FIGURE 3(A) Biodegradable
Mg-MoO3 primary battery work for about 13 days.
Reproduced with permission.[22] Copyright 2018,
Wiley-VCH GmbH. (B) Fully biodegradable Mg-Mo primary batteries.
Reproduced with permission.[19] Copyright 2014,
Wiley-VCH GmbH. (C) Bioresorbable zinc primary battery with zinc
microparticle network coated with chitosan and
Al2O3 double shells as anode. Reproduced
with permission.[20] Copyright 2021, American
Chemical Society. (D) Biodegradable thin film Mg primary battery with
silk fibroin-IL electrolyte. Reproduced with
permission.[21] Copyright 2017, American Chemical
Society.
3.1.2. Rechargeable batteries
Compared with the single-used primary battery, rechargeable batteries
are still a compelling topic in the future research of IMEs energy
storage devices since they can be recharged after the first implantation
and provide long-term stable power in vivo without the need for
replacement surgery. With one-dimensional structures and miniaturised
coplanar configuration, rechargeable batteries are more beneficial for
minimally invasive IMEs application and enable the implanted system to
work with stable power sources. Recently, Peng et al. designed a
one-dimensional fibre-like rechargeable aqueous sodium-ion battery that
can be injected into different parts of the body for energy supply as
can be seen in Figure 4A.[26] With aligned carbon
nanotube (CNT)/Na0.44MnO2 (NMO) hybrid
fibre as cathode and CNT/molybdenum trioxide/polypyrrole
(CNT/MoO3/PPy) hybrid fibre as anode, good mechanical
and electrochemical performance were achieved. With the remarkable
one-dimension structure, the fibre sodium ion battery possessed
advantages including good flexibility and minimised implantation
incision size. Also, the fibre battery is exposed to biofluid which acts
as electrolyte and can be injected into tissue directly. Due to the
fibre structure with high flexibility, the battery can match the soft
tissue well and achieve stable interface contact. The electrochemical
performance of the fibre battery with a power density of 78.9 mW
cm-3 can power most of the biomedical applications in
vivo including the implanted sensor for respiration monitoring.