Crack-Free,Soft Wrinkles Enable Switchable Anisotropic Wetting

Soft skin layers on elastomeric substrates are demonstrated to support mechano-responsive wrinkle patterns that do not exhibit cracking under applied strain. Soft fluoropolymer skin layers on pre-strained poly(dimethylsiloxane) slabs achieved crack-free surface wrinkling at high strain regimes not possible by using conventional stiff skin layers. A side-by-side comparison between the soft and hard skin layers after multiple cycles of stretching and releasing revealed that the soft skin layer enabled dynamic control over wrinkle topography without cracks or delamination. We systematically characterized the evolution of wrinkle wavelength, amplitude, and orientation as a function of tensile strain to resolve the crack-free structural transformation. We demonstrated that wrinkled surfaces can guide water spreading along wrinkle orientation, and hence switchable, anisotropic wetting was realized.     

The role of elastases secreted by fibroblasts in wrinkle formation: implication through selective inhibition of elastase activity

We have previously demonstrated that decreases in skin elasticity, accompanied by increases in the tortuosity of elastic fibers, are important early events in wrinkle formation. In order to study the role of elastases in the degeneration of elastic fibers during wrinkle formation we examined the effects of an inhibitor of skin fibroblast elastase, N-phenethylphosphonyl-L-leucyl-L-tryptophane (NPLT), on wrinkle formation in hairless mice skin following UV irradiation. Dorsal skins of hairless mice were exposed daily to UV light for 18 weeks at doses of 65-95 mJ/cm2 and treated topically with 100 microL of 1 mM NPLT immediately after each UV irradiation. Wrinkles on dorsal skins were evaluated from week 6 through week 18. The daily exposure of mouse skin to UV light with less than 1 minimal erythemal dose significantly enhanced the activity of elastase in the exposed skin by week 4, and the elevated levels of elastase activity were significantly reduced by the in vitro incubation with NPLT in a dose-dependent manner to a level similar to that in unexposed mice skin, indicating that NPLT can efficiently inhibit the UV-inducible elastase activity. Topical application of NPLT significantly suppressed wrinkle formation when compared with vehicle controls by week 15 of treatment (P < 0.05). Histochemistry of elastic fibers with Orcein staining demonstrated that there were no obvious decreases of the fine elastic fibers in UV-exposed NPLT-treated skin in contrast to their marked decreases in the UV-exposed vehicle-treated skin. These findings suggest that skin fibroblast elastase plays a decisive role in wrinkle formation through the degeneration of elastic fiber.     

Microtextured surfaces with gradient wetting properties

Patterned surfaces with microwrinkled surface structures were prepared by thermally evaporating thin aluminum (10-300 nm thick) (Al) layers onto thick prestrained layers of a silicone elastomer and subsequently releasing the strain. This resulted in the formation of sinusoidal periodic surface wrinkles with characteristic wavelengths in the 3-42 μm range and amplitudes as large as 3.6 ± 0.4 μm. The Al thickness dependence of the wrinkle wavelengths and amplitudes was determined for different values of the applied prestrain and compared to a recent large-amplitude deflection theory of wrinkle formation. The results were found to be in good agreement with theory. Samples with spatial gradients in wrinkle wavelength and amplitude were also produced by applying mechanical strain gradients to the silicone elastomer layers prior to deposition of the Al capping layers. Sessile water droplets that were placed on these surfaces were found to have contact angles that were dependent upon their position. Moreover, these samples were shown to direct the motion of small water droplets when the substrates were vibrated.     

