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Materials Used In Medical Implants

Medical implants are tightly regulated by the FDA, and they can only be manufactured from biomaterials that have a proven safety record. This includes several polymers and high performance polymers like PEEK. PEEK is of particular interest to medicine as it has emerged as a frontline biomaterial for a diverse range of applications.

Other polymers used in medical implants include:

  • Polyurethane
  • Polyglycolide (PGA)
  • Polytetrafluoroethylene (PTFE)
  • Polyethylene (PE)

Non-polymer biomaterials are also prominent in medicine and include:

  • Titanium
  • Ceramics
  • Chromium
  • Cobalt

There are several more, but these are the most common biomaterial options.

What medical implants are PEEK used in?

PEEK is a notable biomaterial for its material properties and for its superb processability. As a high performance thermoplastic, PEEK is converted into medical components at high temperatures and using one of several methods. Those methods include injection molding, machining and extrusion, which is particularly useful for creating long segments of medical tubing.

Some of PEEK’s other primary medical applications include:

  • Interbody fusion cages – PEEK was first used in spinal fusion procedures, and it’s now a frontline option for interbody fusion cages. As interbody fusion cages represent an industry worth more than $1 billion, according to industry numbers, PEEK is a valuable biomaterial due to its role in spinal fusion alone.An active area of medical engineering research is making a better PEEK interbody fusion cage. The returns on this research are promising, as the current generation of fusion cages demonstrate better bone-in growth. This is due to superior design features like microporous structures and the use of materials like hydroxyapatite or zeolite.
  • Trauma fixation devices – PEEK has been manufactured into an array of trauma fixation components, including hardware and bone plates. PEEK’s excellent pullout strength and resilience makes it ideal in this role, especially when PEEK is augmented with chopped carbon. Termed CFR PEEK, this polymer grade offers added stiffness and strength and fatigue resistance over unfilled PEEK.
  • Joint replacement devices – Joint replacement systems must withstand a great deal of compressive forces while retaining their shape and position. PEEK is well-suited to these challenges, which is why it can be incorporated into knee and hip replacement procedures. PEEK has a good potential as an effective biomaterial for acetabular cups, in particular, as its wear resistance means it can function long term as a weight-bearing material.
  • Cardiovascular tubing and devices – PEEK is an extremely popular option for cardiovascular tubing, for several reasons. PEEK possesses excellent torsion resistance (the highest among polymer biomaterials), so it can weather the constant push and pull of the vascular network. PEEK also has a low coefficient of friction, so it offers a strong mix of pushability and navigation. In other words, PEEK can be inserted into the vascular network without the need for a lot of force, and it can move through nonlinear vascular segments with ease.PEEK’s processability and machinability means it can be converted into very small components without compromising its material properties. As cardiovascular devices can be inconceivably tiny, PEEK has an advantage in this area.

    Cardiovascular tubing is a commonplace PEEK application, and it has been incorporated into various device delivery systems, including valve replacement and stent placement. PEEK is also used in ablation catheters and auto defibrillators, where its electrical insulating capabilities are important.

  • Dental devices and implants – PEEK is quickly gaining attention in dentistry, and it’s already being used in partial dentures and in dental implants. Dental implants rely on a material that can readily fuse with bone, and PEEK does so better than most biomaterials.For partial dentures, it’s PEEK’s aesthetics and machinability that make it an attractive choice. Patients want their dentures to look natural and blend in with surrounding dental tissues. Patient comfort is also an important consideration, and a snug fit is what’s needed to ensure it. PEEK excels here again, as it can be precisely color matched to produce a natural look, to the point where it would be highly difficult for anyone to notice the difference. Since PEEK can be machined to precise tolerances, it is a perfect material for something as individual as a patient’s teeth and gums. Many practices now rely on computer-aided design and manufacturing, along with 3D imaging of the patient’s mouth, to create dental devices that fit perfectly.

    Furthermore, PEEK does not alter the patient’s taste and it does not trap heat or provoke an allergic response.

PEEK’s durability, processability and machinability has made it one of the most versatile biomaterials in existence. Engineers and device manufacturers are working hard to create better medical devices out of PEEK, providing better outcomes for patients.

 

Artificial Disc Replacement

In recent years, artificial disc replacements made from PEEK have garnered interest from researchers. The initial studies are promising and confirm that the high-performance polymer is ideal for the procedure.

Artificial disc replacement, or disc arthroplasty, is an alternative to anterior spinal fusion procedures, and is indicated in patients suffering from degenerative disc disease (DDD). During an artificial disc replacement procedure, the existing disc is either removed entirely, or only the nucleus is removed. The nucleus is the center of the disc, and is the only part that is replaced if the outside of the disc, the annulus, is in good condition.

Why consider artificial disc replacement?

Artificial disc replacement is used to treat the pain and lack of motion associated with DDD, but it’s not the only procedure available for the condition. Spinal fusion is also indicated in many DDD patients, and in these patients, a PEEK interbody cage is a common implant choice. In some cases, though, artificial disc replacement may make more sense. Here’s why:

  1. Disc arthroplasty preserves the spine’s motion – During spinal fusion, the space between the vertebrae is filled with an implant and a bone graft, locking, or “fusing” the bones together so that they move together. While this is often effective at reducing or eliminating pain, it can somewhat reduce the spine’s motion.

    Disc arthroplasty maintains the spine’s motion because it doesn’t lock vertebrae together. Instead, it replaces natural tissue with a device that aims to perform the same function.

  2. Disc arthroplasty helps patients get back on their feet faster – Following spinal fusion, patients are encouraged to take it slow in getting back to their normal activities. It takes time for the vertebrae to completely fuse, and during this time, it’s essential that the patient not strain or extend themselves.

    Disc arthroplasty, though, is intended to preserve motion, and patients are encouraged to start moving soon after surgery. This is also managed with gradual progression, but at a quicker pace than those who opt for fusion.

