Photoresist with low fluorescence for bioanalytical applications

The negative photoresist SU-8 has found widespread use as a material in the fabrication of microelectrical-mechanical systems (MEMS). Although SU-8 has been utilized as a structural material for biological MEMS, a number of SU-8 properties limit its application in these bioanalytical devices. These attributes include its brittleness, nonspecific adsorption of biomolecules, and high fluorescence in the visible wavelengths. In addition, native SU-8 is a poor substrate for cellular adhesion. Photoresists composed of resins with epoxide side groups and photoacids were screened for their ability to serve as a low-fluorescence photoresist with sufficient resolution to generate microstructures with dimensions of 5-10 microm. The fluorescence of structures formed from 1002F photoresist (1002F resin combined with triarylsulfonium hexafluoroantimonate salts) was as much as 10 times less fluorescent than similar SU-8 microstructures. The absorbance of 1002F in the visible wavelengths was also substantially lower than that of SU-8. Microstructures or pallets with an aspect ratio as high as 4:1 could be formed permitting 1002F to be used as a structural material in the fabrication of arrays of pallets for sorting adherent cells. Several different cell types were able to adhere to native 1002F surfaces, and the viability of these cells was excellent. As with SU-8, 1002F has a weak adhesion to glass, a favorable attribute when the pallet arrays are used to sort adherent cells. A threshold, laser pulse energy of 3.5 microJ was required to release individual 50 microm, 1002F pallets from an array. Relative to SU-8, 1002F photoresist offers substantial improvements as a substrate in bioanalytical devices and is likely to find widespread use in BioMEMS.     

Impact of release dynamics of laser-irradiated polymer micropallets on the viability of selected adherent cells

We use time-resolved interferometry, fluorescence assays and computational fluid dynamics (CFD) simulations to examine the viability of confluent adherent cell monolayers to selection via laser microbeam release of photoresist polymer micropallets. We demonstrate the importance of laser microbeam pulse energy and focal volume position relative to the glass–pallet interface in governing the threshold energies for pallet release as well as the pallet release dynamics. Measurements using time-resolved interferometry show that increases in laser pulse energy result in increasing pallet release velocities that can approach 10 m s⁻¹ through aqueous media. CFD simulations reveal that the pallet motion results in cellular exposure to transient hydrodynamic shear stress amplitudes that can exceed 100 kPa on microsecond timescales, and which produces reduced cell viability. Moreover, CFD simulation results show that the maximum shear stress on the pallet surface varies spatially, with the largest shear stresses occurring on the pallet periphery. Cell viability of confluent cell monolayers on the pallet surface confirms that the use of larger pulse energies results in increased rates of necrosis for those cells situated away from the pallet centre, while cells situated at the pallet centre remain viable. Nevertheless, experiments that examine the viability of these cell monolayers following pallet release show that proper choices for laser microbeam pulse energy and focal volume position lead to the routine achievement of cell viability in excess of 90 per cent. These laser microbeam parameters result in maximum pallet release velocities below 6 m s⁻¹ and cellular exposure of transient hydrodynamic shear stresses below 20 kPa. Collectively, these results provide a mechanistic understanding that relates pallet release dynamics and associated transient shear stresses with subsequent cellular viability. This provides a quantitative, mechanistic basis for determining optimal operating conditions for laser microbeam-based pallet release systems for the isolation and selection of adherent cells.     

Collection and expansion of single cells and colonies released from a micropallet array

The ability to selectively grow out individual cells possessing unique characteristics from within a mixed population is of widespread importance for biomedical investigations. Generation of genetically engineered cell lines, transformation studies, cell-based assays, and stem cell studies are examples where single-cell cloning is of immense value. The vast majority of mammalian cells grow adherent to a surface; therefore, positive selection followed by cloning of cells while the cells remain adherent to their growth surface is an important goal. We recently demonstrated a microfabricated cell array combined with laser-based release of individual array elements for positive selection of single cells. In the current work, a strategy to collect single cells for clonal expansion is described. The system enabled cloning of individual cells with 80-90% efficiency. Single cells were selected and cloned from small populations of fewer than 10,000 cells. Strategies used by cells to migrate from the pallets to form colonies on the surface of the collection device were examined. Implementation of encoded array elements made it possible to follow specific cells throughout the selection, collection, and cloning procedure. Thus, a particular cell can be identified by any number of imaging techniques, isolated, and clonally expanded to generate a homogeneous cell line or a pure sample for genetic or biochemical analysis.     

