The Application of PEEK in the 3D Printing Medical Field --Chinas path in the PEEK field

3D printing, also known as additive manufacturing, is the direct construction of objects through layer by layer stacking of raw materials. Compared to traditional material reduction manufacturing, 3D printing has the advantages of manufacturing complex shaped items without increasing costs, requiring no manufacturing skills, and reducing waste. It is suitable for small batch, customized, and complex shaped products.

 

After more than 30 years of development, 3D printing has gradually matured and formed a relatively complete industrial chain. On its downstream application end, healthcare is an industry that can be deeply linked, as medical devices such as surgical guides, medical implants, and dentures have high requirements for personalized customization.

 

The current 3D printing technology is developing rapidly at an unprecedented speed, including melt deposition molding (FDM) technology, photocuring (SLA) molding technology, 3D spray printing (3DPI) technology, selective laser sintering (SLS) technology, and so on. In the process of continuous maturity of printing technology, the limitations of printing materials make it unable to meet the demanding requirements of the medical field, which hinders the wider application of 3D printing technology in clinical practice. In order to break through the bottleneck of printing materials, researchers have conducted many related basic research, and in recent years, significant breakthroughs have been made, with new materials constantly being applied to medical printing. PEEK (polyether ether ketone) material is one of the best among them.

 

Since PEEK materials have been confirmed to be suitable for 3D printing technology, high-performance implants that can be used in the human body have been obtained through additive manufacturing, which provides another avenue for highly customized medical implants.

 

With the breakthrough of medical technology and the maturity of 3D printing technology, the combination of the two has achieved the effect of "1+1 ≥ 2". In the medical industry, there are also many successful applications of 3D printing in the treatment of difficult surgical cases such as fractures, heart bypass, teeth, etc. For example, researchers at the University of Basel used PEEK to treat orbital fractures, reducing the risk of postoperative rejection.

 

Uncover PEEK

 

PEEK is a high-performance material with excellent mechanical properties, corrosion resistance, and high temperature resistance. Its long-term working temperature can reach 260 ° C, and it can adapt to various extremely harsh working environments. Due to its excellent comprehensive performance, it is also known as one of the most promising materials in the 21st world by the engineering community.

 

PEEK is an ultra-high performance special engineering plastic developed by Imperial Chemical Industries (ICI) in 1978. It began to be developed domestically in the mid-1980s and was patented by Jilin University in 1990. Although PEEK materials have a history of over 30 years of development, their promotion and application are limited by the development of 3D printers due to their melting point of 334 ℃. In recent years, with the rapid development of 3D printers, this material has gradually become available for processing in 3D printing technology, attracting interest from the medical community and even being referred to as the "most promising material of the 21st century.

 

The Development History of PEEK

 

Initial incubation stage (1978-1992): PEEK is an ultra-high performance special engineering plastic developed by Imperial Chemical Industries (ICI) in 1978. ICI applied for a patent and industrialized it, with a production capacity of 1000 tons per year, mainly used in the field of defense and military industry.

 

Monopoly Development and Disintegration Stage (1993-2004): Victrex, a British company, acquired PEEK business from ICI, showing a monopolistic development trend and continuously expanding production scale. In 2003, the production capacity increased to 2800 tons/year. Subsequently, DuPont, BASF, Mitsui East Asia Chemical Company of Japan, and the United States have also launched similar products, and the application field of PEEK has also expanded from the initial military to civilian fields such as industry and biomedicine.

 

For a long time, PEEK has been listed by the Paris Coordinating Committee as a strategic material to implement a blockade and embargo on China. In order to meet the needs of national defense and civilian high-tech development, the country has included it in the "7th Five Year Plan" to "15th Five Year Plan" national key scientific and technological research projects and the "863 Plan" for research. With strong policy support from China, Professor Wu Zhongwen's team from Jilin University independently developed PEEK patented technology with independent intellectual property rights, and established Jida High tech Materials Co., Ltd. and put it into operation.

 

Comprehensive development stage (2005-present): In 2005, Evonik acquired Jida High tech, and Solvay acquired the PEEK business of Garda in India; In 2009, China's Jinfa Technology Co., Ltd. and Panjin Zhongrun Special Plastics Co., Ltd. entered this field, and PEEK entered a comprehensive development stage. In addition, the modified composite and processing technology of PEEK is gradually developing, and its application fields are also constantly expanding. Due to the numerous manufacturers specializing in PEEK production worldwide, the level of market competition will also become increasingly fierce. At present, Wiggs in the UK, Solvay in Belgium, and Evonik in Germany are the three largest PEEK manufacturers in the world.

 

In the medical field, research on PEEK materials is also quite popular, firstly because it has good biocompatibility and elastic modulus similar to human bone. If used as an implant material, there will be no adverse reactions caused by metal ion dissolution, and to some extent, it can also weaken or even eliminate the stress shielding effect, which is conducive to the integration between the implant and bone tissue.

 

PEEK materials generally only have a density of 1.3g per cubic centimeter similar to human bone tissue, with an elastic modulus comparable to that of human bone tissue. They can better collaborate with left and right neighbors and reduce the common stress shielding effect of metals. Stress shielding refers to when two or more materials with different stiffness jointly bear external forces, materials with higher stiffness will bear more loads, while loads with lower stiffness only need to bear lower loads. As a result, bones with lower stiffness do not have good stimulation, leading to degradation. The latest research results indicate that PEEK material implants not only provide suitable bearing strength, but also have a relatively light overall mass.

 

Secondly, compared to traditional medical aluminum alloys, PEEK maintains a high level of accuracy in the 3D printing process, while also being lighter than aluminum alloy materials, reducing the burden on postoperative patients.

