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Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
Stainless steel (usually 316L) is a common industrial alloy that has been very successful as a surgical implant material. Both stainless steel and cobalt-chrome alloys owe their corrosion resistance to the formation of a passive ceramic-like CrO2 coating on the surface, and it is important that this coating not be scratched during implantation. Care must be taken with stainless steel materials in orthopedic applications because of their susceptibility to crevice and stress corrosion. The ductility of these alloys can be increased by heat treatment, and their strength can be increased by cold working of the material. Cast stainless steels are unsuitable for use in weight-bearing situations because of their large grain sizes and low fatigue strengths. Type 316LVM (low carbon [L, typically less than 0.03%], vacuum melt [VM]) material is preferred. The carbon concentration must remain at small amounts in stainless steel materials to maintain resistance to corrosion.
Immobilization of polyphosphoesters on poly(ether ether ketone) (PEEK) for facilitating mineral coating
Published in Journal of Biomaterials Science, Polymer Edition, 2019
Shun Kunomura, Yasuhiko Iwasaki
Recently, titanium-based and cobalt-chrome alloys have been widely used in biomedical implants [1, 2] due to their excellent strength and toughness. Furthermore, several surface modification techniques have been proposed to obtain hard-tissue compatibility [3, 4]. However, metallic implants cause complications such as transient osteoporosis of the hip due to stress shielding, metal allergy, and fatigue fracture [5–7]. To reduce these unfavorable issues, poly(ether ether ketone) (PEEK) has gained interest a new candidate for biomedical and orthopedic implants [8–13]. The Young’s modulus of PEEK (4 GPa) is lower than that of cortical bone, whereas carbon-reinforced PEEK (CFR-PEEK) and cortical bone have similar Young’s moduli [14, 15]; thus, CFR-PEEK implants may avoid stress shielding effects, thereby avoiding bone loss. PEEK is durable and highly resistant to creep and fatigue [8, 16]; thus, it is a reliable material for medical uses. However, the surface properties of PEEK must be improved to generate suitable interfacial aspects, such as non-fouling, lubricity, and tissue compatibility, depending on the intended uses.
Dual mobility acetabular cups for total hip arthroplasty: advantages and drawbacks
Published in Expert Review of Medical Devices, 2018
Thomas Neri, Remi Philippot, Antonio Klasan, Sven Putnis, Murilo Leie, Bertrand Boyer, Frederic Farizon
The original NOVAE® cup was a cementless DMC, impacted in press-fit [1]. Its fixation was supplemented by tripod anchoring with two pegs (one impacted in the ischium and the other in the pubis) and one superior screw inserted into the iliac wing. This tripod fixation system was designed to withstand rotational and pull-out forces and ensure optimal primary stability. This design has evolved overtime and at different levels, especially since the first patent expired in 1996: – The initial alumina coating on the cup was replaced with a bilayer of plasma-sprayed titanium and hydroxyapatite that provides surface roughness to contribute to bone integration and cup fixation. Materials other than stainless steel have been used, namely cobalt-chrome. Titanium is no longer used in the DMC bearing. Macrostructural elements have also been added to reinforce the primary press-fit fixation.– Press-fit only implants were introduced in the 2000s, mainly for primary THA procedures.– For the UHMWPE liner: º The chamfer and retention mechanisms were redesigned to reduce wear in the retaining ring. The PE is denser, and gamma irradiated under vacuum.º The clearances have been altered to avoid jamming of the inner and outer surfaces of the liner.º DM liners made of cross-linked polyethylene (XLPE) have been introduced recently. The benefits of this latest modification are still being debated.