Wrinkle Patterns Research Articles

Replication of Leaf Surface Structures on Flat Phosphor-Converted LEDs for Enhanced Angular Color Uniformity.

We explored the use of biomimetic structures, including those that mimic leaf structures, to enhance the angular color uniformity of flat phosphor-converted light-emitting diodes (pcLEDs). The distinct microstructures found on natural leaf surfaces, such as micro-scale bumps, ridges, and hierarchical patterns, have inspired the design of artificial microstructures that can improve light extraction, scattering, and overall optical performance in LED applications. The effects of these leaf surface microstructures on the phosphor layer of flat pcLEDs were evaluated. An imprinting technique was employed to directly replicate the surface morphology structures from fresh plant leaves. The results indicated that this method provided excellent scattering capability and reduced the disparity in light output between blue and yellow light emissions from flat pcLEDs at various angles. Subsequently, uniform correlated color temperature in the flat pcLEDs was achieved, reducing the yellow ring effect. Furthermore, the availability of diverse wrinkle and surface patterns from a wide range of natural prototypes could reduce design costs compared with traditional mold fabrication, making the method suitable for application in mass production.

Stretching and Bending Moduli of Bilayer Films Inferred from Wrinkle Patterns

Stretching and Bending Moduli of Bilayer Films Inferred from Wrinkle Patterns

Exploring the potential of laser-textured metal alloys: Fine-tuning vascular cells responses through in vitro and ex vivo analysis

Medical stents are vital for treating vascular complications and restoring blood flow in millions of patients. Despite its widespread effectiveness, restenosis, driven by the complex interplay of cellular responses, remains a concern. This study investigated the reactions of vascular cells to nano/microscale wrinkle (nano-W and micro-W) patterns created on laser-textured nitinol (NiTi) surfaces by adjusting laser processing parameters, such as spot overlap ratio and line overlap ratio. Evaluation of topographical effects on endothelial and smooth muscle cells (SMCs) revealed diverse morphologies, proliferation rates, and gene expressions. Notably, microscale wrinkle patterns exhibited reduced monocyte adhesion and inflammation-related gene expression, demonstrating their potential applications in mitigating vascular complications after stent insertion. Additionally, an ex vivo metatarsal assay was utilized to bridge the gap between in vitro and in vivo studies, demonstrating enhanced angiogenesis on laser-textured NiTi surfaces. Laser-textured NiTi exhibits a guided formation process, emphasizing their potential to promote swift endothelialization. These findings underscore the efficacy of laser texturing for tailored cellular interactions on metallic surfaces and offer valuable insights into optimizing biocompatibility and controlling cellular responses, which may pave the way for innovative advances in vascular care and contribute to the ongoing improvement of stent insertion.

Simulating the dynamics of a 2D multicomponent vesicle in time-dependent elongation flow

Abstract This paper is concerned with the nonlinear dynamics of multicomponent vesicles in a time-dependent elongational flow. Using a nonstiff, pseudospectral boundary integral method, we investigate the dynamical patterns induced by negative surface tension and inhomogeneous bending for a two phases system. For both quasi-circular and elongated vesicles, high frequency wrinkles can be excited in flow with strong elongational rate after the flow’s direction is reversed. Unevenly distributed phase diagram leads to asymmetric wrinkling pattern, and the characteristic wavelength for each phase is well reserved. In weak flow, bucking behaviours are observed for elongated vesicles and the membrane bends inward at regions with lower bending moduli.

Time‐Dependent Wrinkle Pattern Based on Photo‐Controlled Stress Relaxation for Multi‐Level Information Encryption and Information Camouflage

