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Elkington RJ, Hall RM, Beadling AR, Pandit H, Bryant MG. Brushing Up on Cartilage Lubrication: Polyelectrolyte-Enhanced Tribological Rehydration. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:10648-10662. [PMID: 38712915 PMCID: PMC11112737 DOI: 10.1021/acs.langmuir.4c00598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Revised: 04/14/2024] [Accepted: 04/18/2024] [Indexed: 05/08/2024]
Abstract
This study presents new insights into the potential role of polyelectrolyte interfaces in regulating low friction and interstitial fluid pressurization of cartilage. Polymer brushes composed of hydrophilic 3-sulfopropyl methacrylate potassium salt (SPMK) tethered to a PEEK substrate (SPMK-g-PEEK) are a compelling biomimetic solution for interfacing with cartilage, inspired by the natural lubricating biopolyelectrolyte constituents of synovial fluid. These SPMK-g-PEEK surfaces exhibit a hydrated compliant layer approximately 5 μm thick, demonstrating the ability to maintain low friction coefficients (μ ∼ 0.01) across a wide speed range (0.1-200 mm/s) under physiological loads (0.75-1.2 MPa). A novel polyelectrolyte-enhanced tribological rehydration mechanism is elucidated, capable of recovering up to ∼12% cartilage strain and subsequently facilitating cartilage interstitial fluid recovery, under loads ranging from 0.25 to 2.21 MPa. This is attributed to the combined effects of fluid confinement within the contact gap and the enhanced elastohydrodynamic behavior of polymer brushes. Contrary to conventional theories that emphasize interstitial fluid pressurization in regulating cartilage lubrication, this work demonstrates that SPMK-g-PEEK's frictional behavior with cartilage is independent of these factors and provides unabating aqueous lubrication. Polyelectrolyte-enhanced tribological rehydration can occur within a static contact area and operates independently of known mechanisms of cartilage interstitial fluid recovery established for converging or migrating cartilage contacts. These findings challenge existing paradigms, proposing a novel polyelectrolyte-cartilage tribological mechanism not exclusively reliant on interstitial fluid pressurization or cartilage contact geometry. The implications of this research extend to a broader understanding of synovial joint lubrication, offering insights into the development of joint replacement materials that more accurately replicate the natural functionality of cartilage.
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Affiliation(s)
- Robert J. Elkington
- Institute
of Functional Surfaces, Mechanical Engineering, University of Leeds, Leeds LS2 9JT, Yorkshire, U.K.
| | - Richard M. Hall
- School
of Engineering College of Engineering and Physical Sciences, University of Birmingham, Birmingham B15 2TT, West
Midlands, U.K.
| | - Andrew R. Beadling
- Institute
of Functional Surfaces, Mechanical Engineering, University of Leeds, Leeds LS2 9JT, Yorkshire, U.K.
| | - Hemant Pandit
- Leeds
Institute of Rheumatic and Musculoskeletal Medicine, Chapel Allerton Hospital, Chapeltown Road, Leeds LS7 4SA, Yorkshire, U.K.
| | - Michael G. Bryant
- School
of Engineering College of Engineering and Physical Sciences, University of Birmingham, Birmingham B15 2TT, West
Midlands, U.K.
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Al Kindi A, Courelli NS, Ogbonna K, Urueña JM, Chau AL, Pitenis AA. Bioinspired Lubricity from Surface Gel Layers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2024; 40:9926-9933. [PMID: 38683632 PMCID: PMC11100014 DOI: 10.1021/acs.langmuir.3c03686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Revised: 04/12/2024] [Accepted: 04/15/2024] [Indexed: 05/01/2024]
Abstract
Surface gel layers on commercially available contact lenses have been shown to reduce frictional shear stresses and mitigate damage during sliding contact with fragile epithelial cell layers in vitro. Spencer and co-workers recently demonstrated that surface gel layers could arise from oxygen-inhibited free-radical polymerization. In this study, polyacrylamide hydrogel shell probes (7.5 wt % acrylamide, 0.3 wt % N,N'-methylenebisacrylamide) were polymerized in three hemispherical molds listed in order of decreasing surface energy and increasing oxygen permeability: borosilicate glass, polyether ether ketone (PEEK), and polytetrafluoroethylene (PTFE). Hydrogel probes polymerized in PEEK and PTFE molds exhibited 100× lower elastic moduli at the surface (E PEEK * = 80 ± 31 and E PTFE * = 106 ± 26 Pa, respectively) than those polymerized in glass molds (E glass * = 31,560 ± 1,570 Pa), in agreement with previous investigations by Spencer and co-workers. Biotribological experiments revealed that hydrogel probes with surface gel layers reduced frictional shear stresses against cells (τPEEK = 35 ± 15 and τPTFE = 22 ± 16 Pa) more than those without (τglass = 68 ± 15 Pa) and offered greater protection against cell damage when sliding against human telomerase-immortalized corneal epithelial (hTCEpi) cell monolayers. Our work demonstrates that the "mold effect" resulting in oxygen-inhibition polymerization creates hydrogels with surface gel layers that reduce shear stresses in sliding contact with cell monolayers, similar to the protection offered by gradient mucin gel networks across epithelial cell layers.
