University of Limerick
Hennessy_2020_Method.pdf (24.25 MB)

A method for implementation of manufacturing traceability in orthopaedic implants

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posted on 2022-11-03, 12:05 authored by Jennifer Emma Hennessy
Over the past decade the orthopaedic implant industry has experienced a number of high profile product recalls. The most widely publicised was the ASRTM Hip System from DePuy Orthopaedics Inc. in 2010. Issues came to light when the National Joint Registry in England and Wales reported a 5 year revision rate of approximately 13% (Johnson&Johnson, 2010). In 2013 the Federal Drug Administration (FDA) announced the Unique Device Identifier (UDI) Rule to “establish a system to adequately identify devices through distribution and use” (FDA, 2013). This was very positive in terms of product traceability and patient care however it does not apply to the manufacturing process which is regulated under FDA 21CFR820 and ISO13485:2016 standards. Unlike the UDI ruling these standards do not specify a need for individual device identification, rather they put the onus on the manufacturer to specify the level of quality assurance and traceability required. The majority of orthopaedic implants are produced in batches using the investment casting process. This is ideally suited to making high volumes of identical product, but as a result no implants are currently manufactured with unique device identifiers from the wax injection stage of the process. This means if a product failure occurs entire batches must be recalled instead of individual devices. This research aims to develop technology to enable individual device traceability. The objective is to develop a prototype device for creating simple dot patterns on wax investments. The device specifications will adhere to ECC200 Data Matrix standards as static versions are being used by a leading manufacturer for batch traceability of knee implants. A literature review determined there was currently no suitable method for creating UDIs on individual cast and injection moulded components. However, the literature did identified a number of technologies which could potentially form a basis for a dynamic marking device. Wax actuators were deemed the most suitable. They work by using the volume expansion during the solid to liquid phase change to do mechanical work. Four experimental phases following a design, build, run and analyse methodology were used to develop a marking device. Phase 1 prototyed technologies from the literature, identifying gaps in the knowledge. From this it was determine a new design of wax actuator would need to be developed along with a compatible heater system and a method of filling wax actuators. Phase 2 developed a PCB heater array. For testing this was bonded to a corresponding array of wax actuators in a polymer block and sealed with an elastomeric membrane. When current was applied, the heater temperature increased, melting the wax causing it to expand. The wax expansion created a raised dot on the top surface of the array. Experiment Phase 3 integrated the heater and wax actuator arrays in one PCB. The top surface of wax actuators was sealed with a membrane. During this phase a new and novel heater design was developed. The heater was an electrically resistive sleeve which completely enveloped the wax. This was a new wax actuator design with a fast response time. At the time of writing, patent protection is pending on the actuator design. A final prototypte was fabricated for a wax injection mould. The prototype device was capable of surviving moulding pressures of up to 30Bar. It was also capable of creating unique dot patterns which could be moulded into wax investments. A patent has been filed on the marking device design. An International Searching Authority (ISA) report conclude the design was novel, new and inventive. The full ISA report can be seen in Appendix C.



  • Doctoral

First supervisor

Southern, Mark

Second supervisor

Ryan, Alan





Department or School

  • School of Education

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