Mechanisms of pulsed laser microbeam release of SU-8 polymer "micropallets" for the collection and separation of adherent cells

The release of individual polymer micropallets from glass substrates using highly focused laser pulses has been demonstrated for the efficient separation, collection, and expansion of single, adherent cells from a heterogeneous cell population. Here, we use fast-frame photography to examine the mechanism and dynamics of micropallet release produced by pulsed laser microbeam irradiation at lambda = 532 nm using pulse durations ranging between 240 ps and 6 ns. The time-resolved images show the laser microbeam irradiation to result in plasma formation at the interface between the glass coverslip and the polymer micropallet. The plasma formation results in the emission of a shock wave and the ablation of material within the focal volume. Ablation products are generated at high pressure due to the confinement offered by the polymer adhesion to the glass substrate. The ablation products expand underneath the micropallet on a time scale of several hundred nanoseconds. This expansion disrupts the polymer-glass interface and accomplishes the release of the pallet from its glass substrate on the microsecond time scale (approximately 1.5 micros). Our experimental investigation demonstrates that the threshold energy for pallet release is constant (approximately 2 microJ) over a 25-fold range of pulse duration spanning the picosecond to nanosecond domain. Taken together, these results implicate that pallet release accomplished via pulsed laser microbeam irradiation is an energy-driven plasma-mediated ablation process.     

基于托盘应用状况的托盘结构创意设计

目的 研究并解决托盘尺寸与应用场景不匹配的问题。方法 对金属材料托盘结构进行创意设计,根据使用场景的不同要求,可以在原有托盘尺寸的基础上,改变托盘的长或宽,能够衍生出各种不同规格的托盘。结果 托盘尺寸可变设计能很好地解决托盘应用存在的问题,提高托盘应对不同场景的适用性,增强托盘与存储的货架、搬运的产品和运载工具等的匹配性,提高托盘的标准化程度,有利于建立托盘循环共用系统,提高托盘利用率,提高物流作业效率,降低物流成本。结论 尺寸可变设计金属材料托盘具有较好的承载性和安全性,有着良好的市场前景。     

Investigation into the load bridging effect for block class pallets as a function of package size and pallet stiffness

Pallets and corrugated boxes are ubiquitous in the global supply chain. However, the interactions that exist between the boxes and pallets are ignored during the pallet design process resulting in the over designing of pallets and the waste of raw materials. The goal of this research is to understand how pallet performance is affected by headspace, box size, and base design across multiple support conditions using block class wooden pallets. Headspace and base design had no effect on pallet deflection for the experimental weights used throughout testing. However, the effect of box size was significant on pallet deflection across multiple support conditions. The effect was greatest for lower stiffness pallets and low‐stiffness support conditions (racking across the width; RAW) with up to a 50% reduction in pallet deflection observed by switching from small to large boxes on a very low‐stiffness pallet. Evaluation of pressure mat data showed an increase in the redistribution of pressure away from the center of the pallet and toward the supports as box size increased. The redistribution of pressure toward the supports is known as load bridging and validates the observed reduction in pallet deflection as a function of box size. The results indicate that incorporating this effect of packages into current pallet design practices could result in more effective and cheaper pallet designs.     

