Rapid self-strengthening in double-network hydrogels triggered by bond scission

Nature Materials · 2025-02-26 · 77 citations

Physiology and pathophysiology of human airway mucus

UNC Libraries · 2025-07-31

The mucus clearance system is the dominant mechanical host defense system of the human lung. Mucus is cleared from the lung by cilia and airflow, including both two-phase gas-liquid pumping and cough-dependent mechanisms, and mucus transport rates are heavily dependent on mucus concentration. Importantly, mucus transport rates are accurately predicted by the gel-on-brush model of the mucociliary apparatus from the relative osmotic moduli of the mucus and periciliary-glycocalyceal (PCL-G) layers. The fluid available to hydrate mucus is generated by transepithelial fluid transport. Feedback interactions between mucus concentrations and cilia beating, via purinergic signaling, coordinate Na⁺ absorptive vs Cl^- secretory rates to maintain mucus hydration in health. In disease, mucus becomes hyperconcentrated (dehydrated). Multiple mechanisms derange the ion transport pathways that normally hydrate mucus in muco-obstructive lung diseases, e.g., cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), non-CF bronchiectasis (NCFB), and primary ciliary dyskinesia (PCD). A key step in muco-obstructive disease pathogenesis is the osmotic compression of the mucus layer onto the airway surface with the formation of adherent mucus plaques and plugs, particularly in distal airways. Mucus plaques create locally hypoxic conditions and produce airflow obstruction, inflammation, infection, and, ultimately, airway wall damage. Therapies to clear adherent mucus with hydrating and mucolytic agents are rational, and strategies to develop these agents are reviewed.

Rubber that lasts longer

Nature Sustainability · 2025-05-07

Polymer Solutions under Steady Solvent Flow between Two Semipermeable Interfaces

Macromolecules · 2025-07-24

Pressure differentials across polymer solutions cause fluid flow. We develop a theory for the spatial variation of polymer concentration in solutions under steady flow between two interfaces permeable to the solvent but not to the polymer. The balance between the external pressure gradient and the osmotic pressure gradient of the polymer solution determines the concentration profile, which increases from the solvent inlet towards the solvent outlet. We find that even if the solution is dilute on average, a semidilute region with overlapping polymers could develop near the outlet. Conversely, even if the solution is semidilute on average, a dilute region with non-overlapping polymers could develop near the solvent inlet. The spatial dependence of polymer concentration implies that polymer dynamics could be significantly slower at the outlet. We apply our theory to the distribution of mucin polymers in human airway mucus. This work suggests that although the average mucin concentration could be near overlap in healthy physiological conditions, water evaporation causes a layer of higher mucin concentration near the air-mucus interface and a dilute mucus layer near the cell surface. On the other hand, even if the average mucin concentration in some diseased states might compress the periciliary layer (PCL), the evaporation-driven redistribution of mucins could sufficiently decrease the concentration near the PCL, delaying the onset of PCL collapse and permitting mucociliary clearance.

Tuning the Ultimate Strain of Single and Double Network Gels Through Reactive Strand Extension

ACS Central Science · 2025-08-15 · 7 citations

The stretchability (ability to be elongated) and toughness (capacity to absorb energy before breaking) of polymer network materials, such as elastomers and hydrogels, often determine their utility and lifetime. Direct correlations between the molecular behavior of polymer network components and the physical properties of the network inform the design of materials with enhanced performance, extended lifetime, and minimized waste stream. Here, we report the impact of the fused ring size in bicyclic cyclobutane mechanophores within the strands of polymer network gels. The mechanophores and their polymer strands share the same initial covalent contour length, whereas the capacity for reactive strand extension (RSE) is varied by changing the size of the ring fused to the cyclobutane from 5 to 12 carbon atoms. We observe the first evidence of covalent RSE effects in a single-network gel, and strands with greater RSE lead to gels with greater stretchability and toughness. The same qualitative correlation between molecular and macroscopic extension is also observed in DN hydrogels with mechanophores in the prestretched first network.

Nonlinear Shear Rheology of Unentangled Polymer Melts

Macromolecules · 2025-07-08 · 6 citations

In the present work, we investigate the nonlinear shear rheology of unentangled polymer melts. We use linear polystyrenes with molar mass of 10 kg/mol, 20 kg/mol, or 30 kg/mol. The measurements of shear and normal stress are performed using cone-and-partitioned-plate rheometry. While the linear viscoelastic response is consistent with predictions of the Rouse model, in the nonlinear regime, the Cox-Merz rule is not fully validated, despite a universal thinning exponent of -0.5. These experimental results are analyzed using the recent shear slit model of Parisi et al. and molecular dynamics simulations. A new molecular picture is proposed to explain the origin of the transient stress overshoot, based on the concept of the advection time that marks the transition between affine and non-affine deformation. Finally, a simple model is developed, by combining Rouse relaxation modes, chain confinement to shear slit in the velocity gradient direction and tension blobs in the velocity direction. The predictions of this model for shear viscosity are in excellent agreement with the experimental data and consistent with simulations.

Reduction of Kuhn Length upon Chain Extension

ACS Macro Letters · 2025-11-19

Both polymer size and chain elasticity depend on long-range bond correlations, which determine the chain Kuhn length. These correlations are gradually cut off with increasing externally applied force or polymer confinement, thereby decreasing the effective Kuhn length. We develop a theory for the strain-dependent Kuhn length and validate it with simulations. Our model explains why the Kuhn length obtained from single-molecule force spectroscopy experiments is smaller than the Kuhn length determined from scattering measurements of unperturbed chains. Finally, we propose a crossover function for the Kuhn length as a function of applied force, which can be used for the interpretation of force-extension curves.

Probing the 3D Awareness of Visual Foundation Models

arXiv (Cornell University) · 2024-04-12 · 1 citations

Recent advances in large-scale pretraining have yielded visual foundation models with strong capabilities. Not only can recent models generalize to arbitrary images for their training task, their intermediate representations are useful for other visual tasks such as detection and segmentation. Given that such models can classify, delineate, and localize objects in 2D, we ask whether they also represent their 3D structure? In this work, we analyze the 3D awareness of visual foundation models. We posit that 3D awareness implies that representations (1) encode the 3D structure of the scene and (2) consistently represent the surface across views. We conduct a series of experiments using task-specific probes and zero-shot inference procedures on frozen features. Our experiments reveal several limitations of the current models. Our code and analysis can be found at https://github.com/mbanani/probe3d.

Fracture of polymer-like networks with hybrid bond strengths

Journal of the Mechanics and Physics of Solids · 2024-11-10 · 16 citations

Light‐Induced Living Polymer Networks with Adaptive Functional Properties

Advanced Materials · 2024-04-09 · 18 citations

The advent of covalent adaptable networks (CANs) through the incorporation of dynamic covalent bonds has led to unprecedented properties of macromolecular systems, which can be engineered at the molecular level. Among the various types of stimuli that can be used to trigger chemical changes within polymer networks, light stands out for its remote and spatiotemporal control under ambient conditions. However, most examples of photoactive CANs need to be transparent and they exhibit slow response, side reactions, and limited light penetration. In this vein, it is interesting to understand how molecular engineering of optically active dynamic linkages that offer fast response to visible light can impart "living" characteristics to CANs, especially in opaque systems. Here, the use of carbazole-based thiuram disulfides (CTDs) that offer dual reactivity as photoactivated reshuffling linkages and iniferters under visible light irradiation is reported. The fast response to visible light activation of the CTDs leads to temporal control of shape manipulation, healing, and chain extension in the polymer networks, despite the lack of optical transparency. This strategy charts a promising avenue for manipulating multifunctional photoactivated CANs in a controlled manner.