@article{PaxtonSmolanBoecketal.2017,
  author    = {Paxton, Naomi and Smolan, Willi and B{\"o}ck, Thomas and Melchels, Ferry and Groll, J{\"u}rgen and Jungst, Tomasz},
  title     = {Proposal to assess printability of bioinks for extrusion-based bioprinting and evaluation of rheological properties governing bioprintability},
  series = {Biofabrication},
  volume    = {9},
  journal   = {Biofabrication},
  number    = {4},
  doi       = {10.1088/1758-5090/aa8dd8},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-254061},
  year      = {2017},
  abstract  = {The development and formulation of printable inks for extrusion-based 3D bioprinting has been a major challenge in the field of biofabrication. Inks, often polymer solutions with the addition of crosslinking to form hydrogels, must not only display adequate mechanical properties for the chosen application but also show high biocompatibility as well as printability. Here we describe a reproducible two-step method for the assessment of the printability of inks for bioprinting, focussing firstly on screening ink formulations to assess fibre formation and the ability to form 3D constructs before presenting a method for the rheological evaluation of inks to characterise the yield point, shear thinning and recovery behaviour. In conjunction, a mathematical model was formulated to provide a theoretical understanding of the pressure-driven, shear thinning extrusion of inks through needles in a bioprinter. The assessment methods were trialled with a commercially available cr{\`e}me, poloxamer 407, alginate-based inks and an alginate-gelatine composite material. Yield stress was investigated by applying a stress ramp to a number of inks, which demonstrated the necessity of high yield for printable materials. The shear thinning behaviour of the inks was then characterised by quantifying the degree of shear thinning and using the mathematical model to predict the window of printer operating parameters in which the materials could be printed. Furthermore, the model predicted high shear conditions and high residence times for cells at the walls of the needle and effects on cytocompatibility at different printing conditions. Finally, the ability of the materials to recover to their original viscosity after extrusion was examined using rotational recovery rheological measurements. Taken together, these assessment techniques revealed significant insights into the requirements for printable inks and shear conditions present during the extrusion process and allow the rapid and reproducible characterisation of a wide variety of inks for bioprinting.},
  language  = {en}
}
@article{SanchoVandersmissenCrapsetal.2017,
  author    = {Sancho, Ana and Vandersmissen, Ine and Craps, Sander and Luttun, Aernout and Groll, J{\"u}rgen},
  title     = {A new strategy to measure intercellular adhesion forces in mature cell-cell contacts},
  series = {Scientific Reports},
  volume    = {7},
  journal   = {Scientific Reports},
  number    = {46152},
  doi       = {10.1038/srep46152},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170999},
  year      = {2017},
  abstract  = {Intercellular adhesion plays a major role in tissue development and homeostasis. Yet, technologies to measure mature cell-cell contacts are not available. We introduce a methodology based on fluidic probe force microscopy to assess cell-cell adhesion forces after formation of mature intercellular contacts in cell monolayers. With this method we quantify that L929 fibroblasts exhibit negligible cell-cell adhesion in monolayers whereas human endothelial cells from the umbilical artery (HUAECs) exert strong intercellular adhesion forces per cell. We use a new in vitro model based on the overexpression of Muscle Segment Homeobox 1 (MSX1) to induce Endothelial-to-Mesenchymal Transition (EndMT), a process involved in cardiovascular development and disease. We reveal how intercellular adhesion forces in monolayer decrease significantly at an early stage of EndMT and we show that cells undergo stiffening and flattening at this stage. This new biomechanical insight complements and expands the established standard biomolecular analyses. Our study thus introduces a novel tool for the assessment of mature intercellular adhesion forces in a physiological setting that will be of relevance to biological processes in developmental biology, tissue regeneration and diseases like cancer and fibrosis.},
  language  = {en}
}