A novel gel liner system with embedded electrodes for use with upper limb myoelectric prostheses
A novel gel liner system with embedded electrodes for use with upper limb myoelectric prostheses
Timothy Reissman 0 1 2 3
Elizabeth Halsne 0 2 3
Robert Lipschutz 0 2 3
Laura Miller 0 2 3
Todd Kuiken 0 1 2 3
0 Current address: Department of Mechanical Engineering, University of Dayton , Dayton, OH , United States of America
1 Department of Biomedical Engineering, Northwestern University , Chicago, IL , United States of America
2 Center for Bionic Medicine, Rehabilitation Institute of Chicago , Chicago, IL , United States of America
3 Editor: Yih-Kuen Jan, University of Illinois at Urbana-Champaign , UNITED STATES
We present the development and evaluation of a gel liner system for upper limb prosthesis users that enables acquisition of electromyographic (myoelectric) control signals through embedded electrodes and flexible, conductive fabric leads. This liner system is constructed using a manufacturing approach rather than by modifying a commercially available liner. To evaluate the efficacy, eight male individuals with transhumeral amputations used this system, with standard myoelectric prostheses, for home trials lasting an average of 7.3 weeks. Before and after the home trials, electrical resistance of the cumulative 218 embedded electrodes and leads within 10 gel liner systems was measured and found to increase slightly (from an average of 13.4 to 27.5 Ω) after usage. While this increase was statistically significant (p = 0.001), all but one of the final resistance values remained low enough to enable consistent myoelectric control. User impressions were evaluated through a questionnaire comparing the liner prototypes to their own myoelectric prosthesis socket interface. Subjects preferred the liner prototype (p = 0.008) over their own system in the clinical areas of comfort, suspension, function, and, especially, ease of use. These results suggest that this gel liner system is a clinically viable option and that it may offer advantages over current clinical technology for users of upper limb myoelectric prostheses.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: Development funding was given through
US Army TATRC W81-XWH-11-1-0720 and
National Institute of Health CDMRP W81XWH
1202-0072 (TK). Funding for the lead author to
conduct the research presented was supported by
NIH T32 HD07418 (TR).
Competing interests: The authors declare the
issuance of two patents related to the technology
For nearly three decades, individuals with amputations have used roll-on elastomeric gel
liners, made from a variety of materials, as an interface between their residual limb and a rigid
outer socket [1±3]. Such liner systems are reported to offer benefits, including cushioning of
soft tissue and bony prominences, protection of the skin from friction caused by relative
motion between the limb and socket, improved suspension via locking mechanisms or suction
sealing, and increased adjustability of fit [
]. Although liners have historically been used for
individuals with lower limb amputations, they have also been increasingly adopted for upper
limb prosthetic fittings due to their comfort, ease of donning/doffing, and optimal device
For individuals who use myoelectric, externally powered upper limb prostheses, which are
controlled by skin-surface electromyographic (EMG) signals, the socket must fit the residual
limb tightly to prevent loss of contact between the electrodesÐtypically mounted in the socket
wallÐand the skin covering the residual limb muscles. This tight fit often necessitates the use
of a donning aid to pull the residual limb tissues into the socket, which has the tendency to
make the donning process time-consuming, physically demanding, and prone to error or
discomfort. In order to address these challenges, numerous attempts have been made to extend
the benefits of a gel liner interface to upper limb myoelectric prosthesis users [6±10].
The fundamental obstacle to using liner systems with myoelectric devices is that the liner
prevents the necessary contact between the user's skin and the socket-mounted electrodes.
Attempts to overcome this issue have generally involved modifying existing liners to allow
access of electrodes to the skin, either by piercing the liner with metal electrode domes [
2, 7, 8
or cutting holes in the liner to expose the skin [
]. While both approaches are functional, they
frequently result in damage to the integrity of the liner, reducing its lifespan. Cutting holes in
liners to allow skin contact requires users to don the liner in the correct position (i.e., so that
the holes line up with the electrodes in the socket) to enable EMG signal transmission.
