Personalized healthcare (PHC) is a booming sector in the health science domain wherein researchers from diverse technical backgrounds are focusing on the need for remote human health monitoring. PHC employs wearable electronics, viz. group of sensors integrated on a flexible substrate, embedded in the clothes, or attached to the body via adhesive. PHC wearable flexible electronics (FE) offer numerous advantages including being versatile, comfortable, lightweight, flexible, and body conformable. However, finding the appropriate mass manufacturing technologies for these PHC devices is still a challenge. It needs an understanding of the physics, performance, and applications of printing technologies for PHC wearables, ink preparation, and bio-compatible device fabrication. Moreover, the detailed study of the operating principle, ink, and substrate materials of the printing technologies such as inkjet printing will help identify the opportunities and emerging challenges of applying them in manufacturing of PHC wearable devices. In this article, we attempt to bridge this gap by reviewing the printing technologies in the PHC domain, especially inkjet printing in depth. This article presents a brief review of the state-of-the-art wearable devices made by various printing methods and their applications in PHC. It focuses on the evaluation and application of these printing technologies for PHC wearable FE devices, along with advancements in ink preparation and bio-compatible device fabrication. The performance of inkjet, screen, gravure, and flexography printing, as well as the inks and substrates, are comparatively analyzed to aid PHC wearable sensor design, research, fabrication, and mass manufacturing. Moreover, it identifies the application of the emerging mass-customizable printing technologies, such as inkjet printing, in the manufacturing of PHC wearable devices, and reviews the printing principles, drop generation mechanisms, ink formulations, ink-substrate interactions, and matching strategies for printing wearable devices on stretchable substrates. Four surface matching strategies are extracted from literature for the guidance of inkjet printing of PHC stretchable electronics. The electro-mechanical performance of the PHC FE devices printed using four surface matching strategies is comparatively evaluated. Further, the article extends its review by describing the scalable integration of PHC devices and finally presents the future directions of research in printing technologies for PHC wearable devices.
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Fabrication of microstructures on curved hydrogel substrates
Emerging wearable devices are very attractive and promising in biomedical and healthcare fields because of their biocompatibility for monitoring in situ biomarker-associated signals and external stimulus. Many such devices or systems demand microscale sensors fabricated on curved and flexible hydrogel substrates. However, fabrication of microstructures on such substrates is still challenging because the traditional planar lithography process is not compatible with curved, flexible, and hydrated substrates. Here, we present a shadow-mask-assisted deposition process capable of directly generating metallic microstructures on the curved hydrogel substrate, specifically the contact lens, one of the most popular hydrogel substrates for wearable biomedical applications. In this process, the curved hydrogel substrate is temporarily flattened on a planar surface and metal features are deposited on this substrate through a shadow mask. To achieve a high patterning fidelity, we have experimentally and theoretically investigated various types of distortion due to wrinkles on 3D-printed sample holders, geometric distortion of the substrate due to the flattening process, and volume change of the hydrogel material during the dehydration and hydration processes of the contact lens. Using this method, we have demonstrated fabrication of various titanium pattern arrays on contact lenses with high fidelity and yield.
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- Award ID(s):
- 2001036
- PAR ID:
- 10417804
- Date Published:
- Journal Name:
- Journal of Vacuum Science & Technology B
- Volume:
- 40
- Issue:
- 5
- ISSN:
- 2166-2746
- Page Range / eLocation ID:
- 052804
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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