanical strengths are observed in the T-NAGAX crosslinked hydrogels. These hydrogels are promising to be exploited as load-bearing soft tissue substitutes. This T-NAGAX crosslinker can be expanded to toughen various types of hydrogels.     

Enhancing the formation of starch-based hybrid hydrogel by incorporating carboxyl groups into starch chains

A novel starch-based hybrid hydrogel was formed by physical and mild steps. Firstly, aqueous solution of a mixture of starch maleic half-ester (SM) and poly(vinyl alcohol) (PVA) was subjected to freezing-thawing cycles to generate a physical functional SM/PVA hydrogel. Subsequently, the SM/PVA/HA hybrid hydrogel was obtained through the alternate soaking process. The structure and morphology of the hydrogels were examined with Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD) analysis, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). It was found that the existence of carboxylic groups on SM chains not only enabled SM/PVA hydrogel to be pH-sensitive, but also enhanced the formation of hydroxyapatite in the hydrogel via chelating calcium ions onto the matrix.     

Structure and mechanical properties of waterborne polyurethane-based composites filled with self-assembled supramolecular nanoplatelets

New composites of waterborne polyurethane (WPU) as a matrix were prepared by incorporating rigid supramolecular nanoplatelets (SNs) as filler, which were self-assembled by the selective inclusion of β-cyclodextrin (β-CD) onto poly(propylene oxide) (PPO) segment in the poly(ethylene oxide)-block-PPO-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO). It is worth noting that, when the loading level of SN is lower than 3wt%, the SNs with moderate PEO length result in the simultaneous increase in strength, elongation and Young’s modulus in contrast with neat WPU. If there is no stretching free PEO chain, both strength and elongation decrease in spite of an increase in Young’s modulus. However, too long PEO chains result in the decrease of mechanical performances while the relatively higher loading-level of SNs also inhibits the enhancement of strength and elongation.     

Reversible aggregation kinetics of poly(N-isopropylacrylamide-co-N-vinylpyrrolidone) in aqueous solutions revealed by elastic light scattering spectroscopy

Poly(N-isopropylacrylamide-co-N-vinylpyrrolidone) [P(NIPAM-co-NVP)] copolymers with different content of N-vinylpyrrolidone (NVP) were synthesized, and reversible aggregation kinetics of the copolymers in aqueous solutions was investigated with elastic light scattering (ELS) spectra. The results indicated that the apparent activation energy of aggregation process during heating and dissociation process during cooling increased with the NVP content increasing. The phase transition temperature also increased as the content of NVP increased, suggesting that the hydrophilic nature of NVP strongly affected the phase behavior of the copolymer solutions. The higher the content of NVP, the higher the temperature required to break the balance between the hydrophilic and hydrophobic interaction. Besides, during heating and cooling process, the phase transition hysteresis of P(NIPAM-co-NVP) chains decreased when the hydrophilic comonomer increased.     

温敏凝胶的合成及其在机械方面的应用

采用紫外光照射及氧化还原等几种不同的方法合成了N-异丙基丙烯酰胺(PNIPAM)凝胶，对凝胶的温度响应性以及力学性能等进行测试，并选择综合性能良好的光二次聚合的温敏凝胶，设计了用于控制流体的机械模型，通过试验证明了凝胶做为机械阀门的可行性．     

聚乙烯醇/聚丙烯酸凝胶聚合物电解质的研究

以丙烯酸、聚乙烯醇、N,N-亚甲基双丙烯酰胺等为原料,采用水溶液聚合法制备聚乙烯醇/聚丙烯酸水凝胶聚合物基质,与6 mol/LKOH溶液制成吸液率约为173%凝胶聚合物电解质,产物在室温时电导率可达567.3 ms.cm-1。并且讨论了聚乙烯醇/聚丙烯酸凝胶聚合物电解质的导电机理及凝胶聚合物吸液率与电导率的关系。     

