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Implantation Testing

Implantation testing is one of several biocompatibility tests, reserved for medical devices that are placed in the body’s internal tissue, bone or cavities. As such, it is an important process for many life-supporting devices, and determines whether the implant causes harmful changes to nearby tissue or bone. Part of the implantation test involves histopathological analysis, so research is done at the cellular and tissue level.

The specifics of implantation testing are defined in ISO 10993, along with other biocompatibility tests that medical device manufacturers use.

Why is Implantation Testing Needed for Medical Devices and Plastics?

If a substance is toxic, it may cause changes to nearby cells long before it produces any symptoms. These changes indicate that the substance could be causing harm, and implantation testing looks for these changes. This gives medical researchers advance warning that a device is not biocompatible, even if no other signs of toxicity or harm are present.

It is critical to note these signs because once an implant is placed, often is a permanent implant or it may be years before it is removed. Implantation testing ensures surgical teams do not have to subject their patients to risky revision procedures.

Which Medical Devices Require Implantation Testing?

Only some devices must pass through implantation testing, depending on how they contact the body and for how long. Here is how ISO 10993 categorizes devices, so manufacturers know if their device requires implantation testing:

  1. Surface device – Surface devices only make contact with external tissues, including intact or breached skin, or mucosal membranes. They include things like latex gloves, bedpans, compression bandages, some dental devices, dermal patches and a variety of intraintestinal devices, like gastroscopes, colonoscopes and stomach tubes.
  2. External communicating device – External communicating devices either make contact with the blood path or are connected, to some extent, to the body’s internal tissues. They may not make direct contact, but can affect the health of internal tissues. Some of these devices include vascular catheters, many forms of medical tubing, surgical instruments and temporary life-supporting technologies, like some pacemakers and oxygenators.

  3. Implant device – Implant devices are placed in the body and maintain direct contact with the body’s internal tissues. Some implants are temporary, but many remain in the body for years or permanently, so they undergo the most stringent testing under the ISO 10993 standard. Some implant devices include artificial joint or heart valve replacements, orthopedic pins and plates and some catheters.

In addition to the above, many PEEK devices, including lumbar and cervical cages, are implants intended to remain in the body forever. As such, they must undergo implantation testing.

Medical devices are further categorized by the duration of contact and placed in one of three classes. They include:

  • Class A – Devices that maintain contact with the body for less than 24 hours.
  • Class B – Devices that maintain contact between 24 hours and 30 days.
  • Class C – Devices that maintain contact for more than 30 days.

According to ISO 10993’s guidelines, all implant devices that contact the blood must undergo implantation testing. Further, all Class B and Class C implants that contact bone or other internal tissues must also pass through testing.

How Do Researchers Perform Implantation Testing?

During implantation testing, a sample of the device is placed in an animal subject, in contact with the tissues the device would contact in a human patient. This could be under the skin, inside the muscle, in contact with bone or anywhere else the implant is expected to go.

Once the implants are placed, the subjects are monitored for several days. Following this, tissue samples are taken from the implant sites and studied by a pathologist under a microscope. This part of the process is similar to what pathologists do with biopsy samples. They look for any changes in nearby cells and tissues, including changes to the cell shape or count, or changes to the cell’s internal structure. These changes are noted in a histopathological report, created by a pathologist specialized in the tested tissues. Additionally, regulatory agencies like the FDA sometime require or are least prefer to see longer term, many weeks, of implantation in an animal to evaluated the overall performance of the device.

Why is the ISO 10993 Standard Important for Medical Device Manufacturers?

Medical device manufacturers reference the ISO 10993 standard when organizing testing because it is the most current and comprehensive resource for biocompatibility research. Its recommended testing guidelines are supported by the FDA and by regulatory agencies around the world, so manufacturers strive to attain ISO 10993 compliance.

Most of ISO 10993’s testing procedures have already been in use for decades among medical researchers, but beyond these procedures, ISO 10993 also helps manufacturers produce usable samples for testing. For example, before a device sample can be used for biocompatibility testing, it must pass through the same processing steps that the final produce would go through, including things like sterilization, packaging and labeling.

Implantation testing is only recommended for devices placed in contact with the body’s internal tissue, bone or cavities. These devices, like PEEK spinal cages, either relieve debilitating pain or are critical life-preserving devices, so their effects on the body must be studied in detail. Implantation testing, because it includes histopathology studies, gives researchers this needed, up-close look.

Injection Molding and Plastics for Medical Devices

What to Consider When Injection Molding PEEK for Medical Devices

The injection molding process allows device manufacturers to quickly convert PEEK into complex component designs. This means injection molding is effective for an array of medical devices, whether they are used inside or outside the body. Many of those devices are used in cardiovascular, trauma fixation, dental, spinal and arthroscopic applications. PEEK can also be injection molded into components for surgical instrumentation and laboratory equipment.

There are several advantages to injection molding medical plastics like PEEK. These advantages include:

  1. High production volumes – The injection molding process only takes seconds, and most of that is dedicated to cooling the material. This quick conversion time means larger production runs are possible, and this is a major reason why medical plastics are replacing metal components in single-use instruments.In some cases, the device’s design is such that it can only be produced by adhering multiple molded components together. These components can be molded in tandem, though, so the process remains time-efficient.
  2. Cost efficiency – Injection molding is also very cost efficient, especially when used for larger production runs. The process requires the production of a mold, which makes up the bulk of initial costs, but the cost to produce each part is much lower compared to machining and other component production techniques. If the production run exceeds a few hundred components, then injection molding is usually the cost-effective choice.

Injection molding is especially useful for surgical instruments and equipment, as medical facilities are tasked with controlling hospital-acquired infections, or HAIs. According to the CDC, HAIs account for nearly 100,000 deaths every year, and 22 percent of them start at the surgical site. Single-use devices help hospitals control infections by switching in a new, sterile instrument every time a different patient is treated. The cost effectiveness of injection molding medical plastics makes this possible.

