Wrinkle Patterns Research Articles

The formation mechanism of Bacillus subtilis biofilm surface morphology under competitive environment.

Material properties and growth environments affect the surface morphology of biofilms. Taken the biofilm growing in competitive environments as the object, which is compared with the single biofilm, we find that the competitive environment has an impact on the biofilm thickness and wrinkle patterns. Through diffusion-limited growth theoretical model analysis, it shows that the competitive environment is caused by cells competing for nutrition, and the competitive environment reacts on biofilms, which affect the phenotypic differentiation, causing changes in the stiffness of the biofilm. Using the theoretical and finite element simulation, we compare these results of bi-layer and tri-layer film-substrate models with experimental observations, and find that tri-layer film-substrate model is in line with the reality, which means that the layer between the biofilm and substrate plays an import role for wrinkle formation. Based on the above analysis, we further study effects of biofilm stiffness and interlayer thickness on wrinkles under competitive environment.

Three-dimensional numerical study on wrinkling of vesicles in elongation flow based on the immersed boundary method.

We study the wrinkling dynamics of three-dimensional vesicles in a time-dependent elongation flow by utilizing an immersed boundary method. For a quasispherical vesicle, our numerical results well match the predictions of perturbation analysis, where similar exponential relationships between wrinkles' characteristic wavelength and the flow strength are observed. Using the same parameters as in the experiments by Kantsler etal. [V. Kantsler etal., Phys. Rev. Lett. 99, 178102 (2007)0031-900710.1103/PhysRevLett.99.178102], our simulations of an elongated vesicle are in good agreement with their results. In addition, we get rich three-dimensional morphological details, which are favorable to comprehend the two-dimensional snapshots. This morphological information helps identify wrinkle patterns. We analyze the morphological evolution of wrinkles using spherical harmonics. We find discrepancies in elongated vesicle dynamics between simulations and perturbation analysis, highlighting the importance of the nonlinear effects. Finally, we investigate the unevenly distributed local surface tension, which largely determines the position of wrinkles excited on the vesicle membrane.

Unparallel improvement patterns of dynamic wrinkles and skin quality after botulinum toxin type A treatment on the upper face.

Botulinum toxin type A (BoNT-A) can not only reduce the dynamic wrinkles but also improve the skin quality. This study aims to quantitaively and comprehensively assess the improvement of dynamic wrinkles and skin quality following BoNT-A treatment on the upper face. Patients were recruited to receive BoNT-A treatment of the glabellar, frontal, and lateral periorbital wrinkles. Antera 3D camera was used to evaluate the skin quality and dynamic wrinkle severity. Follow-up visits were at 1week, 1 month, 3 months, and 6 months after treatment. Different filters were utilized to quantitatively detect the severity of fine wrinkles (FWS), the volume of pores (PV), the roughness of skin texture (STR), and the severity of dynamic wrinkles (DWS). Twenty-four participants (average 30.5±7.2 years) were recruited. The significant improvement of PV, FWS, and STR in different areas usually maintained from 1 to 6 months after injections but of DWS only existed within 3 months. For each area, the improvement rates of FWS, PV, and STR peaked at 3 months or 6 months after treatment while the maximal improvement of DWS was observed at 1 month posttreatment. After BoNT-A treatment for dynamic wrinkles on the upper face, the skin quality of target regions can also be ameliorated. The improvement of skin quality and dynamic wrinkles presented unparallel patterns. The former is with a slower onset but longer duration while the latter exhibits a more rapid onset but shorter duration.

Influence of NCF architecture on the morphology of forming induced wrinkling

Biaxial Non-Crimp Fabrics (NCFs) offer the high deposition rates needed to meet the increased production rate targets of the aerospace industry, but formability remains an issue for complex parts. In this study a large scale, complex geometry with a span of 2 m is used to study wrinkle patterns in NCF preforms and how they are influenced by several key NCF parameters. Wrinkle dimensions are captured in 3D scans and used as a proxy metric for “formability”. Results show that whereas location and shape of the wrinkling are driven by geometry, wrinkle size and its metrics (amplitude, wavelength, aspect ratio) are driven by the NCF architecture. In addition, conflicting trends on wrinkle size observed show the complexity of forming as a process. The results presented show the importance of using several characterisation methods and not reducing wrinkling characterisation to a single data point or set.

