Soft Matter最新文献

Near-field hydrodynamic interactions between bacteria and no-slip solid surfaces are the main mechanism underlying surface entrapment of bacteria. In this study, we employ a chiral two-body model to simulate bacterial dynamics near the surface. The simulation results show that as bacteria approach the surface, their translational velocities and diffusion coefficients decrease. Under the combination of near-field hydrodynamic interactions and DLVO forces, bacteria reach a stable fixed point in the phase plane and follow circular trajectories at this point. In particular, bacteria with left-handed helical flagella exhibit clockwise circular motion on the surface. During this process, as the stable height increases, the near-field hydrodynamic interactions weaken. Consequently, the translational velocity of the bacteria parallel to the surface increases while the rotational velocity perpendicular to the surface decreases, collectively increasing the radius of curvature. Ultimately, our findings demonstrate that near-field hydrodynamic interactions significantly prolong the surface residence time of bacteria. Additionally, smaller stable heights further amplify this effect, resulting in longer residence times and enhanced surface entrapment.

This work presents a compact, general model that predicts static contact angles and upper bounds on contact angle hysteresis for random or periodic local surface topography by accounting for arbitrary fractions of localized air entrapment and liquid infiltration within micro/nanoscale topographic features adjacent to the contact line. The proposed model recovers classical wetting limits (Wenzel, Cassie–Baxter, and hemiwicking), accounts for intermediate states (e.g., impregnating Cassie), and highlights a fourth limiting state with potential realizability and practical implications: a bulk Cassie state with an ambient liquid film, termed the inverse Wenzel state. The model predictions provide actionable guidance for the rational design of micro- and nanostructured surfaces to modulate contact angle hysteresis, under real-world operating conditions that are often uncontrolled and unpredictable due to local variations of the surface topography, fouling or contamination at the liquid–solid and liquid–vapor interfaces, chemical aging, kinetic constraints, and fluctuations of the ambient relative humidity and temperature.

Liquid crystals have gained significant attention worldwide for use in digital displays, sensing, smart textures, etc. Thermochromic liquid crystals, which respond to temperature, find applications in medical diagnostics and industrial monitoring through temperature sensing and mapping. Here, we deposited a thermochromic cholesteric liquid crystal (CLC) ink on surface-modified polyethylene terephthalate (PET) substrates using doctor blade coating and direct ink writing (DIW) methods, enabling its use for monitoring temperature changes in various applications. We investigated the thermochromic responses of the CLC ink films doctor blade-coated at different temperatures and analyzed how the processing temperature influences the surface characteristics, alignment of the liquid crystals, and their thermochromic behavior. Based on these observations, we identified the optimal printing temperature for the DIW process. We elucidated the interaction of CLCs with surface treatment, such as hydrophobic and hydrophilic coatings, and how they affect the spreading behavior and thermochromic response of CLCs printed on the coated PET substrates. The results demonstrate that the hydrophobic coating intensifies the temperature response of the CLC by drastically reducing ink spreading. This result is supported by the wetting studies of the CLC ink on various substrates and the wetting envelopes, which are developed to predict the contact angles of the ink on these surfaces. Direct ink writing of liquid crystals at elevated temperatures together with the surface treatment of substrates provides a facile way to pattern the liquid crystals with desirable alignment and robust thermochromic performance for temperature sensing applications.

We investigate active particles that exhibit distance-independent interactions only restricted by a field of view, which is characterized by an angle β. We show that constraining attractive interactions to a field of view leads to the emergence of a complex pattern that exhibits - depending on the value of β and initial conditions - significantly different topologies and transport properties. We find, in two dimensions, a nematic closed filament in the form of a ring that moves as a chiral active particle, a closed polar filament with one singular topological point that exhibits net polar order and moves ballistically, a structure with two singular topological points that rotates, or an open polar filament that behaves as a persistent random walk. Furthermore, we investigate the process that transforms one structure into another by slowly varying β and observe that the process is non-reversible and presents strong hysteresis. Finally, we find that in three dimensions similar patterns also emerge. The analysis sheds light on the physics of single-species active particles with long-range, non-reciprocal interactions in two and three dimensions, characterized by the absence of gas phases, and provides evidence that in these systems, topological and transport properties are closely related.

