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Hasan MM, Dunn AC. Adhesion Mechanics and Detachment Dynamics of Vanishing Surface Layers on Hydrogels. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:20406-20415. [PMID: 39303160 DOI: 10.1021/acs.langmuir.4c01740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/22/2024]
Abstract
Cross-linked hydrogel surfaces exhibit reduced stiffness when polymerized against polymeric hydrophobic surfaces. As such, these layers play a critical role in contact mechanics, particularly exhibiting strong relative adhesion with colloidal probes when the contact area is small. This prevents the use of continuum models of adhesive soft contact. To connect mechanisms of stretch to the force response, depth-controlled nanoindentation experiments were conducted on polyacrylamide (pAAM) hydrogel samples using colloidal probe atomic force microscopy (AFM). The pAAM sample had a high water content of >90% and was molded against polyoxymethylene (POM) to create a more dilute surface layer with thickness ∼0.5 μm. Indentations to multiple depths between 50 nm and 1.25 μm were repeated 10 times each. First, the force drops during the unloading, and separation segments of each indentation were characterized. This described the detachment progression for increasing areas of contact, revealing that the pull-off force for a single chain was in the single-pN range. Second, the stretched polymer network was modeled as an array of parallel, linear springs. Assuming a constant areal chain density of α = 100 chains/μm2, the maximum force of adhesion was plotted versus the volume of chains stretched upward, and the average chain stiffness was calculated from a linear fit to be 22.8 × 10-6 N/m. A Weibull distribution analysis of detachment events revealed a dependence of chain stiffness on maximum indentation depth (dmax), with higher stiffness at shallower depths approaching kchain ≈ 20 × 10-6 N/m. These findings on adhesion mechanics between a vanishing hydrogel surface and probe can guide the development of multifunctional hydrogels for various biomedical applications.
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Affiliation(s)
- Md Mahmudul Hasan
- Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, 1206 W Green St, Urbana, Illinois 61801, United States
| | - Alison C Dunn
- Department of Mechanical and Aerospace Engineering, University of Florida, 1064 Center Dr, Gainesville, Florida 32611, United States
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Chau AL, Karnaukh KM, Maskiewicz I, Read de Alaniz J, Pitenis AA. Photoresponsive hydrogel friction. SOFT MATTER 2024; 20:7227-7236. [PMID: 39225393 DOI: 10.1039/d4sm00677a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/04/2024]
Abstract
Photoresponsive hydrogels are an emerging class of stimuli-responsive materials that exhibit changes in physical or chemical properties in response to light. Previous investigations have leveraged photothermal mechanisms to achieve reversible changes in hydrogel friction, although few have focused on photochemical means. To date, the tribological properties of photoswitchable hydrogels (e.g., friction and lubrication) have remained underexplored. In this work, we incorporated photoresponsive methoxy-spiropyran-methacrylate monomers (methoxy-SP-MA) into a hydrogel network to form a copolymerized system of poly(N-isopropylacrylamide-co-2-acrylamido-2-methylpropane sulfonic acid-co-methoxy-spiropyran-methacrylate) (p(NIPAAm-co-AMPS-co-SP)). We demonstrated repeatable photoresponsive changes to swelling, friction, and stiffness over three light cycles. Our findings suggest that volume changes driven by the decreased hydrophilicity of the methoxy-SP-MA upon light irradiation are responsible for differences in the mechanical and tribological properties of our photoresponsive hydrogels. Our results could inform future designs of photoswitchable hydrogels for applications ranging from biomedical applications to soft robotics.
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Affiliation(s)
- Allison L Chau
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, USA.
| | - Kseniia M Karnaukh
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA, USA.
| | - Ian Maskiewicz
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA, USA.
| | - Javier Read de Alaniz
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA, USA.
| | - Angela A Pitenis
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, USA.
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3
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Wang H, Wang Q, Su Y, Wang J, Zhang X, Liu Y, Zhang J. Thermosensitive Triblock Copolymer for Slow-Release Lubricants under Ocular Conditions. ACS APPLIED MATERIALS & INTERFACES 2024; 16:1675-1687. [PMID: 38127457 DOI: 10.1021/acsami.3c12389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
The ocular environment is crucial for a biological lubrication system. An unstable condition of tear film may cause a series of ocular diseases due to serious friction, such as dry eye syndrome, which has drawn extensive attention nowadays. In this study, an in vitro biocompatible superlubricity system, containing thermogelling copolymers (PCGA-PEG-PCGA) and slow-release lubricant (PEG 300/Tween 80), was constructed. First, the sol-gel transition temperature and gel strength of PCGA-PEG-PCGA were adjusted based on the ocular environment by regulating the length of PCGA blocks. Furthermore, the copolymer hydrogel exhibited a reliable slow-release property within 10 days and showed low cytotoxicity. Then, the superlubricity (coefficient of friction of approximately 0.005) was achieved with its released PEG 300/Tween 80 aqueous solution at the sliding velocity range of 1-100 mm s-1 and pressure range of 10-22 kPa. However, the lubrication behaviors varied, while PEG 300 chains and Tween 80 micelles were demonstrated to form a multilayer and a single layer adsorption structure on the sliding surface, respectively. On the whole, the composite lubrication systems, especially the one composed of Tween 80, showed excellent tribological properties owing to the stable slow-release and full hydration effects under ocular conditions, which hold great potential for improving ocular lubrication and maintaining human visual health.
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Affiliation(s)
- Hongdong Wang
- School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai 200444, China
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
| | - Qi Wang
- School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai 200444, China
| | - Yunjuan Su
- School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai 200444, China
| | - Junyu Wang
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
| | - Xiacong Zhang
- Department of Polymer Materials, School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
| | - Yuhong Liu
- State Key Laboratory of Tribology in Advanced Equipment, Tsinghua University, Beijing 100084, China
| | - Jianhua Zhang
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai 200444, China
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4
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Chau A, Edwards CER, Helgeson ME, Pitenis AA. Designing Superlubricious Hydrogels from Spontaneous Peroxidation Gradients. ACS APPLIED MATERIALS & INTERFACES 2023; 15:43075-43086. [PMID: 37650860 PMCID: PMC10510045 DOI: 10.1021/acsami.3c04636] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Accepted: 08/17/2023] [Indexed: 09/01/2023]
Abstract
Hydrogels are hydrated three-dimensional networks of hydrophilic polymers that are commonly used in the biomedical industry due to their mechanical and structural tunability, biocompatibility, and similar water content to biological tissues. The surface structure of hydrogels polymerized through free-radical polymerization can be modified by controlling environmental oxygen concentrations, leading to the formation of a polymer concentration gradient. In this work, 17.5 wt % polyacrylamide hydrogels are polymerized in low (0.01 mol % O2) and high (20 mol % O2) oxygen environments, and their mechanical and tribological properties are characterized through microindentation, nanoindentation, and tribological sliding experiments. Without significantly reducing the elastic modulus of the hydrogel (E* ≈ 200 kPa), we demonstrate an order of magnitude reduction in friction coefficient (from μ = 0.021 ± 0.006 to μ = 0.002 ± 0.001) by adjusting polymerization conditions (e.g., oxygen concentration). A quantitative analytical model based on polyacrylamide chemistry and kinetics was developed to estimate the thickness and structure of the monomer conversion gradient, termed the "surface gel layer". We find that polymerizing hydrogels at high oxygen concentrations leads to the formation of a preswollen surface gel layer that is approximately five times thicker (t ≈ 50 μm) and four times less concentrated (≈ 6% monomer conversion) at the surface prior to swelling compared to low oxygen environments (t ≈ 10 μm, ≈ 20% monomer conversion). Our model could be readily modified to predict the preswollen concentration profile of the polyacrylamide gel surface layer for any reaction conditions─monomer and initiator concentration, oxygen concentration, reaction time, and reaction media depth─or used to select conditions that correspond to a certain desired surface gel layer profile.
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Affiliation(s)
- Allison
L. Chau
- Materials
Department, University of California, Santa
Barbara, Santa
Barbara, California 93106, United States
- Materials
Research Laboratory, University of California,
Santa Barbara, Santa Barbara, California 93106, United States
| | - Chelsea E. R. Edwards
- Materials
Research Laboratory, University of California,
Santa Barbara, Santa Barbara, California 93106, United States
- Department
of Chemical Engineering, University of California,
Santa Barbara, Santa Barbara, California 93106, United States
| | - Matthew E. Helgeson
- Materials
Research Laboratory, University of California,
Santa Barbara, Santa Barbara, California 93106, United States
- Department
of Chemical Engineering, University of California,
Santa Barbara, Santa Barbara, California 93106, United States
| | - Angela A. Pitenis
- Materials
Department, University of California, Santa
Barbara, Santa
Barbara, California 93106, United States
- Materials
Research Laboratory, University of California,
Santa Barbara, Santa Barbara, California 93106, United States
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5
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Mees J, O'Connor TC, Pastewka L. Entropic stress of grafted polymer chains in shear flow. J Chem Phys 2023; 159:094902. [PMID: 37668251 DOI: 10.1063/5.0158245] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 08/14/2023] [Indexed: 09/06/2023] Open
Abstract
We analyze the shear response of grafted polymer chains in shear flow via coarse-grained molecular dynamics simulations with an explicit solvent. We find that the solvent flow penetrates into almost the whole brush for "mushroom"-type brushes but only a few bond distances for dense brushes. In all cases, the external stress on the wall equals the entropic stress associated with the distorted polymer conformations. We find that the external stress increases linearly with shear rate at low rates and sublinearly at high rates. The transition from linear to sublinear scaling occurs where chains react to flow by reorienting. Sublinear scaling with shear rate disappears if the shear rate is nondimensionalized with the effective relaxation time of chain subsegments located in the outer part of the brush that experiences flow.
