The essential materials paradigms for regenerative medicine

Medical technology is changing rapidly. Several disease states can now be treated very effectively by implantable devices that restore mechanical and physical functionality, such as replacement of hip joints or restoration of heart rhythms by pacemakers. These techniques, however, are rather limited, and no biological functionality can be restored through the use of inert materials and devices. This paper explores the role of new types of biomaterials within the emerging area of regenerative medicine, where they are able to play a powerful role in persuading the human body to regenerate itself.     

Zirconium-based composites for orthopedic applications

A relatively new composite material consisting of a ZrC matrix reinforced by ZrB₂ platelets and containing residual zirconium exhibits a combination of high strength, fracture toughness, and specific stiffness. In preliminary tests, this material compared favorably to the commonly used implant alloys Ti-6Al-4V and Co-Cr-Mo. In addition, the results of wear tests on this material against ultrahigh-molecular-weight polyethylene indicate promising results for use in orthopedic devices.     

Calcium phosphate scaffolds for bone repair

Calcium phosphates, with their chemical similarity to bone mineral, show biocompatibility with hard and soft tissues and offer massive potential for bone repair, both as scaffolds to be implanted directly into the defect and as structures for cell transplantation or to guide new bone growth in tissue engineering. This paper reviews the requirements and motivation for synthetic bone graft alternatives and the production routes for, particularly, hydroxyapatite porous scaffolds. It also considers the important role of substitution of ions such as silicate into calcium phosphates so as to more closely mirror the chemistry of bone mineral and to elicit specific biological responses.     

Bioactive Ca-P scaffolds used for bone reconstruction

1　INTRODUCTIONSkeletalreconstructionorregenerationisre quiredincasesinvolvinglargedefectscreatedbytu morresection ,trauma ,andskeletalabnormalities .Graftsandflapsofautogenoustissuearetwoofthemostsuccessfulmeansofreconstructionbecausetheyallowthetransplantationofbonecontainingbioactivemolecules,livecells ,andfrequently ,avascularsup plythatallowthetransplanttosurviveandremodeleveninhostileradiatedenvironments .However ,onlyaminimalamountoftissuecanbeharvestedforauto grafts,anditisverydiff…     

Three-dimensional chitosan-nanohydroxyapatite composite scaffolds for bone tissue engineering

We describe the structure of biodegradable chitosan-nanohydroxyapatite (nHA) composites scaffolds and their interaction with pre-osteoblasts for bone tissue engineering. The scaffolds were fabricated via freezing and lyophilization. The nanocomposite scaffolds were characterized by a highly porous structure and pore size of ∼50–125 μm, irrespective of nHA content. The observed significant enhancement in the biological response of pre-osteoblast on nanocomposite scaffolds expressed in terms of cell attachment, proliferation, and widespread morphology in relation to pure chitosan points toward their potential use as scaffold material for bone regeneration.     

Novel nanostructured hydroxyapatite coating for dental and orthopedic implants

A novel hybrid coating process, combining NanoSpray® (built on electrostatic spray coating) technology with microwave sintering process, was developed for synthesizing hydroxyapatite- (HA-) based nanostructured coating with favorable properties for dental and orthopedic implants. Specifically, HA nanoparticles were deposited on commercially pure titanium substrates using NanoSpray technique to produce the HA coating, which was then sintered in a microwave furnace under controlled conditions. The study showed that the use of NanoSpray followed by microwave sintering results in nanoscale HA coating for dental/orthopedic application.     

