L-Aspartic acid based functional polyester for drug delivery and antimicrobial applications

Abstract

Synthetic polymers based on L-amino acids have attracted much attention because of their excellent biocompatibility and diverse functionality which provides them improved hydrophilicity and an opportunity for further modifications with bioactive molecules. Development of synthetic strategy for synthesis of amino acid-based polymers has great research opportunity in biomedical field. In this thesis work, L-amino acid-based amide-functionalized polyester platform was designed and developed and their lysosomal enzymatic-biodegradation aspects was explored to administrate anticancer drugs in cancer cells. L-Aspartic acid was chosen and different amide-side chain functionalized diester monomers were tailor-made having aromatic, aliphatic and bio-source pendant units. Under solvent-free melt polycondensation methodology; these monomers underwent polymerization to yield high molecular weight polyesters with tuneable thermal properties. This amphiphilic polyester was self- assembled into 140±10 nm sized spherical nanoparticle in aqueous medium which exhibited lower critical solution temperature (LCST) at 40-42 ºC. The polyester nano-assemblies showed excellent encapsulation capabilities for anticancer drug doxorubicin (DOX), anti-inflammatory drug curcumin (CUR), biomarkers such as Rose Bengal (RB), and 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) etc. The amphiphilic polyester NP was found to be very stable under extracellular conditions and underwent degradation upon exposure to horse liver esterase enzyme in PBS. Temperature dependent-cellular uptake studies further confirmed the energy dependent endocytosis of polymer NPs across the cellular membranes. Confocal laser scanning microscopy (CSLM) assisted time-dependent cellular uptake analysis directly evident for the of DOX loaded polymer NP endocytosis and their internalization for biodegradation. Further, hydroxyl functionalised TPE tagged fluorescent polyesters based on L -aspartic acid were developed to study the real-time drug delivery aspects. The fluorophore was introduced as main chain as well as side chain to study the role of the polymer topology on the drug loading and delivering capabilities. The photophysical characterisation of the nanoparticle was done using absorbance and emission spectroscopy, TCSPC to establish FRET probe. It was clearly demonstrated that there is transfer of energy from TPE molecule to RB/RhB/DOX in the hydrophobic nanocavity of the nanoparticle which was further confirmed by determining the distance between donor and acceptor, FRET efficiency etc. These polyester-based FRET probes were capable of enzyme responsive behaviour which was supported by enzyme responsive release of DOX. Finally, L-aspartic acid based cationic polyester for antibacterial application. The amine functionalised cationic polyester were designed via thermoselective melt polycondensation approach by employing protection deprotection strategy. These cationic polyesters were characterised for structural, thermal properties. Once the polymer become cationic it becomes water soluble and form polymer nanoparticle. Zeta potential studies suggest that these polymer nanoparticles having positive zeta potential value which is a desired requirement for antibacterial polymers. The antibacterial studies of these polymers were carried out by colony suspension method, disc diffusion method. It was found that polymers are showed antibacterial activity against gram negative E. Coli cells at the concentration of 0.8mg/mL.