Self-organized anisotropic wrinkling of molecularly aligned liquid crystalline polymer

Anisotropic wrinkling which utilizes the anisotropic nature of liquid crystalline polymer (LCP) is demonstrated as a means of physical self-assembly to produce periodic microstructures. Through the plasma treatment on the molecularly aligned LCP film surface, one-dimensionally ordered wrinkle pattern was spontaneously formed on glass substrates without employing external thin-film deposition or prestrain control of the system. Experimental results indicate that the directionality of the wrinkle pattern can be tailored by the structural ordering of LCP molecules in the bilayer system of a hard skin layer on a soft substrate. Studies on process variables, such as the plasma treatment time and the film thickness, were conducted to figure out the effect on the wrinkling morphology. Due to its spatial periodicity over a large area and undemanding requirement of the process, this approach can be a candidate for the microfabrication in various applications.     

Symmetry breaking in biological systems. From molecules to tissues

Chirality of biomolecules is one of the major characteristics of living systems. Molecular asymmetry can be detected in the earliest prokaryotes and stereoselective synthesis of proteins and polysaccharides was recognized since Pasteur’s time. More recently much attention was paid to the molecular origin of asymmetric development of organs. This asymmetry can be followed up to the cellular and tissue levels. We compared the periorbital wrinkle pattern (crow’s feet) around the left and right eyes, as well as the microdepressional skin surface relief on the left and right arms. The pattern of these reliefs was shown to change with age in a typical manner. Apparently this age-dependent modification of the skin surface micro-relief as well as wrinkle formation is largely determined by the progressive modifications of the dermal extracellular matrix (ECM) and especially of the elastic fiber network as the result of the oriented (vectorial) biosynthetic activity of dermal fibroblasts. These cells do not form a homogeneous population as shown by their proliferation pattern. The reaction of these cells to receptor-mediated stimuli—by growth factors, cytokines, and hormones also exhibit microheterogeneity. Cell–cell interactions, especially between the keratinocyte layers of the epidermis and dermal fibroblasts might also play an important role in the regulation of cell-patterning. These mechanisms might well explain the asymmetry detected by our semi-automated image analysis program on left–right microdepressionary skin surface relief, as well as periorbital wrinkle formation.     

THE RHEO-OPTICAL FTIR STUDY OF POLYESTERPOLYETHER SEGMENTED COPOLYMER

The polyester-polyetber segmented copolymer has been investigated by rheo-optical FTIR during stretehing for the informastion on strain induced crystallizatinn of soft segment chains, hard and soft chain orientation.At room temperature 15℃, the soft segment chains of polyester-polyether being to crystallize at 220% strain and the degree of crystallixation increa(?)e with draw ratio, but there will not be any soft segment chains crystallization above 21℃even at bigber strain. The average orientation of hard segment chains are higher than that of the soft chain at high strain level, both are positive oriented into the stretching direction at allover strain level. This indicates that the b(?)d (?)ent ch(?)ins are dispersed into the elastomeric phase and without forming spherulite.     

Highly oriented tunable wrinkling in polymer bilayer films confined with a soft mold induced by water vapor

The authors report the formation of highly oriented wrinkling on the surface of the bilayer [polystyrene (PS)/poly(vinyl pyrrolidone) (PVP)] confined by a polydimethylsiloxane (PDMS) mold in a water vapor environment. When PVP is subjected to water vapor, the polymer loses its mechanical rigidity and changes to a viscous state, which leads to a dramatic change in Young's modulus. This change generates the amount of strain in the bilayer to induce the wrinkling. With a shape-controlled mold, they can get the ordered wrinkles perfectly perpendicular or leaned 45 degrees to the channel orientation of the mold because the orientation of the resultant force changes with the process of water diffusion which drives the surface to form the wrinkling. Additionally, they can get much smaller wrinkles than the stripe spacing of PDMS mold about one order. The wrinkle period changes with the power index of about 0.5 for various values of the multiplication product of the film thicknesses of the two layers, namely, lambda approximately (h(PS)h(PVP))(1/2).     

