UHMWPE Crosslinking with Vitamin E and DCP
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Solution Overview
Problem
Peroxide cross-linking of ultra-high molecular weight polyethylene (UHMWPE) for medical implants results in the generation of undesirable volatile by-products, such as acetophenone, which are difficult to remove without compromising the material's wear resistance and oxidative stability.
Innovation Solution
A method involving the blending of di-cumyl peroxide (DCP) and vitamin E with UHMWPE, followed by high temperature melting above 200°C to enhance material toughness and extract volatile by-products while maintaining wear resistance, involves controlled heating and cooling cycles to minimize chain scission and residual by-product concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If high temperature melting is applied to extract volatile by-products, then the concentration of toxic residual by-products is reduced, but the wear resistance of the polymer deteriorates due to excessive chain scission
Solution Approach 1:
The patent applies parameter changes by precisely controlling the high temperature melting parameters (temperature range of 200-300°C, treatment time of 1-72 hours) to optimize the balance between by-product extraction and wear resistance preservation. This involves changing the thermal processing parameters to achieve the desired outcome without excessive chain scission
Solution Approach 2:
The patent introduces vitamin E as an intermediary substance that acts as an antioxidant during the high temperature melting process. This mediator protects the polymer chains from excessive oxidation and degradation while allowing volatile by-products to be extracted, thus preserving wear resistance
2Object-generated harmful factors
If high temperature melting is applied for prolonged periods to remove by-products, then the concentration of acetophenone is reduced, but the toughness of the material deteriorates due to chain scission
Solution Approach 1:
The patent optimizes the high temperature melting parameters by controlling the temperature (200-300°C) and time (1-72 hours) to achieve the desired reduction in acetophenone concentration while minimizing chain scission. This involves finding the optimal parameter combination that balances by-product removal with property preservation
Solution Approach 2:
Vitamin E serves as a protective intermediary during prolonged high temperature treatment, reducing oxidative chain scission and preserving material toughness while allowing sufficient time for acetophenone extraction
3Strength
If peroxide crosslinking is applied to enhance mechanical properties, then the strength and toughness of UHMWPE are improved, but the oxidative stability deteriorates
Solution Approach 1:
Vitamin E is introduced as an intermediary antioxidant that compensates for the oxidative instability introduced by peroxide crosslinking. It acts as a radical scavenger during and after the crosslinking process, protecting the polymer from oxidation while allowing the crosslinking to proceed and enhance mechanical properties
Solution Approach 2:
The patent creates a composite system by combining UHMWPE with vitamin E and peroxide, where the vitamin E component provides oxidative stability to the crosslinked network. This composite approach allows simultaneous achievement of enhanced mechanical properties through crosslinking and maintained oxidative stability through the antioxidant
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 the concentration of toxic residual by-products below desired levels, enhances the material's oxidation resistance, and maintains high wear resistance and toughness, as demonstrated by reduced acetophenone index and elongation-at-break values.
Implementation Method 1
Perforade cross-linking approaches are disclosed in U.S. Pat. No. 10,981,302 and U.S. Patent Publication No. 2016/0215117
Implementation Method 2
Di-cumyl peroxide (DCP) is one the most commonly used peroxides for this purpose
Implementation Method 3
subjecting the DCP crosslinked UHMWPE to high temperature melting increases the toughness of the material and helps in extracting these volatile by-products
Implementation Method 4
Heating DCP crosslinked UHMWPE during or after crosslinking to above 202° C. accelerates the removal of acetophenone
Implementation Method 5
peroxide crosslinking of UHMWPE results in an oxidatively unstable polymer and that adding an antioxidant, such as vitamin-E or Irganox 1010
Implementation Method 6
These methods may include exposure to temperatures above the melting point of polyethylene, especially temperatures close to or greater than 200° C. for prolonged periods of time also known in the art as high temperature melting (HTM)
Data Source
AI summary
The inventions provide methods of manufacturing peroxide cross-linked and high temperature melted polymeric material, for example ultra-high molecular weight polyethylene (UHMWPE) containing vitamin E, total joint implants with high wear resistance, high oxidation resistance, and very low concentration of residual by-products, as well as products made thereby.