粗糙度对微流道内流体连续自搬运的影响

微流控芯片中各功能单元间样品的运输依赖于流体在微通道中的流动,尺度效应加剧表面作用效果,使得微流道内流体无需外部动力即可实现连续铺展搬运。为了深入研究微流道内流体的流动机制和动力学特性,分析影响微流道内流体自搬运效率的因素,基于近似Derjaguin法的同时充分考虑表面能和Casimir效应,利用数值计算和实验相结合的方法分析了微流道内壁粗糙度对流体流动特性和自搬运效率的影响,明确了微流道内流体的本构方程和流动控制方程,并设计搭建实验台验证所得结果的有效性和可靠性。结果表明：内壁粗糙度是影响微流道内流体流动特性和连续自搬运效率的重要因素;当粗糙度等效齿数、等效齿高和等效齿倾角变化时,微流道内近壁面齿隙间的主漩涡和伴生涡都相应改变,导致流体自搬运效率发生相应变化。研究结果对解决微流控润滑和微流控芯片减阻防粘等设计和使用问题具有重要理论指导意义,对微电子机械系统的小型化和集成化设计具有一定的参考价值。     

塑料微流控芯片的制作及其自动化

实现塑料微流控芯片制作的自动化能够大幅度降低制作成本,稳定芯片质量,并使芯片具有较好的一致性,是推广应用、实现产业化所亟待解决的重要问题。本文简要介绍了微流控芯片的发展现状,指出影响其推广应用的主要障碍及所面临的主要问题。阐述了实现塑料微流控芯片制作自动化的意义。简述了制作塑料微流控芯片的两种主要方法——模塑法和热压法,分析了热压法制作塑料微流控芯片的工艺过程及其实现自动化所需解决的诸如自动脱片、基片与盖片的自动对准及预联接等技术问题。介绍了大连理工大学微系统研究中心同北京航空航天大学机器人研究所合作研制开发的塑料(PMMA)微流控芯片的自动化制造系统,并简要说明了主要的组成设备。     

CO2激光辅助加工PMMA微流控芯片中的重铸物现象

根据实验现象分析了CO2激光制作PMMA微流控芯片储液池过程中,材料的流动与变形过程,以及凸起重铸物形成对芯片制作的影响.考察了激光功率、扫描速度以及材料取向对流变行为的作用及其机理.实验中采用不同的激光光束功率以及扫描速度,分析热量吸收的大小对材料流动与变形的影响,比较了挤出PMMA在顺着挤出方向与垂直于挤出方向切割时实验结果的不同.CO2激光加工PMMA过程中,材料在激光的热作用下发生软化、熔化及汽化.软化材料在汽化材料产生的气体压力作用下发生流动与变形,形成了沟道表面的凸起重铸物.实验结果表明热量及材料内部存在的取向对其流动与变形及凸起重铸的形成起着重要的作用.     

聚甲基丙烯酸甲酯薄膜表面的亚微米级图案化

利用波长为172nm的真空紫外光刻蚀技术(Vacuum ultraviolet lithography,VUV)对聚甲基丙烯酸甲酯(PMMA)薄膜的表面进行了图案化微加工,并采用扫描电镜和原子力显微镜对微图案化的PMMA膜的表面形貌进行了表征.此外,还通过跟踪测试真空紫外光照后PMMA膜表面随时间变化的水接触角研究了表面的亲疏水性.结果表明,利用该方法可以成功地在PMMA基材上一次性制备出保真度较好的亚微米级微流道,而且使微流道内表面具有稳定持久的亲水性.     

石英玻璃微流道超声振动磨削加工及流动阻力特性研究

石英玻璃微流控芯片在医学诊断、生化分析和药物筛选等领域具有广阔的应用前景,高性能石英玻璃微流道的加工质量直接决定微流控芯片的使用性能。本工作采用超声振动磨削加工技术对石英玻璃微流道进行高效精密加工,首先研究了主轴转速N、进给速度v_f、磨削深度a_p和超声功率P对微流道表面质量和形状精度的影响,然后对超声振动磨削工艺参数进行优化,最后测试微流道的水流阻力,研究微流道水力直径对其流动阻力特性的影响。超声振动磨削加工实验结果表明：石英玻璃微流道的表面粗糙度R_a可达较小值0.191μm,形状精度RMS值和PV值分别达到3.332μm和23.783μm,并且微流道表面形貌完整,底部微观表面光滑,边缘整齐无明显崩边。流动性测试实验结果表明：石英玻璃微流道内流动摩擦阻力系数随雷诺数和水力直径的增大而减小,因此设计微流道时应尽量选择较大的水力直径,并且适当增大流速。     

