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Materials Science in Additive Manufacturing Biodegradable sustainable electronics

A

B C

Figure 3. (A) A series of optical microscope images were taken at different points during the dissolution of a meander trace of ZnO (200 nm) submerged
in DI water at room temperature, (B) changes in the relative resistance of a PEDOT: PSS-based printed temperature sensor subjected to cyclic heating
and cooling run between 30°C and 45°C, and (C) the degradation of the flexible temperature sensor over the course of 10 days in an enzymatic (protease)
environment. Reprinted with permission from Dagdeviren et al., Wang et al., and Pradhanand and Yadavalli [6,58,60] .

device using Mg as an active electrode was fabricated on conductivity was observed (≈3 × 10 S/m) . The
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[25]
a polyvinyl alcohol (PVA) substrate. The full degradation conductivity value of 1.124 × 10 S/m for Zn was obtained
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of the device was achieved in DI water in about 20 min. through laser sintering rather than heat sintering. Photonic
Mg-based biodegradable metals have rapid degradation sintering has also been applied, which resulted in high
[48]
rates, resulting in loss of mechanical performance in short conductivity value of 44,634 S/m . An alternate way of
span and thus limiting its applications. Hence, Mg-based enhancing the conductivity of biodegradable metals is
biodegradable materials will benefit from decreased by making the composite with other highly conducting
degradation rates while Fe may need enhanced rates. Zn is materials. The performance of Zn metal was enhanced
heralded as the next promising metal for biodegradability. by adding small amounts of silver nanowires (NWs),
Zn-based materials overcome several drawbacks that were leading to maximum conductivity of 307,664.4 S/m after
observed for other biodegradable materials. Wang et al. sintering . Nevertheless, adding Ag may compromise the
[26]
[52]
studied mechanical properties of Zn alloy as a degradable biodegradability of the overall composite.
biomaterial by casting with Mg. They showed Mg-Zn
alloy degradation behaviors in simulated body fluid (SBF) 3.2. Polymers
solution. Both Mo and W show slow degradation rates. The Polymer materials have better biodegradability and
variation in degradation rates of metals provides multiple biocompatibility than metals and have been much
options to use in different applications. Crystalline Zn films sought after. This is true for both natural and synthetic
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with conductivity of approximately 1.124 × 10 S/m were polymers. Synthetic polymers are particularly attractive
produced on a cellulose substrate. The resulting resistive as their degradation rates can be tuned through triggered
Zn strain gauge array with a gauge factor of ≈1 exhibited depolymerization. Moreover, polymer materials are
no delamination or cracking, or electrical degradation after cheap and easy to process that make them attractive for
repeated stretch-release cycles, and a deflection of ≈16 mm commercialization. Organic polymers show conducting
(radius of curvature) was stably detected . It is interesting properties through introduction of conjugation or doping
[53]
to note that post-processing method has a considerable with conductive materials. Examples of conjugated
effect on the conductivity values of biodegradable metals. polymers are polyaniline (PANI), polypyrrole (PPy),
Electrochemical sintering process of Zn microparticles and poly(3,4-ethylenedioxythiophene) (PEDOT). The
was carried out with acetic acid solution, and enhanced conjugated network in conductive polymers makes

Volume 1 Issue 3 (2022) 6 https://doi.org/10.18063/msam.v1i3.15