The Synthesis Of Star-shaped PLLA And It’s Application In Drug Release

Polylactide(PLA) is an environment-friendly material with good biodegradability andbiocompatibility, which is widely used in the field of medicine. Compared with linearpolylactide,the star-shaped polylactide has lower crystallinity, hydrodynamic volume andhigher functionality of molecular surface. In addition, the star-shaped polylactide is easier toget high molecular weight, meanwhile the lower melt viscosity make it easier to process.The linear PLLA with2arms and star-shaped PLLA with3、4、6arms were synthesizedfrom L-lactide by means of melt ring opening polymerization, using tin octoate（Sn(Oct)2ascatalyst and1,6-hexanediol, trimethylolpropane (TMP), pentaerythritol (PET),dipentaerythritol as branched agents, respectively. The structure of polylactide with differentarms was investigated by1H-NMR. It is proved that all the hydroxyls of branched agentswere involved in the polymerization by analyzing the1H-NMR spectra. So the synthesizedpolymer had corresponding branch structure.The molecular weight and it`s distribution of star-shaped polylactide were studied byGPC-LC. The result showed that4types of polylactides had a similar molecular weight. Butstar-shaped PLLAs had a more narrow molecular weight distribution compared with linearPLLA. Furthermore, the effect of arm number on the intrinsic viscosity, thermal property,thermal degradation property and crystallization property of star-shaped PLLAs werecharacterized by Ubbelohde viscometer, DSC, TG, POM and XRD. The results showed thatthe intrinsic viscosity, glass transition temperature, melting point, decompositiontemperature, degradation, crystallinity and crystallization rate of the star-shaped PLLAswere lower than linear PLLA, and they decreased with the increasing number of arms. Thecold crystallization temperature increased with the increasing number of arms. The growthrate and the size of crystal had some relationship to the number of arms and temperature.The speed of polymer crystal growth and the size of crystal decreased with the increasingnumber of arms. In the temperature range of crystallization, the lower the temperature was,the easier the crystal nucleus formation was and the slower the crystal growth was.The PLLA microspheres were fabricated by W/OW double emulsion solventevaporation method in the paper. First of all, the experiment design of blank polylactide microspheres was tentative explored by changing the emulsifier type, ratio of W1/O/W2,stirring method, stirring time. Then the effects of emulsifier type, emulsifier concentration,PLLA concentration, stirring rate, stirring time on the shape and the size of PLLAmicrospheres were studied by SEM. The result showed that the obtained PLLA microsphereswere the best when the emulsifier was PVA, the concentration of emulsifier was1%, theconcentration of PLLA was40mg/mL, the rate of stirring was500r/min, and the time ofstirring was6h. The4types of PLLA-CEZ microspheres using CEZ as the model drug wereprepared by the best design. The structure of PLLA-CEZ microspheres and blankmicrospheres were characterized by FT-IR. By comparing the analysis, a peak was found at3734cm-1which is the N-H peak of CEZ. The result showed that the PLLA-CEZmicrospheres had loaded CEZ.The drug-loading capacity and encapsulation efficiency of PLLA-CEZ microsphereswere tested by UV. The result showed that the star-shapded PLLAs had higher drug-loadedrate and coating rate than linear PLLA. Furthermore, the drug-loaded rate and coating rateincreased with the increasing number of arms. The result of PLLA-CEZ microspheressustained release in vitro of PBS solution showed that all the4types of PLLA-CEZmicrospheres had the burst release effect. But the burst release effects of star-shaped PLLAmicrospheres were less serious than linear PLLA microspheres. Also the sustained releaseeffect was better with the increasing arms of PLLA-CEZ microspheres.