The effect of pallet top deck stiffness on the compression strength of asymmetrically supported corrugated boxes

During unitized shipment, the components of unit loads are interacting with each other. During floor stacking of unit loads, the load on the top of the pallet causes the top deck of the pallet to bend, which creates an uneven top deck surface resulting in uneven or asymmetrical support of the corrugated boxes. This asymmetrical support could significantly affect the strength of the corrugated boxes, and it depends on the top deck stiffness of the pallet. This study is aimed at investigating how the variations of pallet top deck stiffness and the resulting asymmetric support affect corrugated box compression strength. The study used a scaled-down unit load compression test on quarter-scale pallet designs with different deckboard thicknesses using four different corrugated box designs. Pallet top deck stiffness was determined to have a significant effect on box compression strength. There was a 27%–37% increase in box compression strength for boxes supported by high-stiffness pallets in comparison with low-stiffness pallets. The fact that boxes were weaker on low-stiffness pallets could be explained by the uneven pressure distribution between the pallet deck and bottom layer of boxes. Pressure data showed that a higher percentage of total pressure was located under the box sidewalls that were supported on the outside stringers of low-stiffness pallets in comparison with high-stiffness pallets. This was disproportionately loading one side of the box. Utilizing the effects of pallet top deck stiffness on box compression performance, a unit load cost analysis is presented showing that a stiffer pallet can be used to carry boxes with less board material; hence, it can reduce the total unit load packaging cost.     

Airflow patterns in an enclosure loaded with slotted pallets

A reduced scale model and CFD predictions are used to investigate experimentally and numerically the airflow patterns within a refrigerated truck loaded with slotted but empty pallets. Air velocity measurements are carried out on a reduced scale model with a Laser Doppler Anemometer above and inside the pallets. The numerical predictions obtained with Computational Fluid Dynamics package using the RSM turbulence model showed a satisfactory agreement with experimental data in high velocity zones. An approach was developed to evaluate the local ventilation efficiency and the fresh air within the pallets. The flow rate through the last pallet is about 35 times smaller than for the five first pallets. In terms of fresh air the difference is not so high; the equivalent fresh airflow rate through the last pallet is about six times smaller than for the first pallets.     

Investigation of pallet stacking pattern on unit load bridging

Considering the effect of packages during pallet design will reduce costs and improve the sustainability of supply chains. Currently, many mechanical interactions between the pallet and the package product are not being considered during the pallet design process. This study investigates the effect of the magnitude and type of interlocking between layers of packaged products. The bending of the pallet supporting a unit load of corrugated boxes was measured under four common support conditions, warehouse rack storage spanning the pallet width and length, fork tine support across the pallet width, and floor stacking. Five different pallet stacking patterns were analyzed from column stacking to fully interlocked stacking. It was determined that interlocking packages reduces pallet deflection up to 53%. This is more significant for lower stiffness pallets and when the payload carried by the pallet is greater than the rated load capacity of the pallet. Increasing the magnitude of the interlocking reduces the deflection of the pallet by 11.6%. These results provide a guideline on improving pallet design and help further the understanding of the interaction between pallets and the orientation of packaged products placed on the pallet.     

铝合金托盘有限元分析及优化设计

目的通过对不同托盘结构进行分析,选出满足托盘承载性能要求的轻量化的铝合金托盘结构。方法利用Solid Works软件对不同类型托盘进行三维建模,并用Ansys Workbench对其进行静力分析,对比不同类型托盘应力、变形及安全系数,选出结构最优的铝合金托盘,并对其尺寸进行优化。结果方案C的托盘质量、纵梁应力、纵梁变形和纵梁安全系数分别为19.68 kg,247.39 MPa,3.41 mm和1.13,优于其他类型托盘,对其铺板厚度及纵梁相关尺寸进行优化后,其质量减少22%,纵梁安全系数提高20.4%。结论铺板厚度为1 mm,垫块厚度为1.5 mm,以及其他相关尺寸分别为5,5,30 mm的方案C铝合金托盘为载荷一定条件下的最优结构。     

塑料托盘的有限元分析及实验验证

目的基于Workbench设计和分析塑料托盘结构的可靠性和可行性。方法通过建立塑料托盘的有限元模型,对其施加相应载荷,模拟塑料托盘试验时的受力情况,分别计算托盘在均载堆码、叉举、底铺板、弯曲下的挠度值,并与实验结果进行比较。结果塑料托盘4个挠度值的实验结果和模拟结果相对误差在10%以内。结论采用Workbench对托盘进行受力分析具有可靠性和可行性。     

Parylene Mobile Microplates Integrated with an Enzymatic Release for Handling of Single Adherent Cells

