Tian Jian Lu

Advances in paper-based point-of-care diagnostics

Advanced diagnostic technologies, such as polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), have been widely used in well-equipped laboratories. However, they are not affordable or accessible in resource-limited settings due to the lack of basic infrastructure and/or trained operators. Paper-based diagnostic technologies are affordable, user-friendly, rapid, robust, and scalable for manufacturing, thus holding great potential to deliver point-of-care (POC) diagnostics to resource-limited settings. In this review, we present the working principles and reaction mechanism of paper-based diagnostics, including dipstick assays, lateral flow assays (LFAs), and microfluidic paper-based analytical devices (μPADs), as well as the selection of substrates and fabrication methods. Further, we report the advances in improving detection sensitivity, quantification readout, procedure simplification and multi-functionalization of paper-based diagnostics, and discuss the disadvantages of paper-based diagnostics. We envision that miniaturized and integrated paper-based diagnostic devices with the sample-in-answer-out capability will meet the diverse requirements for diagnosis and treatment monitoring at the POC.

Heat transfer in open-cell metal foams

The paper explores the use of open-celled metal foams as compact heat exchangers, exploiting convective cooling. An analytical model is developed for model foams with simple cubic unit cells consisting of heated slender cylinders, based on existing heat transfer data on convective crossflow through cylinder banks. A foam-filled channel having constant wall temperatures is analyzed to obtain the temperature distribution inside the channel as a function of foam density, cell size and other pertinent heat transfer parameters. Two characteristic length scales of importance to the problem are discussed: the minimum channel length required for heating the fluid to its goal temperature and the thermal entry length beyond which the transfer of heat between fluid and channel wall assumes a constant coefficient. The overall heat transfer coefficient of the heat exchanging system is calculated, and the pressure drop experienced by the fluid flow obtained. These results are used to analyze and guide the design of optimum foam structures that would maximize heat transfer per unit pumping power. Two examples are given to demonstrate the applicability of the analytical model: heat sinks for high power electronic devices and multi-layered heat exchangers for aeronautical applications. The present model perhaps oversimplifies the calculation of transport in a metal foam consisting of non-circular, possibly sharp-edged ligaments, and so likely leads to overestimates. Nevertheless the trends of heat transfer predicted by the model (for dependence on foam relative density, duct geometries, fluid velocity, etc.) are expected to be valid for a wide range of open-cell foams and are in reasonable agreement with available experimental data on aluminum foams (Bastawros and Evans, Proc. Symp. Application of Heat Transfer in Microelectronics Packaging. IMECE, Dallas, TX, 1997).

Interleukin-6 signaling pathway in targeted therapy for cancer

Interleukin-6 (IL-6) is a multifunctional cytokine which plays an important role in a wide range of biologic activities in different types of cell including tumor cells. IL-6 is involved in the host immune defense mechanism as well as the modulation of growth and differentiation in various malignancies. These effects are mediated by several signaling pathways, in particular the signal transducer and transcription activator 3 (Stat3). There exists abundant evidence demonstrating that deregulated overexpression of IL-6 was associated with tumor progression through inhibition of cancer cell apoptosis, stimulation of angiogenesis, and drug resistance. Clinical studies have revealed that increased serum IL-6 concentrations in patients are associated with advanced tumor stages of various cancers (e.g., multiple myeloma, non-small cell lung carcinoma, colorectal cancer, renal cell carcinoma, prostate cancer, breast cancer and ovarian cancer) and short survival in patients. Therefore, blocking IL-6 signaling is a potential therapeutic strategy for cancer (i.e., anti-IL-6 therapy) characterized by pathological IL-6 overproduction. Preliminary clinical evidence has shown that antibody targeted IL-6 therapy was well tolerated in cancer patients. In this review, we detail the progress of the current understanding of IL-6 signaling pathway in cancer as well as an antibody targeted IL-6 therapy for human cancer.