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Affiliation(s)
- Jan Mees
- Department of Microsystems Engineering, University of Freiburg, Georges-Köhler-Allee 103, Freiburg 79110, Germany
- Cluster of Excellence LivMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, Freiburg 79110, Germany
| | - Thomas C O'Connor
- Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
| | - Lars Pastewka
- Department of Microsystems Engineering, University of Freiburg, Georges-Köhler-Allee 103, Freiburg 79110, Germany
- Cluster of Excellence LivMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, Freiburg 79110, Germany
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Nguyen DT, Pedro DI, Pepe A, Rosa JG, Bowman JI, Trachsel L, Golde GR, Suzuki I, Lavrador JM, Nguyen NTY, Kis MA, Smolchek RA, Diodati N, Liu R, Phillpot SR, Webber AR, Castillo P, Sayour EJ, Sumerlin BS, Sawyer WG. Bioconjugation of COL1 protein on liquid-like solid surfaces to study tumor invasion dynamics. Biointerphases 2023; 18:021001. [PMID: 36898958 PMCID: PMC10008099 DOI: 10.1116/6.0002083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 02/02/2023] [Accepted: 02/08/2023] [Indexed: 03/12/2023] Open
Abstract
Tumor invasion is likely driven by the product of intrinsic and extrinsic stresses, reduced intercellular adhesion, and reciprocal interactions between the cancer cells and the extracellular matrix (ECM). The ECM is a dynamic material system that is continuously evolving with the tumor microenvironment. Although it is widely reported that cancer cells degrade the ECM to create paths for migration using membrane-bound and soluble enzymes, other nonenzymatic mechanisms of invasion are less studied and not clearly understood. To explore tumor invasion that is independent of enzymatic degradation, we have created an open three-dimensional (3D) microchannel network using a novel bioconjugated liquid-like solid (LLS) medium to mimic both the tortuosity and the permeability of a loose capillary-like network. The LLS is made from an ensemble of soft granular microgels, which provides an accessible platform to investigate the 3D invasion of glioblastoma (GBM) tumor spheroids using in situ scanning confocal microscopy. The surface conjugation of the LLS microgels with type 1 collagen (COL1-LLS) enables cell adhesion and migration. In this model, invasive fronts of the GBM microtumor protruded into the proximal interstitial space and may have locally reorganized the surrounding COL1-LLS. Characterization of the invasive paths revealed a super-diffusive behavior of these fronts. Numerical simulations suggest that the interstitial space guided tumor invasion by restricting available paths, and this physical restriction is responsible for the super-diffusive behavior. This study also presents evidence that cancer cells utilize anchorage-dependent migration to explore their surroundings, and geometrical cues guide 3D tumor invasion along the accessible paths independent of proteolytic ability.
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Affiliation(s)
- D. T. Nguyen
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - D. I. Pedro
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - A. Pepe
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - J. G. Rosa
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - J. I. Bowman
- Department of Chemistry, College of Liberal Arts and Sciences, College of Medicine University of Florida, Gainesville, Florida 3261
| | - L. Trachsel
- Department of Chemistry, College of Liberal Arts and Sciences, College of Medicine University of Florida, Gainesville, Florida 3261
| | - G. R. Golde
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - I. Suzuki
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - J. M. Lavrador
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - N. T. Y. Nguyen
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - M. A. Kis
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - R. A. Smolchek
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - N. Diodati
- Department of Mechanical and Aerospace Engineering, Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - R. Liu
- Department of Surgery, College of Medicine University of Florida, Gainesville, Florida 3261
| | - S. R. Phillpot
- Department of Materials Science and Engineering Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - A. R. Webber
- Department of Materials Science and Engineering Herbert Wertheim College of Engineering, College of Medicine University of Florida, Gainesville, Florida 3261
| | - P. Castillo
- Department of Pediatrics, College of Medicine University of Florida, Gainesville, Florida 3261
| | | | - B. S. Sumerlin
- Department of Chemistry, College of Liberal Arts and Sciences, College of Medicine University of Florida, Gainesville, Florida 3261
| | - W. G. Sawyer
- Author to whom correspondence should be addressed:
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7
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Zhou Z, Chu Y, Hou Z, Zhou X, Cao Y. Modification of Frictional Properties of Hydrogel Surface via Laser Ablated Topographical Micro-Textures. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:4103. [PMID: 36432390 PMCID: PMC9696626 DOI: 10.3390/nano12224103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 11/10/2022] [Accepted: 11/18/2022] [Indexed: 06/16/2023]
Abstract
Hydrogels and biological cartilage tissues are highly similar in structure and composition due to their unique characteristics such as high-water content and low friction coefficients. The introduction of hydrogel cartilage can effectively reduce the friction coefficient and wear coefficient of the original bone joint and the implanted metal bone joint (generally titanium alloy or stainless steel), which is considered as a perfect replacement material for artificial articular cartilage. How to accurately regulate the local tribological characteristics of hydrogel artificial cartilage according to patient weight and bone shape is one of the important challenges in the current clinical application field of medical hydrogels. In this study, the mechanism by which micro-pits improve the surface friction properties was studied. Ultraviolet lasers were used to efficiently construct micro-pits with different shapes on a polyvinyl alcohol hydrogel in one step. It was shown that by using such a maskless laser processing, the performance of each part of the artificial cartilage can be customized flexibly and effectively. We envision that the approach demonstrated in this article will provide an important idea for the development of a high-performance, continuous and accurate method for controlling surface friction properties of artificial cartilage.
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Affiliation(s)
- Zhuangzhuang Zhou
- International Science and Technology Cooperation Base for Laser Processing Robot, Zhejiang Provincial Key Laboratory of Laser Processing Robot, Wenzhou University, Wenzhou 325035, China
| | - Yihang Chu
- School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Zhishan Hou
- International Science and Technology Cooperation Base for Laser Processing Robot, Zhejiang Provincial Key Laboratory of Laser Processing Robot, Wenzhou University, Wenzhou 325035, China
| | - Xiaopeng Zhou
- International Science and Technology Cooperation Base for Laser Processing Robot, Zhejiang Provincial Key Laboratory of Laser Processing Robot, Wenzhou University, Wenzhou 325035, China
- School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
| | - Yu Cao
- International Science and Technology Cooperation Base for Laser Processing Robot, Zhejiang Provincial Key Laboratory of Laser Processing Robot, Wenzhou University, Wenzhou 325035, China
- Oujiang Laboratory (Zhejiang Lab for Regenerative Medicine, Vision and Brain Health), Wenzhou University, Wenzhou 325000, China
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8
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Composition controls soft hydrogel surface layer dimensions and contact mechanics. Biointerphases 2022; 17:061002. [DOI: 10.1116/6.0002047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Hydrogels are soft hydrated polymer networks that are widely used in research and industry due to their favorable properties and similarity to biological tissues. However, it has long been difficult to create a hydrogel emulating the heterogeneous structure of special tissues, such as cartilage. One potential avenue to develop a structural variation in a hydrogel is the “mold effect,” which has only recently been discovered to be caused by absorbed oxygen within the mold surface interfering with the polymerization. This induces a dilute gradient-density surface layer with altered properties. However, the precise structure of the gradient-surface layer and its contact response have not yet been characterized. Such knowledge would prove useful for designs of composite hydrogels with altered surface characteristics. To fully characterize the hydrogel gradient-surface layer, we created five hydrogel compositions of varying monomer and cross-linker content to encompass variations in the layer. Then, we used particle exclusion microscopy during indentation and creep experiments to probe the contact response of the gradient layer of each composition. These experiments showed that the dilute structure of the gradient layer follows evolving contact behavior allowing poroelastic squeeze-out at miniscule pressures. Stiffer compositions had thinner gradient layers. This knowledge can potentially be used to create hydrogels with a stiff load-bearing bulk with altered surface characteristics tailored for specific tribological applications.
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Mostakhdemin M, Nand A, Ramezani M. Tribological Evaluation of Silica Nanoparticle Enhanced Bilayer Hydrogels as A Candidate for Cartilage Replacement. Polymers (Basel) 2022; 14:polym14173593. [PMID: 36080668 PMCID: PMC9460628 DOI: 10.3390/polym14173593] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2022] [Revised: 08/20/2022] [Accepted: 08/23/2022] [Indexed: 11/24/2022] Open
Abstract
Polymeric hydrogels can be used as artificial replacement for lesioned cartilage. However, modulating the hydrogel formulation that mimics articular cartilage tissue with respect to mechanical and tribological properties has remained a challenge. This study encompasses the tribological evaluation of a silica nanoparticle (SNP) loaded bilayer nanocomposite hydrogel (NCH), synthesized using acrylamide, acrylic acid, and alginate via modulated free-radical polymerization. Multi-factor pin-on-plate sliding wear experiments were carried out with a steel ball counterface using a linear reciprocating tribometer. Tribological properties of NCHs with 0.6 wt% SNPs showed a significant improvement in the wear resistance of the lubricious layer and a low coefficient of friction (CoF). CoF of both non-reinforced hydrogel (NRH) and NCH at maximum contact pressure ranged from 0.006 to 0.008, which is in the order of the CoF of healthy articular cartilage. Interfacial surface energy was analysed according to Johnson, Kendall, and Robert’s theory, and NCHs showed superior mechanical properties and surface energy compared to NRHs. Lubrication regimes’ models were drawn based on the Stribeck chart parameters, and CoF results were highlighted in the elastoviscous transition regime.
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Affiliation(s)
- Mohammad Mostakhdemin
- Department of Mechanical Engineering, Auckland University of Technology, Auckland 1010, New Zealand
- Correspondence: (M.M.); (M.R.)
| | - Ashveen Nand
- Faculty of Engineering, University of Auckland, Auckland 1010, New Zealand
| | - Maziar Ramezani
- Department of Mechanical Engineering, Auckland University of Technology, Auckland 1010, New Zealand
- Correspondence: (M.M.); (M.R.)
