Evaluation of Preparation, Characterisation and Release Properties of Thymol-Containing Gelatin-Based Hydrogels for Varroosis Control

The aim of this study was to investigate the swelling/degradation behaviour of controlled-release system using gelatin, thymol loading capacity, characterisation, morphology and thymol release level in terms of the recommended therapeutic dose for varroosis control. In this context, a series of hydrogels were first produced using glutaraldehyde (GA) crosslinker and swelling tests were performed. Thymol loading was performed on the appropriate hydrogels with swelling values between 269% and 431%. Thymol loading efficiency was determined between 20.07% and 29.80%. The chemical structures of the hydrogels with and without thymol loading were compared by Fourier transform infrared spectrometry (FT-IR) and it was determined that thymol was loaded into the structure. The morphological structures of thymol loaded and unloaded hydrogels were examined by scanning electron microscopy (SEM). It was observed that the non-thymol loaded hydrogel had larger diameter pores than the thymol loaded hydrogel. A model release environment and measurement system were developed to predict the release type, level and duration of the controlled release system in the hive air environment. In this model release environment, release tests were carried out for four weeks using different thymol application systems and the measurements were compared. As a result, it was determined that the controlled thymol release system developed for the control of varroosis infestation exhibited a more stable release compared to existing application systems.