There are, however, challenges that must be solved when injection molding medical plastics, including PEEK. For example:

  1. Process safety – Medical plastics and the processes they are subjected to must be verified as safe and biocompatible. PEEK’s biocompatibility has been proven using the testing protocols outlines in ISO 10993. However, it’s not enough for a polymer converter to utilize medical grade plastic because the converter’s processes must also be verified.This is done through a number of standards, but one of the most relevant is ISO 13485, which is widely considered to be the standard for medical device manufacturers and the processes they use. The ISO 13485 standard, like the ISO 9001 standard it is based on, is focused on the manufacturer’s quality management system (QMS), but it adds important language on risk management, design controls, inspections and traceability. The converter’s QMS is a critical document, formalizing its procedures and policies for achieving its quality and safety goals. With a QMS, manufacturers can quickly and reliably modify their processes to improve output.ISO 13485, being specific to the medical industry, also contains standards on proper sterilization and device handling to prevent contamination. If adhesives or other materials are needed to produce the final component, these must also be accounted for.

    Among the most important parts of ISO 13485, though, is process validation. Process validation is needed to ensure the medical plastic remains safe even after manufacturing.  A validated process, then, is one that reliably produces a safe, quality component. This is a critical part of the ISO 13485 standard because it’s generally not possible to test a manufactured medical component without destroying it.

    Patient safety is paramount, so medical device manufacturers are expected to attain and maintain ISO 13485 certification.

  2. Process control – PEEK is a high-performance polymer that possesses excellent thermal resistance. Compared to other medical plastics, then, it must be subjected to extremely high temperatures to allow for proper processing. Depending on the size and shape of the injection molding barrel and the grade of PEEK being converted, temperatures inside the barrel may range between 650- and 750-degrees Fahrenheit. That’s a large range to cover, so it may take some time for a converter to find the temperature that works best for their production needs.Further, temperature control is also needed inside the mold, usually between 170 and 400 degrees Fahrenheit, and this includes the surface temperature of the mold. This elevated temperature prevents sudden cooling, which can result in the PEEK transitioning to an amorphous state and thereby affecting the physical properties of the component.Pressure control is also an important processing variable during the injection molding process that is essential for consistent, high quality components.  Advanced molding technology utilizing in mold cavity pressure transducers are an important capability to address consistent processing of high intricate components and devices.

    Experienced polymer converters are experts at controlling multiple processing conditions, which ensures consistent output quality and reduced waste.

  3. Equipment cleanliness – PEEK is processed at temperatures that cause other medical plastics to degrade, so the injection barrel must be meticulously cleaned to prevent this contamination from affecting the finished component. Any contamination could lead to hundreds of pounds of useless PEEK – which would be an expensive mistake. If that contamination makes it to the final product, it may compromise its properties and potentially be a safety concern.To prevent this, the injection equipment must be cleaned thoroughly before PEEK is injection molded. This usually requires personnel to remove the screw and be thorough with all cleaning processes. Further, any other surface that comes in contact with the PEEK, like hoppers and drying ovens, must also be kept clean to minimize the risk of contamination.

There are several advantages and challenges associated with injection molding of medical plastics like PEEK. An expert converter is familiar with all of them, so they can make the most of the process.

 

FAQ

Q. Is injection molding or machining better for medical plastic?

A. Injection molding offers significant cost and time efficiency benefits when used in large production runs. Machining is cost-effective for small production runs (usually a few hundred components or less) and offers superior tolerances.

Q. What certification is important for medical device manufacturers?

A. ISO 13485 is built on the ISO 9001 framework but adds industry-specific language for medical device manufacturers. ISO 13485 compliance can help a medical device manufacturer to be in compliance with FDA and European medical device quality standards.

Q. What advantages does PEEK bring to medical devices?

A. As a high performance polymer, PEEK possesses several advantages. It is biocompatible, radiolucent and has excellent material and mechanical properties. When implanted, it can provide a flexural modulus similar to the body’s cortical bone, which makes the material a frontline choice for spinal implants.

Medical Plastics

Medical plastics have been adapted for use in many healthcare fields, including spinal fusion, trauma fixation, orthopedics, cardiovascular, dentistry and prosthetics. Medical polymers are also used in surgical instrumentation and laboratory equipment, so nearly every hospital procedure involves plastic.

Some of these medical plastics include:

  • Polypropylene (PP)
  • Polyethylene (PE)
  • Polystyrene (PS)
  • Polyvinyl chloride (PVC)
  • Polyurethane (PU)
  • Polyethylene terephthalate (PET)

Polyetheretherketone, or PEEK, is also used in medical applications, including surgical procedures like cardiovascular device delivery and trauma fixation. Its elite array of material properties, on top of its complete biocompatibility, has also allowed PEEK to emerge as the frontline choice in spinal fusion procedures, replacing titanium and allograft (donated) in this regard.

What makes PEEK the perfect medical plastic?

PEEK is trusted in some of the most demanding medical applications possible. There’s several reasons for this, including:

  1. An ideal flexural modulus – Compared to metal, PEEK is a much more flexible material and simulates the flexural modulus of natural cortical bone well. This means PEEK will share weight instead of bear it, and will flex and bend more like bone. These are all excellent properties to have in an implant designed to facilitate bone healing and osseointegration.

    PEEK’s cortical-bone like modulus is what inspired medical researchers to consider it for spinal fusion procedures. Its ability to share weight means it will not cause stress shielding in nearby native bone. Stress shielding occurs when bone tissue is no longer subjected to constructive, loadbearing stresses. It results in bone mineral density, similar to the atrophy in muscle tissue if it is not stimulated regularly. This could lead to structural changes in the bone that make it vulnerable to fractures.

    Stress shielding is a major problem for titanium implants, which bear so much weight that they can cause subsidence in native bone. A study published in the European Spine Journal confirmed this. It found that titanium implants were associated with subsidence rates in excess of 20 percent, while subsidence rates with PEEK implants were less than half of titanium’s. The polymer’s optimal modulus is the reason for this.