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Chau AL, Getty PT, Rhode AR, Bates CM, Hawker CJ, Pitenis AA. Superlubricity of pH-responsive hydrogels in extreme environments. Front Chem 2022; 10:891519. [PMID: 36034669 PMCID: PMC9405656 DOI: 10.3389/fchem.2022.891519] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 06/28/2022] [Indexed: 11/13/2022] Open
Abstract
Poly(acrylamide-co-acrylic acid) (P(AAm-co-AA)) hydrogels are highly tunable and pH-responsive materials frequently used in biomedical applications. The swelling behavior and mechanical properties of these gels have been extensively characterized and are thought to be controlled by the protonation state of the acrylic acid (AA) through the regulation of solution pH. However, their tribological properties have been underexplored. Here, we hypothesized that electrostatics and the protonation state of AA would drive the tribological properties of these polyelectrolyte gels. P(AAm-co-AA) hydrogels were prepared with constant acrylamide (AAm) concentration (33 wt%) and varying AA concentration to control the amount of ionizable groups in the gel. The monomer:crosslinker molar ratio (200:1) was kept constant. Hydrogel swelling, stiffness, and friction behavior were studied by systematically varying the acrylic acid (AA) concentration from 0-12 wt% and controlling solution pH (0.35, 7, 13.8) and ionic strength (I = 0 or 0.25 M). The stiffness and friction coefficient of bulk hydrogels were evaluated using a microtribometer and borosilicate glass probes as countersurfaces. The swelling behavior and elastic modulus of these polyelectrolyte hydrogels were highly sensitive to solution pH and poorly predicted the friction coefficient (µ), which decreased with increasing AA concentration. P(AAm-co-AA) hydrogels with the greatest AA concentrations (12 wt%) exhibited superlubricity (µ = 0.005 ± 0.001) when swollen in unbuffered, deionized water (pH = 7, I = 0 M) and 0.5 M NaOH (pH = 13.8, I = 0.25 M) (µ = 0.005 ± 0.002). Friction coefficients generally decreased with increasing AA and increasing solution pH. We postulate that tunable lubricity in P(AAm-co-AA) gels arises from changes in the protonation state of acrylic acid and electrostatic interactions between the probe and hydrogel surface.
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Affiliation(s)
- Allison L. Chau
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Patrick T. Getty
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Andrew R. Rhode
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Christopher M. Bates
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, United States
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Craig J. Hawker
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, United States
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA, United States
| | - Angela A. Pitenis
- Materials Department, University of California, Santa Barbara, Santa Barbara, CA, United States
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11
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Nepita I, Stocchino A, Dodero A, Castellano M, Ferrara M, Romano MR, Repetto R. Dynamic Pressure Measurements During Vitrectomy in a Model of the Eye. Transl Vis Sci Technol 2022; 11:21. [PMID: 35583885 PMCID: PMC9123487 DOI: 10.1167/tvst.11.5.21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Purpose To accurately evaluate pressure changes during vitrectomy in a rigid model of the vitreous chamber and to test the efficiency of the EVA phacovitrectomy system (Dutch Ophthalmic Research Center) in terms of compensation of intraocular pressure variations. Methods We tested 23-, 25-, and 27-gauge double-blade vitreous cutters in both vented global pressure control and automatic infusion compensation (AIC) modes in a vitreous chamber model, mimicking the real surgical procedure. Balanced salt solution and artificial vitreous, similar to the real vitreous body, were used. We tested both standard-flow (SF) and high-flow (HF) infusion systems, varying the infusion pressure between 20 and 40 mm Hg. In each experiment, flow rate was also measured. Results Pressure drop was rapidly and efficiently compensated when 23- and 25-gauge cutters were used in AIC mode, with infusion pressures ranging between 30 and 55 mm Hg. The 27-gauge cutter was less efficient in compensating pressure variations. Pressure fluctuations related to the high-frequency motion of the cutter blade were small compared to the overall pressure variations. The use of the HF infusion system resulted in larger flow rates and lower pressure changes compared to the SF infusion system. Conclusions Despite the rigid material of the model, the present pressure measurements are in line with previous studies performed on porcine eye. The use of AIC mode compensates intraoperative pressure drops efficiently, with both 23- and 25-gauge cutters. The HF infusion system is more efficient than the SF infusion system. Translational Relevance The AIC infusion mode efficiently compensates intraoperative pressure drops, in both 23- and 25-gauge experimental vitrectomy. The HF infusion system resulted in larger flow rate and lower pressure changes.
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Affiliation(s)
- Irene Nepita
- Nanoscopy and NIC@IIT, Istituto Italiano di Tecnologia, Genoa, Italy
| | - Alessandro Stocchino
- Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong
| | - Andrea Dodero
- Adolphe Merkle Institute, University of Fribourg, Fribourg, Switzerland.,Department of Chemistry and Industrial Chemistry, University of Genoa, Genoa, Italy
| | - Maila Castellano
- Department of Chemistry and Industrial Chemistry, University of Genoa, Genoa, Italy
| | | | - Mario R Romano
- Department of Biomedical Sciences, Humanitas University, Pieve Emanuele-Milan, Italy.,Ophthalmology Department, Humanitas Gavazzeni-Castelli, Bergamo, Italy
| | - Rodolfo Repetto
- Department of Civil, Chemical and Environmental Engineering, University of Genoa, Genoa, Italy
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12
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13
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Qin T, Liao W, Yu L, Zhu J, Wu M, Peng Q, Han L, Zeng H. Recent progress in conductive self‐healing hydrogels for flexible sensors. JOURNAL OF POLYMER SCIENCE 2022. [DOI: 10.1002/pol.20210899] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Tao Qin
- College of Health Science and Environmental Engineering Shenzhen Technology University Shenzhen China
| | - Wenchao Liao
- College of Health Science and Environmental Engineering Shenzhen Technology University Shenzhen China
| | - Li Yu
- College of Health Science and Environmental Engineering Shenzhen Technology University Shenzhen China
| | - Junhui Zhu
- College of Health Science and Environmental Engineering Shenzhen Technology University Shenzhen China
| | - Meng Wu
- Chemical and Materials Engineering University of Alberta Edmonton Alberta Canada
| | - Qiongyao Peng
- Chemical and Materials Engineering University of Alberta Edmonton Alberta Canada
| | - Linbo Han
- College of Health Science and Environmental Engineering Shenzhen Technology University Shenzhen China
- Chemical and Materials Engineering University of Alberta Edmonton Alberta Canada
| | - Hongbo Zeng
- Chemical and Materials Engineering University of Alberta Edmonton Alberta Canada
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14
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Gu Y, Distler ME, Cheng HF, Huang C, Mirkin CA. A General DNA-Gated Hydrogel Strategy for Selective Transport of Chemical and Biological Cargos. J Am Chem Soc 2021; 143:17200-17208. [PMID: 34614359 DOI: 10.1021/jacs.1c08114] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The selective transport of molecular cargo is critical in many biological and chemical/materials processes and applications. Although nature has evolved highly efficient in vivo biological transport systems, synthetic transport systems are often limited by the challenges associated with fine-tuning interactions between cargo and synthetic or natural transport barriers. Herein, deliberately designed DNA-DNA interactions are explored as a new modality for selective DNA-modified cargo transport through DNA-grafted hydrogel supports. The chemical and physical characteristics of the cargo and hydrogel barrier, including the number of nucleic acid strands on the cargo (i.e., the cargo valency) and DNA-DNA binding strength, can be used to regulate the efficiency of cargo transport. Regimes exist where a cargo-barrier interaction is attractive enough to yield high selectivity yet high mobility, while there are others where the attractive interactions are too strong to allow mobility. These observations led to the design of a DNA-dendron transport tag, which can be used to universally modify macromolecular cargo so that the barrier can differentiate specific species to be transported. These novel transport systems that leverage DNA-DNA interactions provide new chemical insights into the factors that control selective cargo mobility in hydrogels and open the door to designing a wide variety of drug/probe-delivery systems.
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Affiliation(s)
- Yuwei Gu
- Department of Chemistry and International Institute for Nanotechnology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Max E Distler
- Department of Chemistry and International Institute for Nanotechnology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Ho Fung Cheng
- Department of Chemistry and International Institute for Nanotechnology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Chi Huang
- Department of Chemistry and International Institute for Nanotechnology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Chad A Mirkin
- Department of Chemistry and International Institute for Nanotechnology, Northwestern University, Evanston, Illinois 60208-3113, United States
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15
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Sarkar A, Soltanahmadi S, Chen J, Stokes JR. Oral tribology: Providing insight into oral processing of food colloids. Food Hydrocoll 2021. [DOI: 10.1016/j.foodhyd.2021.106635] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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16
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Simič R, Mandal J, Zhang K, Spencer ND. Oxygen inhibition of free-radical polymerization is the dominant mechanism behind the "mold effect" on hydrogels. SOFT MATTER 2021; 17:6394-6403. [PMID: 34132302 PMCID: PMC8262556 DOI: 10.1039/d1sm00395j] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 06/07/2021] [Indexed: 05/27/2023]
Abstract
Hydrogel surfaces are of great importance in numerous applications ranging from cell-growth studies and hydrogel-patch adhesion to catheter coatings and contact lenses. A common method to control the structure and mechanical/tribological properties of hydrogel surfaces is by synthesizing them in various mold materials, whose influence has been widely ascribed to their hydrophobicity. In this work, we examine possible mechanisms for this "mold effect" on the surface of hydrogels during polymerization. Our results for polyacrylamide gels clearly rule out the effect of mold hydrophobicity as well as any thermal-gradient effects during synthesis. We show unequivocally that oxygen diffuses out of certain molding materials and into the reaction mixture, thereby inhibiting free-radical polymerization in the vicinity of the molding interface. Removal of oxygen from the system results in homogeneously cross-linked hydrogel surfaces, irrespective of the substrate material used. Moreover, by varying the amount of oxygen at the surface of the polymerizing solutions using a permeable membrane we are able to tailor the surface structures and mechanical properties of PAAm, PEGDA and HEMA hydrogels in a controlled manner.
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Affiliation(s)
- Rok Simič
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland.
| | - Joydeb Mandal
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland.
| | - Kaihuan Zhang
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland.
| | - Nicholas D Spencer
- Laboratory for Surface Science and Technology, Department of Materials, ETH Zürich, Switzerland.
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17
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Mostakhdemin M, Nand A, Ramezani M. Articular and Artificial Cartilage, Characteristics, Properties and Testing Approaches-A Review. Polymers (Basel) 2021; 13:2000. [PMID: 34207194 PMCID: PMC8234542 DOI: 10.3390/polym13122000] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 06/13/2021] [Accepted: 06/14/2021] [Indexed: 12/25/2022] Open
Abstract
The design and manufacture of artificial tissue for knee joints have been highlighted recently among researchers which necessitates an apt approach for its assessment. Even though most re-searches have focused on specific mechanical or tribological tests, other aspects have remained underexplored. In this review, elemental keys for design and testing artificial cartilage are dis-cussed and advanced methods addressed. Articular cartilage structure, its compositions in load-bearing and tribological properties of hydrogels, mechanical properties, test approaches and wear mechanisms are discussed. Bilayer hydrogels as a niche in tissue artificialization are presented, and recent gaps are assessed.
