The medical device market is undergoing an unprecedented period of growth due to a dramatic global population boom, an expanding middle class, and an aging population in select regions. These demographic factors are driving the growing demand for quality healthcare throughout the world and prompting an even greater need for safe and effective medical devices. Faced with these new challenges, medical device manufacturers are focused on developing highly creative and functional products that are economical and utilize high-performance materials to meet the necessary design criteria and comply with internationally recognized regulatory standards.

Fig. 1 – Color technologies can offer product differentiation and branding benefits for medical device designers.
The growth and reshaping of the medical device market is perhaps most telling in the drug delivery segment, which has undergone a major transformation. Drug delivery has been summoned out of the doctor’s office, and new easy-to-use delivery methods have emerged. These new systems have won successful adoption and surpassed traditional methods of immunization and oral medication by largely adapting to societal demands and lifestyle requirements. Indeed, designers of medical devices have developed a wider range of drug delivery devices that are user friendly, meet lifestyle needs, and enable patients to treat themselves at home.

These new features and options on injection pens, inhalers, transdermal patches, and patch pumps have relied to a large extent on the innovative use of thermoplastics to create unique products that deliver positive, trackable patient outcomes. Medical designers have capitalized on the many advantages of thermoplastics including strong mechanical performance, part consolidation, complex shapes, color coding, and efficient low-cost manufacturing. The rapid growth of thermoplastics in the drug delivery market reflects the suitability of these materials to meet the new demands of today’s healthcare industry.

Plastics Deliver Performance and Regulatory Compliance

Fig. 2 – Antistatic thermoplastic compounds improve drug delivery in dry powder inhalers.
Thermoplastics like those offered by medical device-focused thermoplastics compounders have played a significant role in the drug delivery device market by facilitating unique designs that are lightweight, easy-to-use, cost-effective, and meet international certification standards such as the FDA 510 (k) requirements and the European CE Mark. They also meet the necessary design and performance criteria and comply with internationally recognized biocompatibility testing, sterilization, and safety standards.

Engineered thermoplastics can be combined with a variety of advanced modifiers to yield specific properties and functional benefits. Most medical thermoplastic technologies possess a successful track record in other industries, providing medical designers with reliable options. These innovative materials can reduce electrostatic buildup, add lubricity, improve ergonomics, add a grip surface, absorb x-rays, and increase strength and stiffness. In addition, they can be engineered for a specific application by combining properties and benefits.

Unique color and effect technologies can offer product differentiation and branding benefits for medical device designers. As devices increasingly move from hospitals and clinics into the consumer and home care markets, consumer-friendly colors, and glow-in-the-dark technologies offer a perceived value that is much higher than their cost. (See Figure 1)

Thermoplastics also permit laser marking capabilities to create high-quality graphics on medical devices where the contrasting mark becomes integral to the part, making it durable and less likely to be affected by solvents and other environmental conditions. Laser graphics can also be applied to complex geometries.

Compounders focus on modifying thermoplastic materials and formulating custom compounds that meet the demands of customers’ specific applications. New proven developments in medical plastic technology help create safe and effective drug delivery devices such as injection pens, inhalers, safety syringes, transdermal patches, and patch pumps. The range of material technologies available include internally lubricated thermoplastics for low wear and friction, which allow for low cost and easy and smooth operation of moving parts.

Recently introduced technologies include low-wear thermoplastic compounds that can be utilized in wear and friction applications requiring high-temperature, high-pressure, and high-speed performance, including pumps and compressors. Meanwhile, antistatic thermoplastic compounds improve drug delivery in dry powder inhalers (DPI) and pressurized metered dose inhalers (pMDI) by more than 80 percent by preventing the drug from statically adhering to the inside of the inhaler. (See Figure 2) In addition, fiber-reinforced thermoplastic compounds replace metal and provide weight reduction, reduced operator fatigue, and durability.

Antistatic Solutions Improve Drug Delivery Performance

Fig. 3 – Conductive plastics, such as these pipette tips, allow for correct dosing.
The plastics industry has made major advances in examining the effect of static on plastics in drug delivery devices. Specifically, drug delivery in dry powder and aerosol inhalers has been hindered by static attraction of the drug substance to plastics used in the drug flow path. One of the key challenges for DPI and pMDI inhalers is to accurately measure the amount of drug that is dispensed versus the amount of drug that effectively reaches the patient’s lungs. Without conductive plastics, inaccurate dosages could result from either too little medicine (micro particles attracted to the walls) or too much medicine being administered (medication builds up and suddenly releases). (See Figure 3)

Antistatic compounds can be formed by blending the base resin with an inherently dissipative polymer (IDP). The IDP and base resin form a co-continuous or network morphology, which allows the blend to transfer electrical charges continuously throughout the IDP phase, while still retaining the physical attributes of the base resin.

