Silkworm silk has attracted considerable attention in recent years due to its excellent mechanical properties, biocompatibility, and promising applications in biomedical sector. However, a clear understanding of the molecular structure and the relationship between the excellent mechanical properties and the silk protein sequences are still lacking. This study carries out a thorough comparative structural analysis of silk fibers of four silkworm species ( Bombyx mori, Antheraea pernyi, Samia cynthia ricini, and Antheraea assamensis). A combination of characterization techniques including scanning electron microscopy, mechanical test, synchrotron X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and NMR spectroscopy was applied to investigate the morphologies, mechanical properties, amino acid compositions, nanoscale organizations, and molecular structures of various silkworm silks. Furthermore, the structure-property relationship is discussed by correlating the molecular structural features of silks with their mechanical properties. The results show that a high content of β-sheet structures and a high crystallinity would result in a high Young's modulus for silkworm silk fibers. Additionally, a low content of β-sheet structures would result in a high extensibility.

Tidal heating is thought to maintain large subsurface oceans on several Jovian and Saturnian satellites (Lunine, 2017;Nimmo & Pappalardo, 2016) and these icy ocean worlds are candidates in the search for extraterrestrial life (Domagal-Goldman et al., 2016;Gaidos et al., 1999). Jupiter's moon Europa will be visited by both the Europa Clipper and JUICE missions (Grasset et al., 2013;Pappalardo et al., 2015) because it is of particular interest in this search. The habitability of Europa's interior ocean depends, among other conditions, on the availability of redox gradients (Chyba & Phillips, 2001;Pasek & Greenberg, 2012;Russell et al., 2017). Sufficient oxidant fluxes into the ocean are feasible if oxidants produced by irradiation at the surface (Carlson et al., 1999;Vance et al., 2016) can be transported through the ice shell. While Europa's ice shell is generally thought to be convecting (McKinnon et al., 2016;Pappalardo et al., 1998), it likely has a conductive lid that prevents surface entrainment (Figure 1a). The presence of such a lid is consistent with the limited observational evidence for direct subduction of the irradiated surface (Kattenhorn & Prockter, 2014) and theoretical arguments against subduction (B. Johnson et al., 2017;Howell & Pappalardo, 2019).Another mechanism to connect the surface to the ocean is the breaching of Europa's ice shell by large impacts (Bray et al., 2014;Cox & Bauer, 2015). Although impact breaching may once have been common, there is scant observational evidence for impact-driven oxidant transfer in the last 30-70 Ma (Bierhaus et al., 2009;Steinbrügge et al., 2020;Zahnle et al., 2008). This leaves poorly defined processes of resurfacing or crustal thickening as potential transport mechanisms for oxidants (Greenberg, 2010). Consequently, the oxidant flux into Europa's ocean is currently not understood and presents a major obstacle to assessing its habitability (Hand et al., 2007).

Root morphology and exudation define a plants’ sphere of influence in soils. In turn, soil characteristics influence plant growth, morphology, root microbiome, and rhizosphere chemistry. Collectively, all these parameters have significant implications on the major biogeochemical cycles, crop yield, and ecosystem health. However, how plants are shaped by the physiochemistry of soil particles is still not well understood. We explored how particle size and chemistry of growth substrates affect root morphology and exudation of a model grass. We grew Brachypodium distachyon in glass beads with various sizes (0.5, 1, 2, 3 mm), as well as in sand (0.005, 0.25, 4 mm) and in clay (4 mm) particles and in particle‐free hydroponic medium. Plant morphology, root weight, and shoot weight were measured. We found that particle size significantly influenced root fresh weight and root length, whereas root number and shoot weight remained constant. Next, plant exudation profiles were analyzed with mass spectrometry imaging and liquid chromatography–mass spectrometry. Mass spectrometry imaging suggested that both, root length and number shape root exudation. Exudate profiles were comparable for plants growing in glass beads or sand with various particles sizes, but distinct for plants growing in clay for in situ exudate collection. Clay particles were found to sorb 20% of compounds exuded by clay‐grown plants, and 70% of compounds from a defined exudate medium. The sorbed compounds belonged to a range of chemical classes, among them nucleosides, organic acids, sugars, and amino acids. Some of the sorbed compounds could be desorbed by a rhizobacterium (Pseudomonas fluorescens WCS415), supporting its growth. This study demonstrates the effect of different characteristics of particles on root morphology, plant exudation and availability of nutrients to microorganisms. These findings further support the critical importance of the physiochemical properties of soils when investigating plant morphology, plant chemistry, and plant–microbe interactions.