Stem cells for tissue engineering of articular cartilage

Articular cartilage injuries are one of the most common disorders in the musculo-skeletal system. Injured cartilage tissue cannot spontaneously heal and, if not treated, can lead to osteoarthritis of the affected joints. Although a variety of procedures are being employed to repair cartilage damage, methods that result in consistent durable repair tissue are not yet available. Tissue engineering is a recently developed science that merges the fields of cell biology, engineering, material science, and surgery to regenerate new functional tissue. Three critical components in tissue engineering of cartilage are as follows: first, sufficient cell numbers within the defect, such as chondrocytes or multipotent stem cells capable of differentiating into chondrocytes; second, access to growth and differentiation factors that modulate these cells to differentiate through the chondrogenic lineage; third, a cell carrier or matrix that fills the defect, delivers the appropriate cells, and supports cell proliferation and differentiation. Stem cells that exist in the embyro or in adult somatic tissues are able to renew themselves through cell division without changing their phenotype and are able to differentiate into multiple lineages including the chondrogenic lineage under certain physiological or experimental conditions. Here the application of stem cells as a cell source for cartilage tissue engineering is reviewed.     

Physico-chemical characterization of functional electrospun scaffolds for bone and cartilage tissue engineering

Mimicking the zonal organization of the bone-cartilage interface will aid the production of functional osteochondral grafts for regeneration of skeletal joint defects. This study investigates the potential of the electrospinning technique to build a three-dimensional construct recapitulating the zonal matrix of this interface. Poly(lactic-co-glycolic acid) (PLGA) and PLGA-collagen solutions containing different concentrations of hydroxyapatite nanoparticles (nHAp) were electrospun on a thin layer of phosphate buffer saline solution spread on the collector in order to facilitate membrane detachment and recovery. Incorporation of increasing amounts of nHAp in PLGA solutions did not affect significantly the average diameter of the fibres, which was about 700 nm. However, in the presence of collagen, fibres with diameters below 100 nm were generally observed and the number of these fibres was inversely proportional to the ratio PLGA:collagen and proportional to the content of nHAp. PLGA membranes were rather hydrophobic, although the aqueous drop contact angles progressively fell from 125 degrees to 110 degrees when the content of nHAp was increased from 0 per cent to 50 per cent (w/v). PLGA-collagen membranes were more hydrophilic with contact angles between 60 degrees and 110 degrees; the values being proportional to the ratio PLGA:collagen and the content of nHAp. Also, the addition of nHAp from 0 per cent to 50 per cent (w/v) in the absence of collagen resulted in decreasing dramatically both the Young's modulus (Ym), from 34.3 +/- 1.8 MPa to 0.10 +/- 0.06 MPa, and the ultimate tensile strain (epsilon max), from a value higher than 40 per cent to 5 per cent. However, the presence of collagen together with nHAp allowed the creation of membranes much stiffer, although more brittle, as shown for membranes made with a ratio 8:2 and 10 per cent of nHAp, for which Ym = 70.0 +/- 6.6 MPa and epsilon max = 7 per cent.     

Prospects for the application of nanostructured titanium alloys in mechanical engineering

The results of the application of nanostructured titanium alloys, in particular the VT6 alloy, for the manufacture of hollow structures by superplastic forming and by a method combining it with pressure welding, are presented. Possibilities of the application of nanostructured titanium alloys are shown by the example of the formation of dome-shaped shells, models of a hollow blade of a jet engine fan, and weld-fabricated semi products.     

XML在机械工程中的应用

主要介绍国际交互联网上最新流行的XML技术在机械工程方面的应用。介绍了XML的基本概念和应用背景,分析了XML的特点和优势,着重介绍了XML在机械工程各方面的应用并给出了应用实例。还介绍了国外研究XML的一些相关结构的研究方向和成果,最后,展望了XML的最新动向和在机械工程领域广阔的应用前景。     

分形理论在机械领域的应用现状

概述了分形理论的基本概念及其发展，指出在自然科学、了分形理论在机械工程的切削加工、机构学、焊接和铸造过程、应用现状。社会科学等各个领域分形理论都获得广泛的应用。综述机械系统运动状态分析和故障诊断、制造业信息化中的应用现状。     

机械天平新规程的理解和应用

本文描述了JJG98-2006《机械天平》新规程内容的变化以及对新规程的理解,并结合实际工作提出了具体应用方法.     

