Development of a cavity ring-down spectrometer toward multi-species composition.

This work presents the development of a cavity ring-down spectrometer (CRDS) designed for the detection of several molecules relevant for air pollution, including the second overtone of ro-vibration transitions from CO at 1.58 µm and NO at 1.79 µm. A unique feature of this CRDS is the use of custom mirrors with a reflectivity of about 99.99% from 1.52 to 1.80 µm, enabling efficient laser coupling into the cavity while ensuring a minimum detectable absorbance of 1.1 × 10-10 cm-1 within an integration time of about 1.2 s. In this work, the successful implementation of the current CRDS is demonstrated in two different wavelength regions. At 1.79 µm, the transitions R17.5 and R4.5 of the second overtone of NO are detected. At 1.58 µm, carbon dioxide and water vapor from untreated ambient air are measured, serving as an example to investigate the suitability of a post-processing procedure for the determination of the molar fraction in a multi-species composition. This post-processing procedure has the benefit of being calibration-free and SI-traceable. Additionally, CRDS measurements of gas mixtures containing CO and CO2 are also shown. In the future, the advantages of the developed cavity ring-down spectrometer will be exploited in order to perform fundamental studies on the transport processes of heterogeneous catalysis by locally resolving the gas phase near a working catalytic surface. The possibility to cover a broad wavelength region with this CRDS opens up the opportunity to investigate different catalytic reactions, including CO oxidation and NO reduction.

Effect of thermal osteonecrosis around implants in the rat tibia: numerical and histomorphometric results in context of implant removal.

The purpose of this rat study was to explore the feasibility of in vivo temperature thresholds affecting bone contact at the implant surface. Based on these data, thermal necrosis should be used for implant removal in the subsequent in vivo study. Rat tibiae of 48 animals at one site were randomly treated with heat or cold before implant insertion. Temperatures of 4 °C, 3 °C, 2 °C, 48 °C, 49 °C and 50 °C for a tempering time of 1 min were evaluated. Numerical simulations of the heat source-implant-bone system were carried out. Effects were assessed by histomorphometrical measurements. The results showed that the selected method of direct tempering using a tempering pin was suitable for maintaining a uniform layer around the pin. Starting at warm temperatures of 48 °C and rising to 50 °C, the BIC ratio revealed declining values and a significant difference was observed when comparing 50 °C to the control group (p = 0.03). However, there were no significant variations within the cold temperatures. This study pinpointed temperature discovered that could lead to the thermo-explantation and so that the number of samples used in future studies on temperature-induced bone necrosis can be reduced to a minimum. Significant BIC value reduction was seen at a temperature of 50 °C for 1 min.

Reversal of Osseointegration as a Novel Perspective for the Removal of Failed Dental Implants: A Review of Five Patented Methods.

Osseointegration is the basis of successful dental implantology and the foundation of cementless arthroplasty and the osseointegrated percutaneous prosthetic system. Osseointegration has been considered irreversible thus far. However, controlled heating or cooling of dental implants could selectively damage the bone at the bone-implant interface, causing the reversal of osseointegration or "osseodisintegration". This review compares five methods for implant removal, published as patent documents between 2010 and 2018, which have not yet been discussed in the scientific literature. We describe these methods and evaluate their potential for reversing osseointegration. The five methods have several technical and methodological similarities: all methods include a handpiece, a connecting device for coronal access, and a controlling device, as well as the application of mechanical and/or thermal energy. The proposed method of quantifying the temperature with a sensor as the sole means for regulating the process seems inadequate. A database used in one of the methods, however, allows a more precise correlation between a selected implant and the energy needed for its removal, thus avoiding unnecessary trauma to the patient. A flapless, microinvasive, and bone-conserving approach for removing failed dental implants, facilitating successful reimplantation, would benefit dental implantology. These methods could be adapted to cementless medical implants and osseointegrated percutaneous prosthetics. However, for some of the methods discussed herein, further research may be necessary.

Heat Analysis of Different Devices for Thermo-explantation of Dental Implants: A Numeric Analysis and Preclinical In Vitro Model.

Thermal treatment may reverse the osseointegration of implants and could become an atraumatic controlled method for implant removal in the future. The aim of this nonrandom in vitro study was to empirically identify suitable sources for a controlled heating process, to generate a homogenous temperature distribution at a threshold level of 47°C for future in vivo research. Two different setups evaluating 4 different sources (water, laser, monopolar, and an electrical joule heater device) were used to carry out infrared measurements and numerical calculations at 47°C along the implant axis and along the peri-implant area at the axial plane. Furthermore, required time intervals to heat up the implant tip from 33°C to 47°C were determined. The monopolar electric device led to the most uneven and unpredictable implant heating and was therefore excluded. The thermal analysis suggested identical thermal distributions without any significant differences for water and electrical joule sources with a heat maximum at the implant shoulder (P > .05). On the other hand, the laser device may produce the temperature maximum in the middle of the implant without any afterglow effect (P < .01). When the implant was heated from 33°C to 47°C, the water device indicated the fastest approach. Thermal distributions of water and laser sources may be suitable for clinical applications. For future research, numerical analysis suggests an ideal time interval of 120 seconds to 180 seconds for a homogenous implant temperature of 47°C.

