Novel pH-sensitive hydrogels for colon-specific drug delivery

The purpose of this study is to develop novel intestinal specific drug delivery systems with pH-sensitive swelling and drug release properties. Acryloyl ester of 5-[4-(hydroxy phenyl) azo] salicylic acid (HPAS) as an azo derivative of 5-amino salicylic acid (5-ASA) was prepared under mild conditions. The HPAS was covalently linked with acryloyl chloride, abbreviated as APAS. Cubane-1,4-dicarboxylic acid (CDA), linked to two 2-hydroxyethyl methacrylate (HEMA) groups, was the cross-linking agent (CA). Methacrylic-type polymeric prodrugs were synthesized by free radical copolymerization of methacrylic acid, poly(ethyleneglycol monomethyl ether methacrylate), and APAS in the presence of cubane cross-linking agent. The effect of copolymer composition on the swelling behavior and hydrolytic degradation were studied in simulated gastric (SGF, pH 1) and intestinal fluids (SIF, pH 7.4). The composition of the cross-linked three-dimensional polymers was determined by FTIR spectroscopy. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing aqueous buffer solutions (pH 1 and pH 7.4) at 37 degrees C. Detection of the hydrolysis product by UV spectroscopy shows that the azo prodrug (HPAS) was released by hydrolysis of the ester bond located between the HPAS and the polymer chain. Drug release studies showed that the increasing content of MAA in the copolymer enhances hydrolysis in SIF. These results suggest that pH-sensitive systems could be useful for preparation of a muccoadhesive system and controlled release of HPAS as an azo derivative of 5-amino salicylic acid (5-ASA).

Modified Chitosan Cross-linked Starch Polymers for Oral Insulin Delivery

A chitosan, with citric acid cross-linked CMS grafted with methacrylic acid and poly(ethyleneglycol monomethyl ether methacrylate), was prepared for oral delivery of insulin. Increases in chitosan content increased the bioadhesivity. The equilibrium swelling and in vitro release profiles in enzyme-free simulated gastric (SGF) and intestinal fluids (SIF) by the insulin entrapped gels were established. Increasing the chitosan content in the copolymer enhanced the hydrolysis in the SIF. In all cases, the biological activity of insulin was retained. The antimicrobial activity of hydrogels was examined against a Staphylococcus aureus. Based on these results, new designs to improve insulin release behavior are being carried out.

New pH-Sensitive Glycopolymers for Colon-Specific Drug Delivery

pH-sensitive hydrogels are suitable candidates for oral delivery of therapeutic peptides, proteins, and drugs, due to their ability to respond to environmental pH changes. New pH-sensitive glycopolymers have been developed by free-radical polymerization of methacrylic acid and 6-acryloyl-glucose-1, 2, 3, 4-tetraacetate, using 1, 6-hexandiol diacrylate and 1, 6-hexandiol propoxylate diacrylate as cross-linking agents. The hydrogels were characterized by differential scanning calorimetry and FTIR. Equilibrium swelling studies were carried out in enzyme-free simulated gastric and intestinal fluids (SGF and SIF, respectively). A model drug, olsalazine [3, 3'-azobis (6-hydroxy benzoic acid)] as an azo derivative of 5-aminosalicylic acid, was entrapped in these gels and the in vitro release profiles were established separately in both enzyme-free SGF and SIF. The drug-release profiles indicated that the amount of drug released depended on the degree of swelling. The hydrogels containing polar propoxylate groups were hydrolyzed rather easily.

Microwave-assisted Preparation of Magnetic Albumin Microspheres

A new microwave-assisted method was used to prepare magnetic Fe3 O4 particles and magnetic bovine albumin microspheres. The microwave method produced smaller particles and is faster than traditional methods. The optimum conditions to prepare the Fe3O4 particles were three minutes at pH 13 and 80°C. Magnetic microspheres containing albumin were synthesized based on heating times and temperatures to form microspheres with different properties. For example, heating for 4min, at 160°C, yielded smaller sized microspheres (30 μm). Confirmed by XRD, SEM, and FT-IR that iron oxide particles were encapsulated in biocompatible proteins, The thermal stability of the microspheres were determined by DSC and TG. The magnetic properties were determined by UV—VIS spectraphotometry and a Guoy magnetic balance. This microwave process could become a preferred method for the synthesis of magnetized protein microspheres.