Conversely, while placing domes in the liner removes this requirement, the user must then attach
individual wires to each electrode after donning the liner, which is cumbersome and requires
the user to manage the wires and ensure proper connections [
]. Additionally, the wires then
run between the liner and the socket, so relative movement of liner and socket can potentially
cause damage, leading to failure. A third approach to eliminating the wire harness involves
pushing metal electrode domes through the liner such that the back of the electrodes align
with magnets that are embedded in the socket and attached to wires [
]. However, while this
approach improved donning alignment through magnetic assistance and reduced the need for
wire manipulation, movement of the residual limb during muscle contractions frequently
disengaged the magnets from the electrodes. Central issues with all of these attempts to modify
existing liners were that (1) all posed challenges to the user (e.g., need for wire management,
precise donning technique to align with socket); (2) all voided manufacturer warranties on the
elastomeric liners; and (3) while somewhat successful in allowing the user to wear the gel liner
with a myoelectric prosthesis, all required lengthy customization of the liner and often the
hard socket. To date, no commercial gel liners suitable for use with a myoelectric prosthesis
are available, and only moderate success has been reported with liner modification
Despite these barriers, gel liners could enhance the use and function of upper limb
myoelectric prostheses by offering superior cushioning and skin protection for improved comfort,
ensuring consistent contact between the residual limb skin and electrodes, increasing the
adjustability of the socket fit, and providing optimal prosthesis suspension via a distal locking
mechanism. Integrating both the electrodes and the wires into the liner would eliminate the
burden of wire management, making donning easier for the user. We hypothesized that such a
myoelectric liner system would provide users with enhanced comfort and ease of use, while
maintaining optimal prosthetic function, and would be advantageous compared to previous
solutions by eliminating the need for post-manufacturing modifications, thus reducing clinical
fabrication time and preserving the integrity of the liner.
Here we describe the development and clinical evaluation of a novel, integrated myoelectric
gel liner system that includes electrode domes and wiring embedded during the
manufacturing process [
] and that provides electrical connections to the socket electronics and
mechanical suspension via a novel distal magnetic locking connector [
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Materials and methods
Integrated myoelectric gel liner system
Commercially available gel liners are made from a range of elastomeric materials (silicone,
urethane, thermoplastic elastomers, etc.). The primary concept behind our gel liner system
was to integrate the components needed for myoelectric controlÐi.e., the electrodes and wires
(or leads)Ðinto the gel liner during the manufacturing process without compromising the
structural or elastic properties of the liner [
]. To achieve this, we encapsulated strips of
bi-directional stretch, silver-coated fabric (A321, Less EMF, Latham, NY) between the outer
fabric cover of the liner and the gel layer to act as insulated electrical leads. The fabric leads
were secured to internally threaded weld nut posts (90611A200, McMaster-Carr, Elmhurst, IL)
that were gold plated to prevent corrosion and maintain conductivity; the height of the weld
nuts was machined prior to plating to match to the thickness of the gel layer, such that only the
top of the weld nuts were exposed on the internal liner surface. Custom stainless steel electrode
domes with extended thread rods could then be secured into the weld nuts, exposing the
convex dome on the gel surface inside of the liner (Fig 1A) to enable contact with the user's skin.
The manufacturing process went as follows: (1) conductive silver-coated fabric was cut to
form a circular area for an electrode and a contiguous linear extension for the lead; (2) the
outer fabric liner cover of the liner (i.e., before the gel layer was added) was turned inside out
such that the leads could be attached to the inner side; (3) gold-plated threaded weld nuts were
attached to the circular part of the fabric, and the fabric leads and electrodes were attached to
the liner cover by ironing with an adhesive (Stitch Witchery, HTC-Retail.com) at desired
electrode locations. Since the weld nuts were rigid components in an otherwise flexible system,
they were additionally anchored to the liner cover fabric with sewing thread to ensure a secure
Fig 1. Donning of myoelectric gel liner system. (a) Gel liner system is inverted and then rolled onto the residual limb
(A blue oval highlights the electrode domes and the connected fabric leads); (b) Donned liner with proximal magnetic
connector at distal end, shown prior to donning myoelectric prosthesis (A yellow oval indicates the proximal
connector); (c) Donning of prosthesis with distal magnetic connector embedded at the distal end of the socket.
Locking of proximal and distal magnetic connector parts aided by magnetic attraction and secured with cam latch; (d)
Securing of myoelectric prosthesis with auxiliary suspension harness.
3 / 15
connection; (4) at the distal end of the liner, the fabric leads were then attached to a custom,
central electrical routing connector, which paired each lead with a corresponding conductive
hollow pin to allow transmission of EMG signals from the inside to the outside of the liner.
