Atomic precision manufacturing of carbon nanotube-a perspective

Carbon nanotube(CNT),particularly single-walled CNT,possesses exceptional properties,and can be utilized in many high-end applications including high-performance electronics.However,the atomic arrangement of a CNT determines its band structure,making the atomic-precision fabrication one of most important topics for the development of this material.In this perspective,the author gives a personal summary on the history,current status of the atomic-precision fabrication of CNT and outlines the remaining challenges as well as the possible paths that may lead the production of atomically precise CNTs from‘fabrication’to‘manufacturing’.

A Large Range Flexure-Based Servo System Supporting Precision Additive Manufacturing

This paper presents the design, development, and control of a large range beam flexure-based nano servo system for the micro-stereolithography （MSL） process. As a key enabler of high accuracy in this process, a compact desktop-size beam flexure-based nanopositioner was designed with millimeter range and nanometric motion quality. This beam flexure-based motion system is highly suitable for harsh operation conditions, as no assembly or maintenance is required during the operation. From a mechanism design viewpoint, a mirror-symmetric arrangement and appropriate redundant constraints are crucial to reduce undesired parasitic motion. Detailed finite element analysis （FEA） was conducted and showed satisfactory mechanical features. With the identified dynamic models of the nanopositioner, real-time control strategies were designed and implemented into the monolithically fabricated prototype system, demonstrating the enhanced tracking capability of the MSL process. The servo system has both a millimeter operating range and a root mean square （RMS） tracking error of about 80 nm for a circular traiectorv.

Topography Measurement for Monitoring Manufacturing Processes in Harsh Conditions

High precision manufacturing, e.g. milling and grinding, which have manufacturing tolerances in the range of <10 μm require microscopic measurement techniques for the inspection of the manufactured components. These measurement techniques are very sensitive to cooling liquids and lubricants which are essential for many manufacturing processes. Therefore, the measurement of the components is usually conducted in separate and clean laboratories and not directly in the manufacturing machine. This approach has some major drawbacks, e.g. high time consumption and no possibility for online process monitoring. In this article, a novel concept for the integration of high precision optical topography measurement systems into the manufacturing machine is introduced and compared to other concepts. The introduced concept uses a reservoir with cooling liquid in which the measurement object is immersed during the measurement. Thereby, measurement disturbance by splashing cooling liquids and lubricants can effectively be avoided.

基于变形力监测数据的残余应力场推断和表征方法

残余应力是材料的基本属性之一,与零件的几何形状、尺寸稳定性和疲劳寿命直接相关。针对具有高精度要求的大型零件,其残余应力场的准确测量和预测一直是一个挑战。目前的残余应力场测量技术可以分为基于应变的破坏性方法和基于射线、声波等物理量的非破坏性方法,但均受限于测量效率和精度,且难以得到工件的整体残余应力场。针对以上问题,本文提出了一种基于加工过程中的变形力监测数据推断工件整体残余应力场的新方法。本方法通过能够反映去除材料后不平衡残余应力场整体效应的变形力推断零件的残余应力场。利用虚功原理建立了变形力与残余应力场之间的力学关系,并引入正则化方法求解整体残余应力场。理论验证和实际实验测试结果均表明,该方法对于大型结构件的残余应力场测量具有可靠的精度和灵活性。在数字化和智能制造的趋势下,该方法的基本原理为利用加工监测数据预测和补偿由残余应力引起的零件加工变形提供了重要参考。

Controlled Vertical Transfer of Individual Au Atoms Using a Surface Supported Carbon Radical for Atomically Precise Manufacturing

To explore a proof-of-concept for atomically precise manufacturing(APM)using scanning probe microscopy(SPM),first principle theoretical calculations of atom-by-atom transfer from the apex of an SPM tip to an individual radical on a surfacebound organic molecule have been performed.Atom transfer is achieved by spatially controlled motion of a gold terminated tip to the radical.Two molecular tools for SPM-based APM have been designed and investigated,each comprising an adamantane core,a radical end group,and trithiol linkers to enable strong chemisorption on the Au(111)surface:ethynyl-adamantanetrithiol and adamantyl-trithiol.We demonstrate the details of controlled Au atom abstraction during tip approach toward and retraction from the radical species.Upon approach of the tip,the apical Au atom undergoes a transfer toward the carbon radical at a clearly defined threshold separation.This atomic displacement is accompanied by a net energy gain of the system in the range−0.5 to−1.5 eV,depending on the radical structure.In the case of a triangular pyramidal apex model,two tip configurations are possible after the tip atom displacement:(1)an Au atom is abstracted from the tip and bound to the C radical,not bound to the tip base anymore,and(2)apical tip atoms rearrange to form a continuous neck between the tip and radical.In the second case,subsequent tip retraction leads to the same final configuration as the first,with the abstracted Au atom bound to radical carbon atom of the molecular tool.For the less reactive adamantyl-trithiol radical molecular tool,Au atom transfer is less energetically favored,but this has the advantage of avoiding other apex gold atoms from rearrangement.

