bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of biphasic material properties of equine articular cartilage from stress relaxation indentation tests with and without tension-compression nonlinearity
Authors: Reuter Thomas , Hurschler Christof 
Published: September 2018

Abstract
The mechanical parameters of articular cartilage estimated from indentation tests depend on the constitutive model adopted to analyze the data. In this study, we present a 3D-FE-based method to determine the biomechanical properties of equine articular cartilage from stress relaxation indentation tests (ε = 6 %, t = 1000 s) whereby articular cartilage is modeled as a biphasic material without (BM) and with tension-compression nonlinearity (BMTCN). The FEmodel computation was optimized by exploiting the axial symmetry and mesh resolution. Parameter identification was executed with the Levenberg-Marquardt-algorithm. The R² of the fit results varies between 0.695 and 0.930 for the BMmodel and between 0.877 and 0.958 for the BMTCN-model. The differences of the R² occur from the more exact description of the initial stress relaxation behaviour by the fiber modulus from the BMTCN-model. The fiber modulus defines the collagen matrix of cartilage. Furthermore, for both models the determined values of Young’s modulus and permeability were in the same order of magnitude.
Molecular processes of corneal collagen cross-linking in keratoconus therapy
Authors: Melcher Steven , Spörl Eberhard , Koch Edmund , Steiner Gerald 
Published: September 2018

Abstract
Corneal collagen cross-linking (CXL) with riboflavin and UVA light is a therapeutic procedure to restore the mechanical stability of corneal tissue. The treatment method applies to pathological tissue changes, such as keratoconus. It induces the photochemical formation of new collagen cross-links. Although therapeutic effects are indisputable, the exact molecular process of CXL and how cross-links are formed is still unclear. In this work, Fouriertransform infrared (FT-IR) spectroscopy is used to investigate the cross-linking process. For that purpose, in-situ experiments with porcine corneas are carried out using attenuated total reflection (ATR) spectroscopy. Furthermore, IR micro-spectroscopic imaging in transmission mode is used to investigate thin tissue sections of the cornea and initial approaches for the distinction of cross-linked and untreated tissue by IR microspectroscopic imaging were performed. Multivariate methods are applied to access changes that occur as a result of CXL. It is shown that spectral changes after cross-linking are caused predominantly by an increase of methyl- and methylene groups as well as primary and secondary amines. In addition, a decrease of carbonyl groups could be observed.
Influence of additives on physico-chemical properties of electrospun poly(L-lactide)
Authors: Arbeiter Daniela , Kohse Stefanie , Eickner Thomas , Grabow Nils , Schmitz Klaus-Peter 
Published: September 2018

Abstract
Electrospun poly(L-lactide) (PLLA) nonwoven represent potential options for biodegradable medical implants. They can be manufactured with high reproducibility and do offer the potential for chemical modification to alter matrix properties. In our study, we investigate the mechanical, thermal and morphological properties of PLLA fiber matrices. Fibrous nonwovens were fabricated from polymer solution by needle electrospinning. The polymer solutions were loaded with Triton X-100 (TX- 100), formic acid and tetraethyl ammonium chloride (TEAC) with respect to polymer weight. Morphology of the PLLA nonwoven scaffolds was examined with SEM. We performed uniaxial tensile tests and differential scanning calorimetry (DSC). Different concentrations of the additives TEAC, formic acid and Triton X-100 lead to strong changes regarding mechanical and thermal properties of the electrospun PLLA fiber matrices. In comparison with mechanical properties of established biological tissue materials, the results indicate the suitability for medical applications.
Development of biodegradable stents for the treatment of Eustachian tube dysfunction
Authors: Schümann Kerstin , Wilfling Tamara , Paasche Gerrit , Schuon Robert , Robert Schuon , Lenarz Thomas , Schmidt Wolfram , Grabow Niels , Müller Heinz , Momma Carsten , Schmitz Klaus-Peter 
Published: September 2018

