Designing medical polymers for chemical resistance requires increased regulation in order to comply with frequent and robust disinfection routines in healthcare. 1,2 Resin manufacturers offer high-performance, thermoengineering polymer blends as potential solutions with a multitude of functional properties.

It is pertinent that resin suppliers provide compelling evidence outlining chemical resistance against harsh disinfectants, aggressive carrier solvents for administering oncology drugs, and biocompatibility to circulating blood contact with low to no platelet adhesion and aggregation. 3-6

Evidence to support chemical resistance reflects the analytical testing performed, which varies. This often presents a challenging proposition for medical device manufacturers that must discern which offerings can be used in their anticipated application. A major source of discrepancy arises from the unregulated, discretionary differences in testing methods introduced through manufacturer practices. Although tests are performed in accordance with standardized institutions, namely the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO), resin manufacturers may still use their discretion for parameters driven by product end-use application.

Fig. 1 - CYROLITE® with balanced optical transmission and mechanical robustness offers chemical resistance to IPA, lipids, blood, disinfectants, and oncology drugs, necessary for infusion therapy and other medical applications such as luer locks, connectors, filter housings, and infusion therapy applications.

The industry suppliers present data based on different methods and properties that make it challenging to compare across numerous material choices. For instance, mechanical testing for property retention is reported as tensile or impact or flexural compression, corresponding to the most suitable strain that a material can withstand. Subsequently, random selection of different chemical agents for exposure, or exposure environment as in “wipe” or “immersion” of the test assembly in chemical agent, or the duration of exposure ranging from 30 minutes to 24 hours or longer where the material retains most of the original mechanical property. More importantly, often material comparisons for property and performance are published to showcase a material’s competitive advantage. Polymethyl methacrylate (PMMA) is routinely used as a reference material compromising the extensive R&D evolution of impact-modified acrylic copolymers designed for superior properties and performance. Such an unregulated approach to test metrics to screen the different resin material choices could be misleading the designers and industry.

Part 1 of this two-part series presents an overview of CYROLITE® acrylic-based medical copolymers, which are designed through extensive R&D to carefully balance properties and performance for healthcare applications. More importantly, this article emphasizes the key role of polymer mechanical behavior in governing its chemical resistance and delivers an understanding of the chemical attack, specifically environmental stress cracking. Part 2 will showcase the key parameters for evaluating chemical resistance and understanding industry-wide testing discrepancies and will identify opportunities for unifying and defining a regulated approach for material evaluation. A case study on chemical resistance testing of CYROLITE® acrylic-based medical copolymers will be presented following these key considerations against various chemical agents. 3, 7

Roehm America’s impact-modified acrylic copolymers are formulated to provide a unique combination of transparency with outstanding UV transmittance, structural resilience, high-volume manufacturability, excellent flow, and moldability into thin-walled components used in infusion therapy applications. Additionally, CYROLITE® can be reliably sterilized using gamma irradiation, e-beam irradiation, and ethylene oxide and offers resistance to medical fluids such as lipids and disinfectants for infusion therapy applications. Furthermore, these products are bisphenol A (BPA)-free, phthalate free, and compliant with USP Class VI and ISO-10993-1 and REACH. These molding compounds are safe to use in medical devices, such as medical filter housings, blood separators and handling devices, IV disposable luer lock connectors and accessories , blood plasma oxygenators, drainage sets for the thorax, medical filter housings, and disposable luer lock connectors (see Figure 1).7, 8

Polymer Mechanical Behavior: What Is Chemical Resistance in Medical Plastics?

The mechanical properties measure the material’s response to a finite strain by an applied stress. The intermolecular arrangement of a polymer, among other attributes, largely governs its mechanical behavior. However, chemical resistance measures the ability of a polymeric material to retain its original properties post exposure to a chemical agent for a specified time period.9 Smart design of the polymer backbone, polymer blending, and formulating with specialty additives to alter the degree of crystallinity, crosslinking, or molecular weight are critical factors that influence the chemical resistance of the blend.10-12

Fig. 2 - Sequence of events induced in the polymer material upon chemical attack. Chemical resistance enables endurance to the polymer against chemical attack.

The inability of a polymer to resist chemical attack could impair physical and/or chemical properties such as surface aesthetics, or color, of polymer to modulus, ductility, impact toughness, and dimensional stability depending on the chemical agent and the duration of exposure. The extent of these detriments depends on the polymer design and the degradation pathway. Common agents leading to chemical attack are detergents, surfaces active or oxidizing chemicals such as disinfectants, alcohols, lipids, processing aids, lubricants, contaminants, or even ultra-pure water (see Figure 2). 13

Fig. 3 - Simultaneous presence of these three factors results in the surface embrittlement of plastic parts by ESC.

