1
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Moreira Lana G, Zhang X, Müller C, Hensel R, Arzt E. Film-Terminated Fibrillar Microstructures with Improved Adhesion on Skin-like Surfaces. ACS APPLIED MATERIALS & INTERFACES 2022; 14:46239-46251. [PMID: 36195314 PMCID: PMC9586108 DOI: 10.1021/acsami.2c12663] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Accepted: 09/16/2022] [Indexed: 06/16/2023]
Abstract
Adhesives for interaction with human skin and tissues are needed for multiple applications. Micropatterned dry adhesives are potential candidates, allowing for a conformal contact and glue-free adhesion based on van der Waals interactions. In this study, we investigate the superior adhesion of film-terminated fibrillar microstructures (fibril diameter, 60 μm; aspect ratio, 3) in contact with surfaces of skin-like roughness (Rz 50 μm). Adhesion decays only moderately with increasing roughness, in contrast to unstructured samples. Sinusoidal model surfaces adhere when their wavelengths exceed about four fibril diameters. The film-terminated microstructure exhibits a saturation of the compressive force during application, implying a pressure safety regime protecting delicate counter surfaces. Applications of this novel adhesive concept are foreseen in the fields of wearable electronics and wound dressing.
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Affiliation(s)
- Gabriela Moreira Lana
- INM—Leibniz
Institute for New Materials, Campus D2 2, 66123Saarbrücken, Germany
- Department
of Materials Science and Engineering, Saarland
University, Campus D2
2, 66123Saarbrücken, Germany
| | - Xuan Zhang
- INM—Leibniz
Institute for New Materials, Campus D2 2, 66123Saarbrücken, Germany
| | - Christian Müller
- INM—Leibniz
Institute for New Materials, Campus D2 2, 66123Saarbrücken, Germany
| | - René Hensel
- INM—Leibniz
Institute for New Materials, Campus D2 2, 66123Saarbrücken, Germany
| | - Eduard Arzt
- INM—Leibniz
Institute for New Materials, Campus D2 2, 66123Saarbrücken, Germany
- Department
of Materials Science and Engineering, Saarland
University, Campus D2
2, 66123Saarbrücken, Germany
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2
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Moreira Lana G, Sorg K, Wenzel GI, Hecker D, Hensel R, Schick B, Kruttwig K, Arzt E. Self‐Adhesive Silicone Microstructures for the Treatment of Tympanic Membrane Perforations. ADVANCED NANOBIOMED RESEARCH 2021. [DOI: 10.1002/anbr.202100057] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Affiliation(s)
- Gabriela Moreira Lana
- INM – Leibniz Institute for New Materials Campus D2 2 Saarbrücken 66123 Germany
- Department of Materials Science and Engineering Saarland University Campus D2 2 Saarbrücken 66123 Germany
| | - Katharina Sorg
- Department of Otorhinolaryngology Saarland University Medical Center Homburg 66421 Germany
| | - Gentiana Ioana Wenzel
- Department of Otorhinolaryngology Saarland University Medical Center Homburg 66421 Germany
| | - Dietmar Hecker
- Department of Otorhinolaryngology Saarland University Medical Center Homburg 66421 Germany
| | - René Hensel
- INM – Leibniz Institute for New Materials Campus D2 2 Saarbrücken 66123 Germany
| | - Bernhard Schick
- Department of Otorhinolaryngology Saarland University Medical Center Homburg 66421 Germany
| | - Klaus Kruttwig
- INM – Leibniz Institute for New Materials Campus D2 2 Saarbrücken 66123 Germany
| | - Eduard Arzt
- INM – Leibniz Institute for New Materials Campus D2 2 Saarbrücken 66123 Germany
- Department of Materials Science and Engineering Saarland University Campus D2 2 Saarbrücken 66123 Germany
