Mathias Kolle

Biomineralized structures produced by living organisms are widely recognized for their exceptional mechanical performance, yet their potential optical roles are relatively less explored. Here, we demonstrate that within the calcitic ossicle-based skeleton of the sea star Protoreaster nodosus , where each ossicle represents a discrete skeletal element, one specialized ossicle, known as the terminal plate, contains a radially arranged array of light-guiding structures (LGSs). These LGSs exhibit an elongated, cone-like geometry (~250 μm in length) and are embedded within the porous stereom, a characteristic meshwork architecture of echinoderms analogous to open-cell cellular solids and composed of magnesium-containing single-crystalline calcite. Optical experiments demonstrate that, unlike other skeletal elements, the terminal plate can transmit and focus light into an internal cavity via the LGS array. Combined optical analyses using ray-tracing and finite-difference time-domain simulations reveal that each LGS transmits ca . 70% of incident light at normal incidence and concentrates it up to 2.8-fold at its exiting surface. Furthermore, when acting collectively as the LGS array within the terminal plate, the LGSs capture light over a broad field of view (~120°), resulting in an integrated transmitted intensity that is sixfold to eightfold greater than the incoming intensity perceived by a single LGS. Although the biological function of this optical capability remains uncertain, this natural porous structure demonstrates that cellular solids can integrate efficient light-guiding behavior while enhancing mechanical properties (i.e., threefold increase in stiffness compared with random stereom), offering design insights for lightweight, multifunctional structures.

ABSTRACT Butterfly scales contribute to a butterfly's vibrant coloration and play crucial roles in functions such as thermoregulation, water repellency, and aerodynamics. However, the underlying mechanisms that drive scale structure formation in vivo are not well understood. In this perspective, we propose that mechanical instabilities are central to the morphogenesis of scales and can lead to the observed wide variety of scale morphologies in adult butterflies. We specifically focus on the interplay between a growing soft compartment formed by the plasma membrane and an epicuticular envelope, the constraints imposed on this compartment by the actin cytoskeleton, and the spatio‐temporally heterogeneous sclerotization of the cuticle precursors. We discuss hypotheses on how intracellular processes control the composition of the cuticle precursor secreted into soft compartments and how mechanical instabilities may lead to the morphological diversity of ridges, lamellae, and other scale structures. Putting forward a set of hypotheses about the fundamental mechanical processes that enable the secretion of non‐living functional biological matter, we aim to inspire novel fabrication approaches in material science and engineering.

Stefan Guldin, Mathias Kolle, Silvia Vignolini, and Bodo D. Wilts introduce the Soft Matter themed collection on Celebrating the 60th birthday and achievements of Professor Ulli Steiner.

During the development of butterfly wing scales, ordered periodic cell membrane modulations occur at the upper surface of scale-forming cells, priming the formation of ridges. Ridges are critical for wing scale functionality, including structural color, wetting characteristics, and thermal performance. Here, we combine a morphoelastic model based on Föppl-von-Kármán plate theory with experimental observations to shed light on the biomechanical processes governing early-stage ridge formation in Painted Lady butterflies. By comparing the model predictions with time-resolved phase imaging data from live butterflies, we provide evidence that the onset of ridge formation is governed by a mechanical buckling transition induced by the interplay of membrane growth and confinement through association with regularly spaced actin bundles. Beyond ridge formation in Painted Lady scales, our theory offers a rationale for the absence of scale ridges in the lower lamina of many lepidopterans and for the alternating ridge pattern of other butterfly species.

This repository contains the raw data for: JF Totz, AD McDougal, L Wagner, S Kang, PTC So, J Dunkel, BD Wilts, and M Kolle, Cell membrane buckling governs early-stage ridge formation in butterfly wing scales, (forthcoming). The raw data is of a volumetric time series of scales growing on the wing of an individual Vanessa cardui pupa, collected with quantitative phase imaging. Additional details may be found in the Materials and Methods, as well as the SI, of the above publication. The companion code repository may be found on Zenodo: JF Totz, AD McDougal, L Wagner, S Kang, PTC So, J Dunkel, BD Wilts, and M Kolle. (Forthcoming). "Cell membrane buckling governs early-stage ridge formation in butterfly wing scales:code" (v1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.8369163 Note that file A-40-01_11_04_34_set_115.mat was previously released in: AD McDougal, S Kang, Z Yaqoob, PTC So, and M Kolle, Data and analysis codes for “In vivo visualization of butterfly scale cell morphogenesis in Vanessa cardui.” Zenodo. https://doi.org/10.5281/zenodo.5532941. We include it here for completeness of this time series.

This repository contains the raw data for: JF Totz, AD McDougal, L Wagner, S Kang, PTC So, J Dunkel, BD Wilts, and M Kolle, Cell membrane buckling governs early-stage ridge formation in butterfly wing scales, (forthcoming). The raw data is of a volumetric time series of scales growing on the wing of an individual Vanessa cardui pupa, collected with quantitative phase imaging. Additional details may be found in the Materials and Methods, as well as the SI, of the above publication. The companion code repository may be found on Zenodo: JF Totz, AD McDougal, L Wagner, S Kang, PTC So, J Dunkel, BD Wilts, and M Kolle. (Forthcoming). "Cell membrane buckling governs early-stage ridge formation in butterfly wing scales:code" (v1.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.8369163 Note that file A-40-01_11_04_34_set_115.mat was previously released in: AD McDougal, S Kang, Z Yaqoob, PTC So, and M Kolle, Data and analysis codes for “In vivo visualization of butterfly scale cell morphogenesis in Vanessa cardui.” Zenodo. https://doi.org/10.5281/zenodo.5532941. We include it here for completeness of this time series.

Abstract Materials capable of dynamically and reversibly altering their emission are relevant for numerous optical applications. Here, the anisotropic morphology‐directed light emission from fluorescent Janus emulsion droplets, an intrinsically chemo‐responsive material platform, is investigated. Informed by experimental observations of morphology‐dependent optical confinement of internally emitted light within the higher refractive index phases, ray‐tracing is used to predict and fine‐tune the droplets’ optical properties and their ability to concentrate light. Theoretical prediction and closely matching experimental results show that the collection of incident light and the confinement of emitted light in the internal droplet phase due to total internal reflection both contribute to the droplets’ anisotropic light emission profile. A novel ratiometric dual‐angle fluorescence detection approach that exploits the gravitational alignment of the droplets is implemented to quantify the morphology‐dependent large‐scale chemically‐induced modulation of the anisotropic emission of droplet layers. Relevant emulsion design parameters are systematically examined to enhance the signal‐to‐noise ratio, and a second emitter is co‐compartmentalized inside the droplets to amplify the anisotropic light confinement via an absorption–emission cascade. Preferential excitation of dyes in proximity to the internal droplet interface enhances the collected light intensity, demonstrating that dye‐loaded Janus emulsion droplets function as stimuli‐responsive, tunable, fluorescent optical elements.