PLA stereo-complex micelles

The most common methods to prepare micelles of water insoluble copolymers are nanoprecipitation, solvent evaporation/film hydration and dialysis.However, all the organic solvents involved in these methods, such as dichloromethane, acetone, dimethylformamide (DMF) and acetonitrile are more or less toxic, and residual solvents might cause side effects to the human body. 

Stereo-complexation not only occurs in melt and in organic solution, but also in aqueous solution. When a water soluble PLLA/PEG block copolymer is mixed with a similar PDLA/PEG in dilute solution, the strong interactions between PLEA and PDLA blocks lead to the formation of stereo-complex micelles. 

Yang et al. systemically investigated the preparation, aggregation properties and drug release behaviour of PLA/PEG stereo-complex mi-celles. °° Predetermined amounts of PLLA/PEG or PDLA/PEG copolymer are separately dissolved in distilled water or phosphate buffered saline (PBS). The two solutions with equal molar concentrations are then mixed to yield a micellar solution by self-assembly due to interactions between l-LA and d-LA blocks.  

Polymeric micelles can be formed only when the block copolymer eon-centration is higher than the critical micellar concentration (CMC) which characterizes the micelle stability. The CMC of PLA/PEG copolymers depends on the EO/LA ratio, molar mass and chain structure, as shown in Table 2.2. Lower EO/LA ratios lead to lower CMC since copolymers are more hydrophobic, and thus can self-assemble more easily to form micelles. Higher molar mass of PEG blocks leads to higher CMC value for similar hydrophilicity or EO/LA ratio. It is also of interest to compare the micelli-zation properties of diblock and triblock copolymers. In fact, triblock copolymers are more inclined to form mieelles than diblock copolymers due to the different structures. In dilute aqueous solutions, dibloek eopolymers tend to form micelles with a stick-like chain structure, while triblock chains 

Chen et ah investigated comparatively single micelles and stereo-complex micelles prepared by nanoprecipitation of PLA-PEG diblock copolymers composed of a monometho PEG with = 5000 Da and PLLA or PDLA blocks with DP of 14, 35 and 70. The CMC and micelle sizes of single 

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