Wnt/ß-catenin signaling induces axial elasticity patterns of Hydra extracellular matrix.

The extracellular matrix (ECM) plays crucial roles in animal development and diseases. Here, we report that Wnt/ß-catenin signaling induces the ECM remodeling during Hydra axis formation. We determined the micro- and nanoscopic arrangement of fibrillar type I collagen along Hydra's body axis using high-resolution microscopy and X-ray scattering. Elasticity mapping of the ECM ex vivo revealed distinctive elasticity patterns along the body axis. A proteomic analysis of the ECM showed that these elasticity patterns correlate with a gradient-like distribution of metalloproteases along the body axis. Activation of the Wnt/ß-catenin pathway in wild-type and transgenic animals alters these patterns toward low ECM elasticity patterns. This suggests a mechanism whereby high protease activity under control of Wnt/ß-catenin signaling causes remodeling and softening of the ECM. This Wnt-dependent spatiotemporal coordination of biochemical and biomechanical cues in ECM formation was likely a central evolutionary innovation for animal tissue morphogenesis.

New Class of Crosslinker-Free Nanofiber Biomaterials from Hydra Nematocyst Proteins.

Nematocysts, the stinging organelles of cnidarians, have remarkable mechanical properties. Hydra nematocyst capsules undergo volume changes of 50% during their explosive exocytosis and withstand osmotic pressures of beyond 100 bar. Recently, two novel protein components building up the nematocyst capsule wall in Hydra were identified. The cnidarian proline-rich protein 1 (CPP-1) characterized by a "rigid" polyproline motif and the elastic Cnidoin possessing a silk-like domain were shown to be part of the capsule structure via short cysteine-rich domains that spontaneously crosslink the proteins via disulfide bonds. In this study, recombinant Cnidoin and CPP-1 are expressed in E. coli and the elastic modulus of spontaneously crosslinked bulk proteins is compared with that of isolated nematocysts. For the fabrication of uniform protein nanofibers by electrospinning, the preparative conditions are systematically optimized. Both fibers remain stable even after rigorous washing and immersion into bulk water owing to the simultaneous crosslinking of cysteine-rich domains. This makes our nanofibers clearly different from other protein nanofibers that are not stable without chemical crosslinkers. Following the quantitative assessment of mechanical properties, the potential of Cnidoin and CPP-1 nanofibers is examined towards the maintenance of human mesenchymal stem cells.

Influence of Perfluorohexane-Enriched Atmosphere on Viscoelasticity and Structural Order of Self-Assembled Semifluorinated Alkanes at the Air-Water Interface.

Semifluorinated alkanes FnHm self-assemble into nanometer-sized surface micelles at the air-water interface. In this study, we investigated how an atmosphere enriched with perfluorohexane (PFH) influences the interfacial viscoelasticity and structural order of a monolayer of FnHm by the combination of dilational rheology and grazing-incidence small-angle X-ray scattering (GISAXS). The monolayers behaved predominantly elastic which can be attributed to the strong dipole repulsions of the surface domains. Enrichment of the atmosphere with PFH lead to an increase of the compressibility and a decrease of the elastic modulus without altering the structural ordering of the FnHm molecules into highly correlated nanodomains, suggesting the adsorption of PFH molecules to the free spaces between the domains. The capability of FnHm domains to retain the structural integrity in the presence of PFH gas is promising for the fabrication of stable microbubbles for sonographic imaging.

Long-Range Lateral Correlation between Self-Assembled Domains of Fluorocarbon-Hydrocarbon Tetrablocks by Quantitative GISAXS.

The structure and lateral correlation of fluorocarbon-hydrocarbon tetrablock di(F10Hm) domains at the air/water interface have been determined by quantitative analysis of grazing incidence small-angle X-ray scattering (GISAXS) data. The measured GISAXS signals can be well represented by the full calculation of the form and structure factors. The form factor suggests that di(F10Hm) domains take a hemiellipsoid shape. Both major and minor axes of the hemiellipsoids monotonically increased in response to the elongation of the hydrocarbon blocks, which can be explained by the concominant increase in van der Waals interaction. The structure factor calculated from the GISAXS signals suggests that the domains take an orthorhombic lattice. Remarkably, the lateral correlation can reach over a distance that is more than 14 times longer than the distance to the nearest neighbors. Our data suggest that quantitative GISAXS enables the optimal design of mesoscopic self-assemblies at the air/water interface by fine-tuning of the structures of molecular building blocks.

