Photolithography‐Based Microfabrication of Biodegradable Flexible and Stretchable Sensors

Abstract

medical devices (IMDs) and transient electronic devices, which can be later dissolved in a controlled manner. In current medical practice, IMDs are used during life-or-death cases only due to a secondary follow-up IMD retrieval surgery requirement which is an additional risk and an economic burden to the patient, doctor, and the government. Biodegradable sensors are expected to enable unprecedented solutions for diagnostic, telemetry, and therapeutic IMDs without secondary IMD retrieval surgery. [4][5][6][7] On the other hand, the increasing number of single-use electronics deepens the electronic waste (e-waste) problem, which is estimated to reach 74 million tons by 2030. [8] Therefore, eco-friendly alternatives such as transient electronics that easily degrade into disposable byproducts are expected to play a vital role in alleviating environmental concerns and increasing the abundance of wearable medical devices. [8][9][10] In addition to biodegradability, miniaturization, flexibility, and stretchability are critical factors that determine the range of applications in medicine and electronics. Microfabrication of flexible and stretchable sensors that occupy a minimal footprint, conformally adhere to host tissue while retaining their electrical features during mechanical loading, and dissolve within bodily fluids are highly desirable for next-generation IMDs and sustainable wearable electronics. [11][12][13][14] Toward this end, none of the recently reported Biodegradable sensors based on integrating conductive layers with polymeric materials in flexible and stretchable forms have been established. However, the lack of a generalized microfabrication method results in large-sized, low spatial density, and low device yield compared to the silicon-based devices manufactured via batch-compatible microfabrication processes. Here, a batch fabrication-compatible photolithography-based microfabrication approach for biodegradable and highly miniaturized essential sensor components is presented on flexible and stretchable substrates. Up to 1600 devices are fabricated within a 1 cm 2 footprint and then the functionality of various biodegradable passive electrical components, mechanical sensors, and chemical sensors is demonstrated on flexible and stretchable substrates. The results are highly repeatable and consistent, proving the proposed method's high device yield and high-density potential. This simple, innovative, and robust fabrication recipe allows complete freedom over the applicability of various biodegradable materials with different properties toward the unique application of interests. The process offers a route to utilize standard micro-fabrication procedures toward scalable fabrication of highly miniaturized flexible and stretchable transient sensors and electronics.

Recent Advances in Biodegradable Green Electronic Materials and Sensor Applications

“…The sensor exhibited selectivity toward interference, and a highly selective sensor with a full circle configuration was achieved. [204] Copyright 2022, John Wiley & Sons. b) Co-functionalized nanocellulose/graphene oxide (GO) composites for gas sensing.…”

“…Bathaei et al proposed a conventional photolithography-based microfabrication process for the development of highly miniaturized and scalable biodegradable sensors on flexible and stretchable substrates (Figure 7a). [204] A significant aspect of the fabrication process is the utilization of biodegradable layers, along with a water-soluble sacrificial layer and an adhesion layer between the polymer and metal layers, which improves the bonding between the metal and polymer layers, thereby enhancing the electrical response of the flexible device under bending. Moreover, the biodegradable sensor accelerated the dissolution of the device in PBS.…”

Carbonized Cotton Fibers for Ultrahigh Power-Density Electrokinetic Energy Harvesting

“…Early developments in nanofluidic research largely delved into lithography-based fabrication technologies. 30 However, the associated infrastructure, expenses, and lack of scalability hindered the adaptation of the same in developing electrokinetic energy conversion devices of feasible deployment outside resourced laboratories. With the advent of 2D layered materials (such as graphene oxides, Mxenes, nanoclays), 31−37 relatively simpler, cost-effective, and scalable fabrication paradigms could give rise to highly charged surfaces along with favorable water permeability of the tiny capillaries bridging the neighboring nanosheets.…”

“…Early developments in nanofluidic research largely delved into lithography-based fabrication technologies . However, the associated infrastructure, expenses, and lack of scalability hindered the adaptation of the same in developing electrokinetic energy conversion devices of feasible deployment outside resourced laboratories.…”

Highly Stretchable, Biodegradable, and Recyclable Green Electronic Substrates

“…[3,4] The environmental and resource issues caused by the explosive use of electronics have led to an urgent need for renewable, biodegradable electronic substrates, and green electronic substrates made of sustainable bio-based materials are an ideal entry point for e-waste reduction. [5][6][7] Polylactic acid (PLA), as one of the most representative biodegradable materials, is an excellent candidate for sustainable green electronic substrates because of its abundant sources, excellent mechanical properties, and processability. [8][9][10][11][12][13] However, PLA suffers from high brittleness and a low degradation rate at room temperature.…”