Design characteristics for temporomandibular joint disc tissue engineering: learning from tendon and articular cartilage

Tissue engineering of chondrocytic or fibroblastic musculoskeletal tissues has been relatively well studied compared with that of the temporomandibular joint (TMJ) disc. Early attempts at tissue engineering the disc have been misguided owing to a lack of understanding of the composition and function of the TMJ disc. The objective of this review is to compare the TMJ disc with a chondrocytic tissue (hyaline articular cartilage) and a fibroblastic tissue (tendon) to understand better the properties of this fibrocartilaginous tissue. The TMJ disc has 25 times more glycosaminoglycan (GAG) per dry weight than tendon but half that of articular cartilage. The disc's tensile modulus is six times more than cartilage but orders less than tendon. The GAG content and tensile modulus suggest that the TMJ disc is characterized as a tissue between hyaline cartilage and tendon, but the disc appears more tendon like when considering its collagen make-up and cell content. Like tendon, the TMJ disc contains primarily collagen type I at 85 per cent per dry weight, while articular cartilage has 30 per cent less collagen, which is type II. Knowledge of quantitative comparisons between joint tissues can give extensive insight into how to improve tissue engineering of the TMJ disc.     

半物理仿真系统在机械工程控制器中的应用

工程机械控制器是工程机械的核心部件之一,但是由于工程机械工作环境差,负载变化大,功率大,无疑加大工程机械控制器的软硬件的设计难度。半物理仿真技术是验证控制系统方案的正确性和可行性的一个有力的工具,因此对工程机械控制器半物理仿真系统进行了研究并构建工程机械控制器半物理仿真体系。     

小波神经网络及其在机械工程领域中的应用

介绍小波神经网络的结构形式及其在机械工程领域的主要应用,并指出今后的发展趋势和需要深入探索的课题.     

机械密封可控性研究及其工程应用问题的探讨

从理论和实践两方面分析了机械密封可控性研究工程应用的可行性。对前人研究成果归纳总结表明,机 械密封的控制参数主要有端面温度、膜厚、摩擦转矩、泄漏量和端面比压,执行机构主要有电磁铁和调节阀和 液压缸等形式。同时指出带有端面温度测量传感器的静环,结构复杂、安装不便;端面膜厚测量可信度低;主 轴间串联传感器测量扭矩只适合于无负荷机械密封测试。根据生产装置上应用的机械密封控制系统的工作要 求,提出了由机械密封、转矩传感器、空心O形密封圈、信号调节器、中央处理器和执行器组成的机械密封控 制系统。     

多Agent系统的研究进展及其在机械制造领域的应用

Agent技术和多Agent系统是目前学术和工程领域的研究热点,在越来越广泛的领域得到了应用。本文首先对Agent技术的概念和特点进行了总结,介绍了Agent和多Agent系统的体系结构、程序设计语言及其开发工具的发展历程,并叙述了目前最广为接受的Agent建立规范——FIPA（Foundation for Intelligent Physical Agents）规范。进而对国内外开发的多Agent系统开发平台进行了总结,并分析了目前多Agent系统在机械制造领域的应用状况,最后对其发展趋势进行了展望。     

反求工程技术在新产品开发中的应用

介绍了反求工程的基本概念和体系结构,着重阐述了反求工程中的两种基本设计方法及其具体实施过程,分析了其实施过程中所运用的CAD/CAE/CAM等计算机辅助技术,以及如何根据测量中所得到的数字化数据构建出实体模型,从而开发出新产品。     

机械光学混合测量法在复杂结构逆向工程中的应用研究

探讨了如何融合CMM(三坐标测量仪)和Photogrammetry(摄影测量)两种技术,来生成用来拼接点云数据（point cloud)的参考点系统(reference pointsystem),同时给出了一种更为简便的坐标变换方法。该融合技术可以有效地应用在对复杂结构的逆向工程中。     

数字样机技术在复杂产品工程设计中的应用研究

简要介绍了数字样机技术的特点和意义,给出了数字样机技术的应用现状,结合复杂产品工程设计的特点,分析了复杂产品工程设计阶段的对数字样机平台的需求,确定了数字样机平台功能分析。基此分析了数字样机平台的总体框架和逻辑架构,重点分析了设计验证与优化、设计协同、维护支持的实现方法,给出了数字样机技术的部分应用示例。结合已开展的研究工作和存在的问题,探讨了下一步急需开展的研究工作。     

基于CATIA的机械零件虚拟装配方法

装配在机械零件设计和机械系统设计占有重要作用。随着计算机软硬技术的发展。机械装配在个人计算机上也能够实现。以管道阀门为例,介绍基于CATIA的兰维实体装配的基本方法,着重强调装配模型的干涉检验等全过程。     

机械虚拟现实技术的应用与发展

为了提高机械虚拟现实技术在机械工程领域的发展速度和水平,文章阐述了虚拟现实技术的内涵、系统的基本构成及其在机械工程领域的作用,探讨了虚拟现实技术在机械工程中的应用现状、发展趋势及其面临的技术挑战以及应对挑战的技术建议或措施.     

