Hot tearing mechanisms of a high-entropy alloy CoCrFeNi additively manufactured by selective laser melting have been investigated. Intergranular hot cracks are present regardless of various parameters used, suggesting poor laser-based printability for the alloy. Elemental segregation does not exist at the grain boundary that favours the hot cracking. We find that severe residual stress induced by the large grain size is the root cause for the intergranular cracking. The classic Rappaz-Drezet-Gremaud model is used to predict the characteristic depression pressure limit beyond which hot tearing will occur for the selective laser melting of metals and alloys.

This work presents a comparative study on the in-situ alloying of NiTi shape memory alloys (SMAs) by directed energy deposition (DED), selective laser melting (SLM) and selective electron beam melting (SEBM) processes using pre-mixed Ni-Ti powders. The influence of process parameters on the microstructural homogeneity, phase formation and thermomechanical properties of NiTi alloy has been systematically studied. DED could build solid NiTi alloys with good interlayer fusion and phase transformation characteristics. However, a substantial amount of uniformly dispersed Ti2Ni intermetallics can embrittle this material. SLM-built NiTi parts show a tradeoff between microstructural inhomogeneity and keyhole defects when the energy densities are varied. In addition, the strong exothermic reaction in Ni-Ti powder mixtures during printing can disturb the melt pool, making it challenging to elaborate this material and obtain desired phases by using SLM. Moreover, SEBM is found to be unsuitable to in-situ synthesize this highly reactive material due to the lack-of-fusion vs. powder-ignition dilemma in the mandatory preheating step. It is suggested to adopt DED to in-situ alloy NiTi parts when using the elementally blended powders as feedstocks.

The combination of Computer Aided Design (CAD) and Rapid Prototyping (RP) system have been aiding tissue engineers in designing customized tissue scaffolds to meet the biological, mechanical and anatomical requirements. Biological requirements include suitable biomaterial and pore size for cell growth, while anatomical requirement can be fulfilled by shaping the scaffold to fit the defect site. Mechanically, scaffolds should have matching mechanical properties, such as compressive stiffness and strength, with the target organ, especially in bone regeneration, as bone is a load-bearing organ. Bone possesses stiffness gradient, depending on its function and the amount of load it needs to bear. Hence scaffolds for bone regeneration should possess stiffness gradient mimicking bone by varying the scaffold porosity and structure. This article presents the sequences on designing bone scaffolds with stiffness gradient using CASTS, which stands for Computer Aided System for Tissue Scaffolds, as a platform. As a case study, the regeneration of human mandibular cancellous bone with stiffness gradient will be presented. These sequences are to be further implemented into the current CASTS system to automate the design of Functionally Graded Scaffolds (FGS).

This letter reports the development of an optofluidic Fabry-Pérot (FP) resonator, which consists of a microcavity and a pair of liquid microlenses. The microcavity forms part of the microchannel to facilitate sample injection. The liquid microlenses are used for efficient light coupling from the optical fiber to the microcavity. The liquid microlens collimates the diverging light from the optical fiber into the FP cavity, which provides real-time tuning to obtain the highest possible finesse up to 18.79. In volume refractive index measurement, a sensitivity of 960 nm per refractive index unit (RIU) and a detection range of 0.043 RIU are achieved.

This paper presents a novel optofluidic Michelson interferometer based on droplet microfluidics used to create a droplet grating. The droplet grating is formed by a stream of plugs in the microchannel with constant refractive index variation. It has a real-time tunability in the grating period through varying the flow rates of the liquids and index variation via different combinations of liquids. The optofluidic Michelson interferometer is highly sensitive and is suitable for the measurement of biomedical and biochemical buffer solutions. The experimental results show that it has a sensitivity of 66.7 nm per refractive index unit (RIU) and a detection range of 0.086 RIU.

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Rapid prototyping (RP) has revolutionized how prototypes are made and small batch manufacturing is carried out. With rapid prototyping, the strategies used to produce a part change a number of important considerations and limitations previously faced by tool designers and engineers. Now in its third edition, this textbook is still the definitive text on RP. It covers the key RP processes, the available models and specifications, and their principles, materials, advantages and disadvantages. Examples of application areas in design, planning, manufacturing, biomedical engineering, art and architecture are also given. The book includes several related problems so that the reader can test his or her understanding of the topics. New to this edition, the included DVD-ROM presents animated illustrations of the working principles of today's key RP processes.

