Evolution Of Wrinkles Research Articles

SCAWA scales: A new digital tool for wrinkles clinical grading based on AI.

Clinical assessment of wrinkle depth is essential for efficacy evaluations of anti-ageing products. Standardized photographic scales, representative of different wrinkle depths are often used by experts to assign subjects reliable grades. These tools, based on real pictures, usually exist as hard copies (printed books or sheets) for invivo gradings. Our project aims at developing a methodology to create digital standardized computer-generated scales, allowing photograph and real-life gradings, and providing raters with greater comfort, accessibility, and flexibility in their construction, thanks to the artificial intelligence significative contribution. A completely new approach, based on machine learning, allows the creation of Standardized ColorFace® AI-based Wrinkle Assessment (SCAWA) scales. Instead of using real photographs, the scale images are computer-generated. A generative adversarial network (GAN) is trained to create realistic wrinkle samples that are finely controllable by exploring the GAN latent space. Finally, the scale images are selected among hundreds of artificial images depicting natural wrinkle appearances, such as the illustrated wrinkle evolution is well-detailed (small gaps between grades), morphologically stable, and mathematically linear according to a criterion of wrinkle conspicuous depth. The created 12-point scale for crow's feet wrinkle evaluation on ColorFace® pictures is proven to be realistic, linear, and robustly and accurately usable for photograph assessments. The scale coherence in terms of image ranking has been validated, as well as its reliability and acceptability in real conditions of use. Additionally, the wrinkle grades obtained by the SCAWA scale are well correlated (R = 0.94) with the ones obtained by the Skin Aging Atlas on the same pictures. The AI methodology and digital format brought also interesting side results, such as an enhanced harmonization between experts and a higher representativeness, that is, a decrease of out-of-range pictures. SCAWA scale makes the most of machine learning to provide an innovative digital tool to ease wrinkles in visual assessment of pictures, while optimizing linearity, homogeneity, and accuracy aspects. The experts' enthusiastic feedback about the scale format and quality is promising regarding the adaptation of the methodology to other signs and a larger distribution of this tool in the market of cosmetic product efficacy assessment.

Predicting the evolution of clinical skin aging in a multi-ethnic population: Developing causal Bayesian networks using dermatological expertise.

Software to predict the impact of aging on physical appearance is increasingly popular. But it does not consider the complex interplay of factors that contribute to skin aging. To predict the +15-year progression of clinical signs of skin aging by developing Causal Bayesian Belief Networks (CBBNs) using expert knowledge from dermatologists. Structures and conditional probability distributions were elicited worldwide from dermatologists with experience of at least 15 years in aesthetics. CBBN models were built for all phototypes and for ages ranging from 18 to 65 years, focusing on wrinkles, pigmentary heterogeneity and facial ptosis. Models were also evaluated by a group of independent dermatologists ensuring the quality of prediction of the cumulative effects of extrinsic and intrinsic skin aging factors, especially the distribution of scores for clinical signs 15 years after the initial assessment. For easiness, only models on African skins are presented in this paper. The forehead wrinkle evolution model has been detailed. Specific atlas and extrinsic factors of facial aging were used for this skin type. But the prediction method has been validated for all phototypes, and for all clinical signs of facial aging. This method proposes a skin aging model that predicts the aging process for each clinical sign, considering endogenous and exogenous factors. It simulates aging curves according to lifestyle. It can be used as a preventive tool and could be coupled with a generative AI algorithm to visualize aging and, potentially, other skin conditions, using appropriate images.

Observations of wrinkling in Non-Crimp Fabrics during multi-ply stack forming using in situ XCT scanning

This paper shows the internal evolution of wrinkles occurring in a single diaphragm forming process using time-resolved in situ XCT scanning. Forming trials were carried out over a curved C-spar geometry using Non-Crimp Fabric (NCF) plies of 45°/135°, 0°/90° and 0°/45° orientations arranged in single-orientation and mixed-orientation stacks. Results show most of the diaphragm movement and change in wrinkle size, shape, and location occurs in the early application (<0.1 bar) of vacuum. The further application of vacuum shows consolidation, with wrinkle size decreasing but shape and location remaining largely unchanged. Single-orientation stacks of 45°/135° plies showed the closest resemblance between initial and final wrinkling, while mixed-orientation stacks showed complex wrinkling due to the 0° plies creating internal ply separation due to excess length. Overall, the study shines a light on the internal interaction between layers that occurs during wrinkling, showing mechanisms only observable with XCT.

