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MEDICAL PHYSICS IN <strong>THE</strong> BALTIC STATES 7 (2009) Proceedings of International Conference “Medical Physics 2009” 8 - 10 October 2009, Kaunas, Lithuania ULTRAVIOLET RADIATION INFLUENCES WETTABILITY AND BIOLOGICAL PROPERTIES <strong>OF</strong> PMMA SURFACE Yuri DEKHTYAR 1 , Linda LANCERE 1 , Nataliya POLAYKA 1 , Alexander RAPOPORT 2 , Anna RUSAKOVA 2 , Alexander SUDNIKOVICH 2 , Valdis VALTERS 3 1 Riga Technical university, 2 University of Latvia, 3 Valter’s Prosthetic laboratory, ltd. Abstract: PMMA (poly-methyl metha acrylate) material is widely used for eye prostheses. During its exploitation the material is under sun radiation, ultraviolet (UV) being the component. Therefore the properties of PMMA influenced by UV could affect biocompatibility of the prostheses. The present article is targeted to explore influence of UV on wettabilty and biological properties of PMMA Keywords: PMMA, ultraviolet radiation, sun radiation, eye prostheses 1. Introduction. The tear liquid should moisten the PMMA eye prosthesis during its exploitation. This could be disturbed by sun ultraviolet, strong radiation destroying molecular couples of the PMMA [1, 3, 5, 6]. Currently there are not experimental data on the soft Sun UV influence on PMMA wettability properties. The article is targeted to explore influence of the simulating sun UV radiation on the PMMA wettability. The latter could be influenced because of the chemical alteration induced by UV [1, 3, 5, 6] or just because of the escaping electrons from the surface layer (photoemission). As the result the surface should acquire an electrical charge. To verify this, the electron work function of the radiated specimens was measured. Disturbance/damage/reconstruction of chemical couples at the PMMA surface could have a negative influence on the cell behaviour. Taking this into account, the viability of the yeast eukaryotic cells deposited on the radiated specimens was tested too. 2.1. Radiation 2. Methods and materials. For physical simulation process, samples from commercial material “Stoma” (Ctoma) were taken with size of ~1x1cm 2 , thickness about 2-4mm. The UV irradiation was supplied from the Hamamatsu Spot Light Source equipped with Hg-Xe lamp (intensity at the source exit was 3500mW/cm 2 at wavelength 365nm), the specimens were placed at 0,4 m distance from the source exit. The room air was the environment 69 for the specimens. The room temperature was +20 0 C +/- 2 0 C and humidity 39+/-7mmHg. The temperature at the specimen’s surface during the radiation was not higher as in the room. Before radiation each specimen was cleaned with 96% ethanol. 2.1. Measurements of wettability Wettability was tested by the modified Axisymmetric Drop Shape Analysis-Profile (ADSA-P) drop method before and after the UV exposure. The physiological solution was used as the testing liquid. The drop with diameter ~10mm was measured using the optical microscope MMI-2 (MMИ-2). The image of the drop was projected via CCD camera (Imaging Source) to the PC screen. The contact angle was measured from images applying in the Photoshop software CS3 version. Before measurements each sample was cleaned with 96% ethanol. The above described sequence was repeated 15 times for each sample to collect statistics. 2.2. Electron work function. The electron work function (ϕ) was determined as the result of the pre-threshold photoelectron emission measurements. For this each specimen was positioned in the hand made spectrometer [8] and photoelectron emission current was detected in dependence on the photon energy in a range 4-6 eV. The duration (exposure) of the experiment was several times less in contrast to the above radiation of the specimens.
2.3. Biological test. Y. Dekhtyar et al. / Medical Physics in the Baltic States 7 (2009) 69 - 71 To verify the UV influence on chemical couples behaviour at the surface of PMMA, non-irradiated and irradiated samples were compared. On both yeast cultivation sacharomyces cerevisiac 14 was deposited and left for 4 days. Then the dried and coloured cells showing differently living and dead cells were counted with Olympus CX31 microscope and results compared (Fig.4). 3. Results UV radiation increased the contact angle, i.e. wettability of the PMMA became worse in the exposure range until 90 minutes, however was directed to the native condition at 160 minutes (Fig. 1) This could be connected with deposition of the electrical charge since the electron work function increases and positively correlates to the contact angle at least in the range until 90 minutes of exposure (Fig. 2). The increase of the work function value evidences that the surface acquired the negative charge. Because of the UV radiation could induce photoemission electrons should leave the specimen, the latter inducing the positive charge of the PMMA surface. However the experiment demonstrated the reversible result. This could be explained that UV reconstructed chemical couples of PMMA. The charged surface relaxed during 2-2.5 months (Fig. 3). The biological test demonstrated that yeast cell viability on the radiated surface falls down (Fig 4). 4. Conclusions. 1. UV radiation has a non monotonic influence on the wettability of the PMMA surface: the surface changed to the hydrophilic until 90 minutes of radiation and turned back to the native state, when the exposure was increased to 160 minutes. 2. Alteration of wettability is probably connected with reconstruction of chemical PMMA couples. 3. The alteration of PMMA properties induced by UV radiation decreases viability of the yeast cells positioned on the PMMA surface. 4 3,5 3 2,5 2 1,5 1 0,5 0 -0,5 0 -1 15 30 45 60 75 90 105 120 135 150 165 180 195 -1,5 Time, min ∆α mean Fig.1. Contact angle (mean) increment after different irradiation exposures. 70 α, o Electron work, eV Viability, % 80 75 70 65 60 55 50 45 40 0 1 2 3 4 Time, months. Fig.2. Irradiated 2 h. Mean contact angle dependence from time. 5,16 5,14 5,12 5,10 5,08 5,06 5,04 5,02 5,0 5,1 5,1 0 15 30 45 60 75 90 Time, min Fig.3. Electron work dependence on exposure time. 55% 53% 51% 49% 47% 45% Non-irradiated Irradiated Non-irradiated 48% 5,1 54% Fig.4. Eukaryotic yeast cell viability on PMMA surface. Irradiated 90min. 5. References. 1. Ratner B.D., Hoffman A.S, Schoen F.J., Lemons J.E. Biomaterial science. Academic press., New York, 484, 1996. 2. Dekhtyar Yu., Polyaka N., Sammons R. Electrically charged hydrohyapatite enhances immobilization and proliferation of osteoblasts. IFMBE proc. Springer , 20, 2008. p. 357-360. 3. Ranby J, Rabek JF. Photodegradation, Photooxidation and Photostabilization of Polymers. London: John Wiley, 156, 1975. 4. Wunderlich B., Pyda M., Encyclopedia of Polymer Science and Technology\Vol.12, Thermodynamic Properties of Polymers, University of Tennessee, Chemical Sciences Division of Oak Ridge National Laboratory, 165, 2002. 5. Caykara T., Guven O., UV degradation of poly(methyl methacrylate) and its 5,1 5,1 5,1
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2009 PROCEEDINGS OF THE 7 th INTERN
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Executive editor: D.Adlienė CONFER
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11.15-11.30 Daiva Leščiute, Valda
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MEDICAL PHYSICS IN THE BALTIC STATE
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