Amphiphilic diblock copolymeric nanospheres composed of methoxy poly(ethylene glycol) and glycolide: properties, cytotoxicity and drug release behaviour.

Amphiphilic diblock copolymers based on methoxy poly(ethylene glycol) (MePEG) and glycolide with different molar composition were synthesized by bulk polymerization without any catalysts. Using diblock copolymers, we have prepared indomethacin-loaded polymeric nanospheres by forming a micelle in selective solvents. The size of nanospheres measured using dynamic light scattering exhibited a narrow monodisperse size distribution and an average diameter in the range of less than 200 nm. The critical micelle concentration (CMC) of MG70 sample determined by fluorescence spectroscopy was 1.57 x 10(-7) mol/l which was lower than the CMC of common low molecular weight surfactant. In vitro release experiments using indomethacin-loaded MePEG/glycolide nanospheres exhibited the sustained release behaviour without any burst effect. In addition, the results of cytotoxicity tests using an MTT assay method showed that these MePEG/glycolide nanospheres could remarkably reduce cell damage compared with unloaded free drug.

Preparation and characterization of biodegradable nanospheres composed of methoxy poly(ethylene glycol) and DL-lactide block copolymer as novel drug carriers.

We synthesized amphiphilic diblock copolymer based on methoxy poly(ethylene glycol) (MePEG) and dl-lactide with different molar composition in bulk without catalyst. Using the resulting amphiphilic diblock copolymers, we prepared drug-loaded polymeric nanospheres by micelle formation through solution behavior of amphiphilic copolymer in selective solvents. The structure of MePEG/dl-lactide diblock copolymers was identified by IR, WAXD, GPC, 1H-NMR. The size of nanosphere measured by dynamic light scattering showed a narrow monodisperse size distribution and average diameter less than 200 nm. From the surface chemical composition of nanosphere by ESCA, the presence of MePEG chains on the nanosphere layers was confirmed. The critical micelle concentration of ML50 sample investigated by fluorescence spectroscopy was 1.44x10-7 mol/l which is lower than common low molecular weight surfactants. In addition, we could obtain nanospheres having a relatively high drug-loading of about 33.0% when the feed weight ratio of indomethacin to polymer was 1:1. In vitro release experiments of the indomethacin-loaded MePEG/dl-lactide nanospheres exhibited sustained release behavior without any burst effects. The results of cytotoxicity tests showed that the MePEG/dl-lactide nanospheres didn't induce any relevant cell damage.

Methoxy poly(ethylene glycol)/epsilon-caprolactone amphiphilic block copolymeric micelle containing indomethacin. I. Preparation and characterization.

Amphiphilic diblock copolymers composed of methoxy polyethylene glycol (MePEG) and epsilon-caprolactone (epsilon-CL) were prepared for the formation of micelles. The copolymer was formed by ring opening mechanism of epsilon-CL in the presence of MePEG containing hydroxyl functional groups at one end of the chain. To estimate their feasibility as vehicles for drugs, MePEG/epsilon-CL block copolymeric micelles were prepared by dialysis against water. Indomethacin was incorporated into the hydrophobic inner core of these micelles as a typical model drug for non-steroidal anti-inflammatory drugs. From the dynamic light scattering measurements, the size of micelle formed was less than 200 mm, and their size increases with the amount of indomethacin encapsulated into the inner core of MePEG/epsilon-CL block copolymers. The selected solvents used to prepare micelles by dialysis in water affect the size of polymeric micelles. As the hydrophobic components of copolymer increase, the critical micelle concentration values and hydrophilic-lipophilic balance decreased. An increase of molecular weight and hydrophobic components of diblock copolymer produced larger micelles.

Methoxy poly(ethylene glycol) and epsilon-caprolactone amphiphilic block copolymeric micelle containing indomethacin. II. Micelle formation and drug release behaviours.

Amphiphilic diblock copolymer composed of methoxy poly(ethylene glycol) and epsilon-caprolactone (epsilon-CL) was prepared by polymerization of epsilon-CL initiated with MePEG. MePEG/epsilon-CL block copolymeric micelles containing indomethacin (IMC) were prepared by a dialysis method and evaluated as a novel drug carrier. The size of micelle formed was less than 200 nm, and the size distribution of the micelle showed a narrow and monodisperse unimodal pattern. Also, the micelles formed by a dialysis method exhibited spherical structures. The indomethacin content in nanospheres was about 42.2%, for those prepared using copolymer, having molecular weight of about 12,000 and polymer/IMC weight ratio of 1/1. A release rate of indomethacin from nanospheres was slow, and thus the release continued over 15 days. As the molecular weights of the copolymer and the amount of drug entrapped increased, the release rate decreased. These results indicated that the drug-loaded nanospheres could be useful as a novel drug carrier in injectable delivery systems for hydrophobic drugs.

Exoplanet detection. A terrestrial planet in a ~1-AU orbit around one member of a ~15-AU binary.

Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth's) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet's temperature is much lower, <60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.