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3
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A Self-Adhesive Elastomeric Wound Scaffold for Sensitive Adhesion to Tissue. Polymers (Basel) 2019; 11:polym11060942. [PMID: 31159156 PMCID: PMC6630294 DOI: 10.3390/polym11060942] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/21/2019] [Accepted: 05/24/2019] [Indexed: 12/18/2022] Open
Abstract
Pressure sensitive adhesives based on silicone materials are used particularly for skin adhesion, e.g., the fixation of electrocardiogram (ECG) electrodes or wound dressings. However, adhesion to sensitive tissue structures is not sufficiently addressed due to the risk of damage or rupture. We propose an approach in which a poly-(dimethylsiloxane) (PDMS)-based soft skin adhesive (SSA) acts as cellular scaffold for wound healing. Due to the intrinsically low surface free energy of silicone elastomers, functionalization strategies are needed to promote the attachment and spreading of eukaryotic cells. In the present work, the effect of physical adsorption of three different proteins on the adhesive properties of the soft skin adhesive was investigated. Fibronectin adsorption slightly affects adhesion but significantly improves the cellular interaction of L929 murine fibroblasts with the polymeric surface. Composite films were successfully attached to explanted tympanic membranes. This demonstrates the potential of protein functionalized SSA to act as an adhesive scaffold in delicate biomedical applications.
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4
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Boyadzhieva S, Fischer SCL, Lösch S, Rutz A, Arzt E, Kruttwig K. Thin Film Composite Silicon Elastomers for Cell Culture and Skin Applications: Manufacturing and Characterization. J Vis Exp 2018. [PMID: 30035765 PMCID: PMC6102035 DOI: 10.3791/57573] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin adhesives. Two different poly-(dimethyl siloxanes) (PDMS and soft skin adhesive (SSA)), have been used for in depth investigation of biological effects and adhesive characteristics. The composite films consist of a flexible backing layer and an adhesive top coating. Both layers have been manufactured by doctor blade application technique. In the present investigation, the adhesive behavior of the composite films has been investigated as a function of the layer thickness or a variation of the Young's modulus of the top layer. The Young's modulus of PDMS has been changed by varying the base to crosslinker mixing ratio. In addition, the thickness of SSA films has been varied from approx. 16 µm to approx. 320 µm. Scanning electron microscopy (SEM) and optical microscopy have been used for thickness measurements. The adhesive properties of elastomer films depend strongly on the film thickness, the Young's modulus of the polymers and surface characteristics. Therefore, normal adhesion of these films on glass substrates exhibiting smooth and rough surfaces has been investigated. Pull-off stress and work of separation are dependent on the mixing ratio of silicone elastomers. Additionally, the thickness of the soft skin adhesive placed on top of a supportive backing layer has been varied in order to produce patches for skin applications. Cytotoxicity, proliferation and cellular adhesion of L929 murine fibroblasts on PDMS films (mixing ratio 10:1) and SSA films (mixing ratio 50:50) have been conducted. We have shown here, for the first time, the side by side comparison of thin composite films manufactured of both polymers and present the investigation of their biological- and adhesive properties.
