Automated calibration of 3D-printed microfluidic devices based on computer vision

With the development of 3D printing techniques, the application of it in microfluidic/Lab-on-a-Chip (LoC) fabrication is becoming more and more attractive. However, to achieve a satisfying printing quality of the target devices, researchers usually require quite an amount of work in calibration trials even for high-end 3D printers. To increase the calibration efficiency of the average priced printers and promote the application of 3D printing technology in the microfluidic community, this work has presented a computer vision (CV)-based method for rapid and precise 3D printing calibration with examples on cylindrical hole/post diameters of 0.2–2.4 mm and rectangular hole/post widths of 0.2–1.0 mm by a stereolithography-based 3D printer. Our method is fully automated, which contains five steps and only needs a camera at hand to provide photos for convolutional neural network recognition. The experimental results showed that our CV-based method could provide calibrated dimensions with just one print of the specific calibration ruler to meet user desire. The higher resolution of the photo provides a higher precision in calibration. Subsequently, only one more print for the target device is needed after the calibration process. Overall, this work has provided a quick and precise calibration tool for researchers to apply 3D printing in the fabrication of their microfluidic/LoC devices with average price printers. Besides, with our open source calibration software and calibration ruler design file, researchers can modify the specific setting based on customized needs and conduct calibration on any type of 3D printer.     

An integrated microfluidic system for screening of phage-displayed peptides specific to colon cancer cells and colon cancer stem cells

Affinity reagents recognizing biomarkers specifically are essential components of clinical diagnostics and target therapeutics. However, conventional methods for screening of these reagents often have drawbacks such as large reagent consumption, the labor-intensive or time-consuming procedures, and the involvement of bulky or expensive equipment. Alternatively, microfluidic platforms could potentially automate the screening process within a shorter period of time and reduce reagent and sample consumption dramatically. It has been demonstrated recently that a subpopulation of tumor cells known as cancer stem cells possess high drug resistance and proliferation potential and are regarded as the main cause of metastasis. Therefore, a peptide that recognizes cancer stem cells and differentiates them from other cancer cells will be extremely useful in early diagnosis and target therapy. This study utilized M13 phage display technology to identify peptides that bind, respectively, to colon cancer cells and colon cancer stem cells using an integrated microfluidic system. In addition to positive selection, a negative selection process was integrated on the chip to achieve the selection of peptides of high affinity and specificity. We successfully screened three peptides specific to colon cancer cells and colon cancer stem cells, namely, HOLC-1, HOLC-2, and COLC-1, respectively, and their specificity was measured by the capture rate between target, control, and other cell lines. The capture rates are 43.40 ± 7.23%, 45.16 ± 7.12%, and 49.79 ± 5.34% for colon cancer cells and colon cancer stem cells, respectively, showing a higher specificity on target cells than on control and other cell lines. The developed technique may be promising for early diagnosis of cancer cells and target therapeutics.     

Lab-on-a-chip workshop activities for secondary school students

The ability to engage and inspire younger generations in novel areas of science is important for bringing new researchers into a burgeoning field, such as lab-on-a-chip. We recently held a lab-on-a-chip workshop for secondary school students, for which we developed a number of hands-on activities that explained various aspects of microfluidic technology, including fabrication (milling and moulding of microfluidic devices, and wax printing of microfluidic paper-based analytical devices, so-called μPADs), flow regimes (gradient formation via diffusive mixing), and applications (tissue analysis and μPADs). Questionnaires completed by the students indicated that they found the workshop both interesting and informative, with all activities proving successful, while providing feedback that could be incorporated into later iterations of the event.     

3D打印技术对物流企业仓储影响研究 ——以UPS公司为例

随着3D打印技术的快速发展,传统物流企业管理模式必然会受到影响与冲击。本文聚焦快递类物流企业仓储模块,基于3D打印技术、新兴技术管理理论,运用案例研究法对UPS公司单案例做深入探索分析,深入剖析3D打印技术对UPS公司仓储过程的运作流程、职能调整、仓储布局、仓储成本等诸多方面的影响,进而启示其他快递类物流企业应了解3D打印技术其仓储模块的全面影响。     

One step high quality poly(dimethylsiloxane)-hydrocarbon plastics bonding

In this paper, one-step air plasma treatment is successfully used for poly(dimethylsiloxane)(PDMS)-plastic chip bonding. The technique is green, cheap, and requires no other reagent other than air. Hydrocarbon plastics: polystyrene (PS), cyclic olefin copolymer (COC), and polypropylene (PP) have all been successfully bonded to PDMS irreversibly. The corresponding compressed air resistances are measured to be around 500 kPa for PDMS-PS, PDMS-COC, and PDMS-PP hybrid chips. The bondings are also of good quality even after storage under different temperatures and subject to solutions from acid to base.     

