Synthesis and characterization of biodegradable copolymers for tissue engineering
Polymers have been extensively used to fabricate scaffolds for tissue regeneration in order to repair or reconstruct damaged tissues in vitro or in vivo. Chitosan (CS), polycaprolactone (PCL) and polylactide (PLA) are among the most widely studied polymers. CS, a natural polysaccharide, is a biocompatible, biodegradable and non-toxic polymer, however, it exhibits low mechanical strength and also, due to its hydrophilicity, it can be slightly dissolved in an aqueous culture medium. On the other hand, PCL and PLA are biocompatible, biodegradable and nontoxic synthetic polymers, with excellent mechanical properties. In this work CS-graft-PCL (CS-g-PCL) and CS-graft-PLA (CS-g-PLA) copolymers were prepared by grafting hydrophobic PCL and PLA polymer chains on the CS backbone in order to alter the solubility of CS and improve its mechanical properties. First, PCL or PLA functionalized with one carboxylic acid terminal group (PCL-COOH or PLA-COOH) was prepared by ring opening polymerization of e-caprolactone or lactide, using glycolic acid as the initiator and tin octanoate as the catalyst. Polymers of different molecular weights were obtained and were characterized by gel permeation chromatography and proton nuclear resonance (1H NMR) spectroscopy. Next, the PCL-COOH or PLA-COOH chains were chemically grafted onto the CS backbone via the hydroxyl groups of CS (Fig. 1). The purified products as well as the intermediates of the reaction were characterized by Attentuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) and 1H NMR spectroscopies. Next, thin films of the CS-g-PCL samples were produced using the spin coating method and cellular compatibility of the materials was examined. The 2D scaffolds were seeded with NRK cells for 7 days and the viability of the cells was tested using live-dead staining and MTT assay. The topographical characteristics of the cells attached onto the polymer surface were visualized using SEM. After a week study the cellular behavior was enhanced showing an increased cell number, very good cell attachment and proliferation.