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Affiliation(s)
- Silviya Boyadzhieva
- INM - Leibniz Institute for New Materials; Department of Materials Science and Engineering, Saarland University
| | - Sarah C L Fischer
- INM - Leibniz Institute for New Materials; Department of Materials Science and Engineering, Saarland University
| | - Svenja Lösch
- INM - Leibniz Institute for New Materials; University of Applied Sciences Kaiserslautern
| | | | - Eduard Arzt
- INM - Leibniz Institute for New Materials; Department of Materials Science and Engineering, Saarland University
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5
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Vasilak L, Tanu Halim SM, Das Gupta H, Yang J, Kamperman M, Turak A. Statistical Paradigm for Organic Optoelectronic Devices: Normal Force Testing for Adhesion of Organic Photovoltaics and Organic Light-Emitting Diodes. ACS APPLIED MATERIALS & INTERFACES 2017; 9:13347-13356. [PMID: 28322055 DOI: 10.1021/acsami.6b15618] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In this study, we assess the utility of a normal force (pull-test) approach to measuring adhesion in organic solar cells and organic light-emitting diodes. This approach is a simple and practical method of monitoring the impact of systematic changes in materials, processing conditions, or environmental exposure on interfacial strength and electrode delamination. The ease of measurement enables a statistical description with numerous samples, variant geometry, and minimal preparation. After examining over 70 samples, using the Weibull modulus and the characteristic breaking strength as metrics, we were able to successfully differentiate the adhesion values between 8-tris(hydroxyquinoline aluminum) (Alq3) and poly(3-hexyl-thiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) interfaces with Al and between two annealing times for the bulk heterojunction polymer blends. Additionally, the Weibull modulus, a relative measure of the range of flaw sizes at the fracture plane, can be correlated with the roughness of the organic surface. Finite element modeling of the delamination process suggests that the out-of-plane elastic modulus for Alq3 is lower than the reported in-plane elastic values. We suggest a statistical treatment of a large volume of tests be part of the standard protocol for investigating adhesion to accommodate the unavoidable variability in morphology and interfacial structure found in most organic devices.
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Affiliation(s)
| | | | | | - Juan Yang
- Department of Physical Chemistry and Soft Matter, Wageningen University , Wageningen 6708 PB, Netherlands
| | - Marleen Kamperman
- Department of Physical Chemistry and Soft Matter, Wageningen University , Wageningen 6708 PB, Netherlands
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6
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Fischer SCL, Arzt E, Hensel R. Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates. ACS APPLIED MATERIALS & INTERFACES 2017; 9:1036-1044. [PMID: 27997118 PMCID: PMC5235241 DOI: 10.1021/acsami.6b11642] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Accepted: 12/06/2016] [Indexed: 05/22/2023]
Abstract
The benefits of synthetic fibrillar dry adhesives for temporary and reversible attachment to hard objects with smooth surfaces have been successfully demonstrated in previous studies. However, surface roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. Toward this aim, we introduce cylindrical two-phase single pillars, which are composed of a mechanically stiff stalk and a soft tip layer. Adhesion to smooth and rough substrates is shown to exceed that of conventional pillar structures. The adhesion characteristics can be tuned by varying the thickness of the soft tip layer, the ratio of the Young's moduli and the curvature of the interface between the two phases. For rough substrates, adhesion values similar to those obtained on smooth substrates were achieved. Our concept of composite pillars overcomes current practical limitations caused by surface roughness and opens up fields of application where roughness is omnipresent.
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Affiliation(s)
- Sarah C. L. Fischer
- INM−Leibniz
Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
- Department
of Materials Science and Engineering, Saarland
University, Campus D2
2, 66123 Saarbrücken, Germany
| | - Eduard Arzt
- INM−Leibniz
Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
- Department
of Materials Science and Engineering, Saarland
University, Campus D2
2, 66123 Saarbrücken, Germany
| | - René Hensel
- INM−Leibniz
Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
- Phone: +49 (0)681-9300-390. Fax: +49 (0)681-9300-223. E-mail:
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7
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Purtov J, Frensemeier M, Kroner E. Switchable Adhesion in Vacuum Using Bio-Inspired Dry Adhesives. ACS APPLIED MATERIALS & INTERFACES 2015; 7:24127-35. [PMID: 26457864 PMCID: PMC4642880 DOI: 10.1021/acsami.5b07287] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 10/12/2015] [Indexed: 05/26/2023]
Abstract
Suction based attachment systems for pick and place handling of fragile objects like glass plates or optical lenses are energy-consuming and noisy and fail at reduced air pressure, which is essential, e.g., in chemical and physical vapor deposition processes. Recently, an alternative approach toward reversible adhesion of sensitive objects based on bioinspired dry adhesive structures has emerged. There, the switching in adhesion is achieved by a reversible buckling of adhesive pillar structures. In this study, we demonstrate that these adhesives are capable of switching adhesion not only in ambient air conditions but also in vacuum. Our bioinspired patterned adhesive with an area of 1 cm(2) provided an adhesion force of 2.6 N ± 0.2 N in air, which was reduced to 1.9 N ± 0.2 N if measured in vacuum. Detachment was induced by buckling of the structures due to a high compressive preload and occurred, independent of air pressure, at approximately 0.9 N ± 0.1 N. The switch in adhesion was observed at a compressive preload between 5.6 and 6.0 N and was independent of air pressure. The difference between maximum adhesion force and adhesion force after buckling gives a reasonable window of operation for pick and place processes. High reversibility of the switching behavior is shown over 50 cycles in air and in vacuum, making the bioinspired switchable adhesive applicable for handling operations of fragile objects.
