Volume 59, Issue 6

Retinal artery occlusion (RAO) is a common ocular vascular occlusive disorder that may lead to partial or complete retinal ischemia with sudden visual deterio ration and visual field defects. Although RAO has been investigated since 1859, the main mechanism is still not fully understood. While hypoperfusion of the ophthalmic artery (OA) due to severe stenosis of the internal carotid artery might lead to RAO, emboli are assumed to be the main reason. Intra-arterial thrombolysis is not a sufficient treatment for RAO, and current research is mainly focused on risk factors. In this study, a computational fluid dynamic model is presented to analyse flow conditions and clot behaviour at the junction of the internal carotid artery and OA based on a realistic geometry from a RAO patient. Clot diameters varied between 5 and 200 μm, and the probability of clots reaching the OA or being washed into the brain was analysed. Results show sufficient blood flow and perfusion pressure at the end of OA. The probability that clots from the main blood flow will to be washed into the brain is 7.32±1.08%. A wall shear stress hotspot is observed at the curvature proximal to the internal carotid artery/OA junction. Clots released from this hotspot have a higher probability of causing RAO. The occurrence of such patient-specific pathophysiologies will have to be considered in the future.

Gelatin (Gel) has been reported as a promising candidate in tissue engineering owing to its easy availability, biocompatibility, and biodegradability. Gel hydrogel is of potential to be cross-linked with different materials to enhance their biocompatibility for cell culture for tissue engineering applications. The mechanical properties of this versatile material, however, have not been thoroughly determined. In this study, the linear elastic (Young’s modulus and maximum stress) and non-linear hyperelastic (hyperelastic coefficients) mechanical properties of prepared hydrogels at different contents of Gel (wt%) were measured, and its Young’s modulus was compared with that of skin tissue. The prepared cylindrical Gel hydrogels were subjected to a series of unconfined compression tests. The hyperelastic strain energy density function was calibrated using the compressive experimental data. The potential ability of the Yeoh hyperelastic constitutive equation, which has been proposed as the best material model to represent the non-linear behavior of hydrogels, was verified using finite element (FE) simulations. The results revealed that the Young’s modulus and maximum stress of hydrogels are increased by the addition of Gel. The highest Young’s modulus (81 kPa) and maximum stress (24 kPa) were observed for hydrogels with 15 wt% Gel. Results also showed that the hydrogels with a relatively lower content (<7.5 wt%) of Gel have suitable Young’s modulus compared with those with a higher content (>7.5 wt%) for skin tissue engineering. The Yeoh material model was closely fitted with the experimental data and could be used in further biomechanical simulations of the hydrogels. The experimental results were also compared well with those predicted by the FE models. The results of this study might have implications not only for the understanding of the mechanical properties of Gel hydrogel but also for the fabrication of polymeric substrate materials suitable for skin tissue engineering applications.

To explain the successful treatment of various inflammatory diseases by using intensive red light, a non-linear theory is presented for the interaction of electric dipoles with light involving frequency doubling. It is applied to analyze the influence of light on organic molecules with permanent electric dipoles. The molecule 5-hydroxy-12-oxo-(5 S ,6 Z ,8 E ,10 E ,14 Z )-6,8,10,14-eicosatetraenoic acid, 12-oxo-leukotriene B 4 (12-Oxo-LTB 4 , an intermediate in the lipoxygenase-catalyzed path of arachidonic acid metabolism), is suspected to play a major role in the healing process, as, first, it plays a key role in the metabolism of leukotriene B 4 (LTB 4 ), which in many diseases acts as a source of inflammatory reactions; second, its dipole resonance is located at a wavelength of 316 nm, which can be excited by a 632 nm source through frequency doubling. From the structure of 12-Oxo-LTB 4 and the knowledge of the partial charges of its 54 atoms, the equivalent values for dipole charges and dipole moment are derived. The power balance demonstrates that intensive red light with a power density of 0.4 W/cm 2 transfers sufficient energy to 12-Oxo-LTB 4 to render it biologically inactive. Hence, by generating a reactive high-energy leukotriene pathway intermediate, the law of mass action steers the chemical equilibrium to interrupt the inflammatory cascade.

Background: Gap at the implant-healing abutment junction can increase the risk of bacterial proliferation. In this study, we determined the leakage at the microgap, and we evaluated hand screwing among clinicians. Materials and methods: The torques tested with nitrogen gas flow were 10, 15, 20, and 30 N cm, and 54 clinicians were asked to torque down a healing abutment as for a surgical procedure. Results: There were no significant differences between 10 and 15 N cm, with a total lack of tightness. For 20 and 30 N cm, there was a notable decrease in leakage. The torque achieved by hand was <10 N cm for 61.7% of the clinicians, between 10 and 15 N cm for 29.1%, between 15 and 20 N cm for 8.0%, and between 20 and 25 N cm for 1.2%. Conclusion: There was a significant difference related to the strength of tightening. Under the conditions of our experiment, the gap of connection was reduced with a torque of ≥20 N cm. Only a small portion of the clinicians could obtain these values by hand. Therefore, a dynamometrical manual wrench should be used to minimize the gap during the osseointegration period.

