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& ORTHOTICS JOURNAL, VOLUME 1, ISSUE 2, 2018; ABSTRACT, POSTER PRESENTATION AT THE AOPA’S 101ST NATIONAL ASSEMBLY, SEPT. 26-29, VANCOUVER, CANADA, 2018.      
DOI: https://doi.org/10.33137/cpoj.v1i2.32048                                                                            

 

1 

 
OPEN  ACCESS 

 

AOPA’S 101 ST NATIONAL ASSEMBLY ABSTRACTS, SEPTEMBER 26-29, VANCOUVER, CANADA, 2018 
 

ABSTRACT (POSTER PRESENTATION) 

Adjustable Liners and Sockets for Prosthetic Devices 

Lenore Rasmussen1*, Simone Rodriguez1, Matthew Bowers1, Damaris Smith1, Greig Martino2, Livia Rizzo3, 

Cole Scheiber4, Jesse d’Almeida5, Curran Dillis6  
 

1 Ras Labs, Synthetic Muscle TM for Prosthetics & Robotics, USA. 
2 United Prosthetics (UPI), Boston, Massachusetts, USA.  
3 Harvard Medical School, MEDscience Program, USA. 
4 Biology, Tufts University, Massachusetts, USA. 
5 Robotics Engineering, Worcester Polytechnic Institute, Massachusetts, USA.  
6 Hingham HS,  Robotics Captain, USA. 

* Email: rasmussl@raslabs.com                                                                             DOI: https://doi.org/10.33137/cpoj.v1i2.32048  
 

INTRODUCTION 

Ras  Labs’ Synthetic  Muscle™  will  allow  amputees  to  

continue  their  active  lives  without  needing  to adjust 

the fitting of their prosthetic device(s) throughout the 

day.  This technology promises to resolve major  issues  

facing  amputees,  most  notably  the  pain  of  prosthetic  

slippage  and  tissue  breakdown. Synthetic  Muscle™,  

comprising  electroactive  polymers  (EAPs),  actively  

expand  or  contract  at  low voltages, while offering 

impact resistance and pressure sensing, all in one 

integrated solution.   The main  objectives  of  this  project  

is  to  determine  the  feasibility  of  the  EAP  pads  

incorporated  into prosthetic  liners  or  sockets  and  to  

create  prototypes  of  these  EAP  based  shape-morphing  

pad systems.  In collaboration with UPI, testing of these 

EAP based pads located in strategic areas of the socket  

was  initiated  with  customers  (BK  and  AK)  for  

evaluation  and  feedback.   Characterization  of Synthetic  

Muscle™  as  dual  use  pressure  sensors  was  initiated.   

This  is  a  continuation  Ras  Labs’ dynamic prosthetic 

pad project, which demonstrated how the volume of the 

EAP can be changed from applying a low voltage and 

operating temperatures for use in adjustable prosthetic 

liners and sockets 1-8. 

METHODS 

The EAP networks were developed by polymerization of 

ionic monomers with specialized cross-linking agents.  

The desired pore sizes and elasticity in the final networks 

were achieved by controlling the cross-link density and 

aqueous solvation during polymerization, followed by 

equilibration of the EAP in electrolyte solution to its final 

volume.   Pad designs were assembled and tested over 

contraction and expansion cycles at 1.5 V. A pre-step of 

expansion for 1 hour (not shown in figures) was 

performed followed by contraction for 4 hours under 

load, an expansion cycle for 30 minutes under static load,  

 

and an expansion for 5+ hours under 1 Hz cyclic on-off 

pressure load to mimic ambulation in the socket. The 

electroactivity of these pad designs were tested by 

attaching the reservoir and EAP electrodes to the 

corresponding polarity for 2-hour contraction and 

expansion cycles over 1.5V, 3V, 6V, and 9V. The 

dimensions were measured after each cycle to follow the 

change in height. 

RESULTS 

All of the EAP based pad design prototypes performed at 

1.5 V, with the 3 lb. testing set-up having a higher pound 

per square inch than the 5 lb. testing set-up due to the 

different sizes of the EAP pads. Contraction occurred 

over the first 5 hours, static load, followed by 30 minutes 

expansion, static load, followed by 5+ hours expansion 

under cyclic load  at  1  Hz  to  mimic  ambulation.   The  

cyclic  load  is  to  demonstrate  actuation  during  daytime  

use  (after  a  long contraction cycle).  In use, these EAP 

based pads will be contracted overnight at low voltage, 

then either allowed to expand back to their neutral state 

at 0 V or the electric input reversed to provide for 

expansion.   Particularly under cyclic load, expansion is 

readily observable even within the first cycle, which 

would be needed for the EAP pads to quickly meet and 

match void changes from shrinkage of the residual limb 

if there is a fast change.  From the testing at 1.5 V, 3 V, 

6 V, and 9 V with 2-hour cycles, all voltage levels 

showed electroactive actuation.  The 3 V, 6 V and 9 V 

testing typically demonstrating incrementally more 

shape-morphing in both expansion and contraction; 