A new perspective and analysis for regenerative machine tool chatter

The paper contains a practical perspective on regenerative machine tool chatter. Chatter is a well known phenomenon, occurrence of which is undesired in manufacturing. Aggressive machining conditions, in the sense of removing more metal rapidly, usually cause chatter. In most cases, these conditions can be determined a priori to the operation. A chatter stability study and its reasoning based on root locus plot analysis of time delayed systems is presented as a new and practical perspective in the field. At the junction of root locus and chatter concepts an area of particular interest to the authors arises: a new method for active vibration suppression, the Delayed Resonator. It is an active vibration absorber tuning of which is achieved utilizing a simple time delayed feedback. The cross linking between the Delayed Resonator study and the subject matter, machine tool chatter, is exciting to share. This is the primary motivation in pursuing this study. One of the highlights of the work appears at the phenomenon called Dual Frequency Delayed Resonator. This feature has been conjectured in the literature using the well known “stability lobes”, but never discussed with detail.     

高温蓄热式锻造加热炉喷口参数的设计

基于传热学及燃烧学,利用有限元分析软件Fluent对某高温蓄热式锻造加热炉内的流场进行了稳态数值模拟研究.通过对烧嘴喷口间距离及喷口角度对炉温及出口烟气浓度的影响分析,获得了加热炉中温度场及污染物的排放情况.结果表明,烧嘴喷口间距离及喷口角度对炉温及污染物的排放量影响均较大;对于本文所研究的某高温蓄热式双室锻造加热炉而言,其最佳喷口间距离为900 mm、最佳喷口角度为0°.     

Optimisation of variable helix tool geometry for regenerative chatter mitigation

It is well known that regenerative chatter can result in excessive tool wear, poor surface finish, and hence limited productivity during metal machining. Various mitigation methods can be applied to suppress chatter; however, the current paper focuses on applying optimal variable helix tool geometry. A semi-discretisation method is combined with Differential Evolution to optimise variable helix end milling tools so as to avoid chatter by modifying the variable helix and variable pitch tool geometry. The semi-discretisation method is first validated experimentally. The numerical optimisation procedure is then used to optimise tool geometry for a machining problem involving a flexible workpiece. The analysis predicted total mitigation of chatter using the optimised variable helix milling tool at a low radial immersion. However, in practice a five fold increase in chatter stability was obtained, compared to the traditional milling tool.     

Biomanufacturing of customized modular scaffolds for critical bone defects

There is a significant unmet clinical need for modular and customized porous biodegradable constructs (scaffolds) for non-union large bone loss injuries. This paper proposes modelling and biomanufacturing of modular and customizable porous constructs for patient-specific critical bone defects. A computational geometry-based algorithm was developed to model modular porous constructs using a parametric femur model based on the frequency of common injuries. The generated modular constructs are used to generate biomimetic path planning for three-dimensional (3D) printing of modular scaffold pieces. The developed method can be used for regenerating bone tissue for treating non-union large bone defects.     

蓄热式加热炉的维护

以唐山钢铁股份有限公司中型厂蓄热式加热炉为例，对影响加热炉使用的蓄热体板结、蓄热室漏火漏气，以及换向阀不到位的问题进行了分析，并介绍了解决其问题的有效措施。     

湿化学法制备磷酸钙/胶原复合材料

人体自然骨的缺损,如断裂、畸变等,形成了对骨替代材料的巨大需求.磷酸三钙/胶原复合材料兼顾了磷酸三钙的生物降解性和胶原的韧性、同时具有良好的生物相容性,正逐渐成为骨替代材料研究的焦点.采用新的合成方法合成出粒径较小的β-TCP颗粒,在pH=2的条件下制备出β-TCP颗粒均匀分布在胶原上的复合材料,并对复合材料的结构进行了研究.     

Modeling regenerative workpiece vibrations in five-axis milling

During milling—especially of thin-walled components—the dynamic behavior of the workpiece-tool-machine-system influences the milling process and particularly the quality of the resulting workpiece surface. This article focuses on the presentation of a simulation concept for predicting regenerative workpiece vibrations, which combines a finite element model for analyzing the dynamic behavior of the workpiece with a time domain simulation for the five-axis milling process. Both concepts, their linking, and the experimental setup for verifying the simulation will be described. A comparison of the simulation results with the data measured in experiments with regard to the vibration frequencies as well as the surface quality will be given.     

