A study has been conducted in order to determine presence of free volume gaps in the structure of structure of polymer hydrogel contact lenses made in phosphoryl choline technology and of the degree of defect of its structure. The study was made by means of positron annihilation lifetime spectroscopy. As a result of the conducted measurements, curves were obtained, which described numbers of counts of the acts of annihilation in the time function. The conducted studies revealed existence of three components τ1, τ2 and τ3. The τ3 component is attributed to the pick-off annihilation of o-Ps orthopositronium trapping by free volume gaps and provides information about geometrical parameters of the volumes. At the same time, the UV–vis–NIR spectrometry examination was conducted on the same samples in the spectral range 200–1,000 nm.

One of the most important field of interest in respect to hydrogel materials is their capability to water storage. The problem mentioned above plays an important role regarding to diffusion of fluid media containing nanoparticles, what is very useful in biomedical applications, such as artificial polymeric implants, drug delivery systems or tissue engineering.In presented work, dehydration process in hydrogels used in ophthalmology as intraocular lenses was observed. Before measurements studied materials were immersed in deionized water and saline solution to obtain equilibrium swelling state. Studies of the dehydration process were carried out by use of gravimetric analysis, Fourier-Transform Infrared and Positron Annihilation Lifetime Spectroscopy. Obtained results revealed changes in hydrogen bonding structure and free volume holes induced by saline solution ingredients.

Positron lifetime spectroscopy has been applied to study free volume related properties of bifocal contact lenses. The measurements were made on new lenses and then after one, two, and three weeks wearing. The longest lifetime, obtained via three-component analyses of the spectra, was associated with the pick-off annihilation of ortho-positronium trapped in the free volume. After wearing of the lenses, changes in the ortho-positronium lifetimes and the relative intensity of the longest component were observed. The results are discussed on the basis of a free volume model.

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