Experimental testing method to characterise the drapability of UD non-crimp fabrics used in wind turbine blades

This scientific article presents a novel approach for characterising the drapability of fabrics used in wind turbine blade production. This study defines drapability as an intrinsic property of fabric to shear. Specifically, it refers to the potential of the rovings to slide with respect to each other. The evolution of wrinkles has been quantified by the ratio of height-to-width corresponding to a shear angle. The growing industrial interest in binder fabrics, for their preforming ability and improved handling leading to faster blade production, has motivated this study. In this research, two types of non-crimp fabrics, with and without binder, were analysed to study the evolution of wrinkles concerning applied shear angles. A state-of-the-art 3D blue light scanning technique is employed to accurately measure the aspect ratio (height/width) of wrinkles at various shear angles, including 0°, 4°, 6°, 8°, 12°, and 16°. A wrinkle having an aspect ratio of 1/10 was determined to correlate with an applied shear angle of 9° for non-binder fabrics, and 3° for binder-based fabrics. The findings clearly demonstrate the influence of binders on fabric drapability, reducing it by a factor of three. These results provide valuable insights into the influence of different parameters on wrinkle formation, aiding in controlling these factors to avoid manufacturing defects in wind turbine blades.

Analysis of biofilm expansion rate of Bacillus subtilis (MTC871) on agar substrates with different stiffness.

The surface morphology of mature biofilms is heterogeneous and can be divided into concentric rings wrinkles (I), labyrinthine networks wrinkles (II), radial ridges wrinkles (III), and branches wrinkles (IV), according to surface wrinkle structure and distribution characteristics. Due to the wrinkle structures, channels are formed between the biofilm and substrate and transport nutrients, water, metabolic products, etc. We find that expansion rate variations of biofilms growing on substrates with high and low agar concentrations (1.5, 2.0, 2.5 wt.%) are not in the same phase. In the first 3 days' growth, the interaction stress between biofilm and each agar substrate increases, which makes the biofilm expansion rate decreases before wrinkle pattern IV (branches) comes up. After 3 days, in the later growth stage after wrinkle pattern IV appears, the biofilm has larger expansion rate growing on 2.0 wt.% agar concentration, which has the larger wrinkle distance in wrinkle pattern IV reducing energy consumption. Our study shows that the stiff substrate does not always inhibit the biofilm expansion, although it does in the earlier stage; after that, mature biofilms acquire larger expansion rate by adjusting the growth mode through the wrinkle evolution even in nutrient extremely depletion.

A unified variational framework of no-tension and no-compression solids and its application to finite element analysis

No-tension and no-compression constitutive models have important applications in solid mechanics, such as modelling of masonry, wrinkled membrane, unilateral contact interface, etc. Although lots of studies on no-tension and no-compression solids have been found, the variational principle constructing the cornerstone of elasticity is not studied thoroughly. The paper presents two concise variational formulations, a principle of minimum potential energy and a principle of minimum complementary energy, which are available both for no-tension and no-compression solids. Linearization of the conic yield surfaces leads to a series of linear complementary constitutive equations that are embedded into the proposed variational framework. Differing from other variational formulations, an approximate total solution rather than the Newton iteration is achieved in finite element analysis. It makes the algorithm stable. The applications include a no-tension panel benchmark test, two masonry structures and a wrinkled membrane. Compared with our previous study on bi-modulus materials, the newly developed variational formulation is capable of capturing the evolution of wrinkles in membranes, and can be used for the analysis and design of wrinkle-free structures.

The universal scaling law for wrinkle evolution in stiff membranes on soft films

The universal scaling law for wrinkle evolution in stiff membranes on soft films

Surface Wrinkling with Memory for Programming Adhesion and Wettability

Modulating surface wrinkling is important for a variety of engineering applications. It has been known for more than two decades that the wavelength of surface wrinkles occurring in a metal film–soft polymer system scales linearly with the deposited film thickness. In the current experimental study of ultrathin gold film (0.2–8 nm) deposition on polydimethylsiloxane (PDMS), an unexplored thickness-dependent wrinkling phenomenon is found. By manipulating the deposition sequence as a degree of freedom for tailoring surface topography, we discovered a morphology memory effect where the wrinkle evolution in the subsequent deposition step inherits the surface pattern already formed in the previous step. Moreover, a stepwise deposition targeting 1 nm thick film can lead to 1 order of magnitude higher surface roughness than the one in the continuous deposition. By programming the sequences within 8 nm Au deposition, a surface strain map varying drastically from 0.2% to 27% is realized. Instructed by the strain map, we show the great potentials of tailored wrinkles in alternating surface wettability, enhancing surface Raman scattering, and on-demand tuning of surface adhesion.