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Affiliation(s)
- Julia Purtov
- Department
of Materials Science and Engineering, Saarland
University, Campus D2 2, 66123 Saarbrücken, Germany
- INM − Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Mareike Frensemeier
- Department
of Materials Science and Engineering, Saarland
University, Campus D2 2, 66123 Saarbrücken, Germany
- INM − Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Elmar Kroner
- INM − Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
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8
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Bauer CT, Kroner E, Fleck NA, Arzt E. Hierarchical macroscopic fibrillar adhesives: in situ study of buckling and adhesion mechanisms on wavy substrates. BIOINSPIRATION & BIOMIMETICS 2015; 10:066002. [PMID: 26496128 DOI: 10.1088/1748-3190/10/6/066002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Nature uses hierarchical fibrillar structures to mediate temporary adhesion to arbitrary substrates. Such structures provide high compliance such that the flat fibril tips can be better positioned with respect to asperities of a wavy rough substrate. We investigated the buckling and adhesion of hierarchically structured adhesives in contact with flat smooth, flat rough and wavy rough substrates. A macroscopic model for the structural adhesive was fabricated by molding polydimethylsiloxane into pillars of diameter in the range of 0.3-4.8 mm, with up to three different hierarchy levels. Both flat-ended and mushroom-shaped hierarchical samples buckled at preloads one quarter that of the single level structures. We explain this behavior by a change in the buckling mode; buckling leads to a loss of contact and diminishes adhesion. Our results indicate that hierarchical structures can have a strong influence on the degree of adhesion on both flat and wavy substrates. Strategies are discussed that achieve highly compliant substrates which adhere to rough substrates.
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Affiliation(s)
- Christina T Bauer
- INM-Leibniz Institute for New Materials, Campus D2 2, D-66123 Saarbrücken, Germany. Saarland University, Campus D2 2, D-66123 Saarbrücken, Germany
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9
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Frensemeier M, Kaiser JS, Frick CP, Schneider AS, Arzt E, Fertig RS, Kroner E. Temperature-Induced Switchable Adhesion using Nickel-Titanium-Polydimethylsiloxane Hybrid Surfaces. ADVANCED FUNCTIONAL MATERIALS 2015; 25:3013-3021. [PMID: 26120295 PMCID: PMC4478996 DOI: 10.1002/adfm.201500437] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 03/16/2015] [Indexed: 05/03/2023]
Abstract
A switchable dry adhesive based on a nickel-titanium (NiTi) shape-memory alloy with an adhesive silicone rubber surface has been developed. Although several studies investigate micropatterned, bioinspired adhesive surfaces, very few focus on reversible adhesion. The system here is based on the indentation-induced two-way shape-memory effect in NiTi alloys. NiTi is trained by mechanical deformation through indentation and grinding to elicit a temperature-induced switchable topography with protrusions at high temperature and a flat surface at low temperature. The trained surfaces are coated with either a smooth or a patterned adhesive polydimethylsiloxane (PDMS) layer, resulting in a temperature-induced switchable surface, used for dry adhesion. Adhesion tests show that the temperature-induced topographical change of the NiTi influences the adhesive performance of the hybrid system. For samples with a smooth PDMS layer the transition from flat to structured state reduces adhesion by 56%, and for samples with a micropatterned PDMS layer adhesion is switchable by nearly 100%. Both hybrid systems reveal strong reversibility related to the NiTi martensitic phase transformation, allowing repeated switching between an adhesive and a nonadhesive state. These effects have been discussed in terms of reversible changes in contact area and varying tilt angles of the pillars with respect to the substrate surface.
