Effect of electron beam irradiation induced grafting of sialic acid onto polycaprolactone – Feasibility study

Abstract

This paper describes a preliminary study on the practical feasibility of covalent attachment or grafting of hydrophilic biological monosaccharide namely, sialic acid (SA) onto the backbone of hydrophobic biodegradable polycaprolactone (PCL) by electron beam (e-beam) irradiation induced free radical polymerization. In the first part of the study, generation of reactive sites/free radicals on PCL backbone, shelf life of these free radicals and a relationship between free radical concentration vs irradiation dose were investigated by electron spin resonance (ESR) study. Later, the grafting of monomer was carried out under different reaction conditions viz., dry method (method 1), wet state co-irradiation (method 2) and water based (method 3) and the same was qualitatively confirmed through Fourier Transfer Infrared Spectroscopy (FTIR) as well as elemental analysis. ESR results showed that the concentration of free radicals increased with an increase in radiation dose. Concentration of these free radicals is very high in initial 1 h with progressive decay and approaches zero concentration in 24 h. The extent of grafting was changed by changing the reaction conditions. The most satisfactory grafting of SA onto PCL was possible under solution state irradiation condition (i.e., in method 2). In FTIR studies, CC and CO stretching were seen at 1176 cm−1 and 1294 cm−1, representing amorphous and crystalline regions respectively. This shift in the crystalline to amorphous domain represents the occurrence of grafting of SA onto PCL and formation of grafted (SA-g-PCL) chains. These changes were observed only in method 2 carried out at lower doses (20, 40 kGy). Further, the presence of element nitrogen (0.178%) in samples obtained from method 2, presented a strong evidence of attachment of SA onto the PCL backbone. Our findings provide new information on the possible grafting of PCL, which could be exploited in future as promising polymeric material to make biocompatible and hydrophilic drug delivery carrier.