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Affiliation(s)
- Ahmed Al Kindi
- Department
of Mechanical Engineering, University of
California, Santa
Barbara, California 93106, United States
| | - Nemea S. Courelli
- Department
of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Kevin Ogbonna
- College
of Creative Studies, Biological Sciences, University of California, Santa
Barbara, California 93106, United States
| | - Juan Manuel Urueña
- NSF
BioPACIFIC Materials Innovation Platform, University of California, Santa
Barbara, California 93106, United States
| | - Allison L. Chau
- Materials
Department, University of California, Santa Barbara, California 93106, United States
| | - Angela A. Pitenis
- Materials
Department, University of California, Santa Barbara, California 93106, United States
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Hasan MM, Dunn AC. Fewer polymer chains but higher adhesion: How gradient-stiffness hydrogel layers mediate adhesion through network stretch. J Chem Phys 2023; 159:184706. [PMID: 37947516 DOI: 10.1063/5.0174530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2023] [Accepted: 10/10/2023] [Indexed: 11/12/2023] Open
Abstract
The presence of gradient softer outer layers, commonly observed in biological systems (such as cartilage and ocular tissues), as well as synthetic crosslinked hydrogels, profoundly influences their interactions with opposing surfaces. Our prior research demonstrated that gradient-stiffness hydrogel layers, characterized by increasing elasticity with depth, control contact mechanics, particularly in proximity to the layer thickness. We postulate that the distribution of polymers within these gradient layers imparts extraordinary stretch and adhesion characteristics due to network adaptability and stress-induced reorganization. To investigate this phenomenon, we utilized Atomic Force Microscopy nanoindentation to assess the depth-dependent adhesion behavior of polyacrylamide hydrogels with varying gradient layer thicknesses. Two gradient layer thicknesses were achieved by employing different molding materials: glass and polyoxymethylene (POM). Glass-molded hydrogels exhibited a thinner gradient layer alongside a stiffer bulk layer compared to their POM-molded counterparts. In indentation experiments, the POM-molded hydrogel had larger adhesion compared to glass-molded hydrogel. We find that indenting within the gradient layer engenders increased load-unload hysteresis due to heightened fluid transport in the sparse outer polymer network. Consequently, this led to augmented adhesion and work of separation at shallow depths. We suggest that the prominent stretching capability of the sparse outer polymer network during probe retraction contributes to enhanced adhesion. The Maugis-Dugdale adhesive model only fits well to indentations on the thin layer or indentations which engage significantly with the bulk. These results facilitate a comprehensive characterization of adhesion mechanics in gradient-stiffness hydrogels, which could foster their application across emerging contexts in health science and environmental domains.
