An example of the successful application of wear-resistant compounds is this glucose meter. It contains internally lubricated, color-matched polycarbonate to reduce wear and motion-induced noise.
While many medical products are still produced in “off-the-shelf” plastics, medical device designers are expanding their knowledge of new thermoplastic technologies and exploring how to apply these materials in medical applications. Here’s a look at the growing palette of properties and options.OEMs are implementing authentication technologies that covertly ‘fingerprint’ products in high margin and liability markets.
AT A GLANCE
• Eight technologies defined
• Capabilities and benefits
• Real-world examples
• Application advice
Kevin Marshall is the medical market manager at RTP Co., 580 E. Front St., Winona, MN 55987. RTP Co. is a specialty compounder that offers customer-driven solutions for injection molding and extrusion. With a global network of plants, the company provides customized formulations in structural, conductive, wear-resistant, elastomeric, flame-retardant, and precolored compounds. Marshall’s experience in plastic material technologies spans 13 years with the last three years dedicated to the medical industry. He can be reached at firstname.lastname@example.org or 507-454-6900, ext 6450.
By Kevin Marshall
The rapid growth of thermoplastics in the medical market reflects the suitability of these materials to meet the demands of today’s healthcare industry. Thermoplastics can be combined with a variety of unique modifiers to yield specific properties and functional benefits. Most “new” medical thermoplastic technologies possess a successful track record in other industries, providing medical designers with a reliable palette of options. These innovative materials can reduce electrostatic buildup, add lubricity, improve ergonomics, add “gripping” surfaces, absorb X-rays, and provide authentication. Additionally, they can be engineered for a specific application by combining properties and benefits. This exclusive article provides an update on popular types of compounds and comments on their benefits for medical applications.
Conductive CompoundsWhen added into thermoplastics, electrically conductive modifiers offer permanent protection against static accumulation and electrostatic discharge (ESD). Conductive thermoplastics allow static to dissipate continuously rather than accumulate and discharge rapidly. ESD can damage sensitive electronic components and initiate explosions in flammable environments. Accumulated static charges can also halt mechanical processes by clogging the flow of materials. Conductive thermoplastics are available in a wide variety of colors and, in some cases, retain transparency. Applications include ECG sensors, pipette tips, electronics protection, and new pharmaceutical delivery systems such as inhalation devices. Inhalation devices, including pMDI spacers and dry powder inhalers, can incorporate conductive thermoplastics to facilitate accurate drug dosages for powders and aerosols. Conductive compounds stabilize the static effect so that the device has a stable environment in which to operate. Without conductive plastics, inaccurate dosages could result from either too little medicine—when micro-particles become attracted to the walls—or too much medicine—when medication builds up over time and then suddenly releases.
Wear-Resistant CompoundsWear-resistant or lubricated compounds can provide a lower coefficient of friction and reduced wear rates. For instance, a blood glucose meter can benefit from wear-resistant additives because their inherent lubricity can extend the life of the meter’s moving component—a cover, which moves back and forth to protect the display. Wear resistant compounds can also achieve critical color matches, even to dissimilar materials. Even high-volume, disposable applications benefit from lubrication technology. Examples include product designs with needles or blades that retract after use. Some of these designs incorporate lubricated materials to provide a consistent “feel” and smooth sliding operation of the safety cover. Other applications for wear-resistant compounds include catheters, bushings, gears, luers, and valves. Additional benefits include the minimizing or elimination of external lubricants, noise reduction due to smooth part motion, enhanced plastic processing, and better extrusion throughput.
