A discussion with the plastics pros at AIP on how to choose the right plastic for your medical application

 

When it comes to selecting a polymer for a medical application, there are a myriad of factors that play into deciding which grade of polymer is the best candidate. Of course, the number one concern in medical device design is safety of human life.

 

For this reason, trends in medical device design are moving toward miniaturization and portability. Additionally, sterilization and cleanliness continue to lead design considerations globally, requiring devices to withstand a range of chemicals and sterilization techniques.

 

As a precision plastics machining company, AIP has over 35+ years of experience working with medical OEMs to develop parts for critical medical devices. In this issue of our monthly blog, we will discuss what makes a polymer medical grade and how to choose the right polymer for a medical device application.

 

What are medical grade plastics?

 

Let’s begin with what a medical grade plastic is. Medical-grade plastics refer to plastics used to make medical products, products for in vitro diagnostics and primary packaging for pharmaceuticals.

 

Most importantly, plastics used in the medical field are coming in contact with human tissue, fluids, chemicals, drugs and many more substances. There are literally thousands of medical applications from packaging to spinal implants. Based on this information, your supplier should be familiar with the types of polymers and composites you need machined. They should additionally know the best machining process for your application. That’s why design conception is crucial as the first step.

 

1. Design requirements and constraints

 

First and foremost, what is the function of the polymer for the device?

 

Your machine shop should be asking you in depth questions about your medical application. Questions to consider include:

 

  • Should the material be biocompatible?
  • Is the product for single use?
  • Will the component undergo sterilization? If so, which method?
  • Does color and aesthetics matter in the machining process?
  • Is UV resistance needed?
  • What tolerances must be met for temperature, wear, impact, etc?

 

The following material selection flow-chart displays the overall process of developing a medical grade plastic part or device:

 

 

2. Industry Standards

 

What industry standards and regulations control the production of the material?

 

At AIP, our plastics are processed with strict hygienic procedures to ensure the highest level of sanitation. Make sure that your machining company is compliant and/or registered with the appropriate regulatory organizations. Some common medical certifications include the following:

 

  • ISO 10993
  • ISO 13485:2016
  • FDA Registered

 

3. Biocompatibility

 

How long does the component need to be in contact with the human body or tissue?

 

There are three categories of contact duration if a component is subject to body tissue or fluid:

 

  • Short-term contact (Less than 24 hours)
  • Medium term contact (Between 1-30 days)
  • Long-term or Permanent contact (Greater than 30 days)

 

4. Sterilization/Cleanliness

 

Will the device need to be resistant to chemicals or undergo multiple sterilizations?

 

Whether it’s a feeding tube, a drug delivery device or a surgical implant, the polymer material must be able to withstand chemical degradation and multiple sterilizations.

 

The most common sterilization methods include:

 

  • Radiation (gamma/e-beam)
  • Chemical (ETO)
  • Autoclave (steam)

 

Chemicals to consider for contact with the device could be:

  • Intravenous medications
  • Blood/Fluids/human tissue
  • Hospital cleaners – bleach, isopropyl alcohol, peroxides

 

5. Polymer Characteristics

 

What mechanical properties does the polymer need to fulfill?

 

Selecting a plastic material is based on a number of traditional material requirements such as strength, stiffness or impact resistance. Engineered thermoplastics like PC, PEEK, PPSU, POM, show excellent mechanical properties at low and high temperatures. These properties are required for a variety of climate conditions, including during transportation, where the influence of temperature on drop impact may result in different outcomes for device integrity.

 

Your machinist should be able to give you details about all the plastics in their portfolio such as:

 

  • High wear resistance
  • Tensile strength
  • Temperature resistance
  • Corrosion resistance
  • Durability
  • Dimensional stability

 

6. Aesthetics

 

Does the end product need to be a certain color or have certain qualities?

 

For instance, if it is a prosthetic for a foot, the polymer needs to be machined a certain shade to match skin tone.

 

7. Other Material Selection Factors

 

Anything else?

