AVS 64th International Symposium & Exhibition
    Tribology Focus Topic Thursday Sessions
       Session TR+AC+TF+VT-ThM

Invited Paper TR+AC+TF+VT-ThM12
Tribology of Cellular Interfaces

Thursday, November 2, 2017, 11:40 am, Room 10

Session: Lubricant, Coatings, and Biotribology
Presenter: Angela Pitenis, University of Florida
Authors: A.A. Pitenis, University of Florida
J.M. Urueña, University of Florida
S.M. Hart, University of Florida
T.T. Hormel, University of Florida
C.S. O'Bryan, University of Florida
S.L. Marshall, University of Florida
K.D. Schulze, University of Florida
P.P. Levings, University of Florida
T.E. Angelini, University of Florida
W.G. Sawyer, University of Florida
Correspondent: Click to Email
Human health, mobility, and quality of life critically hinge on the body’s ability to provide adequate lubrication between most contacting and sliding biological interfaces. Soft, aqueous, and mucinated biopolymer networks lining all moist epithelia enable the body to provide lubricity over a wide range of contact pressures and sliding speeds. The exquisite slipperiness and softness of biological sliding interfaces present significant experimental challenges for fundamental studies on their tribological performance. Physiological contact pressure conditions must be matched in in vivo, ex vivo, and in vitro studies that aim to acquire physiologically-relevant friction measurements. While biotribological investigations using living cells, cell layers, and tissues necessitate low contact pressure measurements, such studies frequently rely on the application of low forces to achieve accomodating contact pressures (kPa range), and traditional methods can decrease the contact area below a physiologically-relevant threshold. The softness of a cell layer (E ~ 10 kPa) provides an order-of-magnitude estimate for the amount of mechanical pressure that may be applied to cells during tribological testing; contact pressures about 5 kPa and shear stresses in excess of 200 Pa are sufficient to wreak significant damage to a cell layer. Recently, direct contact tribological experiments on a living cell layer without incurring any measurable cell death in the sliding path has become possible through the application of a soft, thin, spherically-capped membrane hydrogel probe. With this experimental configuration, in vitro tribological experiments were performed against a monolayer of mucin-producing human corneal epithelial cells (hTCEpi) for 10,000 reciprocating cycles at physiologically-relevant contact pressures and challenging sliding speeds. The gel-cell sliding interface under applied normal loads of ~ 200 µN resulted in measured friction coefficients of µ ~ 0.06 and achieved shear stresses on the order of 60 Pa, which is below the critical shear stress for inducing cell death; excellent cell survival rates (~99.8%) were measured after extended duration tribological experimentation.