纳米科技引领绿色印刷新时代——变革性纳米产业制造技术聚焦纳米绿色印刷与器件制造技术项目研究进展

发展纳米制造技术是从纳米材料到器件规模化制造与应用发展的核心内容。传统的印刷技术主要是基于感光和刻蚀工艺,造成严重的环境污染和资源浪费。绿色印刷是一种增材制造技术,可以从源头大幅度降低能耗和减少环境污染。开发绿色印刷制造技术对我国相关产业的可持续发展具有重要的战略意义。同时,绿色印刷制造与传统微纳加工方法的结合,为器件的制造与集成提供了新的可能途径与方法,可望对产业制造技术产生变革性影响。文章介绍了纳米绿色印刷与器件制造技术项目的研究背景、项目目标与实施概况,以及已经取得的创新成果。     

A simple paper-based sensor fabricated by selective wet etching of silanized filter paper using a paper mask

We developed a novel strategy for fabrication of microfluidic paper-based analytical devices (μPADs) by selective wet etching of hydrophobic filter paper using a paper mask having a specific design. The fabrication process consists of two steps. First, the hydrophilic filter paper was patterned hydrophobic by using trimethoxyoctadecylsilane (TMOS) solution as the patterning agent. Next, a paper mask penetrated with NaOH solution (containing 30% glycerol) was aligned onto the hydrophobic filter paper, allowing the etching of the silanized filter paper by the etching reagent. The masked region turned highly hydrophilic whereas the unmasked region remains highly hydrophobic. Thus, hydrophilic channels, reservoirs, and detection zones were generated and delimited by the hydrophobic barriers. The effects of some factors including TMOS concentration, etching temperature, etching time, and NaOH concentration on fabrication of μPAD were studied. Being free of any expensive equipment, metal mask and expensive reagents, this rapid, simple, and cost-effective method could be used to fabricate μPAD by untrained personnel with minimum cost. A flower-shaped μPAD fabricated by this presented method was applied to the glucose assay in artificial urine samples with good performance, indicating its feasibility as a quantitative analysis device. We believe that this method would be very attractive to the development of simple microfluidic devices for point-of-care applications in clinical diagnostics, food safety, and environmental protection.     

A low cost design and fabrication method for developing a leak proof paper based microfluidic device with customized test zone

This article describes a fabrication process for the generation of a leak proof paper based microfluidic device and a new design strategy for convenient incorporation of externally prepared test zones. Briefly, a negative photolithographic method was used to prepare the device with a partial photoresist layer on the rear of the device to block the leakage of sample. Microscopy and Field Emission Scanning Electron Microscopy data validated the formation of the photoresist layer. The partial layer of photoresist on the device channel limits sample volume to 7 ± 0.2 μl as compared to devices without the partial photoresist layer which requires a larger sample volume of 10 ± 0.1 μl. The design prototype with a customized external test zone exploits the channel protrusions on the UV exposed photoresist treated paper to bridge the externally applied test zone to the sample and absorbent zones. The partially laminated device with an external test zone has a comparatively low wicking speed of 1.8 ± 0.9 mm/min compared to the completely laminated device with an inbuilt test zone (3.3 ± 1.2 mm/min) which extends the reaction time between the analyte and reagents. The efficacy of the prepared device was studied with colorimetric assays for the non-specific detection of protein by tetrabromophenol blue, acid/base with phenolphthalein indicator, and specific detection of proteins using the HRP-DAB chemistry. The prepared device has the potential for leak proof detection of analyte, requires low sample volume, involves reduced cost of production (∼$0.03, excluding reagent and lamination cost), and enables the integration of customized test zones.     

Reagent integration and controlled release for multiplexed nucleic acid testing in disposable thermoplastic 2D microwell arrays

The seamless integration of reagents into microfluidic devices can serve to significantly reduce assay complexity and cost for disposable diagnostics. In this work, the integration of multiplexed reagents into thermoplastic 2D microwell arrays is demonstrated using a scalable pin spotting technique. Using a simple and low-cost narrow-bore capillary spotting pin, high resolution deposition of concentrated reagents within the arrays of enclosed nanoliter-scale wells is achieved. The pin spotting method is further employed to encapsulate the deposited reagents with a chemically modified wax layer that serves to prevent disruption of the dried assay components during sample introduction through a shared microchannel, while also enabling temperature-controlled release after sample filling is complete. This approach supports the arbitrary patterning and release of different reagents within individual wells without crosstalk for multiplexed analyses. The performance of the in-well spotting technique is characterized using on-chip rolling circle amplification to evaluate its potential for nucleic acid-based diagnostics.     