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Affiliation(s)
- Mohammad Mostakhdemin
- Department of Mechanical Engineering, Auckland University of Technology, Auckland 1142, New Zealand
| | - Ashveen Nand
- School of Environmental and Animal Sciences, Unitec Institute of Technology, Auckland 1025, New Zealand;
- School of Healthcare and Social Practice, Unitec Institute of Technology, Auckland 1025, New Zealand
| | - Maziar Ramezani
- Department of Mechanical Engineering, Auckland University of Technology, Auckland 1142, New Zealand
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18
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Firipis K, Boyd-Moss M, Long B, Dekiwadia C, Hoskin W, Pirogova E, Nisbet DR, Kapsa RMI, Quigley AF, Williams RJ. Tuneable Hybrid Hydrogels via Complementary Self-Assembly of a Bioactive Peptide with a Robust Polysaccharide. ACS Biomater Sci Eng 2021; 7:3340-3350. [PMID: 34125518 DOI: 10.1021/acsbiomaterials.1c00675] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Synthetic materials designed for improved biomimicry of the extracellular matrix must contain fibrous, bioactive, and mechanical cues. Self-assembly of low molecular weight gelator (LMWG) peptides Fmoc-DIKVAV (Fmoc-aspartic acid-isoleucine-lysine-valine-alanine-valine) and Fmoc-FRGDF (Fmoc-phenylalanine-arginine-glycine-aspartic acid-phenylalanine) creates fibrous and bioactive hydrogels. Polysaccharides such as agarose are biocompatible, degradable, and non-toxic. Agarose and these Fmoc-peptides have both demonstrated efficacy in vitro and in vivo. These materials have complementary properties; agarose has known mechanics in the physiological range but is inert and would benefit from bioactive and topographical cues found in the fibrous, protein-rich extracellular matrix. Fmoc-DIKVAV and Fmoc-FRGDF are synthetic self-assembling peptides that present bioactive cues "IKVAV" and "RGD" designed from the ECM proteins laminin and fibronectin. The work presented here demonstrates that the addition of agarose to Fmoc-DIKVAV and Fmoc-FRGDF results in physical characteristics that are dependent on agarose concentration. The networks are peptide-dominated at low agarose concentrations, and agarose-dominated at high agarose concentrations, resulting in distinct changes in structural morphology. Interestingly, at mid-range agarose concentration, a hybrid network is formed with structural similarities to both peptide and agarose systems, demonstrating reinforced mechanical properties. Bioactive-LMWG polysaccharide hydrogels demonstrate controllable microenvironmental properties, providing the ability for tissue-specific biomaterial design for tissue engineering and 3D cell culture.
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Affiliation(s)
- Kate Firipis
- Biofab3D, Aikenhead Centre for Medical Discovery, St Vincent's Hospital Melbourne, Fitzroy, VIC 3065, Australia.,Biomedical and Electrical Engineering, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia
| | - Mitchell Boyd-Moss
- Biofab3D, Aikenhead Centre for Medical Discovery, St Vincent's Hospital Melbourne, Fitzroy, VIC 3065, Australia.,Biomedical and Electrical Engineering, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia.,Institute of Mental and Physical Health and Clinical Translation, School of Medicine, Deakin University, Waurn Ponds, VIC 3216, Australia
| | - Benjamin Long
- Faculty of Science and Technology, Federation University, Mt. Helen, VIC 3350, Australia
| | - Chaitali Dekiwadia
- RMIT Microscopy and MicroAnalysis Facility (RMMF), RMIT University, Melbourne, Vic 3000, Australia
| | - William Hoskin
- Faculty of Science and Technology, Federation University, Mt. Helen, VIC 3350, Australia
| | - Elena Pirogova
- Biomedical and Electrical Engineering, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia
| | - David R Nisbet
- Laboratory of Advanced Biomaterials, The Australian National University, Acton, Canberra 2601, Australia
| | - Robert M I Kapsa
- Biofab3D, Aikenhead Centre for Medical Discovery, St Vincent's Hospital Melbourne, Fitzroy, VIC 3065, Australia.,Biomedical and Electrical Engineering, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia.,ARC Centre of Excellence in Electromaterials Science, Department of Medicine, Melbourne University, St Vincent's Hospital Melbourne, Fitzroy, Victoria 3065, Australia.,Department of Medicine, St Vincent's Hospital Melbourne, University of Melbourne, Fitzroy, Vic 3065, Australia
| | - Anita F Quigley
- Biofab3D, Aikenhead Centre for Medical Discovery, St Vincent's Hospital Melbourne, Fitzroy, VIC 3065, Australia.,Biomedical and Electrical Engineering, School of Engineering, RMIT University, Melbourne, VIC 3000, Australia.,ARC Centre of Excellence in Electromaterials Science, Department of Medicine, Melbourne University, St Vincent's Hospital Melbourne, Fitzroy, Victoria 3065, Australia.,Department of Medicine, St Vincent's Hospital Melbourne, University of Melbourne, Fitzroy, Vic 3065, Australia
| | - Richard J Williams
- Biofab3D, Aikenhead Centre for Medical Discovery, St Vincent's Hospital Melbourne, Fitzroy, VIC 3065, Australia.,Institute of Mental and Physical Health and Clinical Translation, School of Medicine, Deakin University, Waurn Ponds, VIC 3216, Australia
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19
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Persson BNJ. Side-leakage of face mask. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:75. [PMID: 34089395 PMCID: PMC8179097 DOI: 10.1140/epje/s10189-021-00081-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 05/20/2021] [Indexed: 05/02/2023]
Abstract
Face masks are used to trap particles (or fluid drops) in a porous material (filter) in order to avoid or reduce the transfer of particles between the human lungs (or mouth and nose) and the external environment. The air exchange between the lungs and the environment is assumed to occur through the face mask filter. However, if the resistance to air flow through the filter is high some air (and accompanied particles) will leak through the filter-skin interface. In this paper I will present a model study of the side-leakage problem.
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Affiliation(s)
- B N J Persson
- PGI-1, FZ Jülich, Jülich, Germany.
- Multiscale Consulting, Wolfshovener str. 2, 52428, Jülich, Germany.
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20
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Porte E, Cann P, Masen M. A lubrication replenishment theory for hydrogels. SOFT MATTER 2020; 16:10290-10300. [PMID: 33047773 DOI: 10.1039/d0sm01236j] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Hydrogels are suggested as less invasive alternatives to total joint replacements, but their inferior tribological performance compared to articular cartilage remains a barrier to implementation. Existing lubrication theories do not fully characterise the friction response of all hydrogels, and a better insight into the lubrication mechanisms must be established to enable optimised hydrogel performance. We therefore studied the lubricating conditions in a hydrogel contact using fluorescent imaging under simulated physiological sliding conditions. A reciprocating configuration was used to examine the effects of contact dimension and stroke length on the lubricant replenishment in the contact. The results show that the lubrication behaviour is strongly dependent on the contact configurations; When the system operates in a 'migrating' configuration, with the stroke length larger than the contact width, the contact is uniformly lubricated and shows low friction; When the contact is in an 'overlapping' configuration with a stroke length smaller than the contact width, the contact is not fully replenished, resulting in high friction. The mechanism of non-replenishment at small relative stroke length was also observed in a cartilage contact, indicating that the theory could be generalised to soft porous materials. The lubrication replenishment theory is important for the development of joint replacement materials, as most physiological joints operate under conditions of overlapping contact, meaning steady-state lubrication does not necessarily occur.
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Affiliation(s)
- Elze Porte
- Tribology Group, Department of Mechanical Engineering, Imperial College London, SW7 2AZ, UK
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21
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Bonyadi SZ, Demott CJ, Grunlan MA, Dunn AC. Cartilage-like tribological performance of charged double network hydrogels. J Mech Behav Biomed Mater 2020; 114:104202. [PMID: 33243694 DOI: 10.1016/j.jmbbm.2020.104202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 10/16/2020] [Accepted: 11/06/2020] [Indexed: 10/23/2022]
Abstract
A synthetic hydrogel material may offer utility as a cartilage replacement if it is able to maintain low friction in different sliding environments and achieve bulk mechanical properties to withstand the severe environment of the joint. In this work, we compared the tribological behavior of four double network (DN) hydrogels to that of fresh porcine cartilage in both water and fetal bovine serum (FBS). The DN hydrogels were comprised of a negatively charged 1st network and a 2nd network wherein comonomers of varying charge (i.e. neutral, positive, negative, and zwitterionic) were introduced at 10 wt% to an otherwise neutral network. A steel ball probe was used to perform microindentation tests to determine the surface elastic modulus of the samples and estimate their contact areas during sliding. Friction tests using a stationary probe with a stage that reciprocated at a range of speeds were performed to develop lubrication curves in both water and FBS. We found that the DN hydrogels with a neutral or zwitterionic 2nd network had the lowest friction and shear stresses, notably below that of cartilage. The differences in charge and structure of the samples were more evident in water than in FBS, as the lubrication responses for all the hydrogels spanned a wider range of values. In FBS, the lubrication responses were pushed towards elasto-hydrodynamics with nearly all friction coefficient values falling below 0.3. This indicates that the FBS interacts with the hydrogels and cartilage samples in a similar manner as that of cartilage by maintaining a robust layer of solution at the interface during sliding. These DN hydrogels prove to fulfill, and in some cases surpass, the lubrication demands for cartilage replacement in load bearing joints.
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Affiliation(s)
- Shabnam Z Bonyadi
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Connor J Demott
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA
| | - Melissa A Grunlan
- Department of Biomedical Engineering, Texas A&M University, College Station, TX, USA; Department of Materials Science & Engineering, Texas A&M University, College Station, TX, USA; Department of Chemistry, Texas A&M University, College Station, TX, USA
| | - Alison C Dunn
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
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22
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Abstract
Since their inception, hydrogels have gained popularity among multiple fields, most significantly in biomedical research and industry. Due to their resemblance to biological tribosystems, a significant amount of research has been conducted on hydrogels to elucidate biolubrication mechanisms and their possible applications as replacement materials. This review is focused on lubrication mechanisms and covers friction models that have attempted to quantify the complex frictional characteristics of hydrogels. From models developed on the basis of polymer physics to the concept of hydration lubrication, assumptions and conditions for their applicability are discussed. Based on previous models and our own experimental findings, we propose the viscous-adhesive model for hydrogel friction. This model accounts for the effects of confinement of the polymer network provided by a solid surface and poroelastic relaxation as well as the (non) Newtonian shear of a complex fluid on the frictional force and quantifies the frictional response of hydrogels-solid interfaces. Finally, the review delineates potential areas of future research based on the current knowledge.