Biopolymer-Based Minimal Formulations Boost Viability and Metabolic Functionality of Probiotics Lactobacillus rhamnosus GG through Gastrointestinal Passage.

The delivery of probiotic microorganisms as food additives via oral administration is a straightforward strategy to improve the intestinal microbiota. To protect probiotics from the harsh environments in the stomach and small intestine, it is necessary to formulate them in biocompatible carriers, which finally release them in the ileum and colon without losing their viability and functions. Despite major progresses in various polymer-based formulations, many of them are highly heterogeneous and too large in size and hence often "felt" by the tongue. In this study, we established a new formulation for probiotics Lactobacillus rhamnosus GG (LGG) and systematically correlated the physicochemical properties of formulations with the functions of probiotics after the delivery to different gastrointestinal compartments. By reducing the stirring speed by 1 order of magnitude during the emulsification of polyalginate in the presence of xanthan gum, we fabricated microparticles with a size well below the limit of human oral sensory systems. To improve the chemical stability, we deposited chitosan and polyalginate layers on particle surfaces and found that the deposition of a 20 nm-thick layer is already sufficient to perfectly sustain the viability of all LGG. Compared to free LGG, the colony-forming units of LGG in these formulations were by factors of 107 larger in stomach fluid and 104 larger in small intestine fluid. The metabolic functionality of LGG in polymer formulations was assessed by measuring the amount of lactate produced by LGG in a human gastrointestinal simulator, showing 5 orders of magnitude larger values compared to free LGG. The obtained results have demonstrated that the minimal formulation of LGG established here boosts not only the viability but also the metabolic functionality of probiotics throughout oral uptake, passage through the gastrointestinal tract, and delivery to the ileum and colon.

Author Correction: Dynamic Mechano-Regulation of Myoblast Cells on Supramolecular Hydrogels Cross-Linked by Reversible Host-Guest Interactions.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Emergence of Strong Nonlinear Viscoelastic Response of Semifluorinated Alkane Monolayers.

Viscoelasticity of monolayers of fluorocarbon/hydrocarbon tetrablock amphiphiles di(FnHm) ((CnF2n+1CH2)(Cm-2H2m-3)CH-CH(CnF2n+1CH2)(Cm-2H2m-3)) was characterized by interfacial dilational rheology under periodic oscillation of the moving barriers at the air/water interface. Because the frequency dispersion of the response function indicated that di(FnHm) form two-dimensional gels at the interface, the viscosity and elasticity of di(FnHm) were first analyzed with the classical Kelvin-Voigt model. However, the global shape of stress response functions clearly indicated the emergence of a nonlinearity even at very low surface pressures (π ≈ 5 mN/m) and small strain amplitudes (u0 = 1%). The Fourier-transformed response function of higher harmonics exhibited a clear increase in the intensity only from odd modes, corresponding to the nonlinear elastic component under reflection because of mirror symmetry. The emergence of strong nonlinear viscoelasticity of di(FnHm) at low surface pressures and strain amplitudes is highly unique compared to the nonlinear viscoelasticity of other surfactant systems reported previously, suggesting a large potential of such fluorocarbon/hydrocarbon molecules to modulate the mechanics of interfaces using the self-assembled domains of small molecules.

Dynamic Mechano-Regulation of Myoblast Cells on Supramolecular Hydrogels Cross-Linked by Reversible Host-Guest Interactions.

A new class of supramolecular hydrogels, cross-linked by host-guest interactions between ß-cyclodextrin (ßCD) and adamantane, were designed for the dynamic regulation of cell-substrate interactions. The initial substrate elasticity can be optimized by selecting the molar fraction of host- and guest monomers for the target cells. Moreover, owing to the reversible nature of host-guest interactions, the magnitude of softening and stiffening of the substrate can be modulated by varying the concentrations of free, competing host molecules (ßCD) in solutions. By changing the substrate elasticity at a desired time point, it is possible to switch the micromechanical environments of cells. We demonstrated that the Young's modulus of our "host-guest gels", 4-11 kPa, lies in an optimal range not only for static (ex situ) but also for dynamic (in situ) regulation of cell morphology and cytoskeletal ordering of myoblasts. Compared to other stimulus-responsive materials that can either change the elasticity only in one direction or rely on less biocompatible stimuli such as UV light and temperature change, our supramolecular hydrogel enables to reversibly apply mechanical cues to various cell types in vitro without interfering cell viability.

