Research On Surface Tension Driven Self-Alignment Capillary Gripper And Its Manipulation Method Of Microfibers

Microfiber assembly and alignment is a crucial enabling technology with wide applications in biomedicine,materials science,and microsystems,such as brain-computer interfaces,fiber-reinforced materials,and fiber optic sensors.Researchers have extensively studied the manipulation and arrangement of microfibers.Various methods have been developed to control the position and orientation of microfibers,including electrostatic spinning,3D printing,and the use of electric and magnetic field-assisted alignment.Although these works have achieved impressive results,the ability to control the position and orientation of individual fibers in the structure is still limited.Additionally,microfiber manipulation has the drawbacks of a complex manipulation process,low manipulation accuracy,and alignment efficiency,which limits the application of these techniques.Currently,there is still a lack of efficient professional tools for assembling and arranging microfibers.It has become imperative to develop an efficient and high-precision microfiber operating tool.This paper presents a surface tension-based microfiber manipulation method and a novel self-alignment capillary gripper for efficient and highprecision manipulation and alignment of microfibers.The self-alignment capillary gripper was created by quantitatively pressing a flat stainless-steel needle and subsequently etching a V-shaped groove at the end of the needle.High-precision self-alignment of microfibers at the end of the capillary gripper was achieved through a two-stage self-alignment strategy.The principle of the two-stage self-alignment strategy was as follows:in the first stage,the liquid meniscus was utilized to pick up the microfibers and roughly self-align the microfibers in the direction of the long axis of the capillary gripper.In the second stage,the volume of the liquid meniscus was reduced,allowing the microfibers to achieve high-precision self-alignment with the V-notch on the end of the capillary gripper.Through the above two-stage self-alignment process,under the conditions of composite bias with a linear bias of 20 μm,an angular bias of 30°,and a gripping bias of 250 μm,the linear alignment error of the microfiber at the end of the capillary gripper is 0.7 ± 0.2 μm,and the angular alignment error is 0.2±0.1°.The manipulation mechanism and performance of the self-alignment capillary gripper were investigated using a combination of theoretical,simulation,and experimental studies.The manipulation mechanism of the microfiber pickup,self-align,and release processes was investigated.A liquid bridge theoretical model of the capillary gripper pick-up,self-align,and release microfibers was established,and the necessary conditions for microfiber pick-up and release were obtained.An arch bridge model was established to evaluate the maximum liquid meniscus volume at the end of the capillary gripper.The relationship between the liquid meniscus height and the meniscus volume confined by the inner hole of the capillary gripper with different tip aspect ratios was obtained.Based on the surface tension theory and the principle of energy minimization,a numerical simulation model for the self-aligned microfibers with the capillary gripper was established using Surface Evolver software.The effects of linear bias,angular bias,tip aspect ratio,microfiber position height,microfiber diameter,and microfiber contact angle on the morphology of the liquid bridge and the free energy of the system were investigated.Additionally,the effects of these key parameters on the restoring force and restoring torque of the microfiber were analyzed.A simulation model for the shape of the liquid meniscus confined to the inner hole of the capillary gripper was developed using Hydro software and the relationship between the meniscus volume and the meniscus height of the liquid was obtained.A microfiber manipulation experimental platform was designed and built according to the microfiber manipulation procedure.The effects of key parameters such as the liquid meniscus volume and the tip aspect ratio of the capillary gripper on the microfiber self-alignment accuracy were experimentally studied.The experimental results showed that utilizing a larger liquid meniscus volume can improve the microfiber self-alignment accuracy.Selecting a capillary gripper with a tip aspect ratio of 4:1 can achieve both good linear alignment accuracy and angular alignment accuracy.It is calculated that when the microfiber is in dry contact with the capillary gripper,the friction torque is about two orders of magnitude greater than the recovery torque,which leads to selfalignment failure.The performance of the self-alignment capillary gripper was evaluated experimentally.Microfibers produced a linear alignment error of 1.6± 0.5 μm and an angular alignment error of 0.5 ± 0.1° at the end of the self-alignment capillary gripper for a composite misalignment of 40 μm for linear bias,30° for angular bias,and 500 μm for gripping bias.The maximum pick-up force of the self-alignment capillary gripper was measured to be 4.2 ± 0.6 μN using a simply supported beam model.The high-accuracy self-alignment of different types of microfibers at the end of the self-alignment capillary gripper was measured,demonstrating the wide applicability of the self-alignment capillary gripper.The transfer stability and manipulation efficiency of the self-alignment capillary gripper were tested.It can stably hold microfibers at rapid movements of 100 mm/s and 30°/s.Theoretically,it is possible to pick up and arrange 900 microfibers with high precision in one hour.Finally,the application of the selfalignment capillary gripper in two-dimensional patterning and three-dimensional spatial arrangement of microfibers was demonstrated,which includes twodimensional patterning of high-density parallel arrays,crosses,triangles,and squares,as well as the insertion of a carbon fiber of diameter is 8 μm into a glass capillary tube of 16 μm inner-diameter and semi-cured polydimethylsiloxane(PDMS).In summary,the self-alignment capillary gripper proposed in this paper can achieve efficient and high-precision manipulation of microfibers.Moreover,the self-alignment capillary gripper is characterized by good performance,high versatility,easy availability of components,and a simple preparation process,which has great potential for application and promotion value.