Stimulus-responsive Injectable Polysaccharide Scaffolds for Soft Tissue Engineering Prepared by O/W High Internal Phase Emulsion

This thesis describes work on the development of several novel stimuli-responsive porous hydrogels prepared from oil-in-water (o/w) high internal phase emulsion (HIPE) as injectable scaffolds for soft tissue engineering. Firstly, by copolymerising glycidyl methacrylate (GMA) derivatised dextran and N-isopropylacrylamide (NIPAAm) in the aqueous phase of a toluene-in-water HIPE, thermo-responsive polyHIPE hydrogels were obtained. The temperature depended modulus of these porous hydrogels, as revealed by oscillatory mechanical measurements, indicated improvements of the mechanical properties of these hydrogels when heated from room temperature to human body temperature, as the polyNIPAAm copolymer segments starts to phase separate from the aqueous phase and causes the hydrogel to form a more compact structure within the aqueous phase of the polyHIPE. Secondly ion responsive methacrylate modified alginate polyHIPE hydrogels were prepared. The physical dimensions, pore and pore throat sizes as well as water uptakes of these ion responsive hydrogels can be controllably decreased in the presence of Ca2+ ions and are fully recovered after disruption of the ionic crosslinking using a chelating agent (sodium citrate). These ion-responsive polyHIPE hydrogels also possess good mechanical properties (modulus up to 20 kPa). Both of these polyHIPE hydrogels could be easily extruded through a hypodermic needle while breaking into small fragments (about 0.5 to 3.0 mm in diameter), but the interconnected porous morphology was maintained after injection as revealed by SEM characterisation. Furthermore, the hydrogel fragments produced during injection can be crosslinked into a coherent scaffold under very mild condition using Ca2+ salts and alginate aqueous solution as the ionically crosslinkable adhesive. In order to increase the pore size of these covalently crosslinked polyHIPE hydrogels and also find a biocompatible nontoxic emulsifier as substitution to traditional surfactants, methyl myristate-in-water and soybean oil-in-water HIPEs solely stabilised by hydroxyapatite (HAp) nanoparticle were prepared. These Pickering- HIPEs were used as template to prepare polyHIPE hydrogels. Dextran-GMA, a water soluble monomer, was polymerised in the continuous phase of the HAp Pickering HIPEs leading to porous hydrogels with a tunable pore size varying from 1.5 μm to 41.0 μm. HAp is a nontoxic biocompatible emulsifier, which potentially provides extra functions, such as promoting hard tissue cell proliferation. HIPE-templated materials whose porous structure is maintained solely by the reversible physical aggregation between thermo-responsive dextran-b-polyNIPAAm block polymer chains in an aqueous environment (for this type of HIPE templated material we coined the name thermo-HIPEs) were prepared. No chemical reaction is required for the solidification of this porous material. This particular feature should provide a safer route to injectable scaffolds as issues of polymerisation/crosslinking chemistry or residual initiator fragments or monomers potentially being cytotoxic do not arise in our case, as all components are purified polymers prior to HIPE formation. Thermo-HIPEs with soybean oil or squalene as dispersed oil phase were prepared. Also in this HIPE system it was possible to replace the original surfactant Triton X405 with colloidal HAp nanoparticles or pH/thermo-responsive polyNIPAAm-co- AA microgel particles. The pore sizes and the mechanical properties of colloidal particles stabilised thermo-HIPEs showed improvement compared with thermo-HIPEs stabilised by Triton X405. In summary new injectable polyHIPEs have been prepared which retain their pore morphology during injection and can be solidified by either a thermal or ion (Ca2+) or chelating ion (Ca2+) stimulus. The materials used are intrinsically biocompatible and thus makes these porous injectable scaffolds excellent candidates for soft tissue engineering

Seismic velocity structure of the crust and uppermost mantle beneath the Tien Shan and its adjacent areas

The Tien Shan and its adjacent areas have been a prime place to understand the process of continental collision, the mechanism of mountain building and the interaction of tectonic blocks. In this study, we collect seismic data recorded by 74 broad-band stations from the China Provincial Digital Seismic Networks and the Regional Kyrgyzstan and Kazakhstan Networks between January, 2007 and September, 2009. A joint inversion technique that combines three types of datasets (receiver functions, phase velocities of Rayleigh wave measured from both ambient noise and teleseismic earthquake data) is applied to image the crustal and upper mantle structure beneath the Tien Shan and its adjacent areas. The average crustal thickness in the study area is about 50 km, however, the Moho depth extends to ∼70 km beneath the Kyrgyz Platform near the southwestern Tien Shan. Our velocity models show a good correlation with subsurface geological features at shallow depths: low velocities are predominantly observed beneath the basins due to thick sedimentary layer, whereas high velocities are mainly distributed beneath the mountain ranges due to crystalline basement rocks. In the upper mantle a low velocity zone is obviously observed beneath the western Tien Shan. Both the crust thickness and S wave velocity structure of the Tien Shan and its adjacent regions display obvious horizontal and vertical heterogeneities from west to east, which suggests that the far-field effects of the collision between Eurasian plate and Indian plate plays an important role in the tectonic activity of the Tien Shan. The apparent velocity heterogeneities beneath the northern Tarim Basin may indicate that the Tarim Basin may have been eroded and damaged by upwelling hot materials from the upper mantle

