Step 3: Mold Top and Bottom Layers

The next step is to fill in the center of the sensor with a softer elastomer to connect the two stiff ends that were just made. The top half of the sensor will also be made (this half is entirely made of the softer elastomer).
Have the top mold ready, alongside bottom mold with stiff pieces in it.
Mix a small amount of Ecoflex 0030 in a cup and prepare to pour (need ~20 g).
Refer to the Bill of Materials section for vendor information for EcoFlex.

Pour EcoFlex and Degas
	Carefully pour the Ecoflex that was just mixed onto both the top and bottom molds. Don't worry if there is excess Ecoflex in the mold.
	Degas like what was just done in the previous step to remove bubbles.

Add Transparency
Line one end of the transparency film up with the pegs and slowly lower it from one end to the other, making sure not to trap any bubbles under the film.


	Once the transparency reaches the other end, let go of the transparency and use tweezers to gently align it with the second set of pegs. At the same time, make sure to push any remaining air gaps/bubbles out of the end. Note: There is a transparency for both the top and bottom mold and they both need to be placed down at this time.

Cover Mold

Now cover the molds with their respective top plate. For the top mold (shown above on the left) this will be the acrylic plate. For the bottom mold (shown above on the right) this will be the reverse side of the plate used in Step 2. Place both molds in the 60 ^oC oven and add weights on top. Let cure for 10 minutes before removing from oven.

Demolding
	Take the acrylic and transparency off the top mold and peel away any excess material around the edges and the alignment pegs.
	For the bottom mold, remove the rigid top but keep the transparency on for now. This will be removed at the last minute before bonding to keep the surface as clean as possible. Make sure to peel off excess material around the alignment pegs however.

Bibliography

Mengüç et al. (2013) Soft Wearable Motion Sensing Suit for Lower Limb Biomechanics Measurements.

Mengüç et al. (To appear in 2014) Wearable Soft Sensing Suit for Human Gait Measurement.

Miserez et al. (2008) The Transition from Stiff to Compliant Materials in Squid Beaks.

Muth et al. (2014) Embedded 3D Printing of Strain Sensors within Highly Stretchable Elastomers.

Vogt, D. M., Park, Y. L., & Wood, R. J. (2013). Design and Characterization of a Soft Multi-Axis Force Sensor Using Embedded Microfluidic Channels.

Contributors

Yiğit Mengüç