 

Other factors to consider and discuss with your machinist include additives for increasing the performance of the polymer, manufacturing process as well as the cost. Take into account the following:

 

  • Radiopacity
  • Conductive
  • Lubrication
  • Manufacturing feasibility
  • What manufacturing processes are you using and why?
  • Technical performance
  • Can we make this product with the material, and can we make it well?
  • Economics
  • If we can make it, can we make it for a reasonable cost?

 

At AIP, we are unrivaled experts in medical grade plastic machining.
Talk to our team about how to bring your project from concept to completion.

 

Contact Us

 

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Which thermoplastics are best suited for your machined medical application?

 

With over three decades of experience machining precision plastic and composite parts for the Medical & Life Sciences industry, AIP Precision Machining knows that biocompatible, sterilization-compatible and lightweight materials are critical for medical devices and surgical components. That’s why we’ve carefully selected, machined and tested all our thermoplastic materials to various ISO medical standards and performance considerations.

 

Here are eight examples of thermoplastics we commonly machine for the Medical & Life Sciences industry.

 

PEEK

PEEK (Polyetheretherketone) has biocompatibility in its medical grades per ISO 10993. In particular, PEEK Optima and Zeniva PEEK are suitable for long term implants and have a uniquely similar modulus to that of human cortical bone. PEEK is radiolucent and also used for dental implants and various medical instruments. PEEK can be used continuously to 480°F (250°C) and in hot water or steam without permanent loss in physical properties. For hostile environments, PEEK is a high strength alternative to fluoropolymers. PEEK is an increasingly popular replacement for metal in the medical industry due to its lightweight nature, mechanical strength, radiolucent properties, creep and fatigue resistance, as well as its ease in processing.

 

ULTEM – PEI

ULTEM PEI (Polyetherimide) is popularly used in medical instrument components, devices and pharmaceutical applications. Medical-grades of PEI are biocompatible per 10993. Not only is ULTEM steam, gamma, EtO and E-beam sterilizable, but it’s also hydrolysis resistant. Being resistant to both hot water and steam, ULTEM can withstand repeated cycles in a steam autoclave and can operate in high service temperature environments (340F or 170C). This makes it especially suitable for reusable medical devices. ULTEM also has one of the lowest rates of thermal conductivity and very high dielectric strength, allowing parts machined from ULTEM to act as thermal insulators. ULTEM however can be consider more brittle than a PEEK or RADEL, therefore it should be avoided for applications experiencing high rates of impact forces.

 

Polysulfone – PSU

Polysulfone (PSU) maintains a consistent modulus in temperatures ranging from -150°F (-100°C) to 300°F (150°C). PSU also exhibits excellent radiation stability, maintains high resistance to acidic and salt solutions, and is hydrolysis-resistant for continuous use in hot water and steam at temperatures up to 300°F (150°C). It’s capable of experiencing repeated autoclaving, but not as many as PEI, PEEK or PPSU. These qualities make it applicable for analytical instrumentation, medical devices and steam-cleaning equipment. In thin cross sections PSU is nearly clear, providing a window like finish with improved chemical resistance to that of PMMA or PC.

 

RADEL – PPSU

RADEL PPSU (Polyphenylsulfone) has been tested for notched izod impact resistance as high as 13 ft.-lbs/in. With high heat and high impact performance, RADEL delivers better impact resistance and chemical resistance than other sulfone-based polymers, such as PSU and PEI. Its toughness and long-term hydrolytic stability mean it performs well even under autoclave pressure. In fact, PPSU has virtually unlimited steam autoclave resistance, making it appropriate for machining reusable medical instruments. When thermal considerations are not extreme, RADEL provides for a less expensive alternative to PEEK. RADEL is also available in numerous color options, making a great choice for hip and knee sizing trials.

