Synthesis and characterization of biocompatible polyurethanes functionalized by chitin and curcumin

Abstract

The present project has been planned to synthesize thermoplastic and thermoset polyurethane elastomers. In the first part, four series consisting of twenty samples of thermoset polyurethane elastomers were prepared with IPDI and TDI by varying the molecular weight of HTPB and further extended with chain extenders (chitin and curcumin). In the first series, five elastomers based on HTPB and cycloaliphatic isocyanate were prepared followed by a second series comprised of aromatic ring in their composition. Moreover, the third series was synthesized by varying the molecular weight of HTPB along with cycloaliphatic isocyanate while part four studied aromatic isocyanate based polyurethanes with the same composition as that of the third series. Step growth polymerization technique was employed for the synthesis of thermoset PU elastomers and characterization of samples has been carried out by FTIR and SS1HNMR to confirm the proposed structure of polyurethane elastomers. From FTIR analysis, it was concluded that urethane group reaction mainly occurred at hydroxyl group of HTPB and -NCO group of isocyanates i.e. TDI and IPDI. Main peaks corresponding to NH-stretching at 3600-3400 cm-1 , CH at stretching 2960-2450 cm-1 and C=O at 1600-1400 cm-1 were appeared in FTIR spectra. The effect of chain extenders upon thermal stability, hydrophilicity and crystallinity index was investigated. The results of XRD revealed that all synthesized samples possess crystalline pattern which was found to be increased by increasing the curcumin content in the PUs formulation. Polyurethane elastomers based on TDI showed optimum hydrophilicity and crystallinity as compared to IPDI based elastomers of polyurethane. Thermal analysis revealed that thermoset polyurethane samples were stable up to 240˚C. The first stage of decomposition ascribed to the breakdown of diisocyanate and second stage to the breakdown of polyol components. A small change in crystallinity pattern was observed by changing the molecular weight of HTPB and isocyanate in formulation of polyurethanes. TGA data revealed slight variation in thermal stability of the proposed polyurethanes due to change in a structure from aliphatic isocyanate to aromatic isocyanate. Contact angle and water absorption measurement also depicted that suggested material was hydrophobic and suitable for various potential applications e.g. biomedical implants. The biological behaviour of the synthesized specimen has been evaluated by using some biological tests e.g. antibacterial, hemolytic, antioxidant activities and Ames assay. Antibacterial analysis by disk diffusion method revealed that 149 elastomers based on cycloaliphatic isocyanate possess a little less antibacterial properties as compared to that polyurethane elastomers based on aromatic isocyanate. This change in antibacterial properties might be correlated to the structural features of isocyanate. TDI based polyurethane elastomers were found to be more reactive in comparison to IPDI based polyurethanes and the curcumin contents had positive impact on biological behaviour of the synthesized sample. Studies also revealed that curcumin interferes with the nucleotide formation of bacterial cell and restrict its production along with prevention of protein organization which ultimately causes bacterial cell death. Antioxidant analysis by DPPH also covered another biological analysis. As a general estimation from data, it has been observed that antioxidant potential was found to be increased with an increase in curcumin concentration. Hemolytic analysis revealed that blood compatibility of thermoset polyurethane elastomers was observed to be increased with increase in curcumin contents. Moreover, it is concluded that these materials might be applicable for internal use in human body as their prolonged interaction with body fluids will cause no harm. Ongoing investigations by Ames assay revealed that polyurethanes based on curcumin were found to be non-mutagenic and would be used as non-absorbable suture in biomedical applications. In the second part, two series of thermoplastic polyurethanes were prepared by extrusion process. In the fifth series, polyurethanes comprised of curcumin, chitosan and nanoclay while in the sixth series starch and chitosan based polyurethanes were prepared and analyzed through FTIR spectroscopy to confirm the molecular structure of purposed polyurethanes. The blend miscibility was evaluated through various analytical tools such as XRD and SEM. XRD confirmed that both set of thermoplastic polyurethanes blended with chitosan-curcumin-nanoclay and chitosan-starch were amorphous in nature and XRD diffractograms revealed that the introduction of blend into polyurethanes reduced the crystallinity owing to the development of inter and intra molecular hydrogen bonding which limited the chain motion of segments and resulted in reduced crystallinity. SEM micrographs provides evidence for the incorporation of nanoclay into PUs matrix. Biological properties i.e. hemolytic, antioxidant and antibacterial activities of thermoplastic polyurethanes were also studied. Curcumin-chitosan and nanoclay based polyurethanes showed improved biological properties in comparison to starch and chitosan based thermoplastic polyurethanes for many biomedical applications. Starch based thermoplastic polyurethanes showed non-significant 150 biological response in comparison to chitosan based polyurethanes. Starch basically is a carbohydrate with insignificant biological properties. Antioxidant potential of curcuminchitosan based polyurethanes were found to be higher in comparison to starch-chitosan based thermoplastic polyurethanes. Inherently, chitosan possess a bacteriostatic mode of action (due to cationic charge) by puncturing cell membrane of bacteria and pushing out the cell contents. Water absorption capacity and contact angle measurements revealed that synthesized materials based on starch imparted hydrophilic character while chitosan and curcumin based polyurethanes exhibited hydrophobic character and no significant increment in water absorption capacity was noted. It is therefore, concluded that thermoplastic polyurethanes blended with polysaccharides, 1,4-BDO and curcumin derived thermoset polyurethanes may find potential applications in biomedical field because incorporation of curcumin assist to impart biological character and thermal stability to the designed PU formulations.