A six-member cyclic carbonate with protected functional groups was synthesized from tetramethylolmethane,benzaldehyde and ethyl choroformate.Coplymerization of（D,L-lactide） with cyclic carbonate was carried out through conventional ring-opening polymerization using Sn（Oct）2 as the catalyst.The effects of different catalysts,polymerization time and monomer-to-catalyst molar ratio on the molecular weight were investigated.The methods of removing protected groups were studied.Results showed the protected groups were effectively removed via catalytic hydrogenation.（Poly（D,L-lactide-co-cycliccarbonate）s） with hydroxyl pendant functional groups was obtained.
A novel pH-sensitive nanoparticle drug delivery system (DDS) derived fl om natural polysaccharide pullulan for doxorubicin (DOX) release was prepared.Pullulan was functionalized by successive carboxymethylization and amidation to introduce hydrazide groups.DOX was then grafted onto pullulan backbone through the pH-sensitive hydrazone bond to form a pullulan/DOX conjugate.This conjugate self-assembled to form nano-sized particles in aqueous solution as a result of the hydrophobic interaction of the DOX.Trans...
Superparamagnetic iron oxide (SPIO) nanoparticles are effective contrast agents for enhancement of magnetic resonance imaging at the tissue, cellular or even molecular levels. High quality SPIO nanoparticles can be synthesized in the organic phase but need to be transferred into water before any biomedical applications. In this study, amphiphilic poly(ε-caprolactone) grafted dextran (Dex-g-PCL) was used as carriers for particle encapsulation and stabilization in the aqueous phase. Multiple SPIO nanoparticles were self-assembled together with the help of Dex-g-PCL during phase transfer from chloroform to water, and diameters of Dex-g-PCL/SPIO nanocomposites were (64 ± 22) nm through dynamic light scattering measurement. These nanocomposites were superparamagnetic at 300 K with saturated magnetization of 88 emu/g Fe. In the magnetic field of 1.5 T, Dex-g-PCL/SPIO nanocomposites had a T2 relaxivity of 363 Fe mL·mol-1·s-1. This unique nanocomposite brought significant mouse liver contrast with signal intensity changes of -60% at 5 min after intravenous administration. However, uptake of Dex-g-PCL/SPIO nanocomposites in liver reticuloendothelial cells (Kupffer cells) did not immediately happen at shorter time points (<4 h) as verified by histology studies, and it was evident that more iron staining would be located in Kupffer cells 24 h after contrast agent administration. After 24 h and 10 d, the signal intensities (SI) gradually recovered, and SI changes were -44% and -31%, respectively. From our observation, the time window for enhanced-MRI could last at least 12 days and totally recovered after 16 days. This novel sensitive MRI contrast agent may find potential applications in discovering small liver lesions such as early tumor diagnosis.