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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, USA
| | - Alison C Dunn
- Department of Mechanical Science and Engineering, University of Illinois Urbana-Champaign, 1206 W Green St., Urbana, Illinois 61801, USA
- Department of Biomedical and Translational Sciences, Carle Illinois College of Medicine, 506 S Mathews Ave., Urbana, Illinois 61801, USA
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Ishihara K, Shi X, Fukazawa K, Yamaoka T, Yao G, Wu JY. Biomimetic-Engineered Silicone Hydrogel Contact Lens Materials. ACS APPLIED BIO MATERIALS 2023; 6:3600-3616. [PMID: 37616500 PMCID: PMC10521029 DOI: 10.1021/acsabm.3c00296] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 08/16/2023] [Indexed: 08/26/2023]
Abstract
Contact lenses are one of the most successful applications of biomaterials. The chemical structure of the polymers used in contact lenses plays an important role in determining the function of contact lenses. Different types of contact lenses have been developed based on the chemical structure of polymers. When designing contact lenses, materials scientists consider factors such as mechanical properties, processing properties, optical properties, histocompatibility, and antifouling properties, to ensure long-term wear with minimal discomfort. Advances in contact lens materials have addressed traditional issues such as oxygen permeability and biocompatibility, improving overall comfort, and duration of use. For example, silicone hydrogel contact lenses with high oxygen permeability were developed to extend the duration of use. In addition, controlling the surface properties of contact lenses in direct contact with the cornea tissue through surface polymer modification mimics the surface morphology of corneal tissue while maintaining the essential properties of the contact lens, a significant improvement for long-term use and reuse of contact lenses. This review presents the material science elements required for advanced contact lenses of the future and summarizes the chemical methods for achieving these goals.
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Affiliation(s)
- Kazuhiko Ishihara
- Division
of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
| | - Xinfeng Shi
- Alcon
Research, LLC, Fort Worth, Texas 76134, United States
| | - Kyoko Fukazawa
- National
Cerebral and Cardiovascular Center Research Institute, Suita, Osaka 564-8565, Japan
| | - Tetsuji Yamaoka
- National
Cerebral and Cardiovascular Center Research Institute, Suita, Osaka 564-8565, Japan
| | - George Yao
- Alcon
Research, LLC, Duluth, Georgia 30097, United States
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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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6
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Zhang S, Ge G, Qin Y, Li W, Dong J, Mei J, Ma R, Zhang X, Bai J, Zhu C, Zhang W, Geng D. Recent advances in responsive hydrogels for diabetic wound healing. Mater Today Bio 2022; 18:100508. [PMID: 36504542 PMCID: PMC9729074 DOI: 10.1016/j.mtbio.2022.100508] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 11/26/2022] [Accepted: 11/29/2022] [Indexed: 12/03/2022]
Abstract
Poor wound healing after diabetes mellitus remains a challenging problem, and its pathophysiological mechanisms have not yet been fully elucidated. Persistent bleeding, disturbed regulation of inflammation, blocked cell proliferation, susceptible infection and impaired tissue remodeling are the main features of diabetic wound healing. Conventional wound dressings, including gauze, films and bandages, have a limited function. They generally act as physical barriers and absorbers of exudates, which fail to meet the requirements of the whol diabetic wound healing process. Wounds in diabetic patients typically heal slowly and are susceptible to infection due to hyperglycemia within the wound bed. Once bacterial cells develop into biofilms, diabetic wounds will exhibit robust drug resistance. Recently, the application of stimuli-responsive hydrogels, also known as "smart hydrogels", for diabetic wound healing has attracted particular attention. The basic feature of this system is its capacities to change mechanical properties, swelling ability, hydrophilicity, permeability of biologically active molecules, etc., in response to various stimuli, including temperature, potential of hydrogen (pH), protease and other biological factors. Smart hydrogels can improve therapeutic efficacy and limit total toxicity according to the characteristics of diabetic wounds. In this review, we summarized the mechanism and application of stimuli-responsive hydrogels for diabetic wound healing. It is hoped that this work will provide some inspiration and suggestions for research in this field.
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Affiliation(s)
- Siming Zhang
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China
| | - Gaoran Ge
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, 215006, Jiangsu, China
| | - Yi Qin
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, 215006, Jiangsu, China
| | - Wenhao Li
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, 215006, Jiangsu, China
| | - Jiale Dong
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China
| | - Jiawei Mei
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China
| | - Ruixiang Ma
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China
| | - Xianzuo Zhang
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China
| | - Jiaxiang Bai
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, 215006, Jiangsu, China
| | - Chen Zhu
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China,Corresponding author.
| | - Weiwei Zhang
- Department of Geriatrics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230022, China,Corresponding author.
| | - Dechun Geng
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, 215006, Jiangsu, China,Corresponding author.
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