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.

Analysing wrinkle interaction behaviour with Z-fold crease pattern in thin-film planar membrane reflector

Limited stowage volume of launch vehicles demands compact packaging of large deployable membrane structures. Employment of different folding approaches led to the unavoidable fold-lines(creases). Moreover, wrinkle reduction is essential in such thin-film solar sail and inflatable antenna structures. This article analyzes the combined effect of multiple creases and wrinkles on deployed thin Kapton’s surface accuracy. Authors have introduced a novel approach for employing membrane length shortening because of multiple creases and fold characteristics. Real-world logarithmic behaviour of crease relaxation and fold-region properties help in computing the crease curvature. A rhombus-shaped shell model with Z-folding is introduced and explored for the effect of the number of creases and their orientation. Stress concentration and wrinkle contours for applied edge tensile loading state that the fold lines affect the stress transfer path. Non-linear post-buckling analyses for the Kapton® membrane express higher wrinkle evolution in the central region over the loading edge. Besides, a discrepancy in wrinkle amplitude and wavelength reveals the effect of fold-line orientation on wrinkling. Sighting actual conditions for antenna structure, creasing profile normal to the loading direction was found preferable for maintaining reflector surface-effectiveness. Additionally, double creased membranes achieve maximum surface correctness for any angular position, as the mirror effect fold shapes reduce wrinkles the most. Results are validated by comparing with experimental outcomes.

Polarization-Dependent Ultrasensitive Dynamic Wrinkling on Floating Films Induced by Photo-Orientation of Azopolymer.

Ubiquitous surface wrinkling has been well-studied theoretically and experimentally. How to modulate the stress state of a liquid-supported system for the unexploited wrinkling capabilities remains a challenge. Here we report a simple linearly-polarized-light illumination to spatiotemporally trigger ultrasensitive in situ dynamic wrinkling on a floating azo-film. The smart combination of the liquid substrate with photoresponsive azo-moieties leads to the light-induced ultrafast wrinkling evolution, accompanied by unprecedented sequential wrinkling orientation conversion (from polarization-parallel to polarization-perpendicular). The involved different polarization-dependent sequential photo-orientation for azo side chains and azo-grafted main chains of azopolymers is disclosed experimentally for the first time. Meanwhile, programmable dynamic wrinkling with all-optical switchable surface topographies is available, which has wide application potentials in photoresponsive soft photonics.

Polarization‐Dependent Ultrasensitive Dynamic Wrinkling on Floating Films Induced by Photo‐Orientation of Azopolymer

AbstractUbiquitous surface wrinkling has been well‐studied theoretically and experimentally. How to modulate the stress state of a liquid‐supported system for the unexploited wrinkling capabilities remains a challenge. Here we report a simple linearly‐polarized‐light illumination to spatiotemporally trigger ultrasensitive in situ dynamic wrinkling on a floating azo‐film. The smart combination of the liquid substrate with photoresponsive azo‐moieties leads to the light‐induced ultrafast wrinkling evolution, accompanied by unprecedented sequential wrinkling orientation conversion (from polarization‐parallel to polarization‐perpendicular). The involved different polarization‐dependent sequential photo‐orientation for azo side chains and azo‐grafted main chains of azopolymers is disclosed experimentally for the first time. Meanwhile, programmable dynamic wrinkling with all‐optical switchable surface topographies is available, which has wide application potentials in photoresponsive soft photonics.

Delamination of multilayer graphene stacks from its substrate through wrinkle formation under high pressures

There is a need to find new paths for van der Waals 2D-systems detachment and transfer or to control their adhesion state in different environments. We have observed that supported multilayer graphene immersed in a fluid can be detached from a substrate through pressure application. The process is based on the development of wrinkles originated by the difference of in-plane-compressibility between the graphene stacks and the substrate. Graphene stacks comprised between 9 and 110 layers and immersed in various fluids allowed to investigate the growth and evolution of wrinkles with increasing pressure. The detachment from the substrate stops at the pressure-induced fluid solidification. Methanol, ethanol or their mixtures favor the pressure-induced wrinkle formation in SiO2/Si substrates. In these cases, the pressure evolution of the delamination process follows a universal behavior independently of the number of graphene layers with a complete delamination at ∼4GPa. The quantitative analysis of the wrinkle geometry evolution can be consistently interpreted as due to a pressure-induced increase of the bending stiffness of the graphene stacks, or a reduction of the adhesion forces between the sample and the substrate, or both. These results should also be of practical use in high-pressure experiments of van der Waals systems.