AbstractStimuli‐responsive surfaces have garnered intensive research attention in addressing the challenges of severe information leakage problems, but they exhibit limitations in terms of intricate preparation and compatibility. Herein, the study reports a time‐dependent wrinkled surface controlled by photo‐induced stress relaxation of azobenzene‐ containing crosslinked polymer network comprised of furan‐containing polymer (PEA‐Fu) and maleimide‐substituted azobenzene (AZO‐2MI) as skin layer. Two kinds of wrinkled surfaces induced by two crosslinked networks (thermal‐ and UV‐induced) can be prepared by Diels‐Alder reaction and UV‐induced radical coupling reaction, exhibiting distinct amplitude decrease rate resulted from different stress relaxation rate induced by photo‐isomerization of azobenzene. By UV preprogramming with photomasks, various time‐dependent wrinkle patterns are obtained and can be identified at specific times under 450 nm irradiation. The time window for information read out can be preset through different UV preprogramming time and boundary conditions to achieve multi‐level information encryption. Furthermore, the written information can be camouflaged as another “false” information by regional‐selective irradiation under 450 nm irradiation, which offers a new method for information protection. Based on distinctive time‐dependent characteristics and excellent stability, this responsive wrinkled surface offers bright prospects in multi‐level information encryption.

Controlled Surface Textures of Elastomeric Polyurethane Janus Particles: A Comprehensive Review.

Colloidal particle research has witnessed significant advancements in the past century, resulting in a plethora of studies, novel applications, and beneficial products. This review article presents a cost-effective and low-tech method for producing Janus elastomeric particles of varied geometries, including planar films, spherical particles, and cylindrical fibers, utilizing a single elastomeric material and easily accessible chemicals. Different surface textures are attained through strain application or solvent-induced swelling, featuring well-defined wavelengths ranging from sub-microns to millimeters and offering easy adjustability. Such versatility renders these particles potentially invaluable for medical applications, especially in bacterial adhesion studies. The coexistence of "young" regions (smooth, with a small surface area) and "old" regions (wrinkled, with a large surface area) within the same material opens up avenues for biomimetic materials endowed with additional functionalities; for example, a Janus micromanipulator where micro- or nano-sized objects are grasped and transported by an array of wrinkled particles, facilitating precise release at designated locations through wrinkle pattern adjustments. This article underscores the versatility and potential applications of Janus elastomeric particles while highlighting the intriguing prospects of biomimetic materials with controlled surface textures.

Nano-achiral complex composites for extreme polarization optics.

Composites from 2D nanomaterials show uniquely high electrical, thermal and mechanical properties1,2. Pairing their robustness with polarization rotation is needed for hyperspectral optics in extreme conditions3,4. However, the rigid nanoplatelets have randomized achiral shapes, which scramble the circular polarization of photons with comparable wavelengths. Here we show that multilayer nanocomposites from 2D nanomaterials with complex textured surfaces strongly and controllably rotate light polarization, despite being nano-achiral and partially disordered. The intense circular dichroism (CD) in nanocomposite films originates from the diagonal patterns of wrinkles, grooves or ridges, leading to an angular offset between axes of linear birefringence (LB) and linear dichroism (LD). Stratification of the layer-by-layer (LBL) assemblednanocomposites affords precise engineering of the polarization-active materials from imprecise nanoplatelets with an optical asymmetry g-factor of 1.0, exceeding those of typical nanomaterials by about 500 times. High thermal resilience of the composite optics enables operating temperature as high as 250 °C and imaging of hot emitters in the near-infrared (NIR) part of the spectrum. Combining LBL engineered nanocomposites with achiral dyes results in anisotropic factors for circularly polarized emission approaching the theoretical limit. The generality of the observed phenomena is demonstrated by nanocomposite polarizers from molybdenum sulfide (MoS2), MXene and graphene oxide (GO) and by two manufacturing methods. A large family of LBL optical nanocomponents can be computationally designed and additively engineered for ruggedized optics.

Prediction of wrinkle patterns in tensioned thin-film structures containing rigid elements

AbstractWith the in-depth study of thin-film structures, nonuniform thin films with rigid elements have been applied in the aerospace and flexible electronics industries. For thin-film structures with rigid elements, there is an interaction force between the rigid element and the thin film; therefore, the wrinkling mode of the thin film changes under the influence of the interaction force. In this study, a wrinkle model was developed to predict the wrinkle morphology of thin-film structures with rigid elements on the diagonal. First, the wrinkle patterns of the rigid elements were observed at different positions using tensile experiments. Then, the relationship between the tilt of the rigid element and the wrinkle wavelength was investigated using a finite-element eigenvalue buckling analysis. Finally, local wrinkling caused by the perturbed stress of the rigid element was introduced, and a wrinkling model of a square thin film with rigid elements on the diagonal under tension was established. The theoretical analysis results were compared with simulation and experimental results, demonstrating that the model can accurately describe the wrinkle patterns of thin-film structures containing rigid elements on the diagonal under tension.

