arXiv subjects

Andrew K. Schulz

Publications and source records attributed to Andrew K. Schulz.

8 recordsLinked to original sources

arXiv2026

Hair is a functionally graded composite, not a uniform fiber

Hair provides mammals with diverse benefits, including protection, thermoregulation, and enhanced sensory perception. Unlike tendons and teeth, which are biomineralized, hair is hypothesized to accomplish its structure-function relationship purely through keratin, a fibrous protein that provides structural integrity. Recent research showed that mechanical properties can vary substantially both within and across hair types: the whiskers of Asian elephant (Elephas maximus) exhibit a two-order-of-magnitude material stiffness reduction from base to tip, whereas elephant body hairs are nearly homogenous. Here, we demonstrate that three hierarchical structures vary significantly along the body hairs and whiskers of domestic cat (Felis catus): the layered outer keratin wall, 250-nm-diameter melanosome-like granules in the cortex, and calcium enrichment of these granules. As occasionally described for human hair, the oblong granules are arranged in longitudinal channels, potentially reinforcing the cortex; their prevalence correlates with local mechanical properties along the hair's length. Prolonged chemical treatment of body hairs removes calcium from the granules while breaking down the outer cuticle and internal cortex, hardening bases and splitting tips. Though previously assumed uniform, morphology, composition, and elemental enrichment can change along hairs, producing composite structures with functional gradients.

physics.bio-ph↗

arXiv2026

Decoupling size from magnetism: A length-scale boundary for curvature control in micrometer FePt Janus particles

Curvature reshapes magnetization when a structure's dimensions approach intrinsic magnetic length scales, but functional magnetic colloids and microrobots are often micrometers in size, where the radius of curvature exceeds these scales by several orders of magnitude. Whether particle diameter remains an effective parameter for tuning magnetic response in this regime is therefore unclear. We synthesized partially ordered FePt Janus caps on spherical SiO$_2$ particles with diameters of 3--10~$μ$m, characterized their structure and magnetic response, and extended the investigated range to 1--20~$μ$m using micromagnetic simulations. Across this range, coercivity, remanence, and hysteresis-loop shape showed no systematic dependence on particle diameter in either experiment or simulation. The ratio between exchange length and radius of curvature ($\ell_{\mathrm{ex}}/R \sim 10^{-3}$--$10^{-4}$) places these particles in a locally planar regime where diameter-dependent curvature effects are weak. Size and magnetic response are therefore effectively decoupled within the investigated regime: particle diameter can be selected according to transport, payload, and biocompatibility requirements without introducing a measurable magnetic penalty, but it does not provide an effective route for tuning magnetization reversal. Instead, the magnetic response is governed primarily by material state, including the balance between magnetically hard L1$_0$ and soft A1 FePt, with additional modulation by processing-induced morphology. The resulting length-scale map identifies the regime in which this decoupling is expected to hold and where diameter-dependent curvature effects may become significant.

cond-mat.mtrl-sci↗

arXiv2026

TAMP-OS: An Open-Source Workflow for Tactile 3D-Printable Lithographs

Describe an animal without using the verb look. Can you effectively provide an alternative method for interpreting complex microscopy images while preserving the length scale? The world is filled with features too small for our eyes to see: the setae on a gecko's feet, the cuticles covering a rat's whisker, or the fuzziness of a bat's wing. Furthermore, these structures are non-homogeneous, often shifting from stiff to soft. We provide a workflow for producing low-data, low-cost, and open-source lithograph files, allowing tactile accessibility in microscopy images. The lithographs made with this workflow can be printed on a 350 USD 3D printer using 3D files under 100 Mb, for a total cost per print of 0.75 USD. This work seeks to leverage advanced 3D printing to create tactile graphics and art that make science more accessible and enable tactile exploration of biological structures. This framework in this text is aligned with a GitHub repository that will be constantly updated, allowing tactile media to be created as 3D printing and lithography become more streamlined in the years to come.

cs.GR↗

arXiv2025

Augmenting knee biomechanics through programmable knitted ExoSkin orthoses

A large subset of the population suffers injury or disease that causes knee pain and difficulty navigating day-to-day tasks. Off-the-shelf knee orthoses that are commonly used to treat these ailments overlook user-specific joint geometry and/or biomechanical needs. They can often be made with materials that lead to discomfort. We explore how the rich programmability of knitted fabrics can be harnessed to augment human biomechanics while promoting comfort. In this pursuit, we define \emph{ExoSkins}, a class of unpowered exoskeletons that are lightweight, comfortable, garment-like devices, and are designed based on user- and joint-specific needs. Although we foresee an expansive space for ExoSkin design (e.g., containing active materials, with sensing capabilities), in this study we focus on the interplay between knit geometry and programmable elasticity in passive orthoses as a means to augment the knee's rotational stiffness. We design geometrically-programmed ExoSkins, abbreviated \emph{G-PExos}, that capitalize on the anisotropies of four types of knitted fabric to provide high stiffness for joint torque without the need for rigid materials. Our findings indicate that G-PExos can achieve rotational stiffness of similar magnitude to off-the-shelf orthoses and can also be tuned to achieve a much broader range of rotational stiffness without sacrificing comfort to the user.

