Dramatic advances in the fields of biochemistry, cell and molecular biology, genetics, biomedical engineering and materials science have given rise to the remarkable new cross-disciplinary field of tissue engineering. Tissue engineering uses synthetic or naturally derived, engineered biomaterials to replace damaged or defective tissues, such as bone, skin, and even organs.
Several technologies come together in tissue engineering. Large-scale culturing of human or animal cells—including skin, muscle, cartilage, bone, marrow, endothelial and stem cells—may provide substitutes to replace damaged components in humans. Naturally derived or synthetic materials may be fashioned into “scaffolds” that when implanted in the body—as temporary structures—provide a template that allows the body’s own cells to grow and form new tissues while the scaffold is gradually absorbed. Biocompatible polymers may be developed to cover implants and shield them from adhesion of circulating proteins that initiate rejection responses. Transgenic animals may provide a source of cells, tissues, and organs for xenografts.
Tissue engineering potentially offers dramatic improvements in medical care for hundreds of thousands of patients annually, and equally dramatic reductions in medical costs. Organ transplants alone present many opportunities because of the significant shortage of donor organs. More than 10,000 people have died during the past five years while waiting for an organ transplant. Infectious agents such as hepatitis C and HIV further complicate the organ transplants, and recipients generally must remain on costly immunosuppressive drugs for the balance of their lives. Outcome studies have shown that the survival rates for major organ transplants are poor despite their high cost. “Engineered” replacement organs could sidestep many of the hazards and problems associated with donor organs, and at lower cost.
Other equally promising applications include replacement of lost skin due to severe burns or chronic ulcers; replacement or repair of defective or damaged bones, cartilage, connective tissue, or intervertebral discs; replacement of worn and poorly functioning tissues such as aged muscles or corneas; replacement of damaged blood vessels; and restoration of cells that produce critical enzymes, hormones, and other metabolites.
Organovo developed the so called “bio-Printer” technology through a partnership with Invetech, a Melbourne, Australia-based engineering design company. The bio-printer is designed to fit inside a standard biosafety cabinet for sterile use, and uses two print heads—one for precisely depositing human tissue cells, the other for depositing a jello-like hydrogel that provides both structural support and nutrients for the human tissue cells. Although the machine operates much like an inkjet printer that uses tissue cells instead of ink, it is conceptually more like a 3D rapid prototyping machine.
By using the 3D bio-printer, scientists and engineers can place cells of almost any type into a desired pattern in three dimensions. Researchers can place liver cells on a preformed scaffold, support kidney cells with a co-printed scaffold, or form adjacent layers of epithelial and stromal soft tissue that grow into a mature tooth. To run it, an operator types instructions into a computerized controller, which guides the automated laser-calibrated print heads. Creating a 5-cm blood vessel (almost 2 inches long) takes about one hour.
The technology is open to any cell type. If technology is developed to use induced pluripotent stem cells to create organs, then these bioprinters could also be designed to make use of this potential as well.