What is 3D printing?
3D printing is the process of printing a three-dimensional object from a computer-generated model. It utilizes an additive process whereby successive layers of materials are laid upon each other in a sequential manner and a solid 3D object is "printed" to life. One can print simple objects such as toys, coffee cups, etc. or extremely complex ones such as electronic devices, bicycles, guns and human organs like kidneys, heart and bladder. Highly sophisticated 3D printers lay down layers of "ink"—which can consist of paper, powders, liquids, metal alloys, plastic, polymers and even living cells—to generate anything that can be 3D modeled on a computer. All one needs is a computer model describing the digital cross-sectional blueprint of the object to be printed.
Bioprinting refers to the technologies whereby living cells are layered by the additive process yielding highly complex three-dimensional human tissues or organs. The ink used for printing tissues/organs consists of live cells that are delivered from the nozzle of a print-head, building up layer after layer of cells to create a complex 3D structure of a human tissue or organ. Bioprinting is a promising alternative to narrow the gap of the growing demand for human tissue and organs.
Traditional tissue engineering methods, where an organ is "grown" in a petri dish, have had considerable success for avascular, thin organs such as bladders and skin; however, highly vascular tissues, thick solid organs such as kidney, liver, and heart still remain a challenge. With 3D bioprinting, we are one step closer to literally printing out organs for patient implants.
Challenges to printing a functional tissue or organ
Cell viability: To bioprint functional tissues/organs for implants, one must ensure that the "printed" cells survive the processing and printing steps. These living cells are exposed to a wide variety of culture conditions, temperatures, and extracellular milieu before, during, and after the printing steps. It is especially challenging for cells types such as neurons, hepatocytes, and pancreatic cells to survive these extreme conditions. Damage to the cell membrane and subsequent cell death has to be restricted to less than 5-10 % total cells to print functional tissues/organs for implants.
Vascularity: Vascularity is currently by far the most challenging technical hurdle in the field of bioprinting. For successful utilization of bioengineered human tissues/organs for implants, they must have a built-in vascular architecture consisting of a complex network of highly branched blood vessels. Scientists are currently testing a number of state-of-the-art approaches to address this challenge.
3D details: Each tissue/organ system contains multiple types of cells, arranged in a very intricate three-dimensional network, coordinating and serving a complex set of functions. It is relatively easy to generate digital models for simple tissues/organs such as cartilage, bladder, or skin. However, the structural complexity of organs such as the brain, heart, and kidney makes it extremely challenging to recapitulate the exact 3D biological details of these organs.
Network activity: Cell-cell interactions play a major role in the biological function of tissues and organ systems; for example, neurons and the human brain. Once the cells have been printed, given the optimum growth conditions, the cells should self-organize into a network to form a functional and usable bioactive implant. Cells within thick, vascular tissues such as heart, brain and kidney require a vast variety of growth factors and signaling factors to help them integrate into a functional network after printing. This final step of networking also depends on the previously mentioned factors: overall cell viability, vascularity, and 3D details of the printed construct.
Future of 3D printing
The cost of 3D-printers has dropped dramatically from the $10,000-$20,000 range in the last decade to $1,000-$2,000 over the last couple of years. 3D printing has already found a place for itself in the consumer market with a number of vendors selling printers and digital models to print toys, coffee mugs, phone safety covers, etc. What else can we expect from 3D printing?
Food: Scientists at MIT have been able to use this technology to print food. Yes—food! The printed food has the same texture and flavor as "real" food. This innovation can save cooking time and control the nutritive value of the food to personalize cooking.
Industrial applications: Additive 3D printing takes only a few hours. Hence from an industrial manufacturing standpoint, 3D printing provides a unique advantage since it can enable, for the first time ever, rapid mass production along with personalized customization.
Personalized medicine: Doctors can obtain the patient"s own cells or specific cell populations, grow them in culture, bioprint the tissues/organs, and implant them. Since the implanted construct was printed using the patient"s cells, organ incompatibility might no longer be a problem. Bioprinting could also be combined with gene transfection and drug delivery during tissue/organ printing to provide therapeutic delivery of modified cells.
Bioprinting directly on the patient: 3D printing might be used for direct tissue repair on patients. Patient wounds will be scanned, 3D modeled, and wounds would be directly printed upon with layers of cells, growth factor, and biomaterial scaffold required to repair the lesions.
Is 3D printing the next big thing after the Internet? Will it revolutionize the consumer market and the way we practice medicine? The future will tell, but as of right now 3D printing is already revolutionizing medicine. 3D printing has the potential to revolutionize the consumer market. However, it comes with new challenges!
Intellectual property and regulatory questions
In the future, we could be living in a world where one could simply download a single file from the Internet and print themselves an electronic device, a car, a gun or bullets. As of right now, working plastic guns and bullets have already been printed and used for experimental purposes. We will have to deal with intellectual property protection issues and regulatory/legal aspects of making 3D printing available for domestic purposes. Currently, only a couple of legal steps have been taken to protect original designs from unauthorized copying. However, the more 3D printing permeates the consumer market, the more pressing these regulatory issues will become.
The 3D printing possibilities are limitless, and our ability to print will only be limited by our imagination!