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- ItemEnergy-dependent dielectric tensor axes in monoclinic Ī±-3,4,9,10-perylene tetracarboxylic dianhydride(Amsterdam [u.a.] : Elsevier, 2023) Alonso, M.I.; Garriga, M.; OssĆ³, J.O.; Schreiber, F.; Scholz, R.We have determined the complex dielectric tensor of single crystalline 3,4,9,10-perylene tetracarboxylic dianhydride (Ī±-PTCDA) as a function of energy in the range between 1.4 and 5.0 eV. The results obtained reflect the monoclinic symmetry of the crystal: The principal axes of the real and the imaginary part of the tensor in general do not coincide and show chromatic dispersion. Monoclinic behavior allows rotation of the components ÉX and ÉZ in the plane perpendicular to the unique symmetry axis Y. The experimental results indicate that the energies of the optical transitions observed in the weak ÉX component coincide with energies in which a resonance effect due to coupling with the stronger ÉZ component occurs. These resonances appear at energies close to electronic excitations such as the optical gap, the transport gap and the highest occupied molecular orbitalālowest unoccupied molecular orbital (HOMOāLUMO) peak-to-peak gap and their assignments are discussed based on theoretical calculations.
- ItemStatic and dynamic 3D culture of neural precursor cells on macroporous cryogel microcarriers(Amsterdam [u.a.] : Elsevier, 2020) Newland, Ben; Ehret, Fanny; Hoppe, Franziska; Eigel, Dimitri; Pette, Dagmar; Newland, Heike; Welzel, Petra B.; Kempermann, Gerd; Werner, CarstenNeural precursor cells have been much studied to further our understanding of the far-reaching and controversial question of adult neurogenesis. Currently, differentiation of primary neural precursor cells from the mouse dentate gyrus via 2-dimentional in vitro culture yields low numbers of neurons, a major hindrance to the field of study. 3-dimentional āneurosphereā culture allows better 3D cell-cell contact, but control over cell differentiation is poor because nutrition and oxygen restrictions at the core of the sphere causes spontaneous differentiation, predominantly to glial cells, not neurons. Our group has developed macroporous scaffolds, which overcome the above-mentioned problems, allowing long-term culture of neural stem cells, which can be differentiated into a much higher yield of neurons. Herein we describe a method for culturing neural precursor cells on RGD peptide functionalized-heparin containing cryogel scaffolds, either in standard non-adherent well-plates (static culture) or in spinner flasks (dynamic culture). This method includes: ā¢ The synthesis and characterization of heparin based microcarriers. ā¢ A āstaticā 3D culture method for that does not require spinner flask equipment. ā¢ āDynamicā culture in which cell loaded microcarriers are transferred to a spinner flask. Ā© 2020 The Authors
- ItemBiomaterial based strategies to reconstruct the nigrostriatal pathway in organotypic slice co-cultures(Amsterdam [u.a.] : Elsevier, 2021) Ucar, Buket; Kajtez, Janko; Foidl, Bettina M.; Eigel, Dimitri; Werner, Carsten; Long, Katherine R.; EmnĆ©us, Jenny; Bizeau, JoĆ«lle; Lomora, Mihai; Pandit, Abhay; Newland, Ben; Humpel, ChristianProtection or repair of the nigrostriatal pathway represents a principal disease-modifying therapeutic strategy for Parkinson's disease (PD). Glial cell line-derived neurotrophic factor (GDNF) holds great therapeutic potential for PD, but its efficacious delivery remains difficult. The aim of this study was to evaluate the potential of different biomaterials (hydrogels, microspheres, cryogels and microcontact printed surfaces) for reconstructing the nigrostriatal pathway in organotypic co-culture of ventral mesencephalon and dorsal striatum. The biomaterials (either alone or loaded with GDNF) were locally applied onto the brain co-slices and fiber growth between the co-slices was evaluated after three weeks in culture based on staining for tyrosine hydroxylase (TH). Collagen hydrogels loaded with GDNF slightly promoted the TH+ nerve fiber growth towards the dorsal striatum, while GDNF loaded microspheres embedded within the hydrogels did not provide an improvement. Cryogels alone or loaded with GDNF also enhanced TH+ fiber growth. Lines of GDNF immobilized onto the membrane inserts via microcontact printing also significantly improved TH+ fiber growth. In conclusion, this study shows that various biomaterials and tissue engineering techniques can be employed to regenerate the nigrostriatal pathway in organotypic brain slices. This comparison of techniques highlights the relative merits of different technologies that researchers can use/develop for neuronal regeneration strategies. Ā© 2020
- ItemElectrically conductive and piezoresistive polymer nanocomposites using multiwalled carbon nanotubes in a flexible copolyester: Spectroscopic, morphological, mechanical and electrical properties(Amsterdam [u.a.] : Elsevier, 2022) Dhakal, Kedar Nath; Khanal, Santosh; Krause, Beate; Lach, Ralf; Grellmann, Wolfgang; Le, Hai Hong; Das, Amit; WieĆner, Sven; Heinrich, Gert; Pionteck, JĆ¼rgen; Adhikari, RameshwarNanocomposites of multiwalled carbon nanotubes (MWCNTs) with poly(butylene adipate-co-terephthalate) (PBAT), a flexible aromaticāaliphatic copolyester, were prepared by melt mixing followed by compression moulding to investigate their spectroscopic, morphological, mechanical and electrical properties. A comparison of the Fourier transform infrared (FTIR) spectra of the neat polymer matrix and the composites showed no difference, implying a physical mixing of the matrix and the filler. A morphological investigation revealed the formation of a continuous and interconnected MWCNT network embedded in the polymer matrix with partial agglomeration. Increasing Martens hardness and indentation modulus and decreasing maximum indentation depth with increasing filler concentration demonstrated the reinforcement of the polymer by the MWCNTs. A volume resistivity of 4.6 Ć 105 Ī© cm of the materials was achieved by the incorporation of only 1 wt.-% of the MWCNTs, which confirmed a quite low percolation threshold (below 1 wt.-%) of the nanocomposites. The electrical volume resistivity of the flexible nanocomposites was achieved up to 1.6 Ć 102 Ī© cm, depending on the filler content. The elongation at the break of the nanocomposites at 374% and the maximum relative resistance changes (ĪR/R0) of 20 and 200 at 0.9 and 7.5% strains, respectively, were recorded in the nanocomposites (3 wt.-% MWCNTs) within the estimated volume resistivity range. A cyclic strain experiment shows the most stable and reproducible ĪR/R0 values in the 2%ā5% strain range. The electrical conductivity and piezoresistivity of the investigated nanocomposites in correlation with the mechanical properties and observed morphology make them applicable for low-strain deformation-sensing.
- ItemProcess Monitoring of a Vibration Dampening CFRP Drill Tube in BTA deep hole drilling using Fibre-Bragg-Grating Sensors(Amsterdam [u.a.] : Elsevier, 2022) Summa, Jannik; Michel, Sebastian; Kurkowski, Moritz; Biermann, Dirk; Stommel, Markus; Herrmann, Hans-GeorgThe large tool length in BTA deep hole drilling often leads to strong torsional vibrations of the tool system, leading to a reduced bore hole quality failures. When substituting steel drill tubes with tubes from composite material, the laminate structure dampens these vibrations. Secondly, the integration of sensors allow to monitor process vibrations. This contribution introduces a new sensor platform to measure process vibrations, feed force and drilling torque using Fibre-Bragg Grating Sensors. The presented experimental results focus on characteristic frequency spectra with natural torsional and compression frequencies of the CFRP drill tube, which show variations due to changed feed.