Medical: PEEK's advantages and disadvantages compared ...

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Traditional hard tissue implant materials such as stainless steel, titanium, and its alloys are widely used in hard tissue repair and replacement due to their high mechanical strength, good biocompatibility, and fatigue resistance. However, the elastic modulus of these traditional metal implant materials is much higher than that of bone tissue, making it difficult to form a reasonable gradient strength. When exposed to special external forces, patients may damage the surrounding normal organs, leading to implant failure, known as the "stress shielding effect."

It's been 10 years since the first patient implanted a 3D-printed titanium alloy hip.

Furthermore, metal implants may release harmful metal ions, causing the formation of osteolysis or allergens. Conventional metal implants are also incompatible with nuclear magnetic resonance imaging and computed tomography, which hinders bone growth and healing monitoring.

Nevertheless, metal implants have their unique advantages.

The chemical structural characteristics of the thermoplastic special engineering plastic PEEK offer it excellent mechanical properties, good biocompatibility, chemical resistance, ease of processing, and repeatable disinfection. Since the 2000s, PEEK has received increasing attention from materials science researchers and osteologists, making it a potential replacement for metal materials in hard tissue repair and replacement. With the advancements in 3D printing applications, PEEK has gained even more attention.

Advantages of PEEK Instead of Metal Implants

Compared to metal implants, PEEK has two outstanding advantages:

First, the elastic modulus of PEEK is close to that of cortical bone, especially in carbon fiber-reinforced PEEK. This close or matched elastic modulus weakens or eliminates the stress shielding effect, promoting bone integration between the implant and bone tissue, and ensuring the long-term stability of the PEEK implant.

Second, PEEK can transmit X-rays, CT, or MRI scans without artifacts, making it easier to monitor bone growth and the healing process. Additionally, PEEK boasts good biocompatibility, wear resistance, fatigue resistance, corrosion resistance, and ease of processing, while being lighter than metal materials. These advantages make PEEK widely used in trauma, spine, and joint applications.

PEEK used for dental implants is lighter, more comfortable than titanium, has no metallic taste, and has received FDA certification.

Compared to stainless steel, titanium alloy, and ultra-high molecular weight polyethylene implants, PEEK and its composite materials have good wear resistance. This minimizes inflammation and osteolysis around the implant caused by wear particles, making PEEK a candidate material to replace traditional implants in orthopedic applications.

Disadvantages of PEEK for Orthopedic Implants

PEEK has a lower surface energy due to its relatively hydrophobic surface, limiting cell adhesion. The biological inertia of PEEK leads to poor bone integration between the PEEK implant and host bone tissue, often resulting in complications like implant displacement, cage formation, or pseudo-joint formation. Both in vitro and clinical applications have shown unsatisfactory results.

The ideal PEEK surface should enable cell adhesion, proliferation, and osteoblast differentiation, promoting mineralization on the surface of the PEEK implant, and producing substantial bone fusion. To achieve this, researchers have developed various PEEK and composite materials through bioactive ceramic filling, fiber reinforcement, and PEEK porosity methods. The objective is to ensure that the implant material maintains vascular functionality, nutrient transfer, sufficient mechanical strength, and wear resistance. However, achieving this balance remains challenging in current research.

In September 2022, the microporous hydrophilic PEEK material developed by the medical polymer company DiFusion was named one of the top ten spine materials by plastic surgeons. Recognized for supporting the growth of orthopedic implants while retaining the mechanical properties and imaging capabilities of traditional PEEK, the material can be used for injection molding, 3D printing, or mechanical processing. It is currently being expanded and put into commercial use.

PEEK has excellent application prospects but also presents significant challenges. Achieving material breakthroughs will be key to its safe application. No product is perfect; even traditional metal implant materials have deficiencies. However, the first patient with a 3D-printed titanium alloy hip joint has been walking healthily for over 10 years. This article aims to provide more insight for professionals, while ordinary patients should rely on their doctors to make the best decisions.

What is PEEK?

