What is medical-grade plastic?

Medical-grade plastic materials refers to plastics designed to make medical products. It's also used for manufacturing products for in vitro diagnostics and primary packaging for pharmaceuticals, which preserves and contains medicines to avoid contamination. In this article we cover:

What is medical grade plastic?
The dangers of non-biocompatible materials for medical devices
What is medical-grade plastic made from?
ISO 10993: risk management for medical grade polymers

What is medical grade plastic?

Believe it or not, there is actually no regulatory definition of a medical-grade polymer. ISO 10993 defines the requirements for materials that can be used for medical devicesin the medical industry. In theory, manufacturers can therefore use any plastic in medical devices, as long as the entire device meets those requirements. Learn more in our guide, What plastic is used for medical devices?

These requirements set the standards of medical plastics and plastic components. Understand more about the manufacturing properties of materials used in medical environments in our guide, Material standards for medical manufacturing.

ISO 10993 certification verifies the biocompatibility of your medical device. In essence, ISO 10933 requires biological evaluation of, but are not limited to:

• Construction of material(s)
• Intended additives, process contaminants, and residues
• Packaging materials
• Leachable substances
• Degradation products

The biocompatibility definition is the same for any material: the device must be compatible with biological systems, meaning the human body. The device that achieves ISO 10993 meets stringent requirements. ISO 10993 is considered the standard for medical-grade materials (or medical grade plastics), even if technically, the materials are not medical grade.

Herein, the problem again is that there is no agreement on what medical grade means.

Consequently, material suppliers and others in the medical-device industry have determined their own definition of what constitutes a medical-grade plastic. As a result, medical-grade polymers can vary in performance and quality from supplier to supplier.

That should change. Recently, the Association of German Engineers, VDI, published a voluntary guidance document outlining the meaning of medical-grade plastics. It’s not yet been adopted, but probably, it’s only a matter of time. The effect would require plastic medical-device manufacturers to prove they use consistent formulations.

The dangers of non-biocompatible materials for medical devices

Plastic, metal or any other material not designed to be biocompatible can have far-reaching consequences, which can be prevented or minimized by medical-grade devices.

• Chronic inflammation at the area of contact
• Cytotoxic substances production
• Cell disruption
• Skin irritation
• Restenosis (narrowing of blood vessels after stenting)
• Thrombosis (forming blood clots)

Other than plastic, surgical stainless steels are used for non-permanent implant devices although the nickel content can be a concern. Read more in our guide, What is surgical steel?

What is medical-grade plastic made from?

Medical-grade plastic types are just about any plastic you want. Take polystyrene, a common polymer. It becomes medical-grade polystyrene through engineering the resins, with processes that enhance the qualities you're after. The result is that it can be used in medical devices that range from petri dishes to implants. Medical-grade ABS plastic is another popular choice, used in drug-delivery systems and tracheal tubes. You'll also find polyethylene in medical applications, such as catheters.

There is no biocompatible plastics list to make life easier for device designers. It depends on how the plastics were engineered to become biocompatible. Generally, plastics used in medical devices are designed to resist temperature, chemical and corrosion. It should also be able to handle repeated sterilization cycles and remain inert when coming into contact with living tissue and bodily fluids. Even single-use plastic devices in healthcare, despite being disposable, are sometimes required to be medical grade, meaning they need ISO 10993 certification to verify the device's biocompatibility.

USP-class plastics designation

While ISO standards are the most well known around the world for all materials, they’re not alone when it comes to polymers. The U.S. Pharmacopeial Convention (USP) dictates testing for plastic medical devices to evaluate biological responses. Their standards are recognized in 140 countries, including the UK. In the U.S., their standards are enforceable by the Food and Drug Administration (FDA). There are no FDA-approved plastics for medical devices. It’s the entire device that is tested, as variables such as manufacturing processes can alter the material’s properties.

Each USP device class is based on duration of use and the application, requiring a different level of regulation and compliance. The important one here for a device to be anywhere close to medical plastics is Class VI.

USP Classifications

Limited: less than 24 hours/ Prolonged: 24 hours to 30 days /Permanent: 30 days and longer

Device category	Contact	Exposure time	USP Class
Surface device	Skin	Limited	Class I
		Prolonged	Class I
		Permanent	Class I
Mucosal surfaces	Limited	USP Class I
		Prolonged	Class III
		Permanent	Class V
	Breached or compromised surfaces	Limited	Class III
		Prolonged	Class V
		Permanent	Class VI
External communicating devices	Blood path, indirect	Limited	Class IV
		Prolonged	Class V
		Permanent	Class VI
	Tissue/bone/dentin communicating	Limited	Class IV
		Prolonged	Class VI
		Permanent	Class VI
	Circulating blood	Limited	Class IV
		Prolonged	Class VI
		Permanent	Class VI
Implant devices	Implant devices	Permanent	Class VI

 

Class VI undertakes rigorous testing for plastic components for medical devices. Those tests are as follows:

(“Test specimens” refer to lab mice or rats.)

Systemic Injection Test	Intracutaneous Test	Implantation Test
Test specimens injected with the extract intravenously and monitored for 72 hours to identify any reactions that relate to abnormal toxicity level	Test specimen injected intracutaneously with the extract before being monitored for 72 hours; any skin reactions are scored and averaged	Product materials implanted into the specimen to identify whether a reaction in live tissue takes place after coming into direct contact with product over a period of around five days

In order to meet Class VI standards, the product/material must exhibit a very low level of toxicity. The tests are similar to ISO 10993 and have some cross-over. However, the USP classification only outlines the tests needed. Unlike ISO standard, it doesn’t include the risk management of medical devices.

ISO 10993: risk management for medical polymers

Risk analysis requires identifying and characterizing all materials that have the potential to be in the final medical device. This will include analyzing the presence of any manufacturing additives. Also, an examination of the impact of processing takes place on material composition and chemistry. It can include assessment of:

ISO 10993 risk assessment

Analysis can include:

• Chemical interactions between materials
• Impact of physical degradation (wear, load, fatigue, friction)
• Environmental interactions (heat and thermal degradation, UV light and light-catalysed degradation)
• Manufacturing processes
  • What additives will be used? Processing aids, such as such as catalysts, antioxidants, pigments, and surface treatments?
  • What are the potential process contaminants?
  • What are the potential process residuals of chemicals and additives?
• Decontamination and sterilisation systems
• Effect of contaminants from packaging materials
• How transportation, storage, and aging will impact the material

USP Class VI vs. ISO 10993

USP Class VI demands an intracutaneous irritation test. So does ISO 10993. However, Class VI also requires subacute toxicity and implantation effects, which many ISO 10993 categories do not.

That said, the lack of risk assessment in USP Class VI can be a problem. It’s possible that a USP Class VI material can also comply ISO 10993. But USP Class VI by itself is not adherence to ISO 10993.

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