Formation Of Hierarchical Patterns Research Articles

En1 and Lmx1b do not recapitulate embryonic dorsal-ventral limb patterning functions during mouse digit tip regeneration.

The mouse digit tip regenerates following amputation. How the regenerate is patterned is unknown, but a long-standing hypothesis proposes developmental patterning mechanisms are re-used during regeneration. The digit tip bone exhibits dorsal-ventral (DV) polarity, so we focus on En1 and Lmx1b, two factors necessary for DV patterning during limb development. We investigate whether they are re-expressed during regeneration in a developmental-like pattern and whether they direct DV morphology of the regenerate. We find that both En1 and Lmx1b are expressed in the regenerating digit tip epithelium and mesenchyme, respectively, but without DV polarity. Conditional genetics and quantitative analysis of digit tip bone morphology determine that genetic deletion of En1 or Lmx1b in adult digit tip regeneration modestly reduces bone regeneration but does not affect DV patterning. Collectively, our data suggest that, while En1 and Lmx1b are re-expressed during mouse digit tip regeneration, they do not define the DV axis during regeneration.

Formation of Hierarchical Porous Films with Breath-Figures Self-Assembly Performed on Oil-Lubricated Substrates.

Hierarchical honeycomb patterns were manufactured with breath-figures self-assembly by drop-casting on the silicone oil-lubricated glass substrates. Silicone oil promoted spreading of the polymer solution. The process was carried out with industrial grade polystyrene and polystyrene with molecular mass . Both polymers gave rise to patterns, built of micro and nano-scaled pores. The typical diameter of the nanopores was established as 125 nm. The mechanism of the formation of hierarchical patterns was suggested. Ordering of the pores was quantified with the Voronoi tessellations and calculation of the Voronoi entropy. The Voronoi entropy for the large scale pattern was , evidencing the ordering of pores. Measurement of the apparent contact angles evidenced the Cassie-Baxter wetting regime of the porous films.

Modeling and numerical investigations for hierarchical pattern formation in desiccation cracking

Desiccation cracking and its pattern formation are widely observed in nature. The network of the surface cracks forms polygonal cells with typical size. This crack pattern is not formed in a simultaneous manner, instead, formed in a sequential and hierarchical manner. The strain energy accumulated by the heterogeneous drying shrinkage strain is systematically released by the cracks. In this sense, desiccation cracking phenomenon can be regarded as a typical example of the pattern formation in the dynamical system with dissipation. We propose a mathematical model for the pattern formation in desiccation cracking with emphasis on the emergence of the typical length scale with the typical geometry resulting from the hierarchical cell tessellation. The desiccation crack phenomenon is modeled as the coupling of desiccation, deformation, and fracture. This coupling model is numerically solved by weakly coupled analysis of the desiccation process and the deformation/fracture process. The basic features of the desiccation crack pattern and its formation process reproduced by the numerical analysis show reasonable agreement with experimental observations. This agreement implies that the proposed coupling model properly addresses the fundamental mechanism for the hierarchical pattern formation in desiccation cracking.

Self-organized formation of hierarchically-ordered structures in laser-activated plasma CVD of sp3-bonded BN films

The hierarchical pattern formation with three stages, that is, (1) film-thickness topography, (2) fractal or concentric-ring pattern, and (3) cone morphology at micron or sub-micrometer order, was found here for the first time in the BN films prepared by plasma CVD assisted with pulsed excimer laser irradiation at 193 nm. The detailed topography consisting of unevenness in the film-thickness was obtained owing to the two-dimensional X-ray diffraction (2D-XRD) mapping method using a collimated X-ray of 0.1 mm in the diameter, where very high sensitivity was realized by selecting the X-ray from the substrate material, that was exponentially attenuated through the absorption from the film material according to Beer’s law. The important roles of the etching reactions in this process were experimentally verified here for the first time due to the 2D-mapping method. The formation mechanism of the hierarchical patterns was discussed.

Metal hierarchical patterning by direct nanoimprint lithography.

