Polyetheretherketone (PEEK) resin is a new type of special engineering plastic. Its elastic modulus is close to that of cortical bone, and it has good biocompatibility and radiation permeability. The advantages such as shadows are increasingly valued by the medical device industry, especially the implanted medical industry, and applications are becoming more and more common and widespread. At present, China's implant-grade polyetheretherketone mainly relies on imports from abroad, and the domestic implant level is still in the experimental stage, and there is still a distance from clinical application. This has largely limited the processing of domestic polyetheretherketone orthopedic implant products. Domestically, it is mainly produced by means of machining by bar.
Beijing Fule Technology Development Co., Ltd. Huang Xiyi
The following is a discussion of the machining process of a polyetheretherketone interbody fusion cage (see Figure 1).
As can be seen from Figure 2, the dimensional tolerance requirements of the product are not high, except for the 2mm × 4mm groove tolerance requirements, the rest are free tolerances. If it is a general engineering plastic machining, there is no big problem with the general equipment. The implant grade polyetheretherketone is an implantable material, plus some characteristics of the material itself, which have special requirements in the processing.
Figure 1 Polyetheretherketone interbody fusion cage
(1) Polyetheretherketone has a slight amount of water absorption. In order to prevent contaminants from entering the interior as a solution, it is necessary to ensure the cleanliness of each process and prevent any contact of the contaminants with the product and its semi-finished products. Therefore, ordinary cutting fluid cannot be used in the machining process.
At present, the special cutting fluid has not been clinically confirmed, and if the cooling is performed with clean water, there are many problems such as the cleaning of the cutting fluid circulation system of the machine Tool and the cost of obtaining clean water. To this end, we use direct processing, that is, direct processing without cutting fluid. This eliminates the contamination of the product due to its water absorption.
(2) Polyetheretherketone as an engineering plastic If the temperature is too high during the processing, coking and deterioration will occur, and toxic substances will remain in the interior, causing the product to be scrapped. Since we use direct machining, it is more prone to excessive surface temperature, so we must strictly control various cutting parameters. Initially, although we realized that direct processing may cause the surface temperature to be too high and reduce various cutting parameters, it is still underestimated that many products are coking and scrapped. In addition to the occurrence of coking metamorphism, the surface hardening may become brittle, so that the crack occurs at the edges when the φ1 mm hole is loaded into the developing needle in the drawing. To this end, we have done a lot of experiments to determine the cutting parameters of various machining methods. The following table shows the cutting parameters of various processing methods that we have finally determined (the parameters in the table are set for the processing of our interbody fusion cage, and the processing of other products may not be applicable). Processing with the cutting parameters in the table eliminates the occurrence of coking deterioration, and the problem of surface hardening is also basically solved.
(3) For implants, having a smooth surface is critical because the presence of defects such as burrs can be a serious hazard to the health of the patient. But burrs have been a nightmare for many medical device manufacturers because of the high cost and time consuming to remove burrs. Plastics with thermoplastics tend to carry a lot of burrs when processed, as do polyetheretherketone. These burrs are soft and tough, and manual elimination is also very labor-intensive. In the interbody cage, there are often a lot of tip angles, which are more prone to burrs. At present, we do not have a particularly good method for removal, and can only be manually scraped with a blade. However, according to the data we have recently found, there are new technologies for removing burrs at low temperatures in foreign countries without affecting the quality or surface integrity of the components. I hope that there will be new processes and equipment in this area as soon as possible in China.
(4) In summary, the processing of three polyetheretherketones, in the final analysis, is that our implant grade polyetheretherketone can not be localized.
Many foreign polyetheretherketone interbody fusion cages are formed by thermoplastic processing, and the injection molding parts do not need to be annealed or traditionally machined, and there is no above-mentioned process problem. Although foreign suppliers of implanted polyetheretherketone materials can also provide polyetheretherketone interbody fusion cage products, they are much more expensive than their own processing. Therefore, we still hope to achieve the localization of implantable polyetheretherketone products, and improve the quality and competitiveness of China's medical device products for the benefit of the people.
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