 

It can achieve porous implants and promote more cell regeneration. The printing of high-temperature, implantable polymer PEEK has paved the way for a more complex generation of biomaterials. Implementing FDM 3D printing in medical facilities can reduce material waste, accelerate implant production, improve cost-effectiveness, and provide targeted treatment for different patients.

 

Finally, metal implants may have more or less CT or X-ray artifacts in future imaging examinations, which can affect the diagnosis of future diseases. PEEK materials can be penetrated by X-rays and do not produce artifacts under CT or MRI, which is more conducive to postoperative observation and tracking of the healing process, thus achieving good monitoring of bone growth and healing. This means that in the medical field, it will be an ideal artificial bone material and can even replace the commonly used titanium alloy material in more future scenarios, with broad application prospects.

 

Implants made from PEEK

 

(1) Bone substitutes - maxillofacial and cranial implants

 

(2) Spinal Surgery - Spinal Intervertebral Fusion Cage

 

(3) Bone and hip substitutes - joint implants

 

(4) Orthopedic equipment: fixed plates and screws

 

(5) Dental substitutes - Dental implants made with CFR-PEEK, dentures, root retention

 

(6) Cardiac Surgery - Cardiac Pumps and Valves

PEEK material printed skull

 

At present, PEEK, with its excellent performance, is widely used in various fields such as trauma, dentistry, spinal and joint surgical implants. However, there are many difficulties in promoting this material at present:

 

Firstly, the price of PEEK is extremely expensive, and the cost of a personalized skull surgery for PEEK is at least 3-5 times that of titanium alloy. However, 3D printing can reduce material loss and thus compensate for its price deficiency. But in order to truly apply PEEK materials, it is necessary to overcome the difficulties in printing technology.

 

The difficulty of printing PEEK materials is widely recognized in the industry, and even some international 3D printing giants have been unable to launch their own PEEK 3D printing, which indirectly reflects the difficulty of this technology.

 

 

Secondly, when PEEK materials are printed and formed using FDM technology, there will inevitably be shortcomings such as obvious stripes on the surface of the printed prototype, lower printing accuracy compared to other printing methods, and slow forming speed. The application range of FDM technology is relatively wide, and the technical difficulty was not particularly high. But the melting point of PEEK material is as high as 343 ℃ and is very sensitive to temperature changes. This not only requires the printer to perform high-temperature printing, but also ensures that the product will not deform due to temperature changes during printing.

 

PEEK Material 3D Printing Technology

 

Unlike thermoplastic materials commonly used in melt deposition 3D printing technology, such as ABS, PLA, etc., PEEK material is a semi crystalline thermoplastic polymer material with high melting point and performance. Therefore, during the 3D printing process, the cooling shrinkage caused by high melting point and the crystallization shrinkage caused by crystallization can easily cause warping deformation of the material during the manufacturing process, which can easily lead to the failure of 3D printing.

 

First generation PEEK material 3D printing technology:

 

Micro thermal environment technology

 

The first generation of PEEK material 3D printing technology mainly uses a micro thermal environment technology of 80 ℃~140 ℃ to appropriately reduce the cooling shrinkage of PEEK material during the printing process. This technology is currently a common technology on the market, mainly represented by German companies such as Apium and Indmatec. However, the current effect of this technology on reducing material cooling shrinkage is limited, It is often difficult to effectively manufacture dense PEEK parts with dimensions of 100mm * 100mm * 100mm.

 

Some samples printed by HPP 155 from Indmatec in Germany

 

Second generation PEEK material 3D printing technology:

 

Ultra High Temperature Environment Technology

 

The second generation PEEK material 3D printing technology mainly uses an ultra-high temperature environment of around 300 ℃ to significantly reduce the shrinkage of PEEK material during the printing process. However, this generation of technology also has certain defects, that is, after printing, PEEK parts will undergo secondary shrinkage deformation or accumulate a large amount of internal stress as the box cools.

 

3D printing technology for third-generation PEEK materials:

 

Controlled Cold Deposition Technology

 

The third-generation PEEK material 3D printing technology is based on the controllable mechanism of polymer chain aggregation of PEEK materials, which greatly solves the problem of shrinkage and warping of PEEK materials. The forming size can reach 300mm * 300mm or above, and combined with certain post-processing processes, the 3D printing of PEEK material parts can be controlled. It can be formed into high toughness and high plasticity products, as well as high-strength and high hardness products, Even combining the two can form functional products with different performance regions.

 

Highly resilient 3D printed PEEK rib prosthesis

 

High intensity 3D printing PEEK skull

 

According to an industry report from Ping An Securities, it is expected that China's 3D printing industry will reach a scale of tens of billions of US dollars by 2023. When an industry matures, downstream application servers will inevitably account for the majority of the output value contribution. At present, the downstream application market for 3D printing is gradually expanding, and it is expected that by 2025, the market size of 3D printing services will account for about 58% of the entire market. Medical treatment will be a flourishing field of 3D printing, and the current aging trend provides broad space for its development in the medical field.

 

3D printing, PEEK materials, and personalized orthopedic implants have put forward new requirements for the design of traditional medical prosthetic models: the additive manufacturing method of 3D printing will cause anisotropy in the parts - stress environment needs to be considered in model design; The application of PEEK materials will change the 3D printing process - the characteristics of PEEK materials need to be considered in model design; The practical application conditions of personalized orthopedic implants are very demanding - high reliability is required in model design.

 

Can the quality of domestic mass production of PEEK materials reach or even surpass the level of similar foreign products, and can the development of 3D printer technology support the further application of PEEK materials. These are all important influencing factors, and we still have some way to go.