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Nitric oxide (NO) and oxygen (O2) transport in the microcirculation are coupled in a complex manner, since enzymatic production of NO depends on O2 availability, NO modulates vascular tone and O2 delivery, and tissue O2 consumption is reversibly inhibited by NO. The authors investigated whether NO bioavailability is influenced by the well-known Fåhraeus effect, which has been observed for over 70 years. This phenomenon occurs in small-diameter blood vessels, where the tube hematocrit is reduced below systemic hematocrit as a plasma boundary layer forms near the vascular wall when flowing red blood cells (rbcs) migrate toward the center of the bloodstream. Since hemoglobin in the bloodstream is thought to be the primary scavenger of NO in vivo, this might have a significant impact on NO transport. To investigate this possibility, the authors developed a multilayered mathematical model for mass transport in arterioles using finite element numerical methods to simulate coupled NO and O2 transport in the blood vessel lumen, plasma layer, endothelium, vascular wall, and surrounding tissue. The Fåhraeus effect was modeled by varying plasma layer thickness while increasing core hematocrit based on conservation of mass. Key findings from this study are that (1) despite an increase in the NO scavenging rate in the core with higher hematocrit, the model predicts enhanced vascular wall and tissue NO bioavailability due to the relatively greater resistance for NO diffusion through the plasma layer; (2) increasing the plasma layer thickness also increases the resistance for O2 diffusion, causing a larger P(O2) gradient near the vascular wall and decreasing tissue O2 availability, although this can be partially offset with inhibition of O2 consumption by higher tissue NO levels; (3) the Fåhraeus effect can become very significant in smaller blood vessels (diameters <30 microm); and (4) models that ignore the Fåhraeus effect may underestimate NO concentrations in blood and tissue.

Advancements in software engineering have enabled the robotics industry to transition from the use of giant industrial robots to more friendly humanoid robots. Soft robotics is one of the key elements needed to advance the transition process by providing a safer way for robots to interact with the environment. Electroactive polymers (EAPs) are one of the best candidate materials for the next generation of soft robotic actuators and artificial muscles. Lightweight dielectric elastomer actuators (DEAs) provide optimal properties such as high elasticity, rapid response rates, mechanical robustness and compliance. However, for DEAs to become widely used as artificial muscles or soft actuators, there are current limitations, such as high actuation voltage requirements, control of actuation direction, and scaling, that need to be addressed. The authors’ approach to overcome the drawbacks of conventional DEAs is inspired by the natural skeletal muscles. Instead of fabricating a large DEA device, smaller sub-units can be fabricated and bundled together to form larger actuators, similar to the way myofibrils form myocytes in skeletal muscles. The current study presents a novel fabrication approach, utilizing soft lithography and other microfabrication techniques, to allow fabrication of multilayer stacked DEA structures, composed of hundreds of micro-sized DEA units.

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