Stretching Hookean ribbons part II: from buckling instability to far-from-threshold wrinkle pattern.

We address the fully developed wrinkle pattern formed upon stretching a Hookean, rectangular-shaped sheet, when the longitudinal tensile load induces transverse compression that far exceeds the stability threshold of a purely planar deformation. At this "far-from-threshold" parameter regime, which has been the subject of the celebrated Cerda-Mahadevan model (Cerda and Mahadevan in Phys Rev Lett 90:074302, 2003), the wrinkle pattern expands throughout the length of the sheet and the characteristic wavelength of undulations is much smaller than its width. Employing Surface Evolver simulations over a range of sheet thicknesses and tensile loads, we elucidate the theoretical underpinnings of the far-from-threshold framework in this setup. We show that the evolution of wrinkles comes in tandem with collapse of transverse compressive stress, rather than vanishing transverse strain (which was hypothesized by Cerda and Mahadevan in Phys Rev Lett 90:074302, 2003), such that the stress field approaches asymptotically a compression-free limit, describable by tension field theory. We compute the compression-free stress field by simulating a Hookean sheet that has finite stretching modulus but no bending rigidity, and show that this singular limit encapsulates the geometrical nonlinearity underlying the amplitude-wavelength ratio of wrinkle patterns in physical, highly bendable sheets, even though the actual strains may be so small that the local mechanics is perfectly Hookean. Finally, we revisit the balance of bending and stretching energies that gives rise to a favorable wrinkle wavelength, and study the consequent dependence of the wavelength on the tensile load as well as the thickness and length of the sheet.

Microscopic Mechanisms Behind the High Friction and Failure Initiation of Graphene Wrinkles.

Wrinkling occurs on the surfaces of large-area graphene ubiquitously. Despite that the wrinkled structures are found to degrade the lubricous property, the behind mechanisms remain less understood. Here, atomic force microscopy is adopted to characterize the friction and wear properties of graphene wrinkles (GWs) with different heights by nanoscratch tests. We verify the phenomena of high friction and reduced load-carrying capacity of wrinkles and report the observation of lubrication deterioration with increased heights. Using molecular dynamics simulations, we reveal that the contact quality at the interface is a dominant role in the friction evolution of wrinkles. The high friction of wrinkles is determined by the increased contact area and commensurability caused by the wrinkle deformation and topography changes. The wrinkle failure initiates near the root of the formed bilayer configuration due to the increased lateral stiffness and reduced atomic distance between the wrinkle layers. The increased interlocking effect results in a local shear stress of 91 GPa and induces the phase transitions of carbon atoms easily. As the wrinkle height decreases, the unstable local configuration weakens the interlocking effects and cannot fail even at a high load. This investigation sheds light on the microscopic frictional contact of GWs and provides guidance for tuning the tribological properties of graphene by controlling the wrinkle structures.

Annealing temperature-driven near-surface crystallization with improved luminescence in self‐patterned alumina films

The impact of annealing on luminescence properties of radio-frequency magnetron sputtering grown alumina films and their possible application in radiation measurement are presented. Here, grazing incidence X-ray diffraction study reveals the growth of amorphous alumina films, while the annealing treatment results in the gradual formation of nanocrystallites. They are found to be embedded in the amorphous matrix by cross-sectional Transmission Electron Microscopy for 1200 °C annealed thin film. The evolution of self-patterned wrinkles has also been observed at the surface by Scanning Electron Microscopy. A comprehensive analysis of optically active defect centers is carried out by room temperature photoluminescence (PL) measurement. This indicates a monotonic increase of oxygen vacancies (F centers) with increasing annealing temperature up to 1200 °C, though they are not directly correlated with the thermoluminescence (TL) results after exposing them to gamma radiation from a 60Co source. Based on PL analysis, the TL glow curves with increasing annealing temperature are elucidated in the light of the involvement of both trap centers and F-type recombination centers residing at grain boundaries. In terms of TL results, 1200 °C annealed alumina film is found to be superior to both the as-grown film, and the one annealed at 1100 °C. Finally, the linear TL response curves in the 1200 °C annealed film after exposing to both gamma radiation (up to 5 kGy) and energetic charged particles (80 MeV carbon ions) are demonstrated up to 130 kGy.

