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Boas M, Burman M, Yarin AL, Zussman E. Electrically-responsive deformation of polyelectrolyte complex (PEC) fibrous membrane. POLYMER 2018. [DOI: 10.1016/j.polymer.2018.10.064] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Raut HK, Baji A, Hariri HH, Parveen H, Soh GS, Low HY, Wood KL. Gecko-Inspired Dry Adhesive Based on Micro-Nanoscale Hierarchical Arrays for Application in Climbing Devices. ACS APPLIED MATERIALS & INTERFACES 2018; 10:1288-1296. [PMID: 29214798 DOI: 10.1021/acsami.7b09526] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The unusual ability of geckos to climb vertical walls underlies a unique combination of a hierarchical structural design and a stiffer material composition. While a dense array of microscopic hierarchical structures enables the gecko toe pads to adhere to various surfaces, a stiffer material (β-keratin) composition enables them to maintain reliable adhesion over innumerable cycles. This unique strategy has been seldom implemented in engineered dry adhesives because fabrication of high-aspect-ratio hierarchical structures using a stiffer polymer is challenging. Herein, we report the fabrication of high-aspect-ratio hierarchical arrays on flexible polycarbonate sheets (stiffness comparable to that of β-keratin) by a sacrificial-layer-mediated nanoimprinting technique. Dry-adhesive films comprising the hierarchical arrays showed a formidable shear adhesion of 11.91 ± 0.43 N/cm2. Cyclic adhesion tests also showed that the shear adhesion of the adhesive films reduced by only about 20% after 50 cycles and remained nearly constant until about 200 cycles. Most importantly, the high-aspect-ratio hierarchical arrays were integrated onto the feet of a miniature robot and the locomotion on a 30° inclined surface was demonstrated.
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Affiliation(s)
- Hemant Kumar Raut
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
| | - Avinash Baji
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
| | - Hassan Hussein Hariri
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
| | - Hashina Parveen
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
| | - Gim Song Soh
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
| | - Hong Yee Low
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
| | - Kristin L Wood
- Division of Engineering Product Development, Singapore University of Technology and Design , 8 Somapah Rd, Singapore 487372, Republic of Singapore
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Cranford SW, Han L, Ortiz C, Buehler MJ. Mutable polyelectrolyte tube arrays: mesoscale modeling and lateral force microscopy. SOFT MATTER 2017; 13:5543-5557. [PMID: 28731083 DOI: 10.1039/c7sm00864c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In this study, the pH-dependent friction of layer-by-layer assemblies of poly(allylamine hydrochloride) and poly(acrylic acid) (PAH/PAA) are quantified for microtube array structures via experimental and simulated lateral force microscopy (LFM). A novel coarse-grain tube model is developed, utilizing a molecular dynamics (MD) framework with a Hertzian soft contact potential (such that F ∼ δ3/2) to allow the efficient dynamic simulation of 3D arrays consisting of hundreds of tubes at micrometer length scales. By quantitatively comparing experimental LFM and computational results, the coupling between geometry (tube spacing and swelling) and material properties (intrinsic stiffness) results in a transition from bending dominated deformation to bending combined with inter-tube contact, independent of material adhesion assumptions. Variation of tube spacing (and thus control of contact) can be used to exploit the normal and lateral resistance of the tube arrays as a function of pH (2.0/5.5), beyond the effect of areal tube density, with increased resistances (potential mutability) up to a factor of ∼60. This study provides a novel modeling platform to assess and design dynamic polyelectrolyte-based substrates/coatings with tailorable stimulus-responsive surface friction. Our results show that micro-geometry can be used alongside stimulus-responsive material changes to amplify and systematically tune mutability.
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Affiliation(s)
- Steven W Cranford
- Center for Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, USA.
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Lee WL, Low HY, Ortiz C. Geometry-dependent compressive responses in nanoimprinted submicron-structured shape memory polyurethane. SOFT MATTER 2017; 13:3314-3327. [PMID: 28418057 DOI: 10.1039/c7sm00574a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
High resolution surface textures, when rationally designed, provide an attractive surface engineering approach to enhance surface functionalities. Designing smart surfaces by coupling surface texture with shape memory polymers has garnered attention in achieving tunable mechanical properties. We investigate the structure-mechanical property relationships for programmable, shape-memorizing submicron-scale pillar arrays subjected to flat-punch compression. The geometrically-dependent deformation of structured surfaces with two different aspect ratios (250 nm-pillars 1 : 1 and 550 nm-pillars 2.4 : 1) were investigated, and their moduli were found to be lower than that of non-patterned surface. From finite element analysis, the pillar deformation is correlated to a mechanistic transition from a discrete, unidirectional compression of 250 nm-pillars to lateral constraints caused by interpillar contact in 550 nm-pillars. This lateral pillar-pillar contact in the 550 nm-pillars resulted in an increased and maximum strain-dependent modulus but lower elastic recovery and energy dissipation as compared with the 250 nm-pillars. Furthermore, the compressive responses of temporarily shaped pillars (programmed by stretching) were compared with the permanently shaped pillars. The extent of lateral constraints controlled by pillar shape and spacing in 550 nm-pillars was responsible for the modulus differences between the original and stretched patterns, whereas the modulus of 250 nm-pillars remained as a constant value with different levels of stretching. This study provides mechanistic insights into how the mechanical behavior can be modulated by designing the aspect ratio of shape memory pillar arrays and by programming the surface geometry, thus revealing the potential of developing ingenious designs of responsive surfaces sensitive to mechanical deformation.
