Multilevel dynamic adjustments of geckos (Hemidactylus frenatus) climbing vertically: head-up versus head-down.

Many climbing animals use direction-dependent adhesives to attach to vertical or inclined surfaces. These structures adhere when activated via a pull but detach when pushed. Therefore, a challenge arises when a change in climbing direction causes external forces such as gravity to change its acting orientation upon the lizard. To investigate how specialized climbers adjust, we studied kinematics and dynamics of six Hemidactylus frenatus geckos climbing head-up and head-down a vertical racetrack. We found that limbs functionally swap their adhesive role: feet above the centre of mass (COM) generated adhesive forces, feet below the COM compressive forces, both equal in magnitude across directions. To investigate how lizards perform this swap, despite the constraint of their direction-dependent adhesives, we analysed kinematic adjustments across multiple smaller levels of hierarchy: limbs, feet and toes. All levels contributed: the hindfoot angle was reoriented realigning the adhesive structure, the hindlimb centre range of motion was further protracted and the hindfoot toe spreading was reduced. Notably, all three variables were adjustments of hindlimbs, suggesting that they make a more flexible contribution in upward versus downward climbing, while forelimbs may be anatomically or functionally constrained. The relevance of multilevel dynamic adjustments might inform the development of performant gaits for legged climbing robots.

Exploring the limits to turning performance with size and shape variation in dogs.

Manoeuvrability, the ability to make rapid changes in direction, is central to animal locomotion. Turning performance may depend on the ability to successfully complete key challenges including: withstanding additional lateral forces, maintaining sufficient friction, lateral leaning during a turn and rotating the body to align with the new heading. We filmed high-speed turning in domestic dogs (Canis lupus familiaris) to quantify turning performance and explore how performance varies with body size and shape. Maximal speed decreased with higher angular velocity, greater centripetal acceleration and smaller turning radii, supporting a force limit for wider turns and a friction limit for sharp turns. Variation in turning ability with size was complex: medium sized dogs produced greater centripetal forces, had relatively higher friction coefficients, and generally aligned the body better with the heading compared with smaller and larger bodied dogs. Body shape also had a complex pattern, with longer forelimbs but shorter hindlimbs being associated with better turning ability. Further, although more crouched forelimbs were associated with an increased ability to realign the body in the direction of movement, more upright hindlimbs were related to greater centripetal and tangential accelerations. Thus, we demonstrate that these biomechanical challenges to turning can vary not only with changes in speed or turning radius, but also with changes in morphology. These results will have significant implications for understanding the link between form and function in locomotory studies, but also in predicting the outcome of predator-prey encounters.

A bio-inspired robotic climbing robot to understand kinematic and morphological determinants for an optimal climbing gait.

Robotic systems for complex tasks, such as search and rescue or exploration, are limited for wheeled designs, thus the study of legged locomotion for robotic applications has become increasingly important. To successfully navigate in regions with rough terrain, a robot must not only be able to negotiate obstacles, but also climb steep inclines. Following the principles of biomimetics, we developed a modular bio-inspired climbing robot, named X4, which mimics the lizard's bauplan including an actuated spine, shoulders, and feet which interlock with the surface via claws. We included the ability to modify gait and hardware parameters and simultaneously collect data with the robot's sensors on climbed distance, slip occurrence and efficiency. We first explored the speed-stability trade-off and its interaction with limb swing phase dynamics, finding a sigmoidal pattern of limb movement resulted in the greatest distance travelled. By modifying foot orientation, we found two optima for both speed and stability, suggesting multiple stable configurations. We varied spine and limb range of motion, again showing two possible optimum configurations, and finally varied the centre of pro- and retraction on climbing performance, showing an advantage for protracted limbs during the stride. We then stacked optimal regions of performance and show that combining optimal dynamic patterns with either foot angles or ROM configurations have the greatest performance, but further optima stacking resulted in a decrease in performance, suggesting complex interactions between kinematic parameters. The search of optimal parameter configurations might not only be beneficial to improve robotic in-field operations but may also further the study of the locomotive evolution of climbing of animals, like lizards or insects.