Viscoelastic properties of tissues, including elasticity and viscosity, are crucial for understanding development and disease progression. However, traditional atomic force microscopy (AFM) indentation methods provide limited insight into these complex tissue properties. This study establishes microrheology via oscillatory AFM to assess both the elastic and viscous components of tissue mechanics. We first compared indentation AFM to oscillatory AFM on mouse retinal tissue and found that the Young's modulus of indentation AFM (956.8 Pa) was statistically similar to the elastic component (storage modulus, E') of oscillatory AFM (920.2 Pa), while also providing the viscous component (loss modulus, E″ = 218.3 Pa), and the loss factor (tan(δ) = 0.238) across a wide range of biologically relevant frequencies (1-100 Hz). We also found that optimization of input probe parameters, such as approach length, approach speed, applied force, and oscillation amplitude, is key for accurate measurements. To examine whether this approach can detect differences between healthy and diseased tissues, we applied it to murine retinas from healthy control mice and diabetic retinopathy mice, using the oxygen-induced retinopathy (OIR) mouse model. OIR retinas exhibited increased stiffness (E' = 3564.0 Pa) and a higher loss factor (tan(δ) = 0.478) compared to healthy retinas (E' = 920.7, tan(δ) = 0.263), suggesting changes in the extracellular matrix and highlighting how retinopathy may alter matrix properties. Finally, to assess the feasibility of using microrheology AFM on banked tissues biospecimens, we examined how tissue fixation affects the measurements. We found that formaldehyde fixation increased stiffness and elasticity, with OIR tissues consistently stiffer than WT tissues in both fixed and unfixed tissues, enabling valid cross-treatment comparisons. Our findings establish the benefits of microrheology in capturing tissue mechanical behavior, which is important for studying disease impact on tissue mechanics. This approach offers new insights into tissue viscoelasticity with implications for studying the dynamics of tissue mechanics in diseases and regeneration.

Retraction of ‘Hydrophobized metallic meshes can ease water droplet rolling’ by Abba Abdulhamid Abubakar et al., Soft Matter, 2021, 17, 7311–7321, https://doi.org/10.1039/D1SM00746G.

Retraction of ‘Liquid droplet impact on a sonically excited thin membrane’ by Abba Abdulhamid Abubakar et al., Soft Matter, 2022, 18, 1443–1454, https://doi.org/10.1039/D1SM01603B.

In this study, we combine coarse-grained Brownian dynamics simulations and mean-field theory to study supercoiling dynamics, as well as the steady-state profiles of twist and writhe, in an open DNA polymer where one of the free ends is subjected to a constant torque. Even though the other end is free, and hence can spin and release torsional stress, we observe that the entire chain transitions between a swollen and a plectonemic phase as the torque increases beyond a critical threshold. In the plectonemic phase, we observe a non-linear twist profile in the steady state, resulting from the mutual interconversion between the injected twist and geometrical writhe, which distributes inhomogeneously along the chain. We also show that the non-equilibrium dynamics of twist accumulation is diffusive, and that writhe diffusion is negligible in this geometry, as plectonemes remain localised near the end that is being rotated. We discuss the feasibility of testing our results with single-molecule experiments.

Retraction of ‘Carbonated water droplets on a dusty hydrophobic surface’ by Abba Abdulhamid Abubakar et al., Soft Matter, 2020, 16, 7144–7155, https://doi.org/10.1039/D0SM00841A.

Understanding how proteins of different origins behave during drying is essential for controlling the mechanical stability and final structure of protein-based materials. Here, we examine the drying dynamics of acoustically levitated droplets containing either napin, a plant-derived seed storage protein, or native phosphocaseinate, a dairy protein complex, to uncover how their intrinsic physicochemical and mechanical properties govern evaporation-driven instabilities. Compared to sessile droplets, levitated droplets dry under symmetric evaporation conditions, minimizing substrate effects and contact-line pinning. During drying, both systems develop a solid skin at the air–liquid interface, which undergoes mechanical buckling once compressive stresses exceed the skin's rigidity. Despite similar overall drying kinetics, differences emerge between the two protein systems: native phosphocaseinate droplets form ductile, crack-free shells, whereas napin droplets display brittle fracture and surface cracking. These contrasting behaviours reflect fundamental differences between plant and animal proteins in terms of interfacial activity and network formation. The results are further supported by comparison with model colloid–polymer films, establishing a direct link between interfacial mechanics, crack formation, and film ductility. By revealing how protein origin governs drying-induced instabilities, this work provides mechanistic insight into the design of protein-based materials and supports the development of sustainable, plant-derived protein alternatives for food, pharmaceutical, and soft-material applications.