Elastomeric platform with surface wrinkling patterns to control cardiac cell alignment.

There is a growing interest in creating 2D cardiac tissue models that display native extracellular matrix (ECM) cues of the heart tissue. Cellular alignment alone is known to be a crucial cue for cardiac tissue development by regulating cell-cell and cell-ECM interactions. In this study, we report a simple and robust approach to create lamellar surface wrinkling patterns enabling spatial control of pattern dimensions with a wide range of pattern amplitude (A ≈ 2-55 μm) and wavelength (λ ≈ 35-100 μm). For human cardiomyocytes (hCMs) and human cardiac fibroblasts (hCFs), our results indicate that the degree of cellular alignment and pattern recognition are correlated with pattern A and λ. We also demonstrate fabrication of devices composed of micro-well arrays with user-defined lamellar patterns on the bottom surface of each well for high-throughput screening studies. Results from a screening study indicate that cellular alignment is strongly diminished with increasing seeding density. In another study, we show our ability to vary hCM/hCF seeding ratio for each well to create co-culture systems where seeding ratio is independent of cellular alignment.

Alignment‐inducement property of physicochemically reconstructed EVA layer via plasma ion‐beam treatment for liquid crystal system

Uniform and homogeneous liquid crystal (LC) alignment on a poly(ethylene‐co‐vinyl acetate) (EVA) layer subject to plasma ion‐beam (IB) treatment is confirmed. The layer molecular concentrations are controlled to 2, 4, and 6 wt%. Scanning electron microscopy exhibits a wrinkle pattern on the EVA surface that hinders LC alignment after IB treatment. However, X‐ray photoelectron spectroscopy shows chemical reconstruction on the surface; this induces strong van der Waals interactions with the LCs, which contribute to uniform LC alignment. The layer with higher molecular concentration is more heavily modified by IB treatment than that with low concentration, thereby achieving uniform LC alignment and overcoming topological disturbance. Contact angle analysis is used to verify that the surface energy increases via IB treatment; the uniform and homogeneous LC alignment is also confirmed by polarized optical microscopy and pretilt angle analysis. The EVA layer shows good optical transmittance and fine electro‐optical performances in terms of the switching and operating properties. Therefore, the plasma IB treatment is an effective method of deriving the surface characteristics of various polymeric materials for LC alignment, and the IB‐treated EVA layer has potential for application to LC systems.

Photo-induced stress relaxation in reconfigurable disulfide-crosslinked supramolecular films visualized by dynamic wrinkling

Stress relaxation in reconfigurable supramolecular polymer networks is strongly related to intermolecular behavior. However, the relationship between molecular motion and macroscopic mechanics is usually vague, and the visualization of internal stress reflecting precise regulation of molecules remains challenging. Here, we present a strategy for visualizing photo-driven stress relaxation induced by infinitesimal perturbations in the intermolecular exchange reaction via reprogrammable wrinkle patterns. The supramolecular films exhibit visible changes in microscopic wrinkle topography through ultraviolet (UV)-induced dynamic disulfide exchange reaction. In accordance with the trans-scale theoretical models, which quantitatively evaluate the chemical-dependent mechanical stresses in the supramolecular network, the unexposed disordered wrinkles evolved into highly oriented patterns and underwent subsequent mutations after thermal treatment. The stress-sensitive wrinkle macro-patterns can be repetitively written/erased through network topology rearrangement using different stimuli. This strategy provides an approach for visualizing and understanding the molecular behavior from dynamic chemistry to mechanical changes, and directly programming wrinkle patterns with regulated structures.