塑料微流控芯片的注塑成型

有别于传统的微流控芯片压塑成型方法,本文提出注塑成型加工塑料微流控芯片的新工艺.采用UV-LIGA技术制作成型微通道的型芯,设计制造了微流控芯片注塑模具.充模试验表明,如何使微通道复制完全是微流控芯片注塑成型的主要技术难点.模拟与理论分析表明,熔体在微通道处出现滞流现象是复制不完全的主要原因;搭建了可视化装置对此加以试验验证.利用正交试验方法进行充模试验,研究各工艺参数对微通道复制度的影响.试验表明模具温度对提高微通道复制度起决定性作用;注射速度和熔体温度是次要因素,而注射压力相对其他因素影响力较差,但必须保持在一个较高的水平.依此形成塑料微流控芯片的注塑成型工艺,对于宽80μm、深50μm截面的微通道而言,可使微通道复制度由70%提高到90%,满足使用要求.     

模板电解法快速制作玻璃微流控芯片

玻璃微流控芯片在许多领域已经得到较广泛的应用,但目前的加工需要繁琐的步骤及昂贵的设备进行图形转移及金属牺牲层开窗口.本文提出一种快速制作金属牺牲层图形窗口以用于玻璃微流控芯片加工的方法.以CO2激光直写加工PET膜模板,微细电解加工玻璃基片上的铬/金牺牲层快速获得窗口,湿法腐蚀及热键合制作玻璃微流控芯片.结果表明该法可在10秒内开窗口,电解加工过程使用的模板厚度、电解液组成及施加的压力与电压对窗口的质量都有显著影响.加工的微通道宽度为145μm,边缘整齐,宽度均匀,相对标准偏差为3.72%,深度μm,底部平整度高,并成功用于氨基酸混合液的芯片毛细管电泳分离.同时使用该方法加工的金微电极阵列,电极宽度为100μm,最小间距可达100μm.     

基于局部溶解性激活的聚合物微流控芯片超声波键合

利用低于临界振幅下的超声波作用在聚合物上仅产生表面热的特点,结合PMMA在异丙醇(IPA)中的温变溶解特性,提出了一种基于局部溶解性激活的超声波聚合物微流控芯片键合方法.理论分析表明当超声振幅小于临界振幅时,只有器件接触表面产生局部表面热,而且在70℃附近IPA对PMMA的溶解性才具有良好的激活作用.在试验研究中,利用精密加工法和热压法制作了带面接触式导能筋结构和80μm×80μm微通道的PMMA微流控芯片基片.在超声振幅为13μm、键合时间8 s、键合压力300 N的条件下进行了键合试验.结果表明,芯片拉伸强度达2.25 MPa,微通道的承压能力超过800 kPa,键合后导能筋无熔融,微沟道变形率小于2%,键合时间仅为8s.该方法的键合强度和键合效率明显高于传统的键合方法,而微结构的变形率却较小,故可作为一种具有产业化前景的聚合物MEMS器件快速封接方法.     

生物微流控PCR荧光芯片微通道动态检测系统研究

研究和建立了生物微流控PCR荧光芯片微流控微通道动态检测系统,对该系统的多光路光纤校准进行了研究,获得了荧光检测的重复性(偏差:2.6%)和稳定性(偏差》2.7%)等.实验结果表明:该系统可用于准分子激光制备高聚物基生物微流控PCR荧光芯片最佳工艺激光制备参数的优化设计;可用于生物微流控PCR荧光芯片生物分析时的实时荧光定量检测;也可用于对激光荧光检测微型化技术与生物芯片光谱检测集成化提供多功能实验基础和性能评估体系.     