Virtual and augmented reality: New tools for visualizing, analyzing, and communicating complex morphology.

Virtual and augmented reality (VR/AR) are new technologies with the power to revolutionize the study of morphology. Modern imaging approaches such as computed tomography, laser scanning, and photogrammetry have opened up a new digital world, enabling researchers to share and analyze morphological data electronically and in great detail. Because this digital data exists on a computer screen, however, it can remain difficult to understand and unintuitive to interact with. VR/AR technologies bridge the analog-to-digital divide by presenting 3D data to users in a very similar way to how they would interact with actual anatomy, while also providing a more immersive experience and greater possibilities for exploration. This manuscript describes VR/AR hardware, software, and techniques, and is designed to give practicing morphologists and educators a primer on using these technologies in their research, pedagogy, and communication to a wide variety of audiences. We also include a series of case studies from the presentations and workshop given at the 2019 International Congress of Vertebrate Morphology, and suggest best practices for the use of VR/AR in comparative morphology.

Tail Base Deflection but not Tail Curvature Varies with Speed in Lizards: Results from an Automated Tracking Analysis Pipeline.

Tail movement is an important component of vertebrate locomotion and likely contributes to dynamic stability during steady-state locomotion. Previous results suggest that the tail plays a significant role in lizard locomotion, but little data are available on tail motion during locomotion and how it differs with morphological, ecological, and phylogenetic parameters. We collected high-speed vertical climbing and horizontal locomotion video data from 43 lizard species from four taxonomic groups (Agamidae, Gekkota, Scincidae, and Varanidae) across four habitats. We introduce a new semi-automated and generalizable analysis pipeline for tail and spine motion analysis including markerless pose-estimation, semi-automated kinematic recognition, and muti-species data analysis. We found that step length relative to snout-vent length (SVL) increased with tail length relative to SVL. Examining spine cycles agnostic to limb stride phase, we found that ranges of inter-tail bending compared with inter-spine bending increased with relative tail length, while ranges of tail deflection relative to spine deflection increased with relative speed. Considering stepwise strides, we found the angular velocity and acceleration of the tail center of mass increased with relative speed. These results will provide general insights into the biomechanics of tails in sprawling locomotion enabling biomimetic applications in robotics, and a better understanding of vertebrate form and function. We look forward to adding more species, behaviors, and locomotor speeds to our analysis pipeline through collaboration with other research groups.

Using a biologically mimicking climbing robot to explore the performance landscape of climbing in lizards.

Locomotion is a key aspect associated with ecologically relevant tasks for many organisms, therefore, survival often depends on their ability to perform well at these tasks. Despite this significance, we have little idea how different performance tasks are weighted when increased performance in one task comes at the cost of decreased performance in another. Additionally, the ability for natural systems to become optimized to perform a specific task can be limited by structural, historic or functional constraints. Climbing lizards provide a good example of these constraints as climbing ability likely requires the optimization of tasks which may conflict with one another such as increasing speed, avoiding falls and reducing the cost of transport (COT). Understanding how modifications to the lizard bauplan can influence these tasks may allow us to understand the relative weighting of different performance objectives among species. Here, we reconstruct multiple performance landscapes of climbing locomotion using a 10 d.f. robot based upon the lizard bauplan, including an actuated spine, shoulders and feet, the latter which interlock with the surface via claws. This design allows us to independently vary speed, foot angles and range of motion (ROM), while simultaneously collecting data on climbed distance, stability and efficiency. We first demonstrate a trade-off between speed and stability, with high speeds resulting in decreased stability and low speeds an increased COT. By varying foot orientation of fore- and hindfeet independently, we found geckos converge on a narrow optimum of foot angles (fore 20°, hind 100°) for both speed and stability, but avoid a secondary wider optimum (fore -20°, hind -50°) highlighting a possible constraint. Modifying the spine and limb ROM revealed a gradient in performance. Evolutionary modifications in movement among extant species over time appear to follow this gradient towards areas which promote speed and efficiency.