Existence of Two-Dimensional Physical Gels even at Zero Surface Pressure at the Air/Water Interface: Rheology of Self-Assembled Domains of Small Molecules.

Films of mesoscopic domains self-assembled from fluorocarbon/hydrocarbon diblock copolymers (FnHm) at the air/water interface were found to display highly elastic behavior. We determined the interfacial viscoelasticity of domain-patterned FnHm Langmuir monolayers by applying periodic shear stresses. Remarkably, we found the formation of two-dimensional gels even at zero surface pressure. These monolayers are predominantly elastic, which is unprecedented for surfactants, exhibiting gelation only at high surface pressures. Systematic variation of the hydrocarbon (n=8; m=14, 16, 18, 20) and fluorocarbon (n=8, 10, 12; m=16) block lengths demonstrated that subtle changes in the block length ratio significantly alter the mechanics of two-dimensional gels across one order of magnitude. These findings open perspectives for the fabrication of two-dimensional gels with tuneable viscoelasticity via self-assembly of mesoscale, low-molecular-weight materials.

Size, Shape, and Lateral Correlation of Highly Uniform, Mesoscopic, Self-Assembled Domains of Fluorocarbon-Hydrocarbon Diblocks at the Air/Water Interface: A GISAXS Study.

The shape and size of self-assembled mesoscopic surface domains of fluorocarbon-hydrocarbon (FnHm) diblocks and the lateral correlation between these domains were quantitatively determined from grazing incidence small-angle X-ray scattering (GISAXS). The full calculation of structure and form factors unravels the influence of fluorocarbon and hydrocarbon block lengths on the diameter and height of the domains, and provides the inter-domain correlation length. The diameter of the domains, as determined from the form factor analysis, exhibits a monotonic increase in response to the systematic lengthening of each block, which can be attributed to the increase in van der Waals attraction between molecules. The pair correlation function in real space calculated from the structure factor implies that the inter-domain correlation can reach a distance that is over 25 times larger than the domain's size. The full calculation of the GISAXS signals introduced here opens a potential towards the hierarchical design of mesoscale domains of self-assembled small organic molecules, covering several orders of magnitude in space.

Fine Adjustment of Interfacial Potential between pH-Responsive Hydrogels and Cell-Sized Particles.

We quantitatively determined interfacial potentials between cell-sized particles and stimulus-responsive hydrogels using a microinterferometer. The hydrogel is based on physically interconnected ABA triblock copolymer micelles comprising an inner biocompatible PMPC block and two outer pH-responsive PDPA blocks. The out-of-plane temporal fluctuation in the position of the cell-sized particles was calculated from changes in the interference pattern measured by Reflection Interference Contrast Microscopy (RICM), thus yielding the particle-substrate interaction potential V (Δh). Measurements in pH buffers ranging from 7.0 to 7.8 resulted in a systematic reduction in height of the potential minima ⟨Δh⟩ and a concomitant increase in the potential curvature V″ (Δh). The experimental data were analyzed by applying the modified Ross and Pincus model for polyelectrolytes, while accounting for gravitation, lubrication and van der Waals interactions. Elastic moduli calculated from V″ (Δh) were in good agreement with those measured by Atomic Force Microscopy. The ability to fine-tune both the gel elasticity and the interfacial potential at around physiological pH makes such triblock copolymer hydrogels a promising biocompatible substrate for dynamic switching of cell-material interactions.

Counteracting the inhibitory effect of proteins towards lung surfactant substitutes: a fluorocarbon gas helps displace albumin at the air/water interface.

Perfluorohexane gas lowers the kinetic barrier that opposes the displacement of albumin by dipalmitoylphosphatidylcholine at the air/water interface submitted to sinusoidal oscillations at frequencies in the range of those encountered in respiration.