Raj Thilak, Roy Srestha, Kumar Ashwin, Roy Basudev, Mani Ethayaraja, Sudhakar Swathi
Department of Applied Mechanics and Biomedical Engineering, Indian Institute of Technology Madras, Chennai 600036, India.
Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India.
J Colloid Interface Sci. 2025 Jan;677(Pt B):986-996. doi: 10.1016/j.jcis.2024.07.237. Epub 2024 Aug 9.
Synthetic micro/nanomotors are gaining extensive attention for various biomedical applications (especially in drug delivery) due to their ability to mimic the motion of biological micro/nanoscale swimmers. The feasibility of these applications relies on tight control of propulsion speed, direction, and type of motion (translation, circular, etc.) along with the exerted self-propulsive force. We propose to exploit the variation of both self-propulsion speed and force of active colloids with different patch coverages (with and without supporting layer) for engineering diffusiophoretic micro/nanomotors.
The microswimmers were designed at various patch coverages (10°, 30°, and 90°) with (Ti/Pt) and without (Pt) an adhesion layer for the catalytic patch through glancing angle metal deposition (GLAD) technique. Mean-square displacement (MSD) analysis was performed to obtain the self-propulsion parameters like speed and angular speed. Using optical tweezers (OT), the self-propulsive force was measured from the force power spectral density.
The findings of our experiments suggest the non-requirement of any adhesion layer preceding the catalyst deposition since the Pt 10° colloidal batch had the maximal self-propulsion speed (4.61±0.3μm/s) and force (345±57fN) for 5% w/v HO fuel concentration. Moreover, the self-propulsion speed and force decreased with increasing patch size, contrary to theoretical estimates. Also, the self-propulsive force obtained from MSD is 2 to 4 times lower in magnitude than the OT based force values. We believe that the self-propelling motion of the micromotors is possibly hindered due to interactions with the surface of the quartz cuvette during the optical microscopic analysis. Further, the MSD is limited to the self-propulsive motion in two dimensions. On the other hand, OT based force measurement involve trapping the particles in the bulk of the solution entirely avoiding the particle-substrate interactions. Hence, OT based force measurements are better than the propulsion velocity based stokes drag force estimates. We believe that this study can lay the foundation in designing efficient micro/nanomotors for translational biomedical applications.
合成微纳马达因其能够模拟生物微纳尺度游动体的运动，在各种生物医学应用（尤其是药物递送）中受到广泛关注。这些应用的可行性依赖于对推进速度、方向和运动类型（平移、圆周运动等）以及所施加的自推进力的严格控制。我们提议利用具有不同斑块覆盖率（有和没有支撑层）的活性胶体的自推进速度和力的变化来设计扩散泳微纳马达。
通过掠角金属沉积（GLAD）技术，设计了具有不同斑块覆盖率（10°、30°和90°）且有（Ti/Pt）和没有（Pt）用于催化斑块的粘附层的微游动体。进行均方位移（MSD）分析以获得诸如速度和角速度等自推进参数。使用光镊（OT），从力功率谱密度测量自推进力。
我们的实验结果表明，在催化剂沉积之前不需要任何粘附层，因为对于5% w/v的HO燃料浓度，Pt 10°胶体批次具有最大的自推进速度（4.61±0.3μm/s）和力（345±57fN）。此外，与理论估计相反，自推进速度和力随着斑块尺寸的增加而降低。而且，从MSD获得的自推进力在大小上比基于OT的力值低2至4倍。我们认为，在光学显微镜分析期间，微马达的自推进运动可能由于与石英比色皿表面的相互作用而受到阻碍。此外，MSD仅限于二维的自推进运动。另一方面，基于OT的力测量涉及将粒子捕获在溶液主体中，完全避免了粒子与底物的相互作用。因此，基于OT的力测量优于基于推进速度的斯托克斯阻力估计。我们相信这项研究可以为设计用于平移生物医学应用的高效微纳马达奠定基础。
