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Abstract Aims This study investigates how lumen roughness and urethral length influence urinary flow speed. Methods We used micro‐computed tomography scans to measure the lumen roughness and dimensions for rabbits, cats, and pigs. We designed and fabricated three‐dimensional‐printed urethra mimics of varying roughness and length to perform flow experiments. We also developed a corresponding mathematical model to rationalize the observed flow speed. Results We update the previously reported relationship between body mass and urethra length and diameter, now including 41 measurements for urethra length and 10 measurements for diameter. We report the relationship between lumen diameter and roughness as a function of position down the urethra for rabbits, cats, and pigs. The time course of urinary speed from our mimics is reported, as well as the average speed as a function of urethra length. Conclusions Based on the behavior of our mimics, we conclude that the lumen roughness in mammals reduces flow speed by up to 25% compared to smooth urethras. Urine flows fastest when the urethra length exceeds 25 times its diameter. Longer urethras do not drain faster due to viscous effects counteracting the additional gravitational head. However, flows with our urethra mimics are still 6 times faster than those observed in nature, suggesting that further work is needed to understand flow resistance in the urethra. 

Since ancient times, Korean chefs have fermented foods in an onggi, a traditional earthenware vessel. The porous structure of the onggi mimics the loose soil where lactic acid bacteria is naturally found. This permeability has been purported to facilitate the growth of lactic acid bacteria, but the details of the process remain poorly understood. In this combined experimental and theoretical study, we ferment salted napa cabbage in onggi and hermetic glassware and measure the time course of carbon dioxide concentration, which is a signature of fermentation. We present a mathematical model for carbon dioxide generation rate during fermentation using the onggi’s gas permeability as a free parameter. Our model provides a good fit for the data, and we conclude that porous walls help the onggi to ‘exhale’ carbon dioxide, lowering internal levels to those favoured by lactic acid bacteria. The positive pressure inside the onggi and the constant outflow through its walls act as a safety valve for bacteria growth by blocking the entry of external contaminants without mechanical components. We hope this study draws attention to the work of traditional artisans and inspires energy-efficient methods for fermenting and storing food products. 

Form-function relationships often have tradeoffs: if a material is tough, it is often inflexible, and vice versa. This is particularly relevant for the elephant trunk, where the skin should be protective yet elastic. To investigate how this is achieved, we used classical histochemical staining and second harmonic generation microscopy to describe the morphology and composition of elephant trunk skin. We report structure at the macro and micro scales, from the thickness of the dermis to the interaction of 10μm thick collagen fibers. We analyzed several sites along the length of the trunk, to compare and contrast the dorsal-ventral and proximal-distal skin morphologies and compositions. We find the dorsal skin of the elephant trunk can have keratin armor layers over 2mm thick, which is nearly 100 times the thickness of the equivalent layer in human skin. We also found that the structural support layer (the dermis) of elephant trunk contains a distribution of collagen-I (COL1) fibers in both perpendicular and parallel arrangement. The bimodal distribution of collagen is seen across all portions of the trunk, and is dissimilar from that of human skin where one orientation dominates within a body site. We hypothesize that this distribution of COL1 in the elephant trunk allows both flexibility and load-bearing capabilities. Additionally, when viewing individual fiber interaction of 10μm thick collagen, we find the fiber crossings per unit volume are five times more common than in human skin, suggesting that the fibers are entangled. We surmise that these intriguing structures permit both flexibility and strength in the elephant trunk. The complex nature of the elephant skin may inspire the design of materials that can combine strength and flexibility.

 

The recent increase in public and academic interest in preserving biodiversity has led to the growth of the field of conservation technology. This field involves designing and constructing tools that use technology to aid in the conservation of wildlife. In this review, we present five case studies and infer a framework for designing conservation tools (CT) based on human–wildlife interaction. Successful CT range in complexity from cat collars to machine learning and game theory methodologies and do not require technological expertise to contribute to conservation tool creation. Our goal is to introduce researchers to the field of conservation technology and provide references for guiding the next generation of conservation technologists. Conservation technology not only has the potential to benefit biodiversity but also has broader impacts on fields such as sustainability and environmental protection. By using innovative technologies to address conservation challenges, we can find more effective and efficient solutions to protect and preserve our planet’s resources.

