Magnetization‐Induced Self‐Assembling of Bendable Microneedle Arrays for Triboelectric Nanogenerators

Abstract

Triboelectrification is a process of charge separation and transfer between tow materials through mechanical contact and friction. [9] The electrical output performance of TENG can be improved by enhancing the surface roughness of the triboelectric materials, which can lead to an enlargement of the contact or friction area. [10] Hence, a lot of investigations focus on developing the protruding surface structures, including the dome array, [2b] cube array, [11] pyramid array, [12] nanorod array, [13] and subwavelength architectures, [14] in order to enhance the output electricity. However, the above structures have some limitations including complex, long-time, high-cost fabrication processes based on photolithography, electrochemical deposition, or soft lithography methods. [9a,14-15] Trinh and Chung [9a] proposed a microneedle array (MA)-based TENG and its novel mechanism of mixed bending-friction-deformation behavior for increasing the output performance. The MA-based TENG exhibited extremely high output power.The key component of MA-based TENG is a bendable MA. Various techniques have been developed to fabricate MA. Typically, MA can be fabricated by the subtractive processes, in which the 3D structures of MA are selectively carved out of a 2D substrate, including lithography with wet or dry etching, [16] laser cutting, [17] micromachining, [18] and wireelectrode cutting. [19] The limitations of these subtractive processes are complex, expensive, time consuming, or not suitable for mass production. Additive processes, such as 3D printing, [20] droplet-born air blowing, [21] electro-drawing lithography, [22] thermal drawing lithography, [23] and magnetorheological drawing lithography, [24] also can form 3D structures of polymer MA from droplets or 2D surfaces. 3D printing is a flexible process that allows personalized customization, but it is not suitable for mass production. The other processes suffer from the limitations of difficult operation and relatively low production efficiency. [22a,25] The micromolding technique is a near-net-shape forming process, which has been employed to fabricate polymer microneedles owing to its potential for mass production. [9a,26] However, it is characterized by multiple costly and time-consuming steps, such as master preparation, mold fabrication, polymer filling, and microneedles separation. [22a,27] Furthermore, Since the invention of triboelectric nanogenerator (TENG) in 2012, it has become one of the most important innovations in energy conversion technologies. A flexible microneedle array (MA)-based TENG is proposed using the closed bending-friction-deformation behavior of MA for the mechanical energy harvest. A novel magnetization-induced self-assembling method is introduced to efficiently fabricate the bendable MA for the TENG. The 3D structures of MA are continuously self-assembled from a moving film of curable magnetorheological fluid under the assistance of a rotating external magnetic field. The mass production of MA may be achieved using this method ...

A Review on Structural Configurations of Magnetorheological Fluid Based Devices Reported in 2018–2020

“…Further, the device can refine the design of damping forces in different directions to realize the control of damping variation in multi-directions. Furthermore, using a drawing lithography approach, some MRF microneedles were fabricated for minimally invasive surgery, transdermal drug delivery, and smart wearable equipment (Chen Z. P. et al, 2018;Chen et al 2019a;Chen et al, 2019b). In a gradient magnetic field, the MRF is magnetized and generates fusiform patterns, which results in different forms of microneedle arrays after heating and solidifying, as shown in Figure 10C.…”

“…(B) Smart ball-socket actuator for upper limb rehabilitation (Wahed and Balkhoyor, 2018). (C) Magnetization-induced self-assembling process of microneedle array (Chen Z. P. et al, 2018;Chen et al 2019a;Chen et al, 2019b).…”

Ultrasensitive Multifunctional Magnetoresistive Strain Sensor Based on Hair‐Like Magnetization‐Induced Pillar Forests

“…The formation process of magnetization-induced pillars is illustrated in Figure 6a. According to the classic Rosensweig pattern [25,34] in a homogeneous perpendicular magnetic field, λ π σ ρ…”

“…[3,4] Various mechanisms, such as triboelectric sensing, [5] mechanic-capacitive, [6] and systems, including functional medical implants, smart packaging, non-contact human-machine interaction elements, etc. [25][26][27][28][29] Some strategies have indeed been tried by packaging conventional magnetic film sensors (e.g., hall sensor, giant magnetoresistive sensor) with soft materials or fabricating them on flexible substrates. [30][31][32] However, the brittle/rigid nature of permanent magnetic materials severely affect their long-term use in deformation.…”

Photothermally Reconfigurable Shape Memory Magnetic Cilia

“…Methods for fabricating artificial cilia can generally be classified according to whether they use templates. [33] Template-based approaches usually involve lithography or pre-defined molds that can require complex, lengthy, or expensive fabrication processes, [13,34,35] but there has been some progress in developing simpler template-based fabrication methods. For example, templates can be fabricated through mechanical punching.…”