Fabrication of ultraviolet/thermal-sensitive PMMA/PDMS wrinkle structures and the demonstration as smart optical diffusers

Although smart optical diffusers have received increasing attention for the next generation of flexible optoelectronics, the exploration and fabrication of low-cost ultraviolet/thermal-sensitive optical diffusers are still challenging. In this study, we used a cost-effective method to fabricate flexible PMMA/PDMS wrinkle structures, demonstrating their applicability as tunable ultraviolet/thermal-sensitive optical diffusers. As the temperature gradually increased, the wrinkle wavelength changed slightly while the amplitude decreased. The wrinkle wavelength remained unchanged after UV light exposure, while the wrinkle amplitude decreased with the illumination time. When the fabricated structures were used as optical diffusers, the number of light diffraction pattern rings decreased with the wavelength of the wrinkle structures. Optical diffusers with different wrinkle patterns and the same aspect ratio exhibited different diffusing properties. The number of apertures and the coverage area of the diffused spot gradually decreased when the optical diffuser structure was exposed to heating. Remarkably, the optical diffusers could recover to their original state quickly after cooling. The number of apertures and the coverage area of the diffused spot gradually decreased with UV irradiation time. The prepared PMMA/PDMS wrinkle structures exhibit great potential for intelligent displays, wise medical systems, and other smart devices.

The behavior of thin curved sheets is ironed out

Two simple geometric rules predict the wrinkle patterns of curved surfaces that are flattened.

Dynamic metal patterns of wrinkles based on photosensitive layers

Regulating metal surfaces with micro-/nanoscale structures is of great significance for both material science and potential applications. However, the intrinsic properties of metals, such as fixed isotropic moduli and inflexible structures, in a sense present major limitations in developing next-generation smart patterned surfaces. In this work, a facile and general patterning strategy is proposed to endow insensitive metal surfaces with controllable spontaneous topologies and dynamic performance by exquisitely introducing an essential photosensitive interlayer. The arresting anthracene-containing photocrosslinking interlayer can selectively predetermine the anisotropic property of compliant bilayers without damaging metals’ homogeneous properties, and realize a changeable stiff/soft layer. Furthermore, the mechanical transition mechanism of the self-adaptive wrinkling modes in metal-based trilayer systems is revealed to pave the pathway for regulating functional wrinkled metal surfaces. This photodriven metal patterning strategy can promote the development of brand-new methods for tuning the instability of multilayered materials, and be potentially applied in smart optical devices with dynamic reflectance, including light gratings and “magic” mirrors.

Composites hydrogels with enhanced solid foam formation

It is discovered that sustainable polymers including gelatin and soy protein polymer assist the transformation of poly (vinyl alcohol) (PVOH) hydrogel into solid foams via freeze-drying process; while freeze-dry neat PVOH hydrogels give rise to solid foams with wrinkle patterns and shrinkage. Simultaneous improvement in the thermal stability was also achieved. The mechanisms for the improved performance were also preliminarily proposed.

Exact solutions for the wrinkle patterns of confined elastic shells

Complex textured surfaces occur in nature and industry, from fingerprints to lithography-based micropatterns. Wrinkling by confinement to an incompatible substrate is an attractive way of generating reconfigurable patterned topographies, but controlling the often asymmetric and apparently stochastic wrinkles that result remains an elusive goal. Here, we describe a new approach to understanding the wrinkles of confined elastic shells, using a Lagrange multiplier in place of stress. Our theory reveals a simple set of geometric rules predicting the emergence and layout of orderly wrinkles, and explaining a surprisingly generic co-existence of ordered and disordered wrinkle domains. The results agree with numerous test cases across simulation and experiment and represent an elementary geometric toolkit for designing complex wrinkle patterns.

Self‐Wrinkling Vapor‐Deposited Polymer Films with Tunable Patterns

AbstractMaterials with complex curvature and micro‐structured surface topography allow scientists to replicate surfaces observed in nature. Initiated chemical vapor deposition is used to grow polymer films on substrates of various 3D shapes which exhibit wrinkling during film growth, termed self‐wrinkling. Self‐wrinkling avoids separate film growth and compression steps and more‐closely mimics processes observed in nature. The self‐wrinkling process is elucidated on flat elastic substrates, revealing control over the amount of compressive stress by changing deposition conditions. Next, a study of films grown on liquid substrates with interface profiles that either resemble cylinders or contain repeating concave cones, saddles, and bowls affirms the principle that the wrinkle roundness increases with interface curvature. The selection of high versus low stress generating conditions allows for the choice of the wrinkle pattern to be directed by either the stress concentration at boundaries or the substrate curvature. Experiments confirm the observation from simulations by other authors that on the inside of a torus, the lowest energy ridge wrinkle state is oriented around the major axis. The ability to control the character of wrinkle patterns via changes to the local and global substrate shape provides a route to generate materials with contrived surface topography.