Analysis of Experimental Biaxial Surface Wrinkling Pattern Based on Direct 3D Numerical Simulation.

This paper presents a direct 3D numerical simulation of biaxial surface wrinkling of thin metal film on a compliant substrate. The selected compliant substrate is a commercial Scotch tape on which a gold metal thin film has been transferred by using low adhesion between the thin metal film and polyimide substrate. Compared with the previous fabrication of a cylindrical thin-film wrinkling pattern, an undulated wrinkling pattern has been implemented by increasing the width of the thin metal film in order to create biaxial straining in the thin film. To understand the wrinkling behavior due to biaxial loading, a simple direct numerical simulation based on material imperfections defined in the compliant substrate has been conducted. Through modeling and simulation, it was found that the wrinkling mode is determined by the biaxiality ratio (BR), the ratio between transversal strain and longitudinal strain. Depending on the BR, the wrinkling mode belongs to one of the cylindrical, undulated (or herringbone), checkerboard, or labyrinth modes as a function of applied strain. The cylindrical wrinkling is dominant at the input of BR less than 0.5, while the undulated (or herringbone) ones become dominant just after the onset of the wrinkling pattern at BR greater than 0.9. Through the comparison of the wrinkling patterns between simulation and experiment, the applied BR of the fabricated thin film has been successfully estimated.

One-step rapid formation of wrinkled fractal antibiofouling coatings from environmentally friendly, waste-derived terpenes

Wrinkled coatings are a potential drug-free method for mitigating bacterial attachment and biofilm formation on materials such as medical and food grade steel. However, their fabrication typically requires multiple steps and often the use of a stimulus to induce wrinkle formation. Here, we report a facile plasma-based method for rapid fabrication of thin (<250 nm) polymer coatings from a single environmentally friendly precursor, where wrinkle formation and fractal pattern development are controlled solely by varying the deposition time from 3 s to 60 s. We propose a mechanism behind the observed in situ development of wrinkles in plasma, as well as demonstrate how introducing specific topographical features on the surface of the substrata can result int the formation of even more complex, ordered wrinkle patterns arising from the non-uniformity of plasma when in contact with structured surfaces. Thus-fabricated wrinkled surfaces show good adhesion to substrate and an antifouling activity that is not observed in the equivalent smooth coatings and hence is attributed to the specific pattern of wrinkles.

Photochemical Design for Diverse Controllable Patterns in Self-Wrinkling Films.

Harnessing the spontaneous surface instability of pliable substances to create intricate, well-ordered, and on-demand controlled surface patterns holds great potential for advancing applications in optical, electrical, and biological processes. However, the current limitations stem from challenges in modulating multidirectional stress fields and diverse boundary environments. Herein, this work proposes a universal strategy to achieve arbitrarily controllable wrinkle patterns via the spatiotemporal photochemical boundaries. Utilizing constraints and inductive effects of the photochemical boundaries, the multiple coupling relationship is accomplished among the light fields, stress fields, and morphology of wrinkles in photosensitive polyurethane (PSPU) film. Moreover, employing sequential light-irradiation with photomask enables the attainment of a diverse array of controllable patterns, ranging from highly ordered 2D patterns to periodic or intricate designs. The fundamental mechanics of underlying buckling and the formation of surface features are comprehensively elucidated through theoretical stimulation and finite element analysis. The results reveal the evolution laws of wrinkles under photochemical boundaries and represent a new effective toolkit for fabricating intricate and captivating patterns in single-layer films.

Why do marionette lines appear? Exploring the anatomical perspectives and role of thread-based interventions.

