| Background&objectiveCurcumin(curcumin,CUR),a hydrophobic polyphenol compounds with a low molecular weight extracted from the rhizome of turmeric,rhizoma zedoariae,curcuma aromatica beling to zingiberaceae,has extensive pharmacological activity and efficacy such as anti-tumor,anti-inflammatory,anti-oxidation,antibacterial,antiviral,anti-Alzheimer's,anti-atherosclerosis,anti-angiogenesis,anti-HIV and so on,especially in cancer prevention and treatment,the role is particularly prominent and worthy of being studied.Depending on its wide antitumor spectrum and small side effects,the U.S.National Cancer Institute has listed curcumin as the 3rd generation cancer chemopreventive drugs,and has entered clinical trials.Curcumin is safe and non-toxic,has been used for centuries as food toner and drug.However,the clinical application of curcumin is severely limited by these shortcomings such as poor water solubility,poor stability to light,heat,acid and alkali,and low bioavailability.To try to solve these problems,have lots of composite modified method have adopted by many Chinese and foreign scholars to develop aqueous curcumin formulations such as a PAMAM dendrimer curcumin conju-gate,a PEG-curcumin conjugate,a cyclodextrin-curcumin gate,liposomal curcumin,and phospholipid-based curcumin-encapsulated microemulsions.Amphiphilic block copolymer composed of hydrophilic and hydrophobic chain can spontaneously assemble in aqueous solution to form a core-shell structure of the suprarmolecular orderly aggregates micelles.Hydrophilic chain call in the shell can prevent the touch of drug and water,stable copolymer micelle,avoid in vivo reticuloendothelial system identification,liver and renal excretion,and reduce plasma protein adsorption,evade opsonin recognition;the hydrophobic chain can provide hydrophobic microenvironment to increase the solubility of poorly soluble substances in the water.In recent years,the polymeric micelles(such as PEG-polyester,PEG-poly(amino acids),etc.)as a effective drug carrier transport has advantages of good dnug loading capacity,good stability,long circulation time in vivo,being targeted modified,sustained release and targeting property,attracted widespread attention.Polycaprolactone(Polycaprolactone,PCL)has been approved by the U.S.Food and Drug Administration(FDA)as a most attractive medical polymer materials with excellent properties such as biocompatibility,biodegradability,non-toxic and extensive application prospects of,drug permeability and mechanical properties.it is a kind of good pharmaceutical carrier materials and has extensive application.Used as carrier materials to curcumin,PCL has some strong advantages.It can improve the solubility,stability and bioavailability of curcumin,can achieve sustained-release and prolong acting time of drug.But it has been limited to applicate as a drug carrier because of its high degree of crystallinity and hydrophobicity,and slow degradation rate in vivo.PEG is the most commonly hydrophilic molecules used to modified other hydrophilic materials and own many good characters as excellent biocompatibility,strong hydrophilicity,high cell penetrability,non-toxic and non-immunogenic in vivo.It has also been approved by FDA to use for human.Considering the the micellar formulations advantages as well as the advantages of biodegradable materials,we choice mPEG114-PCL36 as curcumin drug carriers.In recent years,the material as curcumin carrier composed of mPEG and PCL also has been reported.The nano-precipitation and probe-type ultrasonic emulsion-solvent evaporation method were respectively used to encapsulate curcumin into MPEG45-PCL18 and PCL59-PEG136-PCL59 by zhiyong Qian and runliang Feng group.Qian et.al employ mPEG2000 with equal amounts of:-CL monomers to synthetize block copolymer with the total molecular weight of about 4000 by ring-opening polymerization.The curcumin-loaded micelles prepared with that polymer as carrier material with a mean particle size of 27nm,is expected to be made into intravenous formulation.In order to explore the impact of the change of the molecular weight of the mPEG and PCL block on micelle particle size and drug loading capabilities,to provide a theoretical reference for the preparation of the intravenous formulation,we synthetize polymerization amphiphilic block copolymers of polyethylene glycol monomethyl ether-poly caprolactone(mPEG114-PCL36)from mPEG5000 with an equal amount of ?