For medical device manufacturers that work with different kinds of plastics (i.e., polycarbonate, polyethylene, and polypropylene), utilizing plasma treatments can create competitive advantages and transform specific parts into specialized, engineered components with 10 times the value.
Within medical device manufacturing, the range of uses for plastics is vast. It includes syringes, pipettes, bottles, flasks, vials, multi-well plates, Eppendorf tubes, culture plates, and other polymer labware items manufactured for research, drug discovery, and diagnostics testing. It could also include parts and components for various medical devices.
Plasma is a state of matter, like a solid, liquid, or gas, created by combining energy and gas, which causes ionization. Medical device manufacturers that utilize some plastic parts, for instance, can control the collective plasma properties (i.e., ions, electrons, and reactive species) to clean, activate, chemically graft, and deposit a wide range of chemistries onto a material.
When medical device manufacturers use plastics, the most common plasma application is to improve the bonding power of chemical adhesives. This can involve bonding metal to plastic, silicon to glass, polymers to other polymers, biological content to microtiter plates, and even bonding to polytetrafluoroethylene (PTFE).
When manufacturing plastic parts for medical devices, plasma treatments are used to solve difficult challenges. Typically, this relates to raw plastic material applications with incompatibility issues that exist.
Plasma can transform the surface properties of plastic to achieve aims that normally would not be feasible without treatment. This can include cleaning surfaces, resolving difficulties applying printing inks to plastics, improving the adhesion of plastics to dissimilar materials, and applying protective coatings that repel or attract fluids. Plasma today is being used to treat various medical device products, such as syringes.
Plastic parts manufacturers are always looking for unique ways to gain a technology edge to become a market leader. To achieve this today, top tier products incorporate some form of advanced coating to functionalize the surface. When the medical device industry uses plastics, more specialized offerings can create a competitive advantage and drive up the value of each part or product. When you treat plastic with plasma, it can transform a two-dollar item into a fifty-dollar product.
Some of the essential areas of plasma treatment in the medical device industry include printing on plastics, microfluidic devices, bonding plastic with dissimilar materials, treating plastic labware, coating plastics to prevent leaching, and facilitating R&D.
Printing on Plastics
When printing on plastics is required, binding the ink to the surface can sometimes be challenging; this occurs when the print beads up on the surface or does not sufficiently adhere to the surface. Greater print durability may be needed, including fade resistance even under high heat or repeated washings. For example, to resolve the beading issue, plasma treatment can make the surface hydrophilic (attracted to water). The treatment facilitates spreading out the ink on the surface, so it does not bead up.
For many applications, plasma treatments are utilized to increase the surface energy of the material. Surface energy is defined as the sum of all intermolecular forces on a material, the degree of attraction or repulsion force a material surface exerts on another material.
When a substrate has high surface energy, it tends to attract. For this reason, adhesives and other liquids often spread more easily across the surface. This wettability promotes superior adhesion using chemical adhesives.
On the other hand, substrates with low surface energy — such as silicone or PTFE — are difficult to adhere to other materials without first altering the surface to increase the free energy. Depending on what is required, organic silicones can also be used to create intermediate bonding surfaces with either polar or dispersive surface energy to help printing inks adhere to the surface of the plastic. This approach can facilitate the durable printing of a logo on the surface of bottles when the logo cannot fade after the first wash, for example. Another application includes the printing on plastics used for syringes, which do not bond easily with biodegradable inks that are friendly to the human body.
Typically, microfluidic systems used for medical or industrial applications transport, mix, separate, or otherwise process small amounts of fluids using channels made of plastics, measuring from tens to hundreds of microns.
Microfluidic devices usually have various wells containing different chemistries, either mixed or kept separate. So, it is imperative to either maintain flow through the channel or prevent any residual liquid flow in the channel after the chemistry has passed through it. With microfluidics, plasma treatment is used to disperse liquid on the surface to allow it to flow through easily. Or it can make the surface more hydrophobic (water repellent) to prevent the fluids from clumping together in unintended areas. When the fluids are pushed away, this minimizes the chance of any sticking or getting left behind.
In such cases, plasma treatment of plastic surfaces can facilitate the smooth, precise flow of liquids in the narrow channels. This can be critical not only for safety in medical procedures but also for quality for industrial processes.
Bonding Plastic with Dissimilar Materials
When traditional chemical adhesives fail to sufficiently bond dissimilar types of materials, or if medical device companies are looking to reduce the amount of chemical waste produced, engineers often turn to plasma treatments to solve complex adhesion problems.