  2. Complete radiolucency – In its unfilled state, PEEK is a radiolucent material during medical imaging. In other words, PEEK is invisible when imaged using MRI, CT or X-ray technology, so it will not interfere with post-surgical imaging and assessment. This is especially important for spinal implant procedures, where monitoring bone growth post-operatively is essential.
  3. Modifiability – Polymer function can be augmented with various additives, and PEEK is no different. Two notable additives regarding PEEK are chopped carbon and barium sulfate, and when mixed with chopped carbon (CFR PEEK), the polymer is imparted with additional stiffness and strength. CFR PEEK is ideal for applications where additional loadbearing is required, like orthopedic, trauma fixation and prosthetic procedures.

    PEEK’s radiolucency can also be modified with the use of barium sulfate. Barium sulfate increases the radiopacity of the image, allowing for additional contrast or needed shadowing. This is advantageous for spinal fusion procedures, and gives surgical teams the ability to track the implant’s position, which is critical for early detection of any complications.

  4. Biocompatibility – PEEK, like all medical materials, has passed the most rigorous biocompatibility testing protocols available. Biocompatibility testing is done in accordance with the FDA and other global regulatory bodies, and checks for signs of cytotoxicity, genotoxicity and immunogenic response. These tests are done in many ways including with chemical analyses and with animal tissues, including tissues that PEEK implants interface with in the human body. The results have been uniformly positive. Further, PEEK implants have been placed in patients for decades, and patient studies have confirmed their effectiveness and safety.
  5. Future potential – PEEK has already built an impressive performance record over more than 20 years of use in patients, but there’s still plenty of research and development to be done with the material. The early returns on this development are already available in the form of improved spinal implants. Some of these implants, for instance, are designed with microporous structure and mixed with materials like hydroxyapatite and zeolite, which improve the polymer’s osseointegrative potential. These implants have demonstrated superior bone-in growth, which means they fuse securely with native bone, a critical feature of spinal implants.

    Research into PEEK covers several medical fields, and the polymer’s excellent processability means it can be developed in a variety of forms for a variety of roles. PEEK is already featured in spinal fusion cages, cardiovascular delivery devices, trauma fixation hardware, ablation catheters, dental implants and frameworks, and many other medical applications. PEEK’s untapped potential means it will likely be a frontline choice in several additional medical fields before long.

Medical plastics have helped physicians and surgeons do their job better for decades, and with the introduction of high-performance polymers like PEEK, they are quickly transforming medicine, for the better.

Custom Extrusion of Medical Plastics

Medical thermoplastics like PEEK are compatible with several conversion processes, including custom extrusion. During extrusion, the plastic is melted and converted into a continuous, uniform segment that is suitable for several medical applications. Extruding PEEK, however, is a challenge that few polymer converters are capable of handling. It takes perfectly calibrated extrusion equipment, PEEK conversion experience and a commitment to quality.

Drake Medical Plastics can provide all three, with a 12,000 square foot facility dedicated to high-performance polymer conversion.

Why should medical facilities consider medical plastic extrusion?

Extrusion is the ideal conversion process when long, uniform polymer segments are required. Extruded PEEK segments are a viable alternative to glass, aluminum or steel, as they possess excellent column strength and tensile strength. PEEK also has an impressive flexural modulus, so it’s flexible enough to allow for precise navigation, but stiff enough to resist deformation. PEEK is also a proven biomaterial, with long-term biocompatibility that means it can be safely implanted.

With these combined properties, PEEK tubing is a frontline choice for catheter tubing and cardiovascular delivery devices. Extremely thin PEEK tethers are also found in some advanced surgical procedures, including the Less Invasive Ventricular Enhancement (LIVE) procedure.

Why Medical Facilities Need An Experienced Converter For Custom PEEK Extrusion

High performance polymers like PEEK require specialized experience during the conversion process. Though PEEK is converted using some of the same methods other polymers are subjected to, additional considerations must be made when handling the polymer.

PEEK readily reacts to heat, so thermal control is a major part of the PEEK extrusion process. Though it has one of the highest melting points of any polymer (300 degrees Centigrade, or 572 degrees Fahrenheit), PEEK component quality is heavily dependent on keeping the extrusion temperature range steady.

There isn’t an ideal temperature for PEEK extrusion because it depends on the extruder’s design and size. One extruder may optimally convert PEEK at 675 degrees Fahrenheit, while another may perform optimally at 750 degrees Fahrenheit. There isn’t a formula to follow, so it can take a while before an inexperienced converter has an extruder that can properly handle PEEK.

Once PEEK reaches its melting point, its molecular weight starts dropping. If it drops too much, this may compromise the polymer’s properties, so experienced converters prioritize minimal dwell time (how much time the polymer spends in the extruder). Minimal dwell time, though, is only possible if the extruder’s heat profile is precisely controlled. That, again, takes an experienced PEEK converter.

Further, PEEK converters must keep their extrusion equipment as clean and polished as possible, or abnormalities (termed gels) may appear. Gels emerge when molecular weight is uneven across the extruded product, and this can lead to cosmetic or functional issues. For example, if gels form on the outside of the tube, it may result in dimensional changes that could cause discomfort or tissue damage. An experienced PEEK converter has methods in place to prevent or remove these gels, and those methods are typically proprietary.

PEEK also has a tendency to harden quickly when temperatures drop just a bit, and this can affect costs and conversion times. If too much material is left in the extruder once it cools, it will be difficult to remove it, adding to processing times. That material must also be disposed of, so if a converter isn’t running its processes efficiently, conversion will be much more expensive.

PEEK’s final properties are also affected by how long it is allowed to cool, or if it is allowed to anneal. During annealing, the polymer must be kept in its glass transition phase, which starts at 289 degrees Fahrenheit. Precise processes must also be in place to maintain this.

Custom extrusion of medical plastics like PEEK is complicated, with many potential pitfalls. That’s why medical facilities often look to experienced, certified converters to do the job.

What certifications are important for a PEEK converter?

Medical plastics and devices are covered under several standards, including standards published by the International Organization for Standardization (ISO) and the FDA. Some of those standards and processes relevant to medical device manufacturers and polymer converters include:

  • FDA registration – Every year, medical device manufacturers must register their facilities with the FDA. To maintain FDA registration, the manufacturer must pay a fee and provide relevant FDA premarket submission numbers for any products that require premarket approval. Nearly all implantable devices require premarket approval, so PEEK converters are required to verify their product and process quality and safety every year.