Ultrasonic-Assisted Deposition Method for Creating Conductive Wrinkles on PDMS Surfaces

Harnessing surface wrinkle surfaces in various functional devices has been a hot topic. However, rapidly creating wrinkled surfaces on elastomers of arbitrary shape (especially curved surfaces) is still a great challenge. In this work, an ultrasonic-assisted deposition method has been proposed to achieve nanomodification of the robust layer (e.g., carbon nanotubes (CNTs)) with a labyrinth wrinkle pattern on polydimethylsiloxane (PDMS) fiber, sheet, and porous sponge. It is found that the swelling effect of the dispersion and the ultrasonic treatment play vital roles in the surface wrinkling. As a demonstration, the conductive wrinkled CNTs@PDMS fibers were assembled as stretchable strain sensors. The initial conductivity and the strain-sensing performances could be well tuned by simply adjusting the ultrasonic treatment time. The wrinkled CNTs@PDMS fiber strain sensor exhibited remarkable stretchability (ca. 300%) and good sensitivity, which can be applied in various human motion detection, voice recognition, and air-flow monitoring. It is also expected that the facile ultrasonic-assisted deposition method for surface wrinkling can be extended to fabricate various smart devices with promoted performances.

Wrinkling Patterns and Stress Analysis of Tensile Membrane with Rigid Elements

Heterogeneous membrane structures with rigid elements are often used in flexible electronic and aerospace structures. In heterogeneous membrane structures under tension, the disturbance stress caused by the rigid element changes the stress distribution of the membrane, and it is difficult to calculate the stress distribution of the heterogeneous membrane structure using the traditional stress functions method. In this article, we propose a method for calculating the non-uniform stress field based on the Eshelby elastic inclusion theory, which states that tension membrane structures contain square rigid elements. The wrinkle distribution of the rigid element at different positions is predicted by a stress analysis, and the influence of the position and size of the rigid element on the wrinkle distribution of the membrane is studied by a finite-element simulation. The research results show that the wrinkle pattern of the stretched membrane can be controlled by changing the position of the rigid element to meet some special needs.

Inheritance of The Lip Print Pattern as A Means of Identification in The Case of Cleft Lip and Palate

Lip prints are wrinkle patterns and grooves on the mucosal surface of the lips. Just like fingerprints, every individual in this world has their own unique lip prints patterns. According to the previous studies, the parents of cleft lip and palate (CL/CP) patients have certain lip print patterns. As a result, the lip print pattern can provide information on the inheritance of CL/CP. This review aims to explore the potential of lip print patterns as a means of identification in the inheritance of cleft lip and palate. The online literature search in the PubMed database, Science Direct, and Google Scholar was conducted with a combination of the following keywords: “lip prints”, “cleft lip/palate suffer”, “lip print classification”, and “cleft lip/palate prints”. In addition to online literature searches, reference lists from all the included articles were manually examined for further full-text studies. This review included research and review articles published during the last 10 years period (2012-2022). The result showed that there were 7 articles that met the inclusion criteria. In conclusion, various studies explained that the lip prints pattern type II and whorl/O are the most observed in the inheritance of CL/CP.

