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A Polyurethane, Thermoplastic Toroidal Cast to Treat Carpus, Radial and Ulnar Shaft Fractures

George M. Whitesides Laboratory Harvard University

Research and Development Engineer

 

Abstract

Plaster and fiberglass casts rely heavily on a multi-step, time-consuming fabrication process causing patient discomfort post-application. This senior design project involves the design, fabrication, and testing of a self-hardening toroidal thermoplastic elastomeric skin (containing a two-component polyurethane liquid foam, to be mixed and applied directly onto the injured limb) to treat carpus, radial and ulnar shaft fractures.

 
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About 6.8 million people receive medical attention each year in the U.S. Fractures are among the most common orthopedic problems. The most common fracture under the age of 75 is the WRIST FRACTURE.

Patel, Amar A., et al. Hand, 2014.

 

Engineering the Foam-Fabric Orthopedic Arm Cast

 
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Basis for Design

The water snake wiggly, a popular children’s toy, has a versatile toroidal configuration optimal for the design and fabrication of orthopedic devices.

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Material Characterization

A thermoplastic polyurethane coated fabric’s anisotropic behavior, as observed via SEM (on the right are the images I took), provides an ideal biaxial elasticity for polymer expansion.

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Prototyping

As an elastic membrane that constrains expanding foam, the foam-knit orthopedic cast self-hardens within minutes. This simple yet robust orthopedic cast design offers the high mechanical strength and mold-ability of traditional fiberglass and plaster casts, respectively, but also ensures an ease of removal and a quick self-hardening process that contributes to overall patient discomfort.

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Product Testing

Research and development led to the testing of a successful product. The orthopedic cast applied limited pressure onto the injury during polyurethane expansion. It is exothermically safe and comfortable for the user to wear. At under 16 ounces, the cast is much more lightweight in comparison to plaster and fiberglass casts. The thermoplastic polyurethane coated fabric is water-resistant.

“after the first 24 hours, I didn’t experience any discomfort!”

-1st Human Subject (Post IRB Approval)

*More Information Available Upon Request*

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