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Affiliation(s)
- Wei Li Lee
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
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Li Q, Qu F, Han B, Wang C, Li H, Mauck RL, Han L. Micromechanical anisotropy and heterogeneity of the meniscus extracellular matrix. Acta Biomater 2017; 54:356-366. [PMID: 28242455 PMCID: PMC5413404 DOI: 10.1016/j.actbio.2017.02.043] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 02/22/2017] [Accepted: 02/23/2017] [Indexed: 02/07/2023]
Abstract
To understand how the complex biomechanical functions of the meniscus are endowed by the nanostructure of its extracellular matrix (ECM), we studied the anisotropy and heterogeneity in the micromechanical properties of the meniscus ECM. We used atomic force microscopy (AFM) to quantify the time-dependent mechanical properties of juvenile bovine meniscus at deformation length scales corresponding to the diameters of collagen fibrils. At this scale, anisotropy in the elastic modulus of the circumferential fibers, the major ECM structural unit, can be attributed to differences in fibril deformation modes: uncrimping when normal to the fiber axis, and laterally constrained compression when parallel to the fiber axis. Heterogeneity among different structural units is mainly associated with their variations in microscale fiber orientation, while heterogeneity across anatomical zones is due to alterations in collagen fibril diameter and alignment at the nanoscale. Unlike the elastic modulus, the time-dependent properties are more homogeneous and isotropic throughout the ECM. These results enable a detailed understanding of the meniscus structure-mechanics at the nanoscale, and can serve as a benchmark for understanding meniscus biomechanical functions, documenting disease progression and designing tissue repair strategies. STATEMENT OF SIGNIFICANCE Meniscal damage is a common cause of joint injury, which can lead to the development of post-traumatic osteoarthritis among young adults. Restoration of meniscus function requires repairing its highly heterogeneous and complex extracellular matrix. Employing AFM, this study quantifies the anisotropic and heterogeneous features of the meniscus ECM structure and mechanics. The micromechanical properties are interpreted within the context of the collagen fibril nanostructure and its variation with tissue anatomical locations. These results provide a fundamental structure-mechanics knowledge benchmark, against which, repair and regeneration strategies can be developed and evaluated with respect to the specialized structural and functional complexity of the native tissue.
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Affiliation(s)
- Qing Li
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States
| | - Feini Qu
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States; Translational Musculoskeletal Research Center, Philadelphia Veterans Administration Medical Center, Philadelphia, PA 19104, United States
| | - Biao Han
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States
| | - Chao Wang
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States
| | - Hao Li
- College of Architecture and the Built Environment, Philadelphia University, Philadelphia, PA 19144, United States
| | - Robert L Mauck
- McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States; Translational Musculoskeletal Research Center, Philadelphia Veterans Administration Medical Center, Philadelphia, PA 19104, United States
| | - Lin Han
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA 19104, United States.
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Han B, Chery DR, Yin J, Lu XL, Lee D, Han L. Nanomechanics of layer-by-layer polyelectrolyte complexes: a manifestation of ionic cross-links and fixed charges. SOFT MATTER 2016; 12:1158-1169. [PMID: 26599600 DOI: 10.1039/c5sm01430a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
This study investigates the roles of two distinct features of ionically cross-linked polyelectrolyte networks - ionic cross-links and fixed charges - in determining their nanomechanical properties. The layer-by-layer assembled poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) network is used as the model material. The densities of ionic cross-links and fixed charges are modulated through solution pH and ionic strength (IS), and the swelling ratio, elastic and viscoelastic properties are quantified via an array of atomic force microscopy (AFM)-based nanomechanical tools. The roles of ionic cross-links are underscored by the distinctive elastic and viscoelastic nanomechanical characters observed here. First, as ionic cross-links are highly sensitive to solution conditions, the instantaneous modulus, E0, exhibits orders-of-magnitude changes upon pH- and IS-governed swelling, distinctive from the rubber elasticity prediction based on permanent covalent cross-links. Second, ionic cross-links can break and self-re-form, and this mechanism dominates force relaxation of PAH/PAA under a constant indentation depth. In most states, the degree of relaxation is >90%, independent of ionic cross-link density. The importance of fixed charges is highlighted by the unexpectedly more elastic nature of the network despite low ionic cross-link density at pH 2.0, IS 0.01 M. Here, the complex is a net charged, loosely cross-linked, where the degree of relaxation is attenuated to ≈50% due to increased elastic contribution arising from fixed charge-induced Donnan osmotic pressure. In addition, this study develops a new method for quantifying the thickness of highly swollen polymer hydrogel films. It also underscores important technical considerations when performing nanomechanical tests on highly rate-dependent polymer hydrogel networks. These results provide new insights into the nanomechanical characters of ionic polyelectrolyte complexes, and lay the ground for further investigation of their unique time-dependent properties.