  3. Disc arthroplasty may reduce risk of certain complications – In rare cases, spinal fusion may cause other parts of the spine to bear more weight than normal. This may subject those parts to additional wear and tear, which could result in worsening symptoms.

    Disc replacement, though, doesn’t change the way the spine handles weight. It’s possible that this could lead to fewer complications, and according to a 2018 study published in Neurosurgery, the reoperation rate is extremely low among people who have undergone disc replacement surgery.

Why are PEEK artificial discs ideal?

Artificial discs can be made from one or more biomaterials, and PEEK is among the most promising materials for this procedure. The above Neurosurgery study looked at 33 patients who received a PEEK artificial disc, and in every instance, clinical improvements were seen with every patient. These improvements were maintained at two years, and included assessments of neck and arm pain. These results are comparable with artificial discs made from other biomaterials, so there is no loss in performance between metal and PEEK.

Beyond this, there are compelling reasons to believe that PEEK is the superior choice in artificial disc replacement. For example:

  • PEEK has excellent bearing and wear properties – PEEK is endlessly modifiable, but in its unfilled, natural state, the high-performance polymer has good bearing and wear performance and therefore can be a candidate for motion preservation applications and related device components.  Furthermore, since PEEK can be easily modified with specialty additives, the bearing and wear performance of PEEK can be improved to further reduce potential wear in various motion preservation devices, like artificial discs
  • PEEK offers pure radiolucency – PEEK offers pure radiolucency, so it is invisible on most forms of medical imaging, including MRIs and CT scans. This pure radiolucency is helpful when imaging and assessing the implant site for progress. It’s also useful for detecting any complications early.

    Metal implants, by contrast, produce a lot of image contrast, so they are not as easy to accurately image.

Though it’s a relatively new procedure, PEEK artificial discs are a promising treatment option for people suffering from degenerative disc disease. With the polymer’s excellent bearing and wear capabilities, its pure radiolucency and its biocompatibility, PEEK artificial discs represent a viable alternative to spinal fusion surgery.

 

Medical Plastic Devices

According to a report put together by Grand View Research, the medical plastics market is expected to climb above $33 billion by 2025, up from $17.2 billion in 2018. That means in just seven years, the medical plastics market is expected to double in value. There are several reasons for this, including an aging population, but the effectiveness of plastic biomaterials is one of the most important. Every year, new applications for medical plastics are found, and high-performance polymers like PEEK have shown promise in many medical fields.

Why Plastic Medical Devices Are Becoming Front-line Options

Plastic medical devices are used both in and out of the body, and in a diverse range of applications. Plastics are found in laboratory equipment and in surgical instrumentation. Plastic is also taking over the single-use instrument market, as it is much more practical compared to other materials in a single-use application. Plastic devices are also growing in popularity, as infection control is a major concern among medical facilities.

As impressive as this development is, high-performance polymers like PEEK are pushing medical technology forward. Since the introduction of the first PEEK spinal implant nearly 20 years ago, PEEK has found its way into many more medical devices while gaining more ground in spinal implant procedures.

Why is PEEK drawing so much attention among medical professionals?

  1. A similar modulus to bone – Ideally, biomaterials would mimic the tissues they’re replacing. This would guarantee optimal comfort and ensure the device behaves in a way that facilitates healing. Until the introduction of PEEK, however, it was impossible to find a biomaterial that could provide the same material advantages of cortical bone.

    PEEK, in both its unfilled state and carbon-reinforced state, possesses a modulus that is far more similar to bone than titanium. In fact, titanium’s modulus is about ten times greater than that of bone’s, which is a problem in applications where stress shielding could result.

    Since PEEK flexes and bears weight like bone, it will not cause stress shielding, ensuring nearby bone retains its mineral density and integrity. According to a 2017 study published in the Journal of Spine Surgery, PEEK’s ability to mimic the modulus of bone it interfaces is valuable in that it may reduce postoperative complications.

    PEEK’s modulus advantage isn’t relevant in all of its medical applications, but it is the main driver of PEEK’s success in spinal fusion, trauma fixation and orthopedic procedures.

  2. Radiolucency – PEEK’s radiolucency is a second compelling reason for its adoption among medical professionals. PEEK, in both CFR and unfilled grades, is transparent on X-ray, MRI and CT scans. It is extremely easy for surgical teams to image the implant site and monitor how the implant is positioned and interfacing with neighboring bone. Clear imaging is needed to spot potential complications, and PEEK doesn’t get in the way of this. It’s another point in PEEK’s favor over titanium, which does produce considerable opacity on most medical imaging.

    If, however, radiolucency is not desired, PEEK can be mixed with additives that improve its image contrast. Barium sulfate is the most common additive used for this purpose, and it can be added to PEEK without compromising its material properties.

  3. Processability – As a high-performance polymer, PEEK can be molded and shaped to almost any degree. This allows it to fit into a variety of applications that other biomaterials, because of their inferior processability, can’t match.

    Consider all the ways PEEK can be processed into a medical component. It can be injection molded, machined, extruded or run through exotic processes like film calendaring, which is used for extremely tiny medical components that require special medical film. It’s impossible to process other biomaterials in this fashion, which gives PEEK an advantage that designers and converters can both leverage.

  4. Future potential – PEEK is a worthy frontline biomaterial for some of the most delicate procedures in medicine, like spinal fusion. However, no other biomaterial is being developed at the rate PEEK is. PEEK’s few limitations are being resolved quickly, and they’re being resolved by next generation implants that are rapidly being introduced to the market.

    For example, PEEK implants augmented with hydroxyapatite achieve greater bone-in growth and integrate better with native bone. Implants designed with microporous structures, zeolite and other integration-enabling mechanisms are additional solutions available.

