Identifying differences in the tribological performance of GUR 1020 and GUR 1050 UHMWPE resins associated to pressure × velocity conditions in linear reciprocating sliding tests.

In this work, two commercial UHMWPE (ultra-high molecular weight polyethylene) resins used in orthopedics, GUR 1050 and GUR 1020, were evaluated through linear reciprocating dry friction tests. Average contact pressures (P) of 34 MPa and 50 MPa and sliding velocities (V) of 0.02 m/s and 0.10 m/s were selected to perform tests in four PV conditions. The friction coefficient (COF) with both resins was around 0.18 in average, without significant distinctions by PV; however, a distinction was seen in COF dispersion; it was in the range of 5%-19%, in dependence of the PV condition and resin type. COF with GUR 1020 was more disperse, and it was related to the vulnerability of the resin to undergoing dynamic changes in the intensity of adhesive (higher COF) or abrasive (lower COF) wear mechanisms. Both wear mechanisms are displayed simultaneously, but random changes in intensity may occur during the friction process. Such randomness was associated to the susceptibility to have the structure modified by friction, higher in GUR 1020 than GUR 1050. Concerning wear amount, contact pressure was the most influencing parameter on it. GUR 1020 performed more than 30% inferior than GUR 1050 under contact pressure higher than the yield strength of the material. Under pressures near the material strength, the wear level was in the range of surface roughness and both resins performed equal in average; however, in this case, the dispersion was systematically lower for GUR 1050, evidencing its better tribological stability. It was concluded that analyses on the dispersion of the tribological responses disclosed relevant information on stability related performance. Also, when procedural dependent properties, as such friction and wear, are considered as evaluation parameters, care must be taken to compare results from different tribosystems.

Importance of preclinical evaluation of wear in hip implant designs using simulator machines.

Total hip arthroplasty (THA) is a surgical procedure that involves the replacement of the damaged joint of the hip by an artificial device. Despite the recognized clinical success of hip implants, wear of the articulating surfaces remains as one of the critical issues influencing performance. Common material combinations used in hip designs comprise metal-on-polymer (MoP), ceramic-on-polymer (CoP), metal-on-metal (MoM), and ceramic-on-ceramic (CoC). However, when the design of the hip implant is concerned besides the materials used, several parameters can influence its wear performance. In this scenario, where the safety and efficacy for the patient are the main issues, it is fundamental to evaluate and predict the wear rate of the hip implant design before its use in THA. This is one of the issues that should be taken into account in the preclinical evaluation step of the product, in which simulated laboratory tests are necessary. However, it is fundamental that the applied motions and loads can reproduce the wear mechanisms physiologically observed in the patient. To replicate the in vivo angular displacements and loadings, special machines known as joint simulators are employed. This article focuses on the main characteristics related to the wear simulation of hip implants using mechanical simulators, giving information to surgeons, researchers, regulatory bodies, etc., about the importance of preclinical wear evaluation. A critical analysis is performed on the differences in the principles of operation of simulators and their effects on the final results, and about future trends in wear simulation.

A artroplastia total do quadril (ATQ) é um procedimento cirúrgico que envolve a substituição da articulação danificada por um dispositivo artificial. Apesar do reconhecido sucesso clínico dos implantes de quadril, o desgaste das superfícies articulares ainda é uma das questões críticas que influenciam o desempenho. As combinações de materiais comuns usadas nas próteses incluem metal sobre polímero (MsP), cerâmica sobre polímero (CsP), metal sobre metal (MsM) e cerâmica sobre cerâmica (CsC). No entanto, em relação ao desenho do implante de quadril, além dos materiais utilizados, vários parâmetros podem influenciar o seu desgaste. Neste cenário, onde a segurança e eficácia para o paciente são as principais questões, é fundamental avaliar e prever a taxa de desgaste do modelo de implante de quadril antes de sua utilização em ATQ. Esta é uma das questões que devem ser levadas em conta na etapa de avaliação pré-clínica do produto, na qual testes de simulação em laboratórios são necessários. No entanto, é fundamental que os movimentos e cargas aplicados possam reproduzir os mecanismos de desgaste fisiologicamente observados no paciente. Máquinas especiais, conhecidas como simuladores de articulação, são utilizadas pra replicar os deslocamentos angulares e cargas in vivo. Este artigo enfoca as principais características relacionadas à simulação de desgaste de implantes de quadril por meio de simuladores mecânicos, fornecendo informações a cirurgiões, pesquisadores e órgãos reguladores, dentre outros, sobre a importância da avaliação pré-clínica do desgaste. Foi feita análise crítica sobre as diferenças nos princípios de funcionamento dos simuladores e seus efeitos nos resultados finais, bem como sobre as tendências futuras na simulação de desgaste.

