An Example of the Present State of Tissue Printing
Researchers here demonstrate the ability to print simpler tissues such as muscle and bone, using a novel approach to somewhat increase the size of the tissue that can be constructed and transplanted. Size is limited by the need to supply oxygen and nutrients to cells via a blood vessel network, and reliably producing that blood vessel network in printed tissue is still an open problem:
Scientists have printed ear, bone and muscle structures. When implanted in animals, the structures matured into functional tissue and developed a system of blood vessels. Most importantly, these early results indicate that the structures have the right size, strength and function for use in humans. "This novel tissue and organ printer is an important advance in our quest to make replacement tissue for patients. It can fabricate stable, human-scale tissue of any shape. With further development, this technology could potentially be used to print living tissue and organ structures for surgical implantation."The system deposits both bio-degradable, plastic-like materials to form the tissue "shape" and water-based gels that contain the cells. In addition, a strong, temporary outer structure is formed. The printing process does not harm the cells. A major challenge of tissue engineering is ensuring that implanted structures live long enough to integrate with the body. The scientists addressed this in two ways. They optimized the water-based "ink" that holds the cells so that it promotes cell health and growth and they printed a lattice of micro-channels throughout the structures. These channels allow nutrients and oxygen from the body to diffuse into the structures and keep them live while they develop a system of blood vessels.
It has been previously shown that tissue structures without ready-made blood vessels must be smaller than 200 microns (0.007 inches) for cells to survive. In these studies, a baby-sized ear structure (1.5 inches) survived and showed signs of vascularization at one and two months after implantation. "Our results indicate that the bio-ink combination we used, combined with the micro-channels, provides the right environment to keep the cells alive and to support cell and tissue growth." Another advantage of the system is its ability to use data from CT and MRI scans to "tailor-make" tissue for patients. For a patient missing an ear, for example, the system could print a matching structure.
Link: http://www.eurekalert.org/pub_releases/2016-02/wfbm-spf021116.php