Hydrolytic degradation of electron beam irradiated high molecular weight and non-irradiated moderate molecular weight PLLA.
The purpose of this study is to examine the hydrolytic degradation of electron beam irradiated ring-opening polymerized (ROP) poly(l-lactide) (PLLA-ir) and non-irradiated melt polycondensation polymerized poly(l-lactic acid) (PLLA-pc). It was observed that irradiation increases the hydrolytic degradation rate constant for ROP PLLA. This was due to a more hydrophilic PLLA-ir, as a result of irradiation. The degradation rate constants (k) of PLLA-ir samples were also found to be similar, regardless of the radiation dose, and an empirically formulated equation relating hydrolytic degradation time span to radiation dose was derived. The k value for PLLA-pc was observed to be lower than that for PLLA-ir, though the latter had a higher molecular weight. This was due to the difference in degradation mechanism, in which PLLA-ir undergoes end group scission, through a back- biting mechanism, during hydrolysis and thus a faster hydrolysis rate. Electron beam irradiation, though accelerates the degradation of PLLA, has been shown to be useful in accurately controlling the hydrolytic time span of PLLA. This method of controlling the hydrolytic degradation time was by far an easier task than through melt polycondensation polymerization. This would allow PLLA to be used for drug delivery purposes or as a temporary implant that requires a moderate time span (3-6 months).
Loo
Say Chye Joachim
SC
Nanyang Technological University, School of Materials Science and Engineering, Nanyang Avenue, Singapore 639798, Singapore. joachimloo@ntu.edu.sg
Tan
Hui Tong
HT
Ooi
Chui Ping
CP
Boey
Yin Chiang Freddy
YC
D004583:Electrons; D006868:Hydrolysis; D007700:Kinetics; D019344:Lactic Acid / Q000737:chemistry* / Q000528:radiation effects*; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D008958:Models, Molecular; D008970:Molecular Weight; D011091:Polyesters; D011108:Polymers / Q000737:chemistry* / Q000528:radiation effects*; D017550:Spectroscopy, Fourier Transform Infrared
D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide)