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Chen Z, Chen S, Andrabi SM, Zhao G, Xu Y, Ouyang Q, Busquets ME, Qian X, Gautam S, Chen PY, Xie J, Yan Z. Multifunctional Porous Soft Composites for Bimodal Wearable Cardiac Monitors. AIChE J 2024; 70:e18576. [PMID: 39713103 PMCID: PMC11661810 DOI: 10.1002/aic.18576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Accepted: 08/01/2024] [Indexed: 12/24/2024]
Abstract
Wearable heart monitors are crucial for early diagnosis and treatment of heart diseases in non-clinical settings. However, their long-term applications require skin-interfaced materials that are ultrasoft, breathable, antibacterial, and possess robust, enduring on-skin adherence-features that remain elusive. Here, we have developed multifunctional porous soft composites that meet all these criteria for skin-interfaced bimodal cardiac monitoring. The composite consists of a bilayer structure featuring phase-separated porous elastomer and slot-die-coated biogel. The porous elastomer ensures ultrasoftness, breathability, ease of handling, and mechanical integrity, while the biogel enables long-term on-skin adherence. Additionally, we incorporated ε-polylysine in the biogel to offer antibacterial properties. Also, the conductive biogel embedded with silver nanowires was developed for use in electrocardiogram sensors to reduce contact impedance and ensure high-fidelity recordings. Furthermore, we assembled a bimodal wearable cardiac monitoring system that demonstrates high-fidelity recordings of both cardiac electrical (electrocardiogram) and mechanical (seismocardiogram) signals over a 14-day testing period.
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Affiliation(s)
- Zehua Chen
- Department of Chemical and Biomedical Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Sicheng Chen
- Department of Chemical and Biomedical Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Syed Muntazir Andrabi
- Department of Surgery-Transplant and Mary and Dick Holland Regenerative Medicine Program, University of Nebraska Medical Center, Omaha, NE 68130, USA
| | - Ganggang Zhao
- Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Yadong Xu
- Andrew and Peggy Cherng Department of Medical Engineering, Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA
| | - Qunle Ouyang
- Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Milton E. Busquets
- Department of Surgery-Transplant and Mary and Dick Holland Regenerative Medicine Program, University of Nebraska Medical Center, Omaha, NE 68130, USA
| | - Xiaoyan Qian
- Department of Chemical and Biomedical Engineering, University of Missouri, Columbia, MO 65211, USA
| | - Sandeep Gautam
- Division of Cardiovascular Medicine, University of Missouri-Columbia, Columbia, MO 65212, USA
| | - Pai-Yen Chen
- Department of Electrical and Computer Engineering, University of Illinois, Chicago, IL 60607, USA
| | - Jingwei Xie
- Department of Surgery-Transplant and Mary and Dick Holland Regenerative Medicine Program, University of Nebraska Medical Center, Omaha, NE 68130, USA
| | - Zheng Yan
- Department of Chemical and Biomedical Engineering, University of Missouri, Columbia, MO 65211, USA
- Department of Mechanical & Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA
- Materials Science and Engineering Institute, University of Missouri, Columbia, MO 65211, USA
- NextGen Precision Health, University of Missouri, Columbia, MO 65211, USA
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Zhong F, Wang F, Yang H. Composition and structure analysis of different depths in the stratum corneum using confocal Raman microscopy combined with two-dimensional correlation spectroscopy. Talanta 2024; 270:125559. [PMID: 38141465 DOI: 10.1016/j.talanta.2023.125559] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 12/09/2023] [Accepted: 12/13/2023] [Indexed: 12/25/2023]
Abstract
The chemical composition and structure of the stratum corneum (SC) play a crucial role in the skin barrier function. Therefore, accurately determining the SC thickness and studying the changes in lipid and keratin structure and distribution within it are key aspects of skin barrier research. Currently, there are limited analytical tools and data analysis methods available for real-time and online studies of SC composition and structural changes. In this study, we focus on depth as a perturbation and employ confocal Raman microscopy combined with moving-window two-dimensional correlation spectroscopy (MW2D) technique to investigate the SC thickness. Additionally, we employ confocal Raman microscopy combined with perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) to precisely characterize the stratification of the SC. Furthermore, the two-dimensional correlation spectroscopy (2DCOS) method is utilized to examine the content of various conformations in the keratin secondary structure within the SC, as well as the subtle interrelationships between lipid and keratin structures.
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Affiliation(s)
- Feng Zhong
- The Education Ministry Key Lab of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Municipal Education Committee Key Laboratory of Molecular Imaging Probes and Sensors, and Department of Chemistry, Shanghai Normal University, Shanghai, 200234, PR China
| | - Feng Wang
- The Education Ministry Key Lab of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Municipal Education Committee Key Laboratory of Molecular Imaging Probes and Sensors, and Department of Chemistry, Shanghai Normal University, Shanghai, 200234, PR China.
| | - Haifeng Yang
- The Education Ministry Key Lab of Resource Chemistry, Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Municipal Education Committee Key Laboratory of Molecular Imaging Probes and Sensors, and Department of Chemistry, Shanghai Normal University, Shanghai, 200234, PR China.
