Cross-Linked Polymer Acetabular Cup Liner for Wear Reduction
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Solution Overview
Problem
Current methods for forming polymer components for hip resurfacing prostheses, such as acetabular cups, face issues like pseudo-tumour formation due to metal wear debris, poor fixation leading to deformation, and high failure rates, especially with metal-on-polyethylene combinations, which result in osteolysis and bone loss.
Innovation Solution
A method involving blending polymer particles with antioxidants, followed by irradiation to cross-link molecules, and subsequent consolidation, while minimizing oxygen presence to prevent oxidation, using techniques like direct compression moulding and ultrasound to enhance mechanical properties and reduce wear.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal-on-metal hip resurfacing is used, then structural strength and load-bearing capacity are improved, but pseudo-tumour formation occurs due to metal wear debris and metal ions
Solution Approach 1:
The invention uses a composite structure with a metal outer cup shell providing structural strength and a polymer inner cup liner providing a biocompatible bearing surface. This composite material approach allows the metal shell to bear loads while the polymer liner prevents pseudo-tumour formation by eliminating metal-on-metal contact.
Solution Approach 2:
The invention applies different material properties to different parts of the acetabular cup: the outer shell uses metal for strength and load-bearing, while the inner liner uses polymer for biocompatibility and wear resistance. This local differentiation of material quality resolves the contradiction between needing strength and avoiding harmful metal debris.
2Object-affected harmful factors
If metal outer cup shell with polymer inner cup liner is used, then pseudo-tumour risk is reduced, but wear of bearing surface leads to early loosening and osteolysis
Solution Approach 1:
The invention changes the physical and chemical parameters of the polymer material through cross-linking (increasing molecular bond strength) and oxidation control (managing chemical composition). These parameter changes enable the polymer to resist wear while maintaining joint stability and preventing loosening.
Solution Approach 2:
The invention utilizes phase transition during the polymer processing and curing process, where the polymer transitions from a uncross-linked state to a cross-linked gel state. This phase transition creates a more durable bearing surface that resists wear and prevents early loosening while maintaining the metal-polymer composite structure.
3Ease of manufacture
If press-fit fixation is used, then fixation simplicity is improved, but considerable deformation occurs even with thick metal shells
Solution Approach 1:
The invention segments the acetabular cup into two separate components: a metal outer shell and a polymer inner liner. This segmentation allows the metal shell to be optimized for fixation while the polymer liner provides the bearing surface, enabling simpler press-fit fixation of the metal shell without the deformation issues that would occur in a monolithic thick-metal design.
4Stability of the object's composition
If porous coating is applied to encourage bone in-growth, then bone integration is improved, but coating particles become dislodged and serve as abrasive debris
Solution Approach 1:
The invention replaces the porous metal coating approach with a composite metal-polymer structure. The polymer inner liner provides a stable, non-abrasive bearing surface that does not particleize, while the metal outer shell maintains structural integrity. This composite approach achieves bone integration through the stable polymer surface without generating abrasive debris from dislodged coating particles.
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 produces polymer components with improved mechanical properties and reduced oxidation, leading to enhanced wear resistance and stability, minimizing the risk of pseudo-tumour formation and bone loss, thus providing a more durable and effective hip resurfacing solution.
Implementation Method 1
blending polymer particles with antioxidant to form a mixture in which the antioxidant coats the polymer particles
Implementation Method 2
irradiating the polymer particles to cross-link molecules therein
Data Source
AI summary
This invention related to a method of forming a polymer component and comprises blending polymer particles with antioxidant to form a mixture in which the antioxidant coats the polymer particles, irradiating the polymer particles to cross-link the polymer particles therein and forming the irradiated mixture into a consolidated component. The invention also relates to a method of forming an articular surface for a prosthesis and a prosthesis having a polymer articular bearing surface wherein at least one predetermined portion of the bearing surface is provided with cross-linked polymer bonds.