    What this illustrates is that PEEK can be developed and improved upon, whereas other biomaterials offer a lower potential ceiling. Medical professionals with one eye on the present and one on the future will find everything they want in PEEK.

Plastic medical devices offer a number of benefits that other biomaterials like stainless steel and titanium can’t match. Superior flexibility, weight-bearing, radiolucency and processability are all among PEEK’s defining characteristics, which means it can be integrated into a variety of medical devices. The future of medicine, then, is made with plastics.

PEEK Partial Denture

PEEK possesses a range of properties that make it ideal for partial dentures. These advantages are compelling to both dentists and their patients, which may be why PEEK is replacing other dental biomaterials, like titanium, chromium and porcelain. PEEK is a popular option for partial dentures and dental implants, for several reasons, including:

  • Improved aesthetics – A common concern among patients is that their partial dentures will be obvious and unattractive. The reason why it’s a common concern is because most dental materials are difficult to color match, and are easy to pick out as a result.

    However, PEEK doesn’t have aesthetic limitations. Instead, the high-performance polymer can be color matched with good precision. PEEK can be colored to fit patients, so no matter what aesthetic issues a patient is dealing with, PEEK offers a solution that will leave them feeling confident. Also, the gingiva, or gums, are less likely to resorb away from a PEEK denture, further enhancing aesthetics by not being seen due to resorption of the gingiva like with most materials

  • Improved comfort – After aesthetics, patients place a priority on comfort. Traditional partial dentures may trap heat or alter the patient’s taste. PEEK doesn’t do either, so patients tend to forget that the denture is there. PEEK is also lightweight and can be machined to incredible precision, so it can be used to provide a perfect, individual fit. PEEK weighs far less than metal and the reduction in weight may also help with comfort.
  • Excellent wear resistance – Partial dentures are subjected to a great deal of compressive and shear forces, and not many materials can handle it. However, PEEK is resilient enough to withstand daily chewing and grinding. PEEK’s wear resistance has been recognized in a variety of high-stress applications, so it is ideal for use in the oral cavity.
  • Total biocompatibility – Partial dentures aren’t rooted in the jawbone like implants, but they do remain in close contact with tissues in the oral cavity, so biocompatibility is still important. Some dental materials, including titanium and nickel, can provoke an allergic reaction, but PEEK hasn’t demonstrated immunogenic behavior. It can be placed in the mouth without fear of irritation, adding to patient comfort.

    PEEK has been through the toughest biocompatibility testing protocol there is, proven to be neither cytotoxic nor genotoxic. PEEK put up excellent marks during testing, demonstrating to researchers that it could remain in contact with human tissues for prolonged periods without causing damage. Patients can wear their PEEK partial denture without worry.

  • Hydrolysis resistance – PEEK is highly resistant to hydrolysis, so it will not lose its integrity in the presence of water, saliva or other bodily fluids. In fact, PEEK doesn’t absorb water to a significant degree, so it will remain stable for years.
  • Imaging friendly – In its unfilled state, PEEK does not interfere with medical imaging, including dental X-rays. It can be left in the mouth without fear of it scattering an image and making it difficult or impossible to read the scan.
  • Future potential – PEEK is already an important dental biomaterial, but there’s still plenty of research and development to go with the polymer. In the 20 years since PEEK was introduced to medicine, it has been improved upon steadily, and those improvements keep on coming. A promising area of research into PEEK involves the production of antimicrobial PEEK surfaces, which is of immediate use in the microbe-heavy oral cavity.

How PEEK’s Processability Makes for a Better Denture

Among PEEK’s noteworthy traits is its processability, as the polymer can be converted using one of many methods. It can be converted using conventional conversion technologies like injection molding or machining, or it can be converted using more esoteric methods like extrusion or film calendaring. Most PEEK medical components are machined, however, as this allows for the tightest tolerances and advanced component designs. PEEK’s excellent machinability makes this possible, as the polymer’s properties will not suffer during the process.

PEEK’s machinability is particularly helpful in dentistry and in the production of partial dentures. Before a patient receives their partial denture, their mouth is imaged using 3D imagining technology. These images can be used with computer-assisted manufacturing technology to machine a denture that fits the patient perfectly. PEEK’s ability to undergo extensive machining is key to this process.

A Complete Partial Denture

Partial dentures should be discreet, they should be comfortable and they should be reliable. PEEK partial dentures are all of the above, and they can provide this level of performance for years after placement. Put it all together, and PEEK is ready to be the frontline choice for partial dentures

What Is Medical Plastic And What Are Its Uses

Medical plastics are of great value to the healthcare industry and are used in everything from surgical instrumentation to life-preserving cardiovascular devices. Medical plastics come in a variety of compositions and grades, but what unifies them is that they are safe to use with human tissues. All medical plastics, including high-performance polymers like PEEK, have undergone extensive safety research and testing before they are incorporated into medical components and devices.

PEEK’s uses in medicine are wide-ranging and involve several critical applications. Some of those applications include:

  • Interbody fusion cages for spinal fusion procedures
  • Orthopedic and arthroscopic applications, for knee and hip components
  • Trauma fixation components, which include bone plates and hardware systems
  • Cardiovascular devices and components, like tubing, catheter components and defibrillator components
  • Dental devices, which include partial removable dentures and dental implants

Within these fields of medicine, PEEK is featured in dozens of components, and its number of uses is growing all the time.

How are medical plastics changing healthcare?

Medical plastics like PEEK bring many advantages to medicine, which is why they are quickly replacing other biomaterials. Here are some of the reasons:

  • Medical plastics can be sterilized easily –

    Hospital-acquired infections (HAIs) are a serious problem, resulting in nearly 100,000 deaths in the U.S. every year. Medical plastics are considered a major weapon in the fight against HAIs, as they can either be disposed of after a single use, or they can be designed with antimicrobial surfaces that resist pathogenic growth. PEEK polymer, for example, can also be sterilized for repeated use via all primary sterilization methods including steam, gamma, and ETO sterilization.