A high strength pH responsive supramolecular copolymer hydrogel

Constructing high strength pH sensitive supramolecular polymer hydrogel remains very challenging due to the unavoidable network swelling caused by ionization of acid or basic groups at a specified pH. In this work, we proposed a simple and very convenient approach to fabricate high strength pH responsive supramolecular polymer (SP) hydrogels by one-pot copolymerization of N-acryloyl glycinamide (NAGA) and 2-vinyl-4,6-diamino-1,3,5-triazine (VDT), two feature hydrogen bonding monomers. In these PNAGA-PVDT SP hydrogels obtained, the hydrogen bonding of NAGA was shown to play a dominant role in reinforcing strength, while the hydrogen bonding of diaminotriazine served as a pH sensitive moiety. At pH 3, the mechanical properties of PNAGA-PVDT hydrogels decreased to a different extent due to the breakup of hydrogen bonding; in contrast, the hydrogel resumed the original strength while pH was raised to 7.4 because of reconstruction of hydrogen bonding. Over the selected pH range, the PNAGA-PVDT hydrogels exhibited up to 1.25 MPa tensile strength, 845% breaking strain, 69 kPa Young’s modulus and 21 MPa compressive strength. This novel high strength pH-responsive SP hydrogels may find applications in biomedical and industrial fields.     

Effect of nanopore size on poly(dT)30 translocation through silicon nitride membrane

The nanopore size effect on translocation of poly(dT)30through Si3N4 membrane is investigated.In this paper,we report that the speed of the poly(dT)30 transport through Si3N4 nanopores can be slowed down by half through increasing the nanopore diameter from 4.8 nm to 10.8 nm.The results are consistent with our simulation results.Besides,the current blockage induced by DNA passing through the nanopore is less obvious as pore diameter is larger,which is in good agreement with the theoretical prediction.The conclusion about DNA transport through nanopores is beneficial for the design of DNA sequencing devices.     

Bacteria adherence properties of nitrogen-doped TiO2 coatings by plasma surface alloying technique

In order to obtain a high-performance surface on 316L stainless steel (S. S) that can meet the requirements in medical material field environment, nitrogen-doped titanium dioxide (TiO2-xNx) was synthesized by oxidative annealing the resulted TiNx coatings in air. Titanium nitride coatings on 316L S. S were obtained by plasma surface alloying technique. The as-prepared coatings were characterized by X-ray diffraction, glow discharge optical emission spectrometer (GDOES), scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The bacteria adherence property of the TiO2-xNx coatings on S. S on the oral bacteria Streptococcus Mutans was investigated and compared with that of S. S by fluorescence microscopy. The mechanism of the bacteria adherence was discussed. The results show that the TiO2-xNx coatings are composed of anatase crystalline structure. SEM measurement indicates a rough surface morphology with three-dimensional homogenous protuberances after annealing treatment. Because of the photocatalysis and positive adhesion free energy, the TiO2-xNx coatings inhibit the bacteria adherence.     

Improvement in synthesis of 3'-N-demethylazithromycin and its derivatives

3’-N-demethylazithromycin is an impurity in azithromycin drug. It is derived by demethylation of az- ithromycin,i. e. ,azithromycin loses a methyl group on the 3’-N position. In this study,bulk product was puri- fied with chromatographic separation. It was observed that 3’-N-demethylazithromycin was also a precursor of other impurities. Simultaneously,another derivative was synthesized,i. e. ,3’-N-demethyl-3’-N-formylazithro- mycin. Reaction conditions were optimized with the HPLC method and good-quality and high-yield derivative product was achieved. The structures of derivatives were identified by 1 H-NMR and MS.     

Enrichment of Cd<Superscript>2+</Superscript> from water with a calcium alginate hydrogel filtration membrane

A new method was developed for effective enrichment of Cd²⁺ ions from water with a calcium alginate (CaAlg) hydrogel filtration membrane. First, the CaAlg hydrogel filtration membrane was prepared without a pore-forming agent. This membrane was used to remove Cd²⁺ via ion exchange with Ca2+, and the Cd²⁺ was preserved in the CaAlg hydrogel. Then, the CaAlg hydrogel containing Cd²⁺ was soaked in a sodium citrate solution, and the hydrogel was fully dissolved. The removal rate of the CaAlg filtration membrane reached almost 100% within 120 min when the Cd²⁺ concentration was under 1 mg/L. Factors affecting the removal rate were investigated, such as NaAlg concentration, operating pressure, operating time and the initial concentration of Cd²⁺. The effects of initial Cd²⁺ concentration, pressure and filtration time on the enrichment factor were also investigated. The results show that the enrichment factor reached 87.3 when the pressure was 0.18 MPa and the filtration time was 240 min. Different enrichment factors could be achieved by adjusting the operating pressure and filtration time.     

