Thermo- and pH-sensitive behavior of hydrogels based on oligo (ethylene glycol) methacrylates and acrylic acid

Novel dual stimuli-responsive hydrogels were prepared by free-radical polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO₂MA) and oligo (ethylene glycol) methacrylate (OEGMA), as thermosensitive monomers, and acrylic acid (AAc), as a pH-sensitive monomer. Due to the thermosensitive monomers introduced in the macromolecular network, the synthesized materials possessed tunable thermal behavior. In addition, as well as by introducing in the polymerization feed pH-sensitive monomer AAc, the equilibrium swelling properties of the hydrogels can be tuned by three comonomers. Moreover, the de-swelling kinetics was studied by changing temperature and/or pH, and they could be well described with a first-order kinetics equation. Especially, the faster shrinking rates of hydrogels were observed when the simultaneous temperature and pH stimuli changed from pH 8/18 to pH 2/55 °C because of the cooperative thermo-/pH responses. The prepared dual temperature-/pH-sensitive PMOA hydrogels as a new material candidate may provide significant valuable information for various potential applications.     

Sorption of zinc by novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were applied as adsorbents for the removal of Zn²⁺ ions from aqueous solution. In batch tests, the influence of solution pH, contact time, initial metal ion concentration and temperature was examined. The sorption was found pH dependent, pH 5.5 being the optimum value. The adsorption process was well described by the pseudo-second order kinetic. The hydrogels were characterized by spectral (Fourier transform infrared—FTIR) and structural (SEM/EDX and atomic force microscopy—AFM) analyses. The surface topography changes were observed by atomic force microscopy, while the changes in surface composition were detected using phase imaging AFM. The negative values of free energy and enthalpy indicated that the adsorption is spontaneous and exothermic one. The best fitting isotherms were Langmuir and Redlich-Peterson and it was found that both linear and nonlinear methods were appropriate for obtaining the isotherm parameters. However, the increase of temperature leads to higher adsorption capacity, since swelling degree increased with temperature.     

pH-sensitive hydrogels based on semi-interpenetrating network (semi-IPN) of chitosan and polyvinyl pyrrolidone for clarithromycin release

The aim of this study was to develop a pH-sensitive chitosan/polyvinyl pyrrolidone (PVP) based controlled drug release system for clarithromycin. The hydrogels were synthesized by cross-linking chitosan and PVP blend with glutaraldehyde to form a semi-interpenetrating polymer network (semi-IPN). These semi-IPNs were studied for their content uniformity, swelling index (SI), mucoadhesion, wettability, in vitro release and their release kinetics. The hydrogels showed more than 97% content of clarithromycin. These hydrogels showed high swelling and mucoadhesion under acidic conditions. The swelling may be due to the protonation of a primary amino group on chitosan. In acidic condition, chitosan would be ionized, and adhesion could have occurred between the positively charged chitosan and the negatively charged mucus. In the alkaline condition, less swelling and mucoadhesion was noticed. In vitro release study revealed that formulation containing chitosan (2% w/v) and PVP (4% w/v) in the ratio of 21:4 showed complete drug release after 12?h. Release profile showed that all the formulations followed non-Fickian diffusion mechanism. The cross-linking and compatibility of clarithromycin in the formulation was studied by Fourier transform infrared (FTIR) spectroscopic analysis, differential scanning calorimetry (DSC) and powder X-ray diffraction (p-XRD) study, which confirmed proper formation of semi-IPN and stability of clarithromycin in the formulations. The surface morphology of semi-IPN was studied before and after dissolution in simulated gastric fluid (SGF, pH 1.2) which revealed pores formation in membrane after dissolution. The results of study suggest that semi-IPNs of chitosan/PVP are potent candidates for delivery of clarithromycin in acidic environment.     

pH-sensitive hydrogels based on semi-interpenetrating network (semi-IPN) of chitosan and polyvinyl pyrrolidone for clarithromycin release

