Novel L-tyrosine based polyurethanes and polyphosphate polymers with tunable material properties have been developed by employing tools of molecular design and synthetic chemistry. The evaluation of physico-chemical properties of these materials shows that these polymers have excellent potential for several biomedical applications. The primary monomer desaminotyrosine-tyrosyl hexyl ester (DTH) employed for the synthesis of both polyphosphates and polyurethanes has been developed using L-tyrosine, a non-essential amino acid. Since this monomer has been developed using an amino acid based backbone we hypothesize it will be biocompatible. Further, the choice of other monomers for the development of these polymers has been made to ensure non-cytotoxic and biocompatible nature of the final polymers and their degradation products. The main focus of this study is to test the hypothesis that the polyurethanes and polyphosphate developed using biocompatible monomers are non-cytotoxic, will permit cell adhesion and proliferation and will elicit a minimal degree of inflammatory response in monocytes. The DTH monomer, a novel diphenolic dipepeptide molecule used for the synthesis of polyurethane and polyphosphate polymers is synthesized via a carbodiimide mediated condensation reaction. Further polymerization reaction using this monomer is carried out using the terminal hydroxyl groups present on DTH. Polyphosphate is synthesized by reaction between a phosphodichloridate and the terminal hydroxyl groups of the DTH monomer. Four different polyurethanes are also synthesized by manipulating the soft and hard segment components, i.e., the macrodiols and diisocyanates keeping the chain extender molecule (DTH) the same. Polyethylene glycol (PEG) and polycaprolactone diol (PCL) are used as the macrodiols and hexamethylene diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate) are used as the diisocyanates for polyurethane synthesis. These polymers are currently being investigated for various biomedical applications based on their degradation and other physico-mechanical properties. Cytotoxicity, cell adhesion and proliferation and inflammation assays are used as markers for biocompatibility testing in this study. Cytotoxicity analysis of polyphosphate microparticles and polyurethane films has been performed via direct and indirect contact studies using primary dermal human fibroblasts at passages between 4 and 10 and a LIVE/DEADŽ assay for analysis. Both the films and microparticles are sterilized by exposure to UV light (λ = 265nm) for 10 minutes and incubated with the cells. The incubation times for microparticles are 1, 3, 6 and 10 days whereas those for polyurethane films are 24 hours. The indirect contact studies are performed by incubation of the cells with degradation products of the polyurethane films or polyphosphate microparticles for 24 hours. The cell viability in each of these cases is between 92% and 98%. Statistical analysis of the data showed no statistically significant differences between the positive control, PLGA control and the experimental materials in most cases proving the non-cytotoxic nature of the developed polymers. A p-value of 0.05 is used to determine statistical differences between the treatments. Similar results have also been obtained from the indirect contact studies suggesting that the degradation products of L-tyrosine based polyurethanes and polyphosphate are non-cytotoxic in nature. The morphology of the cells in contact with films of polyurethanes, polyphosphate microparticles and the degradation products of polyurethanes or polyphosphates has been studied using optical microscopy. No significant morphology changes have been observed for the cells incubated with any of the experimental treatments compared to the controls for all the studied time points. Cell adhesion and proliferation studies have been performed using polyurethane films to determine the interaction of cells with the polymeric substrate. The primary human dermal fibroblast cells were found to be completely attached to the polyurethane film surface within 8 hours. At day 1 and 2, the number of adhered cells on the polyurethane surfaces is found to be similar, but upon further incubation the cells are found to proliferate and increase beyond the initial seeded cell density. However, the cell growth on the PEG based polyurethane surfaces is found to be slower compared to the PCL based polyurethane surfaces. These differences can be attributed to the differences in the surface chemistry of the two films and the tendency of PEG to migrate to the surface in case of solvent cast films. Further evaluation and quantification of the cell proliferation studies is currently underway. Finally, the synthetic biomedical devices may influence the amplitude of the monocytes/macrophage interactions occurring at the tissue-polymer interface and the degree of inflammatory response has been found to depend on the chemical characteristics of the polymer itself. Typically as a part of the inflammation process, various cytokines such as IL-1β, IL-6 and IL-10 are released and the concentration of these cytokines can be used as a marker for the degree of inflammation. Currently, we are investigating the inflammatory response elicited by L-tyrosine based polyurethane, polyphosphate and the degradation products of these polymers using porcine monocytes obtained from fresh whole porcine blood. The degree of inflammation will be determined by assaying for the cytokine IL-1β using an ELISA technique. L-tyrosine based polyphosphate is being investigated for micro- and nanoparticles for protein and gene delivery, polyurethanes for soft tissue engineering scaffolds and blends of polyphosphate and polyurethanes as electrospun membranes. The in vitro biocompatibility evaluation of these novel polymers will help us validate the applicability of these materials for biomedical applications and if need arises, modify them to improve their biological compatibility.

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