enabling new biomedical and bioinspired mechatronic systems with electroactive smart elastomers...

Enabling new biomedical and bioinspired mechatronic systems

with electroactive smart elastomers

Federico Carpi

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EAP are materials capable of changing dimensions and/or shapein response to suitable electrical stimuli

(Stanford Research Institute)

Example: dielectric elastomer actuator

Electromechanically Active Polymers (EAP)

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Electromechanically Active Polymers (EAP)

3

• thickness compression

• surface expansionElectrostatic pressure: p = ε0εrE2

Thin insulating elastomeric film sandwiched between two compliant electrodes:

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Dielectric elastomer actuators

Thin film of insulating elastomer sandwiched between two compliant electrodes, so as to obtain a deformable capacitor.Electrical charging results in an electrostatic compression of the elastomer.

Voltage on

V

Polymer film

Electrodes (on topand bottom surfaces)

Voltage off

xy

z

E (electric field)

Strain

Voltage on

V

Polymer film


Voltage off

xy

z

E (electric field)

Strain

Stanford Research InstitutePelrine, Kornbluh, Pei, et al.


(our group)

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How to use the DE actuation principle?

Possibilities for new devices and applicationslimited only by imagination!

The greatest value of this technology lies in the fact that it is extremely ‘poor’

(‘poor’ materials and extremely simple mechanism)

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(Stanford Research Institute)

(Our group) (Our group)

(Our group)


Properties:

1) Inherently capable of changing dimensions and/or shape in response to suitable electrical stimuli, so as to transduce electrical energy into mechanical work.

In that, they show attractive propeties as engineering materials for actuation:- efficient energy output, - high strains, - high mechanical compliance, - shock resistance, - low mass density, - no acoustic noise, - ease of processing, - high scalability - low cost.

2) Can also operate in reverse mode, transducing mechanical energy into the electrical form. Therefore, they can also be used as mechano-electrical sensors, as well as energy harvesters to generate electricity.

3) Capable of stiffness control.

4) Can combine actuation, sensing and stiffness control, not only in the same material, but actually in the viscoelastic matter they are made of, showing functional analogy with natural muscles

artificial muscles


… artificial skeletal muscles

… Not todayMain challenges:- need for improved actuating configurations- need for higher energy density (natural muscle performance can be exceeded, but only in exceptional conditions) - need for lower driving voltages - mechanical interfaces with the body

A dream in the biomedical field…

Voltage on

V

Polymer film


Voltage off

xy

z

E (electric field)

Strain

Voltage on

V

Polymer film


Voltage off

xy

z

E (electric field)

Strain

Compressive stress (Maxwell stress):

ε0=8.854 pF/m: dielectric permittivity of vacuum

E= applied electric field

ε= relative dielectric permittivity of the elastomer

20 Ep

Need for new high-permittivity elastomers: • composites• blends• new synthetic polymers

1) FIRST APPROACH: increasing the material dielectric constant

2) SECOND APPROACH: reducing the film thickness

dVE / V= applied voltage d= thickness

Reducing the driving voltages

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1) Full-page refreshable and portable Braille displays for the blind people

2) Wearable tactile display for virtual interactions with soft bodies

3) Haptic or visual displays of tissue compliance or organ motility

4) Artificial ciliary muscles for electrically tuneable optical lenses for artificial vision systems

5) Artificial muscles for electrically stretchable membrane bioreactors

Contributions from our group:

Biomedical & bioinspired applications

Artistic view of a possible Braille tablet/e-Book

This is science fiction today!

Full-page refreshable and portable Braille displays for the blind people

STATE OF THE ART


STATE OF THE ART

piezoelectric cantilever actuators

Assembling two lines of Braille cells requires putting two series of actuators nose-to-nose, with their cantilevers pointing away from the cells, laterally

10 cm

3 cm

> 20 cm


STATE OF THE ARTpiezoelectric cantilever actuators

25-30 cm

Thickness 3-4 cm

Assembling two lines of Braille cells requires putting two series of actuators nose-to-nose, with their cantilevers pointing away from the cells, laterally


F. Carpi, G. Frediani, D. De Rossi, “Hydrostatically coupled dielectric elastomer actuators”, IEEE/ASME Transactions On Mechatronics, vol. 15(2), pp. 308-315, 2010.

OUR APPROACH:Bubble-like ‘hydrostatically coupled’ DE actuators


Dielectric elastomer film: silicone (Elastosil RT625, Wacker) processed as a thin film by Danfoss PolyPower Film thickness: about 66 m (two films stacked together)Transmission medium: vegetable (corn) oilMax voltage: 2.25 kV

Prototypes


- Simple and compact structure;

- Ease of fabrication ( low cost)

- Electrical safety:

i) passive end-effector (no need for insulating coatings) ii) dielectric fluid (as a further protection);

- Self-compensation against local deformations caused by the finger:the shape and the thickness uniformity of the active membrane are preserved

Attractive features for tactile displays:


Refreshable Braille cell based on Hydrostatically Coupled DE actuators:

External electrodes

Internal electrodes

TOP PASSIVE MEMBRANE

BOTTOM ACTIVE MEMBRANEPlastic frame

Braille dot


Thickness 1-2 mm4 cm 25-30 cm

Thickness 3-4 cm

Potential advantages over the state of the art:1) Compact size2) Suitability for ‘full-page’ displays3) Light weight4) Shock tolerance5) Low cost state of the art



Prototype samples

•Elastomer film: 3M VHB 4905 acrylic polymer.

