Proceedings of the ASME 2016 International Manufacturing Science and Engineering Conference
MSEC2016
June 27-July 1, 2016, Blacksburg, Virginia, USA

MSEC2016-8654

FABRICATING MICROCHANNELS IN ELASTOMER SUBSTRATES FOR
STRETCHABLE ELECTRONICS

Rebecca K. Kramer∗
School of Mechanical Engineering
Purdue University
West Lafayette, IN 47907
Email: rebeccakramer@purdue.edu

Michelle C. Yuen
School of Mechanical Engineering
Purdue University
West Lafayette, IN 47907
Email: yuenm@purdue.edu

ABSTRACTAs flexible devices and machines become more ubiquitous,
there is a growing need for similarly deformable electronics. Softpolymers continue to be widely used as stretchable and flexible substrates for soft electronics, and in particular, soft sensing.
These soft sensors generally consist of a highly elastic substratewith embedded microchannels filled with a conductive fluid. Deforming the substrate deforms the embedded microchannels andinduces a change in the electrical resistance through the conductive fluid. Microchannels, thus, are the foundation of flexible electronic devices and sensors. These microchannels havebeen fabricated using various methods, where the manufacturingmethod greatly impacts device functionality. In this paper, comparisons are made between the following methods of microchannel manufacturing: cast molding, 3D printing of the elastomer
substrate itself, and laser ablation. Further processing of the microchannels into flexible electronics is also presented for all threemethods. Lastly, recommended ranges of microchannel sizes andtheir associated reproducibility and accuracy measures for eachmanufacturing method are presented.

capable of maintaining their functionality throughout the rangeof the deformation. In particular, stretchable strain and pressure sensors have applications in highly conformable devices andlarge deformation systems, such as wearable devices and humanmachine interfaces [1–4]. Some of these sensors are composedof an elastomer substrate embedded with liquid metal-filled microchannels as the sensing element [5]. As the sensor deforms
via strain, curvature or surface pressure, the cross-sectional areaand length of the conductive fluid changes, thereby changing theresistance.
The goal of this paper is to identify the best method to create a desired microchannel size and geometry. The metric bywhich methods are compared will be their reproducibility—thesimilarity of microchannels produced by the same method. Additionally, the accuracy of a manufacturing method relative to thedesign geometry specified in the CAD model is presented.

2

Previous WorkAn early example of a highly deformable sensor was developed by R. J. Whitney, in which mercury was enclosed inside of a rubber tube wrapped around a human leg [6]. One
refinement of this technique embeds microchannels filled witheutectic gallium-indium alloy (eGaIn) or gallium-indium-tin alloy (Galinstan) within a stretchable silicone rubber substrate.
In contrast to Whitney’s work, the channels are patterned intobulk elastomer. Although various manufacturing techniques, described below, have been developed to form microchannels in anelastomer substrate, there has not been a rigorous study compar-

Keywords: additive manufacturing, laser ablation, stretchable
electronics, flexible electronics, microchannels
1

Introduction
Soft electronics are advantageous for highly deformable systems. Such systems require flexible materials and components∗ Address all correspondence to this author.

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FIGURE 1: Overview of the methods and treatments included in this study. Channel dimensions as specified in CAD are listed for two methods: (a)3D printed molds and (b) 3D printed microchannels. Energy levels are listed for (c) laser ablation. Prescribed channel width is specified for raster-modelaser manufacturing.

ing the performance of each of these methods, particularly at the
micro- to millimeter scales. The cross-sectional geometry of microchannels has been shown to impact the functionality of thedevice [7]. This paper will explore manufacturing methods forcreating embedded microchannels for large deformation sensors
and determine each one’s applicability to different microchannel
geometries.

have also been formed using an additive manufacturing method,where diamond-shaped cross-sections were shown to eliminate
the need for support material within the channel [23]. In orderto create flexible electronic devices, conductive fluid may be injected into the pre-formed channels.
Alternate methods of creating flexible circuits with conductive liquid embedded in elastomer focus on first patterning
the liquid, then encapsulating the trace in elastomer [24]. Researchers have encased conductive eGaIn-PDMS composite patterns inside of pure PDMS [25] and selectively wet eGaIn onto asubstrate using masked deposition [26–28]. Using lithographybased techniques, eGaIn has been patterned via imprinting [29]and microcontact printing techniques [30]. Both inkjet [31]and 3D printing [32, 33] have also been used to pattern eGaIn
on stretchable substrates. Others have combined the patterning and encapsulation steps by utilizing additive manufacturing
techniques to extrude conductive fluid traces inside of liquid prepolymer [34] or co-extrude both the conductive fluid and the prepolymer together [35]. These alternate methods depart from thepreviously described molding and etching techniques by eliminating the need to create microchannels in the substrate.

