NIH-funded research successfully imitates the bone marrow environment where platelets form
Researchers funded by the National Institute of Biomedical Imaging and Bioengineering at Tufts University and their collaborators have successfully developed a 3-dimensional (3D) tissue-engineered model of bone marrow that can produce functional human platelets outside the body (ex vivo).
To begin, the researchers knew they would need a structure that could support endothelial cells, ECMs, and megakaryocytes, without adversely activating the cells or platelets. The team knew from their previous work with silk protein scaffolds that silk is a very biocompatible material that is amenable to many manipulations to customize it for a specific use, while also avoiding any cell-specific signaling. They formed silk scaffolds of different thicknesses (ranging from 2 to 5 micrometers) and stiffness combined with growth factors, to test the success of megakaryocyte adhesion and the formation of proplatelets—the parts of the megakaryocytes that fragment into platelets. When they determined the best combination of variables, the researchers attached the silk scaffolds to a plastic framework to guide the growth of cells.
Next, endothelial primary cells (EPCs) were grown on one side of the silk scaffold and megakaryocytes were seeded on the other side. (See image below) EPCs are known to secrete growth factors that help megakaryocytes mature.
In order to mimic the production environment and microvasculature, the structures through which blood flows, the researchers formed silk sponges around porous silk microtubes. The wall thickness of the microtubes was kept below 10 micrometers, which helped proplatelets migrate through the walls and release platelets. By pumping culture media, a solution filled with necessary nutrients, through the microtubes, the researchers mimicked the flow of blood. These nutrients acted as growth factors which, in addition to the EPCs, allowed the resulting silk structure to support the formation of functioning platelets.
The unique features of this model lead to significantly higher numbers of platelets generated than was previously possible; and most importantly, the platelets were functional.
“This is an elegant example of how to deconstruct a complex process into its basic elements, and then build it back up, brick by brick, to give you a basic structure you need for the product you are looking for—in this case a human platelet made to order,” said Rosemarie Hunziker, PhD, program director of Tissue Engineering at NIBIB. “The key is to provide what is necessary and sufficient for the desired outcome. Then you can add other factors (structural complexity, more growth factors, other cell types, etc.) to improve the yields. Taking this incremental approach—adding to the structure one step at a time, this group is making great strides on the path to creating therapeutic quantities of platelets on demand.”
This research was supported in part by the National Institute of Biomedical Imaging and Bioengineering award #EB016041-01.
Buduo, C. A. Di, L. S. Wray, L. Tozzi, A. Malara, Y. Chen, C. E. Ghezzi, D. Smoot, C. Sfara, A. Antonelli, E. Spedden, G. Bruni, C. Staii, L. De Marco, M. Magnani, D. L. Kaplan, and A. Balduini. "Programmable 3D Silk Bone Marrow Niche for Platelet Generation Ex Vivo and Modeling of Megakaryopoiesis Pathologies." Blood 125.14 (2015): 2254-264. Web.
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