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Posted: Jul 20, 2011

Nanopatterned surface maintains stem cells' long-term viability and phenotype

(Nanowerk Spotlight) Mesenchymal stem cells (MSC) are adult stems cells found in bone marrow which can be differentiated into bone, cartilage, fat, and connective tissues. These cells offer tremendous potential for the repair and regeneration of damaged tissues and organs. And, unlike embryonic stem cells, the use of adult stem cells in research and therapy is not controversial because the production of adult stem cells does not require the creation or destruction of an embryo. However, the demand for autologous, patient-specific stem cells for regenerative therapies outstrips their supply.
Currently, when adult stem cells are harvested from a patient, they are cultured in the laboratory to increase the initial yield of cells and create a batch of sufficient volume to kick-start the process of cellular regeneration when they are re-introduced back into the patient. The process of culturing is made more difficult by spontaneous stem cell differentiation, where stem cells grown on standard plastic tissue culture surfaces do not expand to create new stem cells but instead create other cells which are of no use in therapy.
At the moment, stem cell expansion is often boosted by immersing the cells in chemical solutions which help to increase the overall yield of stem cells but are limited in their effectiveness.
New findings by researchers in the UK now show that nanoscale patterning is a powerful tool for the non-invasive manipulation of stem cells. Their facile fabrication process employed – a range of thermoplastics that can be processed with exquisite reproducibility down to 5 nm fidelity using injection moulding approaches – offers unique potential for the generation of cell culture platforms for the up-scale of autologous cells for clinical use.
Reporting their work in the July 17, 2011 online edition of Nature Materials ("Nanoscale surfaces for the long-term maintenance of mesenchymal stem cell phenotype and multipotency") the team demonstrates the use of a nanotopographic surface to control and maintain mesenchymal stem cell characteristics in long-term cultures.
The researchers fabricated a nanoscale growth substrate by electron beam lithography and processed it into thermoplastic polycaprolactone (PCL) by hot embossing or used injection moulding for samples in polycarbonate (PC) and polystyrene (PS). This surface can maintain functional MSCs in culture for up to eight weeks and, importantly, also retains stem-cell phenotype during that period.
A stem cell makes adhesions to the new
A stem cell makes adhesions (shown in green) to the new "nano-patterned" plastic surface. (Image: Nikolaj Gadegaard, University of Glasgow)
"Our results are built on a facile platform which has the short term potential to be commercialized as a general cell culture consumable," Nikolaj Gadegaard, a Senior Lecturer in Biomedical Engineering at the University of Glasgow, and co-author of the Nature Materials paper, tells Nanowerk. "And we are indeed in the process of doing just so. We have used electron beam lithography, best known for making computer chips, to pattern a master substrate with arrays of 120 nm pits in the surface. This master substrate can then be used in an injection moulding machine to produce thousands of identical polymer samples for cell culture."
The injection moulding approach is very similar to the manufacture of CDs, DVDs and Blu-Rays. When mesenchymal stem cells, which can be obtained from bone marrow aspirates, are cultured on these nanopatterned surfaces we are able to maintain their phenotypic characteristics such as multipotency over long culture periods. In contrast, cells cultured on regular flat surfaces found in Petri dishes, cells rapidly loose their multipotent properties effectively rendering them useless for stem cell experiments or clinical use.
"Prior to our results, it has been possible to maintain the stem cell characteristics albeit only using cocktails of different molecules, with a number of associated problems" explains Gadegaard. "Thus our work shows for the first time the ability to expand and maintain stem cells which has implications for both basic research and clinical use. If the same process can be used to culture other types of stem cells too, and this research in under way in our labs, our technology could be the first step on the road to developing large-scale stem cell culture factories which would allow for the creation of a wide range of therapies for many common diseases such as diabetes, arthritis, Alzheimer's and Parkinson's diseases."
The research is a result of an interdisciplinary collaboration between Glasgow (Gadegaard and Matthew Dalby) and Southampton (Richard Oreffo) Universities and has been funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the University of Glasgow. The team, is very excited about the potential applications of the technology and they are already in the early stages of conversations to make the surface commercially available.
A few years ago, the researchers already published a paper in Nature Materials ("The control of human mesenchymal cell differentiation using nanoscale symmetry and disorder"), demonstrating that the use of nanotopography could be used to specifically differentiate mesenchymal stem cell to bone forming cells.
"We think that this is just the tip of the iceberg showing the importance of surface topography in the regulation of stem cell fate" says Gadegaard. "The simplicity of the process makes it adaptable to both cell culture in the lab and clinical applications for improved medical implants. The challenge for the latter will be to provide the patterns in 3D but we are also addressing that at the moments in our labs."
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