Materials and Coatings

Materials

From the crude fabrications of the earliest surgical instruments to the highly sophisticated devices of today, materials are the fundamental component of a medical device. Modern devices are usually composed of a metal, plastic, alloy, or various combinations thereof. Improvements in technology have created lighter, stronger materials as well as "shape-memory" alloys such as nitinol, resulting in major innovations in device design and functionality.

Biomaterials, a relatively new class of materials, are natural or synthetic substances used to treat, augment or replace a tissue, organ, or function of the body. Biomaterials encompass a broad range of functions including tissue engineering, controlled-release drug delivery, and bioadhesives.

Examples of biomaterials include sodium hyaluronate, a naturally occurring biopolymer used to reduce the incidence of postsurgical adhesions; polymer-based materials for controlled-drug release and tissue engineered scaffolds to grow synthetic livers, skin, and cartilage; and collagen-based biomaterials for sutures, wound dressings, and a range of prosthetic devices. Bioadhesives, also known as surgical glues and sealants, are widely used for wound closure, cartilage repair, and bonding of cartilage, tendon, and bone.

Biomaterials research is a key driving force in the medical device arena, and a significant body of literature has developed around both current and potential uses.

Coatings

Despite the sophistication of today's medical devices, the materials used often result in undesirable complications, including bacterial infections, blood clots, tissue trauma due to device insertion, and friction and wear of implants. This is especially true for such devices as catheters, guidewires, stents, probes, and prosthetic implants.

Surface treatments help eliminate or reduce the risk of such problems without altering the device's essential material properties. For example, hydromer coatings are covalently bonded to the device. When wet, the hydromer creates a slippery surface, reducing trauma, and improving ease of insertion.

Some coatings reduce the tendency of platelets, proteins, and encrustation to adhere to a surface, reducing the likelihood of infection. Ions embedded into the material make it less susceptible to friction, thus reducing wear debris on implants. Radio-opaque coatings make cathethers and other devices visible under fluoroscopy. Insulating coatings protect the patient from electrical currents generated by some energy-based devices.

As medical devices continue to improve and change, the materials and processes used must similarly be modified. Predicting and managing the interaction between these materials and the body makes the surface engineer a key player in the device design process.

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