Chemical Characterization of Polymeric Medical Devices: Unveiling the Identity and Risks

Dr. Renjith S. Scientist B, Biomedical Technology Wing, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum

Polymeric medical devices play an inevitable role in day-to-day medical care. We can observe materials of polymeric origin in a wide range of medical devices viz. injection syringes, blood bags, intra-ocular lenses, vascular grafts, hernia patches, facial implants, catheters, personal protective equipment (PPE), and many more (Fig. 1). Every medical device has to undergo strenuous biological evaluations in line with international standards to ensure patient safety and avoid undue health risks. Chemical characterization plays a vital role in the biological evaluation as well as toxicological risk assessment of medical devices.

Fig. 1. Representative polymeric medical devices

Material selection is one of the first and foremost steps in the development of medical devices. One should ensure that the material is fit enough with all the necessary properties and characteristics encompassing physical, chemical, mechanical, morphological, electrical, and biological to be used for the device development. Chemical characterization enables to ascertain the presence or absence of necessary properties and also helps to establish the equivalence of a material with an established biomaterial. Even though chemical characterization alone wouldn’t give a complete evaluation of a medical device; along with toxicological risk assessment it would enable the screening of potential materials/devices for clinical applications and, establish the biological safety of new or reprocessed medical devices. ISO 10993 series of standards describes the biological evaluation of medical devices with direct or indirect contact with patients. ISO 10993-18 lays a framework for the chemical characterization of medical devices involving the identification and qualitative and/or quantitative estimation of medical device components to identify biological hazards and to estimate and control the toxicological risks associated with medical devices. The flow chart of the chemical characterization process as per ISO 10993-18 is outlined in Fig. 2.

The first step in the chemical characterization of a medical device is to identify the materials of construction. It generally means the identification of the components with which the medical device is made (medical device configuration). The components of a medical device can be of polymeric, metallic, or ceramic origin. The detailed configuration of the medical device will give the chemical identity of the components, the physical forms in which they exist in the device, and their geometrical distribution in the device. Further, the composition of the individual components of the medical device has to be estimated. It includes the percentage purity of the component along with the quantity of impurities, process aids, or additives present in it. Catalytic residues, sterilization residues, and possible degradation products are also to be estimated. For establishing the medical device configuration and composition, the information can be gathered (from vendors), generated, and augmented by using various characterization methods. A complete list of characterization techniques suitable for medical device configuration and composition is available in ISO 10993-18.

When the complete picture of the medical device (device configuration, constituent composition, and clinical use) is available, one should check if there’s an equivalent device. The biological equivalence of two devices or materials involves a number of terms such as chemical equivalence, physical equivalence, material equivalence, and contact equivalence. If two medical devices have identical device configurations, constituent compositions, and processing methods, they can be called chemically equivalent. Medical devices with identical configuration, morphology, topography, and tribology are said to be physically equivalent. If two devices have chemical equivalence and physical equivalence, they could be said to have material equivalence. Similarly, two devices with identical clinical use and endpoints of biological evaluation, are said to have contact equivalence. For two devices to be called biologically equivalent, they should demonstrate material and contact  equivalence. If the preliminary chemical characterization of the medical device is successful in establishing its equivalence with an established device, one can stop the chemical characterization with the conclusion that the medical device has an acceptable health risk and this outcome could be used for biological evaluation as per ISO 10993-1.

Fig. 2 Flow chart of chemical characterization process as per ISO 10993-18