Custom Aquatic Prosthetic D4E1

The Custom Aquatic Prosthetic (CAP) is a swimming prosthetic designed for people with a below-knee amputation. Made from affordable and easily accessible materials, it can be built by anyone with basic tools and fabrication skills.

This project was originally developed for Johan, a below-knee amputee who enjoys swimming. However, our goal was to create a solution that could benefit a wider group of users, making the design adaptable for other below-knee amputees looking for a simple and accessible swimming prosthetic.

The prosthetic was developed as part of the Industrial Product Design programme at Howest Kortrijk, within the Human-Centred Design course.

The people involved in the project are:

Myrthe Van Overbeke (Vanoverbeke.myrthe@gmail.com) - Product Designer

Tijs Van de Maele (tijs.vandemaele@gmail.com) - Product Designer

Zeynep Elmas (zeynep.elmas.2003@hotmail.com) - Product Designer

Amber Washington-Mackay (awashingtonmackay@gmail.com) - Product Designer

Sara Vanmeenen (vanmeenensara@gmail.com) - Occupational Therapist

Jutta Van Den Haute (vandenhautejutta@gmail.com) - Occupational Therapist

Tools Needed:

1. Sewing needle and pins
2. Sewing machine (Optional but really helpful)
3. Box cutter
4. Heat gun
5. Ruler + measuring tape
6. Scissors
7. Drill
8. Hole punch
9. Sandpaper

Materials Required:

1. 3 waterproof caps
2. 1 PVC pipe (Ø11 cm)
3. Silicone placemat (1mm thickness)
4. Flat sturdy thin strap (width: 1.5 cm)
5. Thick flat sturdy strap (width: 4 cm) (Note: For wrapping around your leg and the g hook attachment. See step 8 for details)
6. 1 G-hook
7. 4 buttons (Ø17 mm)
8. Standard rivets
9. Thread to sew

Tips:

1. For the caps, straps, buttons and other materials, look in second hand stores. Bag straps are perfect for the nylon straps and can be cut of any bag.
2. Check if the caps can be washed, then they are waterproof.
3. For later steps, to form the PVC, we used a ducttape model of our users leg. This is not necesarry but could be helpful. You just wrap your leg in clingfilm, cover it in duct tape, carefully cut it off, and stuff the form with foam/wool/etc. Without the model, you'll need to form the PVC right on your leg, but this can be hot so wear thick pants or shield your leg with a towel.

By carefully seam ripping (cutting only the thread) along the edge of the visor with either a knife or a seam ripper, you can avoid ripping or damaging the fabric. We need the visor as base of the prothesis.

By opening the fabric of the visors, the inside plastic is visible. carefully cut and sand the outside corners to remove the sharpness.

You can reuse the inside band of the caps as a makeshift bias tape. Pin and carefully sew the 'bias tape' to the open end of the visors. Tip: using a zipper foot on the sewing machine lets you sew just next to the hard insert of the caps.

Hold both the visors on your stump with the bottom one on top of the top one to decide the needed length and amount of overlap. Mark the position and sew both caps together. The plastic is soft enough to sew trough with a sewing machine, by hand this might take a bit of time.

On the corners of the visor for the upper leg and the top visor for the lower leg, mark the location of the holes to sew (see picture). We used a button hole stitch on the sewing machine for a secure finish, but that is optional. If you are using that, you can set the size in the button hole foot with a part of the strap you will use. After sewing, use a knife to carefully cut the slits, taking extra care not to cut the thread of the button hole you just sewed.

Measure on your leg how far apart you want the visors to lay and how much strap to cut. The strap should be double the length so you can loop it trough and sew the ends together. Make sure there is at least 1cm of overlap to securely sew it closed. This part is easiest sewn by hand.

The attachment point of the silicone straps are buttons, so sew on the buttons as shown on the picture. Tip: mark all 4 holes trough the button and pre-pierce them with a pin or a thicker needle so its easier to sew trough later.

Now we're moving on to the nylon strap. Sew a band on top of the strap every 1.5 cm (depending on how big your G-hook is). Do this all along the strap making sure it can fully wrap around your leg and then hook into one of the slots.

If you leave the strap long, you can still choose the length here. Decide where you want the G-hook to attach and loop the strap trough there. Sew it on securely.

Sew the end (not the side with the G-hook but the other side) to the bottom cap. sew in a square with a cross for a secure attachment.

Now we're moving on to the silicone strap. Measure two 4.5 cm wide straps on your silicone mat. The length of the strap will depend on the circumference of your leg. Make sure when measuring the the strap length, try it with the sewn together caps to ensure that the end of the straps can reach both fastening button.

Cut out the straps and round the ends for a nicer finish.

With a hole punch ( we used a 5mm) stamp out holes roughly 2.5cm apart. The amount of holes needed will depend on the size of your leg and the needed adjustability. You can always add holes if you need a tighter fit.

As the last step of our process, we will start doing the plastic part. Print and cut out the given fin template. You can either print the A4 template across four pages and tape them together, or use the A2 template if you can print in large format.

Measure the height for the fin onto the pipe and adjust the top section to your own measurements. In the file, you can find the measurements we used for our user.

Cut the pipe to size. We used a hand saw, but you can do it with a band saw depending on your preference.

Once the pipe is cut to size, find the center points and cut the pipe long ways down the middle. We used a band saw but again, you can easily use a hand saw.

Take your two sections of pipe and slowly heat them so they can be flattened, we used a heat gun. Be careful not to burn the plastic.

Take the printed and adjusted template and lay them on your flattened pieces of PVC pipe. Now trace the template with a pen on the surface.

Now carefully cut around the traced shape. We did so by heating up the plastic again and cutting it out with a utility knife. However you can also use a band saw if you feel confident doing so. Don't forget to sand the edges.

Mark the drill holes according to the template and drill them. We used a 4mm drill bit for the fin holes (you can change this measurement according to your rivet size) and a 3mm drill bit (or any other measurement that the needle can fit through) for the top section holes.

Mark the slits on the back piece of plastic according to the template and adjust accordingly to the placement of the middle band. Cut out the slits.

1. When cutting the slits in the back we repeated the heating of the plastic and using a knife to cut it out.

Now you have to form the top section to the shape of your leg.

1. Start by heating the plastic so it becomes moldable.
2. Then you can either carefully form it on your leg or make and use and mannequined version of your leg. Be careful while forming it on your leg because it can be too hot, you can wear thick pants or use a towel in between ur leg and the hot plastic.

With everthing cut and drilled, line up the two pieces together and use your rivets and a rivet gun to fasten the fin together. (Only the fin, not the top section).

Finally place your plastic component onto the cap and use the smaller holes on the top section to sew it to the bottom two caps. To make the sewing process easier we suggest either carefully drilling a small hole or pre piercing the caps with a needle.

Hope you enjoyed making our prosthesis and have fun swimming!