Amphiphilic block copolymers (PETLA) composed of D

L-lactide

trimethylene carbonate (TMC) and methoxy poly(ethylene glycol) (mPEG) were synthesized with ringopening copolymerization.Initiation of D

L-LA and TMC copolymerization wtih mPEG provided to manipulate the molecular weight of the hydrophobic block. Copolymer characterization with 1H-NMR and gel permeation chromatograph (GPC) illustrated the final copolymer compositions were agreed with the theoretical values in feeding doses. Studies on micellization and drug controlled release behaviors of copolymer PETLA were performed with fluorescence spectroscopy

GPC

dynamic light scattering (DLS)

transmission electron microscope (TEM)

and ultraviolet spectroscopy (UV). Micelles of MT1 to MT4 were prepared from PETLA1 to PETLA4 respectively. Fluorescence technique with pyrene as hydrophobic probe was used to study the formation of core-shell type micelles. As a result

the critical micelle concentration (CMC) of PETLA was decreased from 5×10-3 g/L (PETLA1) to 2.5 × 10-4 g/L (PETLA4) with the increase of chain length in hydrophobic block while keeping constant corona-forming block. GPC characterization was used to describe the aggregation behavior of copolymers in selective solvent

by which the molecular weight of micelles was determined

and it was increased obviously from MT1 (277500 Dalton) to MT3 (644800 Dalton). Consistent to GPC results

DLS tests indicated the micellar diameters from MT1 to MT3 were increased from 30 nm to 60 nm. This would be related to the following reasons: the length of the hydrophobic block determined the space each chain required in the core

and the block copolymer with high hydrophobic length needed more core space to form larger micelles. TEM photograph illustrated that micelles MT1 had typical core-shell structure and regularly spherical morphology with the diameter of 30~40 nm after negative staining by phosphotungstic acid. Taking 9-nitro-20(s)-camptothecin (9-NC) as model drug

release profiles in vitro shown that the release behavior of 9-NC from micelles was in controlled manner and nearly in zero order after the initial burst release. The release rate decreased from MT1 to MT4

this was because the micelles composed of high hydrophobic composition could form large hydrophobic core and could encapsulate more drags through strong hydrophobic interactions

and the incorporated drug would take relatively long time to overcome the hydrophobic interaction then diffuse across the polymer matrix to the medium. Based on the results given above

micelles with hydrophobic part composed of D

L-lactide and TMC were not only help to control the release behavior of hydrophobic drug

but also help to alleviate local inflammation response which was elicited by acid production biodegraded from poly(D

L-lactide). In conclusion

novel copolymer micelles could open new opportunities for the delivery of poorly soluble anticancer drugs.