These hollow pins formed a perimeter of external connections which were concentric to the
distal, internal thread commonly used for securing a locking pin (Fig 2); (5) thermoplastic
elastomeric gel was then injected on the inside surface of the liner fabric, according to standard
manufacturing practice, covering the conductive fabric leads while leaving the top surface of
the weld nuts exposed; (6) stainless steel domes were then threaded into the weld nuts and
secured with a thread locking adhesive (Blue 242, Loctite Inc., Westlake, OH), which was
nonconductive but did not alter the resistivity of the electrode dome and fabric lead conductive
path. The stainless steel domes were used to create an electrode interface that could tolerate
the perspiration and abrasion associated with prolonged contact with the skin of a residual
limb. The domes were machined to be rounded near the base edgesÐto minimize any damage
to the gel layerÐand polished to reduce any skin irritation.
A novel magnetic connector interface was designed to simplify mechanical and electrical
connection of the liner to the myoelectric prosthesis (Figs 1B and 3). The magnetic connector
consisted of two parts: (1) a proximal connector that was attached to the distal end of the liner
and (2) a distal connector that was installed inside the distal end of the socket and connected
to the myoelectric prosthesis. Three magnets (RA22, K&J Magnetics Inc., Pipersville, PA)
incorporated on each connector face served to both assist with mechanical attachment of the
two connector parts and to provide electrical connectivity. The magnets were configured such
that the two connectors would attract to one another when properly aligned, providing an
assistive pull-in force when donning the prosthesis. The force was such that when the two
connectors would be placed near one another, the attractive force would nonlinearly increase up
to a maximum value of 107N (24lbf) until contact. On each connector face, the magnets were
arranged with alternating polarity to assist with proper alignment when donning (i.e., the
connector could only be secured when the magnets were in the correct orientation). This
proved useful for doffing, as the moment required for magnet separation was only 1.1Nm (10
in-lbf). Relative rotation of the connector interface would increase the distance between the
magnet pairs, thereby reducing the attractive force. More relative rotation could bring same
polarity magnets together, and the resulting repulsive force could help push the connectors
apart. To further secure the connectors axially and prevent relative rotation during use of the
prosthesis, a secondary mechanical lock, a cam latch, was used. With this secure and properly
aligned connector interface, electrical connections from the liner to the myoelectric prosthesis
Fig 2. Myoelectric gel liner. (a) Internal view of liner showing central routing of fabric leads; (b) External view of liner
in which each fabric lead is electrically connected to hollow electrical pins, and showing the central threaded bolt that
the proximal magnetic connector part is secured onto.
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Fig 3. Magnetic electrical connector. (a) Exploded-view drawing of proximal magnetic connector part from [
Proximal magnetic connector which is secured to outside of liner; (c) Distal magnetic connector which is secured
within distal end of socket; (d) Complete system with proximal connector attached to gel liner and distal connector
attached to socket.
were ensured by simply securing the cam latch, without the need to manage any wire
The proximal connector was assembled as follows: (1) a threaded bolt extending from the
distal end of the liner (Fig 2B) was inserted through the center of the proximal connector and
axially secured to the liner by a hex nut (Fig 3C); (2) the perimeter of the lid of the proximal
connector was adhered to the outside of the liner using silicone (Fig 2B) to mechanically secure
the connector to the liner in case of twisting moments when in use or when doffing; (3) pins
from the circuit board housed within the proximal connector (see Fig 3A) were inserted into
the hollow pins of the electrical routing connector on the liner. These connected each electrode
dome and lead pair to the circuit board in the proximal connector, which served to amplify
each EMG signal and perform analog to digital conversion; (4) the circuit board was
electrically connected to the three magnets and the center threaded bolt. After conditioning the
EMG signals, the circuit board transmitted the high and low signal pathways to the attached
distal connector unit using a standard controller area network bus for communications, via
two of the three external magnets. The two remaining conduction pathways, the third magnet
and central bolt, were used to supply power and signal ground, respectively, to the circuit
The distal connector was assembled as follows (Fig 3B): (1) a designated space was formed,
using a dummy, at the distal end of the socket to create a cylindrical housing for the distal
connector (Fig 3D). Holes were made in the socket for mechanical attachment of the three
external set screws and positioning of the mechanical latch. (2) magnets were configured such
that when correctly aligned with the proximal connector, the magnets would attract the two
connector parts into proper alignment, enabling operation of the mechanical latch and
ensuring correct electrical connections; (3) the distal connector was secured by three set screws that
secured into internally threaded posts within the wall of the distal connector; (4) the
mechanical latch unit was secured onto the distal connector using additional set screws; (5)
communication lines, including the power and ground, between the distal connector and the
myoelectric prosthesis controller were connected through magnet pairings, and one of two
audio signals was provided to indicate if proper connection was made.
