International Journal of Biological Macromolecules 44 (2009) 23–28 Contents lists available at ScienceDirect International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac Evaluation of biocompatibility and mechanical behavior of chitin-based polyurethane elastomers. Part-II: Effect of diisocyanate structure Khalid Mahmood Zia a , Mohammad Zuber b,∗ , Ijaz Ahmad Bhatti a , Mehdi Barikani c , Munir Ahmad Sheikh a a Department of Chemistry, University of Agriculture, Faisalabad 38040, Pakistan b Department of Textile Chemistry, National Textile University, Faisalabad 37610, Pakistan c Iran Polymers and Petrochemicals Institute, P.O. Box 14965/115, Tehran, Iran article info Article history: Received 13 October 2008 Received in revised form 29 October 2008 Accepted 3 November 2008 Available online 12 November 2008 Keywords: Chitin Polyurethane Diisocyanate Mechanical properties Biocompatibility abstract Chitin-based polyurethane elastomers having potential for biomedical applications with tunable mechan- ical properties were synthesized by step growth polymerization techniques using poly(-caprolactone) (PCL) with different diisocyanates. The prepolymer was extended using chitin and/or 1,4-butane diol (BDO). The structures of the resulted polymers were determined by Fourier transform infrared (FTIR), 1 H NMR and 13 C NMR spectroscopic techniques. The effect of structure of diisocyanates and chain exten- ders on mechanical properties and in vitro biocompatibility were investigated. The results revealed that the final polymers extended with chitin are preferred candidates for surgical threads with on going investigations into their in vitro biocompatibility and non-toxicity. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Surgical threads are used to hold skin and internal organs including blood vessels and all other tissues of the human body together, after surgery or accidental injury. These threads must be strong enough having high tensile strength, non-toxic, flexi- ble and crystalline. There are several materials used for surgical threads. The most common is a natural fiber, silk [1,2] which undergoes a special manufacturing process to make it adequate for its use in surgery. Other surgical threads are made of arti- ficial fibers, like polypropylene [3], polyester [4], polydioxanone [5] or nylon [6,7]. Stainless steel wires are also used in ortho- pedic surgery and for sternal closure in cardiac surgery. In the biomedical area, the use of polyurethanes (PUs) [8,9] exceeds than that of other polymeric materials including natural rubber [10], polyethylene [11], polyvinyl chloride [12], fluoropolymers [13] and silicones [14], because of the various options they offer to mimic the behavior of different tissues and relatively good biocompatibility. Polyurethanes have potential array of commer- cial applications as they can be molded, injected, extruded and recycled [15]. Molecular characterization and morphological stud- ∗ Corresponding author. Tel.: +92 321 6682375; fax: +92 41 9230098. E-mail address: mohammadzuber@gmail.com (M. Zuber). ies of polyurethane elastomers (PUEs) have been reported by many researchers. The effect of the diisocyanate structure [16] and length of chain extender (C.E.) using , -alkane diols on the crystallinity, surface morphology [17] and thermo-mechanical properties [18] of PUEs have been investigated and well doc- umented. Detailed molecular characterization [19], XRD studies with blends of chitin/1,4-butane diol (BDO) [20] and varying diiso- cyanates structure [21], thermal [22] and shape memory properties [23] of chitin-based polyurethane elastomers have also been pre- viously discussed and reported. The physical and elastic properties of PUs developed for durable application is much superior over other competitors mentioned above. Of the developed PUs, the over-whelming majority are biostable materials, designed to stand in service for long periods of time [24]. One of the intended uses of these polymers is the insertion in a living organism for extended period; therefore a great care has to be taken in the choice of their building blocks. Their degradation products have to be biocompatible, non-toxic and metabolized or eliminated by the living organism. Among different macrodiols, polycaprolactone diols (PCL) are known to be biocompatible and slowly, hydrolytically and enzymatically degradable [25]. The degradation product of this polymer (PCL), 6- hydroxyhexanoic acids, is transformed by microsomal -oxidation to adipic acid which is a naturally occurring metabolite. The diisocyanate and chain extenders typically used in the hard seg- 0141-8130/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.ijbiomac.2008.11.002