1. Development of artificial stem cell niches
Presumably the best characterized adult stem cell system in humans is the hematopoietic stem cell niche. This niche system is influenced by a large number of factors with different impact on the maintenance and differentiation of hematopoietic stem cells (fig. 1). A large number of models is already trying to recapitulate the physiologic characteristics of the niche but due to the complexity of the system with different emphasis on (a) certain parameter(s). The group 3D-cell culture systems has developed an own approach that primarily focuses on three-dimensionality and cell-cell-contact aspects.
Fig. 1: Hematopoietic stem cells and their niches in human bone marrow. (With permission of the Nature Publishing Group, Licence-no: 4143030739379).
The basis of most of the work is built by the socalled microcavity arrays (fig. 2). The polymer film-based 3D-cell culture substrates unite many advantages, that can be realized by the manufacturing process called SMART (Surface Modification And Replication by Thermoforming).
Fig. 2: Left: Schematic design of a microcavity array. Right: Scanning electron microscopic image of a porous microcavity, as manufactured with the SMART process.
On the basis of these systems the group 3D-cell culture systems is aiming at building an artificial, hematopoietic stem cell niche that is able to manipulate the HSC behaviour. By incorporating the microcavity arrays in microbioreactors (fig. 3), it could be shown that CD34+ cells over a period of 14 days not only maintained the expression of relevant stem cell markers and formed nearly all colonies that can be expected from freshly isolated cells, but moreover, that the HSC pool can be expanded.
Fig. 3. Left: Microbioreactor with microcavity array as an artificial stem cell niche for the culture of hematopoetic stem cells. Right: Co-culture of mesenchymal stem cells and cells of the mononuclear fraction in a microcavity. Blue = nuclei, green = vimentin.
In a recent paper in Bioengineering ((https://www.mdpi.com/2306-5354/6/2/50/htm) we could demonstrate that the fate of single cells in microcavities can be followed over time (4D-cell culture platform). We have analysed the migration and proliferation behaviour of an ALL-line (KG-1a) and hematopoeitic stem cells depending on the local microenvironment (different co-cultures).
Fig. 4: (A) Distribution of hHSCs in microcavities after day 1 of co-culture. Scale bar: 200 μm. (B) Distribution of hHSCs in microcavities after day 14 of co-culture. (C) Distribution of hHSCs in microcavities atfer day 21 of co-culture. White arrowheads point to CD34+ cells.