Effect of operational conditions and environment on lubricity of hydrophobins in water based lubrication systems

Abstract

In this study, the effect of operational conditions (normal load, sliding velocity) and environment (pH and ionic strength) on the lubrication properties of two different hydrophobin proteins were investigated using pin on disc tribometry and ellipsometry. The studied proteins were wild type HFBI and the glycosylated hydrophobin FpHYD5. It was observed that the friction of a stainless steel versus stainless steel contact lubricated with either of the hydrophobins did not depend on the normal load. However, increased sliding velocity occasionally led to a decrease in friction when the surfaces were lubricated with the glycosylated FpHYD5. The tribological behaviour of FpHYD5 was studied at pH values ranging from 3 to 9 and generally lowered friction by 31-38% and wear by 40-65% compared to the corresponding buffer solutions. An exception was pH 9, where FpHYD5 increased friction and wear compared to the buffer solution. Ionic strength affected both the amount of protein that was adsorbed and the lubrication properties of glycosylated hydrophobins.

Lubrication of aluminium versus diamond-like carbon contacts with hydrophobin proteins

“…8,12,13 However, it was observed that an increase in the amount of hydrophobins adsorbed on the surface may increase the friction and wear of sliding contacts. 8,14 Friction coefficients in hydrophobin-lubricated stainless steel contacts were in the range of 0.1-0.3, which are similar to that measured on mica surfaces lubricated with HFBI. 15 Diamond-like carbon (DLC) coatings are known for their high hardness, low friction, high wear resistance, as well as for their biocompatibility, which makes them suitable for biomedical applications.…”

“…Interestingly, in this study, friction coefficients measured in hydrophobin-lubricated experiments were at the same level (0.1-0.3) as those measured in stainless steel versus stainless steel contacts using hydrophobin additives, as previously reported. 14 We can state that in hydrophobin-containing contacts, hydrophobins played a major role in the lubrication regime. Although the friction coefficients of the original bare stainless steel and DLC coating surfaces in a water environment were quite different, these surfaces showed similar wetting properties (Fig.…”

“…8,12,13 However, it was observed that an increase in the amount of hydrophobins adsorbed on the surface may increase the friction and wear of sliding contacts. 8,14 Friction coefficients in hydrophobin-lubricated stainless steel contacts were in the range of 0.1–0.3, which are similar to that measured on mica surfaces lubricated with HFBI. 15…”

Low friction of phytic acid as a water-based lubricant additive

“…Phospholipids, found in rich quantities in living joints, have been found to act as a kind of effective lubricant in protecting the cartilage from damage (Oloyede et al, 2004). The formation of a hydrophobin protein layer was reported to significantly reduce friction and wear (Ahlroos et al, 2011;Hakala et al, 2014). Notable lubrication performance was also found using lactic acid solutions when silicon nitride ball was sliding silica glass .…”