PEEK (Polyetheretherketone) is a high-performance engineering thermoplastic belonging to the polyaryletherketones family. Known for its exceptional mechanical, thermal, and chemical properties, PEEK is suitable for various industries. This guide provides a deeper understanding of PEEK material, covering:

• Advantages and disadvantages of PEEK plastic
• PEEK plastic applications in different industries
• How PEEK plastic is manufactured
• Considerations when designing for PEEK plastic
• Future developments and trends in PEEK plastic technology

Advantages and Disadvantages of PEEK Plastic

PEEK's characteristics derive from its properties, such as durability and broad temperature range, especially its high-temperature resistance. Demand for this material is growing among manufacturers due to its higher mechanical properties at lighter weight compared to metals. Here are the key properties and disadvantages of PEEK:

Advantages

• High-temperature resistance: PEEK products can generally withstand continuous use at temperatures up to 180°C and up to 250°C for certain grades. The melting temperature is around 343°C.
• Mechanical strength and dimensional stability: Exceptional in strength, stiffness, creep, and fatigue, enabling lightweight parts with better performance over time.
• Lightweight: PEEK's low density is about 1/5 to 1/6 of metal weight, making it a preferred material.
• Chemical resistance: Superb resistance to many acids, bases, hydrocarbons, and organic solvents, even at high temperatures.
• Electrical performance: Excellent insulation characteristics over a wide range of temperatures and frequencies.
• Thermal insulation: The low coefficient of thermal conductivity offers excellent insulation.
• Hydrolysis resistance: With low moisture absorption, PEEK does not hydrolyze in water, even at high temperatures.
• Recyclable: PEEK is halogen-free and complies with the European RoHS directive and REACH.

Disadvantages

• Cost: PEEK is relatively expensive compared to many other thermoplastics, which can limit its use in volume-intensive applications.
• Processing Challenges: The high melting point (around 343°C) requires specialized equipment and techniques, adding complexity and cost to manufacturing processes.
• Limited Availability: PEEK may have limited availability in certain regions, resulting in longer lead times or higher costs.
• Low resistance to UV: Susceptible to degradation from prolonged UV radiation, although additives like UV stabilizers can mitigate this.
• Limited Color Options: Typically available in natural (light brown) or black, offering fewer color choices compared to other polymers.

PEEK Plastic Applications in Different Industries

PEEK is used in various industries due to its properties:

1. Aerospace: Structural parts, brackets, electrical connectors, cable insulation, fuel system components.
2. Automotive: Engine components, electrical connectors, fuel system parts, piston parts, bearings.
3. Oil and Gas: Downhole equipment, pump components, valves, seals, electrical connectors.
4. Electrical and Electronics: Insulation materials, connectors, sockets, circuit boards, cable insulation, high-temperature wire coatings.
5. Medical and Dental: Biocompatible for implants, surgical instruments, orthopedic devices.
6. Chemical Processing: Pumps, valves, seals, gaskets, connectors.
7. Food Processing: Conveyor belts, gears, bearings, seals, suitable for repeated food contact.

How PEEK Plastic is Manufactured

The production of PEEK involves several steps:

1. Monomer Synthesis: Synthesis of para-difluorobenzene (p-DFB) and 4,4'-difluorobenzophenone (DFBP) through chemical reactions and purification processes.
2. Polymerization: High-temperature polymerization using step-growth or condensation polymerization, forming polymer chains.
3. Post-Processing: Transforming PEEK resin pellets into profiles, rods, sheets, or films through extrusion, injection molding, or machining.
4. Additional Treatments: Enhancements like annealing, surface coatings, or UV resistance treatments to improve properties.

Considerations When Designing for PEEK Plastic

When designing with PEEK, consider the following:

• Mechanical Loads: Ensure the component's design optimizes strength and load-bearing capabilities.
• Thermal Stability: Design for the expected temperature range and consider thermal expansion and contraction.
• Chemical Environment: Ensure compatibility with the chemical environment in which the component will operate.
• Machining Challenges: Work with experienced manufacturers for precision and surface finish.

Future Developments and Trends in PEEK Plastic Technology

Future advancements in PEEK technology may include:

• Improved Processing Techniques: More efficient fabrication methods like additive manufacturing.
• Enhanced Reinforcement: Use of carbon fibers or nanoparticles for improved mechanical properties.
• Surface Modifications: Bioactive surfaces for medical implants or antimicrobial coatings for healthcare applications.
• Advanced Testing and Simulation: Better computational tools for modeling and predicting PEEK behavior under different conditions.

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