BIOMED Master's Thesis Defense
Depolarized Light Scattering and Rheology of Hydrogels|
Date: July 7, 2008
at 10:30 AM
Location: Bossone Research Enterprise Center, Room: 302
James T. Kolb
Advisors: Elisabeth Papazoglou, Ph.D., and Leonid Zubkov, Ph.D.
The goal of this thesis was to design, develop and characterize a non-destructive method to assess the mechanical properties of clear hydrogels using information from the depolarized scattering of focused light. There are currently no published commercially available systems with the ability to monitor remotely the crosslinking density of hydrogel systems. This new system will allow for accurate in-process monitoring and process optimization without the loss of product. The optical system developed uses inexpensive off-the-shelf components and measures the relative intensity, a qualitative measure that is correlated to the crosslinking density of ionically (Ca2+) crosslinked alginate gels. The incident laser (685-nm wavelength) is vertically polarized, while the scattered light is collected after having been horizontally polarized The crosslinked sections of hydrogels, are structures where the local index of refraction varies when observed from different directions, that is they exhibit optical anisotropy. Depolarized light scattering is a sensitive measurement method for the investigation of systems exhibiting local anisotropy, such as macromolecules and liquid crystals. The polarized light is scattered from both isotropic and anisotropic structures within the media, and by measuring the depolarized light, the contribution of the anisotropic structures can be separated and assessed. We have used as a model hydrogel system sodium alginate hydrogels crosslinked by Calcium ions (in the form of CaCl2). The scattered depolarized light intensity is related to a “flow index," which is a measure of apparent viscosity, and is directly related to the crosslinking density of the gel structure. The final designed system is sensitive to 1% changes in alginate concentration and .1% changes in calcium ion concentration.
The Bossone Research Enterprise Center is located at the corner of 32nd and Market Streets.