Chain Entanglements and Radiation Crosslinking: Novel Approaches for Improving UHMWPE Wear and Fatigue Properties in Total Knee Replacements

Lead Research Organisation: Durham University
Department Name: Engineering and Computing Sciences

Abstract

The natural human knee is a complex and heavily loaded joint. Therefore, for functional reasons, freedom of movement and stability are important for artificial knee joints. Due to this demand, high stresses are placed on the articulation of the artificial knee joints. Polyethylene (with very high molecular weight, termed as UHMWPE) has been the material of choice for the load-bearing articulating surface in artificial knee joints. As a result, excessive wear and fatigue of the tibial polyethylene bearing are common and result in artificial knee joint failure. Polyethylene-related total knee failures have limited the lifetime of total knee joint replacements.However, there is an increasing demand for total knee replacement operations which now account for nearly half of all joint replacements in the UK. In fact, approximately one million UHMWPE components are implanted worldwide on a yearly basis. Also the number of operations carried out in those aged 55-64 has been rising significantly. The application of joint replacement to younger (aged < 64 years) and more active people plus the general increase in life expectancy make it an urgent need for longer lasting polyethylene with better wear and fatigue resistance. The Project is focused on reducing the incidence of material failure. The hypothesis to be examined is that the cause of material failure of UHMWPE knee-joint components lies in the precise time-temperature history employed during manufacture of the UHMWPE components from the virgin UHMWPE powder. Recent work has shown that toughness at macroscopic UHMWPE welded interface increases with welding time and temperature. This suggests that the toughness of UHMWPE powder particle interfaces may vary similarly with compression moulding time and temperature. Hence there is a need to optimise processing conditions to provide interfaces with adequate toughness at locations in tibial components where stress intensities are high. Radiation crosslinking of UHMWPE for artificial knee joints is still controversial and there is a debate over whether radiation crosslinking is beneficial. While crosslinking reduces UHMWPE wear, the method of post irradiation processing of the material to eliminate residual free radicals can affect the long-term performance of the material in the body. Radiation crosslinking will be incorporated and assessed in the Project in order to resolve the scientific controversy regarding its effects on wear and fatigue.The proposed project seeks to answer two important questions. 1) Does improved interface bonding improve the endurance of UHMWPE tibial components and to what extent? 2) Can an appropriate additional radiation crosslinking treatment be beneficial? The Project uses two novel approaches. One is to improve material integrity using computer-aided methodology for generating a range of actual customised tibial component with varying degrees of interface bonding. The other is to combine improved material integrity with state-of-art post irradiation treatment in order to reduce wear rate and improve fatigue resistance. A side-by-side comparison of a range of non-crosslinked and radiation cross-linked components, based upon evaluation of wear behaviour, wear particles and fatigue strength will be made. Identification of optimised manufacturing conditions will reduce the currently high rate of revision operations.

Publications

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Reay E (2009) Premature failure of Kinemax Plus total knee replacements. in The Journal of bone and joint surgery. British volume

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Wang QQ (2009) Numerical Prediction on Mechanical Contacts Vanguard Knee Joint replacements Tested in the Displacement-Controlled Prosim Simulator in Proceedings of IMeChE Knee Arthroplasty: From Early Intervention to Revision

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Wang QQ (2011) Reptation Modelling and Wear Performance of UHMWPE with Different Moulding Conditions in Proceedings of 57th Annual Meeting of the Orthopaedic Research Society

 
Description 1) Identification of the importance of Type 2 fusion defects (due to incomplete diffusion at interface) to the structural integrity of Ultra-High Molecular Weight Polyethylene (UHMWPE). This finding has led to further IP and its application is ongoing.

2) Identification of the mechanism by which oxidation and fusion defects synergistically accelerate UHMWPE failure in knee replacements.

3) Development of method to achieve medio-lateral displacement of the head and rim for wear testing of hip implants that successfully reproduces clinically relevant stripe wear. These more challenging wear conditions aided regulatory submissions to notified bodies.

4) Development of novel methods for modelling and characterising the influence of chain length and distribution on the rheological behaviour of UHMWPE and its stress response during processing.