  • Medical plastics have a strong safety record –

    Several plastics are considered biomaterials, which means they are inert when in contact with the body’s tissues. Among plastic biomaterials, PEEK stands out for its long, impressive patient outcome history. PEEK has undergone the rigorous safety testing available for potential biomaterials (including ISO 10993 and USP Class VI), but it also has 20 years of patient reports verifying its biocompatibility.

  • Medical plastics exhibit excellent material properties –

    High-performance polymers like PEEK are especially useful for medical applications because they possess a unique combination of attractive physical properties. PEEK’s flexural modulus, for example, is nearly identical to cortical bone, so it bears weight and stress like bone. This makes it an ideal substitute for native bone in many applications, including spinal fusions. The material will move and support neighboring tissues, and it won’t cause stress shielding in nearby bone that can lead to mineral loss and subsequent bone weakness.

  • Medical plastics are extremely versatile –

    Medical plastics can be converted into components through one of several conversion methods. Those methods include injection molding, machining, extrusion, film calendaring and some even more esoteric methods. With several conversion methods available, device manufacturers have a lot of room in producing the most effective components possible.

    Most PEEK medical components are machined, as machining allows for the tightest tolerances, and that’s a priority for any implantable devices. However, medical plastics that aren’t used in vivo, but instead for instruments or equipment, can be converted using injection molding.

How is PEEK being used in medicine?

PEEK is a high-performance polymer, so it possesses a combination of properties that few other materials possess. This gives PEEK a great deal of potential, as it can withstand most any force it might encounter in the human body. As such, here is how medical facilities are making the most of those properties:

  • Interbody fusion cages – PEEK’s initial success in medicine was in spinal fusion procedures, where it serves as a frontline material for interbody fusion cages. Interbody fusion cages provide an optimal support for the vertebras to fuse together, so the implant must be safe and it must facilitate osseointegration.

    PEEK is safe and the newest generation of PEEK cages are designed to optimize bone-in growth, with the use of bone-attracting materials and microporous structures. It’s likely true, then, that PEEK’s status as the first choice in interbody fusion cages is certain.

  • Trauma fixation components – PEEK is regularly converted into bone plates and hardware to secure trauma fixation components. PEEK is perfect in this role because it exhibits excellent resilience and pullout strength.
  • Cardiovascular tubing and components – PEEK can be extruded into long, uniform segments, which makes it an ideal biomaterial for tubing. PEEK has a low coefficient of friction, so it can be steered through the cardiovascular network without getting stuck or causing harm to arteries or veins.

    PEEK tubing can be used to deliver a stent or a replacement heart valve. PEEK components are also found in defibrillators and ablation catheters, as it can prevent harmful electrical discharges.

  • Arthroscopic and orthopedic components – PEEK’s ability to handle weight and resist wear are impressive, and it’s a suitable biomaterial in hip and knee replacement components, as well as arthroscopic procedures. PEEK can be found in acetabular cups, where its resilience and wear resistance are highly valuable.
  • Dental devices – PEEK can function in several roles for dentists, serving as a primary partial denture material, or a dental implant material. PEEK is extremely well-suited for partial dentures, because it can be color matched to nearby tissues, it offers excellent wear resistance and it can be precisely machined to fit a patient perfectly. As a dental implant, PEEK’s bone-like modulus and total biocompatibility make it perfect for interfacing with the jawbone.

Medical plastics, like the versatile and durable PEEK, are found in hundreds of medical devices and instruments. Medical plastics are already achieving a great deal, and with so much research focused on making them even better, the future will continue to focus on plastic and its uses in medicine.

 

 

Advantages of a PEEK Cage vs Titanium Cage

PEEK and titanium are the primary biomaterials used in fusion cages, but PEEK has a few decisive advantages over titanium. Recently published research also suggests that the high-performance polymer is a better fit for fusion procedures.

Though PEEK is one of the newer biomaterials, it has quickly emerged as a top choice in several spinal fusion procedures, including:

  • Anterior cervical discectomy and fusion, or ACDF.
  • Anterior lumbar interbody fusion, or ALIF.
  • Posterior lumbar interbody fusion, or PLIF.

PEEK is also being considered for other spinal devices, including artificial discs. This makes sense, because PEEK is well-suited to handle the physical demands placed on the spine.

PEEK vs. Titanium: Fusion Rates and Subsidence

Studies comparing titanium and PEEK focus on fusion rates and subsidence. Fusion refers to the implant’s capacity to osseointegrate with native bone and subsidence refers to caving in of nearby bone.

Subsidence occurs as a result of stress shielding, and stress shielding occurs when the bone is no longer stimulated by weight bearing forces. Without this stress, affected bone tissue drops in mineral density, compromising its structure to an extent. A loss of bone mineral density could lead to a higher risk of fractures, as has been noted in studies with osteoporosis patients.

PEEK and titanium cages are similar regarding fusion rates, and the research confirms that there isn’t a statistically significant difference between the two. However, there is a significant difference in subsidence rates.

According to a 2013 study published in the European Spine Journal, titanium cages were associated with much higher rates of subsidence (over 30 percent) compared to PEEK (less than 10 percent). Additional studies, including a 2017 study published in the Journal of Clinical Neuroscience, reinforce this research and have found the same thing.

Subsidence remains a significant concern with titanium implants, but PEEK is much more promising in this area due to its bone-like flexural modulus. PEEK, in its unfilled state, possesses a similar flexural modulus to cortical bone, so it bends and bears weight like the body’s own tissues. This is how PEEK is able to avoid stress shielding, and how the polymer encourages more effective healing in native bone.