Importance of preclinical evaluation of wear in hip implant designs using simulator machines / Importância da avaliação pré-clínica do desgaste em projetos de implantes de quadril usando máquinas simuladoras

ABSTRACT Total hip arthroplasty (THA) is a surgical procedure that involves the replacement of the damaged joint of the hip by an artificial device. Despite the recognized clinical success of hip implants, wear of the articulating surfaces remains as one of the critical issues influencing performance. Common material combinations used in hip designs comprise metal-on-polymer (MoP), ceramic-on-polymer (CoP), metal-on-metal (MoM), and ceramic-on-ceramic (CoC). However, when the design of the hip implant is concerned besides the materials used, several parameters can influence its wear performance. In this scenario, where the safety and efficacy for the patient are the main issues, it is fundamental to evaluate and predict the wear rate of the hip implant design before its use in THA. This is one of the issues that should be taken into account in the preclinical evaluation step of the product, in which simulated laboratory tests are necessary. However, it is fundamental that the applied motions and loads can reproduce the wear mechanisms physiologically observed in the patient. To replicate the in vivo angular displacements and loadings, special machines known as joint simulators are employed. This article focuses on the main characteristics related to the wear simulation of hip implants using mechanical simulators, giving information to surgeons, researchers, regulatory bodies, etc., about the importance of preclinical wear evaluation. A critical analysis is performed on the differences in the principles of operation of simulators and their effects on the final results, and about future trends in wear simulation.

RESUMO A artroplastia total do quadril (ATQ) é um procedimento cirúrgico que envolve a substituição da articulação danificada por um dispositivo artificial. Apesar do reconhecido sucesso clínico dos implantes de quadril, o desgaste das superfícies articulares ainda é uma das questões críticas que influenciam o seu desempenho. As combinações mais comuns de materiais usadas nas próteses incluem metal-polímero (M-P), cerâmica-polímero (C-P), metal-metal (M-M) e cerâmica-cerâmica (C-C). No entanto, em relação ao projeto do implante de quadril, além dos materiais usados, vários parâmetros podem influenciar o seu desgaste. Nesse cenário, no qual a segurança e eficácia para o paciente são as principais questões, é fundamental avaliar e prever a taxa de desgaste do modelo de implante de quadril antes de seu uso em ATQ. Essa é uma das questões que devem ser levadas em conta na etapa de avaliação pré-clínica do produto, na qual testes de simulação em laboratórios são necessários. No entanto, é fundamental que os movimentos e as cargas aplicados possam reproduzir os mecanismos de desgaste fisiologicamente observados no paciente. Máquinas especiais, conhecidas como simuladores de articulação, são usadas para reproduzir os deslocamentos angulares e as cargas in vivo. Este artigo enfoca as principais características relacionadas à simulação de desgaste de implantes de quadril por meio de simuladores mecânicos, fornece informações a cirurgiões, pesquisadores e órgãos reguladores, dentre outros, sobre a importância da avaliação pré-clínica do desgaste. Foi feita análise crítica sobre as diferenças nos princípios de funcionamento dos simuladores e seus efeitos nos resultados finais, bem como sobre as tendências futuras na simulação de desgaste.