Electric vehicle charging load forecasting: A comparative study of deep learning approaches

Load forecasting is one of the major challenges of power system operation and is crucial to the effective scheduling for economic dispatch at multiple time scales. Numerous load forecasting methods have been proposed for household and commercial demand, as well as for loads at various nodes in a power grid. However, compared with conventional loads, the uncoordinated charging of the large penetration of plug-in electric vehicles is different in terms of periodicity and fluctuation, which renders current load forecasting techniques ineffective. Deep learning methods, empowered by unprecedented learning ability from extensive data, provide novel approaches for solving challenging forecasting tasks. This research proposes a comparative study of deep learning approaches to forecast the super-short-term stochastic charging load of plug-in electric vehicles. Several popular and novel deep-learning based methods have been utilized in establishing the forecasting models using minute-level real-world data of a plug-in electric vehicle charging station to compare the forecasting performance. Numerical results of twelve cases on various time steps show that deep learning methods obtain high accuracy in super-short-term plug-in electric load forecasting. Among the various deep learning approaches, the long-short-term memory method performs the best by reducing over 30% forecasting error compared with the conventional artificial neural network model

Stimulus-responsive injectable polysaccharide scaffolds for soft tissue engineering prepared by o/w high internal phase emulsion

This thesis describes work on the development of several novel stimuli-responsive porous hydrogels prepared from oil-in-water (o/w) high internal phase emulsion (HIPE) as injectable scaffolds for soft tissue engineering. Firstly, by copolymerising glycidyl methacrylate (GMA) derivatised dextran and N-isopropylacrylamide (NIPAAm) in the aqueous phase of a toluene-in-water HIPE, thermo-responsive polyHIPE hydrogels were obtained. The temperature depended modulus of these porous hydrogels, as revealed by oscillatory mechanical measurements, indicated improvements of the mechanical properties of these hydrogels when heated from room temperature to human body temperature, as the polyNIPAAm copolymer segments starts to phase separate from the aqueous phase and causes the hydrogel to form a more compact structure within the aqueous phase of the polyHIPE. Secondly ion responsive methacrylate modified alginate polyHIPE hydrogels were prepared. The physical dimensions, pore and pore throat sizes as well as water uptakes of these ion responsive hydrogels can be controllably decreased in the presence of Ca2+ ions and are fully recovered after disruption of the ionic crosslinking using a chelating agent (sodium citrate). These ion-responsive polyHIPE hydrogels also possess good mechanical properties (modulus up to 20 kPa). Both of these polyHIPE hydrogels could be easily extruded through a hypodermic needle while breaking into small fragments (about 0.5 to 3.0 mm in diameter), but the interconnected porous morphology was maintained after injection as revealed by SEM characterisation. Furthermore, the hydrogel fragments produced during injection can be crosslinked into a coherent scaffold under very mild condition using Ca2+ salts and alginate aqueous solution as the ionically crosslinkable adhesive. In order to increase the pore size of these covalently crosslinked polyHIPE hydrogels and also find a biocompatible nontoxic emulsifier as substitution to traditional surfactants, methyl myristate-in-water and soybean oil-in-water HIPEs solely stabilised by hydroxyapatite (HAp) nanoparticle were prepared. These Pickering- HIPEs were used as template to prepare polyHIPE hydrogels. Dextran-GMA, a water soluble monomer, was polymerised in the continuous phase of the HAp Pickering HIPEs leading to porous hydrogels with a tunable pore size varying from 1.5 μm to 41.0 μm. HAp is a nontoxic biocompatible emulsifier, which potentially provides extra functions, such as promoting hard tissue cell proliferation. HIPE-templated materials whose porous structure is maintained solely by the reversible physical aggregation between thermo-responsive dextran-b-polyNIPAAm block polymer chains in an aqueous environment (for this type of HIPE templated material we coined the name thermo-HIPEs) were prepared. No chemical reaction is required for the solidification of this porous material. This particular feature should provide a safer route to injectable scaffolds as issues of polymerisation/crosslinking chemistry or residual initiator fragments or monomers potentially being cytotoxic do not arise in our case, as all components are purified polymers prior to HIPE formation. Thermo-HIPEs with soybean oil or squalene as dispersed oil phase were prepared. Also in this HIPE system it was possible to replace the original surfactant Triton X405 with colloidal HAp nanoparticles or pH/thermo-responsive polyNIPAAm-co- AA microgel particles. The pore sizes and the mechanical properties of colloidal particles stabilised thermo-HIPEs showed improvement compared with thermo-HIPEs stabilised by Triton X405. In summary new injectable polyHIPEs have been prepared which retain their pore morphology during injection and can be solidified by either a thermal or ion (Ca2+) or chelating ion (Ca2+) stimulus. The materials used are intrinsically biocompatible and thus makes these porous injectable scaffolds excellent candidates for soft tissue engineering.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A Novel Hierarchical Clustering Algorithm Based on Density Peaks for Complex Datasets