Plasma treatment can assist the bonding of dissimilar materials. While treating the plastic alone can improve its binding, treating both materials enhances the binding of both by improving adhesive wicking across the surface. Whether bonding metal to plastic, silicon to glass, polymers to other polymers [of different durometers], biological content to [polymeric] microtiter plates, or even bonding to PTFE, plasma can be used to promote adhesion.
Like with printing, adhesion promotion is achieved by increasing the surface-free energy through several mechanisms. This includes precision cleaning, chemically or physically modifying the surface, increasing surface area by roughening, and using primer coatings. The net effect is a dramatic improvement in bonding. In some cases, up to a 50x increase in bond strength can be achieved.
Plasma Treatment of Plastic Labware
Each year, billions of multi-well plates, pipettes, bottles, flasks, vials, Eppendorf tubes, culture plates, and other polymer labware items are manufactured for research, drug discovery, and diagnostics testing.
Although many are simple, inexpensive consumables, an increasing percentage of these devices are now being surface treated using gas plasma or have functional coatings specifically designed to improve the quality of research and increase the sophistication of diagnostics. Among the goals of surface modification is improved adhesion and proliferation of antibodies, proteins, cells, and tissue.
Most of the plasma applications for plastic labware can be categorized as simple treatments, such as oxygen or argon plasma for cleaning the substrate at the molecular level. The use of plasma is also well established for surface conditioning to make polymers more hydrophobic or hydrophilic.
Potential plasma treatment applications include coating polypropylene or polystyrene plates with alcohol or to facilitate protein binding to the surface. Gas plasma can provide surface conditioning of in vitro diagnostic platforms before the adsorption of biological molecules (protein/antibody, cells, carbohydrate, etc.) or biomimetic polymers.
Multi-well, or microtiter, plates are a standard tool in analytical research and clinical diagnostic testing laboratories. The most common material used to manufacture microtiter plates is polystyrene, because it is biologically inert, has excellent optical clarity, and is tough enough to withstand daily use.
Most disposable cell culture dishes and plates are made of polystyrene. Other polymers such as polypropylene and polycarbonate are also used for applications that must withstand a broad range of temperatures, such as for polymerase chain reaction (PCR) for DNA amplification.
However, untreated synthetic polymers are highly hydrophobic and provide inadequate binding sites for cells to anchor effectively to their surfaces. To improve biomolecule attachment, survivability, and proliferation, the material must be surface modified using plasma to become more hydrophilic.
When polystyrene is treated with oxygen plasma, it s very hydrophilic, so water spreads everywhere. This allows aqueous solutions containing biological content to spread and deliver biomolecules to the surface while providing a hydrogen bonding platform to adhere to them. Treating the surface in this manner has many benefits, including improved analyte wetting of wells, greater proliferation of cells without clumping, reduced amount of serum, urine, or reagents required for testing, and lower risk of overflow and crosswell contamination.
Coating Plastics to Prevent Leaching
Using plastic labware can raise concerns about leaching. Since plastic labware is susceptible to leaching from plasticizers, stabilizers, and polymerization residues, plasma is used to coat the inside of containers with a quartz-like barrier material. These flexible quartz-like coatings are polymerized onto the plastic by plasmaenhanced chemical vapor deposition.
The resulting coating can be a very thin (100–500 nm), non-crystalline, highly conformal, and highly flexible (180° ASTM D522) coating. Similarly, there can be concerns about potential leaching from plastics in contact with the product in the food and beverage industry.
To prevent plastic leaching, industry producers can coat the plastic using plasma treatment. The two options are a PTFE-type coating, or on the opposite side of the spectrum, a silicone quartz coating to create a near glass-like surface. For example, sports water bottles have a different interior surface, typically due to plasma treatment or application of a coating.
If R&D assistance is required, plasma treatment is standard enough that leading equipment providers can modify existing, mature tools and technology, complete with fixturing, to deliver what are essentially drop-in solutions. Like PVA TePla, some providers provide access to on-site research and development equipment and engineering expertise.
However, for manufacturers that want plasma-treated parts or components without investing in in-house equipment, the solution is to utilize a contract processor. With this approach, the parts are shipped, treated, and returned within a mutually agreed time frame. For small or infrequent batches, this can significantly lower the price per part.
Working with a contract processor has advantages in tapping into the years of technical expertise applying various plasma treatments; this can often speed R&D efforts. As applications and production volumes continue to evolve, collaborating with a partner with deep plasma treatment expertise can provide a quicker time to market for a customer’s product. No matter which way medical device manufacturers choose, altering the surface properties of plastics improves the quality of test results while increasing the value of products.