Preparation of uniform poly(lactide) microspheres by employing the Shirasu Porous Glass (SPG) emulsification technique

Relatively uniform biodegradable poly(lactide) (PLA) microspheres were prepared by employing a Shirasu Porous Glass (SPG) membrane emulsification technique. Poly(lactide) dissolved in co-surfactant (hydrophobic substance)/dichloromethane (DCM) was used as a dispersed phase (oil phase) and an aqueous phase containing poly(vinyl alcohol) (PVA) and sodium lauryl sulfate (SLS) was used as a continuous phase. The oil phase permeated through the uniform pores of the SPG membrane into the continuous phase by a pressure of nitrogen gas to form the droplets. Then, the solid polymer microspheres were obtained by simply evaporating DCM at room temperature for 24 h. The effects of the type and the amount of the co-surfactant, and PLA concentration on the size, size distribution, and the morphologies of the droplets and particles were investigated. A relatively uniform spherical PLA microsphere was obtained successfully by using lauryl alcohol (LOH) rather than hexadecane (HD) as a co-surfactant. PLA concentration was varied from 10 to 20 wt.%/vol., and the LOH/DCM ratio changed from 0.5:11.5 to 2:10 by volume. At the polymer concentration range used in this study (10–20 wt.%), variation of the droplet size was not so apparent when 2 ml of LOH was used, but the droplet size showed a minimum value at 15 wt.% when 0.5 or 1 ml of LOH was used. The variation of CV value (coefficient of variation) was smaller in the PLA concentration range of 10–15 wt.%, then the CV value became larger as the PLA concentration was increased from 15 to 20 wt.%. Although there was a tendency that the droplet size and the CV value decreased as the LOH/DCM ratio increased, the CV value of the particle after the evaporation of DCM showed the lowest value when the amount of LOH was 1 ml (LOH/DCM=1:11, by vol.). Therefore it was most adequate to use 1 ml of LOH to prepare the particles with a relatively narrow size distribution. Furthermore, it was clarified that the phase-separation between PLA and LOH was apparent and the surface of the particle obtained was wrinkled when the PLA concentration was lower after DCM was evaporated, while the particles with the smooth surface were obtained when the PLA concentration was higher. This method provides a unique technique to prepare uniform polymer microspheres composed of natural polymers, bio-degradable polymers, co-polymers or polymer blends, polyesters and those which can not be polymerized by the radical polymerization.