The pathogenesis of marionette lines involves a complex interplay of anatomical, physiological, and age-related factors leading to the development of wrinkles around the oral commissures. This exploration delves into the distinct anatomical predispositions observed among different ethnicities, emphasizing the role of compact modiolus structures and muscle compositions. Notably, individuals of East Asian descent exhibit inherent facial structures that predispose them to pronounced sagging around the oral commissures during aging. The emergence of distinct facial lines, such as the commissural line and the melolabial fold, contributes to the formation of marionette lines. This specific wrinkle pattern, resembling a marionette puppet's mouth contours, is influenced by various factors like bone resorption, gravitational forces, fat compartment variations, muscle compression, ligament tethering, and skin aging. Treatment strategies for marionette lines encompass diverse interventions, including filler injections, botulinum neurotoxin, surgeries targeting fat reduction, thread lifting, and volumizing fillers. These approaches aim to address the underlying causes and mitigate the appearance of marionette lines. Botulinum neurotoxin injections, for instance, weaken specific facial muscles, reducing downward strain and aiding in tissue retraction. Anatomical considerations during procedures are crucial to avoid nerve or vascular damage. Delicate manipulation and precise entry points are essential to prevent inadvertent injuries, particularly concerning blood vessels like the facial artery and nerves like the mental nerve. Technical guidelines for procedures targeting marionette lines involve specific techniques like cogged thread reverse methods and volumizing thread placements. Attention to entry points, tissue engagement, and the direction of threads is crucial for effective treatment outcomes, minimizing complications, and ensuring patient safety.

Comparison of Wrinkle Patterns Generated by Intradermal and Intramuscular Botulinum Toxin Injections by Clinical Evaluation.

Botulinum toxin has played a remarkable role in management of forehead wrinkles. Most used is intramuscular technique due to its deposition into the muscles, however, with adverse effects like brow ptosis. This study has been designed for the evaluation of efficacy for intradermal v/s intramuscular route of botulinum toxin injections for forehead wrinkles using clinical correlation. This study included a clinical trial of 32 facial halves divided equally into intradermal and intramuscular injection technique groups, receiving total dose of 8 U. Results were assessed by clinical examination upto 2weeks and 4weeks with parameters; objective wrinkle rate, eyebrow height, eyebrow movement, pain, and satisfaction after treatment. Results showed least mean for objective wrinkle rate in intramuscular group, showing statistically significant improvement. Overall improvement in eyebrow height and eyebrow movement were slightly more for intramuscular group. Pain was lesser for intradermal group, whereas satisfaction of patient of patient post treatment is similar for both the groups. Among intradermal and intramuscular botulinum toxin injection technique, the effect and potency were better for intramuscular technique, whereas the patient comfort and compliance were better for intradermal technique.

Theoretical analysis of inflated tube wrinkling behavior under pure bending

Inflatable tubes, owing to their lightweight and foldable characteristics, have important applications in soft robots and space expandable structures. The application of a bending load to the inflated tube might induce local instability on its compressed side, leading to the formation of wrinkles that could potentially compromise the structural strength. Therefore, it is necessary to have a comprehensive understanding of the wrinkling behavior exhibited by inflated tubes under bending load. Initially, a theoretical solution is developed for the critical wrinkling behavior of inflated tubes under pure bending, drawing upon the principle of minimum potential energy. According to the energy expression of the system, the critical wrinkling behavior of inflated tubes depends on dimensionless geometrical and internal pressure parameters. The critical wrinkling load and wrinkle pattern of the system are influenced by the thickness-radius ratio and the ratio of internal air pressure to Young's modulus. Subsequently, the theoretical solutions are validated through several finite element analysis examples and a systematic investigation is conducted into the influence of dimensionless geometrical and internal pressure parameters. Finally, the evolution of morphology in post-buckling is investigated through numerical results. The findings suggest that during post-buckling, the wrinkles may undergo a secondary bifurcation and evolve into a non-axisymmetric diamond-like pattern. These results hold significant implications for understanding the bending instability and failure mechanisms of inflated tubes.

