Diffusion Hardened Medical Implants Wear Reduction

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Solution Overview

Problem

Current hard-on-hard medical implants, such as metal-on-metal and ceramic-on-ceramic hip implants, face challenges with wear resistance and metal ion release, limiting their size and longevity, especially for young and active patients who require more stable and durable joint replacements.

Innovation Solution

The development of medical implants with a diffusion hardened surface, specifically a plasma carburized surface, contacting a non-diffusion hardened surface or a surface diffusion hardened with a different species, to reduce wear between metallic components, utilizing CoCr alloys and other metals or metal alloys for the implant components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If metal-on-metal or ceramic-on-ceramic hard-on-hard implants are used to increase joint stability and allow larger sizes, then joint stability and range of motion are improved, but wear resistance decreases and metal ion release occurs

Engineering Contradiction:

Improvejoint stabilityVSAvoidwear resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention applies differential surface treatment to specific regions of the implant components. One articulating surface is diffusion hardened to create a hard, wear-resistant surface layer, while the opposing surface remains unhardened or is treated differently. This local differentiation allows the implant to achieve both high joint stability (through appropriate material selection and sizing) and improved wear resistance (through the hardened surface), resolving the contradiction between strength and reliability.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The invention creates a composite structure at the surface level by combining a hardened surface layer with the base metal material. The diffusion hardened surface provides enhanced wear resistance while the underlying metal provides structural integrity and joint stability. This composite approach allows the implant to simultaneously achieve both wear resistance and joint stability, addressing the technical contradiction.

Inventive Principle:

Principle #40Composite materials

2Volume of stationary object

If metal-on-metal implants are used to allow larger sizes for young and active patients, then joint stability is improved, but metal ion release increases causing physiological concerns

Engineering Contradiction:

Improveimplant sizeVSAvoidmetal ion release

Core Design Contradiction:

Volume of stationary objectVSObject-generated harmful factors

Solution Approach 1:

The invention applies surface hardening to only one of the articulating surfaces rather than treating both surfaces uniformly. This localized treatment reduces the overall metal-on-metal contact area and potential for metal ion release, while still providing the necessary wear resistance for large implant sizes required in young and active patients. The unhardened surface generates fewer metal ions compared to fully hardened metal-on-metal interfaces.

Inventive Principle:

Principle #3Local quality

3Ease of manufacture

If conventional polyethylene is used in hard-on-hard implants, then manufacturing is simpler, but the liner must be thinner limiting mechanical strength and increasing wear

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidliner mechanical strength

Core Design Contradiction:

Ease of manufactureVSStrength

Solution Approach 1:

The invention extracts the polyethylene liner from the articulating surfaces, eliminating the need for a thick polyethylene liner entirely. By using diffusion hardened metal surfaces that provide inherent wear resistance, the design removes the polyethylene component that would otherwise need to be made thin in hard-on-hard implants, thereby avoiding the strength and wear problems associated with thin liners while simplifying the overall structure.

Inventive Principle:

Principle #2Taking out (Extraction)

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

This approach significantly reduces wear rates between metallic surfaces in medical implants, enhancing the durability and longevity of joint replacements, particularly in larger sizes, while minimizing metal ion release and fracture risks, thus addressing the limitations of existing implants.

Implementation Method 1

a first contacting surface comprises a diffusion hardened metallic surface which is diffusion hardened with a diffusion hardening species

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

a plasma carburized surface

Methodology Applied

Scientific EffectPlasma carburizing: Carburizing

Data Source

PatentUS11351031B2Applications of diffusion hardening techniques

Publication Date: 2022.06.07 SMITH & NEPHEW INC

AI summary

A device, for example a medical implant, and a method of making the same, the device having a metal or metal alloy substrate, for example cobalt chrome, and a diffusion hardened metallic surface, for example a plasma carburized surface, contacting a non-diffusion hardened surface or a diffusion hardened surface having a diffusion hardening species different from that of the opposing surface.