Tissue Engineering

In recent years, the prospect of growing artificial tissue either outside or within the body has created a new biomedical field called regenerative medicine and tissue engineering. It is a research area that crosses a number of physical and life science and engineering disciplines, among them chemical engineering, bioengineering, biology, chemistry, materials science, and medicine.

The goal, according to a National Science Foundation report, “The Emergence of Tissue Engineering as a Research Field,” is to make “living replacement parts for the human body.”

Whether or not our tissue can recover from disease or injury is determined by the microenvironment of cells. This microenvironment is called the extracellular matrix. The extracellular matrix is the part of the tissue that lies outside the cells, acts as a framework to support the cells, and guides the cells in the way they grow and function as they become bones, organs, or skin. Made up primarily of fibrous glycosaminoglycans and proteins such as collagen, the extracellular matrix also facilitates signaling between cells and stores growth factors to promote healing.

Yong Wang, an associate professor of bioengineering who came to Penn State in January 2013 from the University of Connecticut, is developing unique methods to make artificial extracellular matrix in the lab. Using polymer hydrogels that mimic the structure of tissue, along with nucleic acid, a biologicallyfunctional molecule, he is trying to bring life to artificial tissue.

“People like to use hydrogel because the structure and mechanical properties are really similar to tissue,”

Wang said during a two-day visit to campus as he prepared to move his family from Connecticut to State College this summer. “But hydrogels themselves are not enough, because most of them have no biological function or lack critical functions. Therefore the second component in our system is nucleic acid, and more specifically nucleic acid aptamers.”

Cells need to communicate with their surrounding environment and do so with receptors on the cell surface. The nucleic acid aptamers are engineered to recognize cell receptors and a variety of other biomolecules. By adding the aptamers to the hydrogel, which is a network of polymers that is 90 percent water, the hydrogel can communicate with the cells.

schematic illustrationIn the past, the vast majority of people trying to make this type of biomimetic system have tried to chemically incorporate peptides into hydrogel to make extracellular matrix. Peptides are chains of amino acids that make up protein, and in nature, protein makes up collagen, and parts of collagen can communicate with cells. “This approach has two major issues. On one hand, most peptides do not bind to cell receptors or soluble signaling molecules with high strength. On the other hand, though some of them may bind to their targets strongly, the strong binding cannot be reversed when needed,” Wang explained. His lab has developed a method to allow the aptamer to be incorporated to the hydrogel until a trigger changes the aptamer and it releases signaling molecules or cells from the hydrogel without damage. The hydrogel can then be reused.

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