In the past few decades, biodegradable and biocompatible nanoparticles of methoxy poly(ethylene glycol)-b-poly( d l-lactide) (MPEG- b-PDLL) and methoxy poly(ethylene glycol)- b-poly(ϵ-caprolactone) (MPEG- b-PCL) amphiphilic diblock copolymers have shown potential as controlled-release drug delivery carriers because of the small size of their nanoparticles, which improves circulation time in the body and decreases the administration frequency when compared to microparticles which are rapidly cleared by the reticuloendothelial tissue [1, 2]. Moreover, for MPEG-b-PDLL and MPEG- b-PCL nanoparticles suspended in water, PDLL and PCL hydrophobic cores are surrounded by hydrophilic MPEG blocks on the nanoparticle surface to solubilize hydrophobic drugs; this increases blood circulation time and decreases uptake by the liver of the nanoparticles [3–6]. The need for surfactants when preparing nanoparticles of amphiphilic diblock copolymer by the nanoprecipitation method can be removed. The protective effect of the hydrophilic MPEG block is adequate for preventing nanoparticle aggregation. The poly(vinyl alcohol), Span series, Tween series, poly(ethylene oxide) (PEO), and poloxamer (PEO-poly(propylene oxide) block copolymer) have been used as surfactants to stabilize emulsion droplets . These surfactants remain at the particle surface and are difficult to remove which affect the biodegradability and drug release profile of the drug-loaded particles. Also, these remaining surfactants can influence the human body, for example, causing an allergy-like reaction.
In previous studies, much attention was paid to the drug-loaded nanoparticles of these amphiphilic diblock copolymers with different types of chemical compositions and lengths of polymer blocks used [8–11]. Drug release profiles of the nanoparticles depended upon these factors. The physical blending of polymers is an alternative method that has been widely used to adjust the properties of biodegradable polyesters [12–15]. Thus unique properties of polymer blends, quite different from the origin polymers, were obtained. The drug release rate from poly(l-lactide)/PCL blend nanoparticles prepared from the nanoprecipitation method using poloxamer 188 as the surfactant has been adjusted by varying the blend weight ratios .
The characteristics and drug release behaviors of the MPEG-b-PCL nanoparticles containing drug prepared by the nanoprecipitation method can be controlled by adjusting the processing parameters, such as the organic/water phase volume ratio, polymer concentration, drug/polymer weight ratio, and stirring speed . However, the effect of MPEG-b-PDLL/MPEG- b-PCL blending on characteristics and drug release of the nanoparticles has not been reported.
In this study, surfactant-free MPEG-b-PDLL/MPEG- b-PCL blend nanoparticles containing a model drug were prepared by the nanoprecipitation method. Indomethacin was selected as the model drug because of its poor water solubility. The effects of different polyester block lengths and blend weight ratios on the nanoparticle characteristics, drug loading efficiency, and drug release profiles were studied and discussed.