Stem cells 2013 July-33

 

Three-dimensional structural niches engineered via two-photon laser polymerization promote stem cell homing.

Acta Biomater. 2013 Jan;9(1):4579-84.

Raimondi MT, Eaton SM, Laganà M, Aprile V, Nava MM, Cerullo G, Osellame R.

LaBS, Department of Structural Engineering, Politecnico di Milano, Milano 20133, Italy. manuela.raimondi@polimi.it

Abstract

A strategy to modulate the behavior of stem cells in culture is to mimic structural aspects of the native cell/extracellular matrix interaction. We applied femtosecond laser two-photon polymerization (2PP) to fabricate three-dimensional (3-D) microscaffolds, or “niches”, using a hybrid organic-inorganic photoresist called SZ2080. The niches, of sizes fitting in a volume of 100×100×100 μm(3), were made by an external containment grid of horizontal parallel elements and by an internal 3-D lattice. We developed two niche heights, 20 and 80-100 μm, and four lattice pore dimensions (10, 20, 30 μm and graded). We used primary rat mesenchymal stem cells (MSCs) to study cell viability, migration and proliferation in the niches, up to 6 culture days. MSCs preferentially stayed on/in the structures once they ran into them through random migration from the surrounding flat surface, invaded those with a lattice pore dimension greater than 10 μm, and adhered to the internal lattice while the cell nuclei acquired a roundish morphology. In the niches, the highest MSC density was found in those areas where proliferation was observed, corresponding to the regions where the scaffold surface density available for cell adhesion was highest. The microgeometry inducing the highest cell density was 20 μm high with graded pores, in which cell invasion was favored in the central region of large porosity and cell adhesion was favored in the lateral regions of high scaffold surface density. Cell density in the niches, 17±6 cells/(100×100 μm(2)), did not significantly differ from that of the flat surface colonies. This implies that MSCs spontaneously homed and established colonies within the 3-D niches. This study brings to light the crucial role played by the niche 3-D geometry on MSC colonization in culture, with potential implications for the design of biomaterial scaffolds for synthetic niche engineering. Copyright © 2012 Acta Materialia Inc.

PMID: 22922332

 

Supplementary picture

 

Manuela Teresa Raimondi-2

Two-photon laser polymerization leads the way to artificial stem cell niches.

To understand how microtopology of the matrix affects mesenchymal stem cell (MSC) proliferation and phenotype maintenance, researchers from Politecnico di Milano and National Research Council (CNR) in Italy have developed a functionalized microscaffold platform. The platform was prepared by an ultra-precise microfabrication technique called two-photon laser polymerization (2PP). Using such a platform, they have demonstrated that the topography of the microscaffolds leads to spontaneous homing, and synergistically improves the self-renewal and maintenance of pluripotency of rat bone marrow-derived MSC.

A unique three-dimensional (3D) microtopology of these microscaffolds supported the highest level of expansion of mesenchymal stem cells, compared with several other topologies tested and compared with standard tissue culture methods. Further work in progress shows that these “mechano-topologically” functionalized microscaffolds provide isotropic anchorage for stem cells and enhance their phenotype maintenance.

The 2PP technology used to fabricate the artificial niches proved satisfactory with regards to material biocompatibility, reduced auto-fluorescence and mechanical properties in relation to their application in advanced cell culture substrates.  Artificial niches were able to increase cell density by 70% with respect to standard culture substrates, by providing increased surface-to-volume ratios and space for stem cells to adhere and renew, respectively.

These very innovative findings published on Acta Biomaterialia suggest that one potential application of the synthetic niches could be to expand MSC to produce therapeutic cell doses, by exploiting the ability of these niches to increase cell renewal while maintaining cell pluripotency in the structured culture layer.

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