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23
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Wan H, Ma C, Vinke J, Vissink A, Herrmann A, Sharma PK. Next Generation Salivary Lubrication Enhancer Derived from Recombinant Supercharged Polypeptides for Xerostomia. ACS APPLIED MATERIALS & INTERFACES 2020; 12:34524-34535. [PMID: 32463670 PMCID: PMC8192052 DOI: 10.1021/acsami.0c06159] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Insufficient retention of water in adsorbed salivary conditioning films (SCFs) because of altered saliva secretion can lead to oral dryness (xerostomia). Patients with xerostomia sometimes are given artificial saliva, which often lacks efficacy because of the presence of exogenous molecules with limited lubrication properties. Recombinant supercharged polypeptides (SUPs) improve salivary lubrication by enhancing the functionality of endogenously available salivary proteins, which is in stark contrast to administration of exogenous lubrication enhancers. This novel approach is based on establishing a layered architecture enabled by electrostatic bond formation to stabilize and produce robust SCFs in vitro. Here, we first determined the optimal molecular weight of SUPs to achieve the best lubrication performance employing biophysical and in vitro friction measurements. Next, in an ex vivo tongue-enamel friction system, stimulated whole saliva from patients with Sjögren syndrome was tested to transfer this strategy to a preclinical situation. Out of a library of genetically engineered cationic polypeptides, the variant SUP K108cys that contains 108 positive charges and two cysteine residues at each terminus was identified as the best SUP to restore oral lubrication. Employing this SUP, the duration of lubrication (Relief Period) for SCFs from healthy and patient saliva was significantly extended. For patient saliva, the lubrication duration was increased from 3.8 to 21 min with SUP K108cys treatment. Investigation of the tribochemical mechanism revealed that lubrication enhancement is because of the electrostatic stabilization of SCFs and mucin recruitment, which is accompanied by strong water fixation and reduced water evaporation.
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Affiliation(s)
- Hongping Wan
- University Medical
Center Groningen, Department of Biomedical Engineering, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
| | - Chao Ma
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
| | - Jeroen Vinke
- University Medical
Center Groningen, Department of Biomedical Engineering, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
| | - Arjan Vissink
- University
Medical Center Groningen, Department of Oral and Maxillofacial Surgery, University of Groningen, 9713 GZ Groningen, The Netherlands
| | - Andreas Herrmann
- Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
- DWI Leibniz Institute
for Interactive Materials, Forckenbeckstr. 50, 52056 Aachen, Germany
- Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Worringerweg 2, 52074 Aachen, Germany
| | - Prashant K. Sharma
- University Medical
Center Groningen, Department of Biomedical Engineering, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
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24
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Bhattacharyya A, O'Bryan C, Ni Y, Morley CD, Taylor CR, Angelini TE. Hydrogel compression and polymer osmotic pressure. ACTA ACUST UNITED AC 2020. [DOI: 10.1016/j.biotri.2020.100125] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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25
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Cuccia NL, Pothineni S, Wu B, Méndez Harper J, Burton JC. Pore-size dependence and slow relaxation of hydrogel friction on smooth surfaces. Proc Natl Acad Sci U S A 2020; 117:11247-11256. [PMID: 32398363 PMCID: PMC7260953 DOI: 10.1073/pnas.1922364117] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Hydrogels consist of a cross-linked polymer matrix imbibed with a solvent such as water at volume fractions that can exceed 90%. They are important in many scientific and engineering applications due to their tunable physiochemical properties, biocompatibility, and ultralow friction. Their multiphase structure leads to a complex interfacial rheology, yet a detailed, microscopic understanding of hydrogel friction is still emerging. Using a custom-built tribometer, here we identify three distinct regimes of frictional behavior for polyacrylic acid (PAA), polyacrylamide (PAAm), and agarose hydrogel spheres on smooth surfaces. We find that at low velocities, friction is controlled by hydrodynamic flow through the porous hydrogel network and is inversely proportional to the characteristic pore size. At high velocities, a mesoscopic, lubricating liquid film forms between the gel and surface that obeys elastohydrodynamic theory. Between these regimes, the frictional force decreases by an order of magnitude and displays slow relaxation over several minutes. Our results can be interpreted as an interfacial shear thinning of the polymers with an increasing relaxation time due to the confinement of entanglements. This transition can be tuned by varying the solvent salt concentration, solvent viscosity, and sliding geometry at the interface.
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Affiliation(s)
| | | | - Brady Wu
- Department of Physics, Emory University, Atlanta, GA 30322
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26
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Chau AL, Rosas J, Degen GD, Månsson LK, Chen J, Valois E, Pitenis AA. Aqueous surface gels as low friction interfaces to mitigate implant-associated inflammation. J Mater Chem B 2020; 8:6782-6791. [PMID: 32364211 DOI: 10.1039/d0tb00582g] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Aqueous surface gels are fragile yet resilient biopolymer-based networks capable of sustaining extremely low friction coefficients despite tribologically-challenging environments. These superficial networks are ubiquitous in natural sliding interfaces and protect mechanosensitive cells from excessive contact pressures and frictional shear stresses from cell-fluid, cell-cell, or cell-solid interactions. Understanding these complex lubrication mechanisms may aid in the development of materials-based strategies for increasing biocompatibility in medical devices and implants. Equally as important is characterizing the interplay between soft and passive yet mobile implant materials and cellular reactions in response to direct contact and frictional shear stresses. Physically interrogating living biological systems without rupturing them in the process is nontrivial. To this end, custom biotribometers have been designed to precisely modulate contact pressures against living human telomerase-immortalized corneal epithelial (hTCEpi) cell layers using soft polyacrylamide membrane probes. Reverse-transcription quantitative polymerase chain-reaction (RT-qPCR) indicated that increased duration and, to a much greater extent, the magnitude of frictional shear stress lead to increased production of pro-inflammatory (IL-1β, IL-6, MMP9) and pro-apoptotic (DDIT3, FAS) genes, which in clinical studies are linked to pathological pain. The hierarchical structure often found in biological systems has also been investigated through the fabrication of high-water content (polyacrylamide) hydrogels through free-radical polymerization inhibition. Nanoindentation experiments and friction coefficient measurements indicate that these "gradient surface gels" reduce contact pressures and frictional shear stresses at the surface of the material while still maintaining stiffness within the bulk. Reducing frictional shear stresses through informed materials and surface design may concomitantly increase lubricity and quiet the immune response, and thus provide bio-inspired routes to improve patient outcomes and quality of life.
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Affiliation(s)
- Allison L Chau
- Materials Department University of California, Santa Barbara, CA 93106, USA.
| | - Jonah Rosas
- Biomolecular Science and Engineering Department University of California, Santa Barbara, CA 93106, USA
| | - George D Degen
- Department of Chemical Engineering, University of California, Santa Barbara Santa Barbara, CA 93106, USA
| | - Lisa K Månsson
- Department of Physics Chalmers, University of Technology, 412 58 Gothenburg, Sweden
| | - Jonathan Chen
- Department of Chemical Engineering, University of California, Santa Barbara Santa Barbara, CA 93106, USA
| | - Eric Valois
- Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, CA 93106, USA
| | - Angela A Pitenis
- Materials Department University of California, Santa Barbara, CA 93106, USA.
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27
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Li H, Choi YS, Rutland MW, Atkin R. Nanotribology of hydrogels with similar stiffness but different polymer and crosslinker concentrations. J Colloid Interface Sci 2020; 563:347-353. [PMID: 31887698 DOI: 10.1016/j.jcis.2019.12.045] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 12/02/2019] [Accepted: 12/12/2019] [Indexed: 11/26/2022]
Abstract
HYPOTHESIS The stiffness has been found to regulate hydrogel performances and applications. However, the key interfacial properties of hydrogels, like friction and adhesion are not controlled by the stiffness, but are altered by the structure and composition of hydrogels, like polymer volume fraction and crosslinking degree. EXPERIMENTS Colloidal probe atomic force microscopy has been use to investigate the relationship between tribological properties (friction and adhesion) and composition of hydrogels with similar stiffness, but different polymer volume fractions and crosslinking degrees. FINDINGS The interfacial normal and lateral (friction) forces of hydrogels are not directly correlated to the stiffness, but altered by the hydrogel structure and composition. For normal force measurements, the adhesion increases with polymer volume fraction but decreases with crosslinking degree. For lateral force measurements, friction increases with polymer volume fraction, but decreases with crosslinking degree. In the low normal force regime, friction is mainly adhesion-controlled and increases significantly with the adhesion and polymer volume fraction. In the high normal force regime, friction is predominantly load-controlled and shows slow increase with normal force.
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Affiliation(s)
- Hua Li
- School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia; Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, WA 6009, Australia.
| | - Yu Suk Choi
- School of Human Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
| | - Mark W Rutland
- School of Chemical Science and Engineering, KTH Royal Institute of Technology, SE100 44, Sweden; Surfaces, Processes and Formulation, RISE Research Institutes of Sweden, SE114 86 Stockholm, Sweden
| | - Rob Atkin
- School of Molecular Sciences, The University of Western Australia, 35 Stirling Highway, Perth, WA 6009, Australia
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28
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Loo SL, Vásquez L, Paul UC, Campagnolo L, Athanassiou A, Fragouli D. Solar-Driven Freshwater Generation from Seawater and Atmospheric Moisture Enabled by a Hydrophilic Photothermal Foam. ACS APPLIED MATERIALS & INTERFACES 2020; 12:10307-10316. [PMID: 32058681 PMCID: PMC7997105 DOI: 10.1021/acsami.9b20291] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Accepted: 02/14/2020] [Indexed: 06/01/2023]
Abstract
The accelerated increase in freshwater demand, particularly among populations displaced in remote locations where conventional water sources and the infrastructure required to produce potable water may be completely absent, highlights the urgent need in creating additional freshwater supply from untapped alternative sources via energy-efficient solutions. Herein, we present a hydrophilic and self-floating photothermal foam that can generate potable water from seawater and atmospheric moisture via solar-driven evaporation at its interface. Specifically, the foam shows an excellent solar-evaporation rate of 1.89 kg m-2 h-1 with a solar-to-vapor conversion efficiency of 92.7% under 1-Sun illumination. The collected water is shown to be suitable for potable use because when synthetic seawater samples (3.5 wt %) are used, the foam is able to cause at least 99.99% of salinity reduction. The foam can also be repeatedly used in multiple hydration-dehydration cycles, consisting of moisture absorption or water collection, followed by solar-driven evaporation; in each cycle, 1 g of the foam can harvest 250-1770 mg of water. To the best of our knowledge, this is the first report of a material that integrates all the desirable properties for solar evaporation, water collection, and atmospheric-water harvesting. The lightweight and versatility of the foam suggest that the developed foams can be a potent solution for water efficiency, especially for off-grid situations.