 

UHMWPE

UHMW-PE (Ultra-High Molecular Weight Polyethylene) is a linear, low-pressure polyethylene resin that has a significantly higher abrasion resistance and impact strength compared to most plastics. Due to its self-lubricating, non-stick surface, it has a low coefficient of friction that makes it desirable in the medical industry. UHMW-PE’s biocompatibility has made it a popular choice for artificial replacement hips, knees, shoulders and other joints as early as the 1960s.

 

TORLON – PAI

TORLON PAI (Polyamideimide) is the highest performing thermoplastic built from the TORLON resin. Its compressive strength is double that of PEEK when unfilled, and about 30% higher than ULTEM PEI. In its medical grades, PAI offers high modulus, radiolucency, sterilization-compatibility and high wear resistance, making it ideal for components inside high performance and peristaltic pumps. PAI’s extremely low coefficient of linear thermal expansion and high creep resistance deliver excellent dimensional stability over its entire service range.

 

Teflon – PTFE

Teflon PTFE (Polytetrafluoroethylene) is a fluoropolymer commonly used for tubing in medical device components. PTFE has non-stick qualities, is inert to most chemicals and has the lowest coefficient of friction of any thermoplastic. It also has very good UV resistance, hot water resistance and electrical insulation even at high temperatures.

 

Delrin – Acetal Homopolymer

Delrin (Acetal Homopolymer) is ideal for smaller lower performance applications and acceptable for a broad range of general components in the medical industry at temperatures below 250°F (121°C). It has flexible design uses (such as in reusable injection pens), is sterilization-compatible (with limited cycles) and offers options for low friction. Delrin is also tested against relevant parts of ISO 10993 and delivers excellent dimensional stability and natural lubricity.

 

Want to explore our full material library?

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Strict Hygienic Procedures for Precision Machining

 

It’s no secret that cleanliness and sterilization are crucial for applications in the medical industry. Any manufacturer you hire for machining your plastic component should be aware of this, and taking actions to prevent any contamination from taking place.

 

Here are three ways you can ensure that your medical application is being precision machined by a manufacturer committed to following strict hygienic procedures.

 

1) Check Industry Standards

 

Ensuring sterilization starts with picking the right manufacturing company, and you’ll want to be sure they take the matter of contamination seriously. To start, check their commitment to quality management and industry standards.

 

All product manufacturing companies must follow industry standards like International Organization for Standardization (ISO) and Food and Drug Administration (FDA). Before you work with a manufacturing company for your medical application, look at their certifications.

 

For example, ISO 13485 specifies requirements for a quality management system where a company demonstrates it can provide medical devices and related services to consistently meet customer and regulatory requirements. ISO 9001 focuses on meeting customer expectations and continually delivering satisfaction, plus reflects constant improvement from the company.

 

If the manufacturer you are interested in using does not have any of the above standards, then you may want to ask them why.

 

Here at AIP Precision Machining, we have been successfully audited by some of the most stringent OEMs in the orthopedic and medical device industries, and are ISO 13485:2016., ISO 9001:2015 , and FDA registered.

 

2) Plastic Machining isn’t Metal MachiningMetal vs Plastic Machining

 

Be wary of any manufacturer who machines both plastics and metals in the same facility. The tiniest sliver of metal embedded in a plastic part can have widespread ramifications, such as an unexpected electrical problem in the medical device.

Additionally, it’s common for metal machining companies to use oil-based cutting fluids. Any equipment that machines metal, then, can contaminate your plastic parts with those fluids. Many plastic materials are especially sensitive to those petroleum-based liquids, and they can degrade when in contact with them; others are hydroscopic and will absorb the oils.

 

It should be noted that plastic parts manufactured using equipment that machines metal parts will not meet FDA-approval, or the other industry standards mentioned above. The safest way to avoid this is to hire a plastics expert, not a metal machining company.

 

AIP takes the matter of sterilization seriously, and ensures the highest level of sanitation down to the sub-molecular level for its products. By designing, stress relieving and machining only plastics, AIP significantly reduces the threat of metallic cross contamination and therefore allows for the highest hygienic products possible.

