The Helfrich-Hurault (HH) elastic instability is a well-known mechanism behind patterns that form as a result of strain upon liquid crystal systems with periodic ground states. In the HH model, layered structures undulate and buckle in response to local, geometric incompatibilities in order to maintain the preferred layer spacing. Classic HH systems include cholesteric liquid crystals under electromagnetic field distortions and smectic liquid crystals under mechanical strains, where both materials are confined between rigid substrates. However, richer phenomena are observed when undulation instabilities occur in the presence of deformable interfaces and variable boundary conditions. Understanding how the HH instability is affected by deformable surfaces is imperative for applying the instability to a broader range of materials. In this review, the HH mechanism is reexamined and special focus is given to how the boundary conditions influence the response of lamellar systems to geometrical frustration. Lamellar liquid crystals confined within a spherical shell geometry are used as the model system. Made possible by the relatively recent advances in microfluidics within the past 15 years, liquid crystal shells are composed entirely of fluid interfaces and have boundary conditions that can be dynamically controlled at will. Past and recent work that exemplifies how topological constraints, molecular anchoring conditions, and boundary curvature can trigger the HH mechanism in liquid crystals with periodic ground states is examined. The review ends by identifying similar phenomena across a wide variety of materials, both biological and synthetic. The fact that the HH mechanism is a generic and often overlooked response of periodic materials to geometrical frustration is highlighted.

HypothesisAlthough the dynamics of colloids in the vicinity of a solid interface has been widely characterized in the past, experimental studies of Brownian diffusion close to an air–water interface are rare and limited to particle-interface gap distances larger than the particle size. At the still unexplored lower distances, the dynamics is expected to be extremely sensitive to boundary conditions at the air–water interface. There, ad hoc experiments would provide a quantitative validation of predictions.ExperimentsUsing a specially designed dual wave interferometric setup, the 3D dynamics of 9 μm diameter particles at a few hundreds of nanometers from an air–water interface is here measured in thermal equilibrium.FindingsIntriguingly, while the measured dynamics parallel to the interface approaches expected predictions for slip boundary conditions, the Brownian motion normal to the interface is very close to the predictions for no-slip boundary conditions. These puzzling results are rationalized considering current models of incompressible interfacial flow and deepened developing an ad hoc model which considers the contribution of tiny concentrations of surface active particles at the interface. We argue that such condition governs the particle dynamics in a large spectrum of systems ranging from biofilm formation to flotation process.

In this article, we present the mobilities of prolate ellipsoidal micrometric particles close to an air–water interface measured by dual wave reflection interference microscopy. Particle's position and orientation with respect to the interface are simultaneously measured as a function of time. From the measured mean square displacement, five particle mobilities (3 translational and 2 rotational) and two translational–rotational cross-correlations are extracted. The fluid dynamics governing equations are solved by the finite element method to numerically evaluate the same mobilities, imposing either slip and no-slip boundary conditions to the flow at the air–water interface. The comparison between experiments and simulations reveals an agreement with no-slip boundary conditions prediction for the translation normal to the interface and the out-of-plane rotation, and with slip ones for parallel translations and in-plane rotation. We rationalize these evidences in the framework of surface incompressibility at the interface.

