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Understanding the role of sugar and glycan structure in natural lubrication mechanisms

English title Understanding the role of sugar and glycan structure in natural lubrication mechanisms
Applicant Spencer Nicholas D.
Number 124405
Funding scheme Project funding
Research institution Laboratory for Surface Science & Technology Department of Materials ETH Zurich
Institution of higher education ETH Zurich - ETHZ
Main discipline Material Sciences
Start/End 01.04.2009 - 31.05.2012
Approved amount 194'648.00
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Keywords (9)

Lubrication; polysaccharides; gradients; sugar; glycoprotein; natural lubrication; water lubrication; copolymers; Poly(l-lysine)-g-dextran

Lay Summary (English)

Lead
Lay summary
Nature lubricates with water, by means of dissolved glycoproteins: protein backbones with sugar chains grafted to them. These molecules seem to function by adsorbing onto the surfaces to be lubricated through the protein backbone, while the sugar side-chains hold water in the near-surface region. This immobilized water seems to play an important role in rendering the surface lubricious. Exactly what properties of the sugar chains are important for holding the water in place are not fully understood. To this end we intend to examine a number of possible modifications to the sugar chains, including stiffening the system by bonding the sugar chains together through intermediate molecules ("crosslinking"), modifying the interactions between charged sugar species, and forming surface-concentration gradients of the sugar chains on surfaces to determine the critical surface coverage at which the sugars start to display lubricating properties. In addition to using sugar chains such as those found in nature, synthetic analogs, such as the graft copolymer, poly(l-lysine)-g-dextran, will be investigated as model systems. These have the advantage of relative simplicity and easy availability, since they can be synthesized in our laboratory.A more thorough understanding of the function of natural lubricants will be interesting, both in a fundamental and in a technological sense. Potential applications of knowledge gained in this project are in the selection of implanted joint materials, in the lubrication of medical devices such as catheters, and in the design of aqueous lubricant additives for industrial applications.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Influence of Solutes on Hydration and Lubricity of Dextran Brushes
Goren Tolga, Crockett Rowena, Spencer Nicholas D (2012), Influence of Solutes on Hydration and Lubricity of Dextran Brushes, in CHIMIA International Journal for Chemistry, 66, 192-195.
Load-Induced Transitions in the Lubricity of Adsorbed Poly( l-lysine)- g-dextran as a Function of Polysaccharide Chain Density
Rosenberg Kenneth J, Goren Tolga, Crockett Rowena, Spencer Nicholas D (2011), Load-Induced Transitions in the Lubricity of Adsorbed Poly( l-lysine)- g-dextran as a Function of Polysaccharide Chain Density, in ACS Applied Materials & Interfaces, 3, 3020-3025.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
International Conference on Biotribology 19.09.2011 London, UK
Swiss Chemical Society 09.09.2011 EPFL, Switzerland
Gordon Research Conference: Triboloy 02.06.2010 Maine, USA


Awards

Title Year
Best Oral Presentation 2011

Associated projects

Number Title Start Funding scheme
140452 Mechanisms of aqueous lubrication with amphiphilic polymers 01.06.2012 Project funding
140343 Understanding the role of sugar structure in natural lubrication mechanisms 01.06.2012 Project funding
136191 Designing Interactions across Interfaces in Ionic Liquids 01.01.2012 Sinergia
140343 Understanding the role of sugar structure in natural lubrication mechanisms 01.06.2012 Project funding
120196 AQUALUBE - Water-based lubricants: theory and experiment 01.04.2008 Project funding (special)
116150 Single- and Multi-dimensional Surface Gradients and their Applications 01.04.2007 Project funding

Abstract

Sugar chains appear to play an important role in natural lubrication. In two preceding projects, the friction-reduction properties of end-grafted polysaccharide chains were investigated for both natural and synthetic systems. The project described here represents a significant extension, as well as a combination of these previous projects. In one case, the behaviour of dextran grafted to poly L-lysine was found to deviate significantly from that of poly(ethylene glycol) in PLL-g-PEG. In the other, the ability of glycoproteins to reduce friction was observed and the arrangement of the glycan residues at the surface determined. Results from both of these projects have led to new and fundamental questions concerning the mechanism of friction reduction by polysaccharides on a molecular level.The aim of this project is to determine how the polysaccharide structure influences friction by carrying out further, in-depth investigations into the behaviour of the synthetic graft copolymer, PLL-g-dextran, as well as alpha-1-acid glycoprotein and alpha-1-antitrypsin. PLL-g-dextran adsorbs onto negatively charged surfaces through the positively charged lysine groups at pH 7. The behaviour of the dextran chains during adsorption will be investigated by forming gradients of PLL-g-dextran and by adsorbing the PLL-g-dextran onto chemical gradients. Of particular interest in these experiments is whether a change in the packing density of the dextran chains can be induced by substrate modification. This will provide information on how adsorption is directed, that is, whether interactions between the chains, such as hydrogen bonding, determine the degree of coverage. This would be in contrast to PLL-g-PEG, where adsorption density is mainly determined by electrostatic repulsion between the positively charged lysine residues. Two methods will be used to modify the flexibility of the dextran chains. Any possible influence of hydrogen bonding on the adsorption behaviour and structure will be interrupted by partial acetylation of the dextran chains. Crosslinking of the dextran chains will be carried out in order to make the structure formed by PLL-g-dextran at the surface less flexible. Firstly, the crosslinking reaction will be carried after adsorbing PLL-g-dextran onto the surface. However, the efficiency of this reaction may be limited by the close proximity of the chains to each other. Alternatively, intramolecular crosslinking will be carried out as intermolecular crosslinking can be expected to result in an insoluble gel. The change in friction caused by modifying the interactions between the dextran chains will be investigated with atomic force microscopy.It has been determined that the glycan residues on glycoproteins can reduce friction. Additionally, it was found that the conformation of the glycans on alpha-1-acid glycoprotein adsorbed on hydrophobic surfaces was the same as that in the native protein. This conformation is caused, partially, by the electrostatic attraction between negatively charged sialic acid groups on the glycans and positively charged lysine residues on the peptide backbone. Another factor influencing the conformation may be steric restrictions on the tetraantennary glycan chains preventing them from extending into the solutions. Alpha-1-antitrypsin contains mainly biantennary glycans that can extend into the aqueous solution when then electrostatic interactions are weakend. The effect of interrupting these interactions on the packing of the glycoproteins on the surface and the effect on friction will be examined. By forming gradients of these two conformations, any transition in the friction behaviour on changing the packing density of the glycoproteins will be detected. Proteins can adsorb onto hydrophilic and hydrophobic surfaces due to the different chemistries of the amino acids. However, alpha-1-acid glycoprotein was found to adsorb more efficiently onto hydrophobic surfaces, therefore, such surfaces will be used in these investigations.These studies on the relationship between friction and structure will allow model systems to be synthesised that combine the optimal structural features of the polysaccharides. At present the optimum structure and interchain interactions cannot be predicted, however, some suggestions for possible synthetic routes can be made.
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