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Berkey CA, Styke C, Yoshitake H, Sonoki Y, Uchiyama M, Dauskardt RH. Carbon dioxide foam bubbles enhance skin penetration through the stratum corneum layer with mechanical mechanism. Colloids Surf B Biointerfaces 2023; 231:113538. [PMID: 37738871 DOI: 10.1016/j.colsurfb.2023.113538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2023] [Revised: 08/25/2023] [Accepted: 09/08/2023] [Indexed: 09/24/2023]
Abstract
Topical skin formulations often include penetration enhancers that interact with the outer stratum corneum (SC) layer to chemically enhance diffusion. Alternatively, penetration can be mechanically enhanced with simple rubbing in the presence of solid particles sometimes included to exfoliate the top layers of the SC. Our goal was to evaluate micron-sized carbon dioxide bubbles included in a foamed moisturizing formulation as a mechanical penetration enhancement strategy. We show that moisturizing foam bubbles cause an increase in SC formulation penetration using both mechanical and spectroscopic characterization. Our results suggest viscous liquid film drainage between coalescing gaseous bubbles creates local regions of increased hydrodynamic pressure in the foam liquid layer adjacent to the SC surface that enhances treatment penetration. An SC molecular diffusion model is used to rationalize the observed behavior. The findings indicate marked increased levels of treatment concentration in the SC at 2 h and that persists to 18 h after exposure, far exceeding non-foamed treatments. The study suggests an alternate strategy for increasing formulation penetration with a non-chemical mechanism.
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Affiliation(s)
- Christopher A Berkey
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
| | - Cassandra Styke
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
| | | | | | | | - Reinhold H Dauskardt
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA.
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Bow JR, Sonoki Y, Uchiyama M, Dauskardt RH. Ectoine disperses keratin and alters hydration kinetics in stratum corneum. Biochem Biophys Rep 2021; 28:101134. [PMID: 34584987 PMCID: PMC8455723 DOI: 10.1016/j.bbrep.2021.101134] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Revised: 09/12/2021] [Accepted: 09/13/2021] [Indexed: 12/02/2022] Open
Abstract
Moisturizing compounds are commonly applied topically to human stratum corneum (SC). Many types of molecular species are employed, most commonly including humectants and occlusives. We find new evidence of keratin dispersion caused by the moisturizing compound ectoine (1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid), and provide the first characterization of its impacts on the hydration kinetics and biomechanics of SC. A second compound, 2-(2-hydroxyethoxy)ethylguanidine succinate (HEG) was investigated for comparison. A suite of biomechanical and biochemical assays including FTIR, drying stress, and cellular cohesion were used. Studies were conducted on normal, lipid-extracted, and lipid plus natural moisturizing factor extracted SC. Ectoine was found to improve the dispersity and hydration of keratin bundles in corneocytes. It also decreased rates of stress development in lipid extracted SC when exposed to a dry environment by ∼30% while improving stress reduction during rehydration by ∼20%. Peak stresses were increased in harsh drying environments of <5% RH, but SC swelling measurements suggest that water retention was improved in ambient conditions. Further, changes up to ∼4 J/m2 were seen in cohesion after ectoine treatments, suggesting corneodesmosome interactions. HEG was tested and found to disperse keratin without impacting corneodesmosomes. These results indicate that keratin dispersants produce beneficial effects on SC hydration kinetics, ultimately resulting in higher SC hydration under ambient conditions. First study demonstrating the biomechanical impact of keratin dispersion on human skin Ectoine disperses keratin bundles in human stratum corneum Rates of drying stress development are reduced in keratin-dispersed skin Rehydration rates are increased in keratin-dispersed skin Keratin dispersion alters corneocyte cohesion profiles
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Affiliation(s)
- Jacob R. Bow
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
| | - Yoshihiko Sonoki
- Skin Care Products Research Laboratory, Kao Corporation, Tokyo, Japan
| | - Masayuki Uchiyama
- Skin Care Products Research Laboratory, Kao Corporation, Tokyo, Japan
| | - Reinhold H. Dauskardt
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, USA
- Corresponding author. Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205.
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Bow JR, Sonoki Y, Uchiyama M, Shimizu E, Tanaka K, Dauskardt RH. Lipid Loss Increases Stratum Corneum Stress and Drying Rates. Skin Pharmacol Physiol 2020; 33:180-188. [DOI: 10.1159/000507456] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Accepted: 03/22/2020] [Indexed: 11/19/2022]
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Ansari F, McGuiness C, Zhang B, Dauskardt RH. Effect of emulsifiers on drying stress and intercellular cohesion in human stratum corneum. Int J Cosmet Sci 2020; 42:581-589. [PMID: 32567061 DOI: 10.1111/ics.12643] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2020] [Revised: 06/09/2020] [Accepted: 06/16/2020] [Indexed: 11/30/2022]
Abstract
OBJECTIVES Emulsifier molecules, with their amphiphilic character, are ubiquitous in moisturizing creams and primarily serve to disperse the water-insoluble molecules such as emollients, oils, lipids and fats in water. The objective of this study was to investigate the effect of emulsifier molecules on the barrier and biomechanical properties of human stratum corneum (SC) and to compare the efficacy of emulsifier molecules when used in a fully formulated moisturizing cream. METHODS We employed methods based on thin-film mechanics to measure the drying stress and intercellular cohesion in the SC. The emulsifier molecules or moisturizing creams formulated with them were applied to a fully hydrated SC adhered to a glass substrate. In-plane stress developed in the SC during drying was then measured by tracking changes in the curvature of the glass substrate. The intercellular cohesion within the SC was measured by means of a double cantilever beam (DCB) set-up, where the treated or untreated SC was sandwiched between two substrates, and the delamination energy calculated by measuring the force required to drive a crack through the SC. Moisturizing cream diffusivity through the stratum corneum was measured by spectroscopic technique and related to internal SC stress and fracture energy. RESULTS We observe significant differences in the biomechanical behaviour of SC when moisturizing creams with different emulsifier molecules are applied on isolated stratum corneum ex vivo. The reduction in maximum stress varied between 12% and 26% depending on the emulsifier molecules used in the formulation. The intercellular cohesion and the diffusion of molecules in the formulated moisturizing creams through the SC were also found to be strongly dependent on the type of emulsifier molecule used in the formulation. CONCLUSIONS The biomechanical and barrier properties of the human stratum corneum show strong dependence on the emulsifier molecule used in the moisturizing creams, even when the creams included only ~3 weight% emulsifier molecules. Moreover, we found that the reduction in SC peak stress was strongly correlated with the formulation diffusivity into the SC. The moisturizing creams diffusing fastest into the SC had the largest reduction in peak stress and vice versa.
