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2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Magnesium-Based Micromotors: Water-Powered
Propulsion, Multifunctionality, and Biomedical
and Environmental Applications
Chuanrui Chen, Emil Karshalev, Jianguo Guan, and Joseph Wang*
C. Chen, E. Karshalev, Prof. J. Wang
Department of Nanoengineering
University of California
San Diego, La Jolla, CA 92093, USA
C. Chen, Prof. J. Guan
State Key Laboratory of Advanced Technology for Materials Synthesis
Wuhan University of Technology
Wuhan 430070, P. R. China
The ORCID identiﬁcation number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/smll.201704252.
sents the ﬁrst step for the miniaturization
of machines into microscales and
When the dimension of the
machine is scaled down, the inertial force
in the low Reynolds number environment
poses a major challenge to their locomo-
tion, requiring a constant driving force
for propulsion at the nanoscale.
addition, the functionalities of these tiny
machines are restricted by the selection of
their component materials and their small
Recent efforts have greatly
expanded the propulsion behavior, motion
control, functionalities, and capabilities
of the various synthetic micro/nanoma-
In particular, the motion of
synthetic micro/nanomotors can be driven
either by chemical fuels or by external
energy, including magnetic or electric
ﬁelds, light, or ultrasound.
materials have been applied as the propel-
lant to provide the driving force for self-
propelled micro/nanomotors by reacting
with surrounding environment.
chemically propelled micro/nanomo-
tors have relied on catalytic noble metals
(primarily Pt) reacting with hydrogen
peroxide to generate oxygen bubbles or
asymmetric chemical gradients (phoretic mechanism), which
serve as the propelling mechanisms.
is largely incompatible with both biological and environmental
systems owing to its strong oxidation ability, corrosion effect,
and considerable toxicity.
The requirement of hydrogen
peroxide fuel thus hinders greatly the practical utility of
chemically powered micromotors. Recently developed enzyme
powered nanomachines use alternative biologically relevant
fuels and offer a great potential for future biomedical applica-
However, despite the tremendous progress in the ﬁeld
of micro/nanomotors, the narrow range of current motor mate-
rials and fuels is inadequate for many future applications.
Water is considered as an ideal fuel for powering future
nanomachines. The use of water as power source can be
traced back to the beginning of recorded history and repre-
sents a signiﬁcant step in the evolution of mankind.
example, water-lifting wheels had appeared in ancient Egypt
by the 4th century BCE, while today water is utilized to power
turbines to acquire electricity in large dams.
Water in the
The new capabilities and functionalities of synthetic micro/nanomotors open
up considerable opportunities for diverse environmental and biomedical
applications. Water-powered micromachines are particularly attractive for
realizing many of these applications. Magnesium-based motors directly use
water as fuel to generate hydrogen bubbles for their propulsion, eliminating
the requirement of common toxic fuels. This Review highlights the develop-
ment of new Mg-based micromotors and discusses the chemistry that makes
it extremely attractive for micromotor applications. Understanding these
Mg properties and its transient nature is essential for controlling the propul-
sion efﬁciency, lifetime, and overall performance. The unique and attractive
behavior of Mg offers signiﬁcant advantages, including efﬁcient water-
powered movement, remarkable biocompatibility, controlled degradation,
convenient functionalization, and built-in acid neutralization ability, and has
paved the way for multifunctional micromachines for diverse real-life applica-
tions, including operation in living animals. A wide range of such Mg motor-
based applications, including the detection and destruction of environmental
threats, effective in-vivo cargo delivery, and autonomous release, have been
demonstrated. In conclusion, the current challenges, future opportunities,
and performance improvements of the Mg-based micromotors are discussed.
With continuous innovation and attention to key challenges, it is expected
that Mg-based motors will have a profound impact on diverse biomedical and
The design of machines at the micro/nanoscale is both funda-
mentally important and practically valuable.
ment and application of these micro/nanodevices are among
the most pressing challenges in current nanoscience and
Small 2018, 14, 1704252