Effect of imperfections on the yielding of two-dimensional foams

The influence of each of the six diAerent types of morphological imperfection—waviness, non-uniform cell wall thickness, cell-size variations, fractured cell walls, cell-wall misalignments, and missing cells—on the yielding of 2D cellular solids has been studied systematically for biaxial loading. Emphasis is placed on quantifying the knock-down eAect of these defects on the hydrostatic yield strength and upon understanding the associated deformation mechanisms. The simulations in the present study indicate that the high hydrostatic strength, characteristic of ideal honeycombs, is reduced to a level comparable with the deviatoric strength by several types of defect. The common source of this large knock-down is a switch in deformation mode from cell wall stretching to cell wall bending under hydrostatic loading. Fractured cell edges produce the largest knock-down eAect on the yield strength of 2D foams, followed in order by missing cells, wavy cell edges, cell edge misalignments, G Voronoi cells, d Voronoi cells, and non-uniform wall thickness. A simple elliptical yield function with two adjustable material parameters successfully fits the numerically predicted yield surfaces for the imperfect 2D foams, and shows potential as a phenomenological constitutive law to guide the design of structural components made from metallic foams. # 1999 Elsevier Science Ltd. All rights reserved.

MEMS actuators and sensors: observations on their performance and selection for purpose

This paper presents an exercise in comparing the performance of microelectromechanical systems (MEMS) actuators and sensors as a function of operating principle. Data have been obtained from the literature for the mechanical performance characteristics of actuators, force sensors and displacement sensors. On-chip and off-chip actuators and sensors are each sub-grouped into families, classes and members according to their principle of operation. The performance of MEMS sharing common operating principles is compared with each other and with equivalent macroscopic devices. The data are used to construct performance maps showing the capability of existing actuators and sensors in terms of maximum force and displacement capability, resolution and frequency. These can also be used as a preliminary design tool, as shown in a case study on the design of an on-chip tensile test machine for materials in thin-film form.

Recent advances in synthesis and surface modification of lanthanide-doped upconversion nanoparticles for biomedical applications

Lanthanide (Ln)-doped upconversion nanoparticles (UCNPs) with appropriate surface modification can be used for a wide range of biomedical applications such as bio-detection, cancer therapy, bio-labeling, fluorescence imaging, magnetic resonance imaging and drug delivery. The upconversion phenomenon exhibited by Ln-doped UCNPs renders them tremendous advantages in biological applications over other types of fluorescent materials (e.g., organic dyes, fluorescent proteins, gold nanoparticles, quantum dots, and luminescent transition metal complexes) for: (i) enhanced tissue penetration depths achieved by near-infrared (NIR) excitation; (ii) improved stability against photobleaching, photoblinking and photochemical degradation; (iii) non-photodamaging to DNA/RNA due to lower excitation light energy; (iv) lower cytotoxicity; and (v) higher detection sensitivity. Ln-doped UCNPs are therefore attracting increasing attentions in recent years. In this review, we present recent advances in the synthesis of Ln-doped UCNPs and their surface modification, as well as their emerging applications in biomedicine. The future prospects of Ln-doped UCNPs for biomedical applications are also discussed.

THE THERMAL SHOCK RESISTANCE OF SOLIDS

Abstract The thermal shock resistance of a brittle solid is analysed for an orthotropic plate suddenly exposed to a convective medium of different temperature. Two types of plate are considered: (i) a plate containing a distribution of flaws such as pores, for which a stress-based fracture criterion is appropriate, and (ii) a plate containing a single dominant crack aligned with the through-thickness direction, for which a critical stress intensity factor criterion is appropriate. First, the temperature and stress histories in the plate are given for the full range of Biot number. For the case of a cold shock, the stress field is tensile near the surface of the plate and gives rise to a mode I stress intensity factor for a pre-existing crack at the surface of the plate. Alternatively, for the case of hot shock, the stress field is tensile at the centre of the plate and gives rise to a mode I stress intensity factor for a pre-existing crack at the centre of the plate. Lower bound solutions are obtained for the maximum thermal shock that the plate can sustain without catastrophic failure according to the two distinct criteria: (i) maximum local tensile stress equals the tensile strength of the solid, and (ii) maximum stress intensity factor for the pre-existing representative crack equals the fracture toughness of the solid. Merit indices of material properties are deduced, and optimal materials are selected on the basis of these criteria, for the case of a high Biot number (high surface heat transfer) and a low Biot number (low surface heat transfer). The relative merit of candidate materials depends upon the magnitude of the Biot number, and upon the choice of failure criterion. The effect of porosity on thermal shock resistance is also explored: it is predicted that the presence of porosity is generally beneficial if the failure is dominated by a pre-existing crack. Finally, the analysis is used to develop merit indices for thermal fatigue.