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Affiliation(s)
- F Ansari
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
| | - C McGuiness
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA.,Solvay USA Inc, 350 George Patterson Blvd, Bristol, PA, 19007, USA
| | - B Zhang
- Solvay Inc, Jindu Road 3966, Xinzhuang Industrial zone, Shanghai, 201108, China
| | - R H Dauskardt
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
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Liu Y, Budhlall BM. Self-healing nanocomposites comprised of poly(urea formaldehyde) nanocapsules in a thermosetting polyurea. Eur Polym J 2020. [DOI: 10.1016/j.eurpolymj.2020.109545] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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8
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Berkey C, Oguchi N, Miyazawa K, Dauskardt R. Role of sunscreen formulation and photostability to protect the biomechanical barrier function of skin. Biochem Biophys Rep 2019; 19:100657. [PMID: 31211250 PMCID: PMC6562193 DOI: 10.1016/j.bbrep.2019.100657] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Revised: 05/02/2019] [Accepted: 06/04/2019] [Indexed: 01/25/2023] Open
Abstract
The impact of sunscreen formulations on the barrier properties of human skin are often overlooked leading to formulations with components whose effects on barrier mechanical integrity are poorly understood. The aim of this study is to demonstrate the relevance of carrier selection and sunscreen photostability when designing sunscreen formulations to protect the biomechanical barrier properties of human stratum corneum (SC) from solar ultraviolet (UV) damage. Biomechanical properties of SC samples were assayed after accelerated UVB damage through measurements of the SC's mechanical stress profile and corneocyte cohesion. A narrowband UVB (305-315 nm) lamp was used to expose SC samples to 5, 30, 125, and 265 J cm-2 in order to magnify damage to the mechanical properties of the tissue and characterize the UV degradation dose response such that effects from smaller UV dosages can be extrapolated. Stresses in the SC decreased when treated with sunscreen components, highlighting their effect on the skin prior to UV exposure. Stresses increased with UVB exposure and in specimens treated with different sunscreens stresses varied dramatically at high UVB dosages. Specimens treated with sunscreen components without UVB exposure exhibited altered corneocyte cohesion. Both sunscreens studied prevented alteration of corneocyte cohesion by low UVB dosages, but differences in protection were observed at higher UVB dosages indicating UV degradation of one sunscreen. These results indicate the protection of individual sunscreen components vary over a range of UVB dosages, and components can even cause alteration of the biomechanical barrier properties of human SC before UV exposure. Therefore, detailed characterization of sunscreen formulation components is required to design robust protection from UV damage.
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Affiliation(s)
- Christopher Berkey
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205, USA
| | - Nozomi Oguchi
- Shiseido Co., Ltd, Advanced Technology Research Group, Global Innovation Center, 2-2-1, Hayabuchi, Tsuzuki-ku, Yokohama, 224-8558, Japan
| | - Kazuyuki Miyazawa
- Shiseido Co., Ltd, Advanced Technology Research Group, Global Innovation Center, 2-2-1, Hayabuchi, Tsuzuki-ku, Yokohama, 224-8558, Japan
| | - Reinhold Dauskardt
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205, USA
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9
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Zhou D, Chen F, Handschuh‐Wang S, Gan T, Zhou X, Zhou X. Biomimetic Extreme‐Temperature‐ and Environment‐Adaptable Hydrogels. Chemphyschem 2019; 20:2139-2154. [DOI: 10.1002/cphc.201900545] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Revised: 07/10/2019] [Indexed: 12/31/2022]
Affiliation(s)
- Dan Zhou
- College of Chemistry and Environmental EngineeringShenzhen University, Shenzhen 518060 P. R. China
| | - Fan Chen
- College of Chemistry and Environmental EngineeringShenzhen University, Shenzhen 518060 P. R. China
| | - Stephan Handschuh‐Wang
- College of Chemistry and Environmental EngineeringShenzhen University, Shenzhen 518060 P. R. China
| | - Tiansheng Gan
- College of Chemistry and Environmental EngineeringShenzhen University, Shenzhen 518060 P. R. China
| | - Xiaohu Zhou
- College of Chemistry and Environmental EngineeringShenzhen University, Shenzhen 518060 P. R. China
| | - Xuechang Zhou
- College of Chemistry and Environmental EngineeringShenzhen University, Shenzhen 518060 P. R. China
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10
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Guo S, Domanov Y, Donovan M, Ducos B, Pomeau Y, Gourier C, Perez E, Luengo GS. Anisotropic cellular forces support mechanical integrity of the Stratum Corneum barrier. J Mech Behav Biomed Mater 2019; 92:11-23. [PMID: 30654216 DOI: 10.1016/j.jmbbm.2018.12.027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 11/26/2018] [Accepted: 12/20/2018] [Indexed: 11/30/2022]
Abstract
The protective function of biological surfaces that are exposed to the exterior of living organisms is the result of a complex arrangement and interaction of cellular components. This is the case for the most external cornified layer of skin, the stratum corneum (SC). This layer is made of corneocytes, the elementary 'flat bricks' that are held together through adhesive junctions. Despite the well-known protective role of the SC under high mechanical stresses and rapid cell turnover, the subtleties regarding the adhesion and mechanical interaction among the individual corneocytes are still poorly known. Here, we explore the adhesion of single corneocytes at different depths of the SC, by pulling them using glass microcantilevers, and measuring their detachment forces. We measured their interplanar adhesion between SC layers, and their peripheral adhesion among cells within a SC layer. Both adhesions increased considerably with depth. At the SC surface, with respect to adhesion, the corneocyte population exhibited a strong heterogeneity, where detachment forces differed by more than one order of magnitude for corneocytes located side by side. The measured detachment forces indicated that in the upper-middle layers of SC, the peripheral adhesion was stronger than the interplanar one. We conclude that the stronger peripheral adhesion of corneocytes in the SC favors an efficient barrier which would be able to resist strong stresses.