Establishment of N m F 2 empirical model in the northern hemisphere based on COSMIC occultation data

Ionospheric peak value of F2 layer (N _m F ₂) is an important parameter in the ionosphere, which has important applications in short-wave communication, ionospheric modeling and so on. In this paper, the empirical orthogonal function (EOF) decomposition method is used to analyze the N _m F ₂ obtained from the occultation data. Daily spatial distribution of N _m F ₂ at the same time is relatively even. Variance of first modal is much larger than the other modals. A local wavelet power spectrum (LWPS) method is applied to analysis the cycle of F _10.7 index and time coefficient of first modal. The result shows that they have similar cycle distribution, indicating that F _10.7 index is the main factor affecting variation of N _m F ₂. A function is established between the tine coefficient of first modal and F _10.7 index, average F _10.7 index value of early 81 days f _p by least squares method. The results show that contribution coefficient of f _p is negative which indicates that f _p has an inert effect existing in the ionosphere. Contribution coefficient of F _10.7 is positive, which is consistent with the fact that it has an anomaly in winter/spring seasons. In summary, it is feasible to establish a mid-latitude empirical N _m F ₂ model in northern hemisphere based on occultation data and EOF decomposition method.     

膜孔中有线形接枝链的微囊的分子识别型控制释放特性研究

研制出了一种用于环境刺激感应控制释放的分子识别型微囊。该微囊具有核壳结构多孔膜，并在膜孔中接枝有作为分子识别开关的聚[异丙基丙烯酰胺－共－（苯并－18－冠－6－丙烯酰胺）]（poly(NIPAM0co-BCAm）线形链。采用了界面聚合法核壳结构多孔微囊膜，并采用了等离子体接枝填孔聚合法在膜孔内接枝poly(NIPAM-co-BCAm)线形链。囊内溶质从该微囊中的释放特性明显受环境溶液中Ba^2 离子的存在与否状态所控制。当环境溶液中没有BaCl2分子存在时，由于微囊膜孔内接枝的Poly(NIAM-co-BCAm）聚合物链呈收缩状态而使 开启，所以释放速度快，相反，当环境溶液中有BaCl2分子存在时，微囊膜孔内接枝的poly(NIPAM-co-BCAm）链呈膨胀状态，于是膜孔关闭，从而导致释放速度变得很慢，该具有poly(NIPAM-co-BCAm）接枝开关的微囊的分子识别刺激应释放特性显示出了良好的可逆性和可重复性。     

具有光催化性能的温敏复合凝胶聚(N-异丙基丙烯酰胺)/纳米TiO_2的制备及表征

采用掺杂法制备具有光催化性能的聚(N-异丙基丙烯酰胺)/纳米TiO2温敏复合凝胶,利用凝胶的温敏性改善纳米TiO2的可回收性。研究TiO2负载率对复合凝胶的微观形貌、化学结构、吸水溶胀性及光催化性能的影响。结果表明:该复合凝胶具有均匀的微观多孔结构,纳米TiO2负载于复合凝胶孔结构内壁,未参与N-异丙基丙烯酰胺的聚合反应,对复合凝胶的化学结构和温敏性没有影响,各负载率复合凝胶的体积突变温度均为33℃,但复合凝胶的吸水溶胀性和光催化性能会随TiO2负载率的变化而变化。光催化实验证明:该复合凝胶的光催化性能随TiO2负载率的提高而增强;负载率50%的复合凝胶,在15W紫外灯作用下,4 h内对100 mg/L活性蓝X-BR的降解率达90%以上。最后对紫外光照射后的复合凝胶样品进行红外分析和热重分析,证明经反复紫外光照射后的复合凝胶不会发生明显降解,凝胶高分子化学结构没有显著变化。     

Preparation and Properties of Poly(amidoamine) Dendrimer/Quaternary Ammonium Chitosan Hydrogels

