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Villeda-Hernandez et al. Soft Sci 2024;4:14 https://dx.doi.org/10.20517/ss.2023.52 Page 7 of 35

electrostatic forces. By arranging two distinct electrodes to ‘zip’ together when an electric charge is applied,
high contraction is achieved, resulting in an EPP. The EPP, weighing only 5.3 grams, can deliver pressures
up to 2.34 kPa and volumetric flow rates of 161 mL/min.

While these advances are significant, the high energy density of certain chemical reactions offers an
untapped opportunity for onboard powering of pneumatic systems; this promising novel approach is
explored in this review.

CHEMICALLY POWERED PNEUMATIC ACTUATION
Applying chemical reactions, specifically GERs and GCRs, has the potential to revolutionize powering
pneumatic actuators by improving portability and energy density. Wehner et al. made a significant
contribution to this approach by using the platinum nanoparticle (PtNP)-catalyzed chemical decomposition
of hydrogen peroxide (H O ) into O and H O . PtNPs were integrated using additive manufacturing
[70]
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techniques into the first entirely soft autonomous robot. A similar system exploring the decomposition of
H O into H O and O as a power source was reported by Kim et al. using manganese dioxide (MnO ) as the
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catalyst, further underscoring the potential of chemical reactions as viable power sources .
[71]
While H O -based reactions offer one set of possibilities, it is critical to also consider using negative
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pressures to drive soft pneumatic actuation. Fortunately, as shown in Figure 4, chemical reactions are not
confined to generating positive pressures; they can also be harnessed for negative pressure applications.
Given this dual capability, a comprehensive understanding of the chemical energy sources and pressures
generated is essential to advance this emerging field.
As recently demonstrated , neutralization reactions are an untapped source to power pneumatic actuators.
[31]
Owing to the small amount of starting material required, these GERs and GCRs stand out as perfect
candidates for wearable and potentially even implantable, pneumatic soft actuators.
Prior to detailing the reactions that could be implemented in chemically driven pneumatic actuation, it is
important to understand the factors influencing the efficiency of both GERs and GCRs such as the kinetics
and thermodynamics behind the reactions, from both a safety and an actuation optimization point of view.

THEORETICAL CONSIDERATIONS
The molar volume of gas
The molar volume of a gas is dependent on the temperature and pressure of the system. In the case of an
isothermal reaction, the system temperature will be constant; therefore, the initial conditions of the system
can be set as room temperature and pressure (RTP) conditions. As an example, the utilized values can be
defined as:

Temperature (T) = 293K;
Pressure (P) = 1 atm;
Molar volume of a gas (V ) = 24 L·mol -1
M
Ideal gas law
According to the ideal gas law, the pressure of the system will be given, among other parameters, by its
volume and the number of moles of gas it contains.