An approach for manipulating single adherent cells is developed that is integrated with an enzymatic batch release. This strategy uses an array of releasable microfabricated mobile substrates, termed microplates, formed from a biocompatible polymer, parylene. A parylene microplate array of 10–70 μm in diameter can be formed on an alginate hydrogel sacrificial layer by using a standard photolithographic process. The parylene surfaces are modified with fibronectin to enhance cell attachment, growth, and stretching. To load single cells onto these microplates, cells are initially placed in suspension at an optimized seeding density and are allowed to settle, stretch, and grow on individual microplates. The sacrificial layer underneath the microplate array can be dissolved on a time‐scale of several seconds without cytotoxicity. This system allows the inspection of selected single adherent cells. The ability to assess single cells while maintaining their adhesive properties will broaden the examination of a variety of attributes, such as cell shape and cytoskeletal properties.     

Large-scale single-cell trapping and imaging using microwell arrays

High-throughput single-cell measurements of cellular responses are of great importance for a variety of applications including drug testing, toxicology, and basic cell biology. We present an optimization study for trapping single cells with high efficiency in large arrays of microwells. The method is compatible with standard fluorescence microscopy equipment and is not dependent on, but is compatible with, cell adherence. We have characterized microwell occupancy by cells for a range of microwell dimensions and seeding parameters and optimized it for fibroblasts (as a model of adherent cell) and rat basophilic leukemia cells (as a model of nonadherent cell). We have been able to obtain phase-contrast and fluorescence micrographs with more than 18,000 single cells per image using a 4x objective.     

Introduction de l'informatique dans la gestion et le contrôle des entrepôts frigorifiquesThe introduction of data processing in the management and control of cold stores

A cold store is required to preserve foodstuffs which may arrive in quantities of a few hundred tons or in boxes weighing only a few kilos. The pallet is the unit of volume allowing rationalization of storage.Two cases can be classified: full pallet storage and order preparation for retailers. With full pallet storage the series of operations carried out are: receiving goods, putting them into a defined place, maintaining the required storage environment, finally delivering pallets. Incidental to these functions are: Inventory control, (invoicing, etc.), management of stocks, (the computer can choose the best storage place for each pallet according to the delivery rate and the shortest distance), instructions to semi-automatic fork lift trucks or to fully automatic stacker cranes, optimization of refrigeration machines to minimize power consumption and to give warning of maintenance requirements or breakdown, security protection against fire and robbery.From full pallets, orders are prepared from a few boxes of each article to deliver to retailers. The computer chooses the right moment to bring out pallets from the main stock, moving them to the best place in the preparation area and finally indicating to the workman in what order he has to take boxes from the pallets.The main advantages are: better use of space, better control of the quality of the materials being stored, and lower energy costs. Paradoxically the main obstacle to further progress is the difficulty of efficiently replacing human operators for single box handling.     

Introduction de l'informatique dans la gestion et le contrôle des entrepôts frigorifiques

A cold store is required to preserve foodstuffs which may arrive in quantities of a few hundred tons or in boxes weighing only a few kilos. The pallet is the unit of volume allowing rationalization of storage.Two cases can be classified: full pallet storage and order preparation for retailers. With full pallet storage the series of operations carried out are: receiving goods, putting them into a defined place, maintaining the required storage environment, finally delivering pallets. Incidental to these functions are: Inventory control, (invoicing, etc.), management of stocks, (the computer can choose the best storage place for each pallet according to the delivery rate and the shortest distance), instructions to semi-automatic fork lift trucks or to fully automatic stacker cranes, optimization of refrigeration machines to minimize power consumption and to give warning of maintenance requirements or breakdown, security protection against fire and robbery.From full pallets, orders are prepared from a few boxes of each article to deliver to retailers. The computer chooses the right moment to bring out pallets from the main stock, moving them to the best place in the preparation area and finally indicating to the workman in what order he has to take boxes from the pallets.The main advantages are: better use of space, better control of the quality of the materials being stored, and lower energy costs. Paradoxically the main obstacle to further progress is the difficulty of efficiently replacing human operators for single box handling.     

