ME Visiting Faculty Seminar
|Event Date:||March 24, 2014|
|Type:||Visiting Faculty Seminar
|Contact Name:||Cynthia Dalton
Hydrogel materials are emerging as biological mimics, especially in biomedical applications such as contact lenses that rely on lubricity for success. Hydrogels can not only emulate the "softness" of biological tissues with low elastic modulus, but can also contain water as an inherent component of 5-95% by mass. When soft hydrated surfaces slide against each other, as in a healthy human eye, the properties of the tissues and tear fluid combine to lubricate the interfaces over thousands of cycles of blinking in 15-18 waking hours per day. Taking the eye as a model system, a technique was developed to reliably measure the low-pressure friction response of hydrogel soft contact lenses using glass probes. The friction coefficients measured in buffered saline exhibit trends related to surface composition and experimental conditions. An open platform instrument was used to gain insights by testing directly on biological materials: a living mouse eye, a cell monolayer, and a stratified corneal tissue. Though glass probes are suited to contact models and material property investigations, they are not present in physiological conditions – therefore, the low-pressure friction instrumentation was adapted for use to match a hydrogel probe with the hydrogel flat sample, a paired "Gemini" interface. This resulted in identification of distinct friction and lubrication behavior when a hydrogel is sliding against itself versus a hard impermeable surface such as glass. Details are provided on hydrogel manufacture, soft materials contact models, instrumentation, and identification of dominating mechanisms of lubricity at the intersection of mechanics, metrology, materials science, and biology.