5 / 15
The final system was a flexible, elastic gel liner system with integrated EMG sensors, lead
wires, and a simple-to-use electrical and mechanical connector. Although initial attempts at
using silver conductive fabric for the electrodes as well as for the leads resulted in successful
EMG acquisition during early lab testing [
], electrical resistance measurements revealed that
prolonged use of the silver-coated fabric as the electrode contact surface led to corrosion of the
silver in the fabric, due to the combined effects of perspiration and skin abrasion, and
subsequent loss of myoelectric signal conduction, i.e., open circuit conditions [
testing of liners with stainless steel electrode domes confirmed that this evolved system design was
a robust means for collecting EMG signals, over prolonged use. Thus we evaluated our liner
system, with stainless steel dome electrodes, in the following clinical study.
Gel liner system evaluation
The study presented within this work was approved by the Institutional Review Board at
Northwestern University, and all subjects provided written consent prior to the study.
Prototype socket interface systems comprising gel liners with embedded electrodes, conductive
fabric leads, and a magnetic connector interface were evaluated by individuals with unilateral
transhumeral amputations who were current myoelectric prostheses users (Table 1). Subject
recruitment for this evaluation coincided with the individuals' participation in a separate,
ongoing study in which they used a standardized transhumeral myoelectric prosthesis after
having undergone targeted muscle reinnervation surgery [
]. The protocol for this other
study required two home trials using different myoelectric control systems (direct control
which used 9 subject specific electrode locations and pattern recognition control which used
13 grid based electrode locations). Thus subjects each wore the two separate patterns of the
domes within their liner systems to test each control strategyÐone dome pattern of the liner
for one home trial and the other dome pattern for the second home trial. Prior to and
immediately after each home trial, separate evaluations for this study were concurrently performed
with the coinciding myoelectric control study. It should be noted that for the other study, the
selection of which control strategy first used was randomized, so Liners 1 and 2 within Table 1
are also randomized and thus simply indicate whether the gel liner system was used in the first
or second home trial respectively. The liner system was evaluated over the course of prototype
Weeks at home±
Weeks at home±
development. As such, some of the subjects used an earlier version (conductive fabric electrode
domes) for part of their study, as noted in Table 1. However, all subjects also used the final
design, described in detail above, in which stainless steel electrode domes were secured to
embedded gold-plated weld nut posts and conductive silver fabric leads in the liner. Only
results from the final liner design are analyzed in this study. It should be noted that Subject 8
used the same final version liner that was used by Subject 2, see Table 1.
Subjects were fit with a standardized transhumeral myoelectric prosthesis, which included a
laminated socket with a Boston Digital Arm System elbow (Liberating Technologies, Inc.;
Holliston, MA), a powered wrist rotator, and their personal terminal deviceÐwhichever powered
hook or hand that they preferred to use with their normal prosthesis (Table 1). The prototype
gel liner system was used as an interface inside of the socket, and the magnetic connector
served as the primary prosthesis suspension method. Auxiliary suspension of the prosthesis
was provided by a standardized harness (AcrocomforT Shoulder Support; Otto Bock,
Duderstadt, Germany). The magnetic connector interface also served as the electrical connection
between the embedded electrodes and the prosthesis, and contained electronics to amplify and
process the collected EMG information.