Abstract
To provide an effective and safe therapy for chronic Eustachian tube dysfunction (ETD), biodegradable stents should be developed to restore important functions, e.g. middle ear ventilation and drainage. After defining general requirements specifications, stent designs of cardiovascular polymeric stents were modified according to dimensions and conditions of the Eustachian tube. Finite element simulations demonstrated the crimping capacity of the developed stent design and the ability of expansion in the specific geometry of the target location. Subsequent in vitro tests of stent prototypes showed satisfying properties concerning crimpability, expansion behavior and elastic recoil to demonstrate general feasibility. Further developments and additional testing will advance the implementation of a new treatment option of ETD.
Impact of anatomical variations on insertion forces
Authors: Hügl Silke , Blum Tobias , Lenarz Thomas , Majdani Omid , Rau Thomas S. 
Published: September 2018

Abstract
The choice of a cochlear implant electrode carrier for the individual patient is influenced by cochlear size, as this parameter has an impact on the risk of scala dislocations. Therefore, size and morphology should be represented in artificial cochlear models too, since these are generally used for insertion studies evaluating newly developed cochlear implant electrode carriers and insertion techniques, before human temporal bone studies are applied for. Within this study custom-made electrode carrier test samples were inserted into nine artificial cochlear models of different shape. To fabricate them, four human temporal bone samples have been processed by a serial cross-sectioning technique; the other four samples have been scanned with micro computed tomography. The cochlea was segmented on this data using rotating, midmodiolar slice planes, followed by the generation of a three-dimensional digital model, which finally was projected on a plane and 2D models were milled out of PTFE. The ratios of length to width of the cochlear basal turn of our samples were found to be within previously reported range. For comparative reasons a model used in previous studies was included in this study too. The maximal insertion forces per cochlear model followed a normal distribution. The insertion depth at initial insertion force increase is correlated to the length of cochlear basal turn. Using the here presented cochlear models with varying anatomical measures may help to increase the clinical relevance of insertion studies in artificial cochlear models.
Novel hot-wire based spirometry is highly accurate at low flow rates
Authors: Perera Arshan , Friedrich Petra , Ledermüller Rosina 
Published: September 2018

Abstract
Spirometry is the most commonly used pulmonary function test. The aim of this comparative study was to evaluate four commercially available spirometers with different measurement principles (turbine-, ultrasound-, differential pressure- and hot-wire anemometer). In particular, the measurement accuracy in breathing manoeuvres with low flow rates was investigated, which is highly relevant for paediatric use. Among the tested devices the hot-wire based spirometer showed the highest measurement accuracy at low flows whilst fully complying with the ATS/ERS standards.
MATLAB Simulation Environment for Estimating the Minimal Number and Positions of Cameras for 3D Surface Reconstruction in a Fully-Digital Surgical Microscope
Authors: Wachter Andreas , Kost Jan , Nahm Werner 
Published: September 2018

Abstract
Contemporary surgical microscope systems have excellent optical properties but some desirable features remain unavailable. The number of co-observers is currently restricted, by spatial and optical limitations, to only two. Moreover, ergonomics poses are a problem: Current microscope systems impede free movement and sometimes demand that surgeons take uncomfortable postures over long periods of time. To rectify these issues, some companies developed surgical microscope systems based on a streaming approach. These systems remove some of the limitations. Multi-observer positions, for example, are not independent from each other, for example. In order to overcome the aforementioned limitations, we are currently developing an approach for the next generation of surgical microscope: Namely the fully digital surgical microscope, where the current observation system is replaced with a camera array, allowing real-time 3D reconstruction of surgical scenes and, consequently, the rendering of almost unlimited views for multiple observers. These digital microscopes could make the perspective through the microscope unnecessary allowing the surgeon to move freely and work in more comfortable postures. The requirements on the camera array in such a system have to be determined. For this purpose, we propose of estimation the minimal number of cameras and their positions needed for the 3D reconstruction of microsurgical scenes. The method of estimation is based on the requirements for the 3D reconstruction. Within the MATLAB simulation environment, we have developed a 3D model of a microsurgical scene, used for the determination of the number of required cameras. In a next step a small, compact and costefficient system with few opto-mechanical components could be manufactured.
Comparing distance measures on assessed medical device incident data using Average Silhouette Width
Authors: Bayer Christian , Seidel Robin 
Published: September 2018

