Induction of Four-Dimensional Spatiotemporal Geometric Transformations in High Cell Density Tissues via Shape-Changing Hydrogels

Developing and healing tissues begin as cellular condensations. Spatiotemporal changes in tissue geometry, transformations in the spatial distribution of the cells, and extracellular matrix are essential for its evolution into a functional tissue. 4D materials, 3D materials capable of geometric changes, may have the potential to recreate the aforementioned biological phenomenon. However, most reported 4D materials are non-degradable and/or not biocompatible, limiting their application in regenerative medicine, and to date, there are no systems controlling the geometry of high density cellular condensations and differentiation. Here, 4D high cell density tissues based on shape-changing hydrogels are described. By sequential photocrosslinking of oxidized and methacrylated alginate (OMA) and methacrylated gelatin (GelMA), bilayered hydrogels presenting controllable geometric changes without any external stimuli are fabricated. Fibroblasts and human adipose-derived stem cells (ASCs) are encapsulated at concentrations up to 1.0 × 10⁸ cells mL^–1 in the 4D constructs, and controllable shape changes are achieved in concert with ASCs differentiated down chondrogenic and osteogenic lineages. Bioprinting of the high density cell-laden OMA and GelMA permits the formation of more complex constructs with defined 4D geometric changes, which may further expand the promise of this approach in regenerative medicine applications.     

挡位离散型车辆经济性加速策略的伪谱法优化

加速过程中, 车辆的油耗与驾驶员的操作策略密切相关. 本文通过最优控制方法定量化地研究了挡位离散型车辆的经济性加速策略. 将加速策略的辨识构建为一个Bolza型最优控制问题(Optimal control problem, OCP), 设计了考虑加速距离影响的经济性定量评价指标. 该问题含有离散型控制变量, 隶属于混合整型最优控制问题, 且性能函数和状态方程呈现强非线性. 为高效地求解该问题, 结合变速器挡位切换规律, 将该整型问题转化为多段光滑问题的协同优化, 采用Legendre伪谱拼接法实现变速器挡位、换挡时机、发动机力矩的数值求解. 解析分析了经济性加速策略的形成机理, 总结了实用化的经济性加速度选择策略和挡位切换规律. 仿真验证了所求策略的节油潜力.     

Absorption Enhancement of Coated Absorbing Aerosols: Validation of the Photo-Acoustic Technique for Measuring the Enhancement

A photo-acoustic absorption spectrometer (PAS) and a cavity ring down aerosol extinction spectrometer (CRD-AES) were used, in conjunction with Mie Theory, to measure the refractive index (RI) of absorbing polystyrene spheres (APSS). The PAS and CRD-AES were also used to measure the absorption and extinction enhancement after these APSS were coated in oleic acid. The experimental enhancements were then compared to predictions from coated-sphere Mie Theory. The measured absorption and extinction enhancements both agreed with modeled enhancements to within an average of 5%. A filter-based absorption technique (particle soot absorption photometer, PSAP) was also used to measure the absorption by the APSS and showed a significant size-dependent bias, as evidenced by the filter-based method measuring significantly lower absorption for both uncoated and coated APSS compared to the PAS. These results suggest the validity of applying photo-acoustics to measure the absorption enhancement created by semi-volatile atmospheric species coating absorbing particles.     

Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine

Polymer hydrogels have been widely explored as therapeutic delivery matrices because of their ability to present sustained, localized and controlled release of bioactive factors. Bioactive factor delivery from injectable biopolymer hydrogels provides a versatile approach to treat a wide variety of diseases, to direct cell function and to enhance tissue regeneration. The innovative development and modification of both natural- (e.g., alginate (ALG), chitosan, hyaluronic acid (HA), gelatin, heparin (HEP), etc.) and synthetic- (e.g., polyesters, polyethyleneimine (PEI), etc.) based polymers has resulted in a variety of approaches to design drug delivery hydrogel systems from which loaded therapeutics are released. This review presents the state-of-the-art in a wide range of hydrogels that are formed though self-assembly of polymers and peptides, chemical crosslinking, ionic crosslinking and biomolecule recognition. Hydrogel design for bioactive factor delivery is the focus of the first section. The second section then thoroughly discusses release strategies of payloads from hydrogels for therapeutic medicine, such as physical incorporation, covalent tethering, affinity interactions, on demand release and/or use of hybrid polymer scaffolds, with an emphasis on the last 5 years.     

Three-dimensional electrospun alginate nanofiber mats via tailored charge repulsions

The formation of 3D electrospun mat structures from alginate-polyethylene oxide (PEO) solution blends is reported. These unique architectures expand the capabilities of traditional electrospun mats for applications such as regenerative medicine, where a scaffold can help to promote tissue growth in three dimensions. The mat structures extend off the surface of the flat collector plate without the need of any modifications in the electrospinning apparatus, are self-supported when the electric field is removed, and are composed of bundles of nanofibers. A mechanism for the unique formations is proposed, based on the fiber-fiber repulsions from surface charges on the negatively charged alginate. Furthermore, the role of the electric field in the distribution of alginate within the nanofibers is discussed. X-ray photoelectron spectroscopy is used to analyze the surface composition of the electrospun nanofiber mats and the data is related to cast films made in the absence of the electric field. Further techniques to tailor the 3D architecture and nanofiber morphology by changing the surface tension and relative humidity are also discussed.     

Students’ attitudes toward foreign-born and domestic instructors.

Based on G. W. Allport’s seminal work on ethnocentric bias, this study compares students’ attitudes toward foreign-born and domestic instructors, using new affect and stereotype measures. Additionally, it explains individual differences in affect toward foreign-born instructors as a function of student personality (Big Five Inventory), contact (previous study with foreign-born teachers and interest in study abroad), stereotype, and affect factors. Participants were 128 students from a predominantly White college in the Midwest. They reported limited previous experience with foreigners and overall preference for domestic instructors. Significant differences were found in student stereotype about communication, favoring domestic instructors over foreign-born ones. Multiple regressions explained 58% of the variance in student affect toward foreign-born instructors and showed positive effects for student agreeableness, conscientiousness, and interest in study abroad. Stereotypes about foreign-born instructors’ competence also strongly influenced student affect toward these instructors. An inverse relationship was found between interest in study abroad and attitudes toward domestic instructors and between affect toward domestic and foreign-born instructors, reflecting dualistic thinking. Results are discussed with regard to globalization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiscale cluster analysis

This article describes how the concept of multiresolution is used with cluster analysis of spectral data. Multiresolution analysis progressively increases the resolution of a spectrum profile by adding levels of details contained in scales obtained from a discrete wavelet transform. At each resolution level a cluster analysis is performed on all the spectra profiles in the data set. This allows the relating of changes in the cluster pattern to various broad and narrow features in the spectral data profiles. The analysis also provides an approximate location of the important features in the original wavenumber domain.     

Interacting with mobile services: an evaluation of camera-phones and visual tags

We present a study of using camera-phones and visual-tags to access mobile services. Firstly, a user-experience study is described in which participants were both observed learning to interact with a prototype mobile service and interviewed about their experiences. Secondly, a pointing-device task is presented in which quantitative data was gathered regarding the speed and accuracy with which participants aimed and clicked on visual-tags using camera-phones. We found that participants’ attitudes to visual-tag-based applications were broadly positive, although they had several important reservations about camera-phone technology more generally. Data from our pointing-device task demonstrated that novice users were able to aim and click on visual-tags quickly (well under 3 s per pointing-device trial on average) and accurately (almost all meeting our defined speed/accuracy tradeoff of 6% error-rate). Based on our findings, design lessons for camera-phone and visual-tag applications are presented.

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