Gelatin Functionalization with Tyrosine Derived Moieties for Increasing the Interaction with Hydroxyapatite Fillers

Abstract

Combining gelatins functionalized with the tyrosine-derived groups desaminotyrosine or desaminotyrosyl tyrosine with hydroxyapatite (HAp) led to the formation of composite materials with much lower swelling ratio than of the pure matrices. Shifts of IR bands related to the free carboxyl groups could be observed in the presence of HAp, which suggested a direct interaction of matrix and filler that formed additional physical crosslinks in the material. In tensile tests and rheological measurements, the composites equilibrated in water had increased Young’s moduli (from 200 kPa up to 2 MPa) and tensile strength (from 57 kPa up to 1.1 MPa) compared to the matrix polymers without affecting the elongation at break. Furthermore, an increased thermal stability from 40 °C to 85 °C of the networks could be demonstrated. The differences of the behaviour of the functionalized gelatins to pure gelatin as matrix suggested an additional stabilizing bond between the incorporated aromatic groups to the hydroxyapatite as supported by the IR results. The composites can potentially be applied as bone fillers.