W. Grill

Mesenchymal Stem Cells in Cartilage Repair: State of the Art and Methods to monitor Cell Growth, Differentiation and Cartilage Regeneration

Degenerative joint diseases caused by rheumatism, joint dysplasia or traumata are particularly widespread in countries with high life expectation. Although there is no absolutely convincing cure available so far, hyaline cartilage and bone defects resulting from joint destruction can be treated today by appropriate transplantations. Recently, procedures were developed based on autologous chondrocytes from intact joint areas. The chondrocytes are expanded in cell culture and subsequently transplanted into the defect areas of the affected joints. However, these autologous chondrocytes are characterized by low expansion capacity and the synthesis of extracellular matrix of poor functionality and quality. An alternative approach is the use of adult mesenchymal stem cells (MSCs). These cells effectively expand in 2D culture and have the potential to differentiate into various cell types, including chondrocytes. Furthermore, they have the ability to synthesize extracellular matrix with properties mimicking closely the healthy hyaline joint cartilage. Beside a more general survey of the architecture of hyaline cartilage, its composition and the pathological processes of joint diseases, we will describe here which advances were achieved recently regarding the development of closed, aseptic bioreactors for the production of autologous grafts for cartilage regeneration based on MSCs. Additionally, a novel mathematical model will be presented that supports the understanding of the growth and differentiation of MSCs. It will be particularly emphasized that such models are helpful to explain the well-known fact that MSCs exhibit improved growth properties under reduced oxygen pressure and limited supply with nutrients. Finally, it will be comprehensively shown how different analytical methods can be used to characterize MSCs on different levels. Besides discussing methods for non-invasive monitoring and tracking of the cells and the determination of their elastic properties, mass spectrometric methods to evaluate the lipid compositions of cells will be highlighted.

Mode-selective excitation and detection of ultrasonic guided waves for delamination detection in laminated aluminum plates

Selective modes of guided Lamb waves are generated in a laminated aluminum plate for damage detection using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Dispersion curves are obtained experimentally by short time Fourier transform of the transient signals. Sensitivity of antisymmetric and symmetric modes for delamination detection are investigated. The antisymmetric mode is found to be more reliable for delamination detection. Unlike other studies, in which the attenuation of the propagating waves is related to the extent of the internal damage, in this investigation, the changes in the time-of-flight (TOF) of guided Lamb waves are related to the damage progression. The mode conversion phenomenon of Lamb waves during progressive delamination is investigated. Close matching between the theoretical and experimentally derived dispersion curves and TOF assures the reliability of the results presented here.

Band Gap Energies and Lattice Vibrations of the Lithium Ternary Compounds LiInSe2, LiInS2, LiGaSe2 and LiGaS2

The band gap energies EG of the lithium compounds have been measured by transmittance and reflectivity measurements as well as measurements of the diffuse reflectivity. At room temperature EG=2.83 eV (LiInSe2), EG=3.56 eV (LiInS2), EG=3.13 eV (LiGaSe2) and EG=3.62 eV (LiGaS2) have been obtained presupposing a direct interband transition. In a first attempt the birefringence of LiInS2 was studied by transmittance measurements. Using infrared and Raman spectroscopy the lattice vibrational properties have been investigated.

Ultrasonic monitoring of zeolite synthesis in real time

Variations of the phase and amplitude of a transmitted ultrasonic wave package were monitored in real time during the synthesis of zeolite A and zeolite X. For both materials, characteristic changes of the measured attenuation and the sound velocity of ultrasonic waves traveling in the reaction fluid were observed, correlating with the processes of gel formation and zeolite crystallization, respectively. Aging effects of the reaction fluids are demonstrated. The observation of the onset of the zeolite crystallization was verified with ex-situ X-ray diffraction (XRD) measurements.

Angular spectrum approach for the computation of group and phase velocity surfaces of acoustic waves in anisotropic materials

The decomposition of an acoustic wave into its angular spectrum representation creates an effective base for the calculation of wave propagation effects in anisotropic media. In this method, the distribution of acoustic fields is calculated in arbitrary planes from the superposition of the planar components with proper phase shifts. These phase shifts depend on the ratio of the distance between the planes to the normal component of the phase slowness vector. In anisotropic media, the phase shifts depend additionally on the changes of the slowness with respect to the direction of the propagation vector and the polarization. Those relations are obtained from the Christoffel equation. The method employing the fast Fourier transformation algorithm is especially suited for volume imaging in anisotropic media, based on holographic detection in transmission of acoustic waves generated by a point source. This technique is compared with measurements on crystals performed by phase-sensitive scanning acoustic microscopy.

Embedded Piezoelectric Sensors for Health Monitoring of Concrete Structures

This paper presents an experimental investigation for detecting defects in concrete structures using so-called “smart aggregates.” The smart aggregates are small cylinders with piezoelectric patches inside that can be embedded in concrete structures and used as both actuators and sensors. Specimens with different types of defects such as notch, hole, and inclusion were used in this study. To evaluate the effectiveness of the smart aggregates for detecting real cracks in concrete structures, three-point bending tests were carried out on two reinforced concrete beams. The test results indicate that not only the passive defects (notch, hole, or inclusion) but also the real cracks in reinforced concrete structures can be detected by the smart aggregates. Sensitivities of different parameters (time-of-flight, energy content of the signals, wavelet packet decomposition-based damage index) for various defects were also investigated.

Scanning acoustic air microscope

A new type of focusing transducer, which works efficiently in air, has been developed and employed in a phase sensitive scanning acoustic microscope (PSAM) with air as a coupling medium. The transducers contain a matching layer, which diminishes the insertion loss of the energy. The ultrasonic microscope working on the base of this transducer has a lateral resolution of about 220 μm and is capable of measuring distance (height of the object) variations with a resolution of at least 1 μm. The instrument is therefore capable of high resolution, non-contact topographical mapping of objects in air at normal conditions.

Characterization of polymer thin films by phase-sensitive acoustic microscopy and atomic force microscopy: a comparative review

The potential of phase‐sensitive acoustic microscopy (PSAM) for characterizing polymer thin films is reviewed in comparison to atomic force microscopy (AFM). This comparison is based on results from three‐dimensional vector contrast imaging and multimodal imaging using PSAM and AFM, respectively. The similarities and differences between the information that can be derived from the AFM topography and phase images, and the PSAM phase and amplitude micrographs are examined. In particular, the significance of the PSAM phase information for qualitative and quantitative characterization of the polymer films is examined for systems that generate surface waves, and those that do not. The relative merits, limitations and outlook of both techniques, individually, and as a complementary pair, are discussed.

Determination of the velocity of ultrasound by short pulse switched sinusoidal excitation and phase-sensitive detection by a computer-controlled pulse-echo system

Abstract For the determination of the velocity and the attenuation of acoustic waves, the resonances caused by reflections from both surfaces of plane parallel transducers and diffraction effects arising from the limited size of the transducers lead to well-known phase shifts of the signal. To avoid the build-up of these effects, fast-switched ultrasonic pulses with a pulse width shorter than the transit time of the transducers are employed. For these excitation conditions, contributions from internal reflections and diffraction can be separated in time. This allows the generation and detection of acoustic signals in an extremely wide frequency range. A fully automatic computer-controlled measuring system including a temperature-controlled sample chamber for the range 1.5–400 K has been constructed for high-accuracy generation and detection of short pulsed ultrasonic signals in the frequency regime 2–500 MHz.

Pipe wall damage detection by electromagnetic acoustic transducer generated guided waves in absence of defect signals

Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.