Author: Gustavo A. Guzman Cardozo

Publisher:

Published: 2016

Total Pages: 192

ISBN-13:

The first part of this study presents a strategy for the synthesis of novel bimodal amphiphilic grafts consisting of hydrophilic poly (N,N-dimethylacrylamide) (PDMAAm) main chains carrying two different molecular weight hydrophobic polydimethylsiloxane (PDMS) branches whose crosslinking leads to bimodal amphiphilic conetworks ([beta]-APCNs). The effect of crosslinker ratio and amount of high molecular weight PDMS on the conetwork's morphology, swelling characteristics and mechanical properties were evaluated. The materials exhibited bulk microphase separation with short-range ordering, and superficial demixing with only the hydrophobic phase present at the surface. A multi-scale, composition-dependent, elastic wrinkling-instability was shown to control surface morphology. The coexistence of low and high molecular weight PDMS in [beta]-APCNs greatly improved ultimate mechanical properties. The second study concerns the structure development of [beta]-APCNs during film processing from solution. Time-resolved gravimetry, low contact angles and negative out-of-plane birefringence provided strong experimental evidence of transitory trapping of thermodynamically unfavorable hydrophilic moieties at the air-film interface due to fast asymmetric solvent depletion. We also find that slow-drying hydrophobic elements progressively substitute hydrophilic domains at the surface as the surface-energy is minimized. The third study proposes a novel approach to zero-order, constant-rate drug delivery from [beta]-APCN-based contact lenses. Quasi-Case II non-Fickian transport was achieved by non-uniform drug and diffusivity distributions within three-layer bimodal amphiphilic conetworks. We demonstrated experimentally and by modeling that the combined effect of non-uniform distribution of drug loading and diffusion constants within the three-layer lens maintains low local drug concentration at the lens-fluid interface and yields zero-order drug delivery.The final study uses in-situ ellipsometry, contact angle measurements, and X-ray photoelectron spectroscopy to investigate the swelling behavior, surface characteristics and adsorption of plasma proteins of bimodal amphiphilic conetworks ([beta]-APCNs). We demonstrated that plasma protein adsorption in [beta]-APCNs is transport-limited. [beta]-APCNs have the ability to reconfigure their surfaces depending on the medium as evidenced by large contact angle hysteresis, so that in aqueous solution hydrophilic moieties populate the surface. Protein adsorption occurred at the hydrophobic PDMS domains (which become buried in the bulk after swelling) and plasma proteins needed to diffuse into the conetwork in order to adsorb. Desorption was dependent on the initial adsorption rate.