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.     

Ion-beam irradiation into biodegradable nanofibers for tissue engineering scaffolds

Tissue engineering scaffolds require cell affinity, biodegradability, and desirable mechanical properties. Poly-_L-lactic acid (PLLA) has been investigated for tissue engineering scaffolds owing to its biodegradability and mechanical strength. Electrospun fibers have large surface area and the fibrous structure provides necessary properties for cell attachment, proliferation, differentiation, and sufficient stiffness. PLLA fibers were irradiated with Kr⁺ at an energy of 50 keV with fluences of 1 × 10¹³, 1 × 10¹⁴, and 1 × 10¹⁵ ions/cm² to improve cell affinity. Morphological change was observed by scanning electron microscopy (SEM). Surface properties were measured by FT-IR-ATR and Raman spectroscopy. L929 cell attachment to Kr⁺-irradiated fibers was evaluated. After the irradiation, the average fiber diameter decreased with high fluence. From the results of the surface analyses, the original chemical bonds were broken and new carbon structures were induced. L929 cell attachment was dramatically improved compared with non-irradiated fibers. Thus, ion-beam irradiated fibers are suitable for tissue engineering scaffolds. This technique is expected to be useful in repairing defects, such as those in nerve, vascular, and liver, in regenerative medicine.     

Fabrication of porous scaffolds for bone tissue engineering via low-temperature deposition

A new process of low-temperature deposition manufacturing (LDM) based on the layer-by-layer manufacturing method of solid freeform fabrication is proposed to fabricate poly(l-lactic acid)/(tricalcium phosphate) composite scaffolds for bone tissue engineering. The LDM system and the manufacturing process are analyzed. The manufactured scaffolds are evaluated as bone regeneration scaffolds.     

A plasma-assisted bioextrusion system for tissue engineering

A challenge for tissue engineering is to produce synthetic scaffolds of adequate chemical, physical and biological cues effectively. This paper describes a plasma-assisted bio-extrusion system to produce functional-gradient scaffolds; it comprises pressure-assisted and screw-assisted extruders, and plasma jets. This paper also describes how the system conducts plasma surface modification during the polycaprolactone scaffold fabrication process. Water contact angle and in vitro biological tests confirm that the plasma modification alters the hydrophilicity properties of synthetic polymers and promotes proliferation of cells, leading to homogeneous cell colonization. The results suggest this system is promising for producing functional gradient scaffolds of biomaterials.     

Directionally solidified biopolymer scaffolds: Mechanical properties and endothelial cell responses

Vascularization is a primary challenge in tissue engineering. To achieve it in a tissue scaffold, an environment with the appropriate structural, mechanical, and biochemical cues must be provided enabling endothelial cells to direct blood vessel growth. While biochemical stimuli such as growth factors can be added through the scaffold material, the culture medium, or both, a well-designed tissue engineering scaffold is required to provide the necessary local structural and mechanical cues. As chitosan is a well-known carrier for biochemical stimuli, the focus of this study was on structure-property correlations, to evaluate the effects of composition and processing conditions on the three-dimensional architecture and properties of freeze-cast scaffolds; to establish whether freeze-east scaffolds are promising candidates as constructs promoting vascularization; and to conduct initial tissue culture studies with endothelial cells on flat substrates of identical compositions as those of the scaffolds to test whether these are biocompatible and promote cell attachment and proliferation.     

Parametric analysis of weld toe stress concentration in longitudinal attachments

Synopsis: A parametric FEM study was undertaken in order to evaluate the influence of the main geometric parameters on the weld toe stress concentration in longitudinal attachments.

The numerical model was prepared on the basis of the results of a number of experimental tests. A simple formula is proposed for determining the stress intensity factor for these types of joint as a function of the main geometrical parameters.

Based on the proposed formula, the influence of these parameters on the fatigue life of such joints is evaluated and discussed.     

