New advances in the 3D characterization of mineral coating layers on paper

Hyperbranched poly(ϵ-lysine) substrate presenting the laminin sequence YIGSR induces the formation of spheroids in adult bone marrow stem cells

Unlike the fibroblast-like cells formed upon monolayer culture of human mesenchymal stem cells, the natural stem cell niche of the bone marrow and other types of tissues favours the formation of 3-dimensional (3D) cell clusters. The structuring and biological activity of these clusters are regulated by the contacts established by cells with both the basement membrane and neighbour cells and results in their asymmetric division and the consequent maintenance of both a stem population and a committed progeny. The present work demonstrates the potential of a synthetic substrate to mimic the stem cell niche in vitro. The side amino groups of a linear Poly-L-lysine were modified with hyperbranched poly-(ϵ-lysine) peptides, named as dendrons, tethered with the laminin-mimicking sequence, YIGSR. These dendrons presented the YIGSR sequence at the uppermost molecular branching ensuring a controlled spacing of the bioligand. When used to coat the surface of tissue culture plates in a serum-free in vitro cell culture system, the substrate was able to mimic the most relevant features of the basement membrane of the stem cell niche, i.e. the mesh structure of Collagen Type IV and the availability of laminin bioligands relevant to integrin biorecognition. The substrate biomimetic properties were tested for their ability to support the formation of human bone marrow mesenchymal stem cells (hMSCs) 3D spheroids similar to those observed in the natural stem cell niches and their ability to maintain stem cell pluripotency markers. These features were related to the substrate-specific expression and localisation of (i) cell adhesion receptors (i.e. β-integrin and N-cadherin), (ii) transcription factors of pluripotency markers and cytoskeleton protein and (iii) regulators of cell migration throughout cell culture passages 2 to 4. The results clearly demonstrate the formation of 3D spheroids starting from the asymmetric division of substrate-adhering spread cells, the clustering of relevant integrins and the expression of specific intracellular pathways controlling cytoskeleton formation suggesting their potential use as a substrate for the handling of stem cells prior to transplantation procedures.

Method for 3D fibre reconstruction on a microrobotic platform

Automated handling of a natural fibrous object requires a method for acquiring the three-dimensional geometry of the object, because its dimensions cannot be known beforehand. This paper presents a method for calculating the three-dimensional reconstruction of a paper fibre on a microrobotic platform that contains two microscope cameras. The method is based on detecting curvature changes in the fibre centreline, and using them as the corresponding points between the different views of the images. We test the developed method with four fibre samples and compare the results with the references measured with an X-ray microtomography device. We rotate the samples through 16 different orientations on the platform and calculate the three-dimensional reconstruction to test the repeatability of the algorithm and its sensitivity to the orientation of the sample. We also test the noise sensitivity of the algorithm, and record the mismatch rate of the correspondences provided. We use the iterative closest point algorithm to align the measured three-dimensional reconstructions with the references. The average point-to-point distances between the reconstructed fibre centrelines and the references are 20-30 μm, and the mismatch rate is low. Given the manipulation tolerance, this shows that the method is well suited to automated fibre grasping. This has also been demonstrated with actual grasping experiments.