 

A dog's nose differs from a human's in that air does not change direction but flows in a unidirectional path from inlet to outlet. Previous simulations showed that unidirectional flow through a dog’s complex nasal passageways creates stagnant zones of trapped air. We hypothesize that these zones give the dog a “physical memory,” which it may use to compare recent odors to past ones. In this study, we conducted experiments with our previously built Gaseous Recognition Oscillatory Machine Integrating Technology (GROMIT) and performed corresponding simulations in two dimensions. We compared three settings: a control setting that mimics the bidirectional flow of the human nose; a short-circuit setting where odors exit before reaching the sensors; and a unidirectional configuration using a dedicated inlet and outlet that mimics the dog’s nose. After exposure to odors, the sensors in the unidirectional setting showed the slowest return to their baseline level, indicative of memory effects. Simulations showed that both short-circuit and unidirectional flows created trapped recirculation zones, which slowed the release of odors from the chamber. In the future, memory effects such as the ones found here may improve the sensitivity and utility of electronic noses.

 

Abstract Elephants have long been observed to grip objects with their trunk, but little is known about how they adjust their strategy for different weights. In this study, we challenge a female African elephant at Zoo Atlanta to lift 20–60 kg barbell weights with only its trunk. We measure the trunk’s shape and wrinkle geometry from a frozen elephant trunk at the Smithsonian. We observe several strategies employed to accommodate heavier weights, including accelerating less, orienting the trunk vertically, and wrapping the barbell with a greater trunk length. Mathematical models show that increasing barbell weights are associated with constant trunk tensile force and an increasing barbell-wrapping surface area due to the trunk’s wrinkles. Our findings may inspire the design of more adaptable soft robotic grippers that can improve grip using surface morphology such as wrinkles. 

Pellet feces are generated by a number of animals important to science or agriculture, including mice, rats, goats, and wombats. Understanding the factors that lead to fecal shape may provide a better understanding of animal health and diet. In this combined experimental and theoretical study, we test the hypothesis that pellet feces are formed by drying processes in the intestine. Inspirational to our work is the formation of hexagonal columnar jointings in cooling lava beds, in which the width L of the hexagon scales as L ∼ J −1 where J is the heat flux from the bed. Across 22 species of mammals, we report a transition from cylindrical to pellet feces if fecal water content drops below 0.65. Using a mathematical model that accounts for water intake rate and intestinal dimensions, we show pellet feces length L scales as L ∼ J −2.08 where J is the flux of water absorbed by the intestines. We build a mimic of the mammalian intestine using a corn starch cake drying in an open trough, finding that corn starch pellet length scales with water flux −0.46 . The range of exponents does not permit us to conclude that formation of columnar jointings is similar to the formation of pellet feces. Nevertheless, the methods and physical picture shown here may be of use to physicians and veterinarians interested in using feces length as a marker of intestinal health. 

Abstract Most mammals sniff to detect odors, but little is known how the periodic inhale and exhale that make up a sniff helps to improve odor detection. In this combined experimental and theoretical study, we use fluid mechanics and machine olfaction to rationalize the benefits of sniffing at different rates. We design and build a bellows and sensor system to detect the change in current as a function of odor concentration. A fast sniff enables quick odor recognition, but too fast a sniff makes the amplitude of the signal comparable to noise. A slow sniff increases signal amplitude but delays its transmission. This trade-off may inspire the design of future devices that can actively modulate their sniffing frequency according to different odors. 

Body size affects nearly every aspect of locomotion and sensing, but little is known of its influence on olfaction. One reason for this missing link is that olfaction differs fundamentally from vision and hearing in that molecules are advected by fluid before depositing on olfactory sensors. This critical role of fluid flow in olfaction leads to complexities and trade-offs. For example, a greater density of hairs and sensory neurons may lead to greater collection, but can also lead to reduced flow through hairs and additional weight and drag due to a larger olfactory organ. In this study, we report the surface area and sensory neuron density in olfactory organs of 95 species of moths and mammals. We find that approximately 12–14% of an olfactory system’s surface area is devoted to chemosensors. Furthermore, total olfactory surface area and olfactory sensing surface area scale with body mass to the 0.49 and 0.38 powers, respectively, indicating that moths have a higher proportion of olfactory surface area than mammals. The density of olfactory neurons appears to be near the limit, at 10,000 to 100,000 neurons per square mm across both insects and mammals. This study demonstrates the need for future work detailing how the scaling of olfaction and other senses vary across taxa.