The incorporation of these compounds into inhalers neutralizes the static effects and helps to ensure that the full dose reaches the patient. For example, studies conducted by RTP Company have shown that their PermaStat® compounds reduce the amount of drug carrier sticking to the molded plastic inhaler from 20 percent down to 2.5 percent, an 87.5 percent improvement in drug delivery. In addition, the compounds reduce the variability in the amount of drug delivered during each use.

Wear-Resistant Compounds Facilitate Smooth Operation

Drug delivery devices also benefit from wear-resistant or internally lubricated thermoplastic compounds that can provide low friction and reduced wear. Single-use and prolonged contact motion in injection pens, safety syringes, and inhalers can have a detrimental effect on these devices, decreasing their ability for safe use. Materials for internal components such as drive screws and actuators, formulated with plastics containing internal lubricants, can reduce friction rates, vibration, and noise. An important benefit of internal lubricants is their ability to eliminate “sticktion” upon initial use and extend the useful life of reusable drug delivery devices, which help to keep them running effectively.

Product development engineers and designers must understand the tribological properties such as wear factor, static coefficient of friction, dynamic coefficient of friction, and pressure-velocity (PV) relationships of thermoplastic compounds to screen the suitability of these compounds for applications involving mechanical contact and motion. It is important that product development engineers have access to extensive tribological data to help engineers screen materials for suitability for particular end uses. In combination with the best resin for the application, engineered thermoplastic product engineers use a variety of wear and friction additives. For example, the industry’s most common wear additive, polytetrafluoro - ethylene (PTFE) can be combined with silicone fluid to produce a thermoplastic compound that exhibits very low friction and wear rates. Glass, carbon, and aramid fibers are also commonly used in these compounds for mechanical strength improvement.

A prime drug delivery candidate for wear-resistant compounds are reusable injection pens whose parts need to move effortlessly to ensure “non-stick” movement of the components. A typical solution is a carbon-reinforced, internally lubricated polycarbonate or acetal compound, which provides smooth and quiet operation, eliminates secondary application of lubricants, and permits laser marking of the pen dosage wheel.

For more demanding drug delivery applications that utilize high-pressure, high-speed pumps and compressors, users should look for friction-resistant compounds. These compounds replace costly competitive materials that need to be machined from stock shapes or require extensive annealing before use. These injection moldable thermoplastic compounds have been tested and shown to perform under high PV and temperature conditions.

To develop these compounds, engineers leveraged synergistic wear additives with high-temperature and chemically resistant polymers, such as polyether ether ketone (PEEK), polyphthalamide (PPA), and polyphenylene sulfide (PPS) resin, to create a new class of compounds. In testing against incumbent thermoset materials, the compounds provide excellent wear and friction performance at PVs up to 100,000 and temperatures up to 400°F (205°C). Other key benefits over thermosets include better mechanical properties and the processing benefits of injection molding, which afford greater design freedom and reduced production time and cost.

These materials are targeted for applications with demanding PVs that require high temperature or chemical resistance such as bearings, bushings, seals, rings, thrust washers, and gears in nebulizers, micropumps, compressors, and other drug delivery pumps.

Fiber-Reinforced Compounds Are Metal Replacement Options

Fiber-reinforced compounds also play a key role in drug delivery devices by allowing plastics to have strengths comparable to metal but at a much reduced weight. The move from metal to fiber-reinforced thermoplastics for lead screws on durable injection pens has dramatically increased the number of options available to design engineers. To withstand the 3 to 7 kgs of force on these screws over thousands of operation cycles requires a high strength-to-weight material. Carbon-reinforced PC and acetal compounds deliver excellent strength and stiffness and provide for a consistent injection force when using the pen. Larger parts, such as pumps and gear housings, also benefit from the unique combination of strength, stiffness, and light weight offered by fiber-reinforced compounds.

Thermoplastic Elastomers

Transdermal patches have also emerged as innovative drug delivery options that benefit from the unique performance of thermoplastic elastomer (TPE) compounds. These patches, which deliver a consistent dosage of medication for drug cessation, pain, and other uses, utilize TPEs to create rubber-like parts, which require short-term skin irritation testing. The production process consists of a two shot molding operation. The first shot, an engineered thermoplastic substrate, provides rigidity and structure while the second shot, over molded TPE, offers a soft, tactile feel. TPEs can be used in place of latex, silicone, or PVC.

The wide-ranging use of engineered thermoplastics in drug delivery is a testament to the unique performance and manufacturing advantages that these materials bring to the market. Thermoplastics have clearly allowed the medical industry to meet unique challenges brought on by sweeping demographic changes throughout the world. They have spawned a new frontier in drug delivery resulting in easy-to-use, lightweight devices that are less costly to produce and meet society’s demand for lifestyle improvement.

This article was written by Josh Blackmore, Global Healthcare Manager, RTP Company, Winona, MN. For more information, Click Here " target="_blank" rel="noopener noreferrer">