•Bi-axial pre-stretching: 4 times.

•Pre-stretched thickness: about 30 µm.

•Electrode material: carbon conductive grease.

•Transmission medium: silicone grease



Early prototype with Braille dots and spacing oversized (up-scaled) with respect to standards.



Braille dot with standard size (diameter = 1.4 mm; height = 0.7 mm)



Wearable tactile display for virtual interactions with soft bodies

G. Frediani, D. Mazzei, D. De Rossi, F. Carpi, “Wearable wireless tactile display for virtual interactions with soft bodies”, Frontiers in Bioengineering and Biotechnology, Vol. 2, 2014.

Wearable tactile display for virtual interactions with soft bodies

G. Frediani, D. Mazzei, D. De Rossi, F. Carpi, “Wearable wireless tactile display for virtual interactions with soft bodies”, Frontiers in Bioengineering and Biotechnology, Vol. 2, 2014.

Video

(dots: liver)

(dots: stomach)

Force feedback in minimally invasive surgery

F. Carpi et al. IEEE Transactions on Biomedical Engineering, Vol. 56(9), pp. 2327-2330, 2009.

Controlling the stiffnessto simulate different tissues

Haptic or visual displays of tissue compliance or organ motility

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(Control via EMG)

(Control via respiration)

(Control via ECG)

Haptic or visual displays of tissue compliance or organ motility

Medical training

Artificial vision (computer vision) systems in the biomedical field:- Social robots (e.g. robot therapy)- Medical diagnostics

(e.g. video endoscopes and other optical instrumentation, lab-on-a-chip units, etc.)

- etc.

Conventional optical focalization :focal length tuning achieved by displacing one or more constant-focus

lenses.

moving parts miniaturization is complex and expensive, bulky structures

Need for tunable-focus lenses with no moving parts

Electrically tuneable optical lenses for artificial vision systems

F. Carpi et al., “Bioinspired tunable lens with muscle-like electroactive elastomers”, Advanced Functional Materials, 2011.

Artificial ciliary muscles for electrically tuneable optical lenses


Bioinspired lens

Human crystalline



3 cm

10 cm


L. Maffli, S. Rosset, M. Ghilardi, F. Carpi, H. Shea, "Ultrafast all-polymer electrically tuneable silicone lenses", Advanced Functional Materials, in press.


WORLD’S FASTEST AND THINNEST tuneable lens:settling time < 175 μs for a 20% change in focal length

• Low-loss silicone • Be-spoke manufacturing

Cooperation with EPFL (Prof. Herbert Shea’s group)

L. Maffli, S. Rosset, M. Ghilardi, F. Carpi, H. Shea, "Ultrafast all-polymer electrically tuneable silicone lenses", Advanced Functional Materials, in press.


WORLD’S FASTEST AND THINNEST tuneable lens:

SLIDES ON THIS PART HAVE BEEN REMOVED FROM THIS ONLINE VERSION OF THIS PRESENTATION, AS RESULTS ARE NOT

PUBLISHED YET

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Artificial muscles for electrically stretchable membrane bioreactors

Inustrialization of the dielectric elastomer technologyis living its infancy nowadays…


Main EAP developers

Today the EAP field is just starting to undergo transition from academia into commercialization

(developers of transducers based on piezoelectric and electrostrictive polymers not included)

EAP industrialization

European Scientific Network for Artificial Muscles (ESNAM)www.esnam.eu

68 Member organizations from 26 European countries:

Relevant website: “EuroEAP”

www.euroeap.eu

‘EAPosters’

‘EAPodiums’

‘EAProducts’

Relevant event: “EuroEAP conference”

Annual International conference on Electromechanically Active Polymer (EAP)transducers & artificial muscles

Relevant event: “EuroEAP conference”

EuroEAP 2015

Tallin, Estonia9-10 June 2015

www.euroeap.eu

• EuroEAP 2011 - Pisa, Italy• EuroEAP 2012 - Potsdam, Germany• EuroEAP 2013 - Zurich, Switzerland• EuroEAP 2014 - Linköping, Sweden

enabling new biomedical and bioinspired mechatronic systems with electroactive smart elastomers...

Documents

electrical energy

biomedical field slide

mechanical energy

film of insulating elastomer

artificial ciliary muscles

artificial skeletal

material dielectric

electrical form