    Device manufacturers are also required to list all medical devices produced at their facilities, so if there are public health emergencies that require immediate attention, the FDA knows where devices are being made.

  • ISO 9001-2015 certification – The ISO 9001 standard is ISO’s general standard for process and quality management. It isn’t specific to the medical device industry, but it is widely adopted because it adds needed accountability, management involvement and regulatory compliance. To attain 9001 certification, a manufacturer must implement a Quality Management System (QMS) that details the above, as well as processes used to continuously improve the QMS. The goal, then, is to put into place a system for steady, responsible process improvement that allows for rapid corrections should they be necessary.

    ISO 9001-2015 is the newest iteration of the standard and streamlines the language and structure for easier compliance with other standards.

  • ISO 13485 certification – ISO 13485 certification addresses medical device manufacturers in particular, making it an extremely important certification for the industry. ISO 13485 builds on ISO 9001, adding requirements for design control, inspection, traceability and risk management. Further, ISO 13485 addresses work environment controls, as well as the use of preventative and corrective actions.

    For example, ISO 13485 contains standards on proper device sterilizing, proper device handling (to prevent contamination) and how to validate the process. Process validation is particularly important, as it is generally impossible to test a device’s properties without destroying that device. A validated process is one that accounts for both the material’s properties and the manufacturing processes that material is subjected to. If a process is validated, that means it produces a device or component that consistently meets safety and quality standards. PEEK converters must be able to verify these validated processes when necessary.

Custom extrusions of medical plastics is an involved process that requires experience, esoteric knowledge and constant improvement. If a PEEK extruder can offer those, they can also offer medical components that meet the industry’s most demanding standards.

 

 

 

 

 

What is a PEEK Lumbar Cage Used to Treat?

Lumbar cages are spinal implants used in patients suffering from chronic or degenerative back conditions, including:

  • Spinal stenosis
  • Degenerative disc disease
  • Scoliosis
  • Spondylolisthesis
  • Fractures, tumors or infections

While some people with the above conditions may not experience symptoms, some experience debilitating pain and loss of flexibility. For these patients, a PEEK lumbar cage can provide relief.

Why is PEEK an Ideal Biomaterial for a Lumbar Cage?

PEEK’s first medical application was in spinal fusion, where it has been used as an interbody implant for roughly two decades. PEEK has been featured in most forms of spinal fusion procedures, including anterior cervical discectomy and fusion (ACDF), anterior lumbar interbody fusion (ALIF) and posterior lumbar interbody fusion (PLIF). Since its introduction, the high-performance polymer has rapidly become the first choice in lumbar cages for several reasons, including:

  1. An ideal flexural modulus – In its unfilled state, PEEK has a flexural modulus that is similar to cortical bone. As such, it isn’t a loadbearing material, but a load-sharing one. Because it behaves like cortical bone, it’s easier for surgical teams to anticipate the implant’s performance and secure a precise fit.More importantly, PEEK’s bone-like modulus means it won’t rob constructive stresses from nearby bone, which results in stress shielding and, potentially, subsidence. A study published in the European Spine Journal confirmed this and showed that subsidence rates associated with titanium implants was at or above 20 percent. By contrast, PEEK spinal implants demonstrated subsidence rates less than 10 percent.

    This may be why the same European Spine Journal study found that patient outcomes were better with PEEK lumbar cages, compared to titanium cages.

  2. Pure radiolucency – Radiolucency (transparency to imaging techniques) is valued in fusion cages, as it ensures the implant will not interfere with attempts to image the spine. PEEK’s pure radiolucency is one of its most important features. PEEK is completely invisible on X-rays, CT scans and MRIs, so surgical teams can spot potential complications before they manifest, and assess how the implant is fusing with native bone.In applications where radiolucency is not preferred, the polymer can be mixed with additives including barium sulfate to add in image contrast. The barium sulfate can impart this contrast without compromising the polymer’s properties.
  3. Total biocompatibility – PEEK has produced excellent outcomes in patients for 20 years, but long before it achieved this success, it was thoroughly tested for biocompatibility. The FDA requires implantable materials to pass through the most demanding safety assessments, and in the U.S., this includes successfully completing multiple tests like ISO 10993 and USP Class VI testing. PEEK is one of the few polymers that has done so, confirming its safety in implant procedures.ISO 10993 is considered the most comprehensive approach to biocompatibility testing and is recognized as such by the FDA. This is why the FDA considers ISO 10993 compliance for premarket approval purposes.

    The ISO 10993 standard includes 20 sections, and several are relevant to lumbar cage manufacturers. This includes recommended testing procedures for cytotoxicity, system toxicity and dermal sensitization. Risk management is also a priority throughout the process, so implants must be studied for any leachables or extractables.

    All testing must be done with a sample representative of the final implant. This means the sample must be converted, processed, packaged and sterilized like an implant intended for the patient. The exact testing procedures are derived from standards produced by other organizations, so they are proven to be effective.

    During USP Class VI testing, the biomaterial is introduced to animal tissues. Testing protocols include a systemic injection test, an intracutaneous test and an implantation test. The goal of biocompatibility testing is to verify that the material is not cytotoxic, genotoxic or immunogenic, and these tests confirm it using a variety of tissues. This includes the tissues that will interface with the implant.

  4. Processability – PEEK’s processability has made it a favored material among engineers, as it can be converted into an incredible array of components. This processability advantage is also relevant in medicine, where PEEK can be machined to extremely tight tolerances. This means a reliable implant, and because PEEK is endlessly processable, it can be sized to fit a patient’s anatomy. Current generation PEEK spinal implants can already be sized up or down to fit different patients, without loss of implant performance.When processed by an experienced PEEK converter, the polymer is also easier to process than metals.

The above advantages have propelled PEEK to frontline status among interbody fusion cages, and with PEEK, the future of lumbar cages is even brighter.

