Three-dimensional fluidic self-assembly by axis translation of two-dimensionally fabricated microcomponents in railed microfluidics

A method for high-throughput 3D self-assembly of 2D photopatterned microstructures using railed microfluidics is presented. Vertical device patterning of heterogeneous materials requires high-level integration using conventional microelectromechanical system (MEMS) technology; however, 3D railed assembly enables easy and fast self-assembly via a fluidic axis-translation process and simple material exchange in microfluidic channels. Individually photopatterned 2D microstructures are axis-translated from in-plane to out-of-plane and fluidically self-assembled, guided by side-rails in microfluidic channels to form a 3D morphology. Since the structures are fabricated in fluidic environments, there are no fixed initial points on the channel substrate allowing fluidic horizontal stacking of erected 2D structures. The guiding mechanism of railed microfluidics enables efficient fluidic handling and deterministic 3D self-assembly of heterogeneous components such as electronic components or polymeric microstructures using only fluidic force.     

High-aspect ratio polymeric pillar arrays formed via electrohydrodynamic patterning

This paper describes a method to increase the aspect ratio of polymeric pillar arrays formed by electrohydrodynamic instabilities. Pillar arrays form spontaneously across a narrow capacitor gap when an electric field is applied normal to a thin, fluidic film. This simple technique is appealing because of its ability to rapidly form arrays of small structures in an inexpensive manner. The columnar structures formed using this technique have low-aspect ratios, which are non-ideal for patterning applications. Theory suggests that stretching the structures post-formation is one of the only ways to increase the aspect ratio of the pillars. We developed a tool to physically stretch these structures to increase their aspect ratio from ∼0.1 to ∼0.5. The capabilities and limits of this stretching technique have been discussed.     

Volumetric Bioprinting of Complex Living‐Tissue Constructs within Seconds

Biofabrication technologies, including stereolithography and extrusion‐based printing, are revolutionizing the creation of complex engineered tissues. The current paradigm in bioprinting relies on the additive layer‐by‐layer deposition and assembly of repetitive building blocks, typically cell‐laden hydrogel fibers or voxels, single cells, or cellular aggregates. The scalability of these additive manufacturing technologies is limited by their printing velocity, as lengthy biofabrication processes impair cell functionality. Overcoming such limitations, the volumetric bioprinting of clinically relevant sized, anatomically shaped constructs, in a time frame ranging from seconds to tens of seconds is described. An optical‐tomography‐inspired printing approach, based on visible light projection, is developed to generate cell‐laden tissue constructs with high viability (>85%) from gelatin‐based photoresponsive hydrogels. Free‐form architectures, difficult to reproduce with conventional printing, are obtained, including anatomically correct trabecular bone models with embedded angiogenic sprouts and meniscal grafts. The latter undergoes maturation in vitro as the bioprinted chondroprogenitor cells synthesize neo‐fibrocartilage matrix. Moreover, free‐floating structures are generated, as demonstrated by printing functional hydrogel‐based ball‐and‐cage fluidic valves. Volumetric bioprinting permits the creation of geometrically complex, centimeter‐scale constructs at an unprecedented printing velocity, opening new avenues for upscaling the production of hydrogel‐based constructs and for their application in tissue engineering, regenerative medicine, and soft robotics.     

Characterization of rapid PDMS casting technique utilizing molding forms fabricated by 3D rapid prototyping technology (RPT)

In this work we characterize a novel possibility for PDMS (PolyDiMethylSiloxane) casting/ micromolding methods with the utilization of molding forms fabricated by a commercially available novel acrylic photopolymer based 3D printing method. The quality and absolute spatial accuracy of 1) different 3D printing modes (‘matt’ vs. ‘glossy’); 2) the molded PDMS structures and 3) the subsequently produced complementary structures made of epoxy resin were investigated. The outcome of these two form transfer technologies were evaluated by the cross sectional analysis of open microfluidic channels (trenches) with various design. Our results reveal the spatial accuracy in terms of real vs. CAD (Computer Aided Design) values for the 3D printed acrylic structures and the limits of their form transfer to PDMS, then to epoxy structures. Additionally the significant differences between the various spatial directions (X, Y, Z) have been characterized, and the conclusion was drawn that the ‘glossy’ printing mode is not appropriate for 3D printing of microfluidic molds.     

