Abstract
Biodegradable electronics are disposable green devices whose constituents decompose into harmless byproducts, leaving no residual waste and minimally invasive medical implants requiring no removal surgery. Stretchable and flexible form factors are essential in biointegrated electronic applications for conformal integration with soft and expandable skins, tissues, and organs. Here a fully biodegradable MgZnCa metallic glass (MG) film is proposed for intrinsically stretchable electrodes with a high yield limit exploiting the advantages of amorphous phases with no crystalline defects. The irregular dissolution behavior of this amorphous alloy regarding electrical conductivity and morphology is investigated in aqueous solutions with different ion species. The MgZnCa MG nanofilm shows high elastic strain (≈2.6% in the nano‐tensile test) and offers enhanced stretchability (≈115% when combined with serpentine geometry). The fatigue resistance in repeatable stretching also improves owing to the wide range of the elastic strain limit. Electronic components including the capacitor, inductor, diode, and transistor using the MgZnCa MG electrode support its integrability to transient electronic devices. The biodegradable triboelectric nanogenerator of MgZnCa MG operates stably over 50 000 cycles and its fatigue resistant applications in mechanical energy harvesting are verified. In vitro cell toxicity and in vivo inflammation tests demonstrate the biocompatibility in biointegrated use.
Highlights
1) It shows large elastic strains owing to its amorphous nature and lack of crystalline defects, such as, dislocation or grain boundaries, which are the source of deformation mechanism in crystalline materials,[21] 2) individual element atoms of metallic glass (MG) maintain their electrochemical behavior on dissolution in aqueous solution,[22,23] and 3) nanofilm formation is relatively easy via well-studied fabrication processes such as, co-sputtering.[24,25,26]
Mg and Ca formed native oxide layers, thereby inducing immediate Zn depletion at the outermost surface owing to exposure to oxygen and moisture in the ambient atmosphere, but the internal MgZnCa MG film has pure Zn in the matrix.[27]
These results suggest that the MgZnCa MG/polybutylene terephthalate (PBAT) examined here is biocompatible and has the potential to be used for long-term implantation of months to years
Summary
Flexibility and excellent electrical performance and sophisticated fabrication can be ensured in inorganic materials, such as Si and metal nanomembranes, nanoribbons, nanomesh, and nanowires, if their thicknesses are made to be nanoscale.[1,2,3,4] Combining geometrical designs such as serpentine and mesh can further change the in-plane to out-of-plane deformation, in nanoscale metal electrodes, thereby making stretchable electronics available.[5,6,7,8] This change in thickness imparts softness to the materials and enhances their dissolubility in mild solutions such as groundwater, biofluids, and other aqueous solutions by tuning the time scale of electrochemical dissolution kinetics by a larger extent.[9]. 1) It shows large elastic strains owing to its amorphous nature and lack of crystalline defects, such as, dislocation or grain boundaries, which are the source of deformation mechanism in crystalline materials,[21] 2) individual element atoms of MG maintain their electrochemical behavior on dissolution in aqueous solution,[22,23] and 3) nanofilm formation is relatively easy via well-studied fabrication processes such as, co-sputtering.[24,25,26] In particular, enhancement of elastic strains maximizes the repeatable stretching ranges as the plastic deformation accompanies the unrecoverable extension which distorts the devices It gives higher fatigue resistance, offering full recovery of deformation without damage accumulation. Biocompatibility testing using in vitro cell toxicity and in vivo inflammation analysis supports the biofriendly usage of MgZnCa MG integrated electronic system
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