Bernd Hoffmann

Publications (2)4.64 Total impact

• Article: Human Platelet Lysate Gel Provides a Novel Three Dimensional-Matrix for Enhanced Culture Expansion of Mesenchymal Stromal Cells.

  Gudrun Walenda, Hatim Hemeda, Rebekka K Schneider, Rudolf Merkel, Bernd Hoffmann, Wolfgang Wagner
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  ABSTRACT: Cell culture in regenerative medicine needs to facilitate efficient expansion according to good manufacturing practice requirements. Human platelet lysate (HPL) can be used as a substitute for fetal calf serum without the risk of xenogeneic immune reactions or transmission of bovine pathogens. Heparin needs to be added as anticoagulant before addition of HPL to culture medium; otherwise, HPL-medium forms a gel within 1 h. Here, we demonstrated that such HPL-gels provide a suitable 3D-matrix for cell culture that-apart from heparin-consists of the same components as the over-layered culture medium. Mesenchymal stromal cells (MSCs) grew in several layers at the interface between HPL-gel and HPL-medium without contact with any artificial biomaterials. Notably, proliferation of MSCs was much higher on HPL-gel compared with tissue culture plastic. Further, the frequency of initial fibroblastoid colony forming units (CFU-f) increased on HPL-gel. The viscous consistency of HPL-gel enabled passaging with a convenient harvesting and reseeding procedure by pipetting cells together with their HPL-matrix-this method does not require washing steps and can easily be automated. The immunophenotype and in vitro differentiation potential toward adipogenic, osteogenic, and chondrogenic lineage were not affected by culture-isolation on HPL-gel. Taken together, HPL-gel has many advantages over conventional plastic surfaces: it facilitates enhanced CFU-f outgrowth, increased proliferation rates, higher cell densities, and nonenzymatic passaging procedures for culture expansion of MSCs.
  Tissue Engineering Part C Methods 06/2012; · 4.64 Impact Factor
• Article: Untersuchung von Raumladungsschichten an Zinkoxid-Oberflächen mit Hilfe der Elektroreflexion

  Bernd Hoffmann
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  ABSTRACT: Using the electroreflectance method space charge layers on crystals of different conductivities have been identified. The space charge layers were formed by adsorption of oxygen or atomic hydrogen. The limit of sensitivity required the irradiation with 51013 photons/cm2sec of band gap energy. After exposure to atomic hydrogen all samples showed accumulation layers. With a partial pressure of oxygen above 350 mm Hg crystals of high conductivity (=47 ohm–1 cm–1) exhibit depletion layers, which change into accumulation layers, if the partial pressure is reduced below the limit. Crystals of a lower conductivity (=10–3–10–1 ohm–1 cm–1) show accumulation layers up to the highest applied oxygen pressure of 760 mm Hg. The phenomena are attributed to a dynamical equilibrium between adsorption and photo-desorption of oxygen. This equilibrium depends on oxygen pressure and free carrier concentration. By comparing a calculated curve with the experimental results the value of 3.31 ev is obtained for the energy gap, light polarized perpendicular to thec-acis.
  Zeitschrift für Physik A Hadrons and Nuclei 07/1969; 219(4):354-363.