Multidirectional Wrinkle Patterns Programmed by Sequential Uniaxial Strain with Conformal yet Nontraceable Masks

Surface wrinkling is a promising route to control the mechanical, electrical, and optical properties of materials in a wide range of applications. However, previous artificial wrinkles are restricted to single or random orientation and lacks selectivity. To address this challenge, this study presents multidirectional wrinkle patterns with high selectivity and orientation through sequential uniaxial strain with conformal polymeric shadow masks. The conformal but nontraceable polymeric stencil with microapertures are adhered to a flat substrate prior to oxidation, which forms discrete and parallel wrinkles in confined domains without any contamination. By fully investigating the process, this study displays compound topography of wrinkles consisting of wrinkle islands and surrounding secondary wrinkles on the same surface. With this topography, various diffusion properties are presented: from semi‐transparent yet diffusive films to multidirectional diffusive films, which will be available for new types of optical diffuser applications.     

Finely Formed,Kinetically Modulated Wrinkle Structures in UV‐Crosslinkable Liquid Prepolymers

Special characteristics of wrinkles such as a scattering source and a high surface area are finding use in high‐tech applications. UV‐crosslinkable prepolymers are occasionally used for fabricating wrinkled films. Wavelength of the wrinkles formed from the prepolymers is several tens and hundreds of micrometers. Here, a UV‐crosslinkable liquid prepolymer is synthesized to spontaneously form wrinkle structures in the order of several micrometers. Double layers with a very thin hard skin and a soft and contractible foundation are formed at the same time, by ensuring that all the absorbance wavelengths of the photoinitiator are shorter than the minimum wavelength at which the prepolymer is transparent. The rate of photo‐crosslinking reaction, R_p, is also found to affect the thickness of the skin and foundation layers at the early UV‐curing stage. The first‐order apparent rate constant, k_app, is between ≈0.20 and ≈0.69 s⁻¹ for the wrinkle formation. This wrinkle structures can be simply modulated by changing R_p.

     

Two dimensional infrared (2D-IR) spectroscopic studies of the viscoelastic behavior of liquid crystalline polyurethanes

Dynamic infrared dichroism techniques have been used to study a complex side chain liquid crystalline segmented polyurethane. The obtained dynamic spectra were analyzed using two dimensional infrared techniques (2D-IR) that allow the easier interperation of the dynamic response of this system. Side chain mesogens are monitored by the cyano tag at the end of the molecule while the hard segments can be viewed in the carbonyl spectral region. A study of the different parts of the macromolecule leads to an understanding of the elastic and the viscous orientation behavior of the polymer. We find that the elastic component of the strain aligns smectic layers parallel and hard domains perpendicular to the direction of strain. The viscous strain component, on the other hand, induces a perpendicular smectic layer and parallel hard domain orientation behavior. These observations are consistent with a model proposed in earlier work that the hard segments and the smectic layers change orientation as the applied strain is increased from low to high strains. In addition, we show further evidence for the coupling of the mechanical deformation behavior of the smectic layers and the hard domains and identified two primary relaxation times in this system.     

Prevention of UV radiation-induced premature skin aging in hairless mice by the novel compound Melanocin A

Repetitive exposure of the skin to UV radiation induces various harmful changes, such as thickening, wrinkle formation, inflammation and carcinogenesis. A variety of natural compounds and synthetic compounds have been studied to determine whether they can prevent UV-induced harmful effects. In this study, we investigated the effect of a novel compound, Melanocin A, which was isolated from Eupenicillium shearii F80695, on UV-induced premature skin aging. First, we studied the effect of Melanocin A on UV-induced matrix metalloproteinase (MMP)-9 expression in an immortalized human keratinocyte cell line, HaCaT, in vitro. Acute UV irradiation induced MMP-9 expression at both the mRNA and protein levels and Melanocin A suppressed this expression in a dose-dependent manner. We then investigated the effect of Melanocin A on UV-induced skin changes in hairless mice in vivo. Chronic exposure of hairless mouse dorsal skin to UV increased skin thickness and induced wrinkle formation and the gelatinase activities of MMP-2 and MMP-9. Moreover, Melanocin A significantly suppressed UV-induced morphologic skin changes and MMP-2 and MMP-9 expression. Taken together, these results show that Melanocin A can prevent the harmful effects of UV that lead to skin aging. Therefore, we suggest that Melanocin A should be viewed as a potential therapeutic agent for preventing and/or treating premature skin aging.     