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Affiliation(s)
- Shuo Guo
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, l'université de recherche Paris Sciences et Lettres, CNRS UMR 8550, Sorbonne Universités, Université Pierre-et-Marie-Curie (UPMC) University of Paris 06, Université Paris Diderot, 75005 Paris, France
| | - Yegor Domanov
- L'Oréal Research and Innovation, Aulnay-sous-Bois, France
| | - Mark Donovan
- L'Oréal Research and Innovation, Aulnay-sous-Bois, France
| | - Bertrand Ducos
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, l'université de recherche Paris Sciences et Lettres, CNRS UMR 8550, Sorbonne Universités, Université Pierre-et-Marie-Curie (UPMC) University of Paris 06, Université Paris Diderot, 75005 Paris, France
| | - Yves Pomeau
- University of Arizona, Department of Mathematics, Tucson, AZ, USA
| | - Christine Gourier
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, l'université de recherche Paris Sciences et Lettres, CNRS UMR 8550, Sorbonne Universités, Université Pierre-et-Marie-Curie (UPMC) University of Paris 06, Université Paris Diderot, 75005 Paris, France
| | - Eric Perez
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, l'université de recherche Paris Sciences et Lettres, CNRS UMR 8550, Sorbonne Universités, Université Pierre-et-Marie-Curie (UPMC) University of Paris 06, Université Paris Diderot, 75005 Paris, France.
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11
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Zeng S, Li R, Freire SG, Garbellotto VMM, Huang EY, Smith AT, Hu C, Tait WRT, Bian Z, Zheng G, Zhang D, Sun L. Moisture-Responsive Wrinkling Surfaces with Tunable Dynamics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1700828. [PMID: 28429495 DOI: 10.1002/adma.201700828] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 03/15/2017] [Indexed: 06/07/2023]
Abstract
The wrinkle dynamics (such as reversibility and stability) of human skin are affected by the external stimuli, as well as the skin's structure and mechanical properties. Inspired by these tunable responses, three types of moisture-responsive wrinkle dynamics are achieved, for the first time, through a single film-substrate system. These dynamics include: (1) completely reversible wrinkles formation; (2) irreversible wrinkles formation I: the initially formed wrinkles can be permanently erased and never reappear; and (3) irreversible wrinkles formation II: once the wrinkles form, they can no longer be erased. The key to success is to control the stiffness and thickness ratios of the film and the substrate, and tailor the crosslink degree/gradient of the film to allow for moisture-dependent changes of modulus and swelling degree. These unique responsive dynamics motivate the invention of a series of optical devices triggered by moisture, including anticounterfeit tabs, encryption devices, water indicators, light diffusors, and antiglare films. This study also paves the road for further understanding of the skin wrinkling dynamics and manipulation.
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Affiliation(s)
- Songshan Zeng
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Rui Li
- Department of Mechanical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Stephan G Freire
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Vivian M M Garbellotto
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Emily Y Huang
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Andrew T Smith
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Cong Hu
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - William R T Tait
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
| | - Zichao Bian
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Guoan Zheng
- Department of Biomedical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Dianyun Zhang
- Department of Mechanical Engineering, University of Connecticut, Storrs, CT, 06269, USA
| | - Luyi Sun
- Department of Chemical and Biomolecular Engineering and Polymer Program, Institute of Materials Science, University of Connecticut, Storrs, CT, 06269, USA
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12
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Meliga SC, Coffey JW, Crichton ML, Flaim C, Veidt M, Kendall MA. The hyperelastic and failure behaviors of skin in relation to the dynamic application of microscopic penetrators in a murine model. Acta Biomater 2017; 48:341-356. [PMID: 27746361 DOI: 10.1016/j.actbio.2016.10.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 09/25/2016] [Accepted: 10/12/2016] [Indexed: 12/20/2022]
Abstract
In-depth understanding of skin elastic and rupture behavior is fundamental to enable next-generation biomedical devices to directly access areas rich in cells and biomolecules. However, the paucity of skin mechanical characterization and lack of established fracture models limits their rational design. We present an experimental and numerical study of skin mechanics during dynamic interaction with individual and arrays of micro-penetrators. Initially, micro-indentation of individual skin strata revealed hyperelastic moduli were dramatically rate-dependent, enabling extrapolation of stiffness properties at high velocity regimes (>1ms-1). A layered finite-element model satisfactorily predicted the penetration of micro-penetrators using characteristic fracture energies (∼10pJμm-2) significantly lower than previously reported (≫100pJμm-2). Interestingly, with our standard application conditions (∼2ms-1, 35gpistonmass), ∼95% of the application kinetic energy was transferred to the backing support rather than the skin ∼5% (murine ear model). At higher velocities (∼10ms-1) strain energy accumulated in the top skin layers, initiating fracture before stress waves transmitted deformation to the backing material, increasing energy transfer efficiency to 55%. Thus, the tools developed provide guidelines to rationally engineer skin penetrators to increase depth targeting consistency and payload delivery across patients whilst minimizing penetration energy to control skin inflammation, tolerability and acceptability. STATEMENT OF SIGNIFICANCE The mechanics of skin penetration by dynamically-applied microscopic tips is investigated using a combined experimental-computational approach. A FE model of skin is parameterized using indentation tests and a ductile-failure implementation validated against penetration assays. The simulations shed light on skin elastic and fracture properties, and elucidate the interaction with microprojection arrays for vaccine delivery allowing rational design of next-generation devices.