3D打印陶瓷铸型研究与应用进展EI北大核心CSCD

陶瓷铸型是一类应用于熔模精密铸造领域、用于成型铸件内外部结构的复杂部件。随着铸件复杂度的提升,需要更加精细、复杂的铸型来满足铸造需求,然而传统的陶瓷铸型成型手段如注射成型等存在成本高、研发周期长等问题,难以满足复杂精细结构的成型要求。3D打印技术作为一种快速成型手段能够精准成型复杂精细结构,将其应用于铸型生产,不仅能够解决复杂结构的成型问题,同时也能降低生产成本、缩短生产周期。本文主要阐述了3D打印技术在陶瓷铸型生产中的应用,从应用于铸型3D打印陶瓷材料的种类及特性、典型铸型3D打印技术及铸型打印后处理手段三个方面对3D打印技术陶瓷铸型的研究与应用进行介绍,并对该技术未来的发展进行展望,指出3D打印技术能够有效解决复杂陶瓷铸型的成型问题,从而满足复杂空心结构金属件的铸造需求。     

Elastic modulus of a silicon thin film fabricated by nanotransfer printing

Transfer printing, a promising method for fabricating multi-scale structures on various substrates such as semiconductors and polymers, has been used to fabricate flexible devices with performance superior to that of conventional organic flexible devices. Although thin films might be expected to suffer damage during the transfer printing process, no reports of the degradation of mechanical properties during transfer printing have been published. The change in mechanical properties before and after transfer printing should be evaluated in terms of reliability and design for transfer printing to be successful. We propose a method of fabricating freestanding 200-nm-thick single-crystal silicon (SCS) thin-film specimens using transfer printing in order to investigate the mechanical properties of the transferred SCS thin-film specimens. The fabrication method combines several techniques such as semiconductor manufacturing, liftoff, and transfer printing processes. The core technology in this method is the fabrication of freestanding SCS thin-film structures suspended between two fixed ends. The mechanical properties of the freestanding SCS thin-film structures were measured using a microtensile machine capable of optical strain measurement. The test results provide insight into device design and reliability evaluation of flexible electronics fabricated by nanotransfer printing.     

Characterization of lithographically printed resistive strain gauges

This paper reports progress in sensor fabrication by the conductive lithographic film (CLF) printing process. Work describing strain-sensitive structures manufactured using a modified printing process and conductive inks is addressed. The performance of a "single-ink" strain-sensitive structure when printed on six alternative substrates (GlossArt, PolyArt, Teslin, Mylar C, Melinex, and Kapton) is analyzed. Though not intending to compete with conventional gauges in high-tolerance measurement, the structures exhibit properties that indicate suitability for novel applications.     

Direct Fused Deposition Modeling 4D Printing and Programming of Thermoresponsive Shape Memory Polymers with Autonomous 2D-to-3D Shape Transformations

Herein, direct 4D printing of thermoresponsive shape memory polymers (SMPs) by the fused deposition modeling (FDM) method that enables programing of 2D objects during printing for autonomous 2D-to-3D shape transformations via simply heating is focused on. The programming process during printing is investigated through designs and experiments. The capability of programming SMPs during printing is illustrated by prestrain and bending capabilities, which are highly related to printing settings, such as nozzle temperature, print speed, layer height, infill patterns, and ratio of active parts in a bilayer structure. A nearly linear relationship for prestrain and bending parameters is experimentally revealed for different printing factors. Quantitative results are presented to be used as a guidance for designing complex 3D structures via 4D printing of 2D structures. Helix structure, twisting structure, DNA-like structures, and functional gripper are designed to demonstrate the potential of direct FDM 4D printing for creating complex 3D structures from simple 2D structures with advantages over traditional manufacturing methods. It is shown that, by removing the need for a layer-by-layer stacking process to achieve a complex 3D shape, FDM can promote sustainability via 4D printing of autonomous 2D-to-3D shape transformer structures with lower materials, time, energy, and longer service life.     

流体排布与介电电泳结合排列组装碳纳米管

流体排布和介电电泳是碳纳米管生长后排列组装的两种方法.流体排布可实现基片上较大范围的碳纳米管定向排列,且流体剪切力作用可将弯曲的碳纳米管在一定程度上拉直,但利用流体难以实现在特定位置组装碳纳米管.而介电电泳通过电极上不均匀电场实现碳纳米管在电极间沿电场方向的定向定位排列组装,介电电泳的不足之处在于电泳力难以将弯曲的碳纳米管拉直.本研究结合这两种组装方法的优势,采用流体与介电电泳结合排列组装碳纳米管.通过选择流体流动和电泳参数,流体结合直流或带直流偏置的交流电泳实现了较好的碳纳米管排列组装.与介电电泳组装相比,结合流体能减少碳纳米管之间的粘连,起到梳理拉直的作用,并提高了组装效率;与流体排布相比,结合介电电泳实现了碳纳米管在指定位置的组装.     

