Collagen, the primary structural protein in the extracellular matrix, plays a critical role in tissue architecture and mechanical integrity. This study investigates the structural and nonlinear optical properties of atelocollagen (Acol) and telocollagen (Tcol) in response to pH variations using Second Harmonic Scattering (SHS), polarization-resolved SHS (P-SHS), and Atomic Force Microscopy (AFM). AFM imaging revealed distinct morphological differences, with Acol forming wavy, non-cross-linked, and randomly arranged fibers, while Tcol exhibited a more interconnected, mesh-like fibrillar network. SHS and P-SHS measurements further confirmed these differences, indicating significant variations in hyperpolarizability and depolarization ratio (DR) between Acol and Tcol. The results suggest that telopeptides play a crucial role in collagen fibrillogenesis, influencing molecular symmetry and optical responses. The observed differences in nonlinear optical properties highlight the potential of SHS as a powerful tool for characterizing collagen self-assembly mechanisms. These findings contribute to the broader understanding of collagen organization in biological and biomaterial contexts, with implications for tissue engineering, fibrosis research, and regenerative medicine. Future work should explore how external factors such as ionic strength and crosslinking agents further modulate collagen fibril formation and its mechanical properties.

Bacteria’s ability to withstand mechanical challenges is enhanced in their biofilm lifestyle, where they are encased in a viscoelastic polymer matrix. Under fluid flow, biofilms can form as streamers – slender filaments tethered to solid surfaces and suspended in the flowing fluid. Streamers thrive in environments subjected to intense hydrodynamic stresses, such as medical devices and water filters, often resulting in catastrophic clogging. Their colonisation success may depend on a highly adaptable mechanical response to varying stress conditions, though the evidence and underlying mechanisms of this adaptation remain elusive. Here, we demonstrate that biofilm streamers exhibit a stress-hardening behaviour, with both differential elastic modulus and effective viscosity increasing linearly with external stress. This stress-hardening is consistent across biofilms with different matrix compositions, formed by various bacterial species, and under diverse growth conditions. We further demonstrate that this mechanical response originates from the properties of extracellular DNA (eDNA) molecules, which constitute the structural backbone of the streamers. In addition, our results identify extracellular RNA (eRNA) as a modulator of the matrix network, contributing to both the structure and rheological properties of the eDNA backbone. Our findings reveal an instantaneous, purely physical mechanism enabling streamers to adapt to hydrodynamic stresses. Given the ubiquity of extracellular nucleic acids (eNA) in biofilms, this discovery prompts a re-evaluation of their functional role in biofilm mechanics, with potential implications for biofilm structural integrity, ecological resilience, and colonisation dynamics.

Pressure is a powerful tool for tuning the magnetic properties of van der Waals magnets owing to their weak interlayer bonding. However, local magnetometry measurements under high pressure still remain elusive for this important class of emerging materials. Here we demonstrate magnetic imaging of a van der Waals magnet under high pressure with sub-micron spatial resolution, using a two-dimensional (2D) quantum sensing platform based on boron-vacancy () centers in hexagonal boron nitride (hBN). We first analyze the performances of centers in hBN for magnetic imaging under pressures up to few GPa, and we then use this 2D sensing platform to investigate the pressure-dependent magnetization in micrometer-sized flakes of 1T-CrTe2. Besides providing a new path for studying pressure-induced phase transitions in van der Waals magnets, this work also opens up interesting perspectives for exploring the physics of 2D superconductors under pressure via local measurements of the Meissner effect.