Spatial Control of Additives in UHMWPE Joint Implants
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Solution Overview
Problem
Radiation cross-linking of ultrahigh molecular weight polyethylene (UHMWPE) enhances wear resistance but decreases its toughness, necessitating a method to control cross-linking spatially to maintain material toughness while improving wear resistance in joint implants.
Innovation Solution
Incorporating additives such as antioxidants into UHMWPE, followed by spatially controlled distribution through blending, consolidation, high-temperature exposure, and irradiation to create a gradient of cross-linking, allowing for selective control of cross-linking density based on the additive concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If radiation cross-linking is applied to UHMWPE to enhance wear resistance, then wear resistance is improved, but toughness decreases
Solution Approach 1:
The patent applies local quality by creating spatially varying cross-linking density within the polymeric material. Different regions of the implant are cross-linked to different degrees based on the local concentration of anti-cross-linking agents, allowing the articular surfaces to have high cross-linking density for wear resistance while the bulk material maintains lower cross-linking density for toughness and fracture resistance.
Solution Approach 2:
The patent utilizes parameter changes by varying the concentration of anti-cross-linking agents throughout the polymeric material and controlling the radiation dose distribution. This creates a gradient of cross-linking density where the degree of cross-linking changes continuously from the surface to the bulk, resolving the contradiction between wear resistance and toughness.
2Manufacturing precision
If high temperature is used to extract anti-cross-linking agents from surfaces, then spatial control of cross-linking is achieved, but oxidation of the polymer and degradation of additives occurs
Solution Approach 1:
The patent applies inert atmosphere by conducting the high temperature extraction process in an inert or nitrogen atmosphere. This prevents oxidation of the polymeric material and degradation of the anti-cross-linking agents during the thermal extraction process, while still achieving the desired spatial control of cross-linking density.
Solution Approach 2:
The patent converts the potentially harmful effect of high temperature into a beneficial process by using controlled thermal extraction to remove anti-cross-linking agents from specific regions. The high temperature, when applied selectively and for controlled durations, enables precise spatial control of cross-linking density while the inert atmosphere prevents harmful oxidation.
3Stability of the object's composition
If additives are blended into polymeric material before consolidation, then uniform distribution is achieved, but extraction of additives during high temperature processing is difficult to control
Solution Approach 1:
The patent applies preliminary action by pre-blending anti-cross-linking agents uniformly throughout the polymeric material before consolidation and shaping. This ensures that the additives are distributed homogeneously in the bulk material, providing a controlled reservoir that can be extracted predictably from the surface during subsequent high temperature processing, enabling precise control of the final cross-linking density profile.
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 achieves a balance between wear resistance and toughness by creating a spatially controlled distribution of cross-links, reducing wear rates and maintaining mechanical integrity in joint implants.
Implementation Method 1
Exposing the consolidated polymeric material containing one or more additives to a high temperature may lead to oxidation of the polymer, and/or oxidation, consumption, degradation, and/or evaporation of the additives
Implementation Method 2
Loss of the additives when exposed to high temperature may be on the surface of the material, creating a concentration gradient in the material with the bulk having higher concentrations of additives than the surface
Implementation Method 3
Radiation cross-linking of polymers enhances many of their mechanical properties. For ultrahigh molecular weight polyethylene (UHMWPE), radiation cross-linking can also enhance its wear resistance
Data Source
AI summary
Provided is a method of making a polymeric material with a spatially controlled distribution of one or more additives including the steps of blending the one or more additives with a polymeric material, consolidating the polymeric material, heating at least a portion of at least one surface of the consolidated additive-blended polymeric material, and cooling the heated consolidated additive-blended polymeric material, thereby forming a polymeric material with a spatially controlled distribution of additive.