The aim of this study was to develop a pH-sensitive chitosan/polyvinyl pyrrolidone (PVP) based controlled drug release system for clarithromycin. The hydrogels were synthesized by cross-linking chitosan and PVP blend with glutaraldehyde to form a semi-interpenetrating polymer network (semi-IPN). These semi-IPNs were studied for their content uniformity, swelling index (SI), mucoadhesion, wettability, in vitro release and their release kinetics. The hydrogels showed more than 97% content of clarithromycin. These hydrogels showed high swelling and mucoadhesion under acidic conditions. The swelling may be due to the protonation of a primary amino group on chitosan. In acidic condition, chitosan would be ionized, and adhesion could have occurred between the positively charged chitosan and the negatively charged mucus. In the alkaline condition, less swelling and mucoadhesion was noticed. In vitro release study revealed that formulation containing chitosan (2% w/v) and PVP (4% w/v) in the ratio of 21:4 showed complete drug release after 12 h. Release profile showed that all the formulations followed non-Fickian diffusion mechanism. The cross-linking and compatibility of clarithromycin in the formulation was studied by Fourier transform infrared (FTIR) spectroscopic analysis, differential scanning calorimetry (DSC) and powder X-ray diffraction (p-XRD) study, which confirmed proper formation of semi-IPN and stability of clarithromycin in the formulations. The surface morphology of semi-IPN was studied before and after dissolution in simulated gastric fluid (SGF, pH 1.2) which revealed pores formation in membrane after dissolution. The results of study suggest that semi-IPNs of chitosan/PVP are potent candidates for delivery of clarithromycin in acidic environment.     

Poloxamer-based hydrogels hardening at body core temperature as carriers for cell based therapies: in vitro and in vivo analysis

Cell-based regenerative therapies for bone defects usually employ bone precursor cells seeded on solid scaffolds. Thermosensitive hydrogels that harden at body core temperature are promising alternative cell carriers as they are applicable minimally invasively. We modified Pluronic^® P123 with different chain extenders and assessed rheology and biocompatibility of the resulting hydrogels. The best candidate was tested in a rat’s femoral defect model. All gels hardened above 25 °C with butane-diisocyanate-hydrogels (BDI-gels) displaying the highest storage moduli. BDI-gels showed the most favourable biocompatibility and did not affect cellular adipogenic or osteogenic differentiation in vitro. Implantation of BDI-hydrogel into femoral defects did not impede bone healing in vivo as evidenced by μCT and histological analysis. We conclude that thermosensitive BDI-gels are promising alternative cell carriers. The gels harden upon injection in vivo without interfering with bone metabolism. Further experiments will assess the gels’ capacity to effectively transport living cells into bone defects.     

Photopolymerisation and characterisation of negative temperature sensitive hydrogels based on N,N-diethylacrylamide

Despite the many advantages of photopolymerisation in the fabrication of hydrogels, studies on the synthesis of poly(N,N-diethylacrylamide) (PDEAAm) using this technique have received limited attention in the literature. A series of temperature sensitive hydrogels were prepared by free-radical crosslinking copolymerisation of N,N-diethylacrylamide (DEAAm) with 1-vinyl-2-pyrrolidinone (NVP) and N,N-dimethylacrylamide (DMAAm), respectively. Two ultraviolet (UV) light sensitive initiators were trialled in the synthesis, namely 1-hydroxycyclohexylphenylketone and 2-hydroxy-1-[4-(hydroxy-ethoxy)phenyl]-2-methyl-1-propanone, with poly(ethylene glycol)dimethacrylate being used as the crosslinking agent. The lower critical solution temperatures (LCSTs) of the hydrogels synthesised were shown to be close to body temperature using cloud point measurement and modulated differential scanning calorimetry, which is favourable particularly for ‘smart’ drug delivery applications. The swelling behaviour of the samples was investigated upon stepwise temperature change revealing that the hydrogels underwent reproducible pulsatile swelling behaviour. Oscillatory rheological studies showed that increasing the ratio of crosslinking agent could be used as a means of improving the mechanical properties of the photopolymerised temperature sensitive hydrogels.     

Comparing transmission potential networks based on social network surveys,close contacts and environmental overlap in rural Madagascar

Social and spatial network analysis is an important approach for investigating infectious disease transmission, especially for pathogens transmitted directly between individuals or via environmental reservoirs. Given the diversity of ways to construct networks, however, it remains unclear how well networks constructed from different data types effectively capture transmission potential. We used empirical networks from a population in rural Madagascar to compare social network survey and spatial data-based networks of the same individuals. Close contact and environmental pathogen transmission pathways were modelled with the spatial data. We found that naming social partners during the surveys predicted higher close-contact rates and the proportion of environmental overlap on the spatial data-based networks. The spatial networks captured many strong and weak connections that were missed using social network surveys alone. Across networks, we found weak correlations among centrality measures (a proxy for superspreading potential). We conclude that social network surveys provide important scaffolding for understanding disease transmission pathways but miss contact-specific heterogeneities revealed by spatial data. Our analyses also highlight that the superspreading potential of individuals may vary across transmission modes. We provide detailed methods to construct networks for close-contact transmission pathogens when not all individuals simultaneously wear GPS trackers.     

