Melt-Stabilized UHMWPE Antioxidant Coating Nitrogen Atmosphere
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Solution Overview
Problem
Highly crosslinked ultra-high molecular weight polyethylene (UHMWPE) used in orthopedic implants experiences high wear rates due to free radical burden, leading to osteolysis and implant failure, and current melt-stabilization methods in oxygen-containing environments result in oxidation and waste of material.
Innovation Solution
A method involving coating UHMWPE with antioxidants like vitamin E and heating in an oxygen-containing environment to melt and stabilize the material, reducing free radical concentration and minimizing oxidation, thereby preventing the formation of an oxidized surface layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly crosslinked UHMWPE is heat stabilized by raising the material temperature above the melting point in an oxygen-containing environment, then the free radical burden is reduced, but an oxidized layer forms on the exterior of the material
Solution Approach 1:
The patent introduces nitrogen gas as an intermediary atmosphere during the melt stabilization process. The nitrogen atmosphere acts as a mediator that allows the UHMWPE to be heated above its melting point for free radical reduction while preventing oxygen from diffusing into the molten material and forming an oxidized layer. This resolves the contradiction by providing a protective intermediate environment.
Solution Approach 2:
The patent employs an inert nitrogen atmosphere during the heat stabilization process. By replacing the oxygen-containing environment with nitrogen, the process eliminates the harmful oxidation that would otherwise occur during melting, while still allowing the temperature to rise above the melting point to reduce free radical burden through recombination.
2Reliability
If the oxidized surface layer is removed during fabrication to prevent contamination, then implant contamination is prevented, but material waste increases
Solution Approach 1:
The patent converts the potential harm of oxidation into a benefit by using nitrogen atmosphere control. The inert nitrogen environment prevents oxidized layer formation during the critical melt stabilization process, transforming what would be a harmful byproduct into a controlled process outcome. This eliminates the need for subsequent oxidized layer removal and reduces material waste.
3Reliability
If UHMWPE is crosslinked by high energy irradiation to reduce wear rate, then wear rate is reduced significantly, but free radical burden increases causing oxidation in-vivo
Solution Approach 1:
The patent applies preliminary melt stabilization treatment after irradiation crosslinking. By heating the irradiated UHMWPE above its melting point in a nitrogen atmosphere, the process enables free radicals to recombine before the implant is introduced into the body. This preliminary action reduces the free radical burden that would otherwise cause oxidation in-vivo, while preserving the wear reduction benefits of crosslinking.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces free radical concentration and prevents oxidation, resulting in a stable UHMWPE implant with reduced wear rates and cost savings by minimizing material waste and avoiding the need for oxygen-free environments.
Implementation Method 1
The UHMWPE includes a first concentration of free-radicals... The UHMWPE in the melt-stabilized material includes a second concentration of free-radicals. The second concentration of free-radicals is less than the first concentration of free-radicals
Implementation Method 2
The heating is sufficient to melt at least part of the UHMWPE
Implementation Method 3
This oxidized layer is removed during fabrication of the implant to prevent contamination of the implant with oxidatively degraded UHMWPE
Implementation Method 4
coating at least part of the solid material with a liquid composition including at least one antioxidant
Data Source
AI summary
Various embodiments disclosed relate to melt-stabilized materials including ultra high molecular weight polyethylene (UHMWPE), methods of making the same, and medical implants including the same. In various embodiments, the present invention provides a method of melt-stabilizing a material including UHMWPE. The method includes obtaining or providing a solid material including UHMWPE including a first concentration of free-radicals. The method includes coating at least part of the solid material with a liquid composition including at least one antioxidant, to provide a coated solid material. The method includes heating the coated solid material in an environment including oxygen, the heating being sufficient to melt at least part of the UHMWPE, to provide a heated material. The method also includes solidifying the heated material, to provide a melt-stabilized material including UHMWPE including a second concentration of free-radicals, wherein the second concentration of free-radicals is less than the first concentration of free-radicals.