Surface Wrinkling versus Global Buckling Instabilities in Thin Film‐Substrate Systems under Biaxial Loading: Direct 3D Numerical Simulations

AbstractWhen a thin film bonded to a compliant substrate is subject to in‐plane compressive loading, wrinkles on the thin film may form as a consequence of deformation instability. The specimen geometry may also favor global buckling. In this study, a recently developed computational approach is employed to directly simulate 3D wrinkling and buckling from pre‐instability to post‐instability in a straightforward manner, covering a wide biaxial loading spectrum. The finite element models contain an embedded imperfection with perturbed material properties at the film‐substrate interface. This approach is capable of activating the first and subsequent bifurcation modes, along with the deformation patterns in between. It is demonstrated that, in addition to the temporal evolution of wrinkle patterns, surface wrinkling and global buckling can form simultaneously as the substrate becomes thinner. Wrinkles and buckle can either co‐develop, or the buckling‐induced curvature may help facilitate wrinkle formation depending on the specimen thickness and loading biaxiality. Different wrinkle patterns, such as parallel waveform and checkerboard, can even coexist on the same buckled structure. The state of biaxiality can influence the deformation instability significantly, and each bifurcation point can be traced back to certain abrupt changes in the overall load–displacement response.

Spontaneous Formation of Oriented Lateral Wrinkles Assisted by Shrinkage Controlled Cracking

AbstractOriented wrinkled surfaces play a vital role in the preparation of functional components. However, existing methods for the fabrication of oriented wrinkle patterns are often limited by specific equipment (e.g., high vacuum systems) and cumbersome processes. In this study, an approach utilizing shrinkage controlled cracking method is proposed to introduce prefabricated topographic patterns on flat semi‐crosslinked polydimethylsiloxane (Semi‐PDMS) substrate for modulating anisotropic release of the interlaminar lateral stresses, where the crosslinking‐induced volumetric shrinkage from the Semi‐PDMS substrate provides the driving force for developing and stabilizing oriented surface wrinkle formation; followed by thickening polydopamine (PDA) capping layer to increase the orientation degree of wrinkles. Moreover, the evolutionary mechanism of oriented wrinkles on the PDA/Semi‐PDMS composite surface are demonstrated. The materials used in the reported method are low cost and environmentally friendly, and the preparation process is simple and green without the need for extreme conditions or strong solvents, which can be scaled up to large‐scale fabrication. According to the biocompatibility, high stability, and reactivity of polydopamine, the prepared oriented wrinkles may find potential applications in electronic skin, enhancement of cell alignment, flexible and stretchable electronics, and as structured templates for surface arrays.

4D Printing of Surface Morphing Hydrogels (Adv. Mater. Technol. 6/2022)

Surface Wrinkling Patterns Murat Guvendiren and colleagues develop smart inks for direct ink writing printing that display preprogrammed surface wrinkling patterns on 2D and 3D surfaces post-printing that appear only when exposed to a solvent in article number 2101118. They demonstrate fabrication of optical devices, solvent sensors, anti-counterfeit devices and high throughput cell culture platforms.

Controlled Wrinkling Analysis of Buckled Thin Films on Gradient Elastic Substrate System: A Numerical Study

Continuous change in wrinkle patterns process of thin films to a gradient substrate is the most challenging problem regarding applying reliable and robust numerical methods for postbuckling analysis of the film/substrate system. For example, in the finite element method, the postbuckling simulation suffers from the convergence issue, while, in spectral methods, it is very difficult to capture the localized behavior in soft matters when the boundary conditions are complex. When a thin film is compressed, it can form a wrinkle of a certain amount of wavelength when the compression exceeds a critical value. The compressed compliant substrate system translates to sinusoidal wrinkles and then to period-doubling wrinkling after further compression. In this work, we investigate the mathematical model arising from the changing nature of wrinkle patterns of postbuckled thin films using a robust and efficient numerical algorithm based on the spectral method to evolve the wrinkle patterns. We consider the gradient substrates of three typical variations in the modulus, namely, the symmetry, exponential, and power-law model. It has been observed that the stable equilibrium path has two bifurcation points. At the first bifurcation point, the buckling instability of wrinkling occurs, while the period-doubling buckling instability occurs at the second bifurcation point. For the substrates of material gradients of various types, the amplitude and wavelength are obtained. This study may help in better understanding of wrinkle patterns formation which could be very useful for the designing of stretchable and flexible electronic devices of most substrate systems and to avoid resonance in the noise environment.