Shape-morphing systems can be found in many areas, including smart textiles, autonomous robotics, biomedical devices, drug delivery and tissue engineering. The natural analogues of such systems are exemplified by nastic plant motions, where a variety of organs such as tendrils, bracts, leaves and flowers respond to environmental stimuli (such as humidity, light or touch) by varying internal turgor, which leads to dynamic conformations governed by the tissue composition and microstructural anisotropy of cell walls. Inspired by these botanical systems, we printed composite hydrogel architectures that are encoded with localized, anisotropic swelling behaviour controlled by the alignment of cellulose fibrils along prescribed four-dimensional printing pathways. When combined with a minimal theoretical framework that allows us to solve the inverse problem of designing the alignment patterns for prescribed target shapes, we can programmably fabricate plant-inspired architectures that change shape on immersion in water, yielding complex three-dimensional morphologies.

/pdf/biomimetic-4d-printing-27deareeqd.pdf

Biomimetic 4D printing

Fuel nitrogen conversion in solid fuel fired systems

https://hal.archives-ouvertes.fr/hal-00288708/document

Detailed chemical kinetic models for the low-temperature combustion of hydrocarbons with application to gasoline and diesel fuel surrogates

Kinetic modeling of hydrocarbon/nitric oxide interactions in a flow reactor

Mechanical responsiveness in many plants is produced by helical organizations of cellulose microfibrils. However, simple mimicry of these naturally occurring helical structures does not produce artificial materials with the desired tunable actuations. Here, we show that actuating fibres that respond to solvent and vapour stimuli can be created through the hierarchical and helical assembly of aligned carbon nanotubes. Primary fibres consisting of helical assemblies of multiwalled carbon nanotubes are twisted together to form the helical actuating fibres. The nanoscale gaps between the nanotubes and micrometre-scale gaps among the primary fibres contribute to the rapid response and large actuation stroke of the actuating fibres. The compact coils allow the actuating fibre to rotate reversibly. We show that these fibres, which are lightweight, flexible and strong, are suitable for a variety of applications such as energy-harvesting generators, deformable sensing springs and smart textiles.

Hierarchically arranged helical fibre actuators driven by solvents and vapours.

The thermal reactions of 2,5-dimethylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1070−1370 K and overall densities of ∼3 × 10-5 mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. A methyl group migration from C(2) to C(3) in the ring with the elimination of CO produces four isomers of C5H8 in unimolecular processes. An additional unimolecular process is the decomposition of 2,5-dimethylfuran to CH3CO and C4H5 which is an important initiator of free radical reactions. Ejection of a hydrogen atom from the methyl group in the molecule is another channel for initiation of free radical reactions in the system. The 2,5-dimethylfuryl radical, which is obtained in the process of H-atom ejection, decomposes in channels similar to those of 2,5-dimethylfuran to produce, among other products, C5H7, which is the precursor of cyclopent...

Thermal Decomposition of 2,5-Dimethylfuran. Experimental Results and Computer Modeling

The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork’s bill (Erodium) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2011.0395

Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn

compatible microcomputer. Thus, this procedure is applicable to real time, on-line kinetic analysis and model testing. Precision in the rate constants of the two more slowly decomposing anion radicals was excellent. However, a visible trend seen in Tables 111 and IV is the deterioration of precision in k at higher rates. While work is being done to fully explain the cause of such behavior, we feel that it is mainly a limitation of electrode size and data acquisition rate of 1 point/ms. Analysis of data for faster reactions is more heavily influenced by instrumental errors in the measured charge. Also, deviation from the model due to the time dependence of charging of the electrode double layer (Qdl) is most pronounced in the first few milliseconds after the potential step. This also contributes to degraded precision for larger rate constants where most of the kinetic information is contained at short times.* This limitation may possibly be removed by using ultramicroelectrodes, decreasing the time window into the submillisecond range and increasing the rate a t which data are collected. Such an approach may also require incorporation of the time dependence of Q d ] in the model. Orthogonalization necessitates deriving an orthogonal form of the model. After the values of regression parameters are obtained by use of such a model, deconvolution to recoup the original set of parameters is required. Fortunately, the nature of GramSchmidt orthogonalization should eventually enable fully automated transitions between the original basis set and the orthogonal one. It is not necessary or practical to use an orthogonalized model for every problem to be solved by nonlinear regression analysis. However, our results demonstrate the usefullness of orthogonalization when serious correlation between parameters creates problems in convergence of nonlinear regression analyses. Since the transformation is made on the model, the method is compatible with currently used general programs for nonlinear regression.

Isomerization and decomposition of pyrrole at elevated temperatures: studies with a single-pulse shock tube

The thermal reactions of 2-methylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1100−1400 K and with overall densities of ∼3 × 10-5 mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. The unimolecular decomposition is initiated by two parallel channels:  (1) 1,2-hydrogen atom migration from C(5) to C(4) and (2) a methyl group migration from C(2) to C(3) in the ring. Each channel is followed by two parallel modes of ring cleavage. In the first channel, breaking the OC(2) and the C(4)C(5) bonds in the ring yields CO and different isomers of C4H6, whereas breaking of the OC(2) and the C(3)C(4) bonds yields CH2CO and two isomers C3H4. In the second channel, breaking the OC(5), and C(2)C(3) bonds in the ring yields again CO and isomers of C4H6, whereas in the second mode OC(5), C(2)C(3), and C(3)C(4) are broken to yield CO, C2H2, ...

Decomposition of 2-Methylfuran. Experimental and Modeling Study

In pure water, zwitterionic lipids form lamellar phases with an equilibrium water gap on the order of 2 to 3 nm as a result of the dominating van der Waals attraction between dipolar bilayers. Monovalent ions can swell those neutral lamellae by a small amount. Divalent ions can adsorb onto dipolar membranes and charge them. Using solution X-ray scattering, we studied how the structure of ions and zwitterionic lipids regulates the charge of dipolar membranes. We found that unlike monovalent ions that weakly interact with all of the examined dipolar membranes, divalent and trivalent ions adsorb onto membranes containing lipids with saturated tails, with an association constant on the order of ∼10 M(-1). One double bond in the lipid tail is sufficient to prevent divalent ion adsorption. We suggest that this behavior is due to the relatively loose packing of lipids with unsaturated tails that increases the area per lipid headgroup, enabling their free rotation. Divalent ion adsorption links two lipids and limits their free rotation. The ion-dipole interaction gained by the adsorption of the ions onto unsaturated membranes is insufficient to compensate for the loss of headgroup free-rotational entropy. The ion-dipole interaction is stronger for cations with a higher valence. Nevertheless, polyamines behave as monovalent ions near dipolar interfaces in the sense that they interact weakly with the membrane surface, whereas in the bulk their behavior is similar to that of multivalent cations. Advanced data analysis and comparison with theory provide insight into the structure and interactions between ion-induced regulated charged interfaces. This study models biologically relevant interactions between cell membranes and various ions and the manner in which the lipid structure governs those interactions. The ability to monitor these interactions creates a tool for probing systems that are more complex and forms the basis for controlling the interactions between dipolar membranes and charged proteins or biopolymers for encapsulation and delivery applications.

Carmen Tamburu

Papers

Thermal Decomposition of 2,5-Dimethylfuran. Experimental Results and Computer Modeling

Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn

Isomerization and decomposition of pyrrole at elevated temperatures: studies with a single-pulse shock tube

Decomposition of 2-Methylfuran. Experimental and Modeling Study

The Structure of Ions and Zwitterionic Lipids Regulates the Charge of Dipolar Membranes