Fabrication of a 40 durometer urethane partial foot By: Alex Brett, R.T.O.(c)
Materials required • Prosthetic foot shell or life cast • 40 Durometer urethane • Urethane pigment • 25 lb/cu ft. Flexible urethane foam • Replicator silicone • 5 Durometer silicone • Cast sealer • Mixing cups • Mixing sticks • 1” Disposable brushes • 1oz Felt, Nylon stockinette • Renia PUR primer • Aquaseal adhesive and leather for sole
Safety • When working with urethane foams and rubbers: always wear gloves and assure there is adequate ventilation (or use a suitable respirator). Avoid contact with skin. • If you are ever unsure of a material, consult the MSDS prior to using. • *All the products used in fabrication of this partial foot are completely safe as long as they are used properly and with care.*
Fabricating negative molds • We will start by fabricating 2 negative molds of a prosthetic foot shell or a life cast. • 1 with Renew materials silicone replicator • 1 with Renew materials 5 durometer silicone
Start by saturating a piece of felt with replicator silicone then place foot on top
Trim excess silicone, remove foot from mold, and punch a 1” hole in the mold (as shown)
Brush 5 durometer silicone over foot. Rotating it as the silicone cures is helpful.
Fabricating the socket • We will now seal the cast, pigment the urethane and brush on four layers. A nylon should be added for reinforcement on the fourth layer.
Brush layers 1-3. Rotating the cast makes getting a uniform thickness much easier.
Pull 1 nylon over cast while 3rd layer is still gooey, and brush on the 4th layer
Fabricating the forefoot • We will now scuff the surface of the socket, and fit it into the replicator mold. After that we will pour 25lb flexible foam into the mold to create a basic foot shape.
Once the foam has cured, we will demold, clean up and reduce the overall thickness of the forefoot by approximately 1 cm.
We will then brush 3 more coats over the socket and foamed forefoot to encapsulate the foam. • This foam is used so that the foot will be lightweight yet still flexible. Pure urethane can be used but this will result in a very heavy partial foot.
We will now take the 5 durometer silicone negative, pour urethane into it, and pull it over the foot to give the finished piece a high definition appearance
Once the urethane has cured, demold the foot and smooth the transition with a 180X cone.
Rotate 1 final layer of urethane (minus the toes) to seal the transition up.
It is best to post cure in the oven @ 50C for 4-6 hours. This will assure the urethane is fully cured and acheives maximum strength.
We will then buff the exterior with 320X sandpaper to take the shine off.
Your foot is now ready for a test fitting! • Urethane can be can cut and modified easily with scissors, and a 180X sanding cone.
Tips and tricks • Always fabricate partial feet 1 size under sound side. They tend to appear larger, so 1 cm under sound side is usually well received. • Aquaseal adhesive can be used to repair or glue a sole to your urethane partial foot. • Renia PUR primer works great to prep urethane surfaces that have cured fully between steps.
And there you have it!Everything you need to know to fabricate your own partial feet.