Naturally grown tissues are intricately structured, and the physical properties of tissue derive from the patterning of cells and their behavior in generating a supporting extracellular matrix. This natural complexity ensures that there is still a great deal of work to be accomplished when it comes to the 3-D bioprinting of functional tissue structures; not all tissues can be produced using the current state of the art systems, or at least not in a useful state. The work here is an example of the sort of incremental advance needed to produce tissues that are closer in form and function to those growing naturally inside bodies.
The 3-D-printing method, which took two years to research, involves taking stem cells from the patient's own body fat and printing them on a layer of hydrogel to form a tendon or ligament which would later grow in vitro in a culture before being implanted. But it's an extremely complicated process because that kind of connective tissue is made up of different cells in complex patterns. For example, cells that make up the tendon or ligament must then gradually shift to bone cells so the tissue can attach to the bone. "This technique is used in a very controlled manner to create a pattern and organizations of cells that you couldn't create with previous technologies. It allows us to very specifically put cells where we want them."
To do that, the team used a 3-D printer typically used to print antibodies for cancer screening applications. The researchers developed a special printhead for the printer that can lay down human cells in the controlled manner they require. To prove the concept, the team printed out genetically-modified cells that glow a fluorescent color so they can visualize the final product. The technology is initially designed for creating ligaments, tendons and spinal discs, but in the future it could be adapted to any type of tissue engineering application, such as the 3-D printing of whole organs, an idea researchers have been studying for years.