Rapid prototyping is an advanced technology that is widely used by engineers and manufacturers to reduce production time and cost. As the number of rapid prototyping applications continues to grow unceasingly, a need is called for to educate individuals from different knowledge backgrounds on this technology. This paper details the development of a multimedia courseware that supports professionals, senior year and graduate students in learning rapid prototyping. The courseware is designed to simulate a virtual tour to "a science museum", whereby users are free to access a topic of their needs or interests. Each display room in the museum contains one piece of information about rapid prototyping. Altogether, they present a complete image on the technology, including its definition, methodology, applications and benchmarking. Due to its efficiency and usability, a CD-ROM is used as a storage medium. Also in this paper, factors such as organization of information, control of visual and auditory components and human computer interface are discussed in terms of how they help to enhance the learning curve of rapid prototyping. This paper presents the latest version of the multimedia courseware which accompanies the third edition of the book "Rapid Prototyping: Principles & Applications". The courseware benefits not only lecturers and students but also industrial professionals who want to keep abreast with rapid prototyping cutting edge.

A novel porous Ti-6Al-4V with an open cell structure was fabricated by powder metallurgy process with the addition of TiH2 as the pore forming and active agent. Control of porosity of porous Ti alloy made it possible to obtain the porous Ti with the Young's modulus value of 5.8-9.5 GPa, which was similar to that of human cancellous bone. This kind of porous Ti alloy with good biomechanical properties is potential to alleviate the problem of mechanical mismatch between the bone and the Ti implant. The porous Ti alloy prepared by the addition of TiH2 as foaming agent had a uniform distribution of pores with pore size of 90-190 mu m and porosity of 43-59%. in order to improve the biological properties, the duplex titania/apatite coatings were applied onto the surface of porous Ti alloy. The titania coating was deposited by chemical treatment and the apatite coating was subsequently applied by immersing the samples in a simulated body fluid. Results showed that a homogeneous nanocrystallite titania coating with a thickness of 0.8 mu m was formed on the surface of the Ti alloy after chemical treatment. The carbonate-containing apatite coating with a thickness of 1 mu m was deposited on the surface of titania coating after immersion in simulated body fluid for 7 days. The nucleation of the carbonate-containing apatite can be induced front the electrostatic interaction between the OH-containing groups on the surface of titania coating and the calcium and phosphate ions in the metastable simulated body fluid on those specific superficial sites. The growth kinetics of the coatings was also discussed. Cell culture test showed the well stretched and proliferated cells on the surface of the sample, indicating the good biocompatibility of porous Ti alloy. (C) 2008 Elsevier B.V. All rights reserved.

This paper reports an integrated micro-optical fluidic system (MOFS) for the realization of long-period grating interferometer using droplet microfluidics. Comparing to normal fiber LPG, it provides a wide tuning range in the parameters of LPG, such as the grating period by changing the flow rate of the liquids and the index modulation in the core by changing the types of liquid used. LPG interferometer is extensively used as sensors especially refractometer. Results show that the designed MOFS chip can be used to measure the refractive indices of FBS protein solutions. It has potential applications in chemical and protein analysis.

This paper reports an enhancement in fluorescence detection via the formation of fluidic microlens in micro-optical fluidic system (MOFS). The fluidic microlens is formed by three laminar flows in the expansion chamber. By changing the flow rate of each flow, the shape and focal length of the fluidic lens will be changed. Therefore, the fluidic microlens provides a wide range of tunability to enhance the detection of fluorescence signal in MOFS chip. With such tunability, the designed MOFS can be used to suit different detection methods and applications especially in lowconcentration bio-molecules.

This paper reports the realization of long-period grating (LPG) interferometer in an integrated micro-optical fluidic system (MOFS) using droplet microfluidics. Comparing to normal fiber LPG, it provides a wide tuning range in the parameters of LPG, such as the grating period by changing the flow rate of the liquids and the index variation in the core by changing the types of liquid used. LPG interferometer is extensively used as sensors especially as a biochemical refractometer. The results show that the designed microfluidic chip can be used to measure the refractive indices of Fetal Bovine Serum (FBS) solutions. It has potential applications in chemical and protein analysis.