Tuning Crystallinity of Poly(L-Lactic Acid) Microspheres through Emulsification Temperature Changes

Crystallinity is a key parameter for technological and medical applications of poly(lactic acid) (PLA) microspheres. This study explores a novel emulsification-based method for regulating the crystalline structure of PLA microspheres. The results unveil the effects of changing the emulsification temperature in an unexplored temperature range above the boiling point of the solvent used to dissolve the polymer. Powder X-ray diffraction, differential scanning calorimetry, and micro-Raman analysis show that poly(L-lactic acid) (PLLA) microsphere batches display a crystalline fraction, which can be varied by a factor 2, from 19 to 38%. Notably, the comparison between macro- and microanalysis supports a model in which the emulsification temperature influences the ratio between amorphous and crystalline parts within each PLLA microsphere. The microspheres do not show any infrared-active changes in the molecular unit after exposure to X-rays, unlike the bulk material. The findings pave the way for innovative strategies for obtaining radiation-resistant microspheres with controlled crystallinity.