Porous ceramic scaffolds with complex architectures

This work compares two novel techniques for the fabrication of ceramic scaffolds for bone tissue engineering with complex porosity: robocasting and freeze casting. Both techniques are based on the preparation of concentrated ceramic suspensions with suitable properties for the process. In robocasting, the computer-guided deposition of the suspensions is used to build porous materials with designed three dimensional geometries and microstructures. Freeze casting uses ice crystals as a template to form porous lamellar ceramic materials. Preliminary results on the compressive strengths of the materials are also reported.     

金属生物材料支架的微结构拓扑优化设计及选区激光熔化制造(英文)

生物材料支架的精确设计和制造是骨组织工程系统研究的基础。生物材料支架应该同时满足大孔隙率和与骨组织匹配的力学性能要求。这两个目标相互制约,大的孔隙率会降低其力学性能。利用拓扑优化的方法,在体积分数的约束下,寻求刚度最大的最优材料分布微结构。建立算法,得到了不同体积分数的2D和3D最优微结构,并提取3D拓扑优化的结果,然后将其转化为STL格式的CAD模型文件。微结构在三维方向整列成支架结构,通过选区激光熔化方法制造30%(体积分数)的Ti支架样品。从SEM图像看出,支架样品的结构和孔径与CAD模型基本一致,500μm微结构单元的平均孔径为231μm。复杂形状金属生物材料支架的精确制造证实了选区激光熔化技术在金属生物医学材料制造中的可行性。     

On the development of ice-templated silicon carbide scaffolds for nature-inspired structural materials

The processing of ceramic scaffolds using the ice-templating, or freeze casting, technique provides a relatively simple means to mimic the hierarchical design of natural materials such as nacre. In the present study, we investigated the architecture of silicon carbide (SiC) scaffolds produced by this technique over a range of cooling rates and suspension characteristics to demonstrate its versatility and effectiveness for fabricating unidirectional porous bodies with controlled lamella thickness, porosity fraction and morphology. An array of microstructures was generated specifically to examine the role of the suspension solid load and cooling rate on the pore morphology and final ceramic fraction. With respect to the morphology of the pores, a transition from lamellar to dendritic structure was found to be triggered by an increase in cooling rate or in suspension concentration. Similarly, the freezing condition and suspension characteristics were seen to influence the transition between particle rejection and entrapment by the ice. Based on this study, the specific processing parameters that result in distinct scaffold morphologies, namely lamellar, dendritic or isotropic morphology (the latter corresponding to particle entrapment), are identified and presented in the form of a “morphology map” to establish the regions of the different architectures of freeze-cast SiC scaffolds.     

SIMODRIVE 611再生馈电式伺服驱动的电压匹配

本文概述了西门子SIMODRIVE 611伺服驱动的再生馈电式电源的特点,并论述了如何对这种驱动进行电压匹配,指出了使用这种类型驱动时需要注意的几个问题。     

蓄热式熔铝炉的设计与应用

介绍了蓄热式熔铝炉的设计与应用情况。生产实践表明 :通过采用蓄热式燃烧技术 ,熔铝炉的油耗指标由原来的 12 0kg柴油 /t铝降为 5 4 66kg柴油 /t铝 ,节油率达 5 4 45 %。能耗指标达到了世界同类炉子的先进水平。改造投资回收期 6个月左右     

高效蓄热式工业炉及其应用

阐述了高效蓄热式工业炉（北岛炉）的原理及其应用情况。北岛炉将蓄热回收和换向式燃烧系统与炉子结合于一体,可将空气和煤气同时预热到1000℃,系统排烟温度低于150℃。在轧钢加热炉上应用,可以以纯高炉煤气为燃料,达到节能30％－50％、提高炉内温度均匀性、减少氧化烧损、保护环境的效果。