A comparison of imaging methodologies for 3D tissue engineering

Imaging of cells in two dimensions is routinely performed within cell biology and tissue engineering laboratories. When biology moves into three dimensions imaging becomes more challenging, especially when multiple cell types are used. This review compares imaging techniques used regularly in our laboratory in the culture of cells in both two and three dimensions. The techniques reviewed include phase contrast microscopy, fluorescent microscopy, confocal laser scanning microscopy, electron microscopy, and optical coherence tomography. We compare these techniques to the current "gold standard" for imaging three-dimensional tissue engineered constructs, histology.     

A Galerkin-type finite element solution for simulation of mass diffusion in the application of tissue engineering: heterogeneous and non-porous media

This study is an effort to produce a generic and comprehensive solution to the simulation of mass diffusion through a multiphasic and heterogeneous material model. A Galerkin-type finite element formulation is developed to solve Fick's equation for steady-state and time-dependent analysis. The effect of the interface in modelling of a liquid-solid medium is presented in this work. To show the robustness of the proposed approach, the gas exchange (oxygen and carbon dioxide) process through the capillary network between the alveolar membrane and red blood cells has been analysed and then validated with experimental data. The current work is a significant asset to modelling the diffusion of oxygen between cells and scaffolds in tissue engineering or tissue regeneration/repair studies. It is one step towards the development of high-order elements for application of the simulation of mass transfer through a multiphasic and porous model with varying degrees of interconnectivity and pore size for tissue engineering applications.     

A new tracking technique for mechanical angle measurement

Resolvers and other types of sine/cosine encoders are used for measurement of mechanical angles. These devices produce quadrature signals in the form of sine and cosine of the unknown angle, and require converters to extract the angle from their signals. This paper describes a new converter based on an angle-tracking technique that employs synchronized reference and oscillatory signals. The tracking is based on quadrature PLL without using VCO, DAC, counter and look-up tables (LUT). The proposed method makes use of reference oscillatory signals to estimate the sine/cosine of the mechanical angle. The present method is simpler than the available techniques, and may be implemented easily using digital or basic analogue electronic circuitry. Beside its simplicity of implementation and its fast tracking capability, the proposed controller exhibits a good linearity and, when used with resolvers, offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The proposed technique results were compared to a high resolution pulse encoder. This paper describes the proposed method, its simulation and experimental results.     

A new method for determining the mechanical stability of lubricating greases

Mechanical stability is of central importance when dealing with the long-term service-length of grease-lubricated roller bearings. Poor stability will lead to consistency degradation of the grease, because of mechanical forces between the rolling parts of the bearing. The result can be leakage of grease through seals, or at worst a total failure of the bearing. The present investigation was initiated because present-day methods for prediction of mechanical stability show weak correlation with real service-length. The aim of the project was to develop a useful alternative. In order to fulfil this, both field tests and laboratory tests were carried out. In the field tests, nine different commercial greases were examined in the wheel bearings of five ore waggons, used for transporting ore by railroad from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. The test ore waggons travelled a distance of about 300,000 km during a period of 3 years. Small samples of greases were taken, on eight different occasions, for consistency testing. After the end of the test period, the damage on the bearings was also studied. In the laboratory tests, new undestroyed greases of the same brand as in the field tests were examined using conventional methods, such as the V2F, the Roll Stability Test and the Grease Worker. Comparisons between the field tests and these laboratory tests indicate poor correlation. In addition to these conventional methods, the relevance of the shear strength of the greases to the prediction of the mechanical stability was also tested. The shear stress τ_L depends on the applied pressure p, thus τ_L=τ₀+γ·p where τ₀ is the shear stress at atmospheric pressure. γ is a property of the lubricant in the same way as viscosity or density. It was found that γ correlates well with the mechanical stability in service. Increased γ values lead to a decrease in the mechanical stability. One reasonable explanation is that high γ values correspond to high shear stresses in the grease, and thus severe conditions for the thickener.