Super‐Soft and Super‐Elastic DNA Robot with Magnetically Driven Navigational Locomotion for Cell Delivery in Confined Space

Soft organisms such as earthworms can access confined, narrow spaces, inspiring scientists to fabricate soft robots for in vivo manipulation of cells or tissues and minimally invasive surgery. We report a super‐soft and super‐elastic magnetic DNA hydrogel‐based soft robot (DNA robot), which presents a shape‐adaptive property and enables magnetically driven navigational locomotion in confined and unstructured space. The DNA hydrogel is designed with a combinational dynamic and permanent crosslinking network through chain entanglement and DNA hybridization, resulting in shear‐thinning and cyclic strain properties. DNA robot completes a series of complex magnetically driven navigational locomotion such as passing through narrow channels and pipes, entering grooves and itinerating in a maze by adapting and recovering its shape. DNA robot successfully works as a vehicle to deliver cells in confined space by virtue of the 3D porous networked structure and great biocompatibility.     

Super-Soft and Super-Elastic DNA Robot with Magnetically Driven Navigational Locomotion for Cell Delivery in Confined Space

Soft organisms such as earthworms can access confined, narrow spaces, inspiring scientists to fabricate soft robots for in vivo manipulation of cells or tissues and minimally invasive surgery. We report a super-soft and super-elastic magnetic DNA hydrogel-based soft robot (DNA robot), which presents a shape-adaptive property and enables magnetically driven navigational locomotion in confined and unstructured space. The DNA hydrogel is designed with a combinational dynamic and permanent crosslinking network through chain entanglement and DNA hybridization, resulting in shear-thinning and cyclic strain properties. DNA robot completes a series of complex magnetically driven navigational locomotion such as passing through narrow channels and pipes, entering grooves and itinerating in a maze by adapting and recovering its shape. DNA robot successfully works as a vehicle to deliver cells in confined space by virtue of the 3D porous networked structure and great biocompatibility.     

EMP as a similarity measure: a geometric point of view

Soft Coulomb potentials constructed by multiplying the classical potential by a Gaussian function (or a linear combination of them) permit to consider a wide family of distributions which limit with the classical potential when the exponent becomes infinite. Soft Coulomb potentials can be employed as potential operators with first order density functions in order to compute families of soft electrostatic molecular potentials (EMP) for any quantum object. The soft EMP family possesses two interesting computational features: being not only formally equivalent to classical EMP, but finite everywhere, even at the atomic nuclei. The structure of the soft Coulomb operator family yielding soft EMP can be easily related with a quantum similarity integral feature.     

Langmuir-Blodgett assembly of graphite oxide single layers

Single-layer graphite oxide can be viewed as an unconventional type of soft material and has recently been recognized as a promising material for composite and electronics applications. It is of both scientific curiosity and technical importance to know how these atomically thin sheets assemble. There are two fundamental geometries of interacting single layers: edge-to-edge and face-to-face. Such interactions were studied at the air-water interface by Langmuir-Blodgett assembly. Stable monolayers of graphite oxide single layers were obtained without the need for any surfactant or stabilizing agent, due to the strong electrostatic repulsion between the 2D confined layers. Such repulsion also prevented the single layers from overlapping during compression, leading to excellent reversibility of the monolayers. In contrast to molecular and hard colloidal particle monolayers, the single layers tend to fold and wrinkle at edges to resist collapsing into multilayers. The monolayers can be transferred to a substrate, readily creating a large area of flat graphite oxide single layers. The density of such films can be continuously tuned from dilute, close-packed to overpacked monolayers of interlocking single layers. For size-mismatched single layers, face-to-face interaction caused irreversible stacking, leading to double layers. The graphite oxide monolayers can be chemically reduced to graphene for electronic applications such as transparent conducting thin films.     