-CL monomer,then prepare curcumin-loaded micelles form them and evaluate the quality of micellar.Methods1 Synthesis and Characterization of mPEG114-PCL36 block copolymerThe amphiphilic block copolymer of polyethylene-polycaprolactone was synthesized via ring-opening polymerization of PEG and PCL at a mass ratio of 1:1,with stannous octoate(1%mol ?-CL)as catalytic agent,and its structure was characterized by Fourier transform infrared spectroscopy(FT-IR)and proton nuclear magnetic resonance('H-NMR)spectroscopy.The molecular weight of the mPEG114-PCL36 was calculated according to NMR spectra,and the critical micelle concentration(CMC)was detected with fluorescence techniques using pyrene as a probe.2 Preparation and characterization of Curcumin-loaded mPEG114-PCL36 micelleThe mPEG114-PCL36 amphiphilic block polymer micelles containing curcumin were prepared by dialysis.The encapsulation efficiency drug loading were determined by HPLC;and the particle size was examined by dynamic light scattering.Effects of the copolymer concentration,drug concentration,volume ratio of aqueous to organic phase on the size,entrapment efficiency and drug loading was evaluated by L9(34)orthogonal design.The optimum formulation and technology was checked out and verified by repeated experiment three times.3 In vitro release study of CUR-loaded mPEG114-PCL36 micellesIn vitro drug-release profile of CUR from drug-loaded micelles was carried out by Dynamic dialysis method.Drug-loaded micelles solution was placed in a dialysis membrane bag with molecular weight cut-off 8000?14,000 g/mol.Dialysis bags were incubated in 30 mL of phosphate buffer solution(pH 7.4)containing SDS(0.5%w/w)at 37±0.5? with gentle shaking at 80 r/min.At predetermined time points,the incubation medium was replaced with fresh incubation medium.The amount of drug released in the incubation medium was quantified by HPLC,and Cumulative release quantity was calculated.Furthermore,the drug release mechanisms of CUR-loaded mPEG114-PCL36 micelles were studied with mathematical models including Weibull distribution modle,Ritger-Peppas model,Higuchi model,etc.Results1 Synthesis and Characterization of mPEG114-PCL36 block copolymermPEG114-PCL36 amphiphilic block polymer was successfully synthesized by ring-opening copolymerization of PEG and s-CL.The structure was verified by FT-IR,1H-NMR and the molecular weight was 9042 calculated according to NMR spectra.measurement the CMC value measured by pyrene fluorescence probe was 8.649×104mg/ml.2 Preparation and characterization of Curcumin-loaded mPEG114-PCL36 micelleThe results of orthogonal design showed that various factors had small effects on the particle size of the CUR-mPEG1,4-PCL36 micelles was,with no statistical significance,while had significant impacts on encapsulation efficiency and drug loading,especially for volume ratio of aqueous to organic phase,in which waterphase volume of the oil phase volume ratio the most significant impact.The optimal preparation parameters were as follows:mPEG114-PCL36 concentration was 25mg/ml,the drug concentration was 2.5mg/ml,the volume ratio of aqueous to organic phase was 3:1.The nanomicelles prepared under the optimum formulation and technology conditions has a mean diameter of(48.5± 1.7)nm with the polydispersity index of 0.20±0.07,drug loading of(49.12±1.26)%as well as encapsulation efficiency of(4.46 ± 0.12)%.3 In vitro release study of CUR-loaded mPEG114-PCL36 micellesThe in vitro release behaviors showed that the cumulative drug release rate of CUR-loaded mPEG114-PCL36 micelles was about 28.5%,the drug cumulative release percentage-time was fitted to zero order release kinetics model,which equation was y=0.0118x+0.007,r=0.9984.After controlled release,the nanomicelles stepped into a slow-release stage,the cumulative drug release rate was only 13.4%during the next 48h.The curcumin-loaded nanomicelles showed a good sustained-release without burst release at initial stage.ConclusionsWe successfully synthesized the amphiphilic block polymer of mPEG114-PCL36.The structure is in consistent with the target substance we designed.Using dialysis method,We prepared CUR-mPEG114-PCL36 nanomicelles and the method was simple and mild.The CUR-mPEG114-PCL36 nanomicelles showed a good sustained-release property with small and evenly distributed particle size,and without burst release at initial stage. |
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