PMMA微流控检测芯片的设计与制作

设计并制作了一种PMMA（polymethyl methacrylate）材料的微流控检测芯片,将外界气体驱动液体用于实际水样的分析和检测．利用精密加工的方法加工出芯片的整体尺寸为86mm×60mm×4．5mm．采用溶胶-凝胶的改性方法对微通道管路进行亲水处理,正硅酸乙酯的水解缩合生成了一层溶胶．凝胶覆盖在PMMA表面,从而大大提高了亲水性．在室温下对芯片进行键合,溶剂为二氯乙烷和无水乙醇按1：1混合的混合液．该方法避免了微通道的坍塌,有效防止了堵塞．实验证明,芯片接触紧密,且冲击强度能够满足要求．同时,芯片上集成了多个阀．阀膜选用0．5mm厚的硅胶膜,采用硅橡胶做黏合剂     

Microchannel edge formation in laser-ablated polyimide

Microchannels in polyimide (PI) have been produced by means of laser ablation (LA). The obtained results confirm the possibility of using the LA technology for the functional structure formation on PI-based microfluidic chips (MFCs). The shape of the channel edge may depend on the thermal properties of PI. This circumstance makes it possible to optimize the process of MFC fabrication by selecting a proper PI and the corresponding LA regime. Optimization of the other characteristics, such as mechanical properties and planarity of the MFCs, requires additional investigations.     

Liquid PMMA: A High Resolution Polymethylmethacrylate Negative Photoresist as Enabling Material for Direct Printing of Microfluidic Chips

Polymethymethacrylate (PMMA) is one of the most important thermoplasts and a commonly used material in microsystem fabrication, for example, microfluidics owning mainly to its optical transparency, biocompatibility, low autofluorescence, and low cost. However, being a thermoplastic material PMMA is typically structured using industrial replication techniques making PMMA unsuitable for rapid prototyping. The fact that neither material nor processing technique can be directly transferred from laboratory to industrial state makes the research‐to‐business conversion often extremely difficult in microfluidics since material properties have a major impact on the final system behavior. This paper presents “Liquid PMMA,” a fast curing viscous PMMA prepolymer which can be used as a negative photoresist and directly structured using ultraviolet or visible light with tens of micron resolution and smooth surfaces. Using this technique microfluidic chips in PMMA can be fabricated within minutes. The cured Liquid PMMA parts show the same high optical transparency, low autofluorescence, and surface properties like commercial PMMA. In this way, microfluidic chips can be rapidly developed and optimized on the laboratory scale in the same material which is later on used on the industrial scale.

     

整合纸基微流控检测芯片的食药纸包装

目的探索纸质食品、药品包装与纸基微流控检测芯片的整合方法与规律。方法在传统纸质食品或药品包装的内表面,通过喷蜡打印的方法,整合具有特定生物化学检测作用的纸基微流控芯片,并探索微流体在包装内表面构成的纸基微流控芯片中的运用规律。结果通过喷蜡打印,成功地将纸基微流控芯片整合在了传统纸质食药包装的内表面,经过测试可以完成液体pH检测等基础生物化学检测应用。结论将纸基微流控芯片与食药纸质包装相结合,为食品、药品的实时和现场自我检测提供了新的思路和手段,该方法不仅成本低廉、易于操作,且检测精度高。     

Preparation and luminescence properties of spin-coated PMMA films containing Si nanocrystallites

We report on the synthesis of Si nanocrystallites by pulsed laser ablation in toluene followed by the preparation of composite films with PMMA and their luminescence studies. Transmission electron microscopy images show that the sizes of silicon nanocrystallites vary from about 4 nm down to below 1 nm. The composite films exhibit strong emissions with their spectral peaks continuously moving from 387 to 506 nm when the excitation wavelength varies from 300 to 440 nm, in accordance with the quantum confinement effect. Their time-resolved photoluminescence spectra reveal a multi-exponential decay, implying that the light emission may be also related to some surface states.     

Effect of Fluence and Pulse Overlapping on Fabrication of Microchannels in PMMA/PDMS Via UV Laser Micromachining: Modeling and Experimentation

This article presents modeling and experimental investigations on the effects of process parameters and the viability of directly fabricating microchannels in polymethyl methacrylate (PMMA) and polydimethylsiloxane (PDMS) polymers which are suitable for the fabrication of microfluidic devices due to their biocompatibility and transparent properties. Experimental work was conducted using a solid-state Nd:YAG laser with 355 nm ultraviolet (UV) wavelength and 5 ns pulse duration at various energy densities and pulse overlapping (PO). The study was focused on understanding the effects of two main process parameters: fluence and PO. This study closely investigates the effect of varying process parameters on the ablation depth and profile achieved and the resultant microchannel dimensional quality. It presents findings indicating that both process parameters have strong effects on the profile shape and variability of the microchannel width and depth. For PMMA polymer, the lowest dimensional variability for the microchannel profile is obtained with low fluence values and highest PO factor, whereas for PDMS polymer, it was observed that microchannel width and depth decreased linearly with increasing fluence and increased nonlinearly with increasing scanning rate. Further, process modeling is utilized for predicting microchannel profile and ablation depth, and these predictions were validated with experimental results obtained with pulsed laser micromachining at UV wavelength.     