 

3) Look for Experience

 

The most important factor to take into account overall is experience. Your supplier should be familiar with the types of polymers and composites you need machined, and should additionally know the best machining process for your application.

 

For the medical industry, you want to know that your manufacturer is experienced with the complex needs of your applications. For example, if your components are going to come into contact with body tissue or fluids, then they must be biocompatible per ISO 10993.

 

Which is to say: If you’re machining implants, your plastics will require different needs than if you’re machining reusable surgical instruments. Both require, however, careful attention to detail. A surgical instrument must be designed with sterilization compatibility for regular cycles in mind, while an implant requires biocompatibility to be safe for use.

 

Be sure that your manufacturer is familiar with the processes that come with your application, and check that they’ve done it before.

With 35+ years of experience, AIP is well acquainted with precision machining for the medical industry and guarantees careful material selection and processing for your medical applications.

 

The #1 Best Way to Avoid Contamination?

Overall, the best thing you can do to avoid contamination is to hire a plastic manufacturer with the experience and the credentials to complete your project to the highest standards of quality possible. Keeping the above three factors in mind will help you do just that.

 

To ask about AIP Precision Machining’s capabilities for precision machining medical applications, please contact us.

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Thermoplastics in Medical ApplicationsWhen it comes to choosing a thermoplastic material for your medical applications, product durability, agency approval, biocompatibility and cleanliness aren’t just desirable—they’re essential. Beyond even that, though, a host of other factors must be considered when determining which high-performance plastic or composite material to use for an implant, orthopedic surgical guides, body fluid contact components, spinal devices, or surgical instruments. Medical product applications are becoming more and more advanced due to critical performance and alignment requirements as well as the need for radiolucency to support minimally invasive procedures. Therefore, the choice of plastic material specified for a given application as well as a manufacturer with battle-hardened experience is the critical first step in your decision process.

 

AIP has well over three decades of expertise with thermoplastic materials, and understands how plastics react when machined. We are one of a very select few companies able to hold incredibly tight tolerances in plastic parts. AIP has been successfully audited by some of the most stringent OEMs in the orthopedic and medical device industries, and are ISO 13485:2016, ISO 9001:2015 and FDA registered.

 

Here are just a few initial, yet critical considerations that take place when we determine the thermoplastic to best suit your particular medical or life science application.

 

Biocompatibility

 

If your components are going to come into contact with body tissue or fluids, then those components must be biocompatible per ISO 10993; if the manufacturer you are working with is not familiar with this standard and cannot provide you with this certification for the material, then move on to a manufacturer with medical industry knowledge. This is especially true if the polymers will undergo long-term contact with body tissues and fluid, such as when used as an implant. Polymers can undergo degradation due to biochemical and mechanical factors in the body, which results in ionic attack and formation of hydroxyl ions and dissolved oxygen. In turn, this can lead to tissue irritation, inflammation, and other reactions with body-like corrosion, wear and potential death. Due to this, very few polymers are available as medical grade for medical application, with an even smaller amount considered a candidate for implants.

 

AIP Precision Machining includes machined PEEK implants among its many capabilities for custom medical applications precisely due to PEEK’s biocompatibility. PEEK is also inert to body fluids, making it exceptional for bone surgery as well as areas of traumatology and orthopaedics. Another valuable trait of PEEK is that this material has a very similar modulus to that of human bone. The similar modulus to bone reduces the potential for stress shielding. Stress shielding is common with metallic implants whereby the metal implant and bone do not become one nor work in unison to form a single construct. By using Invibio’s PEEK Optima or Solvay’s Zeniva PEEK as an implant material, the bone and PEEK will grow into a single construct mimicking the bone’s natural tendency to repair the fracture or fusion.

