Environmentally safe bioadditive allows degradation of refractory poly(lactic acid) in seawater: Effect of poly(aspartic acid-co-L-lactide) on the hydrolytic degradation of PLLA at different salinity and pH conditions

Although poly(L-lactic acid) (PLLA) is supposed to be a biodegradable polymer, actually neat PLLA is basically non-degradable in seawater, and this work reports a means to overcome this limitation. The present study demonstrates that the addition of the environmentally safe bioadditive, poly(aspartic acid-co-L-lactide) (PAL) to PLLA allows its hydrolytic degradation at 40 degrees C under various pH conditions with different salt concentrations. It was found that the mass of neat PLLA hardly decreased upon immersion in water at a pH 3.4-10.4 for 100 days, whereas the addition of 20 wt% of PAL to PLLA resulted in a significant mass reduction at any pH. In acidic and neutral solutions the addition of salt even enhanced the hydrolysis rate of the PLLA/PAL blends, and in alkaline solutions the blends completely disappeared in a relatively short period of time, e.g., 30-40 days at pH 10.4 and 18-25 days at pH 12.0. Thus, the present study demonstrated that the addition of PAL to PLLA causes pristine PLLA to be degradable in salty environments such as seawater and body fluid and that PLLA/PAL with tunable degradation rate is effective as a biomaterial in medical and pharmaceutical applications used in the wide pH range. (C) 2020 Elsevier Ltd. All rights reserved.