Hyder A. Aliyar

Internal Osmotic Pressure as a Mechanism of Retinal Attachment in a Vitreous Substitute

In this study, the possibility of using the internal osmotic pressure of intraocular polymeric hydrogel materials to attach the retina in the repair of a retinal tear or hole was investigated. This is in contrast to the conventional methods of retinal detachment repair (intraocular gas, polydimethylsiloxane, or n-perfluorooctane), which rely on surface tension and have recognized limits. The system selected for implementation of this scheme was based on an acrylamide copolymer that was crosslinked in an aqueous solution to provide a transparent hydrogel which allowed control of the swelling pressure. Synthetic hydrogels, such as those selected here, provide an alternative to materials currently used as vitreous prostheses.

Synthesis of Polyacrylamide Nanogels by Intramolecular Disulfide Cross-linking

Nondegradable polyamides with protein-like properties were designed and prepared as a copolymeric hydrogel by the free-radical polymerization of acrylamide with a disulfide-containing cross-linking agent, N, N-bisacryloylcystamine. Copolyacrylamides containing pendent thiol groups (BSH) were obtained after reduction of the disulfide bonds in the hydrogel, followed by precipitation in methanol. Ellmans analysis and gel-permeation chromatography (GPC) were used to characterize the copolymer. Redissolution of the copolymer in water at very dilute concentrations, followed by air oxidation under physiological conditions (pH 7.5), resulted in nanoparticles (nanogels). The dilute concentration favored intramolecular disulfide crosslinking in the polymer chain, resulting primarily in a single-chain nanogel. Nanogel formation was confirmed and characterized using GPC, dynamic light scattering and atomic force microscopy. The size of the nanogels ranged from 20–200nm.

Tissue Reaction to Prosthetic Materials

Prostheses are manmade materials to replace or augment diseased or damaged body parts in a safe, reliable, economical, and physiologically acceptable manner. This chapter is restricted to materials that remain in intimate contact with blood, tissue, or body fluids for a prolonged time (weeks to years). Eyeglasses, hearing aids, wearable artificial limbs, and so on, although very important to rehabilitation, are not covered. Tissue reactions to disposable devices, such as contact lenses, or extracorporeal materials that are used briefly (dialysis equipment, etc.) are also outside the scope of this discussion. In addition, no particular distinction between blood vs tissue biocompatibility is made, as the molecular events in both are similar and assumed to be a part of the same physiological continuum. This chapter focuses on recent literature (1990 to present) that primarily deals with histopathological investigations of implants in human subjects. Because the interplay between tissues and prostheses involves various aspects of chemical, physical, and biological sciences, some basic concepts that will be useful to both the surgeon and the materials scientist are first introduced. These concepts are subsequently integrated to address the complex interplay between molecular and cellular reactions that occur when a foreign object is placed in the body.