Advanced materials for wearable medical devices

The demand for medical devices that attach to a patient’s body is on the rise. Such devices provide 24/7 monitoring, can send alerts to physicians, and even dispense precise doses of medicine. Momentive Performance Materials, Albany, N.Y., has developed a class of fiber-reinforced liquid silicone rubber (LSR) for designers seeking to enhance the ergonomics and aesthetics of wearable medical devices.

Momentive’s developments build on two proven materials technologies. Silicone elastomers are well accepted in the healthcare industry. They meet biocompatibility standards and have advantageous properties like purity, clarity, strength, and chemical compatibility, as well as relatively easy processing. Further, they’re stable over a wide temperature range, making them suitable in applications requiring repeated sterilization. As a result, they’re used in a broad range of medical devices, including medical tubing, surgical devices, and catheters, to name a few. 

And composite parts made of fiber-reinforced elastomers have been around for decades. Adding fibers made of various materials can enhance a part’s performance, increasing strength, impact resistance and toughness, to name a few. 

The trouble has been getting fibers to bond to silicone - a notoriously "slippery" material. Momentive’s breakthrough is finding the right type of fibers, and the right silicone formulation, that permits good dispersion and bonding of the two. The company's line of fiber-reinforced LSRs reportedly process similarly to traditional LSRs with respect to flowability and cure speed, but incorporating textile fibers that chemically bond to the silicone substrate increases the modulus. The process ensures a heterogeneous fiber distribution in the low viscosity LSR, permitting the development of complex reinforced parts with homogeneous material properties.

The materials are suited for industrial products like hoses that must withstand high pressure, and the reinforcement can lead to significant weight reductions versus unreinforced parts.

The materials are also well suited for wearable medical devices. Combining silicone elastomer flexibility with the high strength of textile fibers, MPM’s fiber-reinforced LSR can be a good option when elastomeric properties have to be combined with a high modulus at low elongations. The materials may be especially useful in applications where high torsional stiffness is required, such as in devices with a wrist band.  The inherent properties of silicone elastomers can provide good wearability, comfort against the skin, and resistance to skin oils.  In addition, such devices can be manufactured in a variety of colors.

This advancement can also potentially serve as a “mono-material,” providing the design freedom and cost-efficient processability of liquid silicone rubber while eliminating the need for a composite fabric layer.  As such, fiber-reinforced LSR may be a candidate for applications such as membranes, flexible robotic “skeletons” that mimic the human body, and numerous biomechanical applications.

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