Thermal transport and fire retardance properties of cellular aluminium alloys

Abstract Closed-cell aluminium alloy foams exhibit exceptional resistance to fire. It is unclear why this happens, although the protection imparted by oxide Al2O3 layers has been suggested. This work attempts to uncover the thermal transport processes in metallic foams. The apparent thermal conductivities of two-dimensional foams having a variety of cellular microstructures are first calculated. These include regular honeycombs, Voronoi structures and Johnson–Mehl models. The effects of several types of geometric imperfection—Plateau borders, cell-edge misalignments, fractured cell edges, missing cells, inclusions and cell size variations—are studied by using analytical as well as finite element methods. The focus is on metallic foams where the transport of heat is dominated by solid conduction and thermal radiation; contributions from gaseous conduction and convection are neglected. The coupling of solid conduction with thermal radiation is dealt with by using the method of finite elements. These results are then applied to solve the transient temperature field of a cellular metal plate subjected to a sudden introduction of a high-temperature source of heat such as fire. The factors which dictate the thermal and structural fire retardance of cellular metallic foams are identified.

Sound absorption in metallic foams

The sound absorption capacity of one type of aluminum alloy foams—trade name Alporas—is studied experimentally. The foam in its as-received cast form contains closed porosities, and hence does not absorb sound well. To make the foam more transparent to air motion, techniques based on either rolling or hole drilling are used. Under rolling, the faces of some of the cells break to form small sharp-edged cracks as observed from a scanning electronic microscope. These cracks become passage ways for the in-and-out movement of air particles, resulting in sound absorption improvement. The best performance is nevertheless achieved via hole drilling where nearly all of the sound can be absorbed at selected frequencies. Combining rolling with hole drilling does not appear to lend additional benefits for sound absorption. Image analysis is carried out to characterize the changes in cell morphologies due to rolling/compression, and the drop in elastic modulus due to the formation of cracks is recorded. The effects of varying the relative foam density and panel thickness on sound absorption are measured, and optimal relative density and thickness of the panel are identified. Analytical models are used to explain the measured increase in sound absorption due to rolling and/or drilling. Sound absorbed by viscous flow across small cracks appears to dominate over that dissipated via other mechanisms.

On the design of two-dimensional Cellular metals for combined heat dissipation and structural load capacity

Sandwich panels with two-dimensional metal cores can be used to carry structural load as well as dissipate heat through solid conduction and forced convection. This work attempts to uncover the nature of heat transfer in these lightweight systems, with emphasis on the effects of varying cell morphologies and cell arrangements. The types of cell shape and cell arrangement considered include regular hexagon, square with connectivity 4 or 3, and triangle with connectivity 6 or 4. Two analytical models are developed: corrugated wall and effective medium. The former models the cellular structure in detail whilst, the latter models the fluid saturated porous structure using volume averaging techniques. The overall heat transfer coefficient and pressure drop are obtained as functions of relative density, cell shape, cell arrangement, fluid properties, and overall dimensions of the heat sink. A two-stage optimization is subsequently carried out to identify cell morphologies that optimize the structural and heat transfer performance at specified pumping power and at lowest weight. In the first stage, the overall heat transfer performance is optimized against relative density. Regular hexagonal cells are found to provide the highest levels of heat dissipation. In the second stage, a constraint on stiffness is added. It is then found that, for panels with thin cores, triangular cells constitute the most compact and yet stiff heat sink design; however, for high heat flux scenarios, hexagonal cells outperform triangular and square cells.