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additive in medical


make it diffi cult to fabricate structures with enough strength to form a clinically applicable size. Our hybrid system can concurrently print a synthetic biopolymer to provide physical strength and a cell-laden hydrogel to promote regeneration.


What Makes the Ideal Biomaterial? As scientists move away from hand-fashioning scaffolds to bioprinting them, additional biomaterials will need to be identifi ed. The material must not only be printable, but also must be compatible with the body and support cellular at- tachment, proliferation and function. Also important is how quickly the material will degrade in the body. The degradation rates of the scaffold must match the cells’ activity in building a “home” from their own extracellular matrix, the molecules they secrete to provide structural and biochemical support. In addition, material selection must be based on the mechanical properties needed for a particular structure. Dif- ferent structural requirements will be needed for tissue types ranging from skin to liver and bone.


3D Bioprinting: The Future While numerous biologic tissues have been printed and


Instructor Hyun-Wook Kang oversees the 3D printer that will be used to print miniature organs for the Body on a Chip system.


used to make a noncellular, bioabsorbable trachea splint that saved a young child’s life.


These printers consist of a pulsed laser beam, a focusing system and a “ribbon” that has a donor transport support, a layer of biological material and a receiving substrate facing the ribbon. Focused laser pulses are used to generate a high- pressure bubble that propels cell-containing materials toward the collector substrate.


Because the technology is laser free, there is no problem with cell clogging. Other advantages are that the printer is compatible with a range of viscosities, can deposit cells at high density and can print mammalian cells with little effect on viability. Disadvantages include that the high resolution results in a low overall fl ow rate, it can be diffi cult to accu- rately target and position cells and that metallic residues are present in the fi nal construct. While some of these challenges can be overcome, it is currently unclear whether this system can be scaled up for larger tissue sizes. To overcome the disadvantages of relying solely on the cell-laden hydrogels used in most 3D printers, our institute has developed a hybrid system. Using hydrogels alone can


tested pre-clinically, challenges remain to further develop and harness 3D printing technologies for more complex tissues and organs. As scientists move away from modifying existing printers and begin to design new technologies, the range of materials can be extended and methods to deposit materi- als and cells with increasing precision and specifi city can be developed.


Areas for future focus include:


• Developing new biocompatible materials with sufficient mechanical strength to maintain their shape and with- stand external stress after implantation.


• Improving printer resolution. Complex organs such as kidney and liver have a detailed inner architecture that must be duplicated.


• Developing methods to vascularize and innervate printed engineered tissue and organs, especially complex volu- metric organs. While some groups have demonstrated generation of a branched vascular tree, a challenge is the time required for assembly and maturation.


• Increase the speed of printing. Currently, conditions that increase printing speed, such as with the extrusion- based bioprinter, can lead to cell damage.


• Develop in vivo bioprinting to regenerate tissues im- mediately after injury or during surgery. For example, 3D bioprinters can potentially be integrated into minimally invasive robotic surgical tools so that tissues can be removed and replaced during the same surgery.


66 — Medical Manufacturing 2015


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