Understanding the limits to the hydraulic leg mechanism: the effects of speed and size on limb kinematics in vagrant arachnids.

Among invertebrates, spiders (order Araneae) may be unique in their relationship between speed and mass as they use a combination of direct muscular contractions to flex their appendages, and internally controlled hydraulic pressure to extend them. To explore this, we measured maximal running speeds in 128 individual lycosids and sparassids, which varied in mass between 0.0054 and 3.01 g. We show maximum speed scaled with M0.353, while mean running speed scaled much lower as M0.197. We show no strong limitation of the hydraulic mechanism, with leg extension speed being equal to or greater than leg flexion speed. The reduction in leg flexion speed, only apparent in the distal most joint of the limb, might be a result of the requirement for flexor muscles to act against the hydraulic system. We explored the role of the limbs and found an alternating pattern of joint use among limbs, which may represent a strategy to avoid interference with adjacent limbs during running. Furthermore, we observed a reduced movement speed (increased leg dragging) in the rearward facing fourth limb with size. This may be linked to the increased size of the abdomen in larger spiders and may suggest a speed limitation in larger individuals.

Development, standardization, and validation of a biofilm efficacy test: The single tube method.

Methods validated by a standard setting organization enable public, industry and regulatory stakeholders to make decisions on the acceptability of products, devices and processes. This is because standard methods are demonstrably reproducible when performed in different laboratories by different researchers, responsive to different products, and rugged when small (usually inadvertent) variations from the standard procedure occur. The Single Tube Method (ASTM E2871) is a standard method that measures the efficacy of antimicrobials against biofilm bacteria that has been shown to be reproducible, responsive and rugged. In support of the reproducibility assessment, a six-laboratory study was performed using three antimicrobials: a sodium hypochlorite, a phenolic and a quaternary/alcohol blend, each tested at low and high efficacy levels. The mean log reduction in viable bacteria in this study ranged from 2.32 to 4.58 and the associated reproducibility standard deviations ranged from 0.89 to 1.67. Independent follow-up testing showed that the method was rugged with respect to deviations in sonication duration and sonication power but slightly sensitive to sonicator reservoir degassing and tube location within the sonicator bath. It was also demonstrated that when a coupon was dropped into a test tube, bacteria can splash out of reach of the applied antimicrobials, resulting in substantial bias when estimating log reductions for the products tested. Bias can also result when testing products that hinder the harvesting of microbes from test surfaces. The culmination of this work provided recommended changes to the early version of the standard method E2871-13 (ASTM, 2013b) including use of splashguards and microscopy checks. These changes have been incorporated into a revised ASTM method E2871-19 (ASTM 2019) that is the basis for the first regulatory method (ATMP-MB-20) to substantiate "kills biofilm" claims for antimicrobials registered and sold in the US.

Inactivation of Pseudomonas aeruginosa biofilms formed under high shear stress on various hydrophilic and hydrophobic surfaces by a continuous flow of ozonated water.

The inactivation of Pseudomonas aeruginosa biofilms grown on glass under high shear stress and exposed to a range of dissolved ozone concentrations (2, 5 and 7 ppm) at 10 and 20 min was investigated. The regression equation, log reduction (biofilm) = 0.64 + 0.59×(C - 2) + 0.33×(T - 10), described the dependence of biofilm inactivation on the dissolved ozone concentration (C, ppm) and contact time (T, min). The predicted D-values were 11.1, 5.7 and 2.2 min at 2, 5 and 7 ppm, respectively. Inactivation of biofilms grown on various surfaces was tested at a single dissolved ozone concentration of 5 ppm and a single exposure time of 20 min. Biofilms grown on plastic materials showed inactivation results similar to that of biofilms on glass, while biofilms grown on ceramics were statistically significantly more difficult to inactivate, suggesting the importance of utilizing non-porous materials in industrial and clinical settings.