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13
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Berkey C, Biniek K, Dauskardt RH. Screening sunscreens: protecting the biomechanical barrier function of skin from solar ultraviolet radiation damage. Int J Cosmet Sci 2016; 39:269-274. [PMID: 27685249 DOI: 10.1111/ics.12370] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Accepted: 09/25/2016] [Indexed: 11/29/2022]
Abstract
OBJECTIVE Solar ultraviolet (UV) radiation is ubiquitous in human life and well known to cause skin damage that can lead to harmful conditions such as erythema. Although sunscreen is a popular form of protection for some of these conditions, it is unclear whether sunscreen can maintain the mechanical barrier properties of skin. The objective of this study was to determine whether in vitro thin-film mechanical analysis techniques adapted for biological tissue are able to characterize the efficacy of commonly used UV inhibitors and commercial sunscreens to protect the biomechanical barrier properties of stratum corneum (SC) from UV exposure. METHODS The biomechanical properties of SC samples were assayed through measurements of the SC's drying stress profile and delamination energy. The drying stresses within SC were characterized from the curvature of a borosilicate glass substrate onto which SC had been adhered. Delamination energies were characterized using a double-cantilever beam (DCB) cohesion testing method. Successive DCB specimens were prepared from previously separated specimens by adhering new substrates onto each side of the already tested specimen to probe delamination energies deeper into the SC. These properties of the SC were measured before and after UV exposure, both with and without sunscreens applied, to determine the role of sunscreen in preserving the barrier function of SC. RESULTS The drying stress in SC starts increasing sooner and rises to a higher plateau stress value after UVA exposure as compared to non-UV-exposed control specimens. For specimens that had sunscreen applied, the UVA-exposed and non-UV-exposed SC had similar drying stress profiles. Additionally, specimens exposed to UVB without protection from sunscreen exhibited significantly lower delamination energies than non-UV-exposed controls. With commercial sunscreen applied, the delamination energy for UV-exposed and non-UV-exposed tissue was consistent, even up to large doses of UVB. CONCLUSION In vitro thin-film mechanical analysis techniques can readily characterize the effects of SC's exposure to UV radiation. The methods used in this study demonstrated commercial sunscreens were able to preserve the biomechanical properties of SC during UV exposure, thus indicating the barrier function of SC was also maintained.
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Affiliation(s)
- C Berkey
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205, USA
| | - K Biniek
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205, USA
| | - R H Dauskardt
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305-2205, USA
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The global mechanical properties and multi-scale failure mechanics of heterogeneous human stratum corneum. Acta Biomater 2016; 43:78-87. [PMID: 27431879 DOI: 10.1016/j.actbio.2016.07.028] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Revised: 07/03/2016] [Accepted: 07/14/2016] [Indexed: 11/20/2022]
Abstract
UNLABELLED The outermost layer of skin, or stratum corneum, regulates water loss and protects underlying living tissue from environmental pathogens and insults. With cracking, chapping or the formation of exudative lesions, this functionality is lost. While stratum corneum exhibits well defined global mechanical properties, macroscopic mechanical testing techniques used to measure them ignore the structural heterogeneity of the tissue and cannot provide any mechanistic insight into tissue fracture. As such, a mechanistic understanding of failure in this soft tissue is lacking. This insight is critical to predicting fracture risk associated with age or disease. In this study, we first quantify previously unreported global mechanical properties of isolated stratum corneum including the Poisson's ratio and mechanical toughness. African American breast stratum corneum is used for all assessments. We show these parameters are highly dependent on the ambient humidity to which samples are equilibrated. A multi-scale investigation assessing the influence of structural heterogeneities on the microscale nucleation and propagation of cracks is then performed. At the mesoscale, spatially resolved equivalent strain fields within uniaxially stretched stratum corneum samples exhibit a striking heterogeneity, with localized peaks correlating closely with crack nucleation sites. Subsequent crack propagation pathways follow inherent topographical features in the tissue and lengthen with increased tissue hydration. At the microscale, intact corneocytes and polygonal shaped voids at crack interfaces highlight that cracks propagate in superficial cell layers primarily along intercellular junctions. Cellular fracture does occur however, but is uncommon. STATEMENT OF SIGNIFICANCE Human stratum corneum protects the body against harmful environmental pathogens and insults. Upon mechanical failure, this barrier function is lost. Previous studies characterizing the mechanics of stratum corneum have used macroscopic testing equipment designed for homogenous materials. Such measurements ignore the tissue's rich topography and heterogeneous structure, and cannot describe the underlying mechanistic process of tissue failure. For the first time, we establish a mechanistic insight into the failure mechanics of soft heterogeneous tissues by investigating how cracks nucleate and propagate in stratum corneum. We further quantify previously unreported values of the tissue's Poisson's ratio and toughness, and their dramatic variation with ambient humidity. To date, skin models examining drug delivery, wound healing, and ageing continue to estimate these parameters.