基于混合神经网络的人类基因组启动子识别研究

提出了基于混合神经网络的人类基因组启动子识别的新方法：PromPredictor。该方法通过对转录起始位点（TSS）信息，调控区、编码区组成成分特征信息及CpG岛相关信息的综合来预测人类基因组启动子。对人类4、21、22号染色体启动子的预测结果为：敏感性达到了64．47％，特异性达到了82．2％。与其它三个算法相比，PmmPredictor具有更高的敏感性和特异性。研究中所用到的数据集合及用MATLAB编写的程序代码都可以从www．whtelecom．com／Prompredictor．htm下载得到。     

A pH-sensitive nanocomposite microsphere based on chitosan and montmorillonite with in vitro reduction of the burst release effect

Objective: The aim of this study was to prepare pH-sensitive ofloxacin (OFL)/montmorillonite (MMT)/chitosan (CTS) nanocomposite microspheres that improve the burst release effect of the drug by the solution intercalation technique and emulsification cross-linking techniques. Methods: First, OFL/MMT hybrids were prepared through the solution intercalation technique. Then, OFL/MMT-intercalated OFL/MMT/CTS nanocomposite microspheres were obtained through emulsification cross-linking technology. The intercalated nanocomposite was confirmed by Fourier-transform infrared spectroscopy and X-ray diffraction. Finally, in vitro release of OFL from the microspheres was performed in simulated gastric fluids and simulated intestinal fluids. The effect of MMT content on drug encapsulation efficiency and the drug release of the nanocomposite microspheres were investigated. Results: The results showed that the release rate of OFL from the nanocomposite microspheres at pH 7.4 was higher than that at pH 1.2. Compared with pure CTS microspheres, the incorporation of certain amount of MMT in the nanocomposite microspheres can enhance the drug encapsulation efficiency and reduce the burst release. Conclusion: A sustained release particulate system can be obtained by incorporating MMT into the nanocomposite microspheres and can improve the burst release effect of the drug.     

Mussel-inspired adhesive hydrogels based on biomass-derived xylan and tannic acid cross-linked with acrylic acid with antioxidant and antibacterial properties

Journal of Materials Science - Inspired by mussel chemistry, adhesive hydrogels represented by polydopamine (PDA) have been widely studied in many fields such as biomedical applications and...     

Macroporous hydrogels based on 2-hydroxyethyl methacrylate. Part 6: 3D hydrogels with positive and negative surface charges and polyelectrolyte complexes in spinal cord injury repair

Macroporous hydrogels are artificial biomaterials commonly used in tissue engineering, including central nervous system (CNS) repair. Their physical properties may be modified to improve their adhesion properties and promote tissue regeneration. We implanted four types of hydrogels based on 2-hydroxyethyl methacrylate (HEMA) with different surface charges inside a spinal cord hemisection cavity at the Th8 level in rats. The spinal cords were processed 1 and 6 months after implantation and histologically evaluated. Connective tissue deposition was most abundant in the hydrogels with positively-charged functional groups. Axonal regeneration was promoted in hydrogels carrying charged functional groups; hydrogels with positively charged functional groups showed increased axonal ingrowth into the central parts of the implant. Few astrocytes grew into the hydrogels. Our study shows that HEMA-based hydrogels carrying charged functional groups improve axonal ingrowth inside the implants compared to implants without any charge. Further, positively charged functional groups promote connective tissue infiltration and extended axonal regeneration inside a hydrogel bridge.     

Investigations on boundary temperature control analysis considering a moving body based on the adjoint variable and the fictitious domain finite element methods

This paper presents an examination of moving‐boundary temperature control problems. With a moving‐boundary problem, a finite‐element mesh is generated at each time step to express the position of the boundary. On the other hand, if an overlapped domain, that is, comprising foreground and background meshes, is prepared, the moving boundary problem can be solved without mesh generation at each time step by using the fictitious domain method. In this study, boundary temperature control problems with a moving boundary are formulated using the finite element, the adjoint variable, and the fictitious domain methods, and several numerical experiments are carried out. Copyright © 2015 John Wiley & Sons, Ltd.     

Macroporous hydrogels based on 2-hydroxyethyl methacrylate. Part 4: Growth of rat bone marrow stromal cells in three-dimensional hydrogels with positive and negative surface charges and in polyelectrolyte complexes