however, the 9 V testing produced some artifacts as well 

with distinct localized effects. As the development of 

sensing in the EAP progressed, the construction methods 

improved.  A challenge was  consistency  between  the  

pads  themselves,  resulting  in  data  that  could  not  be  

regarded  as  overly reliable.  The solution was to create 

mailto:rasmussl@raslabs.com
https://doi.org/10.33137/cpoj.v1i2.32048


 

 

Rasmussen L, Rodriguez S, Bowers M, Smith D, Martino G, Rizzo L, Scheiber C, d’Almeida J,  Dillis C. Adjustable Liners and Sockets for Prosthetic Devices. CANADIAN PROSTHETICS 
& ORTHOTICS JOURNAL, VOLUME 1, ISSUE 2, 2018; ABSTRACT, POSTER PRESENTATION AT THE AOPA’S 101ST NATIONAL ASSEMBLY, SEPT. 26-29, VANCOUVER, CANADA, 2018.      
DOI: https://doi.org/10.33137/cpoj.v1i2.32048                                                                            

 

2 

 
OPEN  ACCESS 

 

AOPA’S 101 ST NATIONAL ASSEMBLY ABSTRACTS, SEPTEMBER 26-29, VANCOUVER, CANADA, 2018 
 

ABSTRACT (POSTER PRESENTATION) 

a specific system of manufacturing that was as close as 

possible for each pad, including: 3D printed molds for 

the silicone casings and 3D printed pads for a point 

electrode. Extensive  design  experiments  were  

performed  to  select  the  most  suitable  system  for  

integration  of electrodes within the EAP pads (Figure 1). 

The most feasible design system is shown, with one 

electrode as carbon mesh (1x1”) and the other as a Pt wire 

as the point electrode. A silicone mold was poured such 

that the EAP and electrodes fit in perfectly, with minimal 

excess casing. 

Figure 1.  Different versions of EAP based  sensors. 

 

Compression Sensing Characterization 

 

When mechanical pressure is applied to Ras Labs’ 

electroactive polymers, the change in resistance can be 

recorded.   The EAP resistance varies  with applied 

pressure.  This has been measured  with several different  

variations  of  EAPs  and  encapsulations,  with  each  

iteration  becoming  more  consistent  and reliable.   The 

EAPs, on average, have a relatively high resistance that 

varies slightly with pressure. The resistance was 

measured using an oscilloscope and reading the 

Wheatstone bridge was attached to EAP (Figure 2).  The  

circuit was attached to a 1V amplitude AC signal and the 

RMS values recorded for each of a series of weight. This 

allows Ras Labs to use these polymers as resistive 

sensors in addition to their contractile properties for 

multiple applications.  The sensing capabilities of these 

EAPs are demonstrated using an oscilloscope and an 

analog multimeter (Figure 3).  

Figure 2.  Voltage RMS vs Mass for each of the Version 2 

EAPs. 

 
Figure 3.  Simple Sensing Demo using Analog Multimeter. 

 

Flexy-Hand 2 Project 

 

The original files, from Thingiverse, represented Steve 

Wood and Jeff Erenstone’s approach to making a hand 

for an UL amputee.   We started  with these open source 

files, edited them  using computer-aided design  (CAD)  

software,  and  scaled  down  to  the  size  of  our  petite  

patient’  hand,  working  with  our customer’s anatomy 

of the vestige hand.  A 3D scanner was used to get the 

patient’s mold scanned into the  software,  which  was  

used  to  cut  a  better  fit  for  the  ‘socket’  of  the  partial  

hand  (Figure  4).  By implementing the scan into the 

established Flexy-Hand 2, the goal was for a more 

comfortable and more stable fit for our patient during 

normal usage. 

Figure 4.   Top Left: The Flexy-Hand 2 (left) next to the 

modified Flexy-Hand 2 (right): Top Right: The modified 

Flexy- Hand 2 (bottom) next to the ideal sized hand for this 

patient (top); Bottom Left: The UPI-Ras Labs’ collaborative 

team constructing the modified hand; Bottom right: The 

patient wearing the modified Flexy Hand 2. 