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Yuk H, Zhang T, Parada GA, Liu X, Zhao X. Skin-inspired hydrogel-elastomer hybrids with robust interfaces and functional microstructures. Nat Commun 2016; 7:12028. [PMID: 27345380 PMCID: PMC4931236 DOI: 10.1038/ncomms12028] [Citation(s) in RCA: 418] [Impact Index Per Article: 52.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2016] [Accepted: 05/23/2016] [Indexed: 01/12/2023] Open
Abstract
Inspired by mammalian skins, soft hybrids integrating the merits of elastomers and hydrogels have potential applications in diverse areas including stretchable and bio-integrated electronics, microfluidics, tissue engineering, soft robotics and biomedical devices. However, existing hydrogel-elastomer hybrids have limitations such as weak interfacial bonding, low robustness and difficulties in patterning microstructures. Here, we report a simple yet versatile method to assemble hydrogels and elastomers into hybrids with extremely robust interfaces (interfacial toughness over 1,000 Jm(-2)) and functional microstructures such as microfluidic channels and electrical circuits. The proposed method is generally applicable to various types of tough hydrogels and diverse commonly used elastomers including polydimethylsiloxane Sylgard 184, polyurethane, latex, VHB and Ecoflex. We further demonstrate applications enabled by the robust and microstructured hydrogel-elastomer hybrids including anti-dehydration hydrogel-elastomer hybrids, stretchable and reactive hydrogel-elastomer microfluidics, and stretchable hydrogel circuit boards patterned on elastomer.
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Affiliation(s)
- Hyunwoo Yuk
- Department of Mechanical Engineering, Soft Active Materials Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Teng Zhang
- Department of Mechanical and Aerospace Engineering, Syracuse University, Syracuse, New York 13244, USA
| | - German Alberto Parada
- Department of Mechanical Engineering, Soft Active Materials Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Xinyue Liu
- Department of Mechanical Engineering, Soft Active Materials Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - Xuanhe Zhao
- Department of Mechanical Engineering, Soft Active Materials Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
- Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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Tear and decohesion of bovine pericardial tissue. J Mech Behav Biomed Mater 2016; 63:1-9. [PMID: 27337412 DOI: 10.1016/j.jmbbm.2016.06.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 05/31/2016] [Accepted: 06/02/2016] [Indexed: 11/22/2022]
Abstract
The aim of this study was to evaluate quantitatively the fracture-by tear and delamination-of bovine pericardium tissues which are usually employed for the manufacture of bioprosthetic valves. A large number of samples (77) were tested in root-to-apex and circumferential directions, according to a standardised tear test (ASTM D 1938). Before performing the tear test, some samples were subjected to 1000 cycles of fatigue to a maximum stress of 3MPa. Fracture toughness of tearing and delamination were computed by following a simple fracture model. The study showed significantly lower values of delamination toughness compared with tear delamination. Moreover, tear forces were different in each test direction, revealing a clear orthotropic behaviour. All these results, as well as the testing procedure, could be of value for future research in the physiological function of pericardium tissues and clinical applications.
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Understanding age-induced alterations to the biomechanical barrier function of human stratum corneum. J Dermatol Sci 2015; 80:94-101. [PMID: 26276440 DOI: 10.1016/j.jdermsci.2015.07.016] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 07/23/2015] [Accepted: 07/29/2015] [Indexed: 11/22/2022]
Abstract
BACKGROUND The appearance and function of human skin are dramatically altered with aging, resulting in higher rates of severe xerosis and other skin complaints. The outermost layer of the epidermis, the stratum corneum (SC), is responsible for the biomechanical barrier function of skin and is also adversely transformed with age. With age the keratin filaments within the corneocytes are prone to crosslinking, the amount of intercellular lipids decreases resulting in fewer lipid bilayers, and the rate of corneocyte turnover decreases. OBJECTIVES The effect of these structural changes on the mechanical properties of the SC has not been determined. Here we determine how several aspects of the SC's mechanical properties are dramatically degraded with age. METHODS We performed a range of biomechanical experiments, including micro-tension, bulge, double cantilever beam, and substrate curvature testing on abdominal stratum corneum from cadaveric female donors ranging in age from 29 to 93 years old. RESULTS We found that the SC stiffens with age, indicating that the keratin fibers stiffen, similarly to collagen fibers in the dermis. The cellular cohesion also increases with age, a result of the altered intercellular lipid structure. The kinetics of water movement through the SC is also decreased. CONCLUSIONS Our results indicate that the combination of structural and mechanical property changes that occur with age are quite significant and may contribute to the prevalence of skin disorders among the elderly.
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18
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Haftek M. Epidermal barrier disorders and corneodesmosome defects. Cell Tissue Res 2014; 360:483-90. [PMID: 25378284 PMCID: PMC4452581 DOI: 10.1007/s00441-014-2019-1] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 09/24/2014] [Indexed: 12/22/2022]
Abstract
Corneodesmosomes are modified desmosomes present in the stratum corneum (SC). They are crucial for SC cohesion and, thus, constitute one of the pivotal elements of the functional protective barrier of human skin. Expression of corneodesmosomes and, notably, the process of their degradation are probably altered during several dermatoses leading to the disruption of the permeability barrier or to abnormal, often compensative, SC accumulation. These different situations are reviewed in the present paper.
