Bubble Casting of robotics is a newly ventured topic that has captured the interests of the soft world domain. Though it cannot completely replace a muscle but it can aid in the movement of the muscles ands limbs.
This is a promising approach for developing soft robotics.
1. Bubble casting
Soft Robotics
Trevor J. Jones , Etiene Jambon-Pulliet , Joel Marthelot and
P.T. Brun
Nature; 599 (7884): 229-233, 2021.
Presented by : Raghav Worah
2. The Process
Table of Contents
Introduction
1 3 Technicalities
4 Merits and demerits
2
3. Introduction
The core of biological soft robotics is the ability to move in the environment, which requires actuators capable
of generating force.
Figure 1:Schematic diagram showing the multi-scale molecular motor assembly used to engineer a biological soft robot.
Image courtesy: Annual reviews on Soft Robotics by Adam Finberg
al soft r
4. Bubble casting of soft robots include the assembly of a monolithic actuator that is programmed
to obey the laws of fluid mechanics.
The tubular mould is filled by
injecting an elastomeric melt.
Then an air bubble is
introduced that creates a void
Figure 2: Representation of the mould being flooded by the polymer and eventually
taking up the shape.
Image Courtesy: Nature
• The flow of the ‘fluid’ in presence of
an air bubble will result in the
formation of the annulus with a
constant thickness.
• Overall. It would result in the
formation of a quasi-uniform film.
5. The process
Bubble casting does not require external control and fluid mechanics itself can dictate the movement
and cause a change in the shape.
The thickness of the membrane is 100µm and the length can go up to a few meters.
This thickness is essential as it is the
responsible for the response against the
inflammation
The actuator bends upon its
length and adopts a uniform
curvature
This bending is independent
of the length and it increases
with increase in elastic shear
modulus and thickness of the
membrane
Overall, upon bending the lower portion of the membrane is under-formed while the upper thin
membrane is quasi-isotropicaly stretchable, indicating that the mechanical response of the actuator is
due the shape in which it has been casted.
6.
7. Technicalities
The flow at the front of the advancing bubble leaves an annulus of constant thickness h
where, Ca is the capillary number, R is the radius and µ is the melt viscosity, with U being the bubble
velocity and γ being the surface tension.
So, the equation stands as : h = 1.34Ca2/3
R 1+3.55Ca2/3
h = 3µR (n+1) Tw n+1
2ρgTc (Tc-Tm) n+1
Ratio of viscous to interfacial flow (in
polymers)
The rate of extrusion
through the orifice
Finishing time Time of drainage after the reagents are mixed
1/2
Ca=µU/γ
However the thickness of the
film would not depend upon
the initial thickness of the
film.
Image Courtesy: Nature
Different polymers would result in different thickness owing to the increase
in velocity up-to its saturation (Ca>3)
8. Merits and Demerits
• This technique is predictive in nature and it could enable the assembly of complex
actuators and render their functionality on the basis of the geometrical design.
• This pneumatic actuator can mimic animal and vegetal movements.
• It requires sequential moulding procedures and the extent of inflammation required to
tailor the shape of the actuator is a tedious process.
• They cannot perform extremely complex movements
Thus, with both merits and demerits in hand, this technique would resonate with
the soft matter community and pave newer ways and interventions that would
enable in developing next-generation robotic materials with tractable complexity.
