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:
- 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.
- 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.
- 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.
- 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.
- 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.