Abstract
Many machine learning algorithms depend on the choice of an appropriate similarity or distance measure. Comparing such measures in different domains and on diversely structured data is common, but often performed in regards of an algorithm to cluster or classify the data. In this study, data assessed by experts is analyzed instead. The data is taken from the database of the Federal Institute for Drugs and Medical Devices (BfArM) and represents free text incident reports. The Average Silhouette Width, a cluster density measure, is used to compare the distance measures’ ability to discriminate the data according to the experts’ assessments. The Euclidean distance and four distance measures derived from the Jaccard similarity, the Simple Matching similarity, the Cosine similarity and the Yule similarity are compared on four subsets of this database. The results show, that a better data preprocessing is necessary, possibly due to boilerplate texts being used to write incident reports. These results will also provide the basis to compare improvements by different methods of data preprocessing in the future.
Investigation of balloon dilation devices for treatment of Eustachian tube dysfunction
Authors: Schubert Julia , Wilfling Tamara , Paasche Gerrit , Lenarz Thomas , Schümann Kerstin , Grabow Niels , Schmidt Wolfram , Schmitz Klaus-Peter 
Published: September 2018

Abstract
The presented three different balloon dilation devices for treating Eustachian tube dysfunction were compared regarding their geometries and designs. The balloon dilation behaviour was investigated by an in vitro test setup consisting of a test chamber with 37 °C water, a 2-axis laser scanner and a pressure controller. All balloons could be properly dilated up to the given nominal pressure (NP) or to rated burst pressure (RBP). The balloons reached their expected balloon diameter and length. The compliance data were 1.07 %/atm (TubaVent short), 1.16 %/atm (Acclarent Aera) and 1.28 %/atm (XprESS LoProfile). The measured profile and compliance data can be used for development of new devices for balloon dilation Eustachian tuboplasty.
Balloon-based measuring system for compliance investigations
Authors: Tautorat Carsten , Schümann Kerstin , Specht Olaf , Kamke Frank , Behrens Peter , Schmitz Klaus-Peter , Grabow Niels , Schmidt Wolfram 
Published: September 2018

Abstract
For the development of new stent designs, the compliance of the surrounding biological tissue has to be considered. We expect to obtain parameters for simulation, stent dimensioning, and the forces acting on the stent after implantation. Starting point of the investigations is the commercially available Metricath system allowing cross-sectional lumen area measurements of arteries. Its working principle is based on the pressure-volume relationship using a balloon catheter, which is inflated to a specific pressure of about 250 mmHg and conforms to the shape and size of the lumen. However, for compliance charts multiple pressure levels and a larger pressure range are needed. To overcome this technical limitation, the Metricath balloon catheter is combined with a new inflation device, called pV-Monitor. The presented cross-sectional lumen area measurements in rigid tubes and compliance investigations of elastic tubes demonstrate the feasibility of the pV-Monitor system.
Efficient feature-based motion estimation in neurosurgery using non-maximum suppression
Authors: Chen Fang , Müller Jan , Müller Jens , Tetzlaff Ronald 
Published: September 2018