A novel quaternary ammonium chitosan hydrogel modified by poly(amidoamine)(PAMAM) dendrimer was prepared by using glutaraldehyde as a cross-linker. The hydrogel was characterized by Fourier transform infrared spectroscopy(FTIR) and scanning electron microscopy(SEM). The results confirmed its highly porous three-dimensional network structure. The swelling test of hydrogel proved that it had excellent swelling and p H-sensitive properties. The increasing PAMAM content or quaternization degree led to the increase in swelling properties. And the hydrogel with lower cross-linking agent concentration or quaternary ammonium chitosan concentration exhibited better swelling properties. The antibacterial results indicated that with the increase in the PAMAM content, quaternary ammonium chitosan concentration or cross-linking agent concentration, the hydrogels showed better antibacterial activities against both Staphylococcus aureus(S. aureus) and Escherichia coli(E. coli). Thus, the hydrogel could serve as a promising antibacterial material in the future.     

Angiogenesis induced by IKVAV-Containing amphiphile peptide <Emphasis Type="Italic">in vivo</Emphasis>

An IKVAV (Isoleucine-Lysine-Valine-Alanine-Valine)-containing peptide amphiphile molecule (IKVAV-PA) was implanted subcutaneouly into rat backbone in the middle. Angiogenesis induced by IKVAV-PA was evaluated in vivo. 200 μL of 10, 2, 1 and 0.5 wt% IKVAV-PA solution were added into DMEM/F₁₂ and self-assembled into nanofiber hydrogel. 1 mL of 1% IKVAV-PA (Experimental Group, EG) and 1 mL of 16.67% gelatin (Control Group, CG) were injected subcutaneously into rat backbone. The specimens were harvested two weeks after injection and examined immunohistochemically for VEGF(Vascular Endothelial Growth Factor). TEM observations of hydrogels revealed a network of nanofibers, and there was a significant positive correlation between IKVAV-PA concentration and nanofiber alignment. Light microscopy observation showed capillary vessel with complete walls formed in hydrogel, with erythrocytes noted inside the vessels in EG; capillary vessels or erythrocytes were not found within gelatin in CG. Immunohistochemical analysis revealed that there were VEGF-positive cells within hydrogel, which were not found in CG. Self-assembled hydrogel from IKVAV-PA was able to induce the angiogenesis in vivo.     

Effect of sonication on a novel designed peptide

The reassembly of a half-sequence ionic self-complementarity peptide CH₃CO-Pro-Ser-Phe-Cys-Phe-Lys-Phe-Glu-Pro-NH₂ was reported, which could self-assemble into stable nanofibers and formed hydrogel consisting of >99% water. In this study, the nanofiber scaffold was sonicated by an ultrasonic cell disruptor. The effects of sonication were detected by circular dichroism (CD), atomic force microscopy (AFM), and rheology. AFM image illustrated that the sonicated fragments could quickly reassemble into nanofibers, while the morphology was distinguishable from the original one. CD spectrum revealed that the conversion occurred mainly between regular β-strand structure and distorted β-strand structure. Rheological analyses showed that the storage modulus (G′) of the peptide solution at the 7th day after sonication decreased by nearly 40% compared with the value of the solution before sonication. Finally, a plausible conversion model was proposed to interpret the reassembly process.     

Two-dimensional effects of hydrogel self-organized from IKVAV-containing peptides on growth and differentiation of NSCs

The neural stem cells (NSCs) were seeded in the surface layer of hydrogels made of IKVAV-containing peptide amphiphile. Two-dimensional effects of hydrogel on growth and differentiation of NSCs were investigated. Peptide was synthesized in solid way. Cells were harvested from the cerebral cortex of neonatal mice, identified by immunohistochemical methods. Cells were incubated in the surface layer of self-assembled peptide hydrogel and coverslips for seven days respectively, detected immunocytochemically for NF and GFAP. The molecular weight (M _W) of Peptide was 1438 and purity was 95.22%. Cells were identified as Nestin-positive NSCs. TEM showed that hydrogel was composed of interactive nanofibers. NSCs extended processes, and were able to be differentiated into NF-positive neurons with red fluorescence and GFAP-positive astrocytes with green one in the surface of hydrogel. However, NSCs only formed undifferentiated neurospheres in the surface layer of coverslips. Results indicate that the self-assembled hydrogel from peptide amphiphile has good cyto-compatibility to NSCs and induced their differentiation. Funded by the National Natural Science Foundation of China (30500511)