Most medical devices evolve quietly over decades. Surgical tools get sharper, imaging machines get faster, drug delivery systems get smarter. But the orthopedic cast has remained stubbornly unchanged for most of its existence. Plaster, fiberglass, a messy application process, and six to eight weeks of itching, sweating, and avoiding puddles. For something that millions of people wear every year, it has always felt like a design problem nobody wanted to solve.
Castomize, a startup out of Singapore, decided to solve it. Their cast, TessaCast, uses what the company calls 4D printing. The terminology is worth pausing on, because it’s easy to assume it’s just marketing language. It isn’t. The fourth dimension here is time. The cast is 3D printed in advance from smart thermoplastic materials, but the real transformation happens at the clinic, when heat is applied. Once warmed, the rigid lattice shell becomes pliable. A clinician wraps it around the patient’s wrist, forearm, elbow, or ankle, clips it into position, and lets it cool. As it hardens, it conforms to the exact shape of that particular limb.
Designer: Castomize
No 3D scan. No casting tape. No plaster dust. The removal process is just as elegant. A simple pin releases the buckles, and the cast slides off. No cast saw, which anyone who has had one used near their skin can tell you is not a small thing. The anxiety of that vibrating blade hovering millimeters from your arm is its own minor trauma, even when you know it won’t cut skin.
Castomize’s design brief reads almost deceptively simple: a cast should hold the body securely while allowing skin to breathe, water to pass through, and clinicians to make adjustments without destroying the device. That sounds obvious when you read it out loud. And yet, until now, no cast on the market had actually delivered on all three at once.
The open lattice structure of TessaCast allows air to circulate continuously against the skin, addressing the itching and sweating that make the traditional cast experience so miserable for patients. It is also fully waterproof. Not water-resistant, waterproof. The team at Castomize notes that it can even be worn while swimming, though they sensibly leave specific medical guidance to clinicians. For anyone who has wrapped a limb in a plastic bag before a shower for weeks on end, this is not a minor feature.
One detail I keep returning to is how this design manages to skip the expensive, time-consuming step of individual 3D scanning. Competitors in the printed cast space often require a custom scan per patient, which raises both cost and complexity. Castomize uses pre-made standard sizes for adults and children that become personalized through the heating and molding process. It’s a smarter workflow, one that clinics can adopt without rebuilding their entire process from scratch.
The startup originated as a student project at the Singapore University of Technology and Design in 2017, which makes its trajectory fairly remarkable. Eleora Teo, Abel Teo, and Johannes Sunarko launched it as a proper company in 2022, and TessaCast reached the market in 2025. It currently holds regulatory approval in Singapore, Australia, South Korea, and Taiwan, with FDA and CE mark applications in progress.
The cost picture is nuanced. TessaCast costs about 30 to 50 percent more to manufacture than a traditional fiberglass cast. But one hospital trial in Singapore recorded average savings of 25 percent overall, because the cast can be reheated and adjusted as the patient heals rather than replaced. Fewer return visits, less material waste, and fewer complications from casts applied too tightly or too loosely all contribute.
The traditional casting process involves ten separate steps and multiple materials, and errors during application can lead to pressure injuries. That’s a significant design failure dressed up as standard practice for a very long time. Castomize has looked at all of it and built something better. The orthopedic cast has been waiting for this moment for a very long time.
The post A 4D-Printed Cast You Can Actually Shower In first appeared on Yanko Design.