5) Pre-clinical evaluations using aggressive techniques on superlattice coated joints have found that superlattice coating has not only excellent wear properties but also prevent metal particle release. This finding has been taken forward by Biomet to generate new joints replacements and will be launched in market in 2015.
Exploitation Route Findings have been taken forward by industries and NHS clinicians. As the medical devices will not only last longer but also reduce post-operative complications, these will be beneficial to patients. Additionally, a consequence of these benefits is the reduction of NHS cost.
Sectors Education,Healthcare,Government, Democracy and Justice,Manufacturing, including Industrial Biotechology,Culture, Heritage, Museums and Collections

 
Description My findings have been used and taken forward by industries and NHS clinicians. NHS clinicians have also used one of my findings to provide understanding to their premature failure of Kinemax Plus total knee replacements (see Journal of Bone and Joint Surgery (Br) 91-B: 604-611). Industry has used my findings to make strategic decisions such as Biomet Rebalance Ankle Joints and superlattice coating for knee and hip joint replacements. As the medical devices will not only last longer but also reduce post-operative complications, these will be beneficial to patients. Additionally, a consequence of these benefits is the reduction of NHS cost.
First Year Of Impact 2009
Sector Education,Healthcare,Manufacturing, including Industrial Biotechology,Culture, Heritage, Museums and Collections,Other
Impact Types Cultural,Societal,Economic,Policy & public services

 
Description NHS and Biomet
Geographic Reach National 
Policy Influence Type Influenced training of practitioners or researchers
Impact Contribute towards new bearing technologies for orthopaedic applications, supporting the Industrial decision making process, providing data to support regulatory submissions to notified bodies and competent authorities such as Medicines and Healthcare products Regulatory Agency (MHRA) for CE marking and to support ethical committee approval to conduct clinical trials as well as influencing clinicians.
 
Description Biomet Europe
Amount £30,000 (GBP)
Organisation Biomet, Inc 
Sector Private
Country United States
Start 10/2008 
End 09/2011
 
Description Biomet Europe
Amount £30,000 (GBP)
Organisation Biomet, Inc 
Sector Private
Country United States
Start 10/2009 
End 09/2012
 
Description High-value manufacturing (Medical Devices)
Amount £219,454 (GBP)
Funding ID TS/H001115/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2010 
End 04/2012
 
Description Knowledge Transfer Account
Amount £29,700 (GBP)
Organisation University of Sheffield 
Department EPSRC KTA Knowledge Transfer Account
Sector Academic/University
Country United Kingdom
Start 01/2011 
End 12/2011
 
Title Aggressive in vitro testing tool to better simulate in vivo performance 
Description Development of the novel method to achieve medio-lateral displacement of the head and rim for the pre-clinical testing of implants that successfully reproduces clinically relevant stripe wear. These more challenging wear conditions aided regulatory submissions to notified bodies. 
Type Of Material Model of mechanisms or symptoms - in vitro 
Year Produced 2011 
Provided To Others? Yes  
Impact Aggressive pre-clinical testing has been incorporated in the latest Prosim Hip Simulator design. 
 
Title Reptation Model 
Description Use reptation modelling to quantitatively simulate the extent of the Type 2 fusion defects (due to incomplete diffusion at interface) important to the structural integrity of Ultra-High Molecular Weight Polyethylene (UHMWPE) used for joint replacements. 
Type Of Material Computer model/algorithm 
Year Produced 2011 
Provided To Others? Yes  
Impact Orthopaedic manufacturing companies have been making efforts to minimise Type 2 fusion defects. 
 