Transparent high-pressure nozzles for visualization of nozzle internal and external flow phenomena.

A new design for transparent high-pressure nozzles is presented in this work. This new design enables using the innovative Selective Laser Etching (SLE) method to manufacture transparent nozzles with outstanding accuracy. Therefore, not only the simultaneous visualization of the flow mechanics inside and outside the nozzle is enabled, but the manufacturing method applied also allows for the realization of individual nozzle geometries. Thus, nozzle internal flow phenomena (e.g., cavitation, swirl, and air inlet) and their influence on primary breakup can be analyzed with realistic nozzle geometries, e.g., for automotive applications. In addition, targeted three dimensional nozzle geometric parameters can be designed and manufactured in order to get specific tailor-made spray characteristics (e.g., droplet size distribution, spray angle, and penetration length). The basis for the transparent nozzle design is a two-parted nozzle, consisting of a re-machined original serial nozzle body and a transparent nozzle tip. The innovative SLE is used to produce the geometry of the transparent nozzle tip in fused silica, and laser polishing is utilized to achieve a maximum optical quality of nozzle surfaces for visualization. Bonding of both nozzle parts is achieved by a specially designed adhesive method. For a first feasibility study, a transparent nozzle with a simplified nozzle geometry is manufactured and used for a first study. In this study, simultaneous investigation of nozzle internal flow phenomena and their impact on spray breakup are visualized. First microscopic images of the nozzle internal flow show the formation of cavitation, its effect on nozzle internal temperature (apparent by differences in the fluid refractive index), and also the corresponding impact on spray breakup during injection. The penetration of ambient gas into the nozzle is verified at the end of injection as well as the influence of this air on the spray formation during the start of injection.

High-speed Fizeau interferometry for film topography measurement during spray film interaction.

This work presents a novel high-speed interferometric thickness measurement system for thin films (1 µm-23 µm). The system is based on a Fizeau-interferometer and combines a high-speed camera for 2-D topographic fringe images with a spectrally resolved white light interferometer. The aim of this combination is to overcome the ambiguities of the phase demodulation process during fringe pattern analysis. The system is able to measure spatially and temporally resolved film thickness distributions during fast processes. The measurement error of the system is around 5% compared to a commercial 0-D interferometer. First, the results during a diesel spray impingement onto a predefined diesel film are shown, and at the impingement point, an increase in a fluid volume of 24.3% can be seen.

Flexible Endoscopic Spray Application of Respiratory Epithelial Cells as Platform Technology to Apply Cells in Tubular Organs.

INTRODUCTION: Inoperable airway stenoses are currently treated by placing stents. A major problem of covered stents is missing mucociliary clearance, which is caused by covering the native respiratory epithelium. By coating a stent with respiratory epithelium, this problem can be overcome. However, no methods are available for efficient endoscopic cell seeding. METHODS: We designed a flexible endoscopic spraying device based on a bronchoscope and tested it with respiratory epithelial cells. With this device cells can also be applied in a thin layer of fibrin glue. We evaluated the survival rate directly after spray application with a live-dead staining and the long-term differentiation capacity with histology and electron microscopy. Furthermore, the random distribution of cells when applied in a tube was analyzed and the macroscopic and microscopic characteristics of the endoscopic spray were investigated using high-speed visualization. RESULTS: Spray visualization revealed a polydisperse character of the spray with the majority of droplets larger than epithelial cells. Spray application does not influence the survival rate and differentiation of respiratory epithelial cells. After 4 weeks, cells built up a pseudostratified epithelial layer with cilia and goblet cells. When cells are applied in a thin layer of fibrin gel into a tube, a nearest neighbor index of 1.2 is obtained, which suggests a random distribution of the cells. CONCLUSIONS: This spraying device is a promising tool for application of various cell types onto stents or implants with high survival rates and homogeneous distribution as shown in this study for ovine respiratory epithelial cells. The system could also be used for cell therapy to locally apply cells to the diseased parts of hollow organs. For the first time, the fluid dynamics of a spray device for cells were examined to validate in vitro results.

Time-gated ballistic imaging using a large aperture switching beam.

Ballistic imaging commonly denotes the formation of line-of-sight shadowgraphs through turbid media by suppression of multiply scattered photons. The technique relies on a femtosecond laser acting as light source for the images and as switch for an optical Kerr gate that separates ballistic photons from multiply scattered ones. The achievable image resolution is one major limitation for the investigation of small objects. In this study, practical influences on the optical Kerr gate and image quality are discussed theoretically and experimentally applying a switching beam with large aperture (D = 19 mm). It is shown how switching pulse energy and synchronization of switching and imaging pulse in the Kerr cell influence the gate's transmission. Image quality of ballistic imaging and standard shadowgraphy is evaluated and compared, showing that the present ballistic imaging setup is advantageous for optical densities in the range of 8 < OD < 13. Owing to the spatial transmission characteristics of the optical Kerr gate, a rectangular aperture stop is formed, which leads to different resolution limits for vertical and horizontal structures in the object. Furthermore, it is reported how to convert the ballistic imaging setup into a schlieren-type system with an optical schlieren edge.