Surface characterization of laser-ablated polymers used for microfluidics

Fabrication of microfluidic devices by excimer laser ablation under different atmospheres may provide variations in polymer microchannel surface characteristics. The surface chemistry and electroosmotic (EO) mobility of polymer microchannels laser ablated under different atmospheres were studied by X-ray photoelectron spectroscopy and current monitoring mobility measurements, respectively. The ablated surfaces of PMMA were very similar to the native material, regardless of ablation atmospheres due to the negligible absorption of 248-nm light by that polymer. The substrates studied that exhibit nonnegligible absorption at this energy, namely, poly(ethylene terephthalate glycol), poly(vinyl chloride), and poly(carbonate), showed significant changes in surface chemistry and EO mobility when the ablation atmospheres were varied. Ablation of these three polymer substrates under nitrogen or argon resulted in low EO mobilities with a loss of the well-defined chemical structures of the native surfaces, while ablation under oxygen yielded surfaces that retained native chemical structures and supported higher EO mobilities.     

Analysis of the PMMA and cornea temperature rise during excimer laser ablation

A general method to analyze the ablation temperature for different materials (in particular in the human cornea and poly-methyl-methacrylate (PMMA)) is provided. The model is comprehensive and provides directly laser beam characteristics and ablative spot properties. The model further provides a method to convert the temperature rise during ablation observed in PMMA to equivalent temperature rises in the cornea. The proposed model can be used for calibration, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results.     

Fabrication and characterization of microstructures with optical quality surfaces in fused silica glass using femtosecond laser pulses and chemical etching

We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.     

Art‐on‐a‐Chip: Preserving Microfluidic Chips for Visualization and Permanent Display

“After a certain high level of technical skill is achieved, science and art tend to coalesce in aesthetics, plasticity, and form. The greatest scientists are always artists as well.” said Albert Einstein. Currently, photographic images bridge the gap between microfluidic/lab‐on‐a‐chip devices and art. However, the microfluidic chip itself should be a form of art. Here, novel vibrant epoxy dyes are presented in combination with a simple process to fill and preserve microfluidic chips, to produce microfluidic art or art‐on‐a‐chip. In addition, this process can be used to produce epoxy dye patterned substrates that preserve the geometry of the microfluidic channels—height within 10% of the mold master. This simple approach for preserving microfluidic chips with vibrant, colorful, and long‐lasting epoxy dyes creates microfluidic chips that can easily be visualized and photographed repeatedly, for at least 11 years, and hence enabling researchers to showcase their microfluidic chips to potential graduate students, investors, and collaborators.     

Analysis of the cornea-to-PMMA ablation efficiency rate

The relative ablation efficiency at different materials (in particular human cornea and poly(methyl methacrylate) (PMMA)) was analysed. A comprehensive model, which directly considers applied correction, including astigmatism, as well as laser beam characteristics and ablative spot properties has been developed. The model further provides a method to convert the deviations in achieved ablation observed in PMMA to equivalent deviations in the cornea. Radiant exposures from about 90?mJ/cm² to about 500?mJ/cm² correspond to cornea-to-PMMA ablation ratios of about 9 and about 1.7, respectively (about 7 and 1.3 optically). Super-Gaussian order from simple Gaussian profile to flat-top profile, and for a radiant exposure of 250?mJ/cm², correspond to cornea-to-PMMA ratios of about 2.3 and about 1.6, respectively (about 1.7 and about 1.2 optically). For a Gaussian beam of 160?mJ/cm² radiant exposure, a severe overcorrection of +50% in PMMA corresponds only to an overcorrection of +29% on corneal tissue, whereas a moderate overcorrection of +20% in PMMA corresponds to an overcorrection of +12% on corneal tissue. For a severe undercorrection of ?50% ablation observed in PMMA, the range for radiant exposures from about 90?mJ/cm² to about 500?mJ/cm² correspond to corneal undercorrections of about ?14% to about ?40%, respectively. The proposed model can be used for calibration, ablation pattern test and development, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results.