Researchers have developed many manufacturing techniques to make flexible circuits with microchannels. Techniquesthat were originally developed in the field of microfluidics [8–12]
have been extended to create stretchable and flexible circuits
and sensors composed of silicone elastomers, commonly PDMS
(poly(dimethylsiloxane)) (Dow Corning Sylgard 184) or Ecoflex
00-30 (Smooth-On). A popular technique is to pour liquid prepolymer solution into a mold containing the negative of the desired features, i.e. raised features typically with rectangularcross-sections [13–15]. Molds for casting silicone elastomers arecommonly formed using photolithography [16], e-beam lithography [17], and fused-deposition modeling [3]. Alternatively,
etching techniques remove material through reactive ion etching [13, 18, 19] or laser ablation [20, 21] of PDMS. After forming the open channels in the substrate, the channels are cappedby bonding to another polymer layer. This is typically accomplished in two ways: plasma bonding [1, 2, 13–15], and bonding
uncured polymer to the patterned polymer [3,22]. Microchannels

Given all the manufacturing methods described above, thispaper will assess the applicability of 3D printed molds, 3D
printed microchannels and laser ablation for different microchannel geometries towards the purpose of liquid metal-embedded

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polymer cured for >12 hours at 20◦ C, to ensure full crosslinking.
Each sample was then removed from the mold and cleaned with asequence of solvents: acetone, isopropanol, ethanol, and distilledwater, to remove mold-release residue. Sensors and electronics
can then be manufactured by capping these microchannels using
any of the methods described in [1–3,13–15,22], filling channels
with liquid conductor (ex: eGaIn) and inserting wires into the microchannels. Microchannels were characterized using a 3D optical surface profiler prior to capping the channels. Due to polymer
overhang obscuring the open face of the channel, samples weresliced perpendicular to the channel orientation to image the fullcross-section geometry. Each image was then processed in ImageJ to determine the cross-sectional area of the microchannel.

elastomer circuits (Fig. 1). Molds composed of photoresist patterned on silicon wafers will not be reviewed in this paper as
the processes required to fabricate precise features at the microscale have already been well-characterized [13–16]. Due to therequired chemicals and equipment, photoresist patterning is amore complex and less accessible process relative to 3D printing. In contrast, fabricating 3D printed molds, as well as direct
3D printing and laser ablating microchannels, are cheaper, moreeasily iterated, and more suitable for larger scales.

3

Manufacturing Methods
Methods of manufacturing microchannels in silicone elastomer can be divided into three primary approaches: casting
channels in a mold, directly manufacturing the microchannels by
3D printing elastomeric materials, and subtractively etching out
the microchannels. In the molding and laser ablation manufacturing methods, all samples were manufactured using Smooth-Sil
950 (Smooth-On). Smooth-Sil 950 is an emerging material for
deformable systems and has a Shore hardness of 50A, comparable to other soft robotics materials such as PDMS and Ecoflex
00-30 which have Shore hardnesses of 45A and 00-30, respectively [36]. Smooth-Sil 950 was chosen primarily for its opacity,
lending itself well to imaging using a 3D optical surface profiler(Zeta-20, Zeta Instruments). The methods explored in this study
are mapped in Fig. 1. Additionally, methods for processing microchannels into flexible electronic devices are detailed below
for each method.

3.2

Direct 3D printing of microchannels
Direct 3D printed samples were produced using an
FDM (Printrbot Simple) method extruding a thermoplastic
polyurethane filament (NinjaFlex) and a polymer inkjet method(Objet Connex 350) printing a rubbery elastomer resin (TangoBlack). The prototype strain sensors consisted of a serpentine pattern of channels embedded inside of a dogbone outline in thisstudy. For both additive manufacturing methods, multiple specimens with the same dimensions were printed (Fig. 1b). Because the microchannels are already capped, in order to examine the microchannels, the sensors were sliced perpendicular tothe channel orientation and imaged using a 3D optical profiler.
Accuracy and reproducibility values were determined from measurements of cross-sections of these sensors.
The FDM printer extruded the NinjaFlex polymer filament
to form the body without support material inside of the void microchannels. The microchannel geometry must be compatible
with the ability of an FDM printer to print unsupported features:for example, if the microchannel is too wide, filament may not
be able to bridge the gap and will collapse into the channel. In
contrast, the polymer inkjet system deposits liquid resin droplets
and UV-cures the part layer-by-layer. Since the polymer resin
is deposited as a liquid, support material for the channels wasnecessary to produce the part. The resulting part was an elastomer body composed of TangoBlack elastomer embedded withmicrochannels composed of support material. The support material is difficult to remove from the part without compromising
the TangoBlack body.
In order to complete fabrication of electronics and sensors from these microchannels, after printing, the NinjaFlex microchannels may be injected with eGaIn. Wires may be inserted
into the ends of the microchannels to make electrical connections. In contrast, the polymer inkjetted sensors contain support
material inside the microchannels and therefore cannot be filledwith eGaIn. However, future work in printing either conductive
support material or removing support material will allow sensor
manufacture similar to that of the NinjaFlex sensors.