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Affiliation(s)
- Mareike Frensemeier
- Saarland University Campus D 2 2, 66123, Saarbrücken, Germany ; INM - Leibniz Institute for New Materials Campus D 2 2, 66123, Saarbrücken, Germany
| | - Jessica S Kaiser
- INM - Leibniz Institute for New Materials Campus D 2 2, 66123, Saarbrücken, Germany
| | - Carl P Frick
- Department of Mechanical Engineering, University of Wyoming Department 3295, 1000 E University Ave, Laramie, WY, 82071, USA
| | - Andreas S Schneider
- INM - Leibniz Institute for New Materials Campus D 2 2, 66123, Saarbrücken, Germany
| | - Eduard Arzt
- Saarland University Campus D 2 2, 66123, Saarbrücken, Germany ; INM - Leibniz Institute for New Materials Campus D 2 2, 66123, Saarbrücken, Germany
| | - Ray S Fertig
- Department of Mechanical Engineering, University of Wyoming Department 3295, 1000 E University Ave, Laramie, WY, 82071, USA
| | - Elmar Kroner
- INM - Leibniz Institute for New Materials Campus D 2 2, 66123, Saarbrücken, Germany
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10
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Isla PY, Kroner E. A Novel Bioinspired Switchable Adhesive with Three Distinct Adhesive States. ADVANCED FUNCTIONAL MATERIALS 2015; 25:2444-2450. [PMID: 26366145 PMCID: PMC4553704 DOI: 10.1002/adfm.201500241] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Revised: 02/13/2015] [Indexed: 05/25/2023]
Abstract
A novel switchable adhesive, inspired by the gecko's fibrillar dry attachment system, is introduced. It consists of a patterned surface with an array of mushroom-shaped pillars having two distinct heights. The different pillar heights allow control of the pull-off force in two steps by application of a low and a high preload. For low preload, only the long pillars form contact, resulting in a low pull-off force. At higher preload, all pillars form contact, resulting in high pull-off force. Even further loading leads to buckling induced detachment of the pillars which corresponds to extremely low pull-off force. To achieve the respective samples a new fabrication method called double inking is developed, to achieve multiple-height pillar structures. The adhesion performance of the two-step switchable adhesive is analysed at varying preload and for different pillar aspect ratios and height relations. Finally, the deformation behavior of the samples is investigated by in situ monitoring.
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Affiliation(s)
- Paula Yagüe Isla
- INM - Leibniz Institute for New Materials Campus D2 2, 66123, Saarbrücken, Germany E-mail: ; Saarland University Campus D2 2, 66123, Saarbrücken, Germany
| | - Elmar Kroner
- INM - Leibniz Institute for New Materials Campus D2 2, 66123, Saarbrücken, Germany E-mail:
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11
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Brodoceanu D, Elnathan R, Prieto-Simón B, Delalat B, Guinan T, Kroner E, Voelcker NH, Kraus T. Dense arrays of uniform submicron pores in silicon and their applications. ACS APPLIED MATERIALS & INTERFACES 2015; 7:1160-1169. [PMID: 25493543 DOI: 10.1021/am506891d] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report a versatile particle-based route to dense arrays of parallel submicron pores with high aspect ratio in silicon and explore the application of these arrays in sensors, optics, and polymer micropatterning. Polystyrene (PS) spheres are convectively assembled on gold-coated silicon wafers and sputter-etched, resulting in well-defined gold disc arrays with excellent long-range order. The gold discs act as catalysts in metal-assisted chemical etching, yielding uniform pores with straight walls, flat bottoms, and high aspect ratio. The resulting pore arrays can be used as robust antireflective surfaces, in biosensing applications, and as templates for polymer replica molding.
