Preparation Of Nanoparticles Based On Amphiphilic Depsipeptide Block Copolymers And Application In Controlled Drug Release Study

Biodegradable amphiphilic block copolymers with stable performance andadjustable structure can self-assemble into hydrophobic core and hydrophilic shellnanomicrospheres, thus they have aroused the great concern of researchers in drugdelivery field. In this paper, morpholine-2,5-dione derivatives containing depsipeptidestructure were deemed as the research objects, a series of novel amphiphilicdepsipeptide block copolymers were constructed by using the ring-openingpolymerization (ROP) and atom transfer radical polymerization (ATRP) technology,meanwhile, the drug release behavior was also studied. The main results aresummarized as follows:1. After successfully preparing morpholine-2,5-dione derivatives, i.e.3(S)-methyl-morpholine-2,5-dione(MMD),3(S)-butyl-morpholine-2,5-monomers,3(S)-isobutyl-morpholino-2,5-dione (IBMD) and aliphatic polyesters poly(p-dioxanone)(PPDO)(Mentioned here, in order to characterize the latter block copolymers). Twokinds of amphiphilic triblock copolymers {i.e.poly(3(S)-methyl-morpholine-2,5-dione-co-p-dioxanone)-block-poly(ethylene glycol)6000-block-poly(3(S)-methyl-morpholine-2,5-dione-co-p-dioxanone)[P(MMD-co-PDO)-b-PEG-b-P(MMD-co-PDO)](PMMD-PPDO-PEG) andpoly(3(S)-butyl-morpholine-2,5-dione-co-p-dioxanone)-block-poly(ethylene glycol)6000-block-poly(3(S)-butyl-morpholine-2,5-dione-co-p-dioxanone)[P(SBMD-co-PDO)-b-PEG-b-P(SBMD-co-PDO)](PSBMD-PPDO-PEG)} which werebased on morpholine-2,5-dione derivatives (MMD and SBMD, respectively), andcombined with PDO and polyethylene glycol (PEG), were synthesized by utilizing thering-opening polymerization (ROP) technique. The structural characteristics of theabove amphiphilic block copolymers were identified by using1H NMR, FT-IR, GPC,DSC and TGA analysis.2. Another ABA triblock copolymers ofpoly(3(S)-isobutyl-morpholine-2,5-dione-co-p-dioxanone)-block-poly(ethylene glycol)6000-block-poly(3(S)-isobutyl-morpholine-2,5-dione-co-p-dioxanone)[P(IBMD-co-PDO)-b-PEG-b-P(IBMD-co-PDO)] were successfully prepared by ROP of3(S)-isobutyl-morpholine-2,5-dione (IBMD) and p-dioxanone (PDO) using PEG6000asinitiator. And then the macroinitiatorsBr-P(IBMD-co-PDO)-b-PEG-b-P(IBMD-co-PDO)-Br were prepared from them by the bromination with2-bromoisobutyryl bromide (BiBB). Finally, hydrophilicpoly(2-(dimethylamino)ethyl methacrylate)(PDMAEMA) blocks were attached to thesehydrophobic triblock copolymers by ATRP, and the amphiphilic multiblock copolymerswere defined asPDMAEMA-b-P(IBMD-co-PDO)-b-PEG-b-P(IBMD-co-PDO)-b-PDMAEMA(PDMAEMA-PIBMD-PPDO-PEG). The structures of the above copolymers were characterizedby using1H NMR,13C NMR, FT-IR, GPC, DSC and TGA analysis.3. Taking the synthetic triblock copolymers PMMD-PPDO-PEG andPSBMD-PPDO-PEG as carriers, doxorubicin (DOX) as model drugs, the blank anddrug-loaded microspheres were prepared by an oil-in water (o/w) emulsion solventevaporation method (through the combination of hydrogen bond and hydrophobic effectbetween DOX and block copolymers), those blank copolymer microspheres werecharacterized by hydrolytic degradation analysis, the critical micellar concentration(CMC)(fluorescene probe method of pyrene)and Zeta potential. Experiments studiesshowed that the copolymers could easily form uniform microspheres in phosphatebuffered solution (PBS), and the number-average molecular weight (Mn) of those blockcopolymers decreased along with degradation time. Copolymer PMMD-PPDO-PEGself-assembled into stable nanosized microspheres with CMC of0.41-0.66μg/mL.Basically, the CMC of microspheres increased slightly with the increase of PDO in feed.Zeta potential measurement of the copolymer microspheres based on SBMD and IBMDindicated that the copolymer microspheres had good stability. The dynamic lightscattering (DLS) and transmission electron microscopy (TEM) results of blank andDOX-loaded copolymers (PMMD-PPDO-PEG and PSBMD-PPDO-PEG) microspheresshowed that the two series of copolymers in PBS self-assembled uniform, dispersed,ellipsoidal and single distribution nanoparticles. The average diameter of the particleswere100and200nm, respectively. In addition, they exhibited high drug loadingcapacity (LC), the encapsulation efficiency (EE) and sustained drug release behavior inPBS.4. Preparing amphiphilic multiblock ATRP copolymers nanomicrospheres,Ibuprofen (IBU) and the combination of IBU-DOX were chosen as model drugs, the LC,EE and the drug release behavior of the multiblock copolymers microspheres wereinvestigated. The tests showed that LC and EE increased with increasing the initialweight ratios of drug to copolymer, but LC and EE decreased after the ratio increased toa certain percentage (16/44and8-8/44, respectively). The LC and EE of the IBU-loadedcopolymer microspheres are slightly higher than that of IBU-DOX-loaded copolymer microspheres. Moreover, LC and EE of the prepared copolymer microspheres arecorrelated with PBS concentration. Meanwhile, we selected PBS of different pH (5.0,7.4) as the release media to further investigate the characteristics of drug-loadedmicrospheres. The results showed that IBU-DOX-loaded copolymer microspheres hadgood pH-responsiveness. The drug release rate of copolymer microspheres in low pH(5.0) was faster than that in pH (7.4), which is likely due to the protonation of the aminogroups of PDMAEMA and DOX, and fast degradation of microsphere core. In addition,experiments explored the self-assembly conditions of the copolymers, the microspheresmorphology of drug-loaded copolymers and particle size distribution through DLS andTEM measurements. The DLS results of PDMAEMA-PIBMD-PPDO-PEGmicrospheres showed that the IBU-and IBU-DOX-loaded nanoparticles werewell-defined uniform spherical particles with diameter about100nm. All copolymermicrospheres size increased slightly after drug loading. From the above results, it can beenvisaged that these copolymer systems are promising candidates for controlled releaseapplication.