Abstract
In this contribution we propose a feature-based method for motion estimation and correction in intraoperative thermal imaging during brain surgery. The motion is estimated from co-registered white-light images in order to perform a robust motion correction on the thermographic data. To ensure real-time performance of an intraoperative application, we optimise the processing time which essentially depends on the number of key points found by our algorithm. For this purpose we evaluate the effect of applying an non-maximum suppression (NMS) to improve the feature detection efficiency. Furthermore we propose an adaptive method to determine the size of the suppression area, resulting in a trade-off between accuracy and processing time.
Hydrophilic silicone elastomer with excellent cell adhesion capability - A promising material for ophthalmic micro-implants
Authors: Brietzke Andreas , Grabow Niels , Schmitz Klaus-Peter , Schmidt Wolfram , Siewert Stefan , Guthoff Rudolph , Stahnke Thomas , Kreiner Christine 
Published: September 2018

Abstract
For minimising tissue reactions of implants hydrophilic silicone elastomers feature a high potential to be utilised as material for micro-implants in ophthalmologic pathology. To estimate the biocompatibility we quantified cell viability of human primary fibroblasts from scleral (hSF) and choroideal (hCF) origin in direct contact test and evaluated cell adhesion and cell morphology with Phalloidin- TRITC stained hSF and EA.hy926. Mechanical properties were analysed by means of uniaxial tensile testing. Direct contact testing revealed a good biocompatibility from 65 to 70% relative cell viability for hCF and moderate viabilities (46 to 63%) for hSF. EA.hy926 and also hSF exhibited typical cell morphology on the silicones. Improvement of cell adhesion was observed with increasing amount of hydrophilic component. Mechanical testing shows a minor decrease in elongation at break from 236% to 155% with increasing amount of hydrophilic component. These findings indicate that the investigated silicones may ensure a reliable integration of implants into the ocular tissues.
Optimization of manufacturing processes for biodegradable polymeric stents regarding improved mechanical properties
Authors: Sahmel Olga , Arbeiter Daniela , Schümann Kerstin , Grabow Niels , Siewert Stefan , Schmitz Klaus-Peter 
Published: September 2018

Abstract
Although current drug eluting stents show low risks of in-stent restenosis and stent thrombosis, the presence of a permanent foreign body inside the vessel represents a major limitation. In order to overcome this limitation, stents made of biodegradable polymeric materials are currently being developed. The present work describes an optimized fabrication process for tubular semi-finished products for manufacturing of stents made of poly-L-lactide (PLLA). The impact of the haul-off speed as a major parameter during extrusion processing on the cross-sectional area of tubular specimens was analyzed. It could be shown that the crosssection of the extrudate, in particular the tubing diameter and wall thickness, can be adjusted by varying haul-off speed. In a subsequent blow molding process the influence of the holding time on polymer cold crystallization was analyzed. Thermal properties of the polymeric material after processing were examined by differential scanning calorimetry (DSC). The results showed that there is almost no cold crystallization using a holding time of at least 20 minutes. The investigations showed that semi-finished products with variable geometry and improved mechanical properties can be produced with the described extrusion and blow molding process.
Fabrication and Characterization of Bending- Independent Capacitive CMOS Pressure Sensor Stacks
Authors: Fischer Roland , Ditler Heinrich , Görtz Michael , Mokwa Wilfried 
Published: September 2018

Abstract
Artificial limbs, equipped with miniaturized tactile sensors, can handle objects with more dexterousness. Next to detecting forces, the sensor devices are also able to measure temperature. With this additional information, the touched objects can be better characterized. As such sensors, active CMOS-based capacitive pressure sensors are used in this work. The Sensors are thinned to 20-30 μm target thickness to make them bendable. One challenge of such thin sensors is the strong dependence of the output signal upon bending. To compensate this dependency, two sensors were mounted back to back. This allows a numerical adjustment of the two characteristic sensor output signals to mechanical stress curves. After electrically contacting of the stacks with a 15 μm thin polyimide foil substrate, the bending dependence of the stacks was characterized with a four-point bending procedure. By this characterization the dependency of the pressure sensor output signal on the height of mechanical stress was determined. Both sensor output signals show an inverted behavior under the same mechanical stress which confirmed prior simulation results with the same setup. Based on this information, a numerical method for compensating the bending dependence was successfully proven.
In vitro investigation of the radial compliance of porcine carotid arteries
Authors: Brandt-Wunderlich Christoph , Specht Olaf , Ortmann Heinrich Erik , Schmidt Wolfram , Grabow Niels , Schmitz Klaus-Peter 
Published: September 2018