3.1

Casting elastomer substrates in 3D printed molds
In this study, 3D printed molds were created using fused
deposition modeling (FDM) (Makerbot Replicator 2, ABS filament; Stratasys Dimension 1200, ABS filament) and polymer
inkjet 3D printing (Objet Connex 350, VeroWhitePlus resin). A
goal of this study was to determine minimum and maximum features sizes across the different manufacturing patterns. Therefore, microchannel features specified in Fig. 1a were printed in
an array. A range of sizes was examined to determine the performance of 3D printed molding as a function of microchannel
size. Channels examined in this quantitative part of the study had
an aspect ratio (AR) of 1, with the exception of a 2000µm wide,
1000µm high (AR=0.5) channel printed using the Makerbot andboth molds printed using the Stratasys. Since features with ARs
less than 1 are more stable than higher ARs, it is assumed that theresults of AR=1 channels can be used to inform low AR channel
design. Higher AR channels (AR>1) were also studied to provide qualitative evaluations of 3D printer capabilities.
Prior to casting, each mold was sprayed with mold-releaseto facilitate removal of the cured polymer. Smooth-Sil 950 prepolymer was mixed at the supplier-recommended 10:1 ratio,
poured into the mold and degassed in a vacuum chamber. The

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FIGURE 2: Fabrication of laser-ablated liquid metal embedded elastomer strain gauges with fabric end pads for interface robustness. (a) Laserpatterned elastomer sheet. (b) Tacky bonding a patterned sheet to a new sheet of elastomer. (c) Complete sensors, filled with eGaIn and with wires
inserted into ports.

solid substrate may be laser-etched. Once cured, the elastomer
sheet is etched (Fig. 2a, 3b) and the resulting patterned sheet
is then cleaned with toluene or acetone in a water bath sonicator (Bransonic 1800 Ultrasonic MH Cleaning Bath), then rinsed
with isopropanol, ethanol, and distilled water to remove soot andother debris (Fig. 3c). The cleaning step is crucial to fabricate
electronic devices, as debris will cause breakages in liquid metal
traces. Channel geometries were imaged using a 3D optical surface profiler using the surface scanning function. A minimum of
8 cross sections along the length of the channels were measured
for their area, depth and width in each image.
Sensor and electronics may be fabricated by capping thelaser-etched microchannels, as previously described. However,
due to possible debris buildup or chemical changes in the material, we have found that plasma bonding is unsuccessful nearlaser ablated features. Here, we have employed tacky bonding [37] (bonding the fully-cured patterned substrate to a partially cured unpatterned substrate) (Fig. 2b, 3e). It should be
noted that bonding often results in stretching of the polymer,
yielding a discrepancy between the actual size of the sensor andthe design that must be accounted for by adding tolerances to thedesign drawings. Finally, the sensor may be cut out (Fig. 3f), thechannels filled with liquid conductor (Fig. 3g), and the wires inserted into the microchannel terminals to interface with external
hardware (Fig. 3h).

FIGURE 3: Fabrication of a liquid metal embedded elastomer strain
gauge using laser manufacturing. (a) Rod-coat a sheet of elastomer. (b)Laser-etch microchannels into substrate. (c) Clean patterned substrate
in a sonicator. (d) Rod-coat a 2nd sheet of elastomer. (e) Tacky bond thepatterned sheet to the new sheet of elastomer. (f) Laser cut the outlineof the sensor. (g) Filling microchannels with eGaIn using a syringe. (h)Insert and seal wires into sensor.