Subjects were instructed to use the gel liner system with their prosthesis over a period of
approximately eight weeks at home and to return to the laboratory for evaluation. Each subject
then repeated the same protocol a second time with a different control system, requiring
another liner, with the same prosthesis. Prior to using each gel liner system at home, subjects
were given five consecutive days of training and use in the laboratory with a prosthetist and
occupational therapist to become familiar with the control system. Training with the
prosthetist and occupational therapist occurred in tandem, with modifications made to the socket and
control as needed by the prosthetist as the subject progressed through therapy and various
tasks. In general, subjects were working with the prosthesis four to six hours on each day as
fatigue would allow. Subjects were also trained to be able to independently and reliably don
and doff the liner system and prosthesis. Directly before and immediately after home use, the
electrical resistance of the embedded electrodes and leads within the liners were measured
with a multimeter (110 True RMS Digital Multimeter; Fluke Corporation, Everett, WA); these
results were used to inform development of the gel liner system (the measurements collected
can be found in the S1 File). The stability of the system's electrical conductivity was monitored
because high electrical resistance (above 200 Ω threshold), and its corresponding reduced
signal to noise ratio, results in a degradation in the ability to effectively use myoelectric control
]. A paired-sample t-test analysis was performed to determine statistical significance of
any changes in resistance with respect to before and after home trials (p<0.05).
To quantify clinical efficacy, user impressions were obtained through a subjective socket
comfort score using an 11 point scale (0±10), where 0 represents the most uncomfortable and
10 represents the most comfortable fit [
]. Subjects were asked prior to their home trials to
score their hard socket interface. Subjects were then asked following both home trials to score
the liner system. A nonparametric Mann Whitney U test was performed to compare socket
comfort scores (statistical significance p<0.05). More detailed user input on comfort, ease of
use, suspension, and prosthetic function while using the gel liner system was obtained through
a custom questionnaire that also asked subjects to compare the final version of the liner system
to their home socket interface. The questions asked in each clinical area are listed in the S2
File. Subjects recorded their perceptions of the liner system by indicating the degree of their
agreement with each survey item using a 5-point Likert scale. A nonparametric Wilcoxon
signed rank test was performed to determine statistical significance (p<0.05).
7 / 15
Fig 4. Electrical resistance of gel liner system before (blue) and after (red) home trials for all eight subjects. Note
that values under 200 O pre-amplification threshold yield useful signal-to-noise ratios for consistent myolectric
8 / 15
storage period, nearly no change in resistance occurred for this liner, with values measured
before storage at 18.6 ±5.4 Ω and afterwards at 18.7 ±6.0 .Ω After 22 weeks of storage time for
Subject 3's liner after the second home trial, resistance was 13.7 ±7.7 ,Ω compared to 9.2 ±3.9
Ω before storage.
Before home trials, subjects indicated their perceived socket comfort scores for their own
socket system (Fig 5). Average subject scores for their own sockets were 6.9 ±1.7. Following
home trials, subjects scored the liner system. Average subject scores were 9.0 ±1.0; higher
scores indicate better comfort. Each subject scored the embedded liner system equal to or
better than their own socket, with significant overall differences between the two groups
(p = 0.02).
Additionally, the custom questionnaire in the S2 File was given to subjects after their
second home trial. The first half of the questionnaire consisted of 11 questions based solely on
each subject's experience with the final liner system (Fig 6). Fig 6 is represented graphically
using a divergent stacked bar chart [
], which represents favorable responses to the right and
neutral/unfavorable responses to the left of the zero count point. Each question was
categorized into one of four clinical areas: ease of use, comfort, suspension, and function. Over all the
questions, subjects' answers tended towards favorable answers for the gel liner system in all
four categories. The ease of use category had sufficient Likert data to perform a separate
Wilcoxon signed rank test, which showed that the favorable response was statistically significant
(p = 0.008). The same significance (p = 0.008) was found over all questions for favorable
evaluation of the liners over a neutral response.
A single question addressed reliability of the liner system with the magnetic electrical and
mechanical connector: Q12. ªHow frequently did you hear the three-tone failure sound
indicating that the liner did not connect to the socket?º Subjects could choose from the following
options: never, once a month, once a week, several times per week, once a day, several times
per day, or every time I put the prosthesis on. Subject 7 selected never. Subjects 3, 4, and 8
Fig 5. Self-reported socket comfort scores (0±10 range) for the subjects' home sockets and the liner system. Higher
scores indicate greater perceived comfort. Indicates statistical significance (p = 0.02).
