Preparation And Characteristics Evaluation Of PH-responsive Polymers

Stimuli-responsive polymers have been extensively investigated and used as smart biomaterials such as drug delivery systems. The phase transition or phase separation of polymer is induced by a change in various conditions such as temperature, pH, electric field and solvent composition. However, the application of polymers to drug delivery systems is difficult because most stimuli-responsive polymers are not biodegradable and some are toxic. Polymeric biodegradability and biocompatibility are the most important factors for the application of polymers to drug delivery systems. Poly (amino acid) s is a kind of biodegradable materials in vivo. They are useful in pharmaceutical and biomedical areas.A series of pH-responsive copolymers were synthesized with N- alkylated threonine and D, L-lactic acid successfully by direct polycondensation under bulk condition. The copolymers comprising of N- alkylated threonine unit and lactic acid unit were confirmed by 1H-NMR spectrum. Copolymers were characterized by 1H-NMR spectroscopy, Gel permeation chromatography (GPC) and Fourier-transform infrared (FT-IR) spectra. In order to prove the pH-sensitivity of copolymer, size and zata potential were determined in different pH by Zetasizer APS.The hydrogen peroxide-acetic acid oxidative system was used to degrade chitosan, and got a series of different molecular weight chitosan, then modified by N- alkylated. Fourier transforms infrared spectrometer (FT-IR), UV-vis spectrophotometer (UV) was carried out to characterized structure and transmittance of different pH. Fe₃O₄ nanoparticles were prepared by the modified controlled chemical co-precipitation method, which can be well dispersed in water by the dispersion of surfactant (KH-570). Then the size of Fe₃O₄ nanoparticles were determined by particle size analyzer, also the Fe₃O₄ nanoparticles were characterized by X-ray powder diffraction (XRD) analysis, Fourier transform infrared spectrometer (FT-IR), and vibrating-sample magnetometer (VSM).Magnctic N-alkylated chitosan microspheres containing etoposide were prepared by the modified water-in-oil-in-water solvent evaporation procedure. X-ray powder diffraction (XRD) analysis. Scanning electron microscopy (SEM), and vibrating- sample magnetometer (VSM), UV-vis spectrophotometer (UV), thermogravimetry- differential thermal analysis (TG) were carried out to examine phase composition, surface morphology, etoposide encapsulation efficiency and magnetic properties of the magnetic microspheres. In vitro release of magnctic N-alkylated chitosan microspheres containing etoposide were performed in phosphate buffered saline (PBS, pH = 5.5, 7.7, 11.5). The results from UV measuring showed that there was two-step release pattern for microspheres: an initial burst release followed by a gradual release phase.