State of the art of bioimplants manufacturing： part I

Bioimplants are becoming increasingly impor-tant in the modem society due to the fact of an agingpopulation and associated issues of osteoporosis andosteoarthritis. The manufacturing of bioimplants involvesan understanding of both mechanical engineering andbiomedical science to produce biocompatible products withadequate lifespans. A suitable selection of materials is theprerequisite for a long-term and reliable service of thebioimplants, which relies highly on the comprehensiveunderstanding of the material properties. In this paper,most biomaterials used for bioimplants are reviewed. Thetypical manufacturing processes are discussed in order toprovide a perspective on the development of manufacturingfundamentals and latest technologies. The review alsocontains a discussion on the current measurement andevaluation constraints of the finished bioimplant products.Potential future research areas are presented at the end ofthis paper.

State of the art of bioimplants manufacturing： part II

The manufacturing of bioimplants not only involves selecting proper biomaterials with satisfactory bulk physicochemical properties, but also requires special treatments on surface chemistry or topography to direct a desired host response. The lifespan of a bioimplant is also critically restricted by its surface properties. Therefore, developing proper surface treatment technologies has become one of the research focuses in biomedical engineering. This paper covers the recent progress of surface treatment of bioimplants from the aspects of coating and topography modification. Pros and cons of various tech- nologies are discussed with the aim of providing the most suitable method to be applied for different biomedical products. Relevant techniques to evaluate wear, corrosion and other surface properties are also reviewed.

Research on Bipolar Pulse Current Electroforming in Precision Molds and Dies

Electroforming is a specialised electroplating process for the manufacture of precision metal parts and mold tooling. Because it can simplify technical process and shorten molding cycles, electroforming is also a rapid manufacturing technology. Compared with direct and unipolar pulse current, bipolar pulse current in electroforming can obtain fine structure and grain size as well as surface leveling, resulting in better precision and surface finish. In this paper, bipolar pulse current electroforming is introduced. The influencing parameters such as electrolyte parameter, additives, current density, pH, temperature, and pulse parameters have been studied by experiments. Experiments on nickel electroforming in molds and dies have been done. The results indicated that bipolar pulse current electroforming could improve the quality and precision further, while reducing internal stress.

Bone tissue regeneration:The role of finely tuned pore architecture of bioactive scaffolds before clinical translation

Spatial dimension of pores and interconnection in macroporous scaffolds is of particular importance in facilitating endogenous cell migration and bone tissue ingrowth.However,it is still a challenge to widely tune structure parameters of scaffolds by conventional methods because of inevitable pore geometrical deformation and poor pore interconnectivity.Here,the long-term in vivo biological performances of nonstoichiometric bioceramic scaffolds with different pore dimensions were assessed in critical-size femoral bone defect model.The 6%Mg-substituted wollastonite(CSi-Mg6)powders were prepared via wet-chemical precipitation and the scaffolds elaborately printed by ceramic stereolithography,displaying designed constant pore strut and tailorable pore height(200,320,450,600μm),were investigated thoroughly in the bone regeneration process.Together with detailed structural stability and mechanical properties were collaboratively outlined.BothμCT and histological analyses indicated that bone tissue ingrowth was retarded in 200μm scaffolds in the whole stage(2-16 weeks)but the 320μm scaffolds showed appreciable bone tissue in the center of porous constructs at 6-10 weeks and matured bone tissue were uniformly invaded in the whole pore networks at 16 weeks.Interestingly,the neo-tissue ingrowth was facilitated in the 450μm and 600μm scaffolds after 2 weeks and higher extent of bone regeneration and remodeling at the later stage.These new findings provide critical information on how engineered porous architecture impact bone regeneration in vivo.Simultaneously,this study shows important implications for optimizing the porous scaffolds design by advanced additive manufacture technique to match the clinical translation with high performance.

Integrating pore architectures to evaluate vascularization efficacy in silicate-based bioceramic scaffolds

Pore architecture in bioceramic scaffolds plays an important role in facilitating vascularization efficiency during bone repair or orbital reconstruction.Many investigations have explored this relationship but lack integrating pore architectural features in a scaffold,hindering optimization of architectural parameters(geometry,size and curvature)to improve vascularization and consequently clinical outcomes.To address this challenge,we have developed an integrating design strategy to fabricate different pore architectures(cube,gyroid and hexagon)with different pore dimensions(-350,500 and 650 lm)in the silicate-based bioceramic scaffolds via digital light processing technique.The sintered scaffolds maintained high-fidelity pore architectures similar to the printing model.The hexagon-and gyroid-pore scaffolds exhibited the highest and lowest compressive strength(from 15 to 55MPa),respectively,but the cube-pore scaffolds showed appreciable elastic modulus.Moreover,the gyroid-pore architecture contributed on a faster ion dissolution and mass decay in vitro.It is interesting that bothμCT and histological analyses indicate vascularization efficiency was challenged even in the 650-μm pore region of hexagon-pore scaffolds within 2weeks in rabbit models,but the gyroid-pore constructs indicated appreciable blood vessel networks even in the 350-μm pore region at 2weeks and high-density blood vessels were uniformly invaded in the 500-and 650-μm pore at 4weeks.Angiogenesis was facilitated in the cube-pore scaffolds in comparison with the hexagon-pore ones within 4weeks.These studies demonstrate that the continuous pore wall curvature feature in gyroid-pore architecture is an important implication for biodegradation,vascular cell migration and vessel ingrowth in porous bioceramic scaffolds.