Synthesis, Characterization And In Vitro Drug Release Of Novel Intelligent Polymeric Nanoparticles

With development of biomedical technology and material science, the stimulus responsive biomaterials, such as thermo, pH, magnet, and light responsive materials, are used as drug and gene delivery systems widely. In this thesis, a series of novel polymeric nanoparticles with temperature and/or pH responsibilities were designed and synthesized. Furthermore, the structure of nanoparticles, the internal relationships between physical and chemical properties of nanoparticles and drug controlled release behaviors were investigated in detail. The main content is listed as follows:In Chapter 1, the recent research progress of stimuli-responsive biomedical polymeric materials, including the synthesis and biomedical applications was reviewed.In Chapter 2, a novel colon targeted nanogel based on pectin was designed and synthesized. Transmission electron microscope (TEM) observation showed that the nano-sized gel particles exhibit a spherical morphology, of which the size ranged from 200 to 300 nm. The optical absorbance study of nanogel suspension revealed its pH sensitivity, which could contract in acidic solution and swell in alkaline solution. Cytotoxicity study showed that the nanogel has no apparent inhibitory effect on cells when its concentration was ranged from 0 to 4.5 g/L. The in vitro drug-release behaviors of the prednisone acetate-loaded nanogel particles in three kinds of media, i.e., simulated gastric fluids, simulated intestine fluids and simulated colon fluids, were studied. PT-GA nanogel exhibited a faster release in simulated colon fluids than in other two fluids for its specific degradation by pectinolytic enzyme. The experimental results indicated that the nanogel was pH sensitive and colon targeted, which may be used for intelligent drug release systems.In Chapter 3, a series of thermosensitive and biodegradable ABA type triblock polycaprolactone-b-poly(N-isopropylacrylamide)-b-polycaprolactone (PCL-PNIPAAm-PCL) copolymers with different molecular weights were synthesized by the combination of ring opening polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The experimental results of SEC-MALLS showed that the molecular weight of each block of copolymers could be controlled by reaction time. The self-assembling micellization behavior of amphiphilic triblock copolymers in water were confirmed by FT-IR,1H NMR and fluorescence spectroscopy. TEM observation and DLS showed that the self-assembled micelles exhibited a well-defined spherical shape with diameter of around 100 nm. Optical absorption measurements showed that the lower critical solution temperatures (LCSTs) of micelles were around 36℃which were close to body temperature. The drug release rate of prednisone acetate loaded micelles at high temperature was faster than that at low temperature, indicating the triblock copolymers had great potential as a drug carrier for temperature trigged controlled release.In Chapter 4, the thermo-responsive amphiphilic diblock copolymer P(NIPAAm-co-NAS)-b-P(MMA) was synthesized by RAFT polymerization and the shell cross-linked (SCL) micelles were further prepared in aqueous solution by copolymer in the presence of ethylenediamine since the NAS was an active ester. The successful preparation of SCL micelles was confirmed by 1H NMR and TEM micropictures shot with DMF as disperse phase. The LCST of SCL micelles was measured to be 41.2℃by turbidity method. The micropictures and average size measured at different temperature showed that the SCL micelles would shrink slowly and steadily without aggregation when temperature range from 25 to 49℃, and still remained spherical shape at 45℃. Compared with uncross-linked micelles, the SCL micelles exhibited more slowly and steadily drug release rate at high temperature since the cross-linking structure in shell would limit the contraction of PNIPAAm chains at high temperature. Taking advantage of the temperature sensitivity as well as more stable and slow drug release rate, the SCL micelles would have great potential for the controllable sustained drug release.In Chapter 5, temperature and pH double responsive diblock copolymer P(NIPAAm-co-MPMA)-b-P(DEA) was synthesized by RAFT polymerization. MPMA was a monomer which could form inorganic silica cross-linked structure by hydrolysis in aqueous solution. As a result, the hybrid core cross-linked (CCL) micelles consisting of PNIPAAm core could be prepared in aqueous solution at pH 2, 45℃and the hybrid shell cross-linked (SCL) micelles consisting of PNIPAAm shell could be prepared in aqueous solution at pH 12,20℃by diblock copolymer. The micelles, of which the building blocks are both stimulus responsive, were defined as "schizophrenic micelles".1H NMR and TEM micropictures showed that the size of CCL micelles and SCL micelles would change with temperature and pH value of aqueous solution. The in vitro drug release study showed that either CCL or SCL micelles exhibited a slowest cumulative release behavior at pH 2,20℃when both core and shell of the cross-linked micelles were hydrophilic; exhibited a fastest release rate at pH 12,45℃when both core and shell were hydrophobic; exhibited a middle release rate at pH 2,45℃and at pH 12,20℃when one of the two blocks kept hydrophilic and the other kept hydrophobic. Taking advantage of their LCSTs being slightly above 37℃as well as double responsive properties, the CCL and SCL micelles would have great potential as novel polymeric carriers for both temperature and pH controlled drug release.In Chapter 6, two well-defined diblock copolymers with the same hydrophobic moiety were prepared by ATRP polymerization, i.e., temperature-responsive P(MMA-co-MPMA)-b-PNIPAAm and pH-responsive P(MMA-co-MPMA)-b-PDEA. Novel hybrid CCL complex micelles could be prepared by co-self-assembly of the two block copolymers in acid aqueous solution at room temperature, which were composed of a hydrophobic PMMA core and a combined temperature/pH double responsive PNIPAAm/PDEA shell. The LCST of the CCL complex micelles was measured to be 33.0℃by the turbidity method. A combination of analytical techniques (TEM, LLS and 1H NMR) revealed when temperature or pH value was increased, the core-shell complex micelles will convert into core-shell-corona (CSC) complex micelles. Namely, the CSC complex micelles consisted of cross-linked hybrid PMMA core, PNIPAAm inner shell, and protonated PDEA outer corona at high temperature (45℃); or cross-linked hybrid PMMA core, hydrophobic PDEA inner shell, and hydrophilic PNIPAAm outer corona in alkaline solution (pH 9). The size of the CCL complex micelle could be readily regulated by adjusting the environmental conditions (temperature and/or pH) due to the dually responsive mixed shell. From this standing point, the CCL complex micelles developed herein would have great potential to be novel carriers for both temperature and pH controlled drug delivery.