Design, Composition Optimization, Fabrication, and Properties of Al2O3/ZrO2/SrO based Articulating Hip Prosthesis

Abstract

Total hip replacement (THR) is a joint replacement surgery used to replace damaged, arthritic hip joint with an orthopedic prosthesis. Continuous research is in progress to develop new biomaterials with improved mechanical, tribological, and biological properties. The present work is focused on developing a new design and fabrication of femoral head (FH) & acetabular socket liner (ASL) through optimized SrO doped zirconia toughened alumina (ZTA) to achieve a competitive mechanical and biological response. The entire work has been divided into four major categories; ‘Designing, femoral head size and material selection through both static and dynamic Finite Element Analysis (FEA)’, ‘Process and composition optimization in consideration of grain size, mechanical properties, and tribological properties’, ‘Designing of tailor-made mold and fabrication of both FH and ASL’, ‘Surface profile and dimension stability, burst strength, and biological response of worn particles generated through articulating motion of FH-ASL’. In the proposed THR design, 30 mm FH- ZTA/ASL- ZTA bearing exhibits minimum stress, and minimum wear depth under stance and jogging activity compare to promising Ti6Al4V/UHMWPE bearing. While ZTA/ZTA ceramic bearing confirms the best performance for 15 years, SrO doped ZTA composition and their sintering profile have been optimized. Strontium (Sr) expedite to form elongated strontium hexaaluminate (SrAl12O19) that eventually enhances fracture toughness; simultaneously, strontium enhances the bone remineralization, an increase in the formation of new bone, and a decrease in the risk of bone fracture. Further competitive FEA analysis endorses the best choice of SrO-ZTA/SrO- ZTA bearing among any other combination of Ti6Al4V/SrO-ZTA, SrO-ZTA/UHMWPE, Co-CrMo/UHMWPE, SS316L/UHMWPE bearing assemblies. Tribological study of hydrothermally aged specimen estimated the critical load of 94 N is required for the transition from mild to severe wear when pre-existing flaw size of ~0.77 µm.
The SrO doped zirconia toughened alumina femoral head (FH; OD – 30 ± 0.01 mm) and acetabular socket liner (ASL; ID – 30.15 ± 0.01 mm) were fabricated through uniaxial pressing followed by sintering, machining, and polishing to develop defect-free precious dimension prototypes for THR. Tailor-made polishing followed by a 3D optical surface profilometer study ensures the surface characteristics of Ra ≈ 0.2 ± 0.01 m and Rq ≈ 0.5 ± 0.01 m for both FH and ASL. The FH and ASL geometrical analysis are measured using a coordinate measuring method to ensure circularity with a tolerance limit ± 0.01 mm. However, the burst strength of independent FH and FH-ASL assembly demands a further ~10 % improvement to fulfill the clinical standard. An impressive cytocompatibility and healthy cell growth behavior are noticed during in vitro C2C12 myoblast cell study in the presence of worn particles generated through a simulated articulating motion of FH-ASL assembly. Within a limited scope, an in vivo study in drosophila fly exhibits excellent growth behavior from larva to adult up to doze of 50 µg worn particles / 1 ml standard, as it is one of the best genetically studied species with having high homology with the human.