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Review
. 2021 Nov 3:7:88.
doi: 10.1038/s41378-021-00312-8. eCollection 2021.

Progress of shrink polymer micro- and nanomanufacturing

Wenzheng He  1 , Xiongying Ye  1 , Tianhong Cui  2
Affiliations
Review

Progress of shrink polymer micro- and nanomanufacturing

Wenzheng He et al. Microsyst Nanoeng. .

Abstract

Traditional lithography plays a significant role in the fabrication of micro- and nanostructures. Nevertheless, the fabrication process still suffers from the limitations of manufacturing devices with a high aspect ratio or three-dimensional structure. Recent findings have revealed that shrink polymers attain a certain potential in micro- and nanostructure manufacturing. This technique, denoted as heat-induced shrink lithography, exhibits inherent merits, including an improved fabrication resolution by shrinking, controllable shrinkage behavior, and surface wrinkles, and an efficient fabrication process. These merits unfold new avenues, compensating for the shortcomings of traditional technologies. Manufacturing using shrink polymers is investigated in regard to its mechanism and applications. This review classifies typical applications of shrink polymers in micro- and nanostructures into the size-contraction feature and surface wrinkles. Additionally, corresponding shrinkage mechanisms and models for shrinkage, and wrinkle parameter control are examined. Regarding the size-contraction feature, this paper summarizes the progress on high-aspect-ratio devices, microchannels, self-folding structures, optical antenna arrays, and nanowires. Regarding surface wrinkles, this paper evaluates the development of wearable sensors, electrochemical sensors, energy-conversion technology, cell-alignment structures, and antibacterial surfaces. Finally, the limitations and prospects of shrink lithography are analyzed.

Keywords: Nanoscale devices; Nanoscience and technology.

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Conflict of interest statement

Conflict of interestThe authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Applications of shrinkable SMPs.
a overview of the recent progress on micro/nanostructures based on heat-shrinkable SMPs.
Fig. 2
Fig. 2
Shrinkage behavior variation with the shrinkage temperature.
Fig. 3
Fig. 3. Wrinkle formation by shrink polymers.
Schematics of (a) before and after (b) uniaxial and (c) biaxial stress release. Schematics of (d) biaxial and (e) uniaxial wrinkles and (f, g) SEM images. Reproduced with permission from Elsevier (2001) and Wiley (2008).
Fig. 4
Fig. 4. High-aspect-ratio devices by shrink polymers.
a Workflow to fabricate protrusive and depressed structures (aspect ratio ≈ 10) via RIE and the shrinking technique. SEM images of microholes before (b) and after (c) shrinking with the nanosecond laser process. d Micropillars with an aspect ratio of 4.4 created by casting UV epoxy. Hot embossing fabrication schematics (e) for high-aspect-ratio microstructures with the shrinking technique. The inserted mold (f) and micropillar with a height of over 1.0 mm (g) obtained with the shrinking technique. Reproduced with permission from Elsevier (1998), Springer Nature (2004), and Elsevier (2013).
Fig. 5
Fig. 5. Microchannels by shrink polymers.
a Summary of the microchannel features after polymer shrinkage. b Generation of Shrinky-Dink microfluidics, (a) before and (b) after shrinking. c Workflow of the print-n-shrink technique to directly fabricate microfluidics chips. d A 10 µm microchannel for chemical sensor applications.
Fig. 6
Fig. 6. Self-folding structures by shrink polymers.
a Classification of the self-folding approaches involving shrink polymers. Self-folding structures induced by unbalanced heat shrinkage: (b), (d) IR light, (e) microwaves, and (f) absorption of differently colored light. c Self-folding robots fabricated by the sandwich structure of shrink polymers. Reproduced with permission from the Royal Society of Chemistry (2012, 2015, and 2017) and the American Association for the Advancement of Science (2014 and 2017).
Fig. 7
Fig. 7. Other applications with size-contraction features by shrink polymers.
a (a) The sub-22-nm wire fabrication process, including hot embossing and shrinking techniques. SEM images of the mold (b) and nanowire (c) and nanostructure atomic force microscopy (AFM) image. b Optical antenna arrays obtained via nanosphere and shrink lithography: (a) before shrinking, (b) after shrinking and (c) nanoplasmonic antenna arrays. Reproduced with permission from the American Institute of Physics (2012) and the American Chemical Society (2011).
Fig. 8
Fig. 8. Wearable sensors by shrink polymers.
a Current applications of shrink-induced wrinkles in wearable sensors. b The fabrication process of wrinkled platinum (wPt) strain sensors. c Flexible wrinkled carbon nanotube (CNT) electrode under different strains. d Wrinkled strain sensor for respiration monitoring. e Wrinkled pressure sensor for blood flow monitoring. Reproduced with permission from the Royal Society of Chemistry (2016), Wiley (2016 and 2019), and Springer Nature (2019).
Fig. 9
Fig. 9. Electrochemical sensors fabricated with shrink polymers.
a (a) Microelectrode arrays after shrinking, (b) nonlinear diffusion on the microelectrode. b Schematic of EASA enhancement by PVP coating. c The water contact-angle variation in the shrink-induced graphene sensor at different treatment temperatures. d Photoelectrochemical signal enhancement effects by shrink-induced wrinkles. e The wrinkled electrode for DNA sensing. Reproduced with permission from the IEEE (2019), Elsevier (2017), and the American Chemical Society (2014 and 2018).
Fig. 10
Fig. 10. Cell-alignment applications with shrink polymers.
a Uniaxial wrinkle surface for anisotropic cell alignment. b The mechanism of different attachment effects of P. aeruginosa and S. aureus on different biaxial wrinkles. Reproduced with permission from the American Chemical Society (2012) and the Royal Society of Chemistry (2018).
Fig. 11
Fig. 11. Enhancing energy-conversion efficiency by shrink polymers.
The schematic of (a) shrink-induced DSSC fabrication and (b) energy conversion. c Enhancement of scattering and catalytic area by nanowrinkles and nanogaps. Reproduced with permission from AIP Publishing LLC (2013).
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