Abstract
The regaining elastic behavior of the artery after treatment with a bioresorbable scaffold is a measure for successful degradation. The investigation of the elastic properties of arteries is often performed using ultrasound based methods. The current study describes an in vitro test setup for the measurement of the elastic radial compliance of blood vessels with an automated laser scanning device. A porcine carotid artery was placed inside a phosphate buffered saline filled chamber and the outer diameter was measured during stepwise pressurization from 20 mmHg to 160 mmHg. Reference measurements were done with an ultrasound based method. The results show that the automated laser scanning device method provides similar values to the ultrasound measurements. Therefore, the automated laser scanning device method appears to be suitable to investigate radial compliance differences of a stented vessel segment during the degradation process of a bioresorbable scaffold in vitro. The high degree of automation allows for an effective investigation of a larger series of measurements.
Development of a drug-eluting microstent for micro-invasive glaucoma surgery
Authors: Siewert Stefan , Pfensig Sylvia , Großmann Swen , Stiehm Michael , Schmitz Klaus-Peter , Schmidt Wolfram , Kohse Stefanie , Wulf Katharina , Grabow Niels , Kopp Franziska , Guthoff Rudolf 
Published: September 2018

Abstract
Glaucoma represents the leading cause of irreversible blindness worldwide. Therapeutic approaches are based on the lowering of intraocular pressure (IOP). Micro-invasive glaucoma surgery (MIGS) offers perspectives for implant based IOP-reduction with reduced complication rates compared to conventional surgical approaches. Nevertheless, available devices suffer from complications like hypotony and fibrotic encapsulation. The current work focuses on the development of a minimally invasive implantable drugeluting microstent for the drainage of aqueous humour into suprachoroidal or subconjunctival space. Technical feasibility of a micro-scale resorbable nonwoven for the prevention of hypotony and of a drug-eluting coating for the prevention of fibrosis is assessed. Microstent base bodies with a length of 10 mm and an inner/outer diameter of 0.20 mm / 0.35 mm were manufactured. For the prevention of hypotony, resorbable nonwovens with an adequate flow resistance of 1.543 mmHg/μl min-1 were manufactured in the inflow area of microstents. A drug-eluting coating in the outflow area of microstents was developed based on the model drug fluorescein diacetate. Micro-invasive ab interno implantation of a microstent prototype into suprachoroidal space of a porcine eye post mortem was successfully performed, using an injector device. Future studies will focus on the development of an antifibrotic drug-eluting coating and further in vitro, ex vivo and in vivo testing of the devices.
Influence of application parameters of ultrasonic-assisted bone instruments on the tear force of a substitute material for spinal dura mater
Authors: Foelkel Marie C. , Herzog Vitali , Meier Markus , Morlock Michael M. 
Published: September 2018

Abstract
An ultrasonic-assisted bone instrument can be used for the dissection of bone in spinal surgery. During surgery, the tip of such a bone instrument can touch spinal dura mater. Especially during critical re-operations, high forces can be unintentionally applied on spinal dura mater. To prevent dural tears, the influence of application parameters on the tear force shall be analyzed. Collagen foil is used as a substitute material for spinal dura mater because of its similar mechanical properties and structure. Sponge cloth is placed below collagen foil to imitate cerebrospinal fluid and nerve tissue. A 3-axis CNC-machine is used to automate the movement of the bone instrument. In a full factorial experiment the influence of amplitude, shape of movement and velocity of movement on the tear force is analyzed. Amplitude has the strongest effect because of the increase in input energy. Velocity also has a significant influence, probably because of the strain rate increasing with velocity. Thus, a surgeon should mainly reduce the amplitude and furthermore the velocity of movement to generate higher safety in critical areas.