Božica Bojović

Contact Lenses Characterization by AFM MFM, and OMF

The contact lens (CL) industry andmarket have displayed a high level of dynamism in the past few decades, and have evolved into a rapidly changing field in which science and everyday practice constantly interact, not only through broadening of material and product portfolio, but through innovative therapeutic and diagnostic solutions as well. Stable market growth with numerous rearrangements in different product segments is constantly taking place, mainly stirred by innovative material and optical design. The standardly used hydrogel materials are being rapidly replaced by silicone doped hydrogel materials. The analyses of customer CL usage and satisfaction indicate continued market growth in future, however with many changes in product profile and significant increase in multifocal and daily disposable lenses market share. The main impulse behind the dynamism of CL industry stems from results of scientific and technological improvements, which are enhancing medical field and reminding us that the focal point of sustainable development lies in scientific investigations.

Remanent Magnetization Measurements of the Fullerene Thin Films

Magnetic properties of carbon vary according to its allotropic modifications. Although carbon atom is known as a diamagnetic, some distinctive features point out that its magnetic properties are not that simple. Fullerene C60, a carbon atoms molecule, is proven to have very different magnetizations than other forms of carbon compounds. Rhombohedral fullerene is shown to have ferromagnetic properties, and thus investigations of fullerene as a magnetic material are necessary. Fullerene C60 in the form of thin film is also shown to have distinctive magnetic properties. In this paper, remanent magnetization of fullerene thin films, thicknesses of 100 and 250 nm were investigated when films are in the dark and exposed to polarized light. Research showed how light is influencing the material and its magnetization.

CHARACTERIZATION OF NANOMATERIAL-BASED CONTACT LENSES BY ATOMIC FORCE MICROSCOPY

In this paper the comparative studies were conducted of the surface areas of nanophotonic contact lens and contact lens made from base material, measured by Nanoprobe Atomic Force Microscope. Nanoprobe atomic force microscopy (AFM) provides information on the size structure on nano scale level, the form of recorded structures (cavities), their distribution of the surface, and the total roughness of the scanned area. The atomic force microscope used in this study is a SPM-5200 of JEOL, Japan. AFM consists of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. Images of the specimen surface are created by measuring the deflection of the cantilever. The cantilever used in this study is produced by MikroMasch (Estonia) by trade name NCS18/Co-Cr. This AFM probe is silicon etched probe tip that has conical shape. It is coated with Co and Cr layers. Images of surface topography were obtained for each type of contact lenses. The base material of contact lens was made from PMMA and the nanophotonic contact lens was made of fullerene doped PMMA. Fullerenes were used because of their good transitive characteristics in ultraviolet, visible and near infrared light spectrums. Measurements were done at room temperature. Results of topography for both materials are presented and compared.

Nanophotonic Rigid Contact Lenses: Engineering and Characterization

Contact lenses are a common optical aid to provide help with refractive anomalies of the human eye. Construction of contact lenses is a complex engineering task as it requires knowledge of optics, materials science, production and characterization methods for product quality. Besides correcting refractive anomalies, by using contact lenses it is possible to change the characteristics of light through the manipulation of material structure properties. Nanomaterials, such as fullerene C60, are candidates for the medium that interacts with light, thus changing its properties. During material syntheses for contact lenses, fullerenes are added to the base material and optical characteristics of the new nanophotonic material are compared with the base material. The engineering, manufacture and characterization of both a commercial and a new nanophotonic contact lens is presented in this paper. The interaction of water with both base and nanophotonic contact lens materials is described. Using experimental techniques, the phenomena of an exclusion zone (EZ) is also identified.

An example of passive micromixer design, simulation and optimization

The paper presents the designing process of the passive micromixer. Design parameters of microfluidic channels geometry are optimized based on flow simulation results. CAD software Solid Works and application Flo Xpress are used for designing and simulation. Aim of presented students work is not connected to any actual research activities. However part of MSc Thesis shows outcome of students ability that is accomplished at Biomedical department. This is one of outcomes of BioEMIS TEMPUS project, and therefore the future work on this topic regarding practical implementation is not given here.

Actual Diamond Engraving of a Fullerene Coated Glass Plate

In this paper, we present the results of fullerene film engraving using a diamond tool. Based on available literature data, to our knowledge the fullerene film machinability is not explored in literature. Therefore, we have investigated wear mechanisms of the engraving process that could be used in micromachining. The engraving process parameters were estimated on the basis of poor quality grooves edge. The flat diamond tip, which remains after wear, has a pitted surface which was observed with a digital optical microscopy and identified using AFM. Soot-like wear debris was observed and spectroscopically analyzed. FTIR spectroscopy results strongly indicate that fullerene C60 disappears as a molecule and interacts with oxygen, nitrogen and water vapor from the atmosphere. The occurrence of tool wear and wear debris were observed by nondestructive thermography testing. Results confirm that development of high temperature in a cutting zone of 1556°C causes extensive thermo-chemical tool wear.

EFFECTS OF IMAGE SIZE AND SAMPLE AREAS ON COMPARISON OF CONTACT LENS SURFACES BASED ON FRACTAL DIMENSION

Methods used for calculation of fractal dimension demand large image resolution and adequate sample size, in terms of roughness threshold that defines spatial scope for rough surface fractal properties. Imaging device operators, on the one hand, recommend the image size and sample area based on experience and expertise, in order to minimize the imaging time. On the other hand, engineers make decisions based on their own requirements. To overcome these problems, in this paper we used ANOVA statistical approach (one-way and multi comparison) so as to establish significant image size and sample area. The conclusion made in this paper will enable decision guidelines on selection of parameters for new nanophotonic lenses imaging by scanning microscopes in near future.

MICRO AND NANO LUBRICANT BEHAVIOR OF TEAR FILM AQUEOUS LAYER

Tears provide moisture and supply oxygen and other important nutrients to the cornea, mechanically trap and flush out foreign bodies and chemicals and keep the surface of cornea smooth and optically clear. Additionally, during blinking, tear film lubricates the friction area between lids and ocular surface. Tear film contains an aqueous layer that includes water, bacteriostatics, proteins and salt. Contact lens wearers often suffer from dry eyes. These changes in the tear film are caused by contact lens design, surface, material and applied solution for conditioning. In case of application of gas-permeable contact lens, the multi-factorial problem of tear film stability and therefore, maintaining of lubrication are main goals in the ongoing investigation. This paper focuses on applied research of the response of material’s surface roughness quality to retain tear film on the micro and nano-level by using a gliding-box method for lacunarity analysis. The topology of contact lens surface with tear film as the lubricant was studied from the point of view of the water as primary consistent in its bulk liquid form, as well as confined water film organized into layers in a nanometer-sized channel. Contact lens surface topology observed on micro and nano-scale indicates different lubrication behavior of aqueous tear layer. As opposed to bulk water as a disordered medium in micro scale that flows very readily, nano-water demonstrates the behavior effectively like some phases of liquid crystals.