Five-year grant to enable further study of tissue engineering and capillary vessel growth
Andrew Putnam, Ph.D., assistant professor of biomedical engineering and chemical engineering and materials science at the
Putnam’s laboratory, Cell Signaling in Engineered Tissues (CSET), focuses on the extracellular matrix (ECM), a complex composite of proteins and polysaccharides that constitutes all of the noncellular components of tissues in the human body. The CSET lab’s research centers on the global hypothesis asserting that expanding on the fundamental understanding of the interactions between cells and the ECM is essential to designing instructive materials that can direct cell function in engineered tissues.
“In tissue engineering, clinical success has been achieved in thin tissues, like skin, or avascular tissues, like cartilage, because diffusion of oxygen and other nutrients is sufficient to sustain the cells in these tissues” Putnam said. “With larger, more complex tissues, capillary vessels are needed to distribute nutrients. Engineering these vessels remains the most significant challenge in our field, one that our lab hopes to address by understanding the ECM’s role in capillary development.”
Better understanding the ECM’s function could have important implications in treating diseases in which capillary growth is improperly regulated, such as cancer, and may have an impact on efforts to engineer many different tissues, including bone and cardiac muscle.
During this research project, the CSET lab will use a novel “biosynthetic” hybrid biomaterial system containing a backbone of fibrinogen, or a natural protein involved in blood clotting, which is held together cross-linked with a synthetic polymer called polyethylene glycol, or PEG. An important feature of this material is that the fibrinogen backbone can be digested by new cell growth, an action required for capillary development to progress. In addition, the synthetic PEG cross-links provide a means to control the physical properties of the material in a way that would not otherwise be possible with purely biological components. The ability of this material to mimic the native ECM and support capillary growth in 3-D tissue constructs will be addressed as well.
Putnam’s CAREER proposal also includes an educational component modeled after the common “see one, do one, teach one” educational paradigm in order to engage students from the middle school to the post-graduate levels. The educational plan will promote the importance of mathematic, chemical, and physical principles, the foundations of engineering science, in addressing questions of biomedical relevance.
Over the five-year project period, an interconnected network of students will assist in the development of web- and streaming media-based educational tools to create a “virtual tissue engineering lab” that will be a featured element of Putnam’s outreach efforts. These tools will demonstrate how math and science intersect with medicine and engineering, and thereby encourage students to consider career options in math and science fields.
Figure 1: Capillary morphogenesis involves endothelial cells proteolytically invading through the 3-D extracellular matrix. Here, the matrix is labeled in green, the nuclei of multiple endothelial cells in blue, and their actin cytoskeleton in red (Scale bar = 20 microns).
Figure 2: The funded studies will explore capillary morphogenesis in a new PEGylated fibrinogen biomaterial pictured here. (1.) Fibrinogen is dissociated into its representative alpha, beta, and gamma chains and then (2.) PEGylated at specific cysteine residues. (3.) Acrylated end groups on PEG are then linked to form a hydrogel network via UV photopolymerization.
Figure 3: Human endothelial cells expressing green fluorescent protein radiate from a microcarrier bead to form capillary-like structures in a 3-D hydrogel matrix. (Scale bar = 250 microns)