Paul F. Salipante

Many responsive polymeric systems exhibit complex phase behavior which require both large and precise experimental data sets to identify phase boundaries and solution properties.

Blood vessels expand and contract actively as they continuously experience dynamic external stresses from blood flow. The mechanical response of the vessel wall is that of a composite material: its mechanical properties depend on its cellular components, which change dynamically as the cells respond to external stress. Mapping the relationship between these underlying cellular processes and emergent tissue mechanics is an ongoing challenge, particularly in endothelial cells. Here we assess the mechanics and cellular dynamics of an endothelial tube using a microstretcher that mimics the native environment of blood vessels. The characterization of the instantaneous monolayer elasticity reveals a strain-stiffening, actin-dependent and substrate-responsive behaviour. After a physiological pressure increase, the tissue displays a fluid-like expansion, with the reorientation of cell shape and actin fibres. We introduce a mechanical model that considers the actin fibres as a network in the nematic phase and couples their dynamics with active and elastic fibre tension. The model accurately describes the response to the pressure of endothelial tubes.

Rod-like particles are efficient rheology modifiers and are commonly found in a variety of biological and industrially relevant suspensions, from biofilaments to worm-like surfactant micelles. These suspensions display strong shear-thinning behavior, and ongoing efforts aim to understand the microstructural changes of these fluids: how they depend upon the properties of the suspended particles and how these changes manifest in the resulting rheology. With suspensions of fd bacteriophage as a model monodisperse rod system, we use capillary microrheometry and flow birefringence to determine rheological behavior across nearly six decades of shear rate up to 6 × 105 s–1, at various semidilute concentrations. A single, and surprisingly large, primary fitting parameter accounting for the characteristic distance of hydrodynamic interactions is consistent with viscosity data up to very high shear rates. These results may prompt other work to understand the mechanics of these interactions.

Glucocorticoids (GCs) are standard‐of‐care treatments for inflammatory and immune disorders, and their long‐term use increases the risk of osteoporosis. Although GCs decrease bone functionality, their role in bone microvasculature is incompletely understood. Herein, the study investigates the mechanisms of bone microvascular barrier function via osteoblast‐endothelial interactions in response to GCs. The animal data shows that prednisolone (Psl) downregulated the osteoblast function and microvessel number and size. To investigate the role of GCs in bone endothelial barrier function further, a bicellular microfluidic in vitro system is developed and utilized, which consists of three‐dimensional (3D) perfusable microvascular structures embedded in collagen I/osteoblast matrix. Interestingly, it is demonstrated that GCs significantly inhibit osteogenesis and microvascular barrier function by interfering with endothelial‐osteoblast interactions. This effect is triggered by MAPK‐induced phosphorylation of connexin43 (Cx43) at Ser282. Collectively, this study sheds light on microvascular function in bone disorders, as osteoporosis, and permits to capture dynamic changes in endothelial‐bone interactions under GCs by dissecting the MAPK/Cx43 mechanism and proposing this as a potential target for bone diseases.

Applications often expose wormlike micelle solutions to a very wide range of shear and temperature conditions. The two-species model presented in Part I [Salipante et al., J. Rheol. 68 (2024)] describes the nonlinear rheology over a wide range of shear rates. Here, we compare the model predictions to measurements using a combination of microcapillary and rotational rheology to measure the viscosity of surfactant solutions across seven decades of shear rate and five decades of viscosity. The effect of temperature is studied between 20 and 60 °C for different surfactant concentrations. Model parameters are determined from both small-amplitude shear measurements and fitting to the nonlinear data. Under shear stress, the model predicts due to hindered combination kinetics that the average micelle length decreases from several micrometers to a few hundred nanometers. At sufficiently high stress, the micelle shear rheology exhibits a transition from entangled wormlike behavior to a dilute rod rheology in agreement with the model. Transient stress-growth measurements exhibit a large overshoot, which is rather well predicted by the model with hindered combination rate. Microcapillary flow birefringence also is adequately predicted by the model, confirming the accuracy of its predicted micelle lengths and exhibiting a marked change in stress-optic response at the transition between entangled polymers and dilute rods. The relaxation of retardance after flow cessation follows model predictions that include micelle-micelle interactions, which are sensitive to the rotational diffusivity and length. These methods can be applied broadly to explore relationships between composition and performance.