The effects of addition of carbon dioxide and water vapor on the dynamic behavior of spherically expanding hydrogen/air premixed flames

Utilizing efficiently and securely hydrogen as clean energy source, it is required not only to analyze the experimental data under a certain condition but also to create the mathematical model for the prediction of flame propagation velocity under various conditions. Thus, it is significant to understand the characteristics of dynamic behavior of hydrogen/air premixed flames and to elucidate the effects of addition of inert gas, i.e. carbon dioxide CO2 and water vapor H2O. We performed the experiments of hydrogen explosion in two types of closed chambers to observe spherically expanding flames using Schlieren photography. Wrinkles on the flame surface were clearly observed in low equivalence ratios. Analyzing the Schlieren images, the flame propagation velocity depending on the flame radius was obtained. Increasing the addition of inert gas, the propagation velocity decreased, especially in the case of CO2 addition. The propagation velocity increased monotonically as the flame radius became larger. The appearance of flame acceleration was found, which was caused by the evolution of wrinkles on the flame surface. Moreover, the Markstein length decreased as the concentration of inert gas became higher, indicating that the addition of inert gas promoted the instability of hydrogen flames. Furthermore, the wrinkling factor, closely related with the increment in propagation velocity, decreased as the inert-gas concentration became higher. The wrinkling factor normalized by the propagation velocity of flat flame increased, on the other hand, under the conditions of high inert-gas concentration, except for near the quenching conditions. This indicated that the addition of CO2 or H2O promoted the unstable motion of hydrogen flames, which could be due to the enhancement of the diffusive-thermal effect. Based on the characteristics of dynamic behavior of hydrogen flames, the parameters used in the mathematical model on propagation velocity including flame acceleration was obtained, and then the flame propagation velocity under various conditions was predicted.

A secure version of asymptotic numerical method via convergence acceleration

The paper deals with the numerical computation of difficult problems requiring many steps and many degrees of freedom such as the finite element analysis of wrinkling of film–substrate systems. The asymptotic numerical method (ANM) is well adapted to such computations but with a progressive loss of accuracy during step chaining. Thus, correction phases are necessary, which are rarely carried out within ANM. A convergence acceleration algorithm and a step-length adaptation have been included to limit the growth of computation time and to strengthen the reliability of the procedure. This modified version of the ANM is assessed by simulating the appearance and evolution of sinusoidal wrinkles under uniaxial compression.

THE EVOLVING WRINKLE PATTERN OF THE BACILLUS SUBTILIS BIOFILM PROVIDING MORE LIVING SPACE FOR CELLS

The biofilm wrinkle evolution is the growth mechanism by which bacteria regulate their physiological state in response to the environmental change. We use the parameter of surface complexity to describe different wrinkle patterns. The surface complexity is defined that the biofilm surface area contact with the air is divided by the projected area of the biofilm. We find that the biofilm surface complexity variation is positively proportional to the number of spores. Although each wrinkle pattern has various wrinkle thickness and width, surface complexities of some patterns are almost same, which guarantees cells have enough living space. Through the observation of the growth of the damaged biofilm, we further find that the biofilm expansion along the circumferential direction is faster than that along radial direction, which means that the internal stress along the circumferential direction contributes the wrinkle formation. Our work provides a new perspective to study biofilm morphologies, and relates the morphology evolution with phenotypes in the Bacillus subtilis biofilm.

Impact on floating thin elastic sheets: A mathematical model

We investigate impact of a sphere onto a floating elastic sheet and the resulting formation and evolution of wrinkles in the sheet. Following impact, we observe a radially propagating wave, beyond which the sheet remains approximately planar but is decorated by a series of radial wrinkles whose wavelength grows in time. We develop a mathematical model to describe these phenomena by exploiting the asymptotic limit in which the bending stiffness is small compared to stresses in the sheet. The results of this analysis show that, at a time $t$ after impact, the transverse wave is located at a radial distance $r\sim t^{1/2}$ from the impactor, in contrast to the classic $r\sim t^{2/3}$ scaling observed for capillary--inertia ripples produced by dropping a stone into a pond. We describe the shape of this wave, starting from the simplest case of a point impactor, but subsequently addressing a finite-radius spherical impactor, contrasting this case with the classic Wagner theory of impact. We show also that the coarsening of wrinkles in the flat portion of the sheet is controlled by the inertia of the underlying liquid: short-wavelength, small-amplitude wrinkles form at early times since they accommodate the geometrically-imposed compression without significantly displacing the underlying liquid. As time progresses, the liquid accelerates and the wrinkles grow larger and coarsen. We explain this coarsening quantitatively using numerical simulations and scaling arguments, and we compare our predictions with experimental data.