Coming clean: The next-gen solvents used to clean medical devices
Jay Tourigny, MicroCare Medical, looks at cleaning medical device components with next generation solvents.
Up until the late 1990s, solvent-based vapour degreasing systems were the preferred method of cleaning because of their ease of use and effective performance. But environmental concerns forced an industry shift from solvents to aqueous (water)-based cleaning systems. Although aqueous systems had many disadvantages, environmental issues linked to many cleaning solvents at that time outweighed a number of the benefits of vapor degreasing systems. With new advances in solvent technology and strict regulatory compliance issues in industries such as medical devices, the pendulum is now swinging back to solvents.
Considerations for medical device component cleaning
Bioburden
There are several key benefits to manufacturers using solvents for cleaning medical devices. Among the top reasons: solvents are well suited to cleanroom use and simplify cleaning by completely dissolving oily contaminates and removing particulate. Most significantly, solvents do not harbour pyrogens. Because solvent based cleaners do not allow bacterial growth, they simplify quality controls associated with good manufacturing practices (GMP) and provide a convenient way to validate a bioburden-free cleaning process.
Water and many detergents are a natural breeding ground for bacteria and mould, meaning bioburden control is an ongoing issue when cleaning devices with any water-based system. Water-based cleaning requires relatively complex process controls to prevent bioburden issues, along with an expensive rinsing and drying process. Blowers or heated dryers – which require additional expense and energy costs to operate – are often necessary to dry water from deep grooves, and there is a significant risk of spotting and corrosion if any steps in the cleaning process are not well engineered. These factors impact process validation and increase ongoing process control costs.
Post-cleaning considerations
When used with a vapour degreaser, solvents easily clean complex parts and dry quickly so they are not trapped in tight spaces and leave the parts ready for the next step in the process – whether sterilising or coating. For many coatings, it’s important that parts be completely clean and dry before applying. The presence of water, moisture, oils or particulate on parts after cleaning will negatively impact the coating quality, and may lead to expensive rework or scrapping of parts. Solvent cleaning with a vapor degreaser not only cleans more effectively, but also creates the opportunity for manufacturing efficiencies. For example, it is possible to combine the vapour degreasing cleaning process with a second-step surface treatment for the application of lubrication or a specialty film. The reliability of the solvent cleaning process means parts are clean and coated in seconds, streamlining the overall process significantly.
Medical device design considerations
Ongoing advances in device design requires cleaning options that can penetrate all areas of complex geometries, including small crevices, without leaving a residue or damaging sensitive materials such as polycarbonate and acrylic. Solvents feature excellent materials compatibility along with low surface tension and high liquid densities, meaning they penetrate, clean and dry very effectively in the nooks and crannies that water in aqueous systems either can’t reach or from which water residues can’t easily be removed. Medical device designers find this benefit of solvent cleaning to be of utmost importance as it doesn’t limit product design compared to water-based cleaners. Also, vapour degreasing systems are not geometry-sensitive, meaning if the component will fit in the machine, the machine will clean it. This is beneficial because it reduces the need for expensive fixtures and it’s an extremely forgiving process even when cleaning large quantities of parts.
Consistency in device performance and process
Engineers and manufacturers need cleaning to be part of a well-engineered process that is cleanroom compatible to ensure it results in the best and most consistent performance out of a finished device. Aqueous cleaning systems require relatively complicated process controls at every stage in the cleaning process because they use special detergent or surfactant additives and the supply water chemistry can be highly variable. This means the cleaning chemistry must be heated, filtered and treated, then filtered and tested continuously throughout the process to ensure the chemistry is consistent and bioburden free. The benefit of a consistently pure solvent chemistry is the peace of mind provided to medical device engineers and manufacturers that there’s no variation in the cleaning solvent chemistry, making initial validation and ongoing process controls that much simpler and less costly.
The economic benefits of cleaning with solvents
The benefits of cleaning with solvents and vapor degreasing systems when manufacturing medical devices is becoming increasingly clear – solvents have gained a lot of traction in terms of safety, effectiveness and being environmentally friendly. The next big logical question that decision makers will be asking is, at what cost and for how big of a return?
Cost-per-part cleaned
The actual cost isn’t the cost of a machine or a drum of solvent, it’s the total cost-per-part-cleaned, putting the focus on cleaning parts at the lowest total cost, and the ease of use in a manufacturing clean room – where your profits are made or lost. Figuring out this cost can help you put together a ‘cleaning scorecard’ – or procedure to help you select the optimal solution for your cleaning needs. The first step is computing which type of cleaning system produces clean parts at the lowest total cost.
It’s important to work with a partner who has experience in the special requirements associated with medical device manufacturing, with technical engineers who work closely with end-users to ensure they are selecting the best product for their specific applications, taking into consideration compliance issues, while always trying to achieve the ‘lowest cost per clean’.
Advances in solvent technology
Nearly all of the recent advances in solvent technology have centered around developing safe chemistries that meet both performance standards and environmental regulations – meaning they must not contribute to global warming or be a volatile organic compound. In the past, high-performing cleaning solvents such as trichlorethylene, methylene chloride and n-Propylbromide (nPb) presented environmental as well as health and safety issues that resulted in layers of regulations established to discourage their use. Efforts to develop alternative solvent chemistries initially resulted in mild chemistries that did not meet cleaning standards – especially those needed in the medical device space. Solvent suppliers returned to the laboratory to develop suitable chemistries to solve this problem.
Current solvent cleaners have successfully focused on chemistries that not only clean, but can multitask in other applications beyond cleaning. The most common: a carrier agent for the application of medical-grade lubricants or pharmaceutical surface treatments. In fact, some of the new chemistries available are multi-purpose – they can be used as both a cleaner and carrier fluid. These advanced new chemistries offer alternatives to existing carrier fluids that pose safety issues – especially around flammability – which becomes even more of an issue when applying surface treatments to devices in high production volumes. Also, depositing silicone oil lubricant presents its own challenge. Most commonly used on disposable hypodermic needles and needles for sutures, silicone lubricants are difficult to put into a solution with many alternative chemistries that are nonflammable and nontoxic. Many of the new nonflammable chemistries may accept less than one to two percent by weight of silicone before separating, resulting in an unacceptable coating. Recently, a new class of nonflammable carrier fluid chemistries have been developed with positive health, safety and environmental profiles and can accept a mix of 15 to 20% by weight of silicone, ensuring a consistent and uniform coating.
Closing
New cleaning solvent technologies and vapor degreasing equipment have brought new attention to their uses in manufacturing medical devices. Solvent cleaners are well suited for use in cleanroom assembly areas and ensure compliance with strict bioburden process controls. They also offer cleaning flexibility making them ideally suited to the development and validation of new device designs. They may also be a safe and effective carrier fluid for deposition of silicone, PTFE lubricant, and pharmaceutical coatings.