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Affiliation(s)
- Marek Haftek
- EA4169 "Fundamental, Clinical and Therapeutic Aspects of the Skin Barrier Function", Université Lyon 1, 8 Avenue Rockefeller, 69373, Lyon, France,
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19
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Von Forell GA, Hyoung PS, Bowden AE. Failure modes and fracture toughness in partially torn ligaments and tendons. J Mech Behav Biomed Mater 2014; 35:77-84. [PMID: 24747098 DOI: 10.1016/j.jmbbm.2014.03.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 03/19/2014] [Accepted: 03/31/2014] [Indexed: 10/25/2022]
Abstract
Ligaments and tendons are commonly torn during injury, yet the likelihood that untreated initial tears could lead to further tearing or even full rupture has proven challenging to predict. In this work, porcine Achilles tendon and human anterior longitudinal ligament samples were tested using both standard fracture toughness methods and complex loading conditions. Failure modes for each of 14 distinct testing cases were evaluated using a total of 131 soft tissue tests. Results showed that these soft tissues were able to completely resist any further crack propagation of an initial tear, regardless of fiber orientation or applied loading condition. Consequently, the major concern for patients with tendon or ligament tears is likely not reduction in ultimate tissue strength due to stress risers at the tip of the tear, but rather a question of whether or not the remaining cross-section is large enough to support the anticipated loading.
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Affiliation(s)
- Gregory A Von Forell
- Brigham Young University, Department of Mechanical Engineering, Provo, UT 84602, USA
| | - Peter S Hyoung
- Brigham Young University, Department of Mechanical Engineering, Provo, UT 84602, USA
| | - Anton E Bowden
- Brigham Young University, Department of Mechanical Engineering, Provo, UT 84602, USA.
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Ananthapadmanabhan K, Mukherjee S, Chandar P. Stratum corneum fatty acids: their critical role in preserving barrier integrity during cleansing. Int J Cosmet Sci 2013; 35:337-45. [DOI: 10.1111/ics.12042] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Accepted: 01/21/2013] [Indexed: 11/28/2022]
Affiliation(s)
| | - S. Mukherjee
- Unilever Research and Development; 40 Merritt Blvd Trumbull CT U.S.A
| | - P. Chandar
- Unilever Research and Development; 40 Merritt Blvd Trumbull CT U.S.A
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Biniek K, Levi K, Dauskardt RH. Solar UV radiation reduces the barrier function of human skin. Proc Natl Acad Sci U S A 2012; 109:17111-6. [PMID: 23027968 PMCID: PMC3479513 DOI: 10.1073/pnas.1206851109] [Citation(s) in RCA: 185] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ubiquitous presence of solar UV radiation in human life is essential for vitamin D production but also leads to skin photoaging, damage, and malignancies. Photoaging and skin cancer have been extensively studied, but the effects of UV on the critical mechanical barrier function of the outermost layer of the epidermis, the stratum corneum (SC), are not understood. The SC is the first line of defense against environmental exposures like solar UV radiation, and its effects on UV targets within the SC and subsequent alterations in the mechanical properties and related barrier function are unclear. Alteration of the SC's mechanical properties can lead to severe macroscopic skin damage such as chapping and cracking and associated inflammation, infection, scarring, and abnormal desquamation. Here, we show that UV exposure has dramatic effects on cell cohesion and mechanical integrity that are related to its effects on the SC's intercellular components, including intercellular lipids and corneodesmosomes. We found that, although the keratin-controlled stiffness remained surprisingly constant with UV exposure, the intercellular strength, strain, and cohesion decreased markedly. We further show that solar UV radiation poses a double threat to skin by both increasing the biomechanical driving force for damage while simultaneously decreasing the skin's natural ability to resist, compromising the critical barrier function of the skin.
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Affiliation(s)
- Krysta Biniek
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
| | - Kemal Levi
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
| | - Reinhold H. Dauskardt
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
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Gerhardt LC, Schmidt J, Sanz-Herrera J, Baaijens F, Ansari T, Peters G, Oomens C. A novel method for visualising and quantifying through-plane skin layer deformations. J Mech Behav Biomed Mater 2012; 14:199-207. [DOI: 10.1016/j.jmbbm.2012.05.014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2012] [Revised: 05/10/2012] [Accepted: 05/22/2012] [Indexed: 10/28/2022]
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Mao G, Flach CR, Mendelsohn R, Walters RM. Imaging the distribution of sodium dodecyl sulfate in skin by confocal Raman and infrared microspectroscopy. Pharm Res 2012; 29:2189-201. [PMID: 22477073 PMCID: PMC3399083 DOI: 10.1007/s11095-012-0748-y] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 03/22/2012] [Indexed: 01/06/2023]
Abstract
Purpose To image SDS distribution across different skin regions, to compare the permeability difference between porcine and human skin, and to evaluate the interaction between SDS and skin. Methods Full thickness porcine and human skin was treated with acyl chain perdeuterated SDS (SDS-d25) at room temperature and at 34 °C for 3, 24 and 40 h. SDS distribution in skin was monitored by confocal Raman and IR microspectroscopic imaging. Permeation profiles of SDS-d25 in skin were derived from the band intensities of the CD2 stretching vibrations. The interaction between SDS and skin was monitored through the CH2 and CD2 stretching frequencies and the Amide I and II spectral region. Results SDS-d25 penetrates both porcine and human skin in a time and temperature-dependent manner, with slightly higher permeability through the stratum corneum (SC) in porcine skin. When SDS permeates into the SC, its chains are more ordered compared to SDS micelles. The secondary structure of keratin in the SC is not affected by SDS-d25. Conclusion The spatial distribution of SDS-d25 in skin was obtained for the first time. Infrared microscopic imaging provides unique opportunities to measure concentration profiles of exogenous materials in skin and offers insights to interaction between permeants and skin. Electronic supplementary material The online version of this article (doi:10.1007/s11095-012-0748-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- G Mao
- Johnson & Johnson Consumer Companies, Inc., 199 Grandview Rd., Skillman, New Jersey 08558-9418, USA.