PEEK vs. Titanium: Radiolucency

PEEK’s flexural modulus is one of its primary advantages, but it’s not the only one. PEEK, again in its unfilled state, offers pure radiolucency. It is completely invisible on MRIs, CT scans and X-rays, so surgical teams can easily monitor post-operative progress and confirm that osseointegration is taking place. If there is a chance of complications emerging, PEEK’s pure radiolucency allows surgical teams to catch them sooner.

PEEK’s pure radiolucency can be modified with the addition of additives like barium sulfate. When mixed in, barium sulfate adds image contrast to the polymer, without affecting PEEK’s properties.

Titanium, unsurprisingly, doesn’t offer the same radiolucency that PEEK does. Titanium, like other metals, is an image-scattering material and creates significant artifacts. This can interfere with attempts to assess the implant’s position and its fusion progress.

PEEK vs. Titanium: Processability

Both PEEK and titanium cages are manufactured using modern CAM processes, and both to excellent tolerances. Titanium, though, poses difficulties during the machining process as it possesses low thermal conductivity. Both expose machining tools to additional wear, which can make the metal more expensive and more challenging to work with.

In the hands of a skilled converter, though, PEEK can be efficiently machined without compromising its properties. The key word here is “skilled,” because PEEK is vulnerable to subtle issues like fiber orientation. A converter experienced with PEEK will be equipped to sidestep these potential obstacles.

In addition to machining, PEEK can be converted using injection molding and extrusion processes. Medical processing facilities can maximize processing economy by opting for large runs of injected PEEK components. Via extrusion, PEEK can also be converted into durable stretches of medical tubing.

PEEK vs. Titanium: The Future

PEEK is a newer biomaterial, so there is more potential to unlock with the polymer. There are already several advanced PEEK cages on the market, mixed with materials that encourage bone growth and osseointegration. Zeolite and hydroxyapatite are two such materials, and initial research confirms that these new PEEK implants are achieving superior bone-in growth.

New PEEK implants are also designed with microporous structures, and these encourage native bone to grow into the implant, with a lock-like fit. Though there are similar initiatives targeted at titanium, PEEK’s superior processability likely means that there is more room to improve upon the polymer.

In the battle of biomaterials, PEEK offers a superior modulus, better radiolucency and a wider range of processing options. These advantages explain why PEEK is the first choice in spinal fusion procedures, and why it is an important biomaterial for several medical fields.

What are the Different Types of Plastic Grades for Medical Plastics?

Plastic in various forms has improved nearly every field of medicine and serves a variety of roles in a medical facility. For example, medical plastics can be incorporated in everything from single-use surgical instruments or tubing, to long term spinal and cardiovascular implants.

Some of the most common medical plastics include:

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

Of these, only a couple medical plastics can be used for long-term implantable devices. Those include some resorbable plastics, like polylactic acid polyglycolic acid, PE and PEEK. While UHMWPE (Ultra-high molecular weight polyethylene) is used in orthopedic applications, PEEK’s material properties make it a frontline choice in an array of more demanding applications. That includes spinal fusion, cardiovascular, dental and trauma fixation applications.

PEEK and CFR PEEK

PEEK can be used in its unfilled form or with the addition of chopped carbon fiber to create CFR PEEK. Both are appropriate in many medical applications, but each possesses its own advantages. Unfilled PEEK is more flexible while still offering strong tensile strength. Unfilled PEEK is a frontline choice in spinal fusion and cardiovascular applications. Both grades are fully radiolucent.

CFR PEEK provides added tensile strength and a greater modulus and thereby is used for trauma applications like bone plates and screws. Both PEEK options are similar to cortical bone’s tensile strength making each an excellent choice in loadbearing or load sharing applications, including applications where bone healing is necessary. CFR PEEK can also be used in some dental implants.

Why are medical plastics replacing other biomaterials?

There are only a handful of materials that are biocompatible and effective enough to be used in the human body. Until the introduction of medical plastics, metal and ceramic were the biomaterials of choice, and titanium remains a primary biomaterial today. High-performance polymers like PEEK and UHMWPE, though, are replacing those biomaterials in many important applications. There are a couple reasons for this, including:

  • Stress shielding and subsidence – PEEK and CFR PEEK, due to their cortical bone-like moduli, can be used as load sharing materials. While titanium and ceramics are structurally strong enough to work as implants, their high moduli mean they bear too much weight in many instances, robbing nearby bone of important, constructive stresses. Over time, this can lead to loss of bone mineral density, and possible subsidence, or caving in. In multiple studies comparing PEEK and titanium, titanium has demonstrated higher rates of subsidence.
  • Efficient manufacturing – In some applications, including arthroscopic and trauma fixation applications, PEEK has shown resiliency, tensile strength and pull out strength comparable or favorable to other biomaterials. However, PEEK possesses a processability advantage over metal and ceramic, as it can be easily injection molded.Injection molding is an economical manufacturing method that is particularly cost-efficient when used to create high component volumes such as anchors, screw systems and any other component needed in large quantities.

What makes PEEK a medical plastic?

PEEK, like every biomaterial, has been subjected to extensive biocompatibility testing to ensure it is safe for use in the human body. ISO 10993 details the most up-to-date testing protocols available to medical device manufacturers, and several of those protocols are relevant to PEEK implant testing. They include:

  1. Cytotoxicity testing –

    Cytotoxicity testing assesses whether the material is likely to cause cell damage. This is usually done by exposing a cell culture directly to a material sample, and then incubating both. Following incubation, the cells are checked for any lysis or malformation, as this potentially indicates cytotoxicity.

  2. Sensitization testing –

    Sensitization testing checks for an immunological response to the material, which may indicate the material is causing adverse systemic effects to the subject. To perform this test, material extracts are applied to subjects and monitored for a response.

  3. Irritation testing –

    Irritation testing looks for the material’s irritant potential, either to the skin or mucosal membranes. For implantable materials, this test is normally done intracutaneously, so extracts are injected under the skin, and any signs of redness or swelling are noted.