Pancreatic cancer is one of the deadliest cancers with an increasing incidence due to a lack ofearly-stage diagnostics and effective treatment [1]. The RAS/RAF/ MAPK/CDK4 pathway is frequentlydysregulated in pancreatic cancer and CDK4 constitutes an attractive target since several drugs havebeen approved by the FDA to inhibit its activity: Abemaciclib, Ribociclib and Palbociclib [2,3] (Figure1) However these inhibitors are not efficient in monotherapy and have only been approved for breastcancer. In order to propose an efficient therapeutic strategy to target CDK4 in pancreatic cancer, wepropose to deliver Abemaciclib using carbon nanotubes.
Carbon nanotubes are promising materials for nanomedicine applications and especially fordrug delivery. [4] In this project, we adsorb Abemaciclib onto single-walled carbon nanotubes (SWNT)for delivery of the drug into pancreatic cancer cells. In order to study adsorption, we investigate thechanges in the optical signatures of SWNTs in the near-infrared (NIR) by coupling NIR absorption,photoluminescence and Raman spectroscopies. [5] Typical kinetic spectroscopic results, assigned tothe adsorption of Abemaciclib on SWNT, dispersed in water using carbomethylcellulose (CMC), arepresented in Figure 2. We discuss the results in terms of changes of the dielectric environment of thenanotubes, leading to modulation of their excitonic and optical properties. We have furtherinvestigated the inhibitory potential of SWNT-Abemaciclib on proliferation of PANC1 cells comparedto Abemaciclib alone and have determined the toxicthreshold of SWNT dispersed in CMC.

Poly(N-isopropyl acrylamide) (PNIPAM) is a thermo-responsive polymer which undergoes a reversible coil-to-globule transition in water at temperatures close to the human body temperature [1]. Consequently, PNIPAM-based microgels show a volume phase transition (VPT) under heating. Photo-responsive hybrid microgels have been prepared by incorporating gold nanoparticles in PNIPAM microgels [2]. The outstanding photo-thermal and optical properties of single-walled carbon nanotubes (SWNTs) make them promising candidates to prepare multi-responsive hybrid microgels. However, no thorough studies have been reported so far.
In this work, we report the preparation and properties of aqueous dispersions of PNIPAM/SWNTs hybrid microgels (Figure 1a). We study their structure by transmission electron microscopy and dynamic light scattering. We investigate their optical properties and changes when heated at the VPT by near infrared (NIR) absorption, Raman and photoluminescence (PL) spectroscopies [3]. Furthermore, we use optical microscopy (Figure 1b), light scattering and NIR Raman/PL spectroscopy to show that the VPT transition can be triggered by NIR photo-thermal excitation.

Mucus is a viscoelastic aqueous fluid that participates in the protective barrier of many mammals' epithelia. In the airways, together with cilia beating, mucus rheological properties are crucial for lung mucociliary function, and, when impaired, potentially participate in the onset and progression of chronic obstructive pulmonary disease (COPD). Samples of human mucus collected in vivo are inherently contaminated and are thus poorly characterized. Human bronchial epithelium (HBE) cultures, differentiated from primary cells at an air–liquid interface, are highly reliable models to assess non-contaminated mucus. In this paper, the viscoelastic properties of HBE mucus derived from healthy subjects, patients with COPD and from smokers are measured. Hallmarks of shear-thinning and elasticity are obtained at the macroscale, whereas at the microscale mucus appears as a heterogeneous medium showing an almost Newtonian behaviour in some extended regions and an elastic behaviour close to boundaries. In addition, we developed an original method to probe mucus adhesion at the microscopic scale using optical tweezers. The measured adhesion forces and the comparison with mucus-simulants rheology as well as mucus imaging collectively support a structure composed of a network of elastic adhesive filaments with a large mesh size, embedded in a very soft gel.

In road environments, real-time knowledge of local weather conditions is an essential prerequisite for addressing the twin challenges of enhancing road safety and avoiding congestions. Currently, the main means of quantifying weather conditions along a road network requires the installation of meteorological stations. Such stations are costly and must be maintained; however, large numbers of cameras are already installed on the roadside. A new artificial intelligence method that uses road traffic cameras and a convolution neural network to detect weather conditions has, therefore, been proposed. It addresses a clearly defined set of constraints relating to the ability to operate in real-time and to classify the full spectrum of meteorological conditions and order them according to their intensity. The method can differentiate between five weather conditions such as normal (no precipitation), heavy rain, light rain, heavy fog and light fog. The deep-learning method’s training and testing phases were conducted using a new database called the Cerema-AWH (Adverse Weather Highway) database. After several optimisation steps, the proposed method obtained an accuracy of 0.99 for classification.