目的 针对毛细晶体管难以同时实现高效液体定向传输和柔性的难题,提出采用牺牲模板辅助3D打印技术（可牺牲3D打印）在聚二甲基硅氧烷（PDMS）表面加工具有互联通道的非对称悬空微结构,从而实现液体毛细爬升方向、高度、宽度、面积的控制,并赋予其三维空间可变形能力。方法 采用光固化3D打印技术制备可牺牲毛细晶体管的负模板,经过PDMS浇注、热固化和碱溶液水解模板过程,最终得到PDMS柔性毛细晶体管。通过超景深显微镜表征毛细晶体管的形貌。通过接触角测量仪表征液体对结构的浸润性,通过端部浸入和输注测试评估液体的毛细行为。结果 确定了光固化打印可牺牲负模板的最优曝光时间为18 s。确定了可牺牲树脂在碱性水溶液中完全水解的时间为140 min。确定2次后处理（异丙醇清洗、紫外固化、加热记为1次后处理循环）有助于去除负模板对PDMS固化的毒性,从而制备出高精度柔性毛细晶体管结构。实验结果表明,无水乙醇在柔性毛细晶体管上的爬升高度可达到25.3 mm,经过等离子体处理后此数值提高至37.0 mm。通过柔性毛细晶体管可以调节液体流动的方向和宽度,并充当毛细流动的开/关阀、放大器、分流器等。通过弯曲PDMS柔性毛细晶体管,可实现复杂曲面上液体定向传输。此外,基于PDMS的疏水和亲油特性,柔性毛细晶体管还实现了自驱动油水分离功能。结论 将可牺牲3D打印技术应用于微流控芯片加工,提高了PDMS三维微结构的加工精度,并成功构建了柔性毛细晶体管,同时实现了高效液体定向传输和三维空间可变形能力。
Abstract
To address the challenge of simultaneously achieving efficient unidirectional liquid transport and flexibility on capillary transistors, a method has been proposed in which the sacrificial template-assisted three-dimensional printing (sacrificial 3D printing) is utilized to fabricate asymmetric overhanging microstructures with interconnected channels on the surface of polydimethylsiloxane (PDMS). The method allows for precise control over the direction, height, width, and area of liquid capillary rise while imparting the ability for three-dimensional spatial deformation of the structure. In this work, a photopolymerization-based 3D printer was used to create a negative template with optimized exposure time and printing resolution for the capillary transistors. After PDMS casting, thermal curing, and alkaline solution hydrolysis of the template, flexible PDMS capillary transistors were obtained. The impact of different post-processing cycles (0, 1, 2, and 3 times) on the PDMS molding effect was evaluated. The morphology of the resulting structures was characterized by a microscope with extended depth of filed, and the dimensions were measured to calculate the dimensional deviations between the designed values and the measured values. A contact angle meter was used to assess the wettability of the structures with various liquids. The flexible capillary transistors with different dimensions were fabricated, and the self-driven capillary rise height in anhydrous ethanol was recorded to determine the optimal structural parameters. Liquid capillary rise and injection tests were performed to evaluate the unidirectional liquid transport behaviors and flexibility of the capillary transistors.
The results showed that the sacrificial template was successfully fabricated by 3D printing, with an optimal exposure time of 18 seconds and a minimum design feature size of 120 μm. The sacrificial resin was completely hydrolyzed in an alkaline aqueous solution within 140 minutes. After two post-processing cycles (including isopropyl alcohol cleaning, UV curing, and heating), high-precision flexible capillary transistor structures were successfully fabricated. Experimental results of liquid capillary rise demonstrated that the maximum capillary rise height of anhydrous ethanol on the flexible capillary transistors reached 25.3 mm. Furthermore, O2 plasma treatment significantly enhanced the capillary rise of anhydrous ethanol, reaching a maximum height of 37.0 mm, which was attributed to the change in contact angle. By adjusting the direction and width of the asymmetric overhanging microstructure in the flexible capillary transistors, various functions such as liquid on/off valves, amplifiers, and attenuators were achieved. The fabricated PDMS flexible capillary transistors demonstrated remarkable structural flexibility. They were capable of bending to any angle, twisting, or even knotting, and could return to their original shape without any damage. This flexibility allowed the flexible capillary transistor to perform unidirectional liquid transport even on complex curved surfaces with angles greater than 360°. Additionally, by leveraging the hydrophobic and oleophilic properties of PDMS, the flexible capillary transistors enabled self-driven water-oil separation.
This study applies sacrificial 3D printing technology to the fabrication of microfluidic chips, enhancing the processing accuracy of PDMS three-dimensional microstructures. It successfully creates flexible capillary transistors that enable efficient unidirectional liquid transport and 3D deformability. Flexible capillary transistors hold significant potential for applications in microfluidics, liquid distribution, and oil-water separation technologies. This research provides important experimental insights for the design and application of flexible capillary transistors and broadens the potential applications of sacrificial 3D printing technology in the manufacturing of microfluidic devices.
关键词
非对称悬空微结构 /
毛细晶体管 /
液体定向传输 /
PDMS /
可牺牲3D打印 /
油水分离
Key words
asymmetric overhanging microstructure /
capillary transistor /
unidirectional liquid transport /
PDMS /
sacrificial 3D printing /
oil-water separation
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基金
国家自然科学基金（52033002,82227808）; 江苏省自然科学基金（BK20241268）; 东南大学和江苏省人民医院开放研究基金（2024-M02）; 江苏省青年科技人才支持项目（JSTJ-2024-096）; 东南大学生创业研究基金（RF028623292）; 东南高校青年跨学科研究计划（2024FGC1003）
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