Furthermore, crazing and environmental stress cracking (ESC) are distinct types of failure phenomena in plastics. The material under critical external (mechanical) or residual molded-in stresses, when exposed to a stress cracking agent, can experience localized weakening at the surface of the material, permitting crack propagation. Depending on the material, macroscopic crazing occurs, sometimes visible as stress whitening in the region of maximum stress. Crazing is physical embrittlement that is induced by the simultaneous presence of critical stress and a chemical agent that can lower the cohesive bond energies of the polymer surface layers (see Figure 3).9 Strategies to incorporate functional moieties such as block, graft, or amphiphilic block copolymers, or impact modifiers, in the polymer design can mitigate crack formation and crack propagation yielding environmental stress crack resistance (ESCR). 11, 12

Conclusion

Table 1. Roehm America’s product portfolio offering CYROLITE® in eight grades designed for performance in healthcare applications. Performance rating: Good (+), Very Good (++), Excellent (+++).

Foremost, patient safety from disease-causing pathogens is propelling the industry to design for ESCR utility in medical assemblies. Designing for ESCR begins with understanding the chemical exposure environment before the polymer material selection. The mechanical behavior of the polymeric material drives the subsequent ESCR performance. Herein, we showcase CYROLITE®’s product portfolio, for example, offering performance attributes for applications in healthcare and medical devices. The design process for CYROLITE® involves understanding the market landscape, customer input, and cognizance for potential indications for use. Furthermore, it combines a methodical assessment of design factors, such as material selection and processing, providing value-added solutions in terms of optical transparency, mechanical performance, chemical resistance, sterilizability, and large-volume processability.

Moreover, the application of aggressive disinfectants is interfering with the structural integrity of medical device assemblies and causing premature failures. It is essential to integrate an objective screening matrix to enable medical device manufacturers in identifying the appropriate material with functional performance and mechanical robustness. But the current property data across numerous materials is challenging to navigate due to differences in pertinent testing practices from the resin manufacturers.

Part 2 will highlight the key considerations for evaluating ESCR, thereby mitigating the aforementioned inconsistencies in testing and meeting customer needs. A case study example of CYROLITE® Med 2 after exposure to a variety of chemical agents, disinfectants, and oncology drugs will also be discussed.

References

  1. Guidelines for Environmental Infection Control in Health-Care Facilities: Recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee,” Company publication by the U.S. Department of Health and Human Services Centers for Disease Control and Prevention, Atlanta, 2018.
  2. Doll, M., Stevens, M., Bearman, G., “Environmental cleaning and disinfection of patient areas,” International Journal of Infectious Diseases 67 (2018): pp. 52–57.
  3. Bajaj, P., Wright, K. D., Bernhard, K., Heyl D., Chemical and Environmental Stress-Crack Resistance of PMMA-Based Compounds in the Medical Environment, 2019: pp. 12–14. 8390588.
  4. Nowatzki, P. J., Chemical Resistance testing of Polycarbonates and blends with Hospital Disinfectants and Cleaners, Antec 2020.
  5. Chemical compatibility with hospital disinfectants and oncology drugs,” Eastman.
  6. Chemical Resistance Performance Testing for Healthcare Materials,” SABIC.
  7. Röhm/Cryolite.
  8. Qosina Utilizes CYROLITE® G-20 HIFLO to create new Disposable Luer Lock Connector”.
  9. M. Ezrin, Plastics Failure Guide: Cause and Prevention, Hanser, Cincinnati, OH, 2013.
  10. E. N. Peters, Engineering Plastics Handbook Thermoplastics, Properties, and Applications, J. Margolis ed., McGraw-Hill, New York (2006) Ch. 9: pp 181–220.
  11. Klingler, A. et al., “The effect of the block copolymer and core-shell rubber hybrid toughening on morphology and fracture of epoxy-based fiber reinforced composites,” Engineering Fracture Mechanics 203 (2018): pp. 81–101.
  12. L. M. Robeson, Polymer blends: a comprehensive review, Hanser, Cincinnati, OH, 2007.
  13. Disinfectants Solutions from Plaskolite”.

This article was written by Pooja Bajaj, PhD, Product Development Manager – BU Molding Compounds, Medical; Kierra D. Wright, PhD, Product Development Manager – BU Molding Compounds, Medical; Kay Bernhard, Director of Global Technical Competency Center – Medical; Dirk Heyl, Technical Marketing Manager – Medical; Maurice Biagini, Global Business Director – Medical; Andrew Sneeringer, Technical Marketing Specialist – Medical Molding Compounds; and Michael Zadrozny, Strategic Account Manager – Medical; Roehm America LLC, Parsippany, NJ. For more information, visit here .


Medical Design Briefs Magazine

This article first appeared in the May, 2021 issue of Medical Design Briefs Magazine.

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