3D Printing by Multiphase Silicone/Water Capillary Inks

3D printing of polymers is accomplished easily with thermoplastics as the extruded hot melt solidifies rapidly during the printing process. Printing with liquid polymer precursors is more challenging due to their longer curing times. One curable liquid polymer of specific interest is polydimethylsiloxane (PDMS). This study demonstrates a new efficient technique for 3D printing with PDMS by using a capillary suspension ink containing PDMS in the form of both precured microbeads and uncured liquid precursor, dispersed in water as continuous medium. The PDMS microbeads are held together in thixotropic granular paste by capillary attraction induced by the liquid precursor. These capillary suspensions possess high storage moduli and yield stresses that are needed for direct ink writing. They could be 3D printed and cured both in air and under water. The resulting PDMS structures are remarkably elastic, flexible, and extensible. As the ink is made of porous, biocompatible silicone that can be printed directly inside aqueous medium, it can be used in 3D printed biomedical products, or in applications such as direct printing of bioscaffolds on live tissue. This study demonstrates a number of examples using the high softness, elasticity, and resilience of these 3D printed structures.     

基于表单的网络印刷客户端色彩再现方法的研究

通过研究计算机网络技术和印刷色彩管理技术,提出了通过表单实现网络印刷客户端显示色彩再现的一种方法。以网络客户的显示色彩为基础,借助网络客户的视觉观察和表单数据,获取了客户端色彩显示数据;经计算再现色彩数据,实现了客户端显示色彩的所见即所得。实验表明,方法可以解决网络印刷客户端显示色彩的再现问题,提高网络印刷质量,缩短周期,降低成本,提高效率。     

基于SFS算法的网点立体形态的获取与解析

目的在印刷传递过程中对网点微观立体形态进行准确提取并解析。方法在显微测试系统准确采集的网点二维数据的基础上,利用明暗恢复形貌(SFS)原理,构建出不同形状的印刷网点微观三维结构模型。结果直观并精确地还原了不同形状网点在承印物表面附着的立体形态,网点微观立体特性的不同会对印刷质量产生相应的影响。结论 SFS算法推导过程严谨,构建出的立体模型精度较高,能真实、细致地反映出印刷过程中网点传递的具体形态,是网点立体形态还原的有效方法。精确获取并解析印刷网点微观立体形态,可以直观有效地检测网点传递效果,并能从源头上控制印刷质量,是图像复制质量评价的新方法。     

流体组装制造的金属-碳纳米管-金属结构

基于碳纳米管的纳米器件制造中,金属-碳纳米管-金属结构是重要部分通过流体组装多壁碳纳米管,并在其上沉积、光刻图形化金属制造了金属-碳纳米管-金属结构．对比不同流体组装条件下的排列效果发现,较大的样品台倾角和较高的气流速度可实现较好的碳纳米管组装．通过对碳纳米管与金属间的接触电阻进行估算和比较,金属包覆碳纳米管比碳纳米管沉积在全电极上的接触方式具有更小的接触电阻和接触电阻分散性,且碳纳米管与金电极接触状态比钛电极好最终通过该方法制造出了接触良好的金属-碳纳米管-金属结构。     

Lifting gate polydimethylsiloxane microvalves and pumps for microfluidic control

We describe the development and characterization of pneumatically actuated "lifting gate" microvalves and pumps. A fluidic layer containing the gate structure and a pneumatic layer are fabricated by soft-lithography in PDMS and bonded permanently with an oxygen plasma treatment. The microvalve structures are then reversibly bonded to a featureless glass or plastic substrate to form hybrid glass-PDMS and plastic-PDMS microchannel structures. The break-through pressures of the microvalve increase linearly up to 65 kPa as the closing pressure increases. The pumping capability of these structures ranges from the nanoliter to microliter scale depending on the number of cycles and closing pressure employed. The micropump structures exhibit up to 86.2% pumping efficiency from flow rate measurements. The utility of these structures for integrated sample processing is demonstrated by performing an automated immunoassay. These lifting gate valve and pump structures enable facile integration of complex microfluidic control systems with a wide range of lab-on-a-chip substrates.     

