In this work, a two phase hydrogel was prepared by physically imbedding a xerogel in the
core of a hydrogel that was subsequently freeze thawed. The outer hydrogel was prepared by freeze
thawing poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA) while the xerogels were prepared by
UV polymerization of 1-vinyl-2-pyrrolidinone (NVP), acrylic acid (AA) and various percentages of an
Active Pharmaceutical Ingredient (API). Attenuated total reflectance Fourier transform infrared
spectroscopy (ATR-FTIR) confirmed that hydrogen bonding had occurred between the constituents of
the two phase hydrogels, while swelling experiments in distilled water indicated that the swelling
of the gels is temperature dependent. The rheological studies confirmed that, by incorporating PAA into
the two phase hydrogel system the strength increased significantly. However, at temperatures under the
same nominal force the hydrogels were observed to lose their physical structure. Thermal analysis
suggested that the incorporation of API into the xerogel reduced the Tg by approximately 13 °C, thus
suggesting that the API acts as a plastcizer within the xerogel matrix. In all cases, drug dissolution
showed that the API was released at a slower rate from hydrogels that contained poly (acrylic acid).
Keywords: Hydrogels; poly (vinyl alcohol); poly (acrylic acid); drug dissolution; wound healing.