The Present and Future of PEEK Lumbar Cages

Though PEEK has already developed an impressive track record in medicine, it is still a relatively new biomaterial. That means there is plenty of potential left to unlock with the material.

One active area of research is improving osseointegration between implant and native bone, and current generation PEEK spinal implants are already showing the fruits of this research. For example, some PEEK implants are now designed with microporous structures, so the bone is encouraged to lock tightly into the implant and integrate in a stable fashion. Additional materials can also be mixed with PEEK to encourage this bone-in growth as well.

For instance, PEEK lumbar cages augmented with hydroxyapatite or zeolite can encourage bone growth by inhibiting osteoclast activity, which results in bone resorption. Several implants featuring these materials have already been studied and research confirms that they stimulate better osseointegration.

The future of PEEK is bright, but so is the present. With compelling advantages like pure radiolucency, a bone-like modulus, excellent biocompatibility and versatile processing options, PEEK lumbar cages are an excellent choice in the present, and the most promising biomaterial well into the future.

What Is A Cervical Cage

A PEEK cervical cage is an interbody spinal implant used during anterior cervical discectomy and fusion (ACDF). It provides a stable surface for bone to fuse to and ensures a secure lock between implant and vertebrae. Most cervical cages are made from high performance biomaterials like PEEK, because the implant is subjected to constant compressive forces, and because the implant is permanent.

Until about 20 years ago, titanium was the primary choice for cervical cages, but the emergence of PEEK has supplanted it. Now, PEEK is the frontline choice and is being improved upon all the time.

Why is PEEK the right choice for cervical interbody implants?

PEEK was introduced to medicine in the form of an interbody cage, used in ACDF procedures. From the beginning, it was clear that PEEK was perfectly suited to this role, for several reasons. Some of them include:

  1. A favorable flexural modulus – Interbody fusion cages provide an interface for two vertebrae to fuse together, so ideally, the cage would behave like bone too. That’s what PEEK does because it possesses an similar modulus to cortical bone. PEEK bears weight like bone, flexes and bends like bone and its tension strength is similar to bone’s as well. With these attributes, PEEK behaves predictably once implanted.

    What is perhaps more important, though, is that this modulus supports proper bone healing. PEEK is a load sharing material, so it will not rob native bone of necessary, bone-stimulating stresses. That means less stress shielding and less subsidence, which is a noted problem with titanium cages.

    If additional stiffness is required, PEEK can be mixed with carbon fiber to provide the required increased stiffness.

  2. Pure radiolucency – PEEK’s other sizeable advantage is its pure radiolucency, which means it is completely invisible on X-rays, CT scans and MRIs. This degree of radiolucency is essential for ACDF procedures, as it ensures surgical teams can track how well it is integrating with native bone. If there are emerging complications, PEEK’s radiolucency ensures they can be caught early and mitigated.

    PEEK’s radiolucency can be modified, if needed. In its natural, unfilled form, PEEK possesses pure radiolucency. When mixed with additives such as barium sulfate, additional image contrast can be imparted into the polymer. This is usually driven by the type of implantable application and is sometimes used for spinal fusion procedures, but it has higher usage in other implantable application areas.

  3. Complete biocompatibility – All implantable biomaterials must pass through the most rigorous safety testing available. In this case, that means the U.S. Pharmacopeia’s (USP) Class VI testing protocols and a number ISO standards, including ISO 10993.

    ISO 10993 is the medical device industry’s leading biocompatibility testing standard, and is recognized by the FDA and most European nations as such. The newest version of the standard was published in 2018, so it includes updated research on proper biocompatibility testing procedures.

    Though ISO 10993 contains 20 sections, only a handful are relevant to cervical implant manufacturers. Among them are sections on cytotoxicity, sensitization and systemic toxicity testing. The ISO 10993 also details how manufacturers are to sample their implants for testing. During testing, the test sample must be identical to a final version of the implant. In other words, the test sample must be converted, processed, sterilized and packaged using the same methods as the finished implant.

    The testing procedures on permanent implants, like a cervical cage, are the most rigorous. Further, ISO 10993 derives its testing recommendations from respected standards and organizations, so they are the best procedures available to researchers.

    During USP Class VI testing, the biomaterial is tested in animal tissues, including tissues that the implant is expected to interface directly with. During this testing, researchers are looking for cytotoxic (harms cells), genotoxic (harms the cells’ genetic material) or immunogenic (produces an allergic reaction) properties. PEEK is one of the few materials to earn excellent marks during USP Class VI testing, and it has been used with confidence in thousands of patients since 1999.

  4. Processability – Like other polymers, PEEK gives device manufacturers a lot of options to work with. In most cases, PEEK is machined using precise CAM and CAD processes, and because it is a high-performance polymer, PEEK withstands machining with no loss of material properties. This takes a skilled PEEK processor, though, because something as subtle as improper fiber orientation may compromise the material.

    In the hands of an experienced processor PEEK can be machined to extremely tight tolerances, even when manufactured with complex shapes. PEEK also can be extruded as well into long lengths of stock shapes (rods) and medical tubing, which is particularly useful in cardiovascular applications.

    Regarding cervical cages, PEEK’s processability ensures it can be machined to fit the patient’s anatomy to precision. Manufacturers are creating implants that can be sized with no loss of function.

  5. Emerging potential – PEEK has only had 20 years to make an impact on medicine, so there is still plenty of research to be done on the polymer. Every new generation of PEEK implant brings better results and additional features. For example, PEEK cervical cages are now designed with materials that enhance bone-in growth and produce better integration between implant and native tissue. Hydroxyapatite and zeolite are two such materials, and many new implants are also manufactured with microporous designs that encourage bone to grow into the cage.

    Research is underway on PEEK implants manufactured with titanium coatings and other surface modifications. These could provide additional solutions for better osseointegration.

PEEK cervical cages are a frontline choice in several spinal fusion procedures, and with 20 years of successful use in patients, it’s a well-deserved position. The future of PEEK implants is just as bright as the present, with advanced interbody fusion cage designs demonstrating even better osseointegration and patient outcomes.

What Are Biocompatible Polymers?