Description Biomet Ltd 
Organisation Biomet, Inc
Department Biomet UK
Country United Kingdom 
Sector Private 
PI Contribution contribute towards new bearing technologies for orthopaedic applications, supporting the Industrial decision making process, providing data to support regulatory submissions to notified bodies and competent authorities such as Medicines and Healthcare products Regulatory Agency (MHRA) for CE marking and to support ethical committee approval to conduct clinical trials.
Collaborator Contribution Studentships, Industrial CASE studentships, cash and in-kind contributions and development of new bearing technologies.
Impact Lots of publications and invitations to give key-note presentations at the international meetings organised by the Company (please see the publications section). It is multidisciplinary. It has involved Materials Scientists, Bioengineers, Clinicians and Industry.
Start Year 2007
 
Description Corin Group PLC 
Organisation Corin Group PLC
Country United Kingdom 
Sector Private 
PI Contribution contribute towards new bearing technologies for orthopaedic applications, supporting the Industrial decision making .
Collaborator Contribution Providing materials, in-kind contribution and leading joint TSB grant.
Impact Wang QQ, Wu JJ, et al (2012). Biotribological Study of Large Diameter Ceramic-on-CFR-PEEK Hip Joint Including Fluid Uptake, Wear and Frictional Heating. Journal of Materials Science: Materials in Medicine 23(6): 1533-1542. Wang QQ, Wu JJ, Simpson D, Collins S, Briscoe A & Jarman-Smith M (2011). Biotribology of 40mm Diameter MOTIS PEEK on Ceramic Hip Joints: A Detailed Simulator Study with Different Inclination Angles. Proceedings of the 24th Annual Congress of ISTA, Bruges, Belgium. Wang QQ, Wu JJ, Simpson D & Collins S (2011). Biotribological and Structural Analyses of Large Diameter Ceramic on Carbon Fibre Reinforced PEEK Hip Joints with Different Inclination Proceedings of International Conference on Biotribology, Imperial College, London.
Start Year 2010
 
Description Morgan Advanced Ceramics 
Organisation Morgan Advanced Materials
Country United Kingdom 
Sector Private 
PI Contribution contribute towards new bearing technologies for orthopaedic applications, supporting the Industrial decision making
Collaborator Contribution Cash and in-kind contributions.
Impact Douillard T, Chevalier J, Warner I, Galais Y, Whitaker P, Wu JJ & Wang QQ (2012). Comparative Ageing Behaviour of Commercial, Unworn and Worn 3Y-TZP and Zirconia-Toughened Alumina Hip Joint Heads. Journal of the European Ceramic Society 32(8): 1529-1540.
Start Year 2010
 
Description NHS 
Organisation NHS England
Country United Kingdom 
Sector Public 
PI Contribution Improve clinical understanding of new bearing technologies and materials failure as well as being invited to give lecturers to clinician.
Collaborator Contribution Materials provider
Impact Reay E, Wu JJ, Holland J & Deehan D (2009). Premature failure of Kinemax Plus total knee replacements. Journal of Bone and Joint Surgery (Br) 91-B: 604-611. Wu JJ, Augustine A, Holland JP, Deehan DJ (2012). Oxidation and fusion defects synergistically accelerate polyethylene failure in knee replacement. The Knee 19(2): 124-129.
Start Year 2008
 
Title Vitamine E Infused Ultra-high molecular weight Polyethylene for Knee and Ankle Joint Replacements 
Description Recently further funding has been initiated by Biomet to pursue more pre-clinical evaluations. 
Type Therapeutic Intervention - Medical Devices
Current Stage Of Development Refinement. Non-clinical
Year Development Stage Completed 2012
Development Status Under active development/distribution
Impact Great work impressed Industry and clinicians and subsequently the devices have been implanted into some patients and will be given to more patients. 
 
Description Conference Oral Presentations 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Participants in your research and patient groups
Results and Impact Improve understanding and help clinical decision making.

More collaborations and high impact upon industrial decision making
Year(s) Of Engagement Activity 2007,2008,2009,2010,2011,2012,2013,2014
 
Description Invited Key-note by Industry 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Participants in your research and patient groups
Results and Impact Excellent feedback and attracted more collaborations.

Inform industrial decision making.
Year(s) Of Engagement Activity 2010
 
Description Invited NHS Lecture 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Excellent feedback from surgeons.

Improve their understanding on biomaterials for total knee joint replacements.
Year(s) Of Engagement Activity 2009
 
Description UK-China Science Bridge 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Participants in your research and patient groups
Results and Impact Leading to further collaborations and research discussions.

UK-China Advanced Materials Institute was formed and I am one of the Board Members.
Year(s) Of Engagement Activity 2007,2008,2009,2010,2011,2012,2013,2014