1. Polymer sheet materials that have a balance of stiffness and flexibility
Copoly (copolymer polypropylene) and modified polyethylene are the plastic sheet materials that have traditionally been used for TLSOs, night splints and pediatric AFOs, SMOs and wrist braces. However, copoly is four times as stiff as modified polyethylene (MPE). This leaves a wide gap for applications where copoly may be too stiff and modified polyethylene may be too flexible for optimal device performance and patient comfort. New polyolefin-based sheet materials are formulated with stiffness in between these two extremes, allowing practitioners to create orthotics and prosthetics that have just the right balance of stiffness and flexibility.
2. Low-friction, silicone-free EVAs with improved performance and outstanding fabrication characteristics
EVA (ethylene vinyl acetate) sheet materials are the industry standard for flexible inner liners in carbon fiber definitive sockets. EVA has the advantage of being a rubbery elastomer, which helps the socket to absorb energy and also reduces the degree to which the hard edges of the carbon fiber composite press against a patient.
It is important to note that EVAs have somewhat high-friction surfaces, which can hinder a patient donning or doffing a prosthesis. The industry has traditionally addressed this issue with the use of silicone lubricants in the EVA formulation to reduce friction against a patient’s skin. However, silicone also reduces the melt strength of EVA sheet, making it difficult to thermoform, and silicone impedes the ability of the plastic sheet to be seamed.
Additionally, silicone-impregnated EVA sheet stains more easily and silicone plasticizes (softens) EVA, which can result in the liner extruding (cold flowing) out of the socket over time. This reduces the fit of the prosthesis, makes it less comfortable for the patient, and causes the liner to have to be replaced sooner.
New EVA formulations have non-silicone lubricants that create low-friction surfaces, while still maintaining EVA’s excellent forming and seaming characteristics. The new formulations also have outstanding cold-flow resistance, which helps the liner to maintain its shape over time.
Rigid polyurethane foam molds are a modern alternative to plaster for forming plastic sheet into custom orthotics and prosthetics. However, unlike plaster, which cools hot plastic very rapidly, foam molds cool plastic slowly, which can result in stockinettes adhering to the molds during fabrication. Silicone mold release can help to alleviate this issue, but some practitioners prefer not to introduce liquid silicones or aerosol silicone sprays into their labs or devices.
4. Carbon fiber-reinforced thermoplastics for orthoses and prosthetic definitive sockets with enhanced stiffness
For many years, carbon fiber has been combined with liquid polymer resins to make composite definitive sockets. Carbon fiber technology is now being used to enhance the stiffness of polypro sheet. These new thermoplastic composite materials consist of polypro sheet laminated with layers of non-woven carbon fiber, creating a sheet that is 25 percent stiffer than standard polypro. This allows practitioners to make lighter, stiffer orthoses and prosthetic definitive sockets. Lower extremity orthosis made using this material often comply with Medicare code L–2755.
5. Transfer papers that create brighter, more visually appealing graphics on orthotics and prosthetics
Practitioners always strive to craft orthotics with the best possible appearance, especially for devices that are intended for children, where aesthetics can play an important role in the patient’s satisfaction and adoption. New transfer papers made from innovative materials printed with eye-catching patterns are now available for practitioners seeking to create devices that are both functional and pleasing to the eye.
Keith Hechtel, DBA, is the Senior Director of Business Development, and Jeff Wilson is the Senior Business Development Manager–Orthotics, Prosthetics, & Podiatry, Curbell Plastics.
