Micromechanical mapping of the intact ovary interior reveals contrasting mechanical roles for follicles and stroma.

Follicle development in the ovary must be tightly regulated to ensure cyclical release of oocytes (ovulation). Disruption of this process is a common cause of infertility, for example via polycystic ovary syndrome (PCOS) and premature ovarian insufficiency (POI). Recent ex vivo studies suggest that follicle growth is mechanically regulated, however, crucially, the actual mechanical properties of the follicle microenvironment have remained unknown. Here we use atomic force microscopy (AFM) spherical probe indentation to map and quantify the mechanical microenvironment in the mouse ovary, at high resolution and across the entire width of the intact (bisected) ovarian interior. Averaging over the entire organ, we find the ovary to be a fairly soft tissue comparable to fat or kidney (mean Young's Modulus 3.3±2.5 kPa). This average, however, conceals substantial spatial variations, with the overall range of tissue stiffnesses from c. 0.5-10 kPa, challenging the concept that a single Young's Modulus can effectively summarize this complex organ. Considering the internal architecture of the ovary, we find that stiffness is low at the edge and centre which are dominated by stromal tissue, and highest in an intermediate zone that is dominated by large developmentally-advanced follicles, confirmed by comparison with immunohistology images. These results suggest that large follicles are mechanically dominant structures in the ovary, contrasting with previous expectations that collagen-rich stroma would dominate. Extending our study to the highest resolutions (c. 5 µm) showed substantial mechanical variations within the larger zones, even over very short (sub-100 µm) lengths, and especially within the stiffer regions of the ovary. Taken together, our results provide a new, physiologically accurate, framework for ovarian biomechanics and follicle tissue engineering.

Direct solution-phase synthesis of 1T' WSe2 nanosheets.

Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties. Access to metastable crystal phases is limited as their direct synthesis is challenging, restricting the spectrum of reachable materials. Here, we demonstrate the solution phase synthesis of the metastable distorted octahedrally coordinated structure (1T' phase) of WSe2 nanosheets. We design a kinetically-controlled regime of colloidal synthesis to enable the formation of the metastable phase. 1T' WSe2 branched few-layered nanosheets are produced in high yield and in a reproducible and controlled manner. The 1T' phase is fully convertible into the semiconducting 2H phase upon thermal annealing at 400 °C. The 1T' WSe2 nanosheets demonstrate a metallic nature exhibited by an enhanced electrocatalytic activity for hydrogen evolution reaction as compared to the 2H WSe2 nanosheets and comparable to other 1T' phases. This synthesis design can potentially be extended to different materials providing direct access of metastable phases.

Thickness-Dependent Characterization of Chemically Exfoliated TiS2 Nanosheets.

Monolayer TiS2 is the lightest member of the transition metal dichalcogenide family with promising applications in energy storage and conversion systems. The use of TiS2 has been limited by the lack of rapid characterization of layer numbers via Raman spectroscopy and its easy oxidation in wet environment. Here, we demonstrate the layer-number-dependent Raman modes for TiS2. 1T TiS2 presents two characteristics of the Raman active modes, A1g (out-of-plane) and Eg (in-plane). We identified a characteristic peak frequency shift of the Eg mode with the layer number and an unexplored Raman mode at 372 cm-1 whose intensity changes relative to the A1g mode with the thickness of the TiS2 sheets. These two characteristic features of Raman spectra allow the determination of layer numbers between 1 and 5 in exfoliated TiS2. Further, we develop a method to produce oxidation-resistant inks of micron-sized mono- and few-layered TiS2 nanosheets at concentrations up to 1 mg/mL. These TiS2 inks can be deposited to form thin films with controllable thickness and nanosheet density over square centimeter areas. This opens up pathways for a wider utilization of exfoliated TiS2 toward a range of applications.

Realization of ground state in artificial kagome spin ice via topological defect-driven magnetic writing.

Arrays of non-interacting nanomagnets are widespread in data storage and processing. As current technologies approach fundamental limits on size and thermal stability, enhancing functionality through embracing the strong interactions present at high array densities becomes attractive. In this respect, artificial spin ices are geometrically frustrated magnetic metamaterials that offer vast untapped potential due to their unique microstate landscapes, with intriguing prospects in applications from reconfigurable logic to magnonic devices or hardware neural networks. However, progress in such systems is impeded by the inability to access more than a fraction of the total microstate space. Here, we demonstrate that topological defect-driven magnetic writing-a scanning probe technique-provides access to all of the possible microstates in artificial spin ices and related arrays of nanomagnets. We create previously elusive configurations such as the spin-crystal ground state of artificial kagome dipolar spin ices and high-energy, low-entropy 'monopole-chain' states that exhibit negative effective temperatures.