On the use of electrokinetics for unraveling charging and structure of soft planar polymer films

During the past decade, much attention has been devoted to the use of electrokinetic phenomena for addressing both charging mechanism and structure of multi-responsive soft polymeric layers whose thickness may range from few tens of nanometers to several microns. In particular, major progress was achieved in the quantitative reconstruction of streaming current data collected over a wide range of physico-chemical conditions using recent theories for electrohydrodynamics of soft diffuse planar interphases. In this article, we review the basics of the methodology adopted for deciphering the mechanisms governing the charging of electric double layers at soft planar films in connection with their structure that may vary according to pH, salt concentration or temperature depending on the responsive character of the system. It is demonstrated how the combination of streaming current, surface conductivity and swelling measurements allows for a comprehensive understanding of the interrelated protolytic, hydrodynamic, electrostatic and structural properties of polymer layers. We discuss the benefits and limits of the approach on the basis of studies carried out on uncharged, moderately charged and highly charged soft polymeric films supported by hard charged carriers. In a final part, the basic processes governing the peculiar electrokinetic properties of soft planar polyelectrolyte multilayers under lateral flow conditions are described.     

Spectroscopic linear dichroism FT-IR studies of synthetic spider silk

This work deals with the analysis of the orientation behavior of different segments of synthetic spider silk samples containing hard and soft segments. Two different types of spider silk were examined, one with an aliphatic hard segment (hexamethylene-diisocyanate) and an amorphous soft segment (polytetramethylene oxide) (A40) and the other with an aromatic hard segment (4,4′-methylene bisphenyl diisocyanate) and a semicrystalline soft segment (polyethylene oxide-polypropylene oxide- polyethylene oxide) (A143). In order to observe the orientation behavior of the hard and the soft segments it was necessary to define marker bands. While for both samples the chosen marker bands for the hard segments were the same, the marker bands for the soft segments were different. FT-IR spectra were recorded while strain was applied to the material at the same time. Two parameters, the dichroic ratio R and the order Parameter f were used to evaluate the behavior of these materials under conditions of strain. It was found that sample A143 broke at a strain level of 37,5 %, while sample A40 showed a high dynamic range up to a strain level of 307 %.     

Controlling the Orientation of Nanowrinkles and Nanofolds by Patterning Strain in a Thin Skin Layer on a Polymer Substrate

We describe herein how to control the orientation of polymer nanowrinkles and nanofolds with large amplitudes. Nanowrinkles were created by chemically treating thermoplastic polystyrene sheets to form a thin skin layer and then heating the substrate to relieve strain. By manipulating the strain globally and locally in the skin layer, we could tune whether wrinkles or folds formed, as well as the distances over which these structures could be produced. This unique materials system provided access to high strain regimes, which enabled mechanisms behind the spontaneous formation of complex structures to be explored.     

FRS-XRSA与SAXS研究硬弹性聚丙烯的结晶度、取向与超结构Ⅲ应变与回复

应用全倒易空间Ｘ 射线散射理论分析（ＦＲＳ ＸＲＳＡ）与ＳＡＸＳ研究了ＨＥＰＰ在应变（ε）与回复（Ｒ）过程中结晶、取向与超结构的变化．结果指出，ε可以诱发结晶，但当ε≥３０％后，结晶度（ＸＷＣ）趋于不变：ε可以导致晶粒破碎；ε与Ｒ对取向分布与平均取向基本上无影响，这符合片晶平行分离模型，而非叶簧弯曲模型；发现，在ε≤３０％时，层状片晶的分离为主要过程，而当ε＞３０％后，则分离的片晶会发生断层滑移；ε可以诱发微孔，类似地当ε＞２０％，微孔尺寸亦趋不变．从凝聚态结构阐明了ＨＥＰＰ在ε Ｒ过程中不同阶段的结构变化