Clustering aims to differentiate objects from different groups (clusters) by similarities or distances between pairs of objects. Numerous clustering algorithms have been proposed to investigate what factors constitute a cluster and how to efficiently find them. The clustering by fast search and find of density peak algorithm is proposed to intuitively determine cluster centers and assign points to corresponding partitions for complex datasets. This method incorporates simple structure due to the noniterative logic and less few parameters; however, the guidelines for parameter selection and center determination are not explicit. To tackle these problems, we propose an improved hierarchical clustering method HCDP aiming to represent the complex structure of the dataset. A k-nearest neighbor strategy is integrated to compute the local density of each point, avoiding to select the nonnecessary global parameter dc and enables cluster smoothing and condensing. In addition, a new clustering evaluation approach is also introduced to extract a “flat” and “optimal” partition solution from the structure by adaptively computing the clustering stability. The proposed approach is conducted on some applications with complex datasets, where the results demonstrate that the novel method outperforms its counterparts to a large extent

Recent Progress in Single-Crystalline Perovskite Research Including Crystal Preparation, Property Evaluation, and Applications

Organic-inorganic lead halide perovskites are promising optoelectronic materials resulting from their significant light absorption properties and unique long carrier dynamics, such as a long carrier lifetime, carrier diffusion length, and high carrier mobility. These advantageous properties have allowed for the utilization of lead halide perovskite materials in solar cells, LEDs, photodetectors, lasers, etc. To further explore their potential, intrinsic properties should be thoroughly investigated. Single crystals with few defects are the best candidates to disclose a variety of interesting and important properties of these materials, ultimately, showing the increased importance of single-crystalline perovskite research. In this review, recent progress on the crystallization, investigation, and primary device applications of single-crystalline perovskites are summarized and analyzed. Further improvements in device design and preparation are also discussed

Customer Concentration and Corporate Innovation: Effects of Financing Constraints and Managers’ Expectation of Chinese Listed Companies

Innovation capability of enterprises will greatly influence the current and future development of companies. This paper investigates the relationship between customer concentration and innovation capability of enterprises through the view of both the financing constraints and the expectation of managers. Based on the data of China’s A-share listed companies over the period from 2012 to 2016, several methods including system GMM, threshold model of fixed effects, and PSM are applied for empirical analysis. The results show that the innovation capability of listed companies in China are negatively correlated with the customer concentration. Higher customer concentration brings about stronger constraints from large customers on enterprises and greater dependence of enterprises on large customers, which result in weaker demand for innovation and lower investment in innovation. Meanwhile, the results demonstrate the double-threshold effect of financing constraints. The effect of customer concentration on innovation can be different in companies with low, medium, or high-financing constraints. Furthermore, optimistic expectations are more conducive to the reduction of customer concentration and the improvement of innovation. In addition, based on the perspective of the manager’s expectation, the research demonstrates the heterogeneous impact of manager’s expectation on the relationship between customer concentration and innovation capability

High-quality perovskite MAPbI(3) single crystals for broad-spectrum and rapid response integrate photodetector

Organic-inorganic single-crystalline perovskites have attracted significant attentions due to their exceptional progress in intrinsic properties' investigation and applications in photovoltaics and optoelectronics. In this study, the large perovskite CH3NH3PbI3 single crystal with the largest length of 80 mm was prepared through the method of inverse-temperature crystallization. Meanwhile, the mass production of integrate photodetectors have been fabricated on the single-crystalline wafer and the photoresponse performances were investigated. The results show that the single-crystalline photodetectors have broad spectrum response to 900 nm, rapid response speed (<40 mu s) and excellent stability. These findings are of great importance for future promising perovskite single crystalline for integrated photoelectronic application. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved