5 research outputs found
Poly(l-lysine)-grafted-poly(ethylene glycol)-based surface-chemical gradients. Preparation, characterization, and first applications
Spontaneous blinking from a tribological viewpoint
The mechanical forces between the lid wiper and the ocular surface, and between a contact lens and the lid wiper, are reported to be related to dry eye symptoms. Furthermore, the mechanical forces between these sliding partners are assumed to be related to the ocular signs of lid-wiper epitheliopathy (LWE) and lid-parallel conjunctival folds (LIPCOF). Recent literature provides some evidence that a contact lens with a low coefficient of friction (CoF) improves wearing comfort by reducing the mechanical forces between the contact lens surface and the lid wiper. This review discusses the mechanical forces during spontaneous blinks from a tribological perspective, at both low and high sliding velocities, in a healthy subject. It concludes that the coefficient of friction of the ocular surfaces appears to be strongly comparable to that of hydrophilic polymer brushes at low sliding velocity, and that, with increased sliding velocity, there is no wear at the sliding partners' surfaces thanks to the presence of a fluid film between the two sliding partners. In contrast, in the case of dry eye, the failure to maintain a full fluid film lubrication regime at high blinking speeds may lead to increased shear rates, resulting in deformation and wear of the sliding pairs. These shear rates are most likely related to tear film viscosity
Reducing Friction in the Eye: A Comparative Study of Lubrication by Surface-Anchored Synthetic and Natural Ocular Mucin Analogues
Biomaterials used
in the ocular environment should exhibit specific tribological behavior
to avoid discomfort and stress-induced epithelial damage during blinking.
In this study, two macromolecules that are commonly employed as ocular
biomaterials, namely, polyÂ(vinylpyrrolidone) (PVP) and hyaluronan
(HA), are compared with two known model glycoproteins, namely bovine
submaxillary mucin (BSM) and α<sub>1</sub>-acid glycoprotein
(AGP), with regard to their nonfouling efficiency, wettability, and
tribological properties when freely present in the lubricant, enabling
spontaneous adsorption, and when chemisorbed under low contact pressures.
Chemisorbed coatings were prepared by means of photochemically triggered
nitrene insertion reactions. BSM and AGP provided boundary lubrication
when spontaneously adsorbed in a hydrophobic contact with a coefficient
of friction (CoF) of ∼0.03–0.04. PVP and HA were found
to be excellent boundary lubricants when chemisorbed (CoF ≤
0.01). Notably, high-molecular-weight PVP generated thick adlayers,
typically around 14 nm, and was able to reduce the CoF below 0.005
when slid against a BSM-coated polyÂ(dimethylsiloxane) pin in a tearlike
fluid