Materials for CNC machined medical devices
The medical device industry encompasses an extensive product line ranging from artificial joints to diagnostic and therapeutic devices. Even so, different applications often have overlapping needs, which helps narrow down material choices. For example, most devices require surfaces that do not absorb moisture and can be easily sterilized. Medical device components are often manufactured through injection molding, 3D printing, and CNC machining, which offers the advantages of high customization, tight tolerances, good surface finish, and certified material selection. When CNC machining is used, parts are typically milled using 3 to 5 axes or turned using a moving tool CNC lathe. This article will discuss the factors to consider when selecting materials for medical device machining and the materials commonly used in the medical industry.
Materials used for CNC machining of medical devices
When CNC machining medical devices, the materials used must meet stringent requirements for biocompatibility, sterilization, and performance, as most medical devices are intended for human health considerations, and if the medical device is manufactured with defects, it will be a massive threat to the patient if the device is used in surgery. The most commonly used materials for the current CNC machining of medical devices are generally the following:
Medical-grade stainless steel: Medical-grade stainless steel is a popular choice for CNC machining medical devices because it is robust, corrosion-resistant, and easy to sterilize.
Titanium: Titanium is strong, lightweight, and biocompatible, so it is commonly used for medical device CNC machining.
PEEK: PEEK is a biocompatible thermoplastic polymer with excellent mechanical properties. It is commonly used for medical device CNC machining components such as spinal implants and dental implants.
The best machinable metals for the medical device industry have inherent corrosion resistance, sterilization capabilities, and ease of cleaning. Stainless steels are very common because they do not rust, have low or no magnetism, and are machinable. Some grades of stainless steel can be further heat-treated to increase hardness. Materials such as titanium have a high strength-to-weight ratio, which benefits handheld, wearable, and implantable medical devices. The other most common plastics for medical devices have low water absorption (moisture resistance) and good thermal properties. Most materials can be sterilized using autoclave, gamma, or EtO (ethylene oxide) methods. The medical industry also prefers low surface friction and better temperature resistance. In addition to direct or indirect contact with housings, fixtures, and guides, plastics can be an alternative to metals where magnetic or RF signals may interfere with diagnostic results.
How to choose the suitable material for medical device processing
Medical device” is a broad umbrella term that covers various instruments and devices, such as band-aids, dental floss, blood pressure cuffs, defibrillators, MRI scanners, and more. Medical device design is an integral part of the mechanical engineering field. The development process for medical devices is no different than any other device: design, prototype, test, and repeat. However, medical devices have more stringent material requirements. Due to testing and clinical trial requirements, many medical device prototypes require biocompatible or sterilizable materials. Selecting the suitable material for medical device processing requires careful consideration of several factors:
Biocompatibility: The materials used must be biocompatible, meaning they will not cause adverse reactions when in contact with the human body. Common biocompatible materials include medical-grade stainless steel, titanium alloys, and PEEK.
Sterilization: The materials used must withstand the sterilization process required for the device. Materials that can withstand autoclaving or gamma radiation sterilization include stainless steel, titanium, and certain plastics.
Performance: The material must have the mechanical properties required for the device to perform its intended function. For example, a robust cloth such as titanium may be necessary if the equipment is subjected to high pressure.
Manufacturing process: The materials used must be suitable for CNC machining to ensure efficient production and high-quality parts.
Biocompatible and sterilizable materials
1. Biocompatible materials
For plastics, the most stringent requirement is USP Class 6 testing. USP Class 6 testing involves three in vivo bioreactivity assessments on animals, including
Acute systemic toxicity test measures irritation when the sample is taken orally, applied to the skin, and inhaled.
Intradermal test: This test measures the wrath of the model when in contact with living subcutaneous tissue.
Implantation test: This test measures the wrath of a sample when implanted intramuscularly into a test animal over five days.
CNC machining is suitable for prototyping and end-use production of medical device parts. More materials are available, and the materials are more robust. However, the design requires more attention to ensure machinability.
The following materials are USP Class 6 tested and certified: POM, PP, PEI, PEEK, PSU, and PPSU.
If you are making early-stage prototypes that will not be used in experimental or clinical trials, consider using a non-certified plastic. You don’t have to pay a higher price for the same mechanical properties.POM 150 is an excellent material for early-stage prototyping.
CNC machining is also available to produce biocompatible metal parts. There are three common implant grades to choose from:
Stainless Steel 316L
Titanium grade 5, also known as Ti6Al4V or Ti 6-4
Cobalt-Chromium (CoCr)
Stainless steel 316L is the most commonly used of the three materials. Titanium has a better weight-to-strength ratio but is much more expensive. CoCr is primarily used for orthopedic implants. We recommend using SS 316L for prototyping when improving your design and using more expensive materials when the procedure is more mature.
2. Sterilizable materials
Any reusable medical device that may come in contact with blood or body fluids must be sterilizable. Therefore, most medical devices used in medical facilities are made of sterilizable materials. There are many methods of sterilization: heat (dry heat or autoclave/steam), pressure, chemicals, irradiation, etc.
Chemicals and irradiation are the preferred methods of sterilizing plastics because heat breaks down plastics. Here is a chart outlining the compatibility of many plastics with different sterilization methods. Autoclaves and dry heat are the standard methods for sterilizing metals.
All USP Class VI certified materials mentioned earlier, as are implant-grade metals, are sterilizable. Again, CNC machining offers the most options for sterilizable materials.
If a medical device is used for patient sterilization at home, the material should also be compatible with sterilizing chemicals such as bleach, ethanol, isopropyl alcohol, iodine, and hydrogen peroxide. ABS and POM are the most chemically resistant plastics.
Conclusion
Selecting suitable materials for CNC-processed medical devices is critical to devise performance, safety, and biocompatibility. Biocompatibility, sterilization, performance, and manufacturing processes must be considered when selecting materials. In addition, CNC machining techniques such as milling, turning, EDM wire cutting, and laser cutting provide precise and efficient methods for manufacturing medical device components. By utilizing suitable materials and CNC machining techniques, medical device manufacturers can produce high-quality and reliable devices that meet the needs of patients and medical professionals. CNC machined medical partsWhether a medical or dental project requires machined titanium or smooth PTFE, Anpllocnc, with its knowledgeable engineers and extensive design resources for manufacturability, takes the guesswork out of guesswork in selecting the best material. Whether a medical or dental project requires machined titanium or smooth PTFE, we can give you a quote and provide lead times. With experienced engineers and extensive design resources for manufacturability, we can advise you in selecting the best material.