Darko Vasiljević

Protective effect of autophagy in laser-induced glioma cell death in vitro.

Laser phototherapy could be potentially used for cancer treatment, but the mechanisms of laser‐induced cell death are not completely understood. Autophagy is the process in which the damaged cellular proteins and organelles are engulfed by and destroyed in acidified multiple‐membrane vesicles. The aim of the present study was to investigate the role of autophagy in laser‐induced tumor cell death in vitro.

Optimization of the Cooke triplet with various evolution strategies and damped least squares

Optimization of the Cooke triplet with various evolution strategies an the damped least squares is presented. All algorithms are described and their advantages and shortcomings are presented. After detailed presentation of the evolution strategies their adaptation to the optimization of optical systems are discussed. Analysis of the Cooke triplet optimizations is given and optimum optimized optical system is chosen.

Influence of cavity design preparation on stress values in maxillary premolar: a finite element analysis

Aim To analyze the influence of cavity design preparation on stress values in three-dimensional (3D) solid model of maxillary premolar restored with resin composite. Methods 3D solid model of maxillary second premolar was designed using computed-tomography (CT) data. Based on a factorial experiment, 9 different mesio-occlusal-distal (MOD) cavity designs were simulated, with three cavity wall thicknesses (1.5 mm, 2.25 mm, 3.0 mm), and three cusp reduction procedures (without cusp reduction, 2.0 mm palatal cusp reduction, 2.0 mm palatal and buccal cusp reduction). All MOD cavities were simulated with direct resin composite restoration (Gradia Direct Posterior, GC, Japan). Finite element analysis (FEA) was used to calculate von Mises stress values. Results The von Mises stresses in enamel, dentin, and resin composite were 79.3-233.6 MPa, 26.0-32.9 MPa, and 180.2-252.2 MPa, respectively. Considering the influence of cavity design parameters, cuspal reduction (92.97%) and cavity wall thickness (3.06%) significantly (P < 0.05) determined the magnitude of stress values in enamel. The influence of cavity design parameters on stress values in dentin and resin composite was not significant. When stresses for enamel, dentine, and resin composite were considered all together, palatal cusp coverage was revealed as an optimal option. Cavity wall thickness did not show a significant effect on stress values. Conclusion Based on numerical simulations, a palatal cusp reduction could be suggested for revealing lower stress values in dental tissues and restorative material. This type of cavity design should contribute to better biomechanical behavior of tooth-restoration complex, consequently providing the long-lasting clinical results.

Single-beam, dual-view digital holographic interferometry for biomechanical strain measurements of biological objects.

Abstract. We describe a method for dual-view biomechanical strain measurements of highly asymmetrical biological objects, like teeth or bones. By using a spherical mirror, we were able to simultaneously record a digital hologram of the object itself and the mirror image of its (otherwise invisible) rear side. A single laser beam was sufficient to illuminate both sides of the object, and to provide a reference beam. As a result, the system was mechanically very stable, enabling long exposure times (up to 2 min) without the need for vibration isolation. The setup is simple to construct and adjust, and can be used to interferometrically observe any object that is smaller than the mirror diameter. Parallel data processing on a CUDA-enabled (compute unified device architecture) graphics card was used to reconstruct digital holograms and to further correct image distortion. We used the setup to measure the deformation of a tooth due to mastication forces. The finite-element method was used to compare experimental results and theoretical predictions.

Real-time measurement of internal stress of dental tissue using holography.

We describe a real-time holographic technique used to observe dental contraction due to photo-polymerization of dental filling during LED lamp illumination. An off-axis setup was used, with wet in-situ processing of the holographic plate, and consequent recording of interference fringes using CCD camera. Finite elements method was used to calculate internal stress of dental tissue, corresponding to experimentally measured deformation. A technique enables selection of preferred illumination method with reduced polymerization contraction. As a consequence, durability of dental filling might be significantly improved.

Computed-tomography scan-based finite element analysis of stress distribution in premolars restored with composite resin

Mechanical properties of restorative material have an effect on stress distribution in the tooth structure and the restorative material during mastication. The aim of this study was to investigate the influence of restorative materials with different moduli of elasticity on stress distribution in the three-dimensional (3D) solid tooth model. Computed tomography scan data of human maxillary second premolars were used for 3D solid model generation. Four composite resins with a modulus of elasticity of 6700, 9500, 14 100 and 21 000 MPa were considered to simulate four different clinical direct restoration types. Each model was subjected to a resulting force of 200 N directed to the occlusal surface, and stress distribution and maximal von Mises stresses were calculated using finite-element analysis. We found that the von Mises stress values and stress distribution in tooth structures did not vary considerably with changing the modulus of elasticity of restorative material.

Thermal analysis of microlens formation on a sensitized gelatin layer

We analyze a mechanism of direct laser writing of microlenses. We find that thermal effects and photochemical reactions are responsible for microlens formation on a sensitized gelatin layer. An infrared camera was used to assess the temperature distribution during the microlens formation, while the diffraction pattern produced by the microlens itself was used to estimate optical properties. The study of thermal processes enabled us to establish the correlation between thermal and optical parameters.

Imaging properties of laser-produced Gaussian profile microlenses

Microlens and microlens arrays have been successfully produced using sensitized gelatin and Nd:YAG laser at 532 nm. Obtained microlenses are divergent (negative), with parabolic profile and 600 &mgr;m useful aperture diameter. Microlenses have near diffraction limited performance with resolution more then 50 cycles/mm for the total field of view (2&ohgr; = 18°). Single microlens is manufactured in just a few seconds using 60 mW unfocused Nd:YAG laser beam.

Holographic Measurement of a Tooth Model and Dental Composite Contraction

We have developed a real-time holographic technique to observe deformation induced by dental composite contraction. The standard split beam method was used, in conjunction with in situ holographic plate processing. Experiments were performed on a mechanical model of a human tooth with cavity. A silicone mold was used to manufacture a number of identical casts, using photoactivated composite. A LED lamp was used to induce photo-polymerization reaction in a composite. We have shown that the proposed method is ideal to analyze various polymerization strategies, with the purpose of recommending one which minimizes the polymerization contraction.

Sensitized gelatin as a versatile biomaterial with tailored mechanical and optical properties

Abstract We have found that gelatin doped with tot’hema (medication used for curing anemia) andeosin becomes elastic, while retaining good optical properties. The mechanical properties oftot’hema–eosin-sensitized gelatin films (TESG) have been investigated for variousconcentrations of tot’hema (ranging from 5 to 30% v/v). TESG specimens were preparedaccording to the ASTM standards for elastic materials. Tensile strength, strain at break andYoung’s modulus were measured. The results show that the extensibility of TESG filmincreases with increasing tot’hema concentration, while the Young’s modulus and stress atbreak exponentially decrease. Mechanical properties can be tailored to suit various biomedicalapplications such as blood vessels, human lens capsules and biosensors based on microlenses.Tunable (strain responsive) TESG microlenses were produced and a mechanical model ofblood vessels was prepared.PACS numbers: 42.70.Jk, 81.40.Jj, 87.85.J−, 87.85.fk(Some figures may appear in colour only in the online journal)