Transient Interfacial Pattern Formation in Block Copolymer Thin Films via Sequential Thermal and Solvent Immersion Annealing.

A variety of structures encountered in nature only arise in materials under highly nonequilibrium conditions, suggesting to us that the scope for creating new functional block copolymer (BCP) structures might be significantly enlarged by embracing complex processing histories that allow for the fabrication of structures quite unlike those created under "near-equilibrium" conditions. The present work examines the creation of polymer film structures in which highly nonequilibrium processing conditions allow for the creation of entirely new types of transient BCP morphologies achieved by transitioning between different ordered states. Most previous studies of BCP materials have emphasized ordering them from their disordered state obtained from a solution film casting process, followed by a slow thermal annealing (TA) process at elevated temperatures normally well above room temperature. We have previously shown that achieving the equilibrium TA state can be accelerated by a direct solvent immersion annealing (DIA) preordering step that creates nascent ordered microstructures, followed by TA. In the present work, we examine the reverse nonequilibrium sequential processing in which we first thermally anneal the BCP film to different levels of partial (lamellar) order and then subject it to DIA to swell the lamellae. This sequential processing rapidly leads to a swelling-induced wrinkle pattern that initially grows with immersion time and can be quenched by solvent evaporation into its corresponding glassy state morphology. The article demonstrates the formation of wrinkling "defect" patterns in entangled BCP films by this sequential annealing that does not form under ordinary TA conditions. At long DIA times, these highly "defective" film structures evolve in favor of the equilibrium morphology of parallel lamellae observed with DIA alone. In conjunction with our previous study of sequential DIA + TA, the present TA + DIA study demonstrates that switching the order of these processing methods for block copolymer films gives the same final state morphology in the limit of long time as any one method alone, but with drastically different intermediate transient state morphologies. These transient morphologies could have many applications.

Wrinkling–dewrinkling transitions in stretched soft spherical shells

Soft shells undergoing intricate buckling and morphological evolutions can serve as a model system for understanding the morphogenesis of organs, tissues, cells, and nuclei. In this paper, we combine experiments, simulations, and theoretical analysis to investigate the wrinkling and subsequent morphological transitions in a soft spherical shell subjected to an outward concentrated force. During loading, the spherical shell first buckles into many shallow radial wrinkles, which soon merge into a single crater-like deep wrinkle, and then the number of wrinkles increases with loading. Surprisingly, after a critical point, all wrinkles disappear and the shell regains an axisymmetric, smooth shape, referred to as dewrinkling. We show how this anomalous wrinkling–dewrinkling transition stems from the interplay between surface curvature and large deformations. Material-independent scaling laws are established from an energy analysis to predict the surface wrinkling pattern, which depends on the loading force. This work provides physical insights into how local forces can regulate the shape evolutions of soft shells, which can take place in, for example, the morphogenesis of developing organisms.

Harnessing multimodal wrinkle patterns in flexible films by three-axial mechanical loading

Controllable wrinkle structures have great application prospects in the fields of flexible electronics, smart sensing, elastic optics, surface wetting, and bio-interfaces. In flexible film-substrate systems, strain actuation is capable of obtaining various wrinkle patterns with single morphological features including labyrinths, herringbones, stripes, hierarchies and ordered arrays. However, it is still a big challenge to obtain multiple wrinkle patterns on a surface of film simultaneously. Here, we propose a facile method for preparing controllable multimode wrinkles by exerting three-axial compression. The morphological features of the wrinkles show a universal position-dependent behavior for different flexible film systems. From a corner of the triangular film sample to the opposite edge, the wrinkles evolve from striped structure to labyrinth-like structure and finally to rippled structure gradually. The finite element simulation and stress theory well explain the formation mechanism and evolution behavior of the multimode wrinkles observed in experiments. The surface friction and light diffraction are strongly dependent on the wrinkle features and show excellent reversibility and stability by cyclic mechanical loading. This work can promote better understanding of stress distribution and wrinkling mechanism under three-axial mechanical loading, and can develop a novel technique for preparing controllable multiple, position-dependent wrinkle patterns.