We develop a rheological model to approximate the nonlinear rheology of wormlike micelles using two constitutive models to represent a structural transition at high shear rates. The model is intended to describe the behavior of semidilute wormlike micellar solutions over a wide range of shear rates whose parameters can be determined mainly from small-amplitude equilibrium measurements. Length evolution equations are incorporated into reactive Rolie-Poly entangled-polymer rheology and dilute reactive-rod rheology, with a kinetic exchange between the two models. Although the micelle length is remarkably reduced during flow, surprisingly, we propose that they are not shortened by stress-enhanced breakage, which remains thermally driven. Instead, we hypothesize that stretching energy introduces a linear potential that decreases the rate of recombination and reduces the mean micelle length. This stress-hindered recombination approach accurately describes transient stress-growth upon start-up shear flow, and it predicts a transition of shear viscosity and alignment response observed at high shear rates. The proposed mechanism applies only when self-recombination occurs frequently. The effect of varying the relative rate of self-recombination on the rheology of wormlike micelles at high shear rates is yet to be explored.

The solution viscosity and protein-protein interactions (PPIs) as a function of temperature (4-40 °C) were measured at a series of protein concentrations for a monoclonal antibody (mAb) with different formulation conditions, which include NaCl and sucrose. The flow activation energy (E_η) was extracted from the temperature dependence of solution viscosity using the Arrhenius equation. PPIs were quantified via the protein diffusion interaction parameter (k_D) measured by dynamic light scattering, together with the osmotic second virial coefficient and the structure factor obtained through small-angle X-ray scattering. Both viscosity and PPIs were found to vary with the formulation conditions. Adding NaCl introduces an attractive interaction but leads to a significant reduction in the viscosity. However, adding sucrose enhances an overall repulsive effect and leads to a slight decrease in viscosity. Thus, the averaged (attractive or repulsive) PPI information is not a good indicator of viscosity at high protein concentrations for the mAb studied here. Instead, a correlation based on the temperature dependence of viscosity (i.e., E_η) and the temperature sensitivity in PPIs was observed for this specific mAb. When k_D is more sensitive to the temperature variation, it corresponds to a larger value of E_η and thus a higher viscosity in concentrated protein solutions. When k_D is less sensitive to temperature change, it corresponds to a smaller value of E_η and thus a lower viscosity at high protein concentrations. Rather than the absolute value of PPIs at a given temperature, our results show that the temperature sensitivity of PPIs may be a more useful metric for predicting issues with high viscosity of concentrated solutions. In addition, we also demonstrate that caution is required in choosing a proper protein concentration range to extract k_D. In some excipient conditions studied here, the appropriate protein concentration range needs to be less than 4 mg/mL, remarkably lower than the typical concentration range used in the literature.

Blood vessels expand and contract actively, while continuously experiencing dynamic external stresses from the blood flow. The mechanical response of the vessel wall is that of a composite material: its mechanical properties depend on a diverse set of cellular mechanical components, which change dynamically as cells respond to external stress. Mapping the relationship between these underlying cellular processes and emergent tissue mechanics is an on-going challenge, in particular in endothelial cells. Here we use a microstretcher mimicking the native environment of blood vessels to assess both the mechanics and cellular dynamics of an endothelial tube in response to a physiological increase in luminal pressure. The characterization of the instantaneous monolayer elasticity reveals a strain-stiffening, actin-dependent and substrate-responsive behavior. In response to a maintained pressure increase, the tissue displays a fluid-like expansion, accompanied by the reorientation of cell shape and of actin fibers. This actin-driven reorientation depends on focal adhesions and adherens junctions, two key mechanosensors. We introduce a mechanical model coupling actin fiber nematodynamics with active and elastic tension generation by actin fibers in the endothelium, which recapitulates the response to pressure of endothelial tubes.

Bamboo composite is an attractive candidate for structural materials in applications such as construction, the automotive industry, and logistics. However, its development has been hindered due to the use of harmful petroleum-derived synthetic adhesives or low-bonding biobased adhesives. Herein, we report a novel bioadhesion strategy based on in situ lignin bonding that can process natural bamboo into a scalable and high-performance composite. In this process, lignin bonds the cellulose fibrils into a strong network via a superstrong adhesive interface formed by hydrogen bonding and nanoscale entanglement. The resulting in situ glued-bamboo (glubam) composite exhibits a record-high shear strength of ∼4.4 MPa and a tensile strength of ∼300 MPa. This in situ lignin adhesion strategy is facile, highly scalable, and cost-effective, suggesting a promising route for fabricating strong and sustainable structural bamboo composites that sequester carbon and reduce our dependence on petrochemical-based adhesives.