Cast21 Helps Mend Broken Bones Sans the Itch and Smell

02.09.24 | By
Cast21 Helps Mend Broken Bones Sans the Itch and Smell

If you’ve ever broken an arm, you probably would like to forget the weeks of incessant discomfort and funky smells associated with wearing a traditional cast. Unwieldy, itchy, and impossible to shower with it on, the cast seems like a crude remnant of another era. In a case of design (and technology) coming to the rescue, biomedical design engineer Ashley Moy co-developed Cast21 to cast off the layers of discomfort experienced while mending a broken arm, wrist, or hand.

Doctor inspected a teal Cast21 orthopedic sleeve on patient's arm.

Cast21’s open lattice design is based upon a mathematically-formed structure offering resilient protection with comfortable breathability and improved mobility.

In lieu of wrapping the entire forearm in a messy melange of plaster or fiberglass, medical practitioners simply slide a sleeve of silicone tubes across the patient’s arm, fill it with a fast hardening resin, and in mere minutes a breathable, yet rigid waterproof layer of protection is set in place.

Three step-by-step photos of the application of the Cast21 orthopedic sleeve onto a patient's arm.

Cast21’s white paper goes into high level detail about the structure’s exceptional resilience and durability when compared to a fiberglass cast. Its maximal displacement measures an impressive 1000 N (newtons) of force – roughly the equivalent of withstanding being hit by a 224-pound falling object!

Yellow Cast21 orthopedic sleeve on patient's arm with get well signatures across it.

Arguably the only good thing about wearing a cast is asking friends and family to sign it. Fortunately, Cast21’s lattice design still allows those near and dear to write their “get well” wishes across its surface.

When healing is complete, the Cast21 can be removed without the necessity of that scary circular saw typically used to cut off wrapped fiberglass casts.

Five different colors options of the Cast21 orthopedic sleeve on five different outstretched arms.

Cast21 also softens the necessity of wearing an orthopedic accessory all day by allowing color customization, including solids, marbled patterns, and gradients.

Cast21 isn’t a new development. Moy co-developed the earliest iteration of the concept in 2015 as a college senior at the University of Illinois alongside fellow Fighting Illini, Jason Troutner, and with the aid of Justin Brooks. Funded with seed capital in 2017, the team would go onto improve the lattice design orthopedic to eventually launch it as the Osteon Defender before renaming it the Cast21.

Woman tying back her hair wearing pink and white Cast21 orthopedic sleeve on her arm while outdoors.

A peek over on TikTok showcases how the open air design permits a degree of freedom and mobility limited while wearing traditional wrapped casts.

Woman outdoors with light blue Cast21 orthopedic sleeve covered arm looking out to her right in the distance.

Woman outdoors with light blue Cast21 orthopedic sleeve covered arm bending down to tie her shoes.

Today, Cast21’s waterproof mesh technology has become an established option to similarly shaped, but pricier custom 3D-printed casts replacing traditional orthopedic ones.

Hopefully a broken bone is not in your future, but those curious about Cast21’s innovative design can request samples via the company’s request page.

Gregory Han is a Senior Editor at Design Milk. A Los Angeles native with a profound love and curiosity for design, hiking, tide pools, and road trips, a selection of his adventures and musings can be found at