Three-dimensional hierarchical patterning of metals is of paramount importance in diverse fields involving photonics, controlling surface wettability and wearable electronics. Conventionally, this type of structuring is tedious and usually involves layer-by-layer lithographic patterning. Here, we describe a simple process of direct nanoimprint lithography using palladium benzylthiolate, a versatile metal-organic ink, which not only leads to the formation of hierarchical patterns but also is amenable to layer-by-layer stacking of the metal over large areas. The key to achieving such multi-faceted patterning is hysteretic melting of ink, enabling its shaping. It undergoes transformation to metallic palladium under gentle thermal conditions without affecting the integrity of the hierarchical patterns on micro- as well as nanoscale. A metallic rice leaf structure showing anisotropic wetting behavior and woodpile-like structures were thus fabricated. Furthermore, this method is extendable for transferring imprinted structures to a flexible substrate to make them robust enough to sustain numerous bending cycles.

Photoinduced Disorder in Strongly Segregated Block Copolymer Composite Films for Hierarchical Pattern Formation

Submicrometer patterns of adjacent, well-ordered and disordered domains were obtained using optical lithography by area-selective, photoinduced disordering transitions within block copolymer composite films. Enantiopure tartaric acid was blended with poly(ethylene oxide-block-tert-butyl acrylate), PEO-b-PtBA, copolymers to yield well-ordered films. In the presence of triphenylsulfonium triflate, a photoacid generator, photoinduced disorder was achieved upon UV-exposure by deprotection of the PtBA block to yield poly(acrylic acid). Poly(acrylic acid) is compatible with both PEO and tartaric acid and deprotection yields a phase mixed material and disorder within seconds. Tartaric acid performs two additional functions in this system. First, it increases segregation strength in PEO-b-PtBA, enabling well-ordered systems at low BCP molecular weights, small domain sizes, and rapid disordering kinetics. Second, the presence of tartaric acid suppresses PEO crystallization, resulting in smooth films and eliminating the influence of PEO crystallization on film morphology.

Interplay of electrohydrodynamic structure formation and microphase alignment in lamellar block copolymers

Electrohydrodynamic (EHD) destabilisation of a lamellar-forming block-copolymer (BCP) film gives rise to hierarchical pattern formation on the micrometre and 10 nm length scale in one single step. Two BCP morphologies were found in the columns that formed from a homogeneous surface instability. At low electric field strength, coaxial concentric lamellae indicate the dominance of surface tension differences of the BCP components over electric field effects. Outward opening lamellae are caused by lateral electric field gradients at sufficiently high field strength. Nucleated instabilities at low field strength give rise to stable bulls-eye-type ring structures consisting of BCP lamellae aligned along the ring perimeter. This is explained in terms of a free energy argument, illustrating the role of the internal energy of the BCP stack, resisting the deformation of the ring. Finally, the EHD experimental configuration was used to fabricate large monodomains of standing oriented lamellae.

Multiscale Pattern Generation in Viscoelastic Polymer Films by Spatiotemporal Modulation of Electric Field and Control of Rheology

Electric-field-induced hierarchical, multiscale patterning of incompletely cross-linked viscoelastic polydimethylsiloxane (PDMS) films is achieved by spatiotemporal variation of the field, which produces a multiplicity of complex mesopatterns from the same electrode. Experiments and simulations are employed to uncover pathways of hierarchical pattern formation. Spatial modulation of the field is introduced by employing different types of simply patterned electrodes: stripes, elevated concentric circular rings, and box-patterned ridges. Multiscale complex structures consisting of increasingly finer primary, secondary, and tertiary hierarchical structures are fabricated by progressively ramping up the electric field while maintaining the integrity of the already formed structures. The latter is achieved by partially cross-linking the films before patterning, which engenders optimal viscosity to prevent a rapid ripening and coalescence of earlier formed patterns. These multiscale structures can be controlled by the geometry and periodicity of patterned electrodes, the strength of the electric field, and its programmable temporal variation. The PDMS patterns are made permanent by complete cross-linking after a desired multiscale structure is obtained.

Inside Cover: Fluorapatite–Gelatine Nanocomposite Superstructures: New Insights into a Biomimetic System of High Complexity (ChemPhysChem 9/2010)

The beauty of complexity is reflected by the formation of hierarchical patterns on various length scales. As shown by J. Brickmann, R. Kniep et al. on p. 1851, the simulation of the fibril pattern inside a fluorapatite-gelatine nanocomposite superstructure reveals excellent agreement with TEM data and seems to be a key scenario for the development of biogenic composite shapes and architectures.