Biocompatible polymers are medical-grade plastics that are safe to use in medical applications. Some of these polymers can be implanted for many years without fear of causing a toxic or allergic reaction. This degree of safety, paired with polymers’ versatility and durability, means biocompatible polymers are a promising area of medical research.

Biocompatible polymers include:

  • Polystyrene (PS)
  • Polypropylene (PP)
  • Polyvinyl chloride (PVC)
  • Polyethylene (PE)
  • Polyurethane (PU)
  • Polycarbonate (PC)
  • Polyethylene terephthalate (PET)
  • Polyetheretherketone (PEEK)

These polymers are featured in an array of medical devices, instruments and components, from single-use medical tubing to highly sophisticated spinal implants.

How are biocompatible polymers used in medicine?

Biocompatible polymers are rapidly replacing metals throughout medicine, especially where it concerns PEEK. PEEK is a high-performance biocompatible polymer, so it provides several important material properties that other polymers, including biocompatible polymers, can’t.

PEEK is found in a number of medical fields, including the following long-term implantable application areas:

  1. Cervical and lumbar spinal fusion – PEEK’s first long-term implantable medical success was in cervical and lumbar spinal fusion, where it is still the first choice for interbody fusion cages. PEEK has steadily replaced titanium as the front-line option in this area, due to its superior flexural modulus, radiolucency and processability. PEEK cervical and lumbar fusion cages have been in use for over 20 years, and two decades of patient reports confirm that the polymer is an effective and safe choice.

    PEEK spinal rods are also gaining traction in lumbar decompression and fusion procedures. Lumbar decompression was once rare, as it was considered a high-risk treatment with more conservative alternatives. Improvements to the procedure and to the implants associated with the procedure have made it more commonplace. PEEK is incorporated into lumbar rods and implanted during lumbar fusion, which is typical following lumbar decompression.

  2. Orthopedic devices – PEEK is found in various orthopedic devices, including devices used during knee and hip replacement. PEEK’s wear resistance and fatigue strength are important traits to have in an orthopedic device, especially in weight-bearing surfaces. As such, PEEK is finding use in acetabular cups, where it can provide stable, reliable support for many years, without fear of shedding particles like metal implants do occasionally.
  3. Cardiovascular devices – PEEK’s processability means it can be converted using one of several methods, including extrusion and more exotic conversion methods like film calendaring. This processability advantage is critical for cardiovascular devices and instruments, many of which require medical tubing to function. PEEK is an ideal medical tubing biomaterial, as it possesses excellent column strength and tensile strength. It is an ideal fit for the constant push and pull found in the cardiovascular network.

    PEEK also has an ideal flexural modulus, which means it is flexible enough to navigate through winding segments, but stiff enough that it will not buckle. It requires a modest amount of force to push into the patient, and PEEK offers a good torque response, which makes it a frontline choice for catheters.

    PEEK is also found in stents and replacement valves, as well as defibrillators, where their ability to isolate electrical pulses prevents accidental shock. PEEK is also an essential biomaterial for some complex cardiovascular procedures, like the Less Invasive Ventricular Enhancement (LIVE) procedure. The LIVE procedure is usually administered to people with severe ischaemic heart failure and involves reshaping the left ventricle so that the heart handles blood more efficiently. The LIVE procedure relies on a pair of anchors to secure the ventricle in its new position, and these anchors are kept in place using a PEEK tether. PEEK’s tensile strength and resilience are major advantages in this context.

  4. Trauma fixation – PEEK is used in a variety of trauma fixation devices, including interference screws and bone plates. The biocompatible polymer’s fatigue strength and pullout strength are notable for trauma fixation applications, as is the material’s flexural modulus.

    Ideally, a trauma fixation device, which is typically used to facilitate bone healing, would do so by encouraging the damaged bone to grow back. PEEK, with its bone-like modulus, does this exceptionally well. The polymer protects the bone from excessive tensile or compressive forces but subjects the bone to enough stress to promote growth.

    PEEK’s pullout strength is important for trauma fixation hardware like screws, nails and anchors. PEEK flexes enough that it resists being pulled out of bone or a bone plate. The result is a more reliable device that promotes total healing.

  5. Dental – PEEK has a sizable role in dentistry and is an ideal option for partial dentures and dental implants. PEEK’s viability as a dental implant is due, again, to its bone-like modulus. As a partial denture, PEEK is prized for its aesthetic qualities, as it can be color matched to nearby tissues, making it nearly impossible to see the device. PEEK dentures also offer superior comfort, as they do not cause allergic reactions, are lightweight, do not trap heat and do not alter the patient’s sense of taste. In short, there’s a lot for patients to like with PEEK.

There are many biocompatible polymers in medicine, but PEEK is the most accomplished among them. With unparalleled versatility, safety and processability, PEEK is quickly becoming the world’s most advanced biomaterial.

How Are PEEK Rods Used in Lumbar Decompression Surgery?

Lumbar decompression surgery is a complicated procedure, and one that requires proper fusion of lumbar vertebrae. The addition of PEEK devices like spinal rods have greatly improved spinal fusion in patients, to the point where PEEK is considered a front line biomaterial for many spinal fusion procedures.

PEEK interbody cages are a popular choice for cervical fusion procedures, but for lumbar decompression surgery, PEEK rods are becoming more common. With a spinal rod made of PEEK, surgical teams can maintain stability at the implant site while also facilitating better fusion between implant and spine. The result is more reliable osseointegration.

Who requires lumbar decompression surgery?

Lumbar decompression is indicated in a number of people suffering from lower back pain. In most instances, more conservative treatments are sufficiently effective. However, there are several spinal conditions that can benefit greatly from lumbar decompression surgery, including:

  • Degenerative disc disease (DDD) – DDD is a common disorder, affecting more than three million people in the U.S. every year. After decades of wear and tear, the support-providing intervertebral discs may deteriorate and begin failing. When this happens, the patient may experience lower back pain that may spread to the thighs and radiate outward. In some cases, the patient may be asymptomatic, or the pain may be minor enough for easy management.

    If DDD is causing debilitating complications, lumbar decompression can relieve pain and lumbar fusion can restore stability to the joint.