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Affiliation(s)
- Siew-Leng Loo
- Smart
Materials, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
| | - Lía Vásquez
- Smart
Materials, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
- Dipartimento
di Chimica e Chimica Industriale (DCCI), Università degli Studi di Genova, Via Dodecaneso 31, Genoa 16146, Italy
| | - Uttam C. Paul
- Smart
Materials, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
| | - Laura Campagnolo
- Smart
Materials, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
- Dipartimento
di Chimica e Chimica Industriale (DCCI), Università degli Studi di Genova, Via Dodecaneso 31, Genoa 16146, Italy
| | | | - Despina Fragouli
- Smart
Materials, Istituto Italiano di Tecnologia, Via Morego 30, Genova 16163, Italy
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29
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Timaeva OI, Kuz'micheva GM, Pashkin II, Czakkel O, Prevost S. Structure and dynamics of titania - poly(N-vinyl caprolactam) composite hydrogels. SOFT MATTER 2020; 16:219-228. [PMID: 31774424 DOI: 10.1039/c9sm01619h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The morphologies and dynamics of poly(N-vinyl caprolactam) (PVCL) based hydrogels with titania nanoparticles in different states (native, air-dried to a constant weight and swollen in H2O or D2O) are studied by a combination of complementary techniques: wide angle X-ray scattering, small angle neutron scattering, neutron spin echo spectroscopy, differential scanning calorimetry. The results suggest the presence of different structural types of water leading to different properties of the hydrogels. We propose a hierarchical structure of hydrogels spanning from the molecular to the microscopic scale consistent with both the static structure (polymer mesh size, association of the nodes of crosslinks and microchains of PVCL) and the dynamics (rate of relaxation of polymer chains, hydrodynamic polymer-polymer correlation length). The presence of nanoscale titania does not change the molecular structure and nanostructure due to its aggregation into meso-domains, but does affect the microstructure, changing the response rate to a temperature jump from 20 to 50 °C. Titania nanoparticles do not change the equilibrium swelling degree of hydrogels.
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Affiliation(s)
- O I Timaeva
- Federal State Budget Educational Institution of Higher Education "MIREA - Russian Technological University", pr. Vernadskogo 86, Moscow, 119571, Russia.
| | - G M Kuz'micheva
- Federal State Budget Educational Institution of Higher Education "MIREA - Russian Technological University", pr. Vernadskogo 86, Moscow, 119571, Russia.
| | - I I Pashkin
- Federal State Budget Educational Institution of Higher Education "MIREA - Russian Technological University", pr. Vernadskogo 86, Moscow, 119571, Russia.
| | - O Czakkel
- Institut Laue-Langevin, CS 20156, F-38042 Grenoble Cedex 9, France
| | - S Prevost
- Institut Laue-Langevin, CS 20156, F-38042 Grenoble Cedex 9, France
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Hoshi S, Okamoto F, Murakami T, Sakai T, Shinohara Y, Fujii T, Nakatani M, Oshika T. Ability of Nonswelling Polyethylene Glycol-Based Vitreous Hydrogel to Maintain Transparency in the Presence of Vitreous Hemorrhage. Transl Vis Sci Technol 2019; 8:33. [PMID: 31857916 PMCID: PMC6910611 DOI: 10.1167/tvst.8.6.33] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2019] [Accepted: 10/23/2019] [Indexed: 01/11/2023] Open
Abstract
Purpose Postoperative vitreous hemorrhage is a vision-impacting complication of vitrectomy. This preclinical in vitro study assessed the potential ability of a nonswelling polyethylene glycol-based artificial vitreous hydrogel to maintain transparency in the vitreous cavity in the presence of vitreous hemorrhage. Methods Samples (1 mL) of diluted blood at concentrations of 0.1%, 0.25%, 0.5%, and 1.25% were added to 1 mL samples of polymerized hydrogel in cuvettes (gel + blood group); 2 mL samples of diluted blood at the same concentrations were prepared as controls (blood only group). Spectral transmission curves for the hydrogel (gel + blood group) and diluted blood (blood only group) were obtained before and on days 1, 2, 5, 7, 14, and 28 of the experiment. Between-group comparisons were made using the Student's t-test. The percentage of transmittance in the visible light spectrum (400–700 nm) was measured at each time point. Results Mean light transmittance was maintained at >90% until day 7 in the gel + blood group and was significantly greater in the gel + blood than in the blood only groups in samples containing blood diluted to 0.25%, 0.5%, and 1.25% during the 28-day study period (P < 0.05). Conclusions A nonswelling polyethylene glycol-based artificial vitreous hydrogel maintained high optical transparency in the presence of blood through the study period. Injection of this hydrogel into the vitreous cavity at the end of surgery might help to prevent or mitigate vitreous hemorrhage-associated postoperative visual loss. Translational Relevance The hydrogel may prevent visual loss due to postoperative vitreous hemorrhage.
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Affiliation(s)
- Sujin Hoshi
- Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan
| | - Fumiki Okamoto
- Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan
| | - Tomoya Murakami
- Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan
| | - Takamasa Sakai
- Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, Tokyo, Japan
| | | | | | | | - Tetsuro Oshika
- Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan
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31
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Meier YA, Zhang K, Spencer ND, Simic R. Linking Friction and Surface Properties of Hydrogels Molded Against Materials of Different Surface Energies. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:15805-15812. [PMID: 31369280 PMCID: PMC6899455 DOI: 10.1021/acs.langmuir.9b01636] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Biological tissues subjected to rubbing, such as the cornea and eyelid or articular cartilage, are covered in brushy, hydrated mucous structures in order to reduce the shear stress on the tissue. To mimic such biological tissues, we have prepared polyacrylamide (PAAm) hydrogels with various concentrations of un-cross-linked chains on their surfaces by synthesizing them in molds of different surface energies. The selected molding materials included hydrophilic glass, polyoxymethylene (POM), polystyrene (PS), polyethylene (PE), polypropylene (PP), and polytetrafluoroethylene (PTFE). After synthesis, demolding, and equilibration in water, the elastic modulus at the hydrogel surface decreased with increasing water contact angle of the mold. The softer, brushier surfaces did not completely collapse under compressive pressures up to 10 kPa, remaining better hydrated compared to their denser, cross-linked analogs. The hydrogels with brushier surfaces displayed an order of magnitude lower coefficient of friction than the cross-linked ones, which is attributed to the ability of their near-surface regions to retain larger amounts of liquid at the interface. The characteristic speed-dependent friction of the denser, cross-linked hydrogel surface is compared to the speed-independent friction of the brushy hydrogels and discussed from the perspectives of (elasto)hydrodynamic lubrication, permeability, and shear-induced hydrodynamic penetration depth.
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32
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McGhee EO, Hart SM, Urueña JM, Sawyer WG. Hydration Control of Gel-Adhesion and Muco-Adhesion. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:15769-15775. [PMID: 31659909 DOI: 10.1021/acs.langmuir.9b02816] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Protective mucin gel layers established by epithelial cell surfaces in biology have water contents above 90% and provide a low-shear stress nonadhesive interfacial boundary on epithelial surfaces throughout the body. Adhesion between gels and mucin layers, muco-adhesion, is an important aspect of drug delivery, biocompatibility, and the prevention of damage during insertion, use, and removal of medical devices in contact with moist epithelial surfaces. This manuscript develops a simple mathematical model to suggest that gel-adhesion and muco-adhesion are controlled by dehydration. For a fully swollen gel, the osmotic pressure is balanced by the elastic stress in the polymer gel, and differences in the elastic modulus are used to calculate dehydration stresses. A model based on Winkler contact mechanics gives a closed form expression for the force of adhesion that is dependent on the contact radius and gel thickness, inversely proportional to the mucin layer stiffness, and proportional to the square of the differences in elastic modulus. Submerged contact experiments conducted on Gemini gel interfaces of polyacrylamide aqueous gels showed increasing adhesion with increasing dehydration of the probe. Additionally, experiments conducted against mucinated epithelial cell monolayers found mucin transfer onto the most dehydrated gels and no transfer on swollen gels. The model and experiments reveal that high water content fully swollen gels are not intrinsically muco-adhesive, which is consistent with previous tribological experience showing increased lubricity with increasing water content and mesh size.
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Affiliation(s)
- Eric O McGhee
- Department of Mechanical and Aerospace Engineering , University of Florida Gainesville , FL 32611 , United States
| | - Samuel M Hart
- Department of Mechanical and Aerospace Engineering , University of Florida Gainesville , FL 32611 , United States
| | - Juan Manuel Urueña
- Department of Mechanical and Aerospace Engineering , University of Florida Gainesville , FL 32611 , United States
| | - W Gregory Sawyer
- Department of Mechanical and Aerospace Engineering , University of Florida Gainesville , FL 32611 , United States
- J. Crayton Pruitt Family Department of Biomedical Engineering , University of Florida Gainesville , FL 32611 , United States
- Department of Materials Science and Engineering , University of Florida Gainesville , FL 32611 , United States
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33
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Paloni JM, Dong XH, Olsen BD. Protein-Polymer Block Copolymer Thin Films for Highly Sensitive Detection of Small Proteins in Biological Fluids. ACS Sens 2019; 4:2869-2878. [PMID: 31702912 DOI: 10.1021/acssensors.9b01020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In nearly all biosensors, sensitivity is greatly reduced for measurements conducted in biological matrices due to nonspecific binding from off-target molecules. One method to overcome this issue is to design a sensor that enables selective size-based uptake of proteins. Herein, a protein-polymer conjugate thin-film biosensor is fabricated that self-assembles into lamellae containing alternating domains of protein and polymer. Analyte is captured in protein regions while polymer domains restrict diffusion of large molecules. Device sensitivity and size-based exclusion properties are probed using two analytes: streptavidin (SA, 52.8 kDa) and monomeric streptavidin (mSA2, 15.6 kDa). Tuning domain spacing by adjusting polymer molecular weight allows the design of films that relatively freely uptake mSA2 and largely restrict SA diffusion. Furthermore, when detecting the smaller mSA2, no reduction in the limit of detection (LOD) is observed when transitioning from detection in the buffer to detection in biological fluids. As a result, LOD measured in fluid samples is reduced by 2 orders of magnitude compared to a traditional surface-immobilized protein monolayer.
