The selection the correct biomaterial for a specific medical application plays an important role for the success of both application and the device. Since different applications require different properties, investigation and improvement of biomaterials with different properties are very important. L-tyrosine derived polymers enable the manipulation of the properties of the material by changing backbone or pendent chain structure. L-tyrosine derived polyarylate is one of the class of these materials.

This study investigates the behavior of the tyrosine derived polyarylates under in vitro conditions. The change of structure caused by incubation in phosphate buffer solution and the effect on the release of p-nitroaniline (PNA) (model drug) has been investigated, primarily with differential scanning calorimetry (DSC). In addition the release profile of PNA has been investigated by UV/visible spectroscopy.

Two different polyarylates were used. poly[(desaminotyrosine dodecyl esterl) dodecondioate] designated Poly(DT 12, 10) and, poly[(desaminotyrosine octyl ester) sebacate] designated Poly(DT 8, 8).

The results obtained from this study indicates that incubation caused significant changes in the solid state organization of the Poly(DT 8, 8). Tg is seen in dry polymers but disappears after the beginning of the incubation, indicating a phase change in the polymer. The enthalpy of phase change of the Poly(DT 8, 8) increases and lay off state in about one half a day. However, in contrast of Poly(DT 8, 8), the enthalpy of Poly(DT 12,10) doesn't change significantly. According to these results, it is concluded that a phase change occurs in Poly(DT 8, 8) by incubation. The incubation in dry conditions also indicates a phase change in Poly(DT 8, 8), and this is accelerated by the presence of moisture. The incorporation of the model drug did not affect the observed enthalpy change of either of the polymers investigated.