Drug loaded silicon based soft contact lenses: effect of terminal sterilization methods on their performancePart of:
The effects of sterilization methods on the intrinsic properties of drug delivery systems (DDS) remains understudied, which ends up delaying the development of new and more effective therapeutic devices. This fact becomes even more critical when considering hydrogel-based DDS, since the presence of water in the structure can lead to alterations in the materials.
In this work, a comparative evaluation of the effects of two terminal sterilization methods, steam heat and gamma-irradiation, in a drug loaded silicon-based hydrogel intended for soft contact lens, was carried out. Two drugs, commonly used for the treatment of ocular diseases, levofloxacin and timolol maleate, were loaded in the material by soaking. A complete characterization was performed before and after the sterilization procedures, as follows: swelling capacity was determined by water uptake studies, transparency was accessed by UV-Vis spectroscopy, surface topography/morphology by scanning electron microscopy (SEM) and mechanical properties through tensile tests. The drug released was quantified by high performance liquid chromatography (HPLC).
For unsterilized drug loaded samples, differences in swelling behavior were observed and, in all cases, the material became more rigid after loading, which can indicate interactions between the drugs and the polymeric matrix. Steam heat led to smoother surfaces and an apparent decrease in surface porosity. It was also observed a significant decrease of the amount of drug released. Gamma-irradiation led to darkening of the drug loaded samples and to the formation of degradation products. Both steam heat and gamma-irradiation led to a significant increase of Young modulus along with a significant decrease of tension at break, elongation at break and toughness.
Our findings offer important insights that can be a useful contribution to the development of new DDS based on silicon-hydrogel contact lenses.