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Affiliation(s)
- Justin M. Paloni
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Xue-Hui Dong
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Bradley D. Olsen
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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34
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Bonyadi SZ, Atten M, Dunn AC. Self-regenerating compliance and lubrication of polyacrylamide hydrogels. SOFT MATTER 2019; 15:8728-8740. [PMID: 31553022 DOI: 10.1039/c9sm01607d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Pristine hydrogel surfaces typically have low friction, which is controlled by composition, slip speeds, and immediate slip history. The stiffness of such samples is typically measured with bulk techniques, and is assumed to be homogeneous at the surface. While the surface properties of homogeneous hydrogel samples are generally controlled by composition, the surface also interfaces with the open bath, which distinguishes it from the bulk. In this work, we disrupt as-molded polyacrylamide surfaces with abrasive wear and connect the effects on the surface stiffness and lubrication to the wear events. At both the nanoscale and the microscale, quasistatic indentations reveal a stiffer surface by up to two times following wear events, even considering roughness. Longitudinal experiments with a series of wear episodes interposed with periods of re-equilibration show that increased stiffness is reversible: more compliant surfaces regenerate within 24 hours. The timescale suggests an osmotic swelling mechanism, and we postulate that abrasive wear removes a swollen surface layer, revealing the stiffer bulk. The newly-revealed bulk becomes the surface, which re-swells over time. We quantify the effects on the self-lubricating ability of these surfaces following abrasive wear using micro-tribometry. The lubrication curve shows that robust low friction is maintained, and that the friction becomes less dependent upon the sliding speed. The unique ability of these materials to regenerate swollen surfaces and maintain robust low friction following abrasive wear is promising for designing their slip behavior into aqueous soft robotics components or biomedicine applications.
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Affiliation(s)
- Shabnam Z Bonyadi
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, MechSE @ UIUC, 1206 W Green St, MC 244, Urbana, IL 61801, USA.
| | - Michael Atten
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, MechSE @ UIUC, 1206 W Green St, MC 244, Urbana, IL 61801, USA.
| | - Alison C Dunn
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, MechSE @ UIUC, 1206 W Green St, MC 244, Urbana, IL 61801, USA.
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35
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Shoaib T, Espinosa-Marzal RM. Influence of Loading Conditions and Temperature on Static Friction and Contact Aging of Hydrogels with Modulated Microstructures. ACS APPLIED MATERIALS & INTERFACES 2019; 11:42722-42733. [PMID: 31623436 DOI: 10.1021/acsami.9b14283] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Biological tribosystems enable diverse functions of the human body by maintaining extremely low coefficients of friction via hydrogel-like surface layers and a water-based lubricant. Although stiction has been proposed as a precursor to damage, there is still a lack of knowledge about its origin and its relation to the hydrogel's microstructure, which impairs the design of soft matter as replacement biomaterials. In this work, the static friction of poly(acrylamide) hydrogels with modulated composition was investigated by colloidal probe lateral force microscopy as a function of load, temperature, and loading time. Temperature-dependent studies enable to build a phase diagram for hydrogel's static friction, which explains stiction via (polymer) viscoelastic and poroelastic relaxation, and a subtle transition from solid- to liquid-like interfacial behavior. At room temperature, the static friction increases with loading time, a phenomenon called contact aging, which stems from the adhesion of the polymer to the colloid and from the drainage-induced increase in contact area. Contact aging is shown to gradually vanish with increase in temperature, but this behavior strongly depends on the hydrogel's composition. This work scrutinizes the relation between the microstructure of hydrogel-like soft matter and interfacial behavior, with implications for diverse areas of inquiry, not only in biolubrication and biomedical applications but also in soft robotics and microelectromechanical devices, where the processes occurring at the migrating hydrogel interface are of relevance. The results support that modulating both the hydrogel's mesh size and the structure of the near-surface region is a means to control static friction and adhesion. This conceptual framework for static friction will foster further understanding of the wear of hydrogel-like materials.
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Affiliation(s)
- Tooba Shoaib
- The Materials Science and Engineering , University of Illinois at Urbana-Champaign , 1304 W Green Street , Urbana , Illinois 61801 , United States
| | - Rosa M Espinosa-Marzal
- Civil and Environmental Engineering , University of Illinois at Urbana-Champaign , 205 N. Matthews Avenue , Urbana , Illinois 61801 , United States
- The Materials Science and Engineering , University of Illinois at Urbana-Champaign , 1304 W Green Street , Urbana , Illinois 61801 , United States
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36
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Wang C, Bai X, Dong C, Guo Z, Yuan C. Friction properties of polyacrylamide hydrogel particle/HDPE composite under water lubrication. POLYMER 2019. [DOI: 10.1016/j.polymer.2019.121703] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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37
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Rudge RED, Scholten E, Dijksman JA. Advances and challenges in soft tribology with applications to foods. Curr Opin Food Sci 2019. [DOI: 10.1016/j.cofs.2019.06.011] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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38
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Zhao J, Liu P, Liu Y. Adjustable Tribological Behavior of Glucose-Sensitive Hydrogels. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:7479-7487. [PMID: 29860837 DOI: 10.1021/acs.langmuir.8b01388] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Stimuli-responsive hydrogels have been considered to have various applications in numerous fields. In the present work, a double-network (DN) hydrogel has been synthesized. The copolymers of 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and acrylamide (AM) [P(AMPS- co-AM)] are prepared as the 1st network and poly(acrylic acid) as the 2nd network. This DN hydrogel is sensitive to glucose by introducing the glucose-sensitive group phenylboronic acid to the network. The tribological properties of this glucose-sensitive DN hydrogel have been investigated using a universal mechanical tester (UMT-5). The tribological results show that the friction coefficient varied with the glucose solution. The friction coefficient increased to a maximum of 0.06, and finally decreased to 0.025 with the increase in the glucose concentration. An adjustable friction coefficient of the hydrogel, between 0.025 and 0.056, was achieved along with the change of lubricant. According to the tribological experimental results and the analysis of the DN structure, it can be deduced that a hydrated layer exists in the interface of the hydrogel. The hydrated layers consisting of water molecules are bounded with the hydrophilic group of the hydrogel network by hydrogen bonds. The change in the number of water molecules leads to the difference in the water content of the hydrogel, which further resulted in the various tribological properties. In addition, the hydrogel's mesh size also has an impact on the change in friction coefficient. In general, the adjustable friction of the hydrogel in a glucose environment is achieved.
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Affiliation(s)
- Jin Zhao
- State Key Laboratory of Tribology , Tsinghua University , Beijing 100084 , China
| | - Pengxiao Liu
- State Key Laboratory of Tribology , Tsinghua University , Beijing 100084 , China
| | - Yuhong Liu
- State Key Laboratory of Tribology , Tsinghua University , Beijing 100084 , China
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39
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Han G, Eriten M. Effect of relaxation-dependent adhesion on pre-sliding response of cartilage. ROYAL SOCIETY OPEN SCIENCE 2018; 5:172051. [PMID: 29892390 PMCID: PMC5990745 DOI: 10.1098/rsos.172051] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 04/16/2018] [Indexed: 06/08/2023]
Abstract
Possible links between adhesive properties and the pre-sliding (static) friction response of cartilage are not fully understood in the literature. The aims of this study are to investigate the relation between adhesion and relaxation time in articular cartilage, and the effect of relaxation-dependent adhesion on the pre-sliding response of cartilage. Adhesion tests were performed to evaluate the work of adhesion of cartilage at different relaxation times. Friction tests were conducted to identify the pre-sliding friction response of cartilage at relaxation times corresponding to adhesion tests. The pre-sliding friction response of cartilage was systematically linked to the work of adhesion and contact conditions by a slip-based failure model. It was found that the work of adhesion increases with relaxation time. Also, the work of adhesion is linearly correlated to the resistance to slip-based failure. In addition, as the work of adhesion increases, the adhered (stick) area at the moment of failure increases, and the propagation rate of the annular slip (crack) area towards its centre increases. These findings offer a mechanistic explanation of the pre-sliding friction behaviour and stick-slip response of soft hydrated interfaces such as articular cartilage and hydrogels. In addition, the linear correlation between adhesion and threshold to slip-based failure enables estimation of the adhesive strength of such interfaces directly from the pre-sliding friction response (e.g. shear wave elastography).
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Affiliation(s)
- Guebum Han
- Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA
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40
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Urueña JM, McGhee EO, Angelini TE, Dowson D, Sawyer WG, Pitenis AA. Normal Load Scaling of Friction in Gemini Hydrogels. ACTA ACUST UNITED AC 2018. [DOI: 10.1016/j.biotri.2018.01.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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41
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Bhattacharjee T, Kabb CP, O'Bryan CS, Urueña JM, Sumerlin BS, Sawyer WG, Angelini TE. Polyelectrolyte scaling laws for microgel yielding near jamming. SOFT MATTER 2018; 14:1559-1570. [PMID: 29450413 DOI: 10.1039/c7sm01518f] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Micro-scale hydrogel particles, known as microgels, are used in industry to control the rheology of numerous different products, and are also used in experimental research to study the origins of jamming and glassy behavior in soft-sphere model systems. At the macro-scale, the rheological behaviour of densely packed microgels has been thoroughly characterized; at the particle-scale, careful investigations of jamming, yielding, and glassy-dynamics have been performed through experiment, theory, and simulation. However, at low packing fractions near jamming, the connection between microgel yielding phenomena and the physics of their constituent polymer chains has not been made. Here we investigate whether basic polymer physics scaling laws predict macroscopic yielding behaviours in packed microgels. We measure the yield stress and cross-over shear-rate in several different anionic microgel systems prepared at packing fractions just above the jamming transition, and show that our data can be predicted from classic polyelectrolyte physics scaling laws. We find that diffusive relaxations of microgel deformation during particle re-arrangements can predict the shear-rate at which microgels yield, and the elastic stress associated with these particle deformations predict the yield stress.
