Synthesis and characterization of L-tyrosine based polyurethanes for biomaterial applications Debanjan Sarkar, Jui-Chen Yang, Anirban Sen Gupta,* Stephanie T. Lopina Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325-3906 Received 28 October 2007; revised 15 March 2008; accepted 26 March 2008 Published online 21 May 2008 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.32095 Abstract: The use of amino acid based polymers for bio- material applications enhance biocompatibility and ensure biodegradability. Two polyurethanes based on L-tyrosine based diphenolic dipeptide, desaminotyrosyl tyrosine hexyl ester as chain extender are synthesized with polyeth- ylene glycol (PEG) and polycaprolactone diol (PCL) as soft segment and hexamethylene diisocyanate as diisocyanate. The chemical structure and molecular characteristics of the polymers were studied by 1 H NMR, FTIR, and gel permea- tion chromatography. Results of DSC and TGA analysis were used for examining the thermal behavior of the poly- urethanes. In addition, DSC results were used to analyze the morphology of the polymers, which shows characteris- tic microphase behavior of the polyurethanes. The tensile properties of the polyurethanes are primarily controlled by the soft segment and are higher in PCL based polymers. Contact angle, water vapor permeation, release of model drug, and water absorption characteristics of the polymers were studied and analyzed in terms of structure of the polyurethanes. In vitro degradation studies show that PEG based polyurethane is more degradable than PCL based polyurethane. The difference in the soft segment structure offers significant variation in the properties of the polyur- ethanes. These polyurethanes show the potential for use in a variety of biomaterial applications including tissue engi- neering. Ó 2008 Wiley Periodicals, Inc. J Biomed Mater Res 90A: 263–271, 2009 Key words: amino acid; L-tyrosine; polyurethanes; bioma- terial; tissue engineering INTRODUCTION The use of poly(amino acid)s as synthetic biomate- rials has been explored for various applications. 1 However, unfavorable physicomechanical properties of poly(amino acid)s, has led to the development of materials that are known as ‘nonpeptide amino acid based polymer’ or as ‘amino-acid-derived polymers with modified backbones’. 2 On the basis of structural configuration, these materials can be classified into several sub-categories: synthetic polymers with amino acid side chains, copolymers of amino acid and nonamino acid monomer, block copolymers con- taining peptides or poly(amino acid) blocks, and pseudo-poly(amino acid)s. 3,4 These materials have improved engineering properties compared with synthetic poly(amino acid)s. L-Tyrosine, a natural amino acid, is a major nutri- ent having a phenolic hydroxyl group. This feature enables use of the tyrosine derived dipeptide as a building block for the design of biodegradable poly- mers. 4,5 The most commonly used monomers are the desaminotyrosyl-tyrosine alkyl esters. 6 Several tyro- sine based pseudo-poly(amino acid)s with different nonpeptide linkages has been developed for bioma- terial applications. Polycarbonate, 7 polyiminocarbon- ate, 8 polyarylate, 9 and polyphosphate 10 developed from tyrosine based dipeptide monomer have been studied extensively. Tyrosine based copolymers, e.g. polyethylene glycol (PEG) based copolymer have also been developed for biomaterial applications. 11 Biocompatibility studies using the tyrosine derived degradable polymer, poly(desaminotyrosinetyrosyl- hexyl carbonate) (poly (DTH carbonate)) have been favorable, suggesting the material is suitable for tis- sue engineering application. 12 Polyurethanes are widely used as biomaterials for different biomaterial applications including tissue en- gineering. 13 The use of polyurethanes for tissue engi- neering applications emerged mainly due to the degradability of the polyurethanes. Since polyur- ethane structures can be tailored to have degradable linkages and a range of chemical, physical and me- *Present address: Department of Biomedical Engineer- ing, Case Western Reserve University, Cleveland, Ohio 44106. Correspondence to: S. T. Lopina; e-mail: lopina@uakron. edu Ó 2008 Wiley Periodicals, Inc.