Colored wax-printed timers for two-dimensional and three-dimensional assays on paper-based devices

Microfluidic paper-based analytical devices (μPADs) are widely used for performing diagnostic assays. However, in many assays, time-delay valves are required to improve the sensitivity and specificity of the results. Accordingly, this study presents a simple, low-cost method for realizing time-delay valves using a color wax printing process. In the proposed approach, the time-delay effect is controlled through a careful selection of both the color and the saturation of the wax content. The validity of the proposed method is demonstrated by performing nitrite and oxalate assays using both a simple two-dimensional μPAD and a three-dimensional μPAD incorporating a colored wax-printed timer. The experimental results confirm that the flow time can be controlled through an appropriate selection of the color and the wax content. In addition, it is shown that nitrite and oxalate assays can be performed simultaneously on a single device. In general, the results presented in this study show that the proposed μPADs provide a feasible low-cost alternative to conventional methods for performing diagnostic assays.     

Microfluidic channel structures speed up mixing of multiple emulsions by a factor of ten

We present a novel use for channel structures in microfluidic devices, whereby two two-phase emulsions, one created on-chip, the other off-chip, are rapidly mixed with each other in order to allow for the coalescence of one emulsion with the other. This approach has been motivated by the difficulty in introducing aqueous cross linking agents into droplets by utilising conventional approaches. These conventional approaches include continuous introduction of the different aqueous reagents before droplet formation or alternatively formation of individual droplets of each reagent and subsequent droplet merging later in the microfluidic device. We show that our approach can decrease the mixing time for these fluidic systems by a factor greater than 10 times when compared to a standard microfluidic channel without structures, thereby also allowing for additional reaction time within the microfluidic device. This method shows an application for microfluidic channel structures not before demonstrated, also demonstrating an alternative method for introducing reagents such as cross linkers which link polymer chains to form particles, and provides an example where enzymes are immobilized in monodisperse particles.     

3D打印技术“峡谷”跨越影响因素研究

基于技术采用生命周期"峡谷"理论,从市场、技术、产品和消费者维度对3D打印技术"峡谷"及跨越影响因素进行探讨。通过问卷找到现实和潜在用户,由现实采用者判断当前该技术处于"峡谷"左端,用户以企业、政府为代表,潜在采用者是"峡谷"右端早期大众市场用户代表,是跨越"峡谷"的关键。进一步对潜在采用者分析发现"技术派"最有可能成为"峡谷"跨越的早期大众市场中的单一缝隙市场,"实用派"是进一步可扩展的细分市场。     

金属薄壁筒平网印花机设计

针对应用油墨印花新技术开发不锈钢壳身系列保温瓶新产品,研制了金属薄壁筒平网印花机。设备在结构上采用了双凸凸轮正弦加速度升降机构,启动平稳,运行稳定,生产效率高。设备的移位机构凸轮、曲柄整体连结,运动协调,结构紧凑,使用、维护方便,在机构的一个运动周期内可以精确的完成两次印花工艺。     

3D打印技术在建筑领域的应用及问题探析

我国对于作为第三次工业革命最具代表性技术之一的3D打印技术还处于探索阶段。针对材料选择、尺寸限制、安全性检验等阻碍推进3D打印技术在我国建筑领域应用的重大障碍,通过对3D打印技术在建筑领域适用性的分析及国内外的应用现状对比,从全寿命的角度出发梳理3D打印技术在决策阶段、实施阶段和使用阶段存在的问题,提出3D打印技术未来的发展方向,可以分成全尺寸打印、分段打印后现场装配和群组机器人打印3种模式;并建议未来进一步从材料、机器设备、标准体系、先进性技术、与传统建造方式协同发展等方向进行研究,促进3D打印技术在建筑领域中广泛应用。     

Single-cell printing based on impedance detection

Label-free isolation of single cells is essential for the growing field of single-cell analysis. Here, we present a device which prints single living cells encapsulated in free-flying picoliter droplets. It combines inkjet printing and impedance flow cytometry. Droplet volume can be controlled in the range of 500 pl–800 pl by piezo actuator displacement. Two sets of parallel facing electrodes in a 50 μm × 55 μm channel are applied to measure the presence and velocity of a single cell in real-time. Polystyrene beads with <5% variation in diameter generated signal variations of 12%–17% coefficients of variation. Single bead efficiency (i.e., printing events with single beads vs. total number of printing events) was 73% ± 11% at a throughput of approximately 9 events/min. Viability of printed HeLa cells and human primary fibroblasts was demonstrated by culturing cells for at least eight days.     