纸基蜂窝托盘柱脚对堆码承载性能的影响

通过ANSYS对蜂窝托盘进行建模,并设计正交试验分析托盘柱脚各因素对蜂窝托盘应力的影响.发现柱脚与托盘面外边缘的距离影响非常显著.最后通过静态堆码试验来验证有限元模型的有效性,有助于为蜂窝托盘的设计提供指导.     

Investigation of the effect of column stacked corrugated boxes on load bridging using partial four‐way stringer class wooden pallets

Pallets are the foundation of the global packaging supply chain. They provide a way to store and transport products in an efficient manner. The load capacity of pallets greatly depends on the type of packages carried by the pallet; however, current pallet design methods do not consider the effect of packages on the load carrying capacity of the pallet. This results in excessive use of materials which reduces the sustainability of unit loads, drives costs up, and creates potential safety issues. The objective of this study was to investigate the effect of corrugated box size and headspace on pallet deflection and stress distribution on the top of the pallet as a function of pallet stiffness across multiple pallet support conditions. Data analysis identified that box size had a significant effect on the deflection of the pallet. This effect was only significant for warehouse racking across the width and length support conditions. As much as a 53% reduction in pallet deflection was observed for high stiffness pallets supporting corrugated boxes with 25.4‐mm headspace when the size was increased from small to large. The redistribution of vertical compression stresses towards the supports as a function of the increasing box size was observed. The increased concentration of compression stresses on top of the supports and the resulting lower pallet deflection could significantly increase the actual load carrying capacity of some pallet designs. The effect of box headspace was significant in some scenarios but inconsistent; thus, more investigation with a larger sample size is recommended.     

Simulation for Transport Pallet Cost Reduction in Pet Food Manufacturing: An Empirical Case Study

This study examined different managerial scenarios for the cost reduction of transport pallets rented by a pet food manufacturer that produces pet food sold in local and international markets. A computer simulation model was developed on the basis of the empirical case to analyse the flow of pallets from the factory, the subcontractors and the distribution centre and to determine the system performance measures in terms of the average waiting times and the number of pallets in queues. The analysis showed that problems occurred when slow‐moving products occupied the rental pallets for a long time and because too much inventory was kept at the distribution centre. Two managerial scenarios were then proposed to alleviate these problems, involving pallet movement decisions by internal management. The results suggested a choice of decision supports to determine which managerial scenario was suitable for the business. The proposed implications may be beneficial to similar industries where a supply system of rental pallet service is applied. Copyright © 2011 John Wiley & Sons, Ltd.     

塑料平托盘的研究进展

目的综述塑料平托盘的现状及发展趋势。方法通过介绍当前塑料平托盘的材料、加工工艺、结构形式及其生产技术现状,以及托盘性能评价标准、传统力学和有限元分析方法在塑料平托盘性能研究上的应用,综述了塑料平托盘性能的研究进展;从塑料平托盘标准化、可视化、循环共用及修补技术等层面说明了托盘的发展趋势。结果无论在塑料平托盘的生产制造层面,还是在其性能分析研究上,塑料平托盘的应用技术都有了很大进步。结论塑料平托盘发展仍然存在不足,还需要政府、应用行业及研究者的共同努力。     

Numerical modelling of the temperature increase in frozen food packaged in pallets in the distribution chainModélisation numérique de l'augmentation de température des produits alimentaires congelés palettisés dans la chaîne de distribution

Frozen food can undergo temperature rise essentially during handling processes which are the weakest links of the cold chain: delivery, loading or unloading operations and temporary storage where pallets are generally handled in an ambience above 0°C. In this study, the temperature rise in a pallet is investigated numerically and experimentally. A three-dimensional finite-volume heat transfer model is developed using Phoenics Computational Fluid Dynamics (CFD) software. Food temperature within the pallet is predicted as a function of time of exposure, ambient conditions, product initial temperature, palletization and thermal characteristics of products and packaging. The experiments are carried out with packaged frozen fish pallets placed on a closed or open dock. The temperatures are recorded, at different levels in pallets over 25- to 85-min periods. The model shows good agreement with experimental results.