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24
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Bhushan B. Nanotribological and nanomechanical properties of skin with and without cream treatment using atomic force microscopy and nanoindentation. J Colloid Interface Sci 2012; 367:1-33. [DOI: 10.1016/j.jcis.2011.10.019] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Revised: 10/06/2011] [Accepted: 10/07/2011] [Indexed: 11/16/2022]
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Taylor D, O'Mara N, Ryan E, Takaza M, Simms C. The fracture toughness of soft tissues. J Mech Behav Biomed Mater 2011; 6:139-47. [PMID: 22301183 DOI: 10.1016/j.jmbbm.2011.09.018] [Citation(s) in RCA: 90] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Revised: 09/29/2011] [Accepted: 09/30/2011] [Indexed: 11/28/2022]
Abstract
Fracture toughness is important for any material, but to date there have been few investigations of this mechanical property in soft mammalian tissues. This paper presents new data on porcine muscle tissue and a detailed analysis of all previous work. The conclusion is that, in most cases, fracture toughness has not in fact been measured for these tissues. Reanalysis of the previous work shows that failure of the test specimens generally occurred at the material's ultimate strength, implying that no information about toughness can be obtained from the results. This finding applied to work on cartilage, artificial neocartilage, muscle and the TMJ disc. Our own data, which was also found to be invalid, gave measured fracture toughness values which were highly variable and showed a strong dependence on the crack growth increment. The net-section failure stress and failure energy were relatively constant in large specimens, independent of crack length, whilst for smaller specimens they showed a strong size effect. These findings are explained by the fact that the process zone size, estimated here using the critical distance parameter L, was similar to, or larger than, critical specimen dimensions (crack length and specimen width). Whilst this analysis casts doubt on much of the published literature, a useful finding is that soft tissues are highly tolerant of defects, able to withstand the presence of cracks several millimetres in length without significant loss of strength.
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Affiliation(s)
- David Taylor
- Trinity Centre for Bioengineering, Trinity College Dublin, Dublin, Ireland.
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27
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Levi K, Kwan A, Rhines AS, Gorcea M, Moore DJ, Dauskardt RH. Emollient molecule effects on the drying stresses in human stratum corneum. Br J Dermatol 2011; 163:695-703. [PMID: 20633012 DOI: 10.1111/j.1365-2133.2010.09937.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Emollient molecules are widely used in skin care formulations to improve skin sensory properties and to alleviate dry skin but little is understood regarding their effects on skin biomechanical properties. OBJECTIVES To investigate the effects of emollient molecules on drying stresses in human stratum corneum (SC) and how these stresses are related to SC components and moisture content. METHODS The substrate curvature method was used to measure the drying stresses in isolated SC following exposure to selected emollient molecules. While SC stresses measured using this method have the same biaxial in vivo stress state and moisture exchange with the environment, a limitation of the method is that moisture cannot be replenished by the underlying skin layers. This provides an opportunity to study the direct effects of emollient treatments on the moisture content and the components of the SC. Attenuated total reflectance Fourier transform infrared spectroscopy was used to determine the effects of emollient molecules on SC lipid extraction and conformation. Results Emollient molecules resulted in a complex SC drying stress profile where stresses increased rapidly to peak values and then gradually decreased to significantly lower values compared with the control. The partially occlusive treatments also penetrated into the SC where they caused extraction and changes in lipid conformation. These effects together with their effects on SC moisture content are used to rationalize the drying stress profiles. CONCLUSIONS Emollient molecules have dramatic effects on SC drying stresses that are related to their effects on intercellular lipids and SC moisture content.
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Affiliation(s)
- K Levi
- Department of Materials Science and Engineering, 496 Lomita Mall, Durand Building, Room 121, Stanford University, Stanford, CA 94305-2205, USA
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Levi K, Weber RJ, Do JQ, Dauskardt RH. Drying stress and damage processes in human stratum corneum. Int J Cosmet Sci 2009; 32:276-93. [PMID: 19889042 DOI: 10.1111/j.1468-2494.2009.00557.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
SYNOPSIS The drying stresses that develop in stratum corneum (SC) are crucial for its mechanical and biophysical function, its cosmetic feel and appearance, and play a central role in processes of dry skin damage. However, quantitative methods to characterize these stresses are lacking and little understanding exists regarding the effects of drying environment, chemical exposures and moisturizing treatments. We describe the application of a substrate curvature technique adapted for biological tissue to accurately characterize SC drying stresses as a function of time following environmental pre-conditioning and chemical treatment in a range of drying environments. SC stresses were observed to increase to stress levels of up to approximately 3 MPa over periods of 8 h depending on pretreatment and drying environment. A unique relationship between the SC stress and water in the drying environment was established. The effect of glycerol on lowering SC stresses and damaging surfactants on elevating SC stresses were quantified. Extensions of the method to continuous monitoring of SC stresses in response to changes in environmental moisture content and temperature are reported. Finally, a biomechanics framework to account for the SC drying stress as a mechanical driving force for dry skin damage is presented.
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Affiliation(s)
- K Levi
- Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA
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Effect of Corneodesmosome Degradation on the Intercellular Delamination of Human Stratum Corneum. J Invest Dermatol 2008; 128:2345-7. [DOI: 10.1038/jid.2008.107] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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