用于骨组织工程的镁基泡沫生物材料的制备与体外降解行为

采用熔体发泡法制备了一种镁基泡沫生物材料,其中以镁钙合金为基体材料,羟基磷灰石(HA)为增粘剂,以碳酸镁(MgCO3)为发泡剂。对结构均匀的镁基泡沫生物材料进行测试,研究其生物可降解行为。用腐蚀前后孔结构、浸泡试验和电化学测试对镁基泡沫材料的生物可降解性进行表征。结果表明,在固定时间内随着试样孔隙率的增加,失重率不断增加;相比于添加了羟基磷灰石(HA)的样品,不含HA颗粒地样品呈现出更高质量损失率。同时,Mg基泡沫生物材料的总孔隙率和羟基磷灰石(HA)含量均对Mg基泡沫材料的开孔率有重要的影响。在相同时间内,开孔率随试样总孔隙率的增加而增加。在模拟体液(SBF)介质中,含有羟基磷灰石(HA)的Mg基泡沫生物材料比不添加羟基磷灰石(HA)的试样具有更高的耐腐蚀性。     

A multi-textured calcium phosphate coating for hard tissue via laser surface engineering

Surface engineering continues to play an important role in improving the biocompatibility of hard tissue replacements. Recently, the hierarchical organization of natural biomaterials has been realized as an important property that guides the attachment of tissues, cells, and proteins at various levels of interactions. Currently, researchers are focusing interest on developing hierarchical bioactive structures for effective osseointegration. The present effort discusses a multi-textured calcium-phosphate-based coating produced by laser surface engineering. The chemical and morphological evolution of these bio-actively textured coatings was studied along with biomimetic precipitation of calcium phosphates when immersed in simulated body fluids.     

Production and fluoride treatment of Mg-Ca-Zn-Co alloy foam for tissue engineering applications

Highly porous Mg-Ca-Zn-Co alloy scaffolds for tissue engineering applications were produced by powder metallurgy based space holder-water leaching method. Mg-Ca-Zn-Co alloy foam can be used as a scaffold material in tissue engineering. Carbamide was used as a space holder material. Fluoride conversion coating was synthesized on the alloy by immersion treatment in hydrofluoric acid (HF). Increasing Zn content of the alloy increased the elastic modulus. Ca addition prevented the oxidation of the specimens during sintering. Electrochemical corrosion behaviour of the specimens was examined in simulated body fluid. Corrosion rate decreased with Zn addition from 1.0% up to 3.0% (mass fraction) and then increased. Mass loss of the specimens initially decreased with Zn addition up to about 3% and then increased. Fluoride conversion coating increased the corrosion resistance of the specimens.     

Degradation phenomena of magnetic attachments used clinically in the oral environment

The purpose of this study was to investigate the mechanisms involved in the failure of magnetic attachments used to retain dental prostheses. Dyna magnets were retrieved from dentures that had failed after 34 months of clinical use. These magnetic attachments were prepared and sectioned so as to observe the corrosion surface and layer in order to analyze the corrosion behaviors of the attachments. The corroded surface was observed under a field emission scanning electron microscope (FE-SEM) (JSM 840A, JEOL, Japan). An X-ray diffractometer (XRD) was used to analyze the corrosion product formed due to corrosion in the oral environment. Erosion-corrosion started in the uneven portion of the stainless steel cover in the magnetic attachments composed with Nd−Fe−B alloy. Corrosion was initiated on the worn stainless steel surface, followed by spalling of magnetic material due to corrosive solution. The corrosion rate increased drastically after the corrosion product caused spalling in Nd−Fe−B alloy. Corrosion initiated in the uneven stainless steel surface as well as in the welded zone. In conclusion, the failure of magnetic attachments may occur by either welding failure or breakdown of the encapsulating material. Thus, we believe that treating the surface of magnetic attachments would resolve the corrosion problem seen in magnetic attachments to some extent.     