  4. Acute system toxicity testing –

    Acute systemic toxicity testing checks for systemic (in contrast to local) effects to the body following extended exposure. Material extracts are injected in a group of test subjects, and are checked immediately for any adverse signs. The subjects are checked several more times before the test’s conclusion, to verify that the material is not affecting the subject’s vitals.

  5. Genotoxicity testing –

    Genotoxicity testing considers the material’s mutagenic potential, or its potential to cause genetic damage to the subject. During genotoxicity testing, the test subjects are salmonella bacteria, which are sensitive to mutagens. Following exposure to the material, only mutated salmonella will survive, so researchers can note the prevalence of mutations among the bacteria.

  6. Implantation testing –

    Implantation testing is designed to simulate the implantation environment, so the material is exposed to the tissues it is likely to contact when used in a human body. After extended implantation in an animal subject, tissue samples are taken from the subject and inspected microscopically for any signs of disease.

There are many medical plastics, but only a couple, like PEEK grades, are safe enough to use in the body. These plastics have undergone comprehensive biocompatibility testing to earn that distinction, and have proven their effectiveness in an array of medical applications.

FAQ

What is the difference between PEEK and CFR PEEK?

PEEK is an unfilled high-performance polymer, while CFR PEEK is PEEK polymer with the addition of chopped carbon fiber. CFR PEEK offers additional stiffness and strength, while unfilled PEEK provides additional flexibility. Both are radiolucent.

What standard is used to regulate medical plastics?

Medical plastics are tested for biocompatibility, and the recommended biocompatibility testing procedures are outlined in ISO 10993. ISO 10993 and ISO 13485 (which regulates medical device manufacturers) meet the regulatory guidelines of European and Asian agencies. The FDA also considers ISO standards to be sufficient for most medical devices, and will consider it during premarket approval.

Why is PEEK replacing titanium in bone healing applications?

Titanium, ceramic and other loadbearing biomaterials are strong and durable, but they may rob neighboring bone of important, bone-stimulating stresses. This is called stress shielding, and it can result in bone mineral density loss in nearby bone. That can lead to subsidence, or caving in of bone.

PEEK subsidence rates are much lower, according to several research studies. PEEK can also be injection molded, which gives it a major processability advantage in many medical applications.

What Medical Devices Can Be Made From PEEK?

PEEK’s superior material properties make it a fit for many areas of medicine, including spinal fusion, dentistry, trauma fixation and cardiovascular medicine, among other fields. This high-performance polymer has been used in medicine for over 20 years, and there are still exciting developments to come for PEEK medical devices.

In the present, there are many medical devices where PEEK serves as a frontline material choice, including:

  1. Interbody fusion cages –

    Interbody fusion cages are used in spinal fusion applications to provide additional stability thereby helping to relieve pain. Spinal fusion is indicated in patients suffering from degenerative disc disease, spondylolisthesis, spinal stenosis, or damage due to fractures or tumors.

    During spinal fusion, the problematic disc is removed from the body and replaced with a bone graft and interbody fusion cage. The cage provides an ideal environment for the bone graft to fuse the two vertebrae together, ensuring predictable, stable growth. The fusion cage becomes a permanent part of the spine, so it must be manufactured from biocompatible materials.

    PEEK provides that total biocompatibility and offers several more advantages. For example, PEEK’s flexural modulus is similar to cortical bone, so it shares weight and handles force like bone. This makes PEEK an ideal bone replacement material, because it will not bear too much weight and cause subsidence. Subsidence is a noted issue with titanium implants for this reason, and PEEK’s subsidence rates are much lower, according to multiple research studies.

    PEEK’s pure radiolucency is also useful in spinal fusion applications, as it allows surgical teams to assess the patient without the implant interfering with medical imaging. This includes CT, MRI and X-ray scans, so PEEK can be used with a variety of imaging technologies.

  2. Dentistry –

    PEEK is a frontline choice for some dental applications, including dental implants and removable partial dentures. PEEK’s biocompatibility means it can be implanted in the jaw or used in the oral cavity without causing issues.

    The rise of CAD/CAM dentistry has been especially beneficial for PEEK, as CAD/CAM dentistry takes precise 3D models of a patient’s mouth and machines a device that fits that patient perfectly. As PEEK tolerates machining extremely well, it is a good fit for a CAD/CAM approach.

    PEEK partial dentures are prized for their excellent aesthetics and comfort. Aesthetically, PEEK can be color matched to surrounding tissues, which is something that can’t be done with other dental materials. This means PEEK devices are inconspicuous, even when the patient’s mouth is open. PEEK partial dentures are also comfortable, as they are lightweight and shaped to fit the patient precisely. Also, PEEK does not alter the patient’s taste and does not irritate tissues, so it doesn’t interfere with the patient’s ability to eat or talk.

  3. Cardiovascular devices –

    PEEK is also a top choice for several cardiovascular devices, including medical tubing. PEEK tubing can be used to deliver cardiovascular devices like replacement valves and stents. It is also incorporated into defibrillators and ablation catheters.

    What makes PEEK an ideal tubing material is its low coefficient of friction and flexibility. Together, these properties make PEEK well-suited for the cardiovascular network, and the polymer offers strong pushability and navigation. Pushability refers to the amount of force required to advance the tubing to the treatment site, while navigation refers to how well the material can move through nonlinear segments of the cardiovascular network. These two traits are usually at odds, because improving one usually adversely affects the other. Fortunately, PEEK tubing provides an optimal mix of both, so it can be used in most locations of the vascular network.

    PEEK’s electrical properties also make it a good fit for ablation catheters, defibrillators and any device that works by delivering precise electrical discharges. PEEK can help control these discharges, reducing risk of electrocution and burn injuries to the patient.