cond-mat.soft↗

arXiv2025

Functionally graded keratin facilitates tactile sensing in elephant whiskers

Keratin composites enable animals to hike with hooves, fly with feathers, and sense with skin. These distinct functions arise from variations in the underlying properties and microscale arrangement of this natural polymer. One well-studied example is mammalian whiskers, elongated keratin rods attached to tactile skin structures that extend the animal's sensory volume. Here, we investigate the non-actuated whiskers that cover Asian elephant (Elephas maximus) trunks and find they are geometrically and mechanically tailored to facilitate tactile perception by encoding contact location in vibrotactile signal amplitude and frequency. Elephant whiskers emerge from armored trunk skin and shift from a thick, circular, porous, stiff root to a thin, ovular, dense, soft point. This smooth transition enables interaction with widely varying substrates, reduces wear, and increases the vibrotactile signal information generated during contact. The functionally graded geometry, porosity, and stiffness of elephant whiskers tune the neuromechanics of trunk touch, facilitating highly dexterous manipulation.

physics.bio-ph↗

arXiv2025

Materials Matter: Investigating Functional Advantages of Bio-Inspired Materials via Simulated Robotic Hopping

In contrast with the diversity of materials found in nature, most robots are designed with some combination of aluminum, stainless steel, and 3D-printed filament. Additionally, robotic systems are typically assumed to follow basic rigid-body dynamics. However, several examples in nature illustrate how changes in physical material properties yield functional advantages. In this paper, we explore how physical materials (non-rigid bodies) affect the functional performance of a hopping robot. In doing so, we address the practical question of how to model and simulate material properties. Through these simulations we demonstrate that material gradients in the leg of a single-limb hopper provide functional advantages compared to homogeneous designs. For example, when considering incline ramp hopping, a material gradient with increasing density provides a 35% reduction in tracking error and a 23% reduction in power consumption compared to homogeneous stainless steel. By providing bio-inspiration to the rigid limbs in a robotic system, we seek to show that future fabrication of robots should look to leverage the material anisotropies of moduli and density found in nature. This would allow for reduced vibrations in the system and would provide offsets of joint torques and vibrations while protecting their structural integrity against reduced fatigue and wear. This simulation system could inspire future intelligent material gradients of custom-fabricated robotic locomotive devices.

cs.RO↗

arXiv2024

Nonlinear optical response and spontaneous polarization in layer-stacked gallenene using second harmonic generation

Gallenene is a promising low-dimensional material with a structure down to the thickness of a single atom, similar to graphene. However, van der Waals stacking of two-dimensional (2D) gallenene under confinement remain poorly understood. In this study, we present evidence of the formation of parallel-stacked hexagonal gallenene (a100) structures in liquid gallium. The present study demonstrates the AB stacking of 2D gallenene a100 crystals in liquid gallium sandwiched between two graphene layers, as observed through transmission electron microscopy. A nonlinear optical response of the confined hexagonal gallenene was investigated through second harmonic generation (SHG) microscopy. The SHG signal exhibits periodic peak intensity shifts upon angular rotation up to 90 degrees and intensity dampening at elevated temperatures. These findings offer insights on device applications of 2D gallenene.

cond-mat.mtrl-sci↗

arXiv2024

Expanding Conservation Science through Emerging Interdisciplinary STEM Fields

Conservation science is an interdisciplinary field that primarily draws on knowledge from the natural sciences, social sciences, and humanities to inform policy, planning, and practice. Since its formalization as a discipline, conservation science has also increasingly incorporated tools from integrative biological fields, such as animal behavior, genetics, and, more recently, physiology. Given that the biodiversity crisis constitutes one of the greatest challenges of the 21st century, with tremendous consequences for global sustainability and human health, creating a diverse conservation toolbox is important for addressing complex conservation threats. To assess the integration of three emerging integrative biological disciplines (physiology, biomechanics, and technology) into recent conservation science research, we queried publications from five broad-scope conservation-focused journals from 2010-2022. We found that the proportion of published articles incorporating these integrative biological techniques was low, ranging from 0-4% per year. With only 2.1% of total articles accessing tools or techniques from conservation physiology, conservation technology, and conservation biomechanics, we propose that there is still a substantial opportunity for further integration. We provide a case study for each integrative field to illustrate the capacity for its tools to contribute to positive conservation outcomes. We further outline how each field promotes novel or reimagined opportunities for collaborations. Finally, we discuss the interconnectedness of the three fields and how they can support the continuing expansion of conservation science as an evidence-based, action-oriented discipline through the application of a Challenge-Mechanism-Partnership framework.

cs.DL↗