Why Consider Cross-Linking Based on Uhmwpe Materials?
03. 17, 2020
The traditional UHMWPE lining is the first-generation UHMWPE lining used in clinical orthopedics. The process that affects the performance of this lining has only two steps: compression molding (including forming nitrogen annealing treatment) and sterilization of the prosthesis. Acetabular Cup prosthesis manufacturer shares with you.
Initially, UHMWPE linings were chemically sterilized, such as formaldehyde vapor sterilization. However, due to insufficient treatment of spore-forming microorganisms, 25-40KGy gamma-ray irradiation was selected to improve sterilization quality. At the same time, it was found that the use of this small dose of radiation caused slight cross-linking inside the material, which improved the wear resistance of UHMWPE to a certain extent, which also inspired the subsequent research and development of highly cross-linked UHMWPE prostheses.
It can be said that the first-generation UHMWPE has been successfully used for joint replacement and has achieved satisfactory clinical results. However, with the younger and more active patients, the long-term survival rate based on the first-generation UHMWPE prosthesis has gradually encountered Problems, especially failures due to wear and oxidative degradation. Therefore, subsequent research focused on the cross-linking modification of UHMWPE materials, while maintaining the existing mechanical properties, further increasing the wear resistance and oxidation resistance of the material (although the wear resistance of the first-generation UHMWPE materials is already very high).
Based on the experience of the first-generation UHMWPE prosthesis, the development of the highly cross-linked (second-generation) UHMWPE prosthesis is more comprehensive. The high wear resistance, creep resistance, and oxidation resistance of the prosthesis are achieved through a three-step process: radiation Cross-linking, heat treatment, sterilization.
The first step is gamma radiation or electron beam irradiation, which results in cross-linking of polymer chains-so-called cross-linking refers to the formation of lateral covalent bonds between individual macromolecules. The three-dimensional network structure is formed between the molecular chains. The amount of crosslinking depends on the radiation dose during the irradiation. And it is not that the higher the radiation dose, the better.
The second step is heat treatment. After the irradiation of UHMWPE materials, some of the cracked molecular chains remained in the material as highly active residual free radicals. These reactive groups can react with air oxygen to cause oxidative degradation, which can accelerate the deterioration of all important properties of UHMWPE materials. Therefore, it is absolutely necessary to remove free residual free radicals from the material.
The third step is sterilization, which is necessary for the implant.
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