3.3

Subtractive manufacturing using laser ablation
In contrast to molding microchannel features into elastomer
substrates, we have also etched the features using a laser ablation
method (30W CO2 laser; Universal Laser Systems VLS 2.30) in
both raster and vector mode. The depth of features is definedby the amount of energy deposited into the substrate. Multiple
energy levels were tested to examine the effect on microchannel
size.
Prior to laser etching, elastomer substrates were preparedand cast using a rod coating technique in which uncured polymer is scraped across PET (polyethylene terephthalate) film using a threaded rod to control the thickness of the resulting substrate. Although we used rod-coating to form the substrate, any

4Results and Discussion
The performance metric by which the effectiveness of amanufacturing technique is measured is its reproducibility—howmuch variation there is within a treatment level of a specificmethod (Fig. 4). The amount of variation was measured across aminimum of 12 replicates of the same manufacturing technique.
As the amount of variability across replicates increases, the measure of reproducibility of a manufacturing method decreases. For
this study, a coefficient of variation of 10% is the maximum variability beyond which a manufacturing method is no longer ap-

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Manufacturing method

Recommended range (µm2 )Expected error

Expected variation

Laser Vector Single Pass

100 - 100,000

n/a10.44%

Laser Vector Multi Pass

50,000 - 200,000

n/a

3.73%

Direct 3D Printing (Objet)

100,000 - 500,000

29.54%

6.77%

Casting in 3D Printed Molds>100,000

31.10%

3.40%

TABLE 1: Recommended manufacturing methods based on desired microchannel cross-sectional areas. Lower expected error and expected variationrefer to higher measures of accuracy and reproducibility, respectively. Laser vectored microchannels have triangular cross-sections; 3D printed and castmicrochannels have rectangular cross-sections with AR≤1. The expected error for laser vectored channels is not an applicable value because channel
dimensions are not directly prescribed prior to fabrication using laser ablation methods.

FIGURE 5: Accuracy of manufacturing methods indicated as percent
error of experimental values of microchannel width compared to nominal dimensions specified in CAD models. Error bars indicate a 95%
confidence interval. 0% error is indicative of a perfectly accurate manufacturing method. A positive percent error indicates a measured arealarger than nominal dimensions, and vice versa for negative percent error. This plot contains data relevant to samples made from both 3D
printed molds and additively manufactured microchannels.

FIGURE 4: Reproducibility of microchannel size is represented as variation in cross-sectional area of multiple microchannel sizes for different
manufacturing methods. A smaller variation indicates a higher degree of
reproducibility. For reference, the dashed line indicates 10% variation,a threshold at which a manufacturing method may no longer be suitable
for the desired cross-sectional area. A boxed inset has been inserted toclarify the position of overlapping points.

cedure.
In addition to reproducibility, measures of accuracy—howclosely the resulting microchannel conforms to the specified dimensions, are reported for the 3D printed molding and additive
manufacturing techniques (Fig. 5). The width of the error bars
in this plot are analogous to the coefficient of variation in Fig. 4.
At smaller feature sizes, slight variations in printer operation willmore severely decrease the accuracy of the part. These channel
sizes are near the limit of printability due to the fixed size of thenozzle or spot size and the precision of its positioning.
Setting the maximum variability permissible to be 10%, asshown in Fig. 4, the appropriate manufacturing methods can be

propriate for the desired microchannel size. From Fig. 4 it isapparent that, in general, laser ablation is capable of repeatedly
producing smaller microchannels, whereas 3D printed molding
and additive manufacturing are not. In the instance of a particularly high variation value in channels created by a single-passvectored laser-etched channel, there is a significant range bothabove and below this channel size in which the variation is below the 10% threshold. The recommended range for single-passvectored laser etch thus does not reflect this singular point. Thisoutlier is most likely due to inhomogeneity in the polymer or a
failure to ensure flatness of the substrate prior to the etching pro-5

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FIGURE 7: Images of the cross-section of microchannels created using(a) NinjaFlex printed in a Printrbot, and (b) TangoPlus printed with an
Objet Connex 350. The overlaid box indicates the nominal 500x500µm
channel drawn in CAD.