The growth of bone marrow stromal cells was assessed in vitro in macroporous hydrogels based on 2-hydro- xyethyl methacrylate (HEMA) copolymers with different electric charges. Copolymers of HEMA with sodium methacrylate (MA⁻) carried a negative electric charge, copolymers of HEMA with [2-(methacryloyloxy)ethyl] trimethylammonium chloride (MOETA⁻) carried a positive electric charge and terpolymers of HEMA, MA⁻ and MOETA⁺ carried both, positive and negative electric charges. The charges in the polyelectrolyte complexes were shielded by counter-ions. The hydrogels had similar porosities, based on a comparison of their diffusion parameters for small cations as measured by the real-time tetramethylammonium iontophoretic method of diffusion analysis. The cell growth was studied in the peripheral and central regions of the hydrogels at 2 hours and 2, 7, 14 and 28 days after cell seeding. Image analysis revealed the highest cellular density in the HEMA-MOETA⁺ copolymers; most of the cells were present in the peripheral region of the hydrogels. A lower density of cells but no difference between the peripheral and central regions was observed in the HEMA-MA⁻ copolymers and in polyelectrolyte complexes. This study showed that positively charged functional groups promote the adhesion of cells.     

Modelling of a thermal insulation system based on the coldest temperature conditions by using artificial neural networks to determine performance of building for wall types in Turkey

In formation of building external envelope, as two important criteria, climatic data and wall types must be taken into consideration. In the selection of wall type, the thickness of thermal insulation layer (d_i) must be calculated. As a new approach, this study proposes determining the thermal insulation layer by using artificial neural network (ANN) technique. In this technique five different wall types in four different climatic regions in Turkey have been selected. The ANN was trained and tested by using MATLAB toolbox on a personal computer. As ANN input parameters, U_w, T_e,Met, T_e,TSE, R_wt, and q_TSE were used, while d_i was the output parameter. It was found that the maximum mean absolute percentage error (MRE, %) is less than 7.658%. R² (%) for the training data were found ranging about from 99.68 to 99.98 and R² for the testing data varied between 97.55 and 99.96. These results show that ANN model can be used as a reliable modeling method of d_i studies.     

Refractive index and temperature sensors based on no-core fiber cascaded with long period fiber grating

A kind of compact fibre-optic sensor based on no-core fibre (NCF) cascaded with a strong coupling long-period fibre grating (LPFG) is proposed and experimentally demonstrated. The sensing mechanism is based on the Mach–Zehnder-like interference between the core fundamental mode and cladding mode of the fibre structure. The NCF and LPFG are used as the mode exciter and combiner, respectively. Due to the particular properties of the strong coupling LPFG, the measurements of refractive index (RI) and temperature with high sensitivity are realized by monitoring the transmission spectrum with intensity and wavelength interrogation techniques, respectively. The achieved RI sensitivity reaches ?580.269 dB/RIU in the range of 1.436–1.454 and the temperature sensitivity reaches 27.2 pm/°C.     

基于小波包和PSO优化神经网络的刀具状态监测

为改进BP神经网络进行刀具磨损状态识别时训练时间较长、收敛速度较慢、测试精度不够高、甚至完全不能训练等问题,引入一种全局搜索能力强,收敛速度快的算法——粒子群优化算法(PSO),用其来优化BP神经网络参数,改进网络的训练和识别性能。实验证明:经粒子群算法优化后的BP神经网络较原网络有更快的训练迭代收敛速度和更高的测试准确度,达到优化的目标,对实现数控刀具磨损状态的智能化在线监测具有重要意义。     

Cartesian网格结合无网格法处理的二维柱体

本文发展了基于四叉树数据结构的网格生成和二维流动的N-S方程数值求解器及动边界问题的Euler方程求解方法。采用压力梯度或者密度梯度的绝对值作为网格自适应的控制参量,同时采用基于最小二乘法的无网格方法处理对于一般Cartesian网格难于处理的物面边界条件。文中采取了绕方柱流动和绕圆柱流动的经典算例对所发展的方法进行了验证。计算的结果验证了所发展的方法在处理绕流流动时的合理性和有效性。采用Naca0012翼型的几种工况验证了所发展的动网格技术在处理无粘流动的合理性和可行性。从而为数值模拟具有复杂几何外形的流动提供了一种网格布局合理、高效,边界处理简单易行的新思路。     

All-fiber, low-cost single-point and quasi-distributed evanescent field temperature sensors with extended temperature measurement range, based on standard telecommunication graded index fibers

Fiber-optic single-point and quasi-distributed evanescent temperature sensors recoated with a blend of poly(methyl methacrylate) and poly(vinylidene fluoride) are proposed. Solid cladding enables the construction of small-size, low-cost, relatively wide-range and fast-response temperature sensors. The diameter of the sensor does not exceed the dimensions of the original optical fiber, while the response time of the sensor is 7.4 ms. Different mass ratios of polymers in the blend enable fine tuning of the applied cladding's refractive index. This allows the construction of sensors for different temperature ranges, while the application of all-silica graded-index multimode fibers enables the construction of quasi-distributed sensor systems with considerably reduced cross talk.