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Müller-Renno C, Ziegler C. The Contribution of Scanning Force Microscopy on Dental Research: A Narrative Review. MATERIALS (BASEL, SWITZERLAND) 2024; 17:2100. [PMID: 38730904 PMCID: PMC11084532 DOI: 10.3390/ma17092100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Revised: 04/23/2024] [Accepted: 04/24/2024] [Indexed: 05/13/2024]
Abstract
Scanning force microscopy (SFM) is one of the most widely used techniques in biomaterials research. In addition to imaging the materials of interest, SFM enables the mapping of mechanical properties and biological responses with sub-nanometer resolution and piconewton sensitivity. This review aims to give an overview of using the scanning force microscope (SFM) for investigations on dental materials. In particular, SFM-derived methods such as force-distance curves (scanning force spectroscopy), lateral force spectroscopy, and applications of the FluidFM® will be presented. In addition to the properties of dental materials, this paper reports the development of the pellicle by the interaction of biopolymers such as proteins and polysaccharides, as well as the interaction of bacteria with dental materials.
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Affiliation(s)
- Christine Müller-Renno
- Department of Physics and Research Center OPTIMAS, RPTU Kaiserslautern, 67663 Kaiserslautern, Germany;
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2
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Thompson A, Pollet TV. An exploratory psychometric network analysis of loneliness scales in a sample of older adults. CURRENT PSYCHOLOGY 2023:1-15. [PMID: 37359673 PMCID: PMC10182353 DOI: 10.1007/s12144-023-04697-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/21/2023] [Indexed: 06/28/2023]
Abstract
To examine the relationships within and between commonly used measures of loneliness to determine the suitability of the measures in older adults. Further, to determine whether certain items in these measures are more psychometrically robust in terms of capturing different types of loneliness across this population. Data were obtained from 350 older adults via completion of an online survey. Four measures of loneliness were completed. These were the University of California Los Angeles Loneliness Scale 4 (Version 3), the de Jong Gierveld Loneliness Scale, the Social and Emotional Loneliness Scale for Adults (Short Version) and a direct measure of loneliness. Analysis via a regularized partial correlation network and via clique percolation revealed that only the SELSA-S encompassed loneliness relating to deficits in social, family and romantic relationships. The remaining measures tapped mostly into social loneliness alone. The direct measure of loneliness had the strongest connection to the UCLA item-4 and the de Jong Gierveld item-1 exhibited the strongest bridge centrality, being a member of the most clusters. The results indicate that should researchers be interested in assessing loneliness resulting from specific relationships, then the SELSA-S would be the most suitable measure. Whereas the other measures are suitable for assessing loneliness more generally. The results further suggest that the de Jong Gierveld item-1 may be a more suitable direct measure of loneliness than that currently employed as it taps into a greater number of relationships.
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Affiliation(s)
- Alexandra Thompson
- Department of Psychology, Northumbria University, Newcastle Upon Tyne, UK
| | - Thomas V. Pollet
- Department of Psychology, Northumbria University, Newcastle Upon Tyne, UK
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Sotres J, Boyd H, Gonzalez-Martinez JF. Locating critical events in AFM force measurements by means of one-dimensional convolutional neural networks. Sci Rep 2022; 12:12995. [PMID: 35906466 PMCID: PMC9338096 DOI: 10.1038/s41598-022-17124-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 07/20/2022] [Indexed: 11/09/2022] Open
Abstract
Atomic Force Microscopy (AFM) force measurements are a powerful tool for the nano-scale characterization of surface properties. However, the analysis of force measurements requires several processing steps. One is locating different type of events e.g., contact point, adhesions and indentations. At present, there is a lack of algorithms that can automate this process in a reliable way for different types of samples. Moreover, because of their stochastic nature, the acquisition and analysis of a high number of force measurements is typically required. This can result in these experiments becoming an overwhelming task if their analysis is not automated. Here, we propose a Machine Learning approach, the use of one-dimensional convolutional neural networks, to locate specific events within AFM force measurements. Specifically, we focus on locating the contact point, a critical step for the accurate quantification of mechanical properties as well as long-range interactions. We validate this approach on force measurements obtained both on hard and soft surfaces. This approach, which could be easily used to also locate other events e.g., indentations and adhesions, has the potential to significantly facilitate and automate the analysis of AFM force measurements and, therefore, the use of this technique by a wider community.