    The polymer is also relied on in some emerging cardiovascular procedures. One of these is the Less Invasive Ventricular Enhancement (LIVE) procedure, which is indicated in patients who have suffered heart damage, usually caused by a heart attack. During the LIVE procedure, a pair of anchors are positioned over the scar tissue and held together by a PEEK tether. The anchors move scar tissue out of the way in order to restore ventricular function, and the tether keeps the anchors properly aligned. The LIVE procedure is a safer alternative to previous forms of ventricular enhancement, which required several incisions to the heart.

  4. Trauma fixation –

    Among biomaterials, PEEK possesses elite mechanical properties, making it a strong choice for bone plates and screw systems. PEEK’s cortical bone-like modulus, resiliency and pull-out strength are particularly important for trauma fixation applications. In short, PEEK can handle the compressive and tension forces applied to trauma fixation devices, resist failure and prevent subsidence with appropriate load-sharing abilities.

Many medical devices are made from PEEK, and some of these devices, like interbody fusion cages, are being improved upon constantly. New fusion cages, for example, are being developed with materials that attract bone growth, like hydroxyapatite and zeolite.

With its existing, impressive capabilities and future potential, PEEK has established itself as a critical biomaterial, and one that will only become more essential with time.

FAQ

Why are PEEK implants replacing titanium implants?

PEEK implants have a flexural modulus that’s similar to cortical bone, so they are less likely to cause stress shielding, and by extension, subsidence. Subsidence refers to settling, or caving in, of bone. Titanium implants are more likely to cause subsidence because titanium bears weight instead of sharing it.

What additives can be mixed with PEEK medical devices?

PEEK can be augmented with chopped carbon fibers (CFR PEEK), and this provides additional strength and stiffness to the polymer. Barium sulfate can also be added to PEEK to make it more radiopaque for applications where it would be helpful to see the implant on medical imaging.

What makes PEEK a good choice for cardiovascular tubing?

PEEK can be converted into extremely small cross sections and is a low-friction material. This makes it an ideal choice for the cardiovascular network, which is nonlinear in design. PEEK tubing offers excellent pushability and navigation, so it can be steered through vascular branches with little difficulty.

The Polymer Engineering and Science Behind PEEK

For PEEK manufacturers, it’s the physics and materials properties behind the polymer that are most relevant. PEEK’s chemistry is also noteworthy because its chemical structure is what makes the polymer so useful. PEEK is a high-performance thermoplastic, so it possesses an elite range of material properties and is processable using heat.

What is a thermoplastic?

A thermoplastic is a polymer that retains its plastic properties at standard temperatures, but can be melted at elevated temperatures. When the polymer is returned to its solid, plastic state, it retains its material properties. This is particularly useful for PEEK manufacturers because it means the polymer can be converted into an array of components without compromising its excellent durability and strength.

Thermoplastics are versatile during the conversion process. For example, PEEK is commonly used in the injection and compression molding processes to manufacture large batches of identical components. PEEK can also be machined using CAM technology to create components that adhere to extremely tight tolerances. PEEK can even be extruded to produce medical tubing or used with film calendaring to produce special, atomically-small films.

In medicine, PEEK is converted using injection molding when manufacturing surgical instruments and laboratory components. This is a cost-effective approach that helps medical facilities control infections with single-use instruments. In vivo and implantable PEEK components, though, are primarily converted via machining, which offers better tolerances, smaller production campaigns, and intricate component designs.

What is a semicrystalline thermoplastic?

There are two primary categories of thermoplastics, which are either amorphous thermoplastics or semicrystalline thermoplastics. In practical terms, all polymers sit between perfectly crystalline and amorphous states, but those with a greater degree of crystallinity are called semicrystalline polymers. Both terms refer to the polymer’s molecular structure, and hint at the kind of properties the polymer is likely to exhibit. Here’s a quick look at what amorphous and crystalline mean in a polymer science context:

  • Amorphous – Amorphous polymers are organized randomly with molecular chains. With little underlying structure, amorphous polymers tend to melt at lower temperatures, though they perform well at lower temperatures. Amorphous polymers are more flexible than crystalline polymers, but they are more likely to crack under stress and possess poor fatigue strength. Amorphous polymers are also usually transparent. Examples of amorphous polymers include polystyrene, polycarbonate, ABS, polyetherimide and polysulfone.
  • Crystalline – Crystalline polymers exhibit structure at the molecular level, most often in small pockets referred to spherulites. In other words, there is significant crystal organization in spots, as well as amorphous areas between the spherulites. This partial crystal structure is what gives PEEK and other semi-crystalline thermoplastics their excellent thermal and fatigue resistance. Because crystalline structures are formed out of more durable bonds, the polymer melts consistently and is tougher once converted into components. Semicrystalline thermoplastics tend to have enhanced bearing and wear properties. Examples of polymers with a high degree of crystallinity include poly-ether-ether-ketone (PEEK), poly-amide (nylon), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and polytetrafluoroethylene (PTFE).

What are PEEK’s material properties?

PEEK stands out among other polymers with its excellent material properties. It’s these superior properties that have made the polymer a frontline choice in many aerospace, automotive, oil & gas and medical applications. PEEK’s role in medicine has expanded greatly in the last 20 years, and it is now featured in several medical fields, including spinal fusion, orthopedics, cardiovascular medicine, trauma fixation, dentistry and prosthetics, among others.