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Affiliation(s)
- Biao Han
- School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104, USA.
| | - Daphney R Chery
- School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104, USA.
| | - Jie Yin
- Department of Mechanical Engineering, Temple University, Philadelphia, PA 19122, USA
| | - X Lucas Lu
- Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA
| | - Daeyeon Lee
- Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Lin Han
- School of Biomedical Engineering, Science, and Health Systems, Drexel University, Philadelphia, PA 19104, USA.
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7
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Borges J, Mano JF. Molecular Interactions Driving the Layer-by-Layer Assembly of Multilayers. Chem Rev 2014; 114:8883-942. [DOI: 10.1021/cr400531v] [Citation(s) in RCA: 609] [Impact Index Per Article: 60.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- João Borges
- 3B’s
Research Group—Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark, Zona Industrial da Gandra,
S. Cláudio do Barco 4806-909 Caldas das Taipas, Guimarães, Portugal
- ICVS/3B’s
− PT Government Associate Laboratory, Braga/Guimarães, Portugal
| | - João F. Mano
- 3B’s
Research Group—Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark, Zona Industrial da Gandra,
S. Cláudio do Barco 4806-909 Caldas das Taipas, Guimarães, Portugal
- ICVS/3B’s
− PT Government Associate Laboratory, Braga/Guimarães, Portugal
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Song J, Jańczewski D, Guo Y, Xu J, Vancso GJ. Redox responsive nanotubes from organometallic polymers by template assisted layer by layer fabrication. NANOSCALE 2013; 5:11692-11698. [PMID: 24100304 DOI: 10.1039/c3nr03927g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Redox responsive nanotubes were fabricated by the template assisted layer-by-layer (LbL) assembly method and employed as platforms for molecular payload release. Positively and negatively charged organometallic poly(ferrocenylsilane)s (PFS) were used to construct the nanotubes, in combination with other polyions. During fabrication, multilayers of these polyions were deposited onto the inner pores of template porous membranes, followed by subsequent removal of the template. Anodized porous alumina and track-etched polycarbonate membranes were used as templates. The morphology, electrochemistry, composition and other properties of the obtained tubular structure were characterized by fluorescence microscopy, scanning (SEM) and transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy. Composite nanotubes, consisting of poly(acrylic acid) anions with PFS(+) and nanoparticles including fluorophore labelled dextran and decorated quantum dots, with PFS polyelectrolytes were also fabricated, broadening the scope of the structures. Cyclic voltammograms of PFS containing nanotubes showed similar redox responsive behaviour to thin LbL assembled films. Redox triggered release of labelled macromolecules from these tubular structures demonstrated application potential in controlled molecular delivery.
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Affiliation(s)
- Jing Song
- Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Research Link 3, 117602, Singapore
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Ghostine RA, Markarian MZ, Schlenoff JB. Asymmetric Growth in Polyelectrolyte Multilayers. J Am Chem Soc 2013; 135:7636-46. [DOI: 10.1021/ja401318m] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Ramy A. Ghostine
- Department of Chemistry
and Biochemistry, The Florida State University, Tallahassee, Florida
32306-4390, United States
| | - Marie Z. Markarian
- Department of Chemistry
and Biochemistry, The Florida State University, Tallahassee, Florida
32306-4390, United States
| | - Joseph B. Schlenoff
- Department of Chemistry
and Biochemistry, The Florida State University, Tallahassee, Florida
32306-4390, United States
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10
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Cranford SW, Buehler MJ. Variation of Weak Polyelectrolyte Persistence Length through an Electrostatic Contour Length. Macromolecules 2012. [DOI: 10.1021/ma3008465] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Steven W. Cranford
- Center for Materials Science
and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United
States
- Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-235A&B, Cambridge, Massachusetts 02139, United States
| | - Markus J. Buehler
- Center for Materials Science
and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United
States
- Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-235A&B, Cambridge, Massachusetts 02139, United States
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