  • Scoliosis – Specifically, people with adult scoliosis may get relief from lumbar decompression surgery. Adult scoliosis can be caused by a few things, including poor posture and muscle spasms. It can also be caused by spinal abnormalities or degenerative neurological conditions like muscular dystrophy.
  • Spondylolysis – Spondylolysis is caused by a defect with the vertebral arch, and specifically the pars interarticularis. This condition is present in up to six percent of people, but the majority of those people are asymptomatic. If symptoms are present, they usually involve pain, which may radiate from the lower back into the legs or buttocks, and which may be intense enough to restrict daily activity.

There are millions of people living with these conditions, and though only a portion will require lumbar decompression surgery, that’s still a lot of people who will eventually receive a PEEK implant.

What are the benefits of PEEK lumbar rods?

PEEK has long been used in spinal fusion procedures as a fusion cage, with nearly 20 years of patient reports attesting to the polymer’s utility and safety. PEEK spinal rods have many compelling advantages that PEEK interbody cages have. They include:

  1. Ideal flexural modulus – This is what drove medical facilities to adopt PEEK cervical devices, as the polymer’s flexural modulus is similar to cortical bone’s. In short, PEEK bends and handles weight like cortical bone, which affords it a few critical advantages. For one, PEEK’s bone-like modulus means it behaves like bone in the body, which means it is predictable for surgical teams. More importantly, though, since PEEK reacts to physical forces like bone, it will not bear too much weight, instead sharing the load so that positive, bone-stimulating stresses remain.
  2. Radiolucency – In a spinal fusion context, PEEK’s other critical advantage is its pure radiolucency. In its natural, unfilled form, PEEK is radiolucent (invisible) on X-rays, CT scans and MRIs, giving surgical teams clear pictures to work with when assessing postoperative progress. With no visual interference, surgical teams can verify the implant’s position and successful osseointegration, and do so with greater accuracy. Complications can be caught sooner with greater image clarity, so PEEK’s radiolucency has helped it become an ideal option for spinal fusion.
  3. Durability – As a high-performance polymer, PEEK is an extremely durable material. It possesses strong tensile strength and fatigue strength, so it will maintain its physical integrity even after years of stretching and compressing.

 

  1. Machinability – PEEK medical devices are almost always machined, as this allows for tightest tolerances. This ensures a reliable implant, but PEEK’s machinability also makes it possible to manufacture a range of implant sizes and shapes to fit a variety of patients. Precise, computer-aided manufacturing (CAM) technology is also used to create implants that fit the patient perfectly, optimizing patient comfort and outcomes.
  2. Potential – PEEK’s medical potential has already been realized to a large extent, but there’s still more research and development to come with the material. There are plenty of reasons to be optimistic about PEEK’s future, as the newest generation of cervical interbody fusion implants exhibits superior osseointegration capabilities. It’s just one development in PEEK spinal devices, but it illustrates how much higher the ceiling is for PEEK in medicine.

Lumbar decompression surgery is an involved procedure, but with the introduction of PEEK lumbar rods, it has the potential to be safer and more effective than ever. That’s because PEEK is a natural fit for lumbar decompression and fusion procedures, with its ideal material properties and excellent biocompatibility.

What are Important Applications of Polymers in Medicine?

Polymers are serving critical roles for the medical field, from single use instruments to life-preserving in vivo devices. These instruments and devices are made from a variety of plastics and high performance polymers, including:

  • Polyetheretherketone, or PEEK
  • Polyethylene, or PE
  • Polypropylene, or PP
  • Polystyrene, or PS
  • Polytetrafluoroethylene, or PTFE
  • Polyethylene terephthalate, or PET

There are others, but the above polymers are most widely used in plastic instruments and devices. Among them, PEEK is a primary biomaterial, which means it can be used in or around the human body without causing harm to the patient.

If all polymers and their medical applications are considered, there are at least hundreds of uses for medical plastics. Polymers are useful for a variety of medical applications, from repairing blood vessels to replacing heart valves. They can also be used to anchor a bone plate or keep a suture in place. High performance polymers like PEEK are particularly notable, as their excellent physical properties ensure they can fit into many applications.

What are PEEK’s applications in medicine?

PEEK exhibits excellent biocompatibility, verified through extensive testing. It can be used in implantable devices and implanted permanently, without toxicity to the patient. Given PEEK’s comprehensive biocompatibility, it has found use in several fields of medicine, including:

  1. Spinal fusion – PEEK was introduced to medicine first as an interbody fusion cage, intended for use in spinal fusion operations. That was 20 years ago, and PEEK is now the frontline choice for interbody fusion cages, replacing titanium in many instances.

    In fact, PEEK’s success in spinal fusion procedures has pushed medical engineering firms to develop better PEEK spinal implants. This new generation of interbody fusion cages attract bone-in growth better than previous cages, allowing for better integration between the implant and native bone.

    Spinal fusion can be used to treat several debilitating conditions, like degenerative disc disease, spinal stenosis, scoliosis, spondylolisthesis or tumors. PEEK can be used to give these patients relief from pain and loss of motion and can be used when there is serious trauma to the spine.

  2. Trauma fixation – PEEK’s impressive fatigue and pull-out resistance and resilience make it an ideal choice for trauma fixation components, like anchors and screws. PEEK bone plates are also being considered, due to PEEK’s impressive flexibility and its ability to maintain its shape. Trauma fixation devices and components must be able to withstand repeated tensile stress, and PEEK stands out in this regard.
  3. Orthopedics – PEEK is found in many orthopedic screw systems and suture anchors. Beyond that, PEEK can be used in knee and hip replacements, as it is an ideal weight-bearing material. PEEK’s fatigue strength and ideal modulus also factor in as both are important traits to have in a stress-bearing device.

    Acetabular cups produced from PEEK exhibit strong wear resistance, according to the Journal of Engineering in Medicine. A study published in the journal determined that such acetabular cups only wear at a rate of 1mm3 every 1 million cycles. In short, PEEK is a long lasting, tough material for tough orthopedic applications.