9 / 15
Fig 6. Experience with myoelectric gel liner system. Divergent stacked bar chart structured such that counts to the right indicate a favorable
response to the questions within the four clinical areas: ease of use, comfort, suspension, and function. Note: Question 12 and subjects'
responses are included separately in the Results section, as the Likert scale was not used.
selected once per month. Subjects 1, 2 and 6 selected once per week, and Subject 5 selected
several times per week. Thus, the median frequency was between once a month and once a week.
The second half of the questionnaire consisted of 10 questions (Fig 7) that asked each
subject to compare their experience using the liner system to that using their home system. The
same graphical representation used in Fig 6 was applied for Fig 7. For all but one of the
10 / 15
Fig 7. Comparison of myoelectric gel liner system to own system. Divergent stacked bar chart structured such that counts to the right indicate
a favorable response to the questions within the four clinical areas: ease of use, comfort, suspension, and function.
questions, a trend emerged that indicated a favorable bias by the subjects towards our liner
system over their own systems. The one question that did not follow this trend was Q21, which
asked about the length of the prosthesis with the liner. Performing Wilcoxon signed rank tests
on the ease of use and on the overall responses, indicated that subjects preferred the gel liner
system over their present home systems (p = 0.008).
Our final liner system design with stainless steel electrode domes was stable in terms of
electrical resistance, with an average increase in resistance of only 14.1 Ω after a home trial, over the
11 / 15
average initial resistance of 13.4 .Ω Additionally, extended use of the same final liner design
over two home trial periods, 11 weeks total, showed nearly the same rate of increase in
resistance, with a total increase of 18.8 Ω over the initial 13.9 .Ω While noting that the increased
resistance after each home trial period was statistically significant, it is important to note that
the final resistance values measured remained sufficiently small, well under 200 ,Ω to maintain
useful signal-to-noise ratios for consistent myoelectric control. As such, the increases in
resistance observed did not appear to be functionally significant. Only one of the stainless steel
electrode dome and fabric lead pairs exhibited values over 70 Ω after home trial use, and none
exhibited open circuit conditions. Thus 99% of all electrode sites maintained values well within
the pre-amplification thresholds for effective myoelectric control. In more direct comparison
to the improvement over the previous liner design, Subjects 1, 2, 3, 7, and 8 wore the initial
liner design with conductive fabric electrodes for one of their home trials within this study.
The results showed an average increase in resistance per home trial of 134.6 Ω after the home
trial compared to an initial average resistance of 17.4 .Ω As in the previous benchtop study
], some electrodes even reached infinite resistance or open circuit conditions. These results
further indicate that the use of silver-coated fabric electrodes for long-term EMG acquisition is
not feasible, as they are susceptible to the corrosive effects of perspiration and abrasion
conditions. Thus, using stainless steel domes as the EMG contact surface proved necessary and
highly effective at providing stable electrical performance during prolonged use.
The importance of this relatively stable performance can be estimated with respect to the
present mean warranty times of 6 to 12 months for prosthetic liners. Applying the approximate
rate of 14.1 Ω increase per 7.3 weeks of usage (average increase per trial period), the projected
final value after one year of usage is 100.4 Ω over the nominal 13.4 .Ω Thus, even at the end of
the liner's warranty, the electrical performance is projected to be within myoelectric control
thresholds and thus functional. As for storage of the liners, examining two liners after 22
weeks of storage showed only a slight increase in mean values of 2.2 Ω over their nominal 13.9
.Ω As such, these liners can likely be stored for long periods of time without degradation of
electrical performance. However, as this study is limited in the number of liners tested
(N = 10) and the length of usage time, additional testing over longer periods of time is
necessary in order to test the accuracy and merit of such projections.
The use of rigid, gold-plated weld nuts and stainless steel electrode domes did not
noticeably alter elastic properties of the liner, including bi-directional stretch. No defects were visible
to the naked eye in the liner fabric or on the gel layer after the home use trials. Fig 1A displays
a picture of the interior of a liner before home use, and Fig 3D shows the exterior of the same
liner after home use. Additionally, pictures of the subjects' skin on their residual limb after
using the liner showed only temporary indentation marks, similar to dome imprints found
after using their clinical prostheses, and no signs of irritation from the electrode domes were
The magnetic connector interface design proved useful in assisting with donning and
doffing of the device. Users informally commented that they could feel the connector pull into
place near the end of the donning process and could confirm proper connection and
alignment easily with a click sound from the contact of the magnet pairs. Total time observed for
subjects to don the liner and prosthesis was approximately 30 seconds, not including
securement of the auxiliary harness (an additional 30 seconds). Subjects also commented that with
the latch open, the system was easy to doff as they could use the proximal trim lines of the
socket as a moment arm to provide the necessary torque to rotate and separate the connector
interface, lowering the attractive force via misalignment of the magnet pairs. Total time
observed for subjects to doff the liner and prosthesis was approximately 20 seconds, not
including detachment of the auxiliary harness.