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Affiliation(s)
- Javier Sotres
- Department of Biomedical Science, Faculty of Health and Society, Malmö University, 20506, Malmö, Sweden. .,Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden.
| | - Hannah Boyd
- Department of Biomedical Science, Faculty of Health and Society, Malmö University, 20506, Malmö, Sweden.,Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
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Wang S, Olarte Mantilla SM, Smith PA, Stokes JR, Smyth HE. Tribology and QCM-D approaches provide mechanistic insights into red wine mouthfeel, astringency sub-qualities and the role of saliva. Food Hydrocoll 2021. [DOI: 10.1016/j.foodhyd.2021.106918] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Boyd H, Gonzalez-Martinez JF, Welbourn RJL, Ma K, Li P, Gutfreund P, Klechikov A, Arnebrant T, Barker R, Sotres J. Effect of nonionic and amphoteric surfactants on salivary pellicles reconstituted in vitro. Sci Rep 2021; 11:12913. [PMID: 34155330 PMCID: PMC8217253 DOI: 10.1038/s41598-021-92505-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Accepted: 06/11/2021] [Indexed: 11/15/2022] Open
Abstract
Surfactants are important components of oral care products. Sodium dodecyl sulfate (SDS) is the most common because of its foaming properties, taste and low cost. However, the use of ionic surfactants, especially SDS, is related to several oral mucosa conditions. Thus, there is a high interest in using non-ionic and amphoteric surfactants as they are less irritant. To better understand the performance of these surfactants in oral care products, we investigated their interaction with salivary pellicles i.e., the proteinaceous films that cover surfaces exposed to saliva. Specifically, we focused on pentaethylene glycol monododecyl ether (C12E5) and cocamidopropyl betaine (CAPB) as model nonionic and amphoteric surfactants respectively, and investigated their interaction with reconstituted salivary pellicles with various surface techniques: Quartz Crystal Microbalance with Dissipation, Ellipsometry, Force Spectroscopy and Neutron Reflectometry. Both C12E5 and CAPB were gentler on pellicles than SDS, removing a lower amount. However, their interaction with pellicles differed. Our work indicates that CAPB would mainly interact with the mucin components of pellicles, leading to collapse and dehydration. In contrast, exposure to C12E5 had a minimal effect on the pellicles, mainly resulting in the replacement/solubilisation of some of the components anchoring pellicles to their substrate.
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Affiliation(s)
- Hannah Boyd
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
| | - Juan F Gonzalez-Martinez
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
| | - Rebecca J L Welbourn
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
| | - Kun Ma
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
| | - Peixun Li
- ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
| | - Philipp Gutfreund
- Institut Laue Langevin, 71 Avenue des Martyrs, 38000, Grenoble, France
| | - Alexey Klechikov
- Institut Laue Langevin, 71 Avenue des Martyrs, 38000, Grenoble, France
- Department of Physics and Astronomy, Uppsala University, 75120, Uppsala, Sweden
| | - Thomas Arnebrant
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden
| | - Robert Barker
- School of Physical Sciences, University of Kent, Canterbury, CT2 7NZ, UK
| | - Javier Sotres
- Biomedical Science Department, Biofilms-Research Center for Biointerfaces, Malmö University, 20506, Malmö, Sweden.
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Fischer NG, Aparicio C. The salivary pellicle on dental biomaterials. Colloids Surf B Biointerfaces 2021; 200:111570. [PMID: 33460965 PMCID: PMC8005451 DOI: 10.1016/j.colsurfb.2021.111570] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Revised: 12/23/2020] [Accepted: 01/07/2021] [Indexed: 12/18/2022]
Abstract
The salivary pellicle, an adlayer formed by adsorption of salivary components on teeth and dental biomaterials, has direct consequences on basic outcomes of dentistry. Here, we provide an overview of salivary pellicle formation processes with a critical focus on dental biomaterials. We describe and critique the array of salivary pellicle measurement techniques. We also discuss factors that may affect salivary pellicle formation and the heterogeneity of the published literature describing salivary pellicle formation on dental biomaterials. Finally, we survey the many effects salivary pellicles have on dental biomaterials and highlight its implications on design criteria for dental biomaterials. Future investigations may lead to rationally designed dental biomaterials to control the salivary pellicle and enhance material function and patient outcomes.