  4. Cardiovascular – In addition to its remarkable strength, durability and flexibility, PEEK’s extensive processability and hydrolysis resistance are also considerable. This means the polymer is a perfect fit for the cardiovascular environment, and its uses in heart and pulmonary medicine are expanding quickly.

    PEEK can be converted via extrusion, which can be used to make uniform, long strands of medical tubing. PEEK tubing is prized for its low coefficient of friction, so it can be pushed and steered through the cardiovascular network without causing damage to artery walls.

    PEEK tubing can be used to deliver other cardiovascular devices, like a replacement valve or used in implantable defibrillator components. PEEK is also used as an anchor in a few cardiovascular surgeries, including the less invasive ventricular enhancement procedure, or LIVE.

  5. Dental – PEEK’s potential in dentistry is also impressive, and it is used in partial dentures and in implants. It makes sense for partial dentures because PEEK can be optically matched to the patient’s dental tissues, so they look identical to the patient’s teeth and gums.  It is unlikely that anyone would notice anything made from PEEK in anyone’s mouth.

    In addition to PEEK’s superior aesthetics, PEEK doesn’t affect the patient’s taste, it won’t trap heat and it’s lightweight, making for a more comfortable fit.

    PEEK’s strong resilience and favorable modulus make it a frontline choice for dental implants. It integrates well into bone, which is a deciding factor for an effective dental implant, and it is flexible enough to handle biting and chewing forces well.

Medical plastics are one of the most encouraging areas of biomedical research, and their role in the industry will only expand as technology improves. In many ways, the future is already here for high performance polymers like PEEK. With more than 20 years of success in spinal fusion, orthopedic, arthroscopic, cardiovascular, dental and trauma fixation applications, PEEK is the biomaterial of choice for many.

How Are PEEK Screws Used?

PEEK screws are replacing stainless steel and titanium surgical screws in many instances, and they can be found in various orthopedic and trauma fixation applications. Screws can be used to directly interface with bone, or they can be used in conjunction with other trauma fixation and orthopedic devices. For example, PEEK screws can be installed in bone plates to hold a fracture together. They can also be implanted in cortical or cancellous bone, so PEEK’s versatility is a valuable trait in this regard.

Why are PEEK screws emerging as a frontline option?

Stainless steel and titanium have traditionally been the favored materials for surgical screws. In recent years, the introduction of resorbable materials and high performance polymers like PEEK have given surgical teams additional options. Here’s why those surgical teams are increasingly turning to PEEK screws for their patients:

  1. Biocompatibility and bioinertness – PEEK’s biocompatibility has been confirmed through USP Class VI testing and through extensive patient reports. In 20 years of medical use, PEEK hasn’t demonstrated any toxic or allergic properties, so it can be trusted for long-term or permanent implantation.

    PEEK is bioinert in ways that metal implants may not be. For instance, patients can develop sensitivity to certain metals after prolonged exposure, but this hasn’t been seen with PEEK. Further, when PEEK is used as a bearing material, it does not liberate extremely small, potentially toxic particles like some metal implants have done in the past.

    In addition to its biocompatibility, PEEK also resists attack in an organic or aqueous setting, so it will not corrode and it will not absorb minimal moisture. PEEK screws can be implanted anywhere in the body and remain intact for years.

  2. Excellent material properties – PEEK is a high performance polymer, so it possesses an elite array of properties, several of them important for trauma fixation and orthopedic applications. High fatigue strength and an ideal flexural modulus are the standout traits, as they approximate cortical bone well. In short, PEEK ‘micro flexes, compresses and bears weight like bone, so it behaves more like a load-sharing material than a load-bearing one.

    This load-sharing capacity is especially important for trauma fixation and orthopedic procedures. Because it shares the load, PEEK does not cause stress shielding, a common complication among metal, weight-bearing implants. Research published in the European Spine Journal has shown that titanium implants cause bone subsidence (caving in) at rates that far exceed PEEK implants.

    PEEK’s fatigue strength is what makes it an ideal screw, as it can withstand tension and compressive forces without losing shape or integrity. The result is a screw that’s better designed for dynamic areas of the body, like the legs, arms, hands and feet.

    Since PEEK screws can be installed in cortical bone or softer cancellous bone, they can be used in additional hip and knee arthroscopic procedures.

  3. Radiolucency – In its natural state, PEEK is radiolucent, so it will not interfere with any form of medical imaging, whether X-ray, MRI or CT scan. This will allow surgical teams to make more accurate, timely assessments, especially where it concerns osteosynthesis.

    If radiolucency, or imaging transparency is undesirable, additives like barium sulfate can be incorporated into PEEK to provide radiopacity. The addition of barium sulfate does not adversely affect the PEEK, so it can be added without fear of affecting the implant’s function or durability. In either case, PEEK provides an imaging advantage.

  4. Processability – PEEK’s extensive processability may not be an obvious advantage to patients or physicians, but it’s still a critical consideration. PEEK is a thermoplastic, so it is converted at extremely high temperatures and while using special equipment. Experienced converters use a variety of methods, like extrusion and machining, to turn PEEK into an array of useful medical components.

    PEEK is almost endlessly processable when machined, as the polymer retains its strong material properties even when subjected to machining stresses. It is essential, however, that an experienced PEEK converter handle machining, as issues with fiber orientation, for example, may compromise the polymer’s function.

    For surgical teams, PEEK’s processability allows for a variety of screw sizes and designs, so it’s easier to produce and find screws for a particular patient or implant. PEEK can also be machined to extremely tight tolerances, making a custom fit possible.

  5. Easier to adjust – Although infrequent, trauma fixation or orthopedic implants may need to be adjusted after implantation. Some PEEK screw systems have been designed with this potential scenario in mind, and they are easier to remove than stainless steel or titanium screws.

In many areas of medicine, PEEK is so successful that it is pushing other biomaterials into lesser roles. That is also true of fixation hardware like screws, where PEEK’s fatigue strength, pullout strength and all-round durability are valuable properties to have. PEEK’s unmatched processability also ensures component manufacturers can develop a full spectrum of screw and screw system designs.