12 / 15
Analysis of socket comfort scores and questionnaire responses supported our hypothesis
that our liner system would enhance comfort and ease of use in comparison to currently
available prosthetic interface and suspension systems. In terms of the socket comfort scores, the
improvement may have been expected as the subjects received a new socket for the study and
had five consecutive days of training with a prosthetist. However, the significant difference in
comfort scores between the liner system and subjects' own systems does indicate a
fundamental change in the perceived comfort between the two interfaces. Suspension was shown to also
be highly favorable, with only one individual, Subject 5, noting that the liner could have been a
size smaller for better fit. It should be noted that this lack of an ideal fit may have contributed
to this individual's high rate of connectivity issues compared to other subjects' experiences as
reflected in the responses to Question 12.
Prosthesis length was increased by addition of the magnetic connector, and subjects had a
more varied response to this feature. The connector assembly added approximately 24mm
(0.94in) in arm length, so for individuals with long residual limbs this additional length may
The following comments were written by the subjects as a part of the questionnaire: ªI love
the linerº; ªThere was no problem putting it onº; ªI thought the liner was easy and
comfortableº; ªI like the suspension of the linerº; ªIt prevents air pocketsº; ªI like it a lot better than
what I haveº. Areas in which the liner system scored lower than the users' own systems on the
questionnaire also correlate with users' written commentsÐon comfort: ªTemperature OK till
end of day then sweatingº; suspension: ªThe only change would be a better way of securing a
loose fitting linerº; and function: ªMake liner connector shorterº. The first two issues are
difficult to resolve as they are inherent to the use of gel liners in general. Making the magnetic
connector shorter may be a possibility; however as noted previously for individuals with long
residual limbs, this issue may continue to be a problem. Additionally, the length of the
magnetic connector system in its current configuration is comparable to commercially available
upper limb pin-locking liner suspension systems; the Otto Bock 14A1 Upper Extremity Lock
Set is 22mm in length.
Here we present the development and evaluation of a novel gel liner system with embedded
electrodes and leads for use with upper limb myoelectric prostheses. Integrating the electrical
components within the gel liner during the manufacturing process maintained low electrical
resistance even after an average of 7.3 weeks of home usage. Additionally, combining rigid
electrodes with flexible fabric leads did not affect the structural integrity or elastomeric
properties of the liner during the evaluation period. Subjects perceived the liner system as more
favorable than their current system in many areas that are clinically important for a myoelectric
prosthesis interface: ease of use, comfort, suspension, and function. In conclusion, we have
shown that the benefits of a gel liner system can be provided to myoelectric prosthesis users
using a manufactured approach.
S1 File. Study data. Resistivity measurements collected from the 10 gel liner systems using the
final design is provided. Additionally data from the socket comfort scores and questionnaires
is provided with respect to each subject.
13 / 15
S2 File. Questionnaire used in the study. The original questionnaire given to subjects
following their second home trial is provided.
Institutional Review Board: Northwestern University's IRB approved this study under
#STU00068547 and consent was acquired by all subjects involved, including permission for
photographs and video.
Additional contributions: Materials and the gel layer application process were supplied
through a collaboration with ALPS South, LLC.
Conceptualization: Timothy Reissman, Elizabeth Halsne, Robert Lipschutz, Todd Kuiken.
Data curation: Timothy Reissman, Elizabeth Halsne, Laura Miller.
Formal analysis: Timothy Reissman, Todd Kuiken.
Funding acquisition: Timothy Reissman, Todd Kuiken.
Methodology: Timothy Reissman.
Supervision: Todd Kuiken.
Validation: Timothy Reissman.
Visualization: Timothy Reissman.
Writing ± original draft: Timothy Reissman, Elizabeth Halsne.
Writing ± review & editing: Timothy Reissman, Robert Lipschutz, Laura Miller, Todd
14 / 15
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