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Materials Science in Additive Manufacturing Biodegradable sustainable electronics

function, thus obviating the need of physical removal. softens in contact with hot water or in high humidity.
The first report on transient electronics was published by In another work, the performance of PCBs made from
Hwang et al. in 2012, where a platform technology was biodegradable cellulose acetate and PLA was compared
[17]
demonstrated. Since then, much research has been focused with those created on Flame-Retardant Class 4 (FR-4)
on developing biodegradable materials for electronic substrates [160] . Bharath et al. [161] explored rice husk-epoxy
systems, investigating material degradation behavior resin as a potential candidate for PCB. Although the
and dissolution chemistries, modeling degradation, and performance of the PCBs and devices is far from that of
creating fabrication techniques. Numerous biodegradable the conventional devices, yet they hold promise to bring
devices that operate reliably for a certain amount of time sustainability in electronics and make it environmentally
have been demonstrated for environmental applications, friendly. For device applications, the functional lifetime
hardware security applications, and other applications such is defined by the degradation time, thickness of material
as biomedical implants and energy storage devices. Some layers, and water permeability of the encapsulation
of the examples for biomedical devices are implantable materials. External stimulus triggers, namely, moisture,
transient silicon-based devices with microheaters for light, temperature, and mechanical force, have also been
[17]
thermal therapy , pressure and temperature sensors explored to degrade the materials in mostly non-aqueous
for the treatment of brain surgery and monitoring of environments.
cardiovascular activities [146] , hydration sensors for wound Most of the initial devices using biodegradable materials
healing applications , pH sensors [111] , and devices for used conventional manufacturing techniques of lithography,
[10]
drug delivery applications [117,148,149] . Transient electronics etching, and vapor or chemical deposition. Electrospinning
protect the environment by reducing electronic waste. and transfer techniques have also been explored but have
Some recent studies have focused on enzymatic been less successful when it comes to repeatability. Despite
degradation of PEDOT: PSS polymer [150] and development there are very few reports using additive manufacturing
of an all-carbon thin-film paper-based transistor, which (AM) techniques to print biodegradable materials,
is 95% recyclable [151] . To make transient electronics self- discussion on this topic based on droplet-based printing
sufficient, the development of transient batteries is a pre- techniques and 3D micro-additive manufacturing
requisite. In 2017, Zn-Cu galvanic cell was used to power techniques has been initiated in a few papers [162-164] .
a temperature sensor and a wireless communication device PEDOT: PSS was converted into ink and printed using
in the gastrointestinal tract of pigs [152] . Recently, a one- inkjet printer, which uses a piezoelectric nozzle and is a
dimensional battery, consisting of chitosan as separator, well-known drop-on-demand technique [164] . In a recent
MnO as cathode and a fiber conductor coated with work by Williams et al., [151] the emerging AM technique of
2
polydopamine/polypyrrole composite material as anode, aerosol jet printing was explored to fabricate an all-carbon
was developed. Due to its high flexibility, it could be thin-film transistor employing biodegradable material inks
easily injected into the body to power a biosensor [153] . To of nanocellulose and carbon nanotubes on paper substrate.
further extend the application, Mg-Mo-based battery was A conductive paste of Zn, PVP, glycerol, and methanol
used in wearable electronics to power an electronic watch was found to be suitable to create interconnects for screen
and wearable health-care devices for electromyography printing. By combining screen printing with hot rolling
applications [154] . Transient electronics are particularly and photonic sintering, a high conductivity of 60,213.6 S/m
useful for hardware secured devices containing sensitive was achieved . It was reported that among all printing
[28]
information. For the purpose, an MgO-based device was methods, aerosol jet printing has the best resolution (line
developed which can degrade within 8 min in the presence width >10 m) and thus this technique offers better printing
of DI water at room temperature [155] . Similarly, a CsPbBr - on a wide range of substrates and on 3D surfaces [164] .
3
based device was capable of dissolving in DI water within
60 s [156-158] . Focus has also been directed to develop high- 8. End of life of electronics
performance degradable printed circuit boards (PCBs). Increasing electronic waste is an obstacle in the path of
In one of the early works, Huang et al. demonstrated circular economy. Only 20% of e-waste gets recycled
transient PCB using different materials that dissolved and a majority of it ends up in landfills, contributing
into benign end products on exposure to water . The to environmental problem. Researchers are exploring
[67]
multilayered PCB device used biodegradable metals such biodegradable materials to develop transient electronics
as Mg, W, and Zn for interconnects and PEO on a flexible in an effort to reduce e-waste. These devices have the
sodium carboxymethylcellulose substrate. A plant-based capacity to dissolve in aqueous solutions to produce
biodegradable PCB was made from agricultural waste of harmless products or to self-destruct themselves after
natural cellulose [159] . The biocomposite used in the work operating for a predetermined period of time. The aim is to

Volume 1 Issue 3 (2022) 14 https://doi.org/10.18063/msam.v1i3.15