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42
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Shoaib T, Heintz J, Lopez-Berganza JA, Muro-Barrios R, Egner SA, Espinosa-Marzal RM. Stick-Slip Friction Reveals Hydrogel Lubrication Mechanisms. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:756-765. [PMID: 28961012 DOI: 10.1021/acs.langmuir.7b02834] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
The lubrication behavior of the hydrated biopolymers that constitute tissues in organisms differs from that outlined by the classical Stribeck curve, and studying hydrogel lubrication is a key pathway to understand the complexity of biolubrication. Here, we have investigated the frictional characteristics of polyacrylamide (PAAm) hydrogels with various acrylamide concentrations, exhibiting Young's moduli (E) that range from 1 to 40 kPa, as a function of applied normal load and sliding velocities by colloid probe lateral force microscopy. The speed-dependence of the friction force shows an initial decrease in friction with increasing velocity, while, above a transition velocity V*, friction increases with speed. This study reveals two different boundary lubrication mechanisms characterized by distinct scaling laws. An unprecedented and comprehensive study of the lateral force loops reveals intermittent friction or stick-slip above and below V*, with characteristics that depend on the hydrogel network, applied load, and sliding velocity. Our work thus provides insight into the closely tied parameters governing hydrogel lubrication mechanisms, and stick-slip friction.
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Affiliation(s)
- Tooba Shoaib
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States
| | - Joerg Heintz
- Health Care Engineering Systems Center, University of Illinois at Urbana-Champaign , 1206 West Clark Street, Urbana, Illinois 61801, United States
| | - Josue A Lopez-Berganza
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States
| | - Raymundo Muro-Barrios
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States
| | - Simon A Egner
- Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign , 1304 West Green Street, Urbana, Illinois 61801, United States
| | - Rosa M Espinosa-Marzal
- Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign , 205 North Matthews Avenue, Urbana, Illinois 61801, United States
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Krajina BA, Tropini C, Zhu A, DiGiacomo P, Sonnenburg JL, Heilshorn SC, Spakowitz AJ. Dynamic Light Scattering Microrheology Reveals Multiscale Viscoelasticity of Polymer Gels and Precious Biological Materials. ACS CENTRAL SCIENCE 2017; 3:1294-1303. [PMID: 29296670 PMCID: PMC5746858 DOI: 10.1021/acscentsci.7b00449] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Indexed: 05/22/2023]
Abstract
The development of experimental techniques capable of probing the viscoelasticity of soft materials over a broad range of time scales is essential to uncovering the physics that governs their behavior. In this work, we develop a microrheology technique that requires only 12 μL of sample and is capable of resolving dynamic behavior ranging in time scales from 10-6 to 10 s. Our approach, based on dynamic light scattering in the single-scattering limit, enables the study of polymer gels and other soft materials over a vastly larger hierarchy of time scales than macrorheology measurements. Our technique captures the viscoelastic modulus of polymer hydrogels with a broad range of stiffnesses from 10 to 104 Pa. We harness these capabilities to capture hierarchical molecular relaxations in DNA and to study the rheology of precious biological materials that are impractical for macrorheology measurements, including decellularized extracellular matrices and intestinal mucus. The use of a commercially available benchtop setup that is already available to a variety of soft matter researchers renders microrheology measurements accessible to a broader range of users than existing techniques, with the potential to reveal the physics that underlies complex polymer hydrogels and biological materials.
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Affiliation(s)
- Brad A. Krajina
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - Carolina Tropini
- Department
of Microbiology and Immunology, Stanford
University School of Medicine, Stanford, California 94305, United States
| | - Audrey Zhu
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
| | - Philip DiGiacomo
- Department
of Bioengineering, Stanford University, Stanford, California 94305, United States
| | - Justin L. Sonnenburg
- Department
of Microbiology and Immunology, Stanford
University School of Medicine, Stanford, California 94305, United States
| | - Sarah C. Heilshorn
- Department
of Materials Science and Engineering, Stanford
University, Stanford, California 94305, United States
| | - Andrew J. Spakowitz
- Department
of Chemical Engineering, Stanford University, Stanford, California 94305, United States
- Department
of Materials Science and Engineering, Stanford
University, Stanford, California 94305, United States
- Department
of Applied Physics, Stanford University, Stanford, California 94305, United States
- Biophysics
Program, Stanford University, Stanford, California 94305, United States
- E-mail:
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Pitenis AA, Urueña JM, Hormel TT, Bhattacharjee T, Niemi SR, Marshall SL, Hart SM, Schulze KD, Angelini TE, Sawyer WG. Corneal cell friction: Survival, lubricity, tear films, and mucin production over extended duration in vitro studies. ACTA ACUST UNITED AC 2017. [DOI: 10.1016/j.biotri.2017.04.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Dolan GK, Yakubov GE, Bonilla MR, Lopez-Sanchez P, Stokes JR. Friction, lubrication, and in situ mechanics of poroelastic cellulose hydrogels. SOFT MATTER 2017; 13:3592-3601. [PMID: 28443922 DOI: 10.1039/c6sm02709a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The tribology between biphasic materials is challenging to predict and interpret due to the interrelationship between mechanical properties, microstructure and movement of the fluid phase contained within. A new approach is presented to deconvolute these effects for cellulose hydrogels, which have a fibrous network that is akin to the microstructure of articular cartilage and plant cell walls. This is achieved by developing a tribo-rheological technique that uniquely incorporates in situ mechanical characterisation (compression-relaxation and small amplitude oscillatory shear) immediately prior to measuring the tribological response between pairs of hydrogels. A radial pressure gradient is generated upon compression-relaxation of the poroelastic hydrogels that results in a non-uniform film thickness at the interface between them. Simulations of this process show that contact between gels occurs in an outer annulus region. Accounting for the predicted contact area between hydrogels varying in cellulose density and pectin solution viscosity causes measured tribology data to collapse onto a single curve; the apparent static friction between hydrogel tribopairs increases with the storage modulus of the hydrogels according to a power law with exponent 0.67. The method is used to compare the influence of plant cell wall polysaccharides, xyloglucan and arabinoxylan, on the interactive forces between cellulose fibres; xyloglucan is found to reduce the static friction between the hydrogels while arabinoxylan had no significant effect. The methodologies presented should provide a new framework for studying the friction between gels and other biphasic soft materials and polymeric surface films.
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Affiliation(s)
- G K Dolan
- School of Chemical Engineering, The University of Queensland, Brisbane 4072, Australia. and Australian Research Council Centre of Excellence in Plant Cell Walls, The University of Queensland, Brisbane 4072, Australia
| | - G E Yakubov
- School of Chemical Engineering, The University of Queensland, Brisbane 4072, Australia. and Australian Research Council Centre of Excellence in Plant Cell Walls, The University of Queensland, Brisbane 4072, Australia
| | - M R Bonilla
- School of Chemical Engineering, The University of Queensland, Brisbane 4072, Australia. and Australian Research Council Centre of Excellence in Plant Cell Walls, The University of Queensland, Brisbane 4072, Australia
| | - P Lopez-Sanchez
- Australian Research Council Centre of Excellence in Plant Cell Walls, The University of Queensland, Brisbane 4072, Australia
| | - J R Stokes
- School of Chemical Engineering, The University of Queensland, Brisbane 4072, Australia. and Australian Research Council Centre of Excellence in Plant Cell Walls, The University of Queensland, Brisbane 4072, Australia
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Reale ER, Dunn AC. Poroelasticity-driven lubrication in hydrogel interfaces. SOFT MATTER 2017; 13:428-435. [PMID: 27901546 DOI: 10.1039/c6sm02111e] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
It is widely accepted that hydrogel surfaces are slippery, and have low friction, but dynamic applied stresses alter the hydrogel composition at the interface as water is displaced. The induced osmotic imbalance of compressed hydrogel which cannot swell to equilibrium should drive the resistance to slip against it. This paper demonstrates the driving role of poroelasticity in the friction of hydrogel-glass interfaces, specifically how poroelastic relaxation of hydrogels increases adhesion. We translate the work of adhesion into an effective surface energy density that increases with the duration of applied pressure from 10 to 50 mJ m-2, as measured by micro-indentation. A model of static friction coefficient is derived from an area-based rules of mixture for the surface energies, and predicts the friction coefficient changes upon initiation of slip. For kinetic friction, the competition between duration of contact and relaxation time is quantified by a contacting Péclet number, PeC. A single length parameter on the scale of micrometers fits these two models to experimental micro-friction data. These models predict how short durations of applied pressure and faster sliding speeds, do not disrupt interfacial hydration; this prevailing water maintains low friction. At low speeds where interface drainage dominates, the osmotic suction works against slip for higher friction. The prediction of friction coefficients after adhesion characterization by micro-indentation makes use of the interplay between poroelasticity, adhesion, and friction. This approach provides a starting point for prediction of, and design for, hydrogel interfacial friction.
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Affiliation(s)
- Erik R Reale
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, 1206 W Green St MC 244, Urbana, IL 61801, USA.
| | - Alison C Dunn
- Department of Mechanical Science & Engineering, University of Illinois at Urbana-Champaign, 1206 W Green St MC 244, Urbana, IL 61801, USA.
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Kim J, Dunn AC. Soft hydrated sliding interfaces as complex fluids. SOFT MATTER 2016; 12:6536-6546. [PMID: 27425448 DOI: 10.1039/c6sm00623j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Hydrogel surfaces are biomimics for sensing and mobility systems in the body such as the eyes and large joints due to their important characteristics of flexibility, permeability, and integrated aqueous component. Recent studies have shown polymer concentration gradients resulting in a less dense region in the top micrometers of the surface. Under shear, this gradient is hypothesized to drive lubrication behavior due to its rheological similarity to a semi-dilute polymer solution. In this work we map 3 distinct lubricating regimes between a polyacrylamide surface and an aluminum annulus using stepped-velocity tribo-rheometry over 5 decades of sliding speed in increasing and decreasing steps. These regimes, characterized by weakly or strongly time-dependent response and thixotropy-like hysteresis, provide the skeleton of a lubrication curve for hydrogel-against-hard material interfaces and support hypotheses of polymer mechanics-driven lubrication. Tribo-rheometry is particularly suited to uncover the lubrication mechanisms of complex interfaces such as are formed with hydrated hydrogel surfaces and biological surfaces.
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Affiliation(s)
- Jiho Kim
- Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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