Research On Nano-micelles Used As Drug Carriers Based On NIPAM Thermosensitive Amphiphilic Triblock Copolymers

In recent years,stimuli-responsive polymeric micelles,which are sensitive to environmental stimuli such as pH,ionic strength,temperature,ultrasonic and magnetic field,have attracted more and more interest and have been developed and actively investigated for the preparation of intelligent drug carriers.Among them, thermo-responsive polymeric micelles,which are generally formed by self-assembly of amphiphilic block copolymers having both thermo-responsive hydrophilic segments and hydrophobic segments in aqueous media,are especially focused on.The reason is that temperature is easy to be controlled and has practical advantages in vitro and in vivo, and thermo-responsive polymeric micelles combine both passive targeting to tissue sites with their small size and the potential active targeting with their switchable physicochemical characteristic.Up to date,a series of thermo-responsive polymeric micelles are formed by self-assembly from thermo-responsive diblock copolymers based on poly(N-isopropylacrylamide)(PNIPAM),since PNIPAM undergoes a sharp coil-to-globule phase-transition at a critical temperature,namely,lower critical solution temperature(LCST) of 32℃,close to physiological temperature,37℃.Moreover,the LCST can be modulated via copolymerization with hydrophobic or hydrophilic monomers.Up to now,however,there are still scarce reports on a drug release system based on thermo-responsive amphiphilic multiblock copolymer micelles due to the difficulty in synthesis and the complicated structure of the triblock copolymers to some extent.In this paper,a series of thermo-responsive triblock copolymers and their micelles were designed and preperated and their controlled drug release on folic acid (FA) were also investigated.The work was complised as follow:1.A novel amphiphilic ABC triblock copolymer,poly(N-isopropylacrylamide)-b-poly (styrene-alternate-maleic anhydride)-b-polystyrene(PNIPAM-b-PSMA-b-PSt),was designed and synthesized by reversible addition fragmentation chain transfer polymerization(RAFT).The copolymer can self-assemble into pH- and thermo-responsive core-shell-corona micelle with the hydrophobic PSt block as core, the pH-sensitive PSMA block as shell and the thermo-sensitive PNIPAM block as corona in aqueous media at room temperature.The aqueous copolymer solutions exhibited lower critical solution temperature(LCST) values around 33.5-35℃under pH 2.1-9.2 conditions via optical transmittance measurements.The critical micelle concentration values of the self-assembled micelles were about 18.6 mg/L at pH 2.1 and 21.1 mg/L at pH 6.9 relying on fluorescent probe technique,respectively.An interesting pH- and thermo-dependant size of the micelles was observed by dynamic light scattering technique,which showed the micelle diameters about 100-120 nm at 40℃and 120-160 nm at 25℃,corresponding to pH 2.1-9.2,respectively.Transmission electron microscopy observations showed that the resulting micelles as uniform nanoparticles existed in regularly spherical shape.The folic acid-loaded micelles showed a remarkable pH- and thermo-responsive drug release behavior.2.An amphiphilic thermo-responsive ABA triblock copolymer,poly(methyl methacrylate)-b-poly(N-isopropylacrylamide-co-poly(ethylene-glycol) methyl ether methacrlate)-b-poly(methyl methacrylate)(PMMA-b-P(NIPAM-co-PEGMEMA)-b-PMMA ),was designed and synthesized via reversible addition fragmentation chain transfer(RAFT) polymerization,and subsequently characterized by FTIR,~1H NMR and GPC.The copolymer can disperse in water and self-assemble into nanoscaled micelles in a"flower-like"arrangement at room temperature.The resulting micelles were investigated using fluorescence spectroscopy,dynamic light scattering technique(DLS) and transmission electron microscopy(TEM).The copolymer exhibited a lower critical solution temperature(LCST) of around 39℃via optical transmittance measurements. Notably,there was no copolymer precipitation observed at the LCST,which was propitious to in vivo use of the micelle.The micelles loaded with FA showed a remarkable thermo-responsive drug release behavior.3.An amphiphilic thermo-responsive ABC triblock copolymer,poly(N-vinyl pyrrolidone)-b-poly(N-isopropylacrylamide-co-N-vinyl pyrrolidone)-b-poly(methyl methacrylate)(PVP-b-P(NIPAM-co-VP)-b-PMMA),was designed and synthesized via reversible addition fragmentation chain transfer(RAFT) polymerization,and subsequently characterized by FTIR,~1H NMR and GPC.The triblock copolymer undergoes self-assembly into the nanoscaled micelles with a core-shell-corona structure in water.Morphological investigations by transmission electron micrograph (TEM) showed that the self-assembled micelles had spherical and uniform shapes.The average diameters of the resulting micelles were about 128 nm at 25℃and 97 nm at 41℃,as measured by dynamic light scattering(DLS),respectively.The LCST of the triblock copolymer were determined to be around 38.1℃at 0.4 mg/ml and 39.2℃at 0.2 mg/ml,respectively.Noticeably,there was no copolymer precipitation observed at the LCST,which was beneficial to in vivo use as a drug delivery carrier through systemic administration.The micelles loaded with folic acid as a model drug showed a special thermo-responsive drug release behavior,which was confirmed by the in vitro rug release studies.The results above indicate that the nanoscaled thermo-sensitive micelles nanoparticles would be a promising"smart"drug delivery system.