What has driven this surge in PEEK’s popularity? Several reasons, including:

  1. An ideal flexural modulus – PEEK can be mixed with several additives, but in its unfilled state, PEEK has a flexural modulus similar to cortical bone. Because it bends and handles weight like bone, it can stand in for bone in several applications. This is most important in spinal fusion, orthopedic and trauma fixation procedures, where the implant must not provoke stress shielding in nearby bone. Stress shielding occurs when the implant bears too much weight and robs native bone of the stimulating stresses it needs to heal and grow properly. Stress shielding is a problem with metal implants and can cause nearby bone to drop in mineral density and suffer from subsidence, or caving in.
  2. Pure radiolucency – In its unfilled state, PEEK is completely invisible on medical imaging, including CT scans, MRIs and X-rays. This pure radiolucency is essential in spinal fusion applications and any applications where accurate imaging is critical. Because PEEK does not interfere with medical imaging, surgical teams can better monitor the implant’s positioning and potential for osseointegration.
  3. Total biocompatibility All implantable biomaterials, PEEK included, must undergo the most demanding safety tests available to ensure the material is safe. PEEK has passed through these tests with no concerns, demonstrating zero cytotoxicity, genotoxicity and immunogenic potential. After 20 years of use in patients, PEEK still hasn’t demonstrated any concerns that would threaten its status as a primary biomaterial.
  4. Modifiability – PEEK is plenty capable in its natural state, but it can be mixed with other materials to augment its properties. For example, with the addition of chopped carbon (CFR PEEK), the polymer is stiffer and stronger, so it can be used in applications where additional weight bearing capabilities are needed. PEEK’s radiolucency can also be modified with the addition of barium sulfate. This adds a degree of image contrast without affecting the polymer’s properties.

The polymer engineering and science behind PEEK is astounding, but you don’t have to be a scientist to understand what makes the polymer so useful. With its favorable material and mechanical characteristics, PEEK is at the peak of polymer engineering.

What is PEEK’s Thermal Conductivity?

PEEK is a thermal isolator, so it does not readily conduct heat into nearby materials. It’s also an ideal electrical isolator, and together, these properties make it useful in several medical applications. These applications include cardiovascular devices and surgical tools, where heat and electricity must be controlled for patient comfort and safety.

Some examples include:

  • Ablation catheters
  • Implantable automatic defibrillators
  • Surgical tools designed for electrosurgical procedures

Thermal and electrical isolation may not seem like a primary concern in medicine, but the above devices and tools are used with thousands of patients every year. PEEK’s ability to isolate thermal energy and electrical discharges make it a frontline choice in the above devices and instruments.

PEEK’s Role in Cardiovascular Medicine

The heart runs on electricity, and precise impulses are needed to keep it functioning properly. PEEK’s role as an isolator ensures that these electrical impulses are controlled and that patients are protected from harmful discharges.

For example, ablation catheters are used in patients suffering from heart arrhythmias, specifically to scar cardiac tissue that is contributing to the arrhythmia. Whenever electricity is applied to the heart, it must be done with extreme caution to avoid accidentally burning or scarring healthy tissue. PEEK is a common choice in ablation catheters for this reason, as it can isolate any stray discharges and prevent them from affecting the patient.

For the same reasons, implantable automatic defibrillators must also be sheathed in materials that isolate electrical discharges. PEEK is an ideal choice for this purpose.

PEEK’s Role in Electrosurgery

Electrosurgery is utilized in nearly every field of medicine, as it is an effective means of stopping bleeding and ablating tissues. Electrosurgical instruments work by using an electrical current to generate heat. While in use, these instruments can precisely cauterize and scar tissues, much like ablation catheters.

Like ablation catheters, electrosurgical instruments are frequently built with PEEK, due to its lack of thermal and electrical conductivity. PEEK is especially important in electrosurgery as the surgical environment is conducive to conductivity, with the presence of electrical equipment and body fluids.

A Thermal Isolator and Thermoplastic

PEEK may be an ideal thermal and electrical isolator, but it is still melt processable. As a high performance thermoplastic, PEEK doesn’t melt until it hits about 650 degrees Fahrenheit (343 degrees Celsius), but once it does, it can be processed through one of several methods.

For example, PEEK can be extruded once heated. Extruded PEEK is particularly useful as medical tubing in cardiovascular applications. That’s because PEEK possesses a perfect mix of flexibility and a low-friction surface, so it can be readily steered through the vascular network.

The high performance polymer can be injection molded into an array of components as well. Injection molding is used with implantable devices, but not to the extent that it is used for producing components intended for surgical instruments. These components can be of almost any size, shape or design, as PEEK maintains its excellent material properties through processing.

Why consider PEEK for surgical instruments?

PEEK is used in a large number of surgical instruments, for reasons that go beyond its thermal and electrical conductivity properties. PEEK also offers the following advantages:

  • Versatility – Since PEEK can be converted through various means, it can be adapted for use with a variety of instrument designs. This includes electrosurgical instruments and unpowered instruments.
  • Durability – PEEK is extremely resistant to nearly all forms of damage. It possesses strong impact strength, compression strength, tensile strength and it is impervious to corrosion. PEEK also resists water absorption and can withstand repeated autoclaving without being damaged.
  • Cleanliness – Hospitals have an infection problem on their hands, as there are about 1.7 million instances of hospital-acquired infections (HAIs) every year. These result in close to 100,000 deaths, so the problem is far from trivial. PEEK provides a solution here, too. Since PEEK can be injection molded during large production runs, it is a clean and economical option for single-use instruments. Single-use instruments eliminate the likelihood of infection altogether, and in some cases (like with medical tubing), they may be the only option in preventing infection. PEEK is also highly chemical resistant and will withstand exposure to most hospital cleaning regimes.
  • Comfort – Patient comfort is paramount, but surgeon comfort also needs consideration. Again, PEEK solves a problem because the polymer weighs much less than metal biomaterials. With its lightweight nature, PEEK reduces strain on the surgeon’s fingers, hand and shoulder, and ensures they can control the instrument for longer. PEEK’s versatility also lends itself to any ergonomic-focused design, and it can be converted to fit any hand with maximum comfort.

PEEK’s intriguing thermal conductivity is just one of its many material properties, and one that makes it suitable for an array of medical applications. With its ability to isolate electrical and thermal energy, PEEK has a place in every surgical room, whether in the form of medical tubing, medical equipment or medical instruments.