Department of Biomedical Engineering, University of Iowa, Iowa City, Iowa 52242, USA.
Department of Electrical and Computer Engineering, University of Iowa, Iowa City, Iowa 52242, USA.
Rev Sci Instrum. 2021 Mar 1;92(3):034101. doi: 10.1063/5.0039696.
In this work, we present a single-pole magnetic tweezers (MT) device designed for integration with substrate deformation tracking microscopy and/or traction force microscopy experiments intended to explore extracellular matrix rheology and human epidermal keratinocyte mechanobiology. Assembled from commercially available off-the-shelf electronics hardware and software, the MT device is amenable to replication in the basic biology laboratory. In contrast to conventional solenoid current-controlled MT devices, operation of this instrument is based on real-time feedback control of the magnetic flux density emanating from the blunt end of the needle core using a cascade control scheme and a digital proportional-integral-derivative (PID) controller. Algorithms that compensate for a spatially non-uniform remnant magnetization of the needle core that develops during actuation are implemented into the feedback control scheme. Through optimization of PID gain scheduling, the MT device exhibits magnetization and demagnetization response times of less than 100 ms without overshoot over a wide range of magnetic flux density setpoints. Compared to current-based control, magnetic flux density-based control allows for more accurate and precise magnetic actuation forces by compensating for temperature increases within the needle core due to heat generated by the applied solenoid currents. Near field calibrations validate the ability of the MT device to actuate 4.5 μm-diameter superparamagnetic beads with forces up to 25 nN with maximum relative uncertainties of ±30% for beads positioned between 2.5 and 40 µm from the needle tip.
在这项工作中，我们展示了一种单极磁镊（MT）设备，该设备设计用于与基底变形跟踪显微镜和/或牵引力显微镜实验集成，旨在探索细胞外基质流变学和人类表皮角质形成细胞机械生物学。该 MT 设备由商用现货电子产品硬件和软件组装而成，可在基础生物学实验室中进行复制。与传统的螺线管电流控制 MT 设备相比，该仪器的操作基于使用级联控制方案和数字比例积分微分（PID）控制器实时反馈控制从针芯钝端发出的磁通密度。实现了补偿在致动过程中发展的针芯的空间不均匀剩磁的算法反馈控制方案。通过优化 PID 增益调度，该 MT 设备在磁场密度设定点的宽范围内表现出小于 100 ms 的磁化和退磁响应时间，没有过冲。与基于电流的控制相比，基于磁通密度的控制通过补偿由于施加的螺线管电流产生的热量而导致的针芯内温度升高，可以实现更准确和精确的磁致动力。近场校准验证了 MT 设备能够以高达 25 nN 的力致动 4.5 µm 直径的超顺磁珠，对于位于针尖端 2.5 到 40 µm 之间的珠子，最大相对不确定度为±30%。
