Investigation of the free volume changes in one day hydrogel and one day silicone-hydrogel contact lenses by means of positron annihilation lifetime spectroscopy.
PURPOSE OF JOB: The evolution of materials used to manufacture contact lenses, there is a need to increase comfort and visual acuity man while improving biocompatibility and minimizing the impact of the material on the physiology of the cornea. There is still a problem with limiting the level of oxygen available to the cornea, resulting in various diseases. Therefore, the aim of this work is to investigate the physical and structural properties of hydrogel and silicone-hydrogel contact lenses.


METHODS
To achieve the main objective, the project involves the complete, systematic and comprehensive research methodology, techniques of positron lifetime spectroscopy PAL associated with polymerization, nanovoid natural structure of modern polymeric materials used in ophthalmology. This method is particularly sensitive to detect the structure of disordered materials with structural defects. Therefore it is reasonable to use PAL spectroscopy in studies of polymer nanostructures change contact lenses used in ophthalmology.


RESULTS
As a result of the measurements obtained curve describing the dependence of the number of counts of acts of annihilation as a function of time. Distribution of positron lifetime spectra into three components, allows to extract the longest third component which gives information about the geometrical parameters of free volume. Clear changes were observed long-living component lifetimes of ortho-positronium and their intensities between the lenses tested.


CONCLUSIONS
The measurements allowed us to isolate and calculate the value of long-living tau3 and its intensity I3, which values are component of positron lifetime associated with the formation of ortho-positronium (o-Ps) and is a measure of the density distribution of free volume creation. The results of these measurements indicate that the formation of free volume holes takes place both in the hydrogel lens and silicone-hydrogel. However, the size of free volume and the amount of free volume occurring for silicone-hydrogel lenses are greater than for hydrogel lenses. The study nanovoid structure of polymeric materials, their size and number suggest a relationship with the oxygen permeability of contact lenses, which implies a continuation and extension of the initial research.
Institute of Physics, Jan Dlugosz University, al. Armii Krajowej 13/15, 42-200 Czestochowa, Poland.
Agnieszka
A
Kocela
Jacek
J
Filipecki
Piotr
P
Korzekwa
Edmund
E
Golis
D001672:Biocompatible Materials / Q000737:chemistry*; D003261:Contact Lenses; D003263:Contact Lenses, Hydrophilic; D004583:Electrons / Q000145:classification; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry*; D008422:Materials Testing; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D010539:Permeability; D058105:Polymerization; D011108:Polymers / Q000737:chemistry; D012828:Silicones / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*
D001672:Biocompatible Materials; D011108:Polymers; D012828:Silicones; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D010100:Oxygen