JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE 10 (1999) 635±639 Linear poly(ethylene oxide)-based polyurethane hydrogels: polyurethane-ureas and polyurethane- amides P. PETRINI*, M. C. TANZI Department of Bioengineering, Politecnico di Milano, Piazza L. Da Vinci, 32, 20133 Milan, Italy C. R. MORAN, N. B. GRAHAM Department of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham Building, 295 Cathedral Street, Glasgow G1 1XL, UK Over the last 30 years, water-swellable and water-insoluble hydrogels have been extensively investigated and developed, leading to a large family of materials which have found uses in a wide range of biomedical applications. While hydrogels usually present a crosslinked structure, linear polyurethane-ureas (PUUs) based on poly(ethylene oxide) have been shown to be able to absorb and swell with aqueous media without dissolving. This behavior is due to the phase separated domain morphology, where hydrogen bonded urethane/urea hard segment domains are dispersed in a PEO soft segment domain. This work investigates the possibility of obtaining linear poly(ethylene oxide)-based polyurethane-amide (PUA) hydrogels using two amide diols as chain extenders, a mono amide diol (AD) and a diamide diol (DD), and a dicarboxylic acid (maleic acid, MA). Poly(ethylene oxide) based PUAs were obtained using a ``one-shot'' bulk polymerization technique. The chemicophysical characterization and water-solubility tests showed that these materials, while having molecular weights similar to the PUUs, do not possess suf®cient phase separation, hydrogen bonding and hydrophobicity of the hard segment domains to exhibit hydrogel behavior. Crosslinked PUAs using maleic acid as chain extender show interesting hydrogel properties. # 1999 Kluwer Academic Publishers 1. Introduction Over the last 30 years, water-swellable and water- insoluble hydrogels have been extensively investigated and developed, leading to a large family of materials which have found use in a wide range of biomedical applications such as carriers of drugs and bioactive molecules, the replacement of soft tissues, wound healing, ophthalmological applications, membranes for arti®cial kidneys, and materials for blood compatible and other medical devices [1±3]. While hydrogels usually present a crosslinked structure, linear polyurethane-ureas (PUUs) based on poly(ethylene oxide) have been shown to be able to absorb and swell with aqueous media without dissolving [4±6]. This behavior is due to the phase separated domain morphology, where strongly hydrogen bonded urethane/ urea hard segment domains are dispersed in a PEO soft segment domain. As a result of their linear structure, the PUU hydrogels are soluble in organic solvents (e.g. methanol, ethanol and methyl ethyl ketone) and devices and coatings can be fabricated using solvent casting techniques. The PUU hydrogels may also be processed using common thermoplastic fabrication techniques such as extrusion and injection molding. This work investigates the possibility of obtaining linear polyurethane-amide (PUA), hydrogels using two amide diols as chain extenders, a mono amide diol (AD) and a diamide diol (DD), and a dicarboxylic acid (maleic acid, MA). Thermoplastic PUAs, using dicarboxylic acid chain- extenders, have been studied over the last 10 years [7, 8]. Due to the presence of amide bonds in the macro- molecular chains, these materials are capable of forming stronger intermolecular hydrogen bonds, leading to well developed hard domains, in comparison with polyether- urethanes. Moreover, the use of maleic acid as the chain- extender allows the insertion of reactive double bonds in the copolymer chains. These double bonds can perform as grafting sites for further derivatization, thus allowing speci®c tailoring of the base polymers [9]. 2. Experimental procedure 2.1. Materials Pharmaceutical grade poly(ethylene glycols) (PEGs), PEG1500 and PEG3000, were obtained from B.P. * Author to whom correspondence has been addressed. 0957±4530 # 1999 Kluwer Academic Publishers 635