The desire to accelerate and streamline manufacturing processes often drives innovation, including in the medical device industry. Acting on this desire, researchers at the University of Delaware Center for Composite Materials (Newark), supported by a grant from the Defense Advanced Research Projects Agency, is developing a rapid prototyping process to print ankle-foot orthoses for wounded soldiers.

Headed by Professor Jack Gillespie, Dr. Shridhar Yarlagadda, and Professor Steven Stanhope, the team starts with a prescription provided by a doctor that consists of functional requirements for rehabilitating the patient, such as stiffness tuning. This prescription, Gillespie explains, also consists of customized geometry for achieving fit and comfort.

Using CAD/CAE/CAM software to link a prescription to customized patient geometry, the team then produces finite-element models to optimize the orthotic geometry and select the composite material to tune the stiffness of the device. "In this step, we ensure that the orthotic device exhibits the required minimum weight and thickness, using the anisotropic properties of composites to tune the stiffness and load paths to meet the patient's rehabilitation needs, while ensuring long-term durability in terms of strength and stiffness retention," Gillespie remarks.

The researchers use the design environment to conduct trade studies in which different composite materials and composite processing methods are evaluated, enabling them to determine the best approach for fabricating the device. The team expects to use carbon-fiber composites in tow, tape, or fabric forms because they are some of the lightest, stiffest, and strongest materials available. These materials, Gillespie notes, can have properties 40 times greater than those of current bulk polymers. The researchers estimate that the use of carbon-fiber composite will significantly reduce the wall thickness of the orthosis while improving fit and functionality. However, they also expect that the best solution for each patient may lead to different choices of materials and processes.

"The manufacturing process we are considering includes using robot-based tow and fiber-placement processes in which the unidirectional material is placed in a prescribed pattern for stiffness-tuning the ankle-foot orthosis," Gillespie says. "The carbon-fiber material can be impregnated with either thermosetting resin that can be heat or UV cured or with thermoplastic matrices that can be rapidly heated, softened, and welded into the prescribed pattern."

In producing foot-ankle orthoses and conducting clinical trials to be carried out through the university's Bridging Advanced Development for Exceptional Rehabilitation consortium, the team hopes to demonstrate the feasibility of their prototyping technology. Because the orthosis is tunable and its springlike action mimics the motion of the ankle, the technology meets wounded soldiers' changing needs. However, the prototyping methodology, together with the CAD/CAE/CAM-driven hardware on which it relies, will be applicable to the fabrication of many other medical devices, according to Gillespie.