Tunable wrinkle patterns in Moiré pattern of interlayer-bonding strained bilayer graphene

Moiré patterns are important structures in two-dimensional (2D) materials, showcasing unique electronic correlated states, which have garnered considerable research interests in recent years. However, current researches on moiré patterns primarily focus on honeycomb patterns induced by lattice mismatches at 2D material hetero-interfaces. In this work, we have demonstrated the ability to generate diverse and tunable wrinkle patterns in interlayer bonding strained bilayer graphene (IB-SBG) through a “stretch-crosslink-release” strategy, facilitated by the interlayer bonding that provides effective in-plane load transfer and interlayer constraint. Three energetically favorable wrinkle patterns are identified, including herringbone, irregular hexagon and honeycomb patterns. In general, wrinkle patterns are determined by two parameters, i.e., pre-strain and the portion of interface with interlayer bonding, and the phase diagram of wrinkle patterns corresponding to the two parameters is provided. Furthermore, strain engineering can be employed in IB-SBG to generate a series of new patterns by precisely adjusting the biaxial strain applied to IB-SBG. The present strategy to achieve tunable wrinkle patterns holds the potential to open new avenues for novel electronic applications based on bilayer graphene systems.

Distribution and Uniqueness in the Pattern of Lip Prints.

Introduction Lip prints are the characteristic pattern of wrinkles and grooves on the labial mucosa. Lip prints can be classified into various patterns and can be used for personal identification as they are unique and do not change during the life of a person. Cheiloscopy is a forensic investigation technique that deals with the identification of humans based on lip traces. Objectives This study aimed to investigate the distribution of lip print patterns, to assess gender differences, and to calculate the lip score using a weighted value scoring system. Material and methods A cross-sectional study was carried out in the Department of Anatomy, All India Institute of Medical Sciences (AIIMS), Guwahati, India, from May to October 2023, after getting approval from the Institutional Ethics Committee (IEC). A total of 200 individuals (100 males and 100 females) were included in the study. Each lip print was divided into four quadrants. In each quadrant, up to 14 grooves were marked from the midline, and the pattern of each groove was observed. Each pattern was given an Arabic numeral score. Weighted values were given for the grooves in descending order from 15 to 1 with reference to their position from the midline of the lip print.The product of the Arabic numeral score of the groove and the weighted value of the groove is the lip line score. The sum of the lip line scores was calculated. Results The most common pattern observed in the present study is type II, with 3,816/12,000 (31.8%), followed by type I'with 3,146/12,000 (26.21%), type I with 1,865/12000 (15.54%), type III with 1,491/12,000 (12.42%), type IV with 1,133/12,000 (9.44%), and type V with 549/12,000 (4.5%). The mean total lip score is 1,467.68 (1,486.41 in males and 1448.96 in females). Conclusion Lip prints are unique and useful for personal identification, as the lip score in various quadrants and the total lip score are different for different individuals.

Wrinkle, fold, and ridge patterns of thin films attached to a compliant substrate: Direct numerical simulations involving plastic yielding

Surface wrinkling is a frequently observed form of deformation instability when a thin film bonded to a compliant substrate is under in-plane compression. In this study, a recently developed computational approach is applied to study the formation and transformation of wrinkles involving plastic yielding of the thin film. The two-dimensional (2D) finite element models contain an embedded imperfection with perturbed material properties at the film-substrate interface, which serves to activate the bifurcation modes. The extension of this technique to allow for film plasticity is demonstrated, including the evolution of surface patterns and its correlation with the overall load-displacement and amplitude responses. More localized forms of wrinkles are revealed by the simulations, including the transition of periodic wrinkles to more isolated folds and how it can be influenced by the elastoplastic properties of the film material. A through-thickness variation of material properties is shown to significantly alter the wrinkle morphology. Plastic folding can be suppressed by only a very thin elastic sub-layer, and the waveform can become ridge-like. We also present a preliminary analysis by applying the same numerical methodology to three-dimensional (3D) models, which generates consistent results compared to the 2D counterpart.