The micellar-like particle systems produced from poly-D,L-lactide-poly(ethylene glycol) (PLA-PEG) copolymers have been assessed using a range of physicochemical characterisation methods, followed by in vivo studies of their biodistribution after intravenous administration to the rat. The size of the PEG chain was kept constant at 5 or 2 kDa, while the PLA size increased within a series from 2 to 25 kDa. The results obtained reveal, that in an aqueous medium the copolymers assembled into micellar-like structures, with the PLA segments forming the core and the PEG segments the surrounding corona. The size of the PLA segments dominated the process of assembly of the molecules and the characteristics of the resultant micellar-like particles. The PLA-PEG micellar particles were found to be less dynamic than those obtained from conventional surfactants. Particles formed from the lower molecular weight PLA polymers allowed a level of chain mobility while the cores of the micellar particles formed from higher molecular weight PLA appeared to be solid-like in nature. The size of the micellar particles was dependent on the copolymer molecular weight and the z-average diameter increased from 25 to 76 nm as the molecular weight of the PLA moiety increased. This provides an ability to control the particle size by adjusting the molecular weight of the PLA moiety. Following intravenous administration to the rat model, micellar-like particles smaller than approximately 70 nm accumulated in the liver, despite the fact that the PEG corona provided an effective steric stabilization effect. Micellar-like particles with a diameter of more than approximately 70 nm exhibited prolonged systemic circulation and reduced liver uptake, although the steric stabilisation of these particles was shown to be less effective. These findings agree with recent observations from other research groups; that indicate a possibility that very small particulates can pass through the sinusoidal fenestrations in the liver and gain access to the parenchymal cells of the liver.
Water swollen gels of (unbranched) dialkyl ethers (n = 16, 17, 18, 20 and 21) of poly(ethy1ene oxide) (a,, = 10OO0, 20000 and 30000) have been investigated using NMR spectroscopy and differential scanning calorimetry (DSC). Aggregates of the alkyl segments were found to undergo a 'solid/liquid' transition at a temperature approximating the melting point of an unbranched hydrocarbon about three to four carbon atoms shorter than the alkyl chain. Below the transition temperature, the alkyl component gave a broad NMR line whose second moment was approximately one-quarter that of a crystalline alkane of similar length. The enthalpy of the transition was approximately one-third that of the corresponding unbranched alkane. These results indicate a partially crystalline structure for the 'solid' aggregates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.