Fluorapatite–Gelatine Nanocomposite Superstructures: New Insights into a Biomimetic System of High Complexity

The beauty of complexity is reflected by the formation of hierarchical patterns on various length scales. The simulation of the fibril pattern inside a fluorapatite-gelatine nanocomposite superstructure reveals excellent agreement with TEM data and seems to be a key scenario for the development of biogenic composite shapes and architectures.

Flow waves of hierarchical pattern formation induced by chemical waves: The birth, growth and death of hydrodynamic structures

We introduce a short review of chemically driven convection together with a series of our experiments on hydrodynamic instabilities induced by chemical waves excited in the batch reactor of a Belousov–Zhabotinsky reaction. Several unresolved phenomena are picked out and possible mechanisms are discussed extensively. Interesting features of these phenomena can be summarized as being caused by the ‘global and dynamic hydrodynamic pattern induced by chemical waves’. These chemically induced global pattern of hydrodynamic phenomena may not be simply explained by the reaction–diffusion–convection model based on Marangoni instability (surface tension-driven convection), which produces only a localized structure of the convection pattern. Observed flow waves show global and dynamic patterns of convection that generate a functional structure associated with hierarchical patterns appearing in the reaction–diffusion–convection system. In particular, we clarify the existence of a continuous stream of hydrodynamic flow with growing amplitude and its rotating direction. We find that the flow does not stabilize to a motionless state until the system has self-collapsed. This new picture of the flow waves requires a revision of the reaction–diffusion–convection model. The established flow structure can be regarded as a mixing and/or transport process to supply the substrate from the peripheral region to the centre of the chemical waves to sustain the reaction. This characteristic may be a function of the hierarchical structure. A new mechanism for the viscous–elastic feature of the gas–liquid interface is discussed in order to understand these curious phenomena of interest.

A hierarchical structure through imprinting of a polyimide precursor without residual layers

A patterned polyimide without a residual layer is obtained by imprinting with the assistance of a residual solvent. The effects of the wetting behaviors of the poly-amic acid (PAA) solution coated on various surfaces are examined and the formation of hierarchical patterns without residual layers is demonstrated. polydimethylsiloxane (PDMS) and PEI/PDMS are used as imprinting molds with Si and 300 nm SiO2/Si as substrates. The results indicate that the various ambits of patterns without a residual layer are formed due to the dewetting phenomena caused by surface tension (Suh 2006 Small 2 832). During imprinting, PDMS with a low surface energy makes the PAA solution flow away from its surface exposing the contact area due to dewetting. Self-organized hierarchical structures are also obtained from this process due to effective dewetting. The present study provides a new approach for fabricating patterns without residual layers and the consequent preparation of hierarchical structures, which is considered to be impossible using the lithographic technique.

Hierarchical Pattern Formation in Thin Polymer Films Using an Electric Field and Vapor Sorption

AbstractThe experimental observation of electric‐field‐induced instabilities of polymer films exposed to toluene vapors is reported. When using a laterally structured electrode, the pattern that forms in the polymer film is governed by the interplay of the intrinsic film instability and the periodicity of the electrode structure. By adjusting the applied voltage, it is possible to switch between two different pattern‐replication modes. A further important parameter is the aspect ratio of the structured electrode. For high ratios of polymer film thickness to capacitor‐plate spacing, structures with hierarchical length scales have been observed.

Small‐angle neutron scattering studies of dynamics and hierarchical pattern formation in binary mixtures of polymers and small molecules

AbstractWe present the dynamics of the composition fluctuations and pattern formation of two‐component systems in both single‐phase and two‐phase states as studied by time‐resolved small‐angle neutron scattering and light scattering. Two‐component systems to be covered here include not only dynamically symmetric systems, in which each component has nearly identical self‐diffusion coefficients, but also dynamically asymmetric systems, in which each component has different self‐diffusion coefficients. We compare the dynamic behaviors of the two systems and illuminate their important differences. The scattering studies presented for dynamically asymmetric systems highlight that stress–diffusion coupling and viscoelastic effects strongly affect the dynamics and pattern formation. For dynamically symmetric systems, we examine the universality existing in both polymer systems and small‐molecule systems as well as new features concerning the time evolution of hierarchical structures during phase separation via spinodal decomposition over a wide range of wave numbers (up to four orders of magnitude). For both systems, we emphasize that polymers provide good model systems for studying the dynamics and pattern formation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3027–3062, 2004

Some Factors Affecting the Development of Mud-Cracks

Some Factors Affecting the Development of Mud-Cracks