FIGURE 6: Microchannel cross-sections in which the actual channel
deviates significantly from the original CAD design due to drawbacksof 3D printing manufacture. The issues demonstrated arise from (a)imprecise filament stacking, (b) filament overhang, and (c) polymer
resin spreading. These issues result in molded microchannels that deviate heavily from the the red box overlaid onto the cross-section, indicating the CAD specification for the cross-sectional area. (a) Box:
400x800µm. Printer: Makerbot Replicator 2. (b) Box: 200x200µm.
Printer: Makerbot Replicator 2. (c) Box: 200x200µm. Printer: Objet
Connex 350.

accuracy when comparing the nominal area of the microchannel
as specified in a CAD design to the area of the resulting molded
microchannel, even at AR=1. At smaller microchannel geometries, the percent errors can range to nearly 200% (Fig. 5). Moreover, there is a hard limit on the smallest printable trace for each
3D printer. For example, Makerbot Replicator 2 printers areincapable of printing microchannels with a CAD dimension of
50x50µm. The smallest microchannels attempted were printed
with an Objet Connex 350 as it is capable of printing traces ofheight 30µm and with a precision of ±5µm, as specified by the
manufacturer. Larger features (≥ 100µm) were printed using a
Makerbot Replicator 2, which has a rated 100µm layer resolution
and an x-y precision of 11µm, also specified by the manufacturer.
While the percent error may be quite large for some channel sizes, 3D printing may still be a viable option as long as theamount of variation is within design thresholds. A designer may
account for the known level of inaccuracy expected for a certain
3D printer printing a specific channel size. For both the Objet
and Makerbot molds, as the feature size is increased, there is aclear decrease in both percent error and variability, as evidencedby smaller confidence intervals around each point (Fig. 5) anddecreasing coefficient of variation (Fig. 4).

identified for a given range and are listed in Table 1. The expected error, shown in Fig. 5, of a manufacturing method (Table1) should be factored into the design. If a method is highly reproducible, the level of inaccuracy will be consistent for every
sample produced.
4.1

Casting elastomer substrates in 3D printed molds
As seen in the cross-sectional images (Fig. 6a, b), microchannel features created using the FDM printer suffer fromtwo key deficiencies: void volume due to filament overhang andpoor filament stacking/alignment. Both of these problems result in channels that deviate from the ideal rectangular crosssection. High aspect ratio features are difficult to accomplishusing 3D printed molds due to poor alignment capabilities of
FDM (Fig. 6a). Similar results occurred on AR>1 parts printed
with the Stratasys printer, contributing to a higher variability on
AR>1 parts when compared to AR<1 parts. Furthermore, thevoid space between the widest part of the channel filament andthe bottom surface of the mold creates thin protrusions in the
cast polymer that may cause complications such as clots or collapse of the channel when bonding to a sealing sheet of elastomer(Fig. 6b). In contrast, microchannel features in polymer inkjetted molds present the opposite of overhang: spreading of resin(Fig. 6c). Though this results in a smooth casting of elastomer,
smaller channel features may be lost due to the resin spreading
across the surface of the part before it is solidified by exposure
to the UV light.
As a result of these limitations, there is often significant in-

4.2

Direct 3D printing of microchannels
The NinjaFlex and ObjetFlex sensors displayed −28.47%
and 29.54% deviations from the intended geometry (Fig. 5).
Since the NinjaFlex filament collapsed into the void microchannels, the measured cross-section was smaller than the nominal
dimensions (Fig. 7a). Conversely, due to resin spread of the
support material, the microchannels printed with the Objet werelarger than the nominal dimensions (Fig. 7b). In terms of reproducibility, the ObjetFlex sensors had a much lower variability inmicrochannel geometry, due to the presence of support material(Fig. 4). This is expected because the NinjaFlex sensors are being printed without support material, hence, it is reasonable to6

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FIGURE 9: Cross-sections of a) rastered, and b) vectored channels thathave been capped with a second layer. The laser settings for both channels are 25% power and 50% speed. Scale bar is 100µm.

jecting the material to multiple passes of the laser. However,issues arise when soot and debris from previous cuts occlude thepath of the laser, rendering subsequent passes less effective atremoving material. Scaling the amount of ablation by the number of passes is inaccurate due to reduced energy transfer for
subsequent passes. Additionally, since the soot accumulation is
non-uniformly distributed across the surface due to its particulate nature, the resulting etch has a much rougher surface anda less uniform cross-section. Theoretically, the soot could becleaned out of the channels in between multiple passes, however,realignment with previous cuts will add error into the process.
Therefore, ideally, subtractive manufacturing of microchannels
requires a single pass across the substrate.
In addition to vectoring, the laser also operates in a rastering mode (Fig. 9). Vectoring is used for single-pass lines to beetched partially or cut fully through the material; rastering is used
for large area patterning. In raster mode, the area to be etched isdefined, however, the depth remains a function of the laser’s operating parameters and the material properties. Rastering may be
used to create channels wider than those produced by vectoring,
however, the channel surface may be rougher and less uniform
and the time to produce a channel is much longer. The accuracyof a raster cut can be determined by comparing the actual widthof a channel to the design width. To test the accuracy of a rastercut, a rastered channel was measured using the optical profiler.
The specified channel width was 508µm. The 95% confidence
interval of the actual width was 540.644±17.599µm, with an average percent error of 6.42% and a coefficient of variation of
3.26%.
The vectoring results presented in Fig. 8 can be translated tothe expected size of the rastered channel. The expected rasteredchannel cross-sectional area (Ar ) can be calculated from a vectored area (Av ) for the same laser energy level:

