The Travelling Pod | Part 4 | Turning bottle caps into orthotics

I have been providing podiatry service for the passing migrants since April 2023, and despite the limitations of my environment and resources, my level of service has been getting better. I am learning how to maximise the little resources that I have by using old unused thongs/flip flops and making semi-customised orthotics (using the recycled thongs method). Unable to measure its effectiveness due to the lack of feedback, I have been able to use my girlfriend’s foot pain as a ‘case study’.

What I have learned

I have been able to measure the effectiveness of the ‘recycled thongs method’ to be effective up until three months, at which point, it loses its supportive properties.

For more context, my girlfriend has always had chronic medial sesamoiditis for years, which was problematic after long walks. In March 2024 we went to Guatemala and hiked four volcanoes with the highest point of 4000 meters above sea level. Two weeks before leaving for our vacation, using the recycled thongs method, her orthotics were effective in reducing her foot pain completely using the same pair of shoes. However, after three months her pain returned with signs of planter fasciitis around the medial longitudinal arch (MLA).

The process

I have always wanted to create a customised orthotic using plastic similar to what I was doing in a private clinic in Australia. This was not without limitations, I was not able to use a scanner, computer CAD program, or 3D printer. Therefore, I was to use the old-school method of using plaster to make a positive cast and using polypropylene plastic to mold an orthotic. However, I had to make a cost-effective orthotic  within a couple of hours. That meant that I had to modify the steps of orthotic design that I had learned at university.

The challenges

The first problem to tackle was casting:  do I cast weight-bearing or non-weight-bearing? Previously in Australia, I scanned the foot holding it in a position that I thought was appropriate and non-weight bearing. Therefore, with intrinsic modifications, I did not have to externally modify much using the CAD computer program when designing the orthotics. However, the situation in Mexico was different, and to save time I decided to cast weight bearing.

Advice along the way

I got some much-needed advice from my orthotics teacher Derick at Western Sydney University about how to cast weight bearing, and he suggested using sand. Absolute genius, I had not thought of that. However, my first attempt was a massive failure because the sand in the box was uneven and influenced my cast in the sagittal plane.

Therefore, I used a flat piece of wood and surrounded the unilateral foot whilst the person held onto a chair for stability. This meant that the weight-bearing foot was under a lot of load, I dorsi-flexed the big toe to activate the windlass mechanism, then slightly supinated the rearfoot. Furthermore, once in this altered foot position, I added more sand to form this new position, then the  person removed their foot slowly. I was able to get their current shoe innersole and mold the forefoot to the exact shape for fitting purposes. Then, I added plaster to make the shape and did the same process for the other foot. Once the plaster was set, I smoothed the harsh edges with more plaster.

Trial and error

I thought finding polypropene 3mm sheets would be easy, recycling unwanted offcuts or even purchasing. Nothing was easily available so I continued the thought of recycling my own plastic to use.

Last year, I had this idea and tried to melt HDPE 2 plastic that I had collected and cut, arranged in different densities. I researched that 180 degrees was safe and appropriate to melt plastic, as demonstrated on YouTube. This was a massive disaster. After nearly an hour it had not melted so I turned the oven heat up and the plastic started to burn and release dangerous toxins. Then, when removing the glass baking tray from the oven, it exploded near my face, without any injuries. I was discouraged in recycling plastic.

A promising method

Since I could not find polypropylene plastic, I decided to return to my journey into recycling plastic but found another video that demonstrated melting plastic from bottle caps. I collected over 200 Coke plastic bottle caps for this project, bought a flat sandwich press, and heat appropriate material to melt the bottle caps. After a few failed attempts, I created an even-density rectangle shape of 4mm plastic that I transferred onto my positive cast.

The plastic was fine to work with, but needing to do everything quickly whilst it was hot, I molded the heel cup and MLA as priorities. I used my heat gun to alter the edges until I was satisfied with the shape. I used my Dremel to cut off excess plastic and shape the orthotic. Lastly, I glued a 2mm medium-density material on the posterior side, and a 5mm EVA-like material as a top cover to make a full-length orthotic.

One month after using her new orthotics, her feedback has been encouraging. She has never had anything more comfortable; she continues to wear and exercise in her custom orthotics. Also, her symptoms have significantly reduced since the first week of wearing them.

This entire process has been filmed and is captured in this Part 1 video and this Part 2 video.

A case for sustainability

This opens the conversation for sustainability in podiatry, and I have videos about this on my YouTube. Are there opportunities for an eco-friendly customised orthotic using the recycled bottle cap technique? I would be interested in hearing your thoughts.

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