Mechanical properties of AM Ti6Al4V porous scaffolds with various cell structures

Porous scaffolds as succedaneum of natural bone were investigated and applied in medical field.In this work, we carried out studies on mechanical properties of solid parts and porous scaffolds obtained by additive manufacturing(AM) technique.It is found that productions of AM process have a higher yield strength and higher microhardness compared to commercial Ti6Al4V.Roughened surface was observed for layer-by-layer process of AM and sticking of powder particles.The machining accuracy is affected by both dimensions and angles.Meanwhile, mechanical properties of porous scaffolds are influenced by machining accuracy and microdefects.In addition, the unit cell structures also impact the mechanical properties of porous scaffolds in terms of elastic modulus, yield strength and failure mode.Overall,considering the mechanical properties and biological properties, scaffolds with cube(CB) crystal cells are the best choice in our study.     

BioCell Printing: Integrated automated assembly system for tissue engineering constructs

The production methodology of 3D constructs for tissue regeneration is usually a complex discontinuous process involving three different stages: (1) production of 3D matrices; (2) matrix sterilisation and cell seeding; (3) in vitro dynamic cell culture. This paper presents a novel automated bench-top manufacturing system called BioCell Printing, designed for the integrated, continuous and fully automated production and in vitro dynamic culture of tissue engineering constructs. The BioCell aims at the rapid production of tissue-engineered substitutes with low risk of contamination, increasing the chances of direct clinical application.     

有限元法在机电工程中的应用

本文在有限元法基本思路的基础上，介绍了有限元的优越性及其发展趋势，研究了有限元法在机电工程中的应用情况。     

再制造工程和表面工程对循环经济贡献分析

阐述了再制造工程在循环经济中的地位和发展背景,剖析了废旧发动机在材料水平、零件水平和整机水平循环利用的节能效益和环保效益,讨论了再制造工程与表面工程的关系。研究表明,以再制造方式实施整机水平的循环利用,其节能效益和环境保护效益最佳,再制造1万台废旧发动机可节电1.45×108kWh,减少CO2排放0.6kt;表面工程在发动机再制造中的应用,可使发动机的旧件利用率由72.3%提高到90%。     

Applying texture analysis to materials engineering problems

Textures in materials have been studied extensively since the 1930s following the pioneering work of Wassermann.^1,2 The modern era of texture measurement started in 1949 with the development of the x-ray pole figure technique for texture measurement by Schultz.³ Finally, modern texture analysis was initiated with the publication by Bunge⁴ and Roe⁵ of a mathematical method of pole figure inversion, which is now used to calculate the orientation distribution function (ODF). This article cannot summarize such an extensive body of work, but it does endeavor to provide the background necessary to understand texture analysis; it also illustrates several applications of texture.     

EPC工程总承包管理中设计的思考

概述了工程设计与EPC工程总承包的关系;分析了EPC工程总承包管理模式（以下简称EPC模式）下设计工作的特点和要求;针对目前设计在工程总承包项目中存在的不足。提出了在EPC模式下对设计工作的几点建议;阐述了逐步完成传统设计管理体制向现代国际工程公司方向观念和意识的转变。尽快建立适应EPC模式特点的新型工程设计管理体制。充分发挥设计的核,心作用和优势。使设计工作逐步纳入EPC工程总承包管理的重要性和意义。     

On equilibrium solutions to joint optimization problems in engineering design

Seeking optimal solutions has been one of important tasks in engineering design. Design optimization problems have normally been formulated by aggregating diverse criteria into one single objective function subject to a set of constraints. There is a growing number of engineering systems, however, involving coupling of multiple optimization problems that are competing in nature and yet must simultaneously satisfy various conflicting objectives. Such joint optimization of multiple competing optimization problems is very difficult, if not impossible, to be modelled and solved with traditional multi-objective optimization methods. This paper presents an approach to joint optimization problems based on a Stackelberg game to achieve equilibrium solutions that leverage upon multiple conflicting goals of design.