title: Hydrophobins as aqueous lubricant additive for a soft sliding contact.
abstract: Two type II fungal hydrophobins, HFBI and FpHYD5, have been studied as aqueous lubricant additive at a nonpolar, compliant sliding contact (self-mated poly(dimethylsiloxane) (PDMS) contact) at two different concentrations, 0.1 mg/mL and 1.0 mg/mL. The two hydrophobins are featured as non-glycosylated (HFBI, m.w. ca. 7 kDa) vs glycosylated (FpHYD5, m.w. ca. 10 kDa) proteins. Far UV CD spectra of the two hydrophobins were very similar, suggesting overall structural similarity, but showed a noticeable difference according to the concentration. This is proposed to be related to the formation of multimers at 1.0 mg/mL. Despite 10-fold difference in the bulk concentration, the adsorbed masses of the hydrophobins onto PDMS surface obtained from the two solutions (0.1 and 1.0 mg/mL) were nearly identical, suggesting that a monolayer of the hydrophobins are formed from 0.1 mg/mL solution. PDMS-PDMS sliding interface was effectively lubricated by the hydrophobin solutions, and showed a reduction in the coefficient of friction by as much as ca. two orders of magnitude. Higher concentration solution (1.0 mg/mL) provided a superior lubrication, particularly in low-speed regime, where boundary lubrication characteristic is dominant via 'self-healing' mechanism. FpHYD5 revealed a better lubrication than HFBI presumably due to the presence of glycans and improved hydration of the sliding interface. Two type II hydrophobins function more favorably compared to a synthetic amphiphilic copolymer, PEO-PPO-PEO, with a similar molecular weight. This is ascribed to higher amount of adsorption of the hydrophobins to hydrophobic surfaces from aqueous solution.
authors.affiliation: Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark. Electronic address: seele@mek.dtu.dk.
authors.forename: Seunghwan
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Troels
authors.initials: T
authors.lastname: Røn
authors.affiliation: Department of Mechanical Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
authors.forename: Kirsi I
authors.initials: KI
authors.lastname: Pakkanen
authors.affiliation: Technical Research Centre of Finland, VTT Biotechnology, FIN-02044 VTT, Finland; Department of Biotechnology and Chemical Technology, Aalto University, 00076 Aalto, Finland.
authors.forename: Markus
authors.initials: M
authors.lastname: Linder
mesh_terms: D000327:Adsorption; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D017276:Friction; D005656:Fungal Proteins / Q000737:chemistry* / Q000302:isolation & purification; D005670:Fusarium / Q000737:chemistry; D006031:Glycosylation; D054327:Lubricants / Q000737:chemistry*; D008153:Lubrication; D011092:Polyethylene Glycols / Q000737:chemistry; D011409:Propylene Glycols / Q000737:chemistry; D055503:Protein Multimerization; D012996:Solutions; D013499:Surface Properties; D014242:Trichoderma / Q000737:chemistry; D014867:Water
chemical_list: D004129:Dimethylpolysiloxanes; D005656:Fungal Proteins; D054327:Lubricants; C116176:PEO-PPO-PEO; D011409:Propylene Glycols; D012996:Solutions; D014867:Water; D011092:Polyethylene Glycols
keywords: Amphiphilic; FpHYD5; HFBI; Hydrophobin; Lubrication