Abstract
The ionizable constituent, methacrylic acid, MAA, in copolymers of 2-hydroxyethyl methacrylate, HEMA, and MAA leads to complex physicochemical behavior of gels in environments where the pH, ionic strength, and other aspects of the chemical solvent composition are changeable. Specifically, small changes of pH near a critical value can produce massive changes of physical properties, such as the swollen volume or water content of these gels. Urine exhibits a changeable composition, and importantly, the critical pH of pHEMA/MAA copolymers is within the common range of urine compositions. The physicochemical changes of these copolymers were exploited in the design of a prosthetic material for use in the urinary tract.Included in this dissertation are protocols for purification of HEMA monomer, analytical procedures for analyzing impurities in HEMA monomer, protocols for polymerizing bulk pHEMA under pressure, a protocol for grafting pHEMA to a polyether polyurethane, Tecoflex HR, and a protocol for bonding pHEMA to hydrogel grafts. A formulation, and a protocol for fabricating a urine compatible biomaterial are proposed, and numerous laboratory experiments are presented that demonstrate the responsive nature of the gel in environments mimicing urological and physiological situations. In vitro tests using physiological urine are presented that clearly demonstrate the shrink/swell behavior of the gel. Results of short term In vivo tests (6 months), showing no calcium encrustation of these materials, are also presented.The availability of a responsive material of this nature, for use in the changing environment of the urinary tract, lays the foundation for an entirely new class of materials that may have numerous applications in other non-regulated environments, such as those found in the intestinal tract, or bile ducts, or in non-physiological environments such as pipes or ships, where a responsive surface may provide an economical way to effect descaling.