After the rapid growth in the use of CoCrMo metal-on-metal hip replacements since the second generation was introduced circa 1990, metal-on-metal hip replacements have experienced a sharp decline in the last two years due to biocompatibility issues related to wear and corrosion products. Despite some excellent clinical results, the release of wear and corrosion debris and the adverse response of local tissues have been of great concern. There are many unknowns regarding how CoCrMo metal bearings interact with the human body. This perspective article is intended to outline some recent progresses in understanding wear and corrosion of metal-on-metal hip replacement both in-vivo and in-vitro. The materials, mechanical deformation, corrosion, wear-assisted corrosion, and wear products will be discussed. Possible adverse health effects caused by wear products will be briefly addressed, as well as some of the many open questions such as the detailed chemistry of corrosion, tribochemical reactions and the formation of graphitic layers. Nowadays we design almost routinely for high performance materials and lubricants for automobiles; humans are at least as important. It is worth remembering that a hip implant is often the difference between walking and leading a relatively normal life, and a wheelchair.

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The coupling of hybrid organic-inorganic gate dielectrics with emergent unconventional semiconductors has yielded transistor devices exhibiting record-setting transport properties. However, extensive electronic transport measurements on these high-capacitance systems are often convoluted with the electronic response of the semiconducting silicon substrate. In this report, we demonstrate the growth of solution-processed zirconia self-assembled nanodielectrics (Zr-SAND) on template-stripped aluminum substrates. The resulting Zr-SAND on Al structures leverage the ultrasmooth (r.m.s. roughness <0.4 nm), chemically uniform nature of template-stripped metal substrates to demonstrate the same exceptional electronic uniformity (capacitance ∼700 nF cm(-2), leakage current <1 μA cm(-2) at -2 MV cm(-1)) and multilayer growth of Zr-SAND on Si, while exhibiting superior temperature and voltage capacitance responses. These results are important to conduct detailed transport measurements in emergent transistor technologies featuring SAND as well as for future applications in integrated circuits or flexible electronics.

Cobalt chromium molybdenum alloys have been extensively used for biomedical implants, but are susceptible to grain boundary corrosion resulting from local chromium depletion, which is called sensitization. This work extended the understanding of chromium depleted zones in CoCrMo alloys and their role in corrosion to the nanoscale. Selected boundaries were analyzed from the millimeter to the nanometer scale in order to link the chemical composition and crystallographic structure to the observed local corrosion properties. The shape and severity of grain boundary corrosion crevices were measured, linked with the coincidence site lattice geometry. Additionally, direct high-resolution energy dispersive x-ray spectroscopy maps of chromium depleted zones at the grain boundaries were measured to completely characterize the grain boundary properties. Chromium depleted zones were found in 100% of corroded grain boundaries, yet were too small to follow classical models of sensitization. Nanoscale regions of chromium depletion were found to have significant effects on corrosion initiation. This led to a grain boundary crevice corrosion model connecting the chemical composition with electrochemical driving forces that control crevice corrosion propagation. The conclusions and model presented can be used to better develop processing techniques for CoCrMo and other alloys.

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