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Affiliation(s)
- Daniel Brodoceanu
- INM-Leibniz Institute for New Materials , Campus D2 2, 66123, Saarbrücken, Germany
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12
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Jin X, Heepe L, Strueben J, Adelung R, Gorb SN, Staubitz A. Challenges and Solutions for Joining Polymer Materials. Macromol Rapid Commun 2014; 35:1551-70. [DOI: 10.1002/marc.201400200] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 05/18/2014] [Indexed: 12/13/2022]
Affiliation(s)
- Xin Jin
- Institute for Materials Science; Faculty of Engineering; University of Kiel; Kaiserstr. 2 24143 Kiel Germany
| | - Lars Heepe
- Zoological Institute: Functional Morphology and Biomechanics; University of Kiel; Am Botanischen Garten 1-9 24098 Kiel Germany
| | - Jan Strueben
- Otto-Diels-Institute for Organic Chemistry; University of Kiel; Otto-Hahn-Platz 4 24098 Kiel Germany
| | - Rainer Adelung
- Institute for Materials Science; Faculty of Engineering; University of Kiel; Kaiserstr. 2 24143 Kiel Germany
| | - Stanislav N. Gorb
- Zoological Institute: Functional Morphology and Biomechanics; University of Kiel; Am Botanischen Garten 1-9 24098 Kiel Germany
| | - Anne Staubitz
- Otto-Diels-Institute for Organic Chemistry; University of Kiel; Otto-Hahn-Platz 4 24098 Kiel Germany
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13
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Micciché M, Arzt E, Kroner E. Single macroscopic pillars as model system for bioinspired adhesives: influence of tip dimension, aspect ratio, and tilt angle. ACS APPLIED MATERIALS & INTERFACES 2014; 6:7076-7083. [PMID: 24779439 DOI: 10.1021/am405873j] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The goal of our study is to better understand the design parameters of bioinspired dry adhesives inspired by geckos. For this, we fabricated single macroscopic pillars of 400 μm diameter with different aspect ratios and different tip shapes (i.e., flat tips, spherical tips with different radii, and mushroom tips with different diameters). Tilt-angle-dependent adhesion measurements showed that although the tip shape of the pillars strongly influences the pull-off force, the pull-off strength is similar for flat and mushroom-shaped tips. We found no tilt-angle dependency of adhesion for spherical tip structures and, except for high tilt angle and low preload experiments, no tilt-angle effect for mushroom-tip pillars. For flat-tip pillars, we found a strong influence of tilt angle on adhesion, which decreased linearly with increasing aspect ratio. The experiments show that for the tested aspect ratios between 1 and 5, a linear decrease of tilt-angle dependency is found. The results of our studies will help to design bioinspired adhesives for application on smooth and rough surfaces.