 

 

Rasmussen L, Rodriguez S, Bowers M, Smith D, Martino G, Rizzo L, Scheiber C, d’Almeida J,  Dillis C. Adjustable Liners and Sockets for Prosthetic Devices. CANADIAN PROSTHETICS 
& ORTHOTICS JOURNAL, VOLUME 1, ISSUE 2, 2018; ABSTRACT, POSTER PRESENTATION AT THE AOPA’S 101ST NATIONAL ASSEMBLY, SEPT. 26-29, VANCOUVER, CANADA, 2018.      
DOI: https://doi.org/10.33137/cpoj.v1i2.32048                                                                            

 

3 

 
OPEN  ACCESS 

 

AOPA’S 101 ST NATIONAL ASSEMBLY ABSTRACTS, SEPTEMBER 26-29, VANCOUVER, CANADA, 2018 
 

ABSTRACT (POSTER PRESENTATION) 

CONCLUSIONS AND FUTURE WORK 

The modulation of the EAP shape-morphing control as 

needed by controlling the voltage level were very 

promising. This technology is expected to provide for an 

adjustable prosthetic liner or socket that can maintain 

dynamic perfect fit throughout the day, for an advanced 

standard of care for amputees. Ras Labs is working with 

its collaborators (UPI) and partners to gather evaluation 

and feedback from AK and BK amputees, with 

promising results. More patient testing is required over 

longer durations of use.  Ras Labs’ Synthetic Muscle™ 

has the potential to sense pressure and provide for self-

adjusting prosthetic liners, with no need for the patient to 

adjust the fit of their device.   As sensors, variable voltage  

was  observed  when  the  EAP  sensor  was  mechanically  

compressed.    Moving  towards pixilation of the sensing 

data will provide a wider range of data and feedback 

control.  The goal is to give  amputees  natural  

locomotion  with  a  worry-free  prosthesis,  maintaining  

dynamic  perfect  fit throughout  the  day and  preventing  

tissue  damage  from  even  beginning  to  occur.   With  

the  Flexy- Hand 2 modifications, we are advancing the 

design to fit any patient’s individual needs.   Next, we 

plan to add EAP fingertip sensors to replicate touch while 

providing life-like compliancy and grip. 

ACKNOWLEDGE 

We    gratefully    acknowledge    the    National    Science    

Foundation,    Breakout    Labs,    Children’s    Hospital    

of Philadelphia/Philadelphia Pediatric Medical Device 

Consortium, CASIS, US DOE, and US DOD for funding 

of the synthetic  muscle  projects.  Prosthetic  

applications  are  in  collaboration  with  United  

Prosthetics  and  additional partners.  The MLSC 

Internship Challenge graciously provided intern support. 

REFERENCES 

1.Rasmussen L et al. Synthetic Muscle electroactive polymer 

(EAP) based actuation and sensing for prosthetic and robotic 

applications," Proc. SPIE 10594, Electroactive Polymer 

Actuators and Devices (EAPAD) XX, 105942C. doi: 

10.1117/12.2297660, 2018. 

2.Rasmussen L, Editor, “Electroactivity in Polymeric 

Materials,” Springer-Verlag, GmbH & Co. KG © 2012. 

3.Rasmussen L, Meixler L.D, Gentile C. Contractile 

Electroactive Materials and Actuators. SPIE EAPAD 2012, 

Proc. SPIE 8340, 1O:1-14, 2012. 

4.Rasmussen L et al. Considerations for Contractile 

Electroactive Polymer Based Materials and Actuators. Proc. 

SPIE 7976, 2B1-2B13, 2011. 

5.Wood S, Erenstone J, Flexy-Hand 2, ttps://www.thingiverse. 

com/thing:380665 © 2018 

6.Sanders JE, Fatone S. Residual Limb Volume Change: 

Systematic Review of Measurement and Management. J 

Rehabil Res Dev, 48(8): 949-986, 2011. 
DOI:10.1682/JRRD.2010.09.0189 

7.Rasmussen L, et al. Considerations for Contractile 

Electroactive       Polymeric Materials and Actuators. Polym. 

Int. 59: 290-299, 2010. https://doi.org/10.1002/pi.2763 

8.Zachariah SG et al. Shape and Volume Change in the 

Transtibal Residuum over the Short Term. J Rehabil Rev Dev, 

41(5): 683-694, 2004. DOI: 10.1682/JRRD.2003.10.0153 

 

 

https://doi.org/10.1002/pi.2763

