APRIL 2022 | The Surgical Technologist | 173 osseous ingrowth.72 Furthermore, the material of the scaffold is integral to maintaining cell viability and facilitating osteogenic differentiation.61 Calcium phosphate is one of the most commonly used materials for 3D-printed bone scaffolds and has gained attention for its superior biodegradability. Ogose et al73 reported that nearly all of the tricalcium phosphate implanted in bone defects after the excision of bone tumors were absorbed and replaced with newly formed bone, whereas HA did not demonstrate any biodegradation. The bioprinting process is a threat to the viability of the cells because they must endure the pressure and shear stress of the printing process and then manage to migrate and proliferate appropriately while receiving sufficient blood supply.74 For this reason, long-term viability of bioprinted cells has become a major concern, yet 3D bioprinting remains an exciting new technology that has countless applications for orthopaedic surgeons. Four-dimensional Printing Four-dimensional (4D) printing uses the same set of technologies as 3D printing but adds in one more dimension by allowing the printed part to change shape over time in response to a specific environment. Although similar to 3D bioprinting, this process uses smart materials to create self-reconfigurable proteins, tissue, and organs.75 Four-dimensional printed objects can selfrepair or self-assemble by changing or reshaping their parts in response to varying environmental conditions (eg, temperature, pH, magnetic field, and solvent interaction). For example, photothermal-responsive shape memory bone tissue engineering scaffolds were constructed and exposed to near-infrared radiation before implantation so that they could be easily molded and configured into a bony defect. After implantation, the temperature rapidly decreased to 37 degrees Celsius, at which temperature the scaffold displayed mechanical properties analogous to those of cancellous bone. This method was successful in treating irregularly sized rat cranial bone defects with improved new bone formation observed.76 Summary Three-dimensional printing is an exciting technology that is pervasive in every major industry. This rapidly advancing field has created access to almost limitless 3D structures created from a growing variety of materials, including metals, plastics, and even living cells. The benefits of 3D printing include extreme flexibility to customize shapes, increased intricacy/complexity of manufactured products, elimination of assembly steps, and waste and inventory reduction. In general, disadvantages of 3D printing are similar to those of any new technology and include cost and lack of data, both of which are important to the economically strapped and litigious medical field regarding custom medical implants. However, patient-specific 3D-printed implants offer a new technology to successfully treat a variety of pathologies in orthopaedic surgery. Three-dimensional printing technology will continue to advance and improve patient care and satisfaction. References 1. Lal H, Patralekh MK: 3D printing and its applications in orthopaedic trauma: A technological marvel. 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ANZ J Surg 2016;86:648-653. 14. Frame M, Huntley JS: Rapid prototyping in orthopaedic surgery: A user’s guide. ScientificWorldJournal 2012;2012:838575. Journal of the AAOS Global Research & Reviews® ----- April 2021, Vol 5, No 4 ----- © American Academy of Orthopaedic Surgeons 9 Review Article Colleen M. Wixted, BS, et al
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