STRUCTURAL CHARACTERIZATION OF PH-SENSETIVE ACRYLIC HYDROGELS PREPARED FOR CONTROLED RELEASE OF DRUGS.

Menemse KIREMITÇI GÜMÜSDERELIOGLU*°

*Hacettepe University, Chemical Engineering Department, 06532 Beytepe, Ankara, TURKEY.
°Corresponding Author

Summary:
Crosslinked copolymers of 2-hydroxyethyl methacrylate (HEMA) with varying concentrations of anionic or cationic monomers, i.e. acrylic acid (AA) and dimethylaminoethyl methacrylate (DMAEMA), were prepared by bulk polymerization in the membrane form for possible controlled drug release applications. Surface structures of these copolymers were characterized by the measurement of surface free energy, SEM, XPS, and ATR-FTIR. Their bulk properties were investigated by means of swelling experiments conducted in water and in buffered solution at various pH values from 2 to 11.90. Thermal and mechanical properties of the copolymers were studed by DSC and DMTA techniques. It was observed that the incorporation of ionic comonomers to HEMA significantly affects both surface and bulk properties, except the surface free energies and texture. Results indicate that gels having ionizable groups are pH-sensitive and their equilibrium water contents (EWC) strognly depend upon the ionizable monomer content. Increasing the percentage of ionic comonomer in the polymer increases the EWC without changing the time for equilibration. In the case of AA-containing copolymers, a sharp increase of the EWC between pH 5 and 7 is observed. In contrast, a sharp decrease of the EWC between 7 and 8 is observed for DMAEMA-containing gels. The results indicated that these polymeric systems can be considered as good candidates for oral colon-specific delivery of some drugs.

Key words:
pH Sensitive hydrogels, p(HEMA-EGDMA), Controlles drug release, Surface characteristics, Bulk structure, Phase transition.