More than 285,000 total hip replacement surgeries are performed in the US each year. Most prosthetic hip joints consist of a cobalt-chromium (CoCr) femoral head that articulates with a polyethylene acetabular component, lubricated with synovial fluid. The statistical survivorship of these metal-on-polyethylene prosthetic hip joints declines significantly after 10 to 15 years of use, primarily as a result of polyethylene wear and wear debris incited disease. The current engineering paradigm to increase the longevity of prosthetic hip joints is to improve the mechanical properties of the polyethylene component, and to manufacture ultra-smooth articulating surfaces. In contrast, we show that adding a patterned microtexture to the ultra-smooth CoCr femoral head reduces friction when articulating with the polyethylene acetabular liner. The microtexture increases the load-carrying capacity and the thickness of the joint lubricant film, which reduces contact between the articulating surfaces. As a result, friction and wear is reduced. We have used a lubrication model to design the geometry of the patterned microtexture, and experimentally demonstrate reduced friction for the microtextured compared to conventional smooth surrogate prosthetic hip joints.

Investigations into the use of gold nanorods (Au-NRs) for biological applications are growing exponentially due to their distinctive physicochemical properties, which make them advantageous over other nanomaterials. Au-NRs are particularly renowned for their plasmonic characteristics, which generate a robust photothermal response when stimulated with light at a wavelength matching their surface plasmon resonance. Numerous reports have explored this nanophotonic phenomenon for temperature driven therapies; however, to date there is a significant knowledge gap pertaining to the kinetic heating profile of Au-NRs within a controlled physiological setting. In the present study, the impact of environmental composition on Au-NR behavior and degree of laser actuated thermal production was assessed. Through acellular evaluation, we identified a loss of photothermal efficiency in biologically relevant fluids and linked this response to excessive particle aggregation and an altered Au-NR spectral profile. Furthermore, to evaluate the potential impact of solution composition on the efficacy of nano-based biological applications, the degree of targeted cellular destruction was ascertained in vitro and was found to be susceptible to fluid-dependent modifications. In summary, this study identified a diminution of Au-NR nanophotonic response in artificial physiological fluids that translated to a loss of application efficiency, pinpointing a critical concern that must be considered to advance in vivo, nano-based bio-applications.

Plasma jet devices that use a helium gas flow mixed with a small percentage of argon have been shown to operate with a larger discharge current and enhanced production of the Ar(1s5) metastable state, particularly in the discharge afterglow. In this experiment, time-resolved quantitative measurements of He(23S1) and Ar(1s5) metastable species were combined with current and spectrally resolved emission measurements to elucidate the role of Penning ionization in a helium plasma jet with a variable argon admixture. The plasma jet was enclosed in a glass chamber through which a flowing nitrogen background was maintained at 600 Torr. At 3%–5% Ar admixture, we observed a ∼50% increase in the peak circuit current and streamer velocity relative to a pure helium plasma jet for the same applied voltage. The streamer initiation delay also decreased by ∼20%. Penning ionization of ground-state argon was found to be the dominant quenching pathway for He(23S1) up to 2% Ar and was directly correlated with a sharp increase in both the circuit current and afterglow production of Ar(1s5) for Ar admixtures up to 1%, but not necessarily with the streamer velocity, which increased more gradually with Ar concentration. Ar(1s5) was produced in the afterglow through recombination of Ar+ and dissociative recombination of Ar2+ as the local mean electron energy decreased in the plasma channel behind the streamer head. The discharge current and argon metastable enhancement are contingent on the rapid production of He(23S1) near the streamer head, >5×1012 cm−3 in 30 ns under the conditions of this experiment.

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