To predict the clinical performance of zirconia abutments, it is crucial to examine the mechanical behavior of different dental implant-abutment connection configurations. The international standard protocol for dynamic fatigue tests of dental implants (ISO 14801) allows comparing these configurations using standardized superstructure geometries. However, from a mechanical point of view, the geometry of clinical crowns causes modified boundary conditions. The purpose of this finite element (FE) study was to evaluate the influence of the superstructure geometry on the maximum stress values of zirconia abutments with a conical implant-abutment connection. Geometry models of the experimental setup described in ISO 14801 were generated using CAD software following the reconstruction of computerized tomography scans from all relevant components. These models served as a basis for an FE simulation. To reduce the numerical complexity of the FE model, the interaction between loading stamp and superstructure geometry was taken into account by defining the boundary conditions with regard to the frictional force. The results of the FE simulations performed on standardized superstructure geometry and anatomically shaped crowns showed a strong influence of the superstructure geometry and related surface orientations on the mechanical behavior of the underlying zirconia abutments. In conclusion, ISO testing of zirconia abutments should be accompanied by load-bearing capacity testing under simulated clinical conditions to predict clinical performance.

The use of short implants has increased widely within the last years. However, the stability of these implants has not yet been comprehensively investigated, in particular the difference in geometry and dimension of short implants. The aim of the present study was to investigate experimentally the difference of the secondary stability of different commercial short implants by measuring their displacements. Eleven implant geometries were investigated in this study. A total of 22 implants were inserted in porcine rib segments, two implants for each system. Implant displacements were measured using a self-developed biomechanical hexapod measurement system (HexMeS). The highest displacement was observed with Straumann BL NC 3.3×8.0 mm (266 μm), followed by Straumann Standard 4.1×6.0 mm (156 μm), while the lowest displacement of 61 μm was shown by Dentaurum type 1 implant (4.2×5.0 mm). No obvious difference of displacements was observed between hammered and screw-shaped implants with relevant dimensions. The experimental results were in good agreement with the numerical ones (19–42%) for Dentaurum implants. However, a difference of 70–80% was obtained for the Astra implant (4.0×6.0 mm) and Bicon implant (6.0×5.7 mm). The geometry of short implants directly affects their stability within the bone.

Electrocardiographic imaging (ECG imaging) is a method to depict electrophysiological processes in the heart. It is an emerging technology with the potential of making the therapy of cardiac arrhythmia less invasive, less expensive, and more precise. A major challenge for integrating the method into clinical workflow is the seamless and correct identification and localization of electrodes on the thorax and their assignment to recorded channels. This work proposes a camera-based system, which can localize all electrode positions at once and to an accuracy of approximately 1±1 mm. A system for automatic identification of individual electrodes is implemented that overcomes the need of manual annotation. For this purpose, a system of markers is suggested, which facilitates a precise localization to subpixel accuracy and robust identification using an error-correcting code. The accuracy of the presented system in identifying and localizing electrodes is validated in a phantom study. Its overall capability is demonstrated in a clinical scenario.

A saccade is one of the characteristic types of eye movements. The accurate detection and location of saccades in the signal representing the movement activity of the eyes are essential in medical applications. The main purpose of this paper is to present a new, robust approach to the detection of saccadic eye movements. The procedure is based on a so-called detection function, which is the result of the electronystagmographic (ENG) myriad signal filtering, nonlinear operation, and fuzzy median clustering. Smooth peaks of the detection function waveform correspond to the location of saccades in the ENG signal. The median fuzzy clustering-based method allows for calculating the amplitude threshold of the detection function, which improves the accurate saccade recognition. Both of these robust methods provide a two-step protection against outliers. The proposed algorithm was tested using artificial as well as real optokinetic nystagmus signals under different noise conditions. The results show the usefulness of the procedure when the precise detection and location of saccades are necessary.

Electrical impedance tomography (EIT) is a radiation-free technique generating cross-sectional images of the lung. EIT visualizes global and regional ventilation by illustrating the distribution of electrical bioimpedance. With an electrode belt around the patient’s thorax, rotating injection-couples of a harmless alternating current allow voltage measurement of the remaining electrodes. This enables the reconstruction of a tomogram with highly dynamic changes within ventilation. We report on a female six-year-old patient with cystic fibrosis and complete destruction of the upper and middle lobe of the right lung. Lobectomy, a rare therapeutic option in patients with cystic fibrosis that needs to be considered in cases of severe localized destruction, was performed. We show a pre- and postoperative documentation of static (radiology) and dynamic investigation tools (spirometry) in correlation with EIT as a new non-invasive and radiation-free diagnostic tool for this patient group.