Multifunctional And Supramolecular Materials Through The Hydrophobic Effect
Ever since the discovery of liposomes by A.D Bangham in 1961, they have attracted significant attention as drug delivery systems because they are biologically inert and weakly immunogenic, have low intrinsic toxicity and possess target delivery properties. Since steric stabilization of liposomes in the biologic milieu is a necessary condition for their utility as drug carriers, significant surface modification methods have been applied to liposomes to increase their stability. In this thesis, we describe a modification of the bilayer surface of liposomes using a hydrophobically modified watersoluble polymer (hydrophobically modified chitosan, hm-chitosan) based on the hydrophobic interaction between the polymer hydrophobes and liposome bilayer. Subsequently, we describe the structure transition of liposome/hm-chitosan systems from hm-chitosan coated liposome solutions at low hm-chitosan concentrations to hmchitosan/ liposome gels at high hm-chitosan concentrations. Beside the application of liposomes in drug delivery, they also have been investigated intensively as biolubricants. This is due to the fact that they contain surface active phospholipids, which form liposome bilayers, reported as major lubricants in the synovial fluid of human joints. We describe filling the interior void of liposomes with a soft biocompatible material, silk fibroin, to enable the system to perform as rolling lubricants. Since rolling friction is always less than sliding friction, this liposome/silk fibroin system results in a low coefficient of friction (COF). Additionally this system shows an enhanced property to minimize surface wear. Based on the projects described above, we developed another lubricant, a biopolymer film with liposomes tethered on the surface. Here, an hm-chitosan film was made and was then used to tether liposomes based on hydrophobic interactions between hm-citosan and liposomes. This method of tethering liposomes leads to a densely packed liposome layer on the film surface. Such liposomal surfaces are effective lubricant, reducing COF values to as low as 10-3 and minimizing surface wear. Also, the compliancy and robustness of these tethered liposomes allow retention on the film surface upon repeated applications of shear. Because films can be used to cover the damaged area of cartilage to protect the surface and reduce pain, such film lubricants may be better than solution based lubricants in severe joint damage treatment. Carbon microspheres have been used extensively as supports for nanoscale zerovalent iron (NZVI) in in-situ ground water remediation, as carbon serves as an adsorbent for chlorinated hydrocarbons, bringing the contaminant to the vicinity of the decontaminating agent of NZVI. However, colloidal instability of carbon microspheres limits their application in ground water remediation. Here, we extend the idea of the hydrophobic interaction between hm-chitosan and liposome bilayer to carbon microspheres, and report a strategy of stabilizing carbon microspheres by adding hmchitosan coatings on carbon surface to create steric repulsions among particles. Such hmchitosan stabilized carbon microspheres show markedly improved colloidal stability against sedimentation. More importantly, the hm-chitosan stabilized carbon microspheres move more effectively through soil. These results indicate the potential use of such environmental benign hydrophobically modified biopolymers in groundwater remediation.