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Affiliation(s)
- Maurizio Micciché
- INM - Leibniz Institute for New Materials, Functional Microstructures Group, Campus D2 2, 66123 Saarbrücken, Germany
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14
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Bioinspired polymeric surface patterns for medical applications. J Appl Biomater Funct Mater 2013; 10:287-92. [PMID: 23242878 DOI: 10.5301/jabfm.2012.10365] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/10/2012] [Indexed: 11/20/2022] Open
Abstract
PURPOSE A powerful principle in nature is the presence of surface patterns to improve specific characteristics or to enable completely new functions. Here, we present two case studies where bioinspired surface patterns based on the adhesive system of geckos may be applied for biomedical applications: residue-free adhesion to skin and gecko-inspired suture threads for knot-free wound closure. METHODS Gecko-inspired skin adhesives were fabricated by soft lithography of polydimethylsiloxane with successive inking and dipping steps. Their adhesion was measured using a home built adhesion tester designed for patterned surfaces. Preliminary lap shear tests on the back of a human hand were also performed. Commercial suture threads from different materials were patterned in the group of A. del Campo at the Max-Planck-Institute for Polymer Research (Mainz, Germany) using oxygen plasma. The treated threads were pulled through artificial skin in both directions measuring the peak force and the pull through force. RESULTS AND CONCLUSIONS Unpatterned reference samples of the skin adhesive did not stick to human skin, while the patterned samples all showed notable adhesion up to 1.2 Newton for a sample size of approximately 3 cm². First results with the patterned suture threads indicated that the surface patterning of the thread has only a minor effect on the pull-through forces. To achieve knot-free sewing the surface geometry of the suture threads needs to be optimized and more realistic testing procedures, e.g. testing on human skin, are necessary.
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15
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Bartlett MD, Crosby AJ. Scaling normal adhesion force capacity with a generalized parameter. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:11022-11027. [PMID: 23924148 DOI: 10.1021/la4013526] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The adhesive response of a rigid flat cylindrical indenter in contact with a compliant elastic layer of varying confinement is investigated experimentally and described analytically. Using a soft elastic gel with substrate thickness, t, and indenter radius, a, 28 unique combinations of the confinement parameter, a/t, are examined over a range of 0.016 < a/t < 7.2. Continuous force capacity predictions as a function of a/t and material properties are provided through a scaling theory and are found to agree well with the experimental data. We further collapse all of the data over orders of magnitude in adhesive force capacity onto a single line described by a generalized reversible adhesion scaling parameter, A/C, where A is the contact area and C is the compliance. As the scaling analysis does not assume a specific separation mechanism the adhesive force capacity is well described during both axisymmetric edge separation and during interfacial fingering and cavitation instabilities. We discuss how the geometry of the contact, specifically increasing the degree of confinement, allows reversible adhesive materials to be designed that are not "sticky" or "tacky", yet can be very strong and provide high performance.
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Affiliation(s)
- Michael D Bartlett
- Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, Massachusetts 01003, USA
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16
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Paretkar D, Kamperman M, Martina D, Zhao J, Creton C, Lindner A, Jagota A, McMeeking R, Arzt E. Preload-responsive adhesion: effects of aspect ratio, tip shape and alignment. J R Soc Interface 2013; 10:20130171. [PMID: 23554348 DOI: 10.1098/rsif.2013.0171] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We tested the adhesive response of polymer surfaces structured with arrays of cylindrical fibrils having diameters of 10-20 µm and aspect ratios 1-2.4. Fibrils had two different tip shapes of end-flaps and round edges. A preload-induced mechanical buckling instability of the fibrils was used to switch between the states of adhesion and non-adhesion. Non-adhesion in fibrils with round edges was reached at preloads that caused fibril buckling, whereas fibrils with end-flaps showed adhesion loss only at very high preloads. The round edge acted as a circumferential flaw prohibiting smooth tip contact recovery leading to an adhesion loss. In situ observations showed that, after reversal of buckling, the end-flaps unfold and re-form contact under prevailing compressive stress, retaining adhesion in spite of buckling. At very high preloads, however, end-flaps are unable to re-form contact resulting in adhesion loss. Additionally, the end-flaps showed varying contact adaptability as a function of the fibril-probe alignment, which further affects the preload for adhesion loss. The combined influence of preload, tip shape and alignment on adhesion can be used to switch adhesion in bioinspired fibrillar arrays.
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Affiliation(s)
- Dadhichi Paretkar
- INM-Leibniz Institute for New Materials, Functional Surfaces Group, Saarland University, Saarbruecken, Germany.
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