 

Sterilization Compatibility

 

Plastics react differently to various sterilization methods, and if a product is not a single-use device and involves body tissue and fluid contact, then it may regularly undergo sterilization. The usual sterilization methods are radiation (gamma/e-beam), chemical (ETO), or autoclave (steam). ETO is rarely a concern, but radiation and autoclaving both require resistance from plastics. Several radiation resistant thermoplastics are:

 

 

When it comes to autoclaving, the best polymers for resistance are PPSU and PEEK, with both capable of handling exposure to thousands of cycles.

 

AIP takes the matter of sterilization seriously and ensures the highest level of sanitation down to the sub-molecular level for its products. By designing, stress relieving and machining only plastics, AIP significantly reduces the threat of metallic cross-contamination and therefore allows for the highest hygienic products possible.

 

Chemical Resistance

 

A polymer can be exposed to plenty of disinfection chemicals in a hospital. That exposure can deteriorate plastics, and negatively affect part performance. Polymer chains can be affected by isopropyl alcohol, bleaches, and peroxides. Semi-crystalline polymers like PP, PE, PTFE and PEEK can be expected to have better chemical resistance than amorphous polymers like ABS and PC. However, it’s important to check the performance to be certain of resistances, as exceptions can take place.

 

With decades of experience working with thermoplastics, AIP guarantees extreme chemical resistance in its material selection for your medical applications.

 

Electrical & Thermal Properties

 

Dielectric strength and thermal resistance are necessary for medical devices enclosed in areas that require high heat resistance. Thermoplastics such as PC (Polycarbonate), PC blends, PPS (polyphenylene sulfide), PEI and PS (polystyrene) blends have electrical properties that perform well, some even at elevated temperatures.

 

AIP’s material library includes thermoplastics that exhibit extreme thermal performance, and we are familiar with machining them in applications for medical life & sciences.

 

Mechanical Properties

 

Properties such as tensile and compressive strength, wear resistance, impact strength, and bending stiffness also must be considered when choosing your thermoplastic. Engineered thermoplastics such as PC, PEEK, PPSU, POM, PEI and reinforced grades of these same materials (glass, aramid and carbon fillers) perform very well in this respect, making them ideal for a variety of climate conditions, such as during transportation.

 

AIP provides thermoplastics that show extreme wear resistance, x-ray visibility or invisibility and high structural performance.

 

These are just a few of the many considerations that take place when choosing the right plastic for your medical applications. AIP offers you our full material consultancy from concept to completion, so that together, we find the right thermoplastic for your projects.

 

 

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We can’t wait for the biggest Medtech event on the East coast: MD&M East! We’ll be there, ready to talk about implantable devices, medical material components and more. Visit us at our Booth #2370 to learn about our unmatched precision in plastics manufacturing.

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AIP Precision Machining recently attended the 2017 American Academy of Orthopedic Surgeons (AAOS) Conference in San Diego, California, and had a blast reconnecting with old friends and getting to know new members within the orthopedic field.

 

The AAOS sets out to bring together medical professionals and exhibitors, allowing attendees to meet with their peers and have the opportunity to learn about the latest in medical trends and advancements. It provides a venue for all members of the orthopedic community to gather: attendees range from basic component suppliers to implant designers, surgeons and even patients.

 

AIP has been attending the AAOS for over a decade now and every year we bring technically advanced products to the show. This year, we showcased our new PREFORM technology, which was a huge hit as trends are moving more and more toward production efficiency and cost reduction.

 

PREFORM technology weaves PEEK plastic fibers together, molding trauma guides and reusable nailing instruments together to form a one-piece, complex instrument. Combining creative radiolucent guide design with added strength and cost-efficiency, many new and existing OEMs were very excited by the range of opportunities this machinery presents.

 

Another impressive theme that kept popping up during the show was a major push to move the surgery market towards robotic control. Several new OEM projects already have projects in development that rely solely on robots to prevent human error and increase surgery success rates.

 

Looking to 2018, we can’t wait for another successful AAOS Meeting—New Orleans, here we come!

 

If you’d like more information about the creative manufacturing and materials solutions AIP can provide you, give us a call at 386-274-5335.

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