Synthesis Of Acid-Labile Biodegedable Polymers As Drug Carriers

The pH-sensitive of polymer, is refers as a result of the pH change in the environment, stimulates responsiveness based on the molecular and macromolecular level, it can be possible to have the volume or the shape change. Due to the diffenert pH values of gastrointestinal tract, the pH-sensitive polymer carrier can be used to control the drug release. In the other hand, the pH of endosome in cell is 5.5-6.5, but that of body fluid is 7.0-7.4. After the pH-sensitive polymer carry polypeptide, protein and nudeic acid into the endosome, the structure was changed, and the stability of endosomal membrane was destroyed. So, the pH-sensitive polymer with the drug can escape from the endosome into the cytoplasm, avoiding being break up by the enzyme in the lysosome or acidity.The pH-sensitive polymers were synthesized through introducing acetal groups into the backbone of poly(dl-lactide)-poly(ethylene glycol). The chemical structures were determined by FT-IR and NMR, respectively. Electrospinning was applied to prepare ultrafine fibers, whose degradation behaviors were further investigated with respect to the molecular weight reduction, mass loss and morphological changes after incubated in buffer solution of different pH values. The electrospun fiber of polymer with 10% of acid-sensitive segments showed significant degradation with ca. 15% and 4.5% of molecular weight reduction, ca. 42% and 13% of mass loss and breakdown of fibers after incubated in pH4.0 and pH7.4 buffer solution at 37℃for 72 hours.Drug loading fibrous mats were prepred by blending electrospinning of paracetamol and the obtained acid-sensitive polymers. The drug release profiles were investigated in buffer solution of different pH values, and the drug concentration were determined by UV. There was two-step release pattern for microspheres: an initial burst release followed by a gradual release phase. The results showed that PBELA-10 cumulate release 78.14% and 26.3% after incubated in pH4.0 and pH7.4 buffer solution at 37℃for 120 hours. The electrospun fiber of drug carrier polymer with 10% of acid-sensitive segments showed significant degradation with ca. 24.6% and 8.4% of molecular weight reduction, ca. 49% and 20% of mass loss and breakdown of fibers after incubated in pH4.0 and pH7.4 buffer solution at 37℃for 120 hours.It indicated form the degradation and drug release profiles that the obtained polymers were pH-sensitive, and the sensitivity increased with the increase of the acetal contents.