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Affiliation(s)
- Nicholas G Fischer
- MDRCBB, Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, Minneapolis, Minnesota, 55455, USA
| | - Conrado Aparicio
- MDRCBB, Minnesota Dental Research Center for Biomaterials and Biomechanics, University of Minnesota, Minneapolis, Minnesota, 55455, USA.
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Wang S, Olarte Mantilla SM, Smith PA, Stokes JR, Smyth HE. Astringency sub-qualities drying and pucker are driven by tannin and pH – Insights from sensory and tribology of a model wine system. Food Hydrocoll 2020. [DOI: 10.1016/j.foodhyd.2020.106109] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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Boyd H, Gonzalez-Martinez JF, Welbourn RJL, Gutfreund P, Klechikov A, Robertsson C, Wickström C, Arnebrant T, Barker R, Sotres J. A comparison between the structures of reconstituted salivary pellicles and oral mucin (MUC5B) films. J Colloid Interface Sci 2020; 584:660-668. [PMID: 33198975 DOI: 10.1016/j.jcis.2020.10.124] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2020] [Revised: 10/06/2020] [Accepted: 10/27/2020] [Indexed: 01/01/2023]
Abstract
HYPOTHESIS Salivary pellicles i.e., thin films formed upon selective adsorption of saliva, protect oral surfaces against chemical and mechanical insults. Pellicles are also excellent aqueous lubricants. It is generally accepted that reconstituted pellicles have a two-layer structure, where the outer layer is mainly composed of MUC5B mucins. We hypothesized that by comparing the effect of ionic strength on reconstituted pellicles and MUC5B films we could gain further insight into the pellicle structure. EXPERIMENTS Salivary pellicles and MUC5B films reconstituted on solid surfaces were investigated at different ionic strengths by Force Spectroscopy, Quartz Crystal Microbalance with Dissipation, Null Ellipsometry and Neutron Reflectometry. FINDINGS Our results support the two-layer structure for reconstituted salivary pellicles. The outer layer swelled when ionic strength decreased, indicating a weak polyelectrolyte behavior. While initially the MUC5B films exhibited a similar tendency, this was followed by a drastic collapse indicating an interaction between exposed hydrophobic domains. This suggests that mucins in the pellicle outer layer form complexes with other salivary components that prevent this interaction. Lowering ionic strength below physiological values also led to a partial removal of the pellicle inner layer. Overall, our results highlight the importance that the interactions of mucins with other pellicle components play on their structure.
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Affiliation(s)
- Hannah Boyd
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden.
| | - Juan F Gonzalez-Martinez
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Rebecca J L Welbourn
- ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
| | - Philipp Gutfreund
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble 38000, France
| | - Alexey Klechikov
- Institut Laue Langevin, 71 avenue des Martyrs, Grenoble 38000, France; Department of Physics and Astronomy, Uppsala University, 75120 Uppsala, Sweden
| | - Carolina Robertsson
- Department of Oral Biology and Pathology & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Claes Wickström
- Department of Oral Biology and Pathology & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Thomas Arnebrant
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden
| | - Robert Barker
- School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK
| | - Javier Sotres
- Department of Biomedical Science & Biofilms-Research Center for Biointerfaces, Malmö University, 20506 Malmö, Sweden.