FIGURE 8: Cross-sectional areas of single-pass, laser-etch vectored
channels. Error bars indicate 95% confidence interval for the area. The
dotted line indicates the linear relationship between the amount of energy deposited into the material and the resulting cross-sectional area.

assume that some of the extruded filament will sink into the void
as it is printed, as shown in Fig. 7a. As a result, the size of the microchannels produced by printing NinjaFlex varies greatly fromsensor to sensor.
4.3

Subtractive manufacturing using laser ablation
The geometry of microchannels created using laser ablation
are dependent on the amount of energy deposited by the laser into
the material. For example, the power density output of our 30W
laser is calculated as %Power ∗ 30W /in. Due to multiple pulses
hitting the same spot on the substrate, the energy entering thesubstrate per unit length is calculated as %Power%Speed ∗ 30W /in. Whilethese equations are specific to the VLS 2.30 laser system usedin this paper, other laser cutting systems have similar means ofcontrolling energy input into the material. Fig. 8 illustrates thelinearity of the relationship between the energy deposited andthe resulting cross-sectional area. As energy levels increase, theconfidence interval around the expected cross-sectional area isgenerally larger due to increased soot deposition on the material,
compromising the effectiveness of the laser. Variations can arise
from non-uniform heat diffusion within the material due to nonhomogeneous compositions or varying substrate thicknesses.
The cross-section of a typical vectored microchannel is triangular, as seen in Fig. 9b. As such, high aspect ratio rectangular cross-section channels are difficult to accomplish using thelaser. Attempts to create high aspect ratio features involve sub-Ar = Av ∗w ∗ PPI + 1,
2

where w is the channel width specified in the vector graphic illustration and PPI is the pulses per inch fired by the laser. This

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equation assumes half the width of one pulse overlaps with halfof the adjacent pulses. For example, in Fig. 9, the rastered channel has an average area of 82879.09µm2 ; the vectored area has
an average area of 7933.32µm2 . The width of the channel wasprescribed to be 508µm or 0.02in. Substituting these values into
the above equation, the theoretical Ar is 83299.98µm2 , which is a
0.5% error compared to the actual area of 82879.09µm2 . Therefore, once the area of a channel from a single vectored pass of thelaser is known, the approximate area of a rastered channel can be
determined.

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using a combination of wet and dry etching”. Journal of Microme-5

Conclusion
In this paper, methods of patterning microchannels into silicone elastomers for highly deformable sensors were compared
to determine which manufacturing technique is most appropriate for a given cross-sectional area. Studies were performed forthree manufacturing techniques: casting microchannels in 3D
printed molds, laser ablation of microchannels, and 3D printing
the substrate with embedded void microchannels. Both the reproducibility and accuracy of these techniques were determined.
Using these values as metrics for the compatibility for various
channel geometries, recommended manufacturing techniques areprescribed for ranges of channel geometry sizes. By employing
more compatible manufacturing techniques, fabrication of liquid
metal-embedded elastomer sensing and electrical devices may betuned for increased yield and increased reliability.

6

Acknowledgments

The authors would like to thank Dr. J. William Boley, R. Adam
Bilodeau, Edward White, and Jennifer Case for their input and sensor
manufacturing insights. The authors would also like to thank Trevor
Lear for assistance with microchannel measurements. Lastly, the authors would like to thank Prof. Thomas Siegmund and Ying Long Chenfor their assistance with the Objet 3D printer. This work was supported
by an Early Career Faculty grant NNX14A052G from NASA’s SpaceTechnology Research Grants Program. MCY is supported by the National Science Foundation Graduate Research Fellowship (Grant DGE1333468). Any opinion, findings, and conclusions or recommendations
expressed in this material are those of the authors and do not necessarilyreflect the views of the National Aeronautics and Space Administrationor the National Science Foundation.

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