Radiopaque CompoundsSpecific additives can increase the density of thermoplastics. These high-density thermoplastics can duplicate the feel of metal while retaining the processability of thermoplastics. The medical market continues to seek lead replacement alternatives for environmental reasons. Some of the same additives that increase a thermoplastic compound’s density also render radiopaque properties. Injection molded parts, tubing, or sheet made from radiopaque compounds absorb X-rays and are not transparent to radiation. During radiation therapy or surgical procedures, radiopaque sheet, which can be made drapable and flexible, can selectively protect equipment and personnel from scattered or indirect X-rays. Catheters containing barium sulfate allow its position to be monitored inside the body via fluoroscopy or X-ray imaging. Baxter Healthcare developed an annuloplasty system for heart valve repair procedures. The reusable handles and the disposable snap-on ring templates are made of polycarbonate specialty compounds. The radiopaque plugs, which allow for X-ray visibility, are insert-molded into the template. The autoclavable plugs are made from a polyethersulfone specialty compound. The entire device is steam autoclavable.
Thermoplastic Elastomer CompoundsCustomizable for color, softness, conductivity, lubricity, and other attributes, thermoplastic elastomers allow designers to create unique rubber-like parts. Two-shot overmolding can add an ergonomic, slip-resistant “gripping” surface to medical devices such as surgical tools. This process consists of two molding operations where the first material provides the rigidity while the overmolded elastomer gives the finished product a softer feel. Elastomers can also be overmolded onto non-plastics or co-extruded. Thermoplastic elastomer compounds can be used instead of latex, silicone, and PVC. They are compatible with steam autoclaving, gamma radiation, and EtO sterilization. Applications include tubing, catheters, grips, seals, vial closures, connectors, and drug delivery patches.
Precolored CompoundsColor technologies have evolved in recent years. For medical applications, designers can select from FDA-compliant pigments plus non-migratory pigments. Unique color and effect technologies can offer product differentiation benefits for medical device designers. As devices move from hospitals and clinics into the consumer and home markets, consumer-friendly colors and glow-in-the-dark technologies offer a perceived value that is much higher than their cost. Additionally, elastomers can be used to enhance perceived value via their “soft-touch” feel. Appropriate color selection may also improve patient medication compliance since devices that look trendy can be used in public without a negative stigma.
Authentication CompoundsDriven by counterfeiting, outsourced manufacturing, better traceability, and rising warranty and liability costs, OEMs are implementing authentication technologies that covertly “fingerprint” products in high margin and liability markets. The addition of microscopic taggant particles to thermoplastic compounds provides a means of identification and authentication. Taggants are multi-colored, multi-layered, highly cross-linked polymeric particles where the color sequence represents a unique code to which meaning is assigned such as identifying an OEM’s product, manufacturing location, or end-customer. For example, a pharmaceutical company can use this technology to ensure specific thermoplastic compounds are being used by the molder. Optical pigments and dyes can be used to convert short wavelength radiation and re-emit it at longer wavelengths. This facilitates discreetly differentiating between two products, which may appear the same under standard lighting conditions but have different colors under specific light wavelengths.
Laser-Markable CompoundsLaser marking involves the use of a laser beam to create a permanent graphic by permeating a thermoplastic part’s surface. Unlike hot stamping or pad printing, the contrasting mark becomes integral to the part, making it more durable and less affected by solvents. Unlike direct contact methods, laser graphics can be applied to complex or inaccessible geometries. One example is a reusable insulin pen, which has dark gray dosage numbers laser marked into a white cylindrical surface. Laser marking also can permanently apply manufacturing lot numbers, dates, or unique identification codes. It also reduces supply costs by eliminating inks, paints, and dyes.
Long-Fiber CompoundsLiquid drugs can be introduced into the body using a needleless drug injector. Current designs use compressed air or springs to move a plunger and force medication through a micro-orifice into tissue under the skin without a needle. They are said to deliver medicine with little or no pain and minimize the chance of infection. The compressed gas canisters are typically made from long-fiber reinforced nylon, providing the proper balance of burst strength plus chemical, impact, creep, and permeation resistance. Such long-fiber compounds increase flexural modulus and impact strength while providing better stiffness and dimensional stability than short-glass fiber-reinforced plastics.
For additional information on the technologies discussed in this article, see Medical Design Technology online at www.mdtmag.com or RTP Co. at www.rtpcompany.com.