Cheng C, Aplin F P, Fridman G Y
Annu Int Conf IEEE Eng Med Biol Soc. 2020 Jul;2020:3544-3548. doi: 10.1109/EMBC44109.2020.9176474.
Direct current (DC) has potential as a clinical and scientific tool to accelerate wound healing, increase the permeability of the skin to drug treatment and modulate neural activity. But long duration delivery of DC unavoidably causes hazardous electrolysis at the tissue-electrode interface. To be able to deliver long duration DC, we previously proposed a design for a safe direct current stimulator (SDCS). This device uses alternating current that does not cause chemical reactions at the metal electrodes within the device, but delivers ionic direct current output to the tissue via microfluidic valves. We previously developed and published designs of multiple SDCS components including microfluidic, electronic, data processing, and energy systems. In this paper we focus on the development of the integrated microfluidics needed by the SDCS system. We developed a fabrication method and characterized valve performance within the multi-valve microfluidic system. We used poly-dimethylsiloxane (PDMS) to fabricate three microfluidic chips that integrated valves actuated by 50-µm Nitinol (NiTi) shape memory alloy (SMA) wire. We tested system operation by driving SMA valves with a current pulse and recording the valve response with an electrical assay. The valve operation complied with the SDCS system requirements. The time for valves to open was rapid at 0.177 ± 0.04 seconds, and the time for the valves to close was 0.265 ± 0.05 seconds. Open microfluidic channel impedance for unrestricted ionic current flow was 15.90 ± 8.28 kΩ and it increased by a factor of 40 to restrict ionic current flow at 678 ± 102 kΩ for the closed valves.
直流电（DC）作为一种临床和科学工具，具有加速伤口愈合、提高皮肤对药物治疗的通透性以及调节神经活动的潜力。但长时间输送直流电不可避免地会在组织-电极界面处引发有害的电解反应。为了能够长时间输送直流电，我们之前提出了一种安全直流刺激器（SDCS）的设计方案。该设备使用交流电，不会在设备内部的金属电极上引发化学反应，但会通过微流控阀向组织输送离子直流电输出。我们之前开发并发表了多个SDCS组件的设计，包括微流控、电子、数据处理和能量系统。在本文中，我们专注于SDCS系统所需的集成微流控技术的开发。我们开发了一种制造方法，并对多阀微流控系统内的阀门性能进行了表征。我们使用聚二甲基硅氧烷（PDMS）制造了三个微流控芯片，这些芯片集成了由50微米镍钛诺（NiTi）形状记忆合金（SMA）丝驱动的阀门。我们通过用电流脉冲驱动SMA阀门并用电气检测记录阀门响应来测试系统运行。阀门操作符合SDCS系统要求。阀门打开的时间很快，为0.177±0.04秒，阀门关闭的时间为0.265±0.05秒。对于不受限制的离子电流流动，开放微流控通道的阻抗为15.90±8.28 kΩ，而对于关闭的阀门，为了限制离子电流流动，阻抗增加到678±102 kΩ，增加了40倍。
