Clear Nonionic Polyurethane Hydrogels for Biomedical Applications

Abstract

Clear nonionic polyurethane hydrogels having a broad range of mechanical properties and degrees of swelling were prepared by both bulk (compression molding) and solution polymerization processes. Hydrogels con taining 70% water were also prepared which had an elongation of 1150% and a tensile strength of 280 kPa. The effects of the chemical structure, molecular weight, and functionality of polyether polyols and type of diisocyanate on hydrogel properties were studied. In addition, the type and concentration of crosslinker, and concentration of ethylene glycol, which was used as chain ex tender were investigated. In order to achieve transparency in the hydrogels, it was determined that poly(oxypropylene) glycols (PPGs) should be present in the system to disrupt the crystallinity of the poly(oxyethylene) glycol (PEG) soft segments. The PEG segments of the network which contain the hydrophilic moiety are responsible for the absorption of water. However, in addition to the concentration of oxyethylene, the degree of swelling of the hydrogels was also determined by measuring the elasticity of the polymer network. The elasticity of the polymer network is determined by the molecular weight between cross links (crosslink density) and the concentration of hard segments in the net work. The concentration of hard segments was controlled by the concentration of chain extender. The crosslink density was controlled by the diol/triol ratio and the respective molecular weight of each component.