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Kratz F, Grass S, Umanskaya N, Scheibe C, Müller-Renno C, Davoudi N, Hannig M, Ziegler C. Cleaning of biomaterial surfaces: Protein removal by different solvents. Colloids Surf B Biointerfaces 2015; 128:28-35. [DOI: 10.1016/j.colsurfb.2015.02.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Revised: 02/06/2015] [Accepted: 02/08/2015] [Indexed: 02/07/2023]
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Zhang Y, Zheng J, Zheng L, Zhou Z. Effect of adsorption time on the adhesion strength between salivary pellicle and human tooth enamel. J Mech Behav Biomed Mater 2015; 42:257-66. [DOI: 10.1016/j.jmbbm.2014.11.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2014] [Revised: 11/17/2014] [Accepted: 11/22/2014] [Indexed: 01/30/2023]
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Aroonsang W, Sotres J, El-Schich Z, Arnebrant T, Lindh L. Influence of substratum hydrophobicity on salivary pellicles: organization or composition? BIOFOULING 2014; 30:1123-1132. [PMID: 25377485 DOI: 10.1080/08927014.2014.974155] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Different physico-chemical properties (eg adsorption kinetics, thickness, viscoelasticity, and mechanical stability) of adsorbed salivary pellicles depend on different factors, including the properties (eg charge, roughness, wettability, and surface chemistry) of the substratum. Whether these differences in the physico-chemical properties are a result of differences in the composition or in the organization of the pellicles is not known. In this work, the influence of substratum wettability on the composition of the pellicle was studied. For this purpose, pellicles eluted from substrata of different but well-characterized wettabilities were examined by means of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The results showed that substratum hydrophobicity did not have a major impact on pellicle composition. In all substrata, the major pellicle components were found to be cystatins, amylases and large glycoproteins, presumably mucins. In turn, interpretation of previously reported data based on the present results suggests that variations in substratum wettability mostly affect the organization of the pellicle components.
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Sotres J, Madsen JB, Arnebrant T, Lee S. Adsorption and nanowear properties of bovine submaxillary mucin films on solid surfaces: Influence of solution pH and substrate hydrophobicity. J Colloid Interface Sci 2014; 428:242-50. [DOI: 10.1016/j.jcis.2014.04.058] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Revised: 04/23/2014] [Accepted: 04/26/2014] [Indexed: 10/25/2022]
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Barrantes A, Arnebrant T, Lindh L. Characteristics of saliva films adsorbed onto different dental materials studied by QCM-D. Colloids Surf A Physicochem Eng Asp 2014. [DOI: 10.1016/j.colsurfa.2013.05.054] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Sotres J, Barrantes A, Lindh L, Arnebrant T. Strategies for a direct characterization of phosphoproteins on hydroxyapatite surfaces. Caries Res 2013; 48:98-110. [PMID: 24296726 DOI: 10.1159/000351871] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2013] [Accepted: 05/08/2013] [Indexed: 11/19/2022] Open
Abstract
We show in this work how systems formed by phosphoproteins on calcium phosphate surfaces can be directly characterized, in real time, in liquid medium, without the need for elution or labeling. Specifically, we show how this is possible by applying three different techniques: ellipsometry, quartz crystal microbalance with dissipation, and atomic force microscopy-based friction force spectroscopy. We apply these techniques to study two different model systems, i.e. those formed upon the adsorption of two model phosphoproteins (κ- and β-casein) on hydroxyapatite (HA) surfaces. Information on the kinetics of adsorption, surface excess, viscoelasticity, water content, thickness of the layers, and protein-surface interaction is provided. Results indicate that both phosphoproteins form homogeneous elastic highly hydrated monolayers on the HA surfaces, the strength of β-casein layers being higher by approximately a factor of 4. Based on the experimental results, models for the conformation of κ- and β-casein molecules adsorbed on HA surfaces are proposed.