基于多尺度结构相似度的印刷图像质量评价研究

目的为了简化印刷图像质量主观评价方法。方法提出基于多尺度结构相似度的印刷图像质量评价研究,将多尺度结构相似度应用在印刷图像质量评价上。结果实验仿真表明,多尺度结构相似度模型客观评价结果与主观评价结果的相关系数最高,为0.7698,表明两者是强相关关系。结论提出的基于多尺度结构相似度的印刷图像质量评价方法,是印刷图像质量评价的一种有效的新方法。     

Fabrication of extremely conductive high-aspect silver traces buried in hot-embossed polycarbonate films via the direct gravure doctoring method

Depositing inks on a planar substrate by printing is a facile way to fabricate conductive traces and other complicated functional devices. However, irrespective of the printing methods used, the thickness of the inks has an upper limit due to their fluidic property and subsequent wetting on the substrates. Herein, we present a method for creating high-aspect ratio conductive traces by combining hot-embossing and gravure doctoring techniques. Binary-sized colloidal pastes containing Ag nanoparticles and micrometer-sized spherical Ag powder additives were filled using a doctor blade in the grooves of polycarbonate (PC) films inscribed via hot-embossing to create buried traces. Under optimal mixing conditions in which the minimum resistivity was achieved, voids between the microparticles provided a pathway for the volatile solvents to smoothly escape from the filled ink and minimized thickness reduction during the thermal sintering process. A fabricated trace buried in the PC film with an aspect ratio of around 3:1 and a linewidth of 55 μm showed extremely low resistance of less than 10 Ω/m. A flexible transparent heater was developed using the reported binary colloidal paste.     

Guided and fluidic self-assembly of microstructures using railed microfluidic channels

Fluidic self-assembly is a promising pathway for parallel fabrication of devices made up of many small components. Here, we introduce 'railed microfluidics' as an agile method to guide and assemble microstructures inside fluidic channels. The guided movement of microstructures in microfluidic channels was achieved by fabricating grooves ('rails') on the top surface of the channels and also creating complementary polymeric microstructures that fit with the grooves. Using the rails as a guiding mechanism, we built complex one- and two-dimensional microsystems in which all the microstructures initially involved in the fabrication method were incorporated as components in the final product. Complex structures composed of more than 50 microstructures (each sized smaller than 50 microm) were fluidically self-assembled with zero error. Furthermore, we were able to use the rails to guide microstructures through different fluid solutions, successfully overcoming strong interfacial tension between solutions. On the basis of rail-guided self-assembly and cross-solution movement, we demonstrated heterogeneous fluidic self-assembly of polymeric microstructures and living cells. In addition to such assembly of in situ polymerized structures, we also guided and assembled externally fabricated silicon chips-demonstrating the feasible application of railed microfluidics to other materials systems.     

包装印刷材料中甲醛快速检测方法的探索研究

本文开展了包装印刷材料中甲醛快速检测方法的探索研究,基于比色法,系统研究了关键因素显色剂和比色方式对显色产物的稳定性和灵敏度的影响,研究开发了甲醛检测的膜富集-紫外可见光谱法。结果表明：1)乙酰丙酮显色法具有良好的抗干扰能力和稳定性。2)直接比色法适用于包装印刷材料中甲醛定性快速筛查;紫外可见光谱法适用于包装印刷材料中甲醛的定量检测。3)膜富集-紫外可见光谱法相比较传统紫外可见光谱法灵敏度更高,适合于低含量甲醛检测。该研究有望为印刷材料中甲醛的快速检测提供参考,为产品包装的绿色、安全印刷提供技术支撑。     

非均衡训练集过采样的印刷套准识别方法

目的 针对印刷标志图像训练数据集非均衡性导致印刷标志图像中少类数据套准状态识别准确率低的问题,提出改进的SMOTE训练集过采样方法,以提高少类数据的识别准确率。方法 提取印刷标志图像灰度行程矩阵的纹理特征,组成多维的模型输入特征数据。基于少类样本的邻域信息,得到少类样本的过采样参数。对少类样本采取不同的过采样策略,实现训练集样本的均衡。使用均衡的训练集建立支持向量机模型,实现对印刷套准状态的识别。结果 实验结果表明,文中方法在不同非均衡印刷数据集上,获得的平均分类准确率几何平均数Gmean为0.8507,召回率Re为0.7192,ROC曲线下面积A为0.8549。结论 文中方法在不同非均衡印刷套准数据集上的分类性能要优于实验中的SMOTE,IS和SVM等方法。