Dynamic interfacial behavior of viscoelastic aqueous hyaluronic acid: effects of molecular weight, concentration and interfacial velocity
Tuesday, February 11, 2014 – 3:30pm – 4:45pm
An aqueous hyaluronic acid (HA(aq)) pericellular coat, when mediating the tactile aspect of cellular contact inhibition, has three tasks: interface formation, mechanical signal transmission and interface separation. To quantify the interfacial adhesive behavior of HA(aq), we induce simultaneous interface formation and separation between HA(aq) and a model hydrophobic, hysteretic Si-SAM surface. While surface tension ‘g’ remains essentially constant, interface formation and separation depend greatly on concentration (5 < C < 30 mg/mL), molecular weight (6 < MW < 2000 kDa) and interfacial velocity (0 < V < 3 mm/sec), each of which affect shear elastic and loss moduli G’ and G”, respectively. Viscoelasticity dictates the mode of interfacial motion: wetting/dewetting, capillary necking, or rolling. Wetting/dewetting is quantified using advancing and receding contact angles qA and qR, and the hysteresis between them, yielding data landscapes for each C above the [MW, V] plane. The landscape sizes, shapes, and curvatures disclose the interplay, between surface tension and viscoelasticity, which governs interfacial dynamics. Gel point coordinates modulus G and angular frequency ‘w’ appear to predict wetting/dewetting (G < 75w**0.2), capillary necking (75w**0.2 < G < 200w**0.075) or rolling (G > 200w**0.075). Dominantly dissipative HA(aq) sticks to itself and distorts irreversibly before separating, while dominantly elastic HA(aq) makes contact and separates with only minor, reversible distortion. We propose the dimensionless number (G’V)/(w*g), varying from ~10**-5 to ~10**3 in this work, as a tool to predict the mode of interface formation-separation by relating interfacial kinetics with bulk viscoelasticity. Cellular contact inhibition may be thus aided or compromised by physiological or interventional shifts in [C, MW, V], and thus in (G’V)/(w*g) which affect both mechanotransduction and interfacial dynamics. These observations, understood in terms of physical properties, may be broadened to probe interfacial dynamics of other viscoelastic aqueous biopolymers.
REFRESHMENTS AT 3:20 PM IN REGENTS HALL 109
Host: Makarand Paranjape
Discussion Leader: Makarand Paranjape