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Affiliation(s)
- J Sotres
- Biomedical Sciences, Faculty of Health and Society, Malmö University, Malmö, Sweden
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Experimental Investigations of Biological Lubrication at the Nanoscale: The Cases of Synovial Joints and the Oral Cavity. LUBRICANTS 2013. [DOI: 10.3390/lubricants1040102] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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AFM volumetric methods for the characterization of proteins and nucleic acids. Methods 2013; 60:113-21. [DOI: 10.1016/j.ymeth.2013.02.005] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 01/28/2013] [Accepted: 02/14/2013] [Indexed: 11/19/2022] Open
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Wagner KC, Wang Y, Regen SL, Vezenov DV. Yield strength of glued Langmuir–Blodgett films determined by friction force microscopy. Phys Chem Chem Phys 2013; 15:14037-46. [DOI: 10.1039/c3cp50444a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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AFM-Based Friction Force Spectroscopy: A Novel Methodology for the Study of the Strength and Lateral Diffusion of Proteinaceous Films. ACTA ACUST UNITED AC 2012. [DOI: 10.1021/bk-2012-1120.ch006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Sotres J, Pettersson T, Lindh L, Arnebrant T. NanoWear of Salivary Films vs. Substratum Wettability. J Dent Res 2012; 91:973-8. [DOI: 10.1177/0022034512456704] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The pellicle serves as a multifunctional protective layer, providing, e.g., lubrication and remineralization and also acting as a diffusion barrier. In addition, since the formation of the pellicle precedes the adhesion of micro-organisms, it is also important as a conditioning film. We present a novel approach to study the influence of the water wettability of solid surfaces on the strength of adsorbed salivary films. It is based on studying the wear resistance of the films with an atomic force microscope operated in the friction force spectroscopy mode. This methodology provides the strength of the films in terms of the forces needed for breaking and removing them. Our results indicate that these forces are highly dependent on the water wettability of the underlying substrata, decreasing with increasing hydrophobicity. Thus, this study provides valuable information for the design of materials exposed in the oral cavity, i.e., materials that will minimize plaque formation and be easy to clean.
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Affiliation(s)
- J. Sotres
- Biomedical Science, Faculty of Health and Society, Malmö University, 20506 Malmö, Sweden
| | - T. Pettersson
- Fibre and Polymer Technology, KTH Royal Institute of Technology, 10044 Stockholm, Sweden
| | - L. Lindh
- Prosthetic Dentistry, Faculty of Odontology, Malmö University, 20506 Malmö, Sweden
| | - T. Arnebrant
- Biomedical Science, Faculty of Health and Society, Malmö University, 20506 Malmö, Sweden
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Harvey NM, Yakubov GE, Stokes JR, Klein J. Lubrication and load-bearing properties of human salivary pellicles adsorbed ex vivo on molecularly smooth substrata. BIOFOULING 2012; 28:843-856. [PMID: 22881290 DOI: 10.1080/08927014.2012.714777] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In a series of Surface Force Balance experiments, material from human whole saliva was adsorbed to molecularly smooth mica substrata (to form an 'adsorbed salivary film'). Measurements were taken of normal (load bearing, F (n)) and shear (frictional, F (s)*) forces between two interacting surfaces. One investigation involved a salivary film formed by overnight adsorption from undiluted, centrifuged saliva, with the adsorbed film rinsed with pure water before measurement. Measurements were taken under pure water and 70 mM NaNO(3). In a second investigation, a film was formed from and measured under a solution of 7% filtered saliva in 10 mM NaNO(3). F (n) results for both systems showed purely repulsive layers, with an uncompressed thickness of 35-70 nm for the diluted saliva investigation and, prior to the application of shear, 11 nm for the rinsed system. F (s)* was essentially proportional to F (n) for all systems and independent of shear speed (in the range 100-2000 nm s(-1)), with coefficients of friction μ ≈ 0.24 and μ ≈ 0.46 for the unrinsed and rinsed systems, respectively. All properties of the rinsed system remained similar when the pure water measurement environment was changed to 70 mM NaNO(3). For all systems studied, shear gave rise to an approximately threefold increase in the range of normal forces, attributed to the ploughing up of adsorbed material during shear to form debris that stood proud of the adsorbed layer. The results provide a microscopic demonstration of the wear process for a salivary film under shear and may be of particular interest for understanding the implications for in vivo oral lubrication under conditions such as rinsing of the mouth cavity. The work is interpreted in light of earlier studies that showed a structural collapse and increase in friction for an adsorbed salivary film in an environment of low ionic strength.
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Affiliation(s)
- Neale M Harvey
- The Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK
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