Piezoelectric-driven droplet impact printing with an interchangeable microfluidic cartridge

Microfluidic impact printing has been recently introduced, utilizing its nature of simple device architecture, low cost, non-contamination, and scalable multiplexability and high throughput. In this paper, we have introduced an impact-based droplet printing platform utilizing a simple plug-and-play microfluidic cartridge driven by piezoelectric actuators. Such a customizable printing system allows for ultrafine control of droplet volume from picoliters (∼23 pl) to nanoliters (∼10 nl), a 500 fold variation. The high flexibility of droplet generation can be simply achieved by controlling the magnitude of actuation (e.g., driving voltage) and the waveform shape of actuation pulses, in addition to nozzle size restrictions. Detailed printing characterizations on these parameters have been conducted consecutively. A multiplexed impact printing system has been prototyped and demonstrated to provide the functions of single-droplet jetting and droplet multiplexing as well as concentration gradient generation. Moreover, a generic biological assay has also been tested and validated on this printing platform. Therefore, the microfluidic droplet printing system could be of potential value to establish multiplexed micro reactors for high-throughput life science applications.     

Ultraviolet-assisted microfluidic generation of ferroelectric composite particles

We report on the feasible fabrication of microfluidic devices for ferroelectric polymers'' synthesis in a rapid and stable fashion. Utilizing micro-mixing and flow-focusing in microchannels, poly(vinylidene fluoride-trifluoroethylene) and copper phthalocyanine are uniformly dispersed in one hydrogel particle, which are then demonstrated to immediate and complete on-chip steady polymerization by moderate ultraviolet treatment. The advantage of our droplet-based microfluidic devices is generating versatile particles from simple spheres to disks or rods, and the lengths of particles can be precisely tuned from 30 to 400 μm through adjusting the flow rates of both disperse and oil phases. In addition, this mixed technique allows for the continuous production of dielectric microparticles with controlled dielectric properties between 10 and 160. Such a microfluidic device offers a flexible platform for multiferroic applications.     

Protein and cell patterning in closed polymer channels by photoimmobilizing proteins on photografted poly(ethylene glycol) diacrylate

Definable surface chemistry is essential for many applications of microfluidic polymer systems. However, small cross-section channels with a high surface to volume ratio enhance passive adsorption of molecules that depletes active molecules in solution and contaminates the channel surface. Here, we present a one-step photochemical process to coat the inner surfaces of closed microfluidic channels with a nanometer thick layer of poly(ethylene glycol) (PEG), well known to strongly reduce non-specific adsorption, using only commercially available reagents in an aqueous environment. The coating consists of PEG diacrylate (PEGDA) covalently grafted to polymer surfaces via UV light activation of the water soluble photoinitiator benzoyl benzylamine, a benzophenone derivative. The PEGDA coating was shown to efficiently limit the adsorption of antibodies and other proteins to <5% of the adsorbed amount on uncoated polymer surfaces. The coating could also efficiently suppress the adhesion of mammalian cells as demonstrated using the HT-29 cancer cell line. In a subsequent equivalent process step, protein in aqueous solution could be anchored onto the PEGDA coating in spatially defined patterns with a resolution of <15 μm using an inverted microscope as a projection lithography system. Surface patterns of the cell binding protein fibronectin were photochemically defined inside a closed microfluidic device that was initially homogeneously coated by PEGDA. The resulting fibronectin patterns were shown to greatly improve cell adhesion compared to unexposed areas. This method opens for easy surface modification of closed microfluidic systems through combining a low protein binding PEG-based coating with spatially defined protein patterns of interest.     

One step antibody-mediated isolation and patterning of multiple cell types in microfluidic devices

Cell-cell interactions play a key role in regeneration, differentiation, and basic tissue function taking place under physiological shear forces. However, current solutions to mimic such interactions by micro-patterning cells within microfluidic devices have low resolution, high fabrication complexity, and are limited to one or two cell types. Here, we present a microfluidic platform capable of laminar patterning of any biotin-labeled peptide using streptavidin-based surface chemistry. The design permits the generation of arbitrary cell patterns from heterogeneous mixtures in microfluidic devices. We demonstrate the robust co-patterning of α-CD24, α-ASGPR-1, and α-Tie2 antibodies for rapid isolation and co-patterning of mixtures of hepatocytes and endothelial cells. In addition to one-step isolation and patterning, our design permits step-wise patterning of multiple cell types and empty spaces to create complex cellular geometries in vitro. In conclusion, we developed a microfluidic device that permits the generation of perfusable tissue-like patterns in microfluidic devices by directly injecting complex cell mixtures such as differentiated stem cells or tissue digests with minimal sample preparation.