Medical Applications for 3D Printing: Current and Projected Uses C. Lee Ventola, MS INTRODUCTION files, allowing the creation of complex, customized anatomical Medical applications for 3D printing are expanding rapidly and medical structures (Figure 2).3,5,10 and are expected to revolutionize health care.1 Medical uses for 3D printing, both actual and potential, can be organized THE HISTORY OF 3D PRINTING into several broad categories, including: tissue and organ Charles Hull invented 3D printing, which he called “ste- fabrication; creation of customized prosthetics, implants, and reolithography,” in the early 1980s.1 Hull, who has a bach- anatomical models; and pharmaceutical research regarding elor’s degree in engineering physics, was working on making drug dosage forms, delivery, and discovery.2 The application plastic objects from photopolymers at the company Ultra Violet of 3D printing in medicine can provide many benefits, includ- Products in California.6 Stereolithography uses an .stl file format ing: the customization and personalization of medical products, to interpret the data in a CAD file, allowing these instructions drugs, and equipment; cost-effectiveness; increased produc- to be communicated electronically to the 3D printer.6 Along tivity; the democratization of design and manufacturing; and with shape, the instructions in the .stl file may also include enhanced collaboration.1,3-6 However, it should be cautioned information such as the color, texture, and thickness of the that despite recent significant and exciting medical advances object to be printed.6 involving 3D printing, notable scientific and regulatory chal- Hull later founded the company 3D Systems, which developed lenges remain and the most the first 3D printer, called a “ste- transformative applications reolithography apparatus.” 6 In for this technology will need 1988, 3D Systems introduced time to evolve.3-5,7 the first commercially avail- able 3D printer, the SLA-250.6 WHAT IS 3D PRINTING? Many other companies have Three-dimensional (3D) since developed 3D printers printing is a manufacturing for commercial applications, method in which objects such as DTM Corporation, are made by fusing or Z Corporation, Solidscape, depositing materials—such and Objet Geometries.6 Hull’s as plastic, metal, ceramics, work, as well as advances powders, liquids, or even made by other researchers, living cells—in layers to has revolutionized manufac- produce a 3D object.1,8,9 This Figure 1 A 3D printer uses instructions in a digital file to create turing, and is poised to do the process is also referred to as a physical object.12 same in many other fields— additive manufacturing (AM), including medicine.6 rapid prototyping (RP), or solid free-form technology (SFF).6 Some 3D printers are similar to traditional inkjet printers; OVERVIEW OF CURRENT APPLICATIONS however, the end product differs in that a 3D object is pro- Commercial Uses duced.1 3D printing is expected to revolutionize medicine and 3D printing has been used by the manufacturing industry other fields, not unlike the way the printing press transformed for decades, primarily to produce product prototypes.1,9 Many publishing.1 manufacturers use large, fast 3D printers called “rapid prototyping There are about two dozen 3D printing processes, which machines” to create models and molds.11 A large number of .stl use varying printer technologies, speeds, and resolutions, files are available for commercial purposes.1 Many of these printed and hundreds of materials.9 These technologies can build objects are comparable to traditionally manufactured items.1 a 3D object in almost any shape imaginable as defined in a Companies that use 3D printing for commercial medical appli- computer-aided design (CAD) file (Figure 1).9 In a basic setup, cations have also emerged.2 These include: Helisys, Ultimateker, the 3D printer first follows the instructions in the CAD file and Organovo, a company that uses 3D printing to fabricate to build the foundation for the object, moving the printhead living human tissue.2 At present, however, the impact of 3D along the x-y plane.5 The printer then continues to follow printing in medicine remains small.1 3D printing is currently the instructions, moving the printhead along the z-axis to a $700 million industry, with only $11 million (1.6%) invested build the object vertically layer by layer.5 It is important to in medical applications.1 In the next 10 years, however, 3D note that two-dimensional (2D) radiographic images, such as printing is expected to grow into an $8.9 billion industry, with x-rays, magnetic resonance imaging (MRI), or computerized $1.9 billion (21%) projected to be spent on medical applications.1 tomography (CT) scans, can be converted to digital 3D print Disclosures: The author reports no commercial or financial relation- The author is a consultant medical writer living in New Jersey ships in regard to this article. 704 P&T® • October 2014 • Vol. 39 No. 10 Medical Applications for 3D Printing: Current and Projected Uses one, to form the object.11 Laser sintering can be used to create metal, plastic, and ceramic objects.11 The degree of detail is limited only by the precision of the laser and the fineness of the powder, so it is possible to create especially detailed and delicate structures with this type of printer.11 Thermal Inkjet Printing Inkjet printing is a “noncontact” technique that uses thermal, electromagnetic, or piezoelectric technology to deposit tiny droplets of “ink” (actual ink or other materials) onto a substrate according to digital instruc- tions.10 In inkjet printing, droplet deposition is usually done by using heat or mechanical compression to eject 10 Figure 2 Radiographic images can be converted to 3D print files to the ink drops. In TIJ printers, heating the printhead create complex, customized anatomical and medical structures.12 creates small air bubbles that collapse, creating pres- sure pulses that eject ink drops from nozzles in volumes Consumer Uses as small as 10 to 150 picoliters.10 Droplet size can be 3D printing technology is rapidly becoming easy and inexpen- varied by adjusting the applied temperature gradient, pulse sive enough to be used by consumers.9,11 The accessibility of frequency, and ink viscosity.10 downloadable software from online repositories of 3D printing TIJ printers are particularly promising for use in tissue engi- designs has proliferated, largely due to expanding applications neering and regenerative medicine.10,13 Because of their digital and decreased cost.2,4,11 It is now possible to print anything, from precision, control, versatility, and benign effect on mammalian guns, clothing, and car parts to designer jewelry.2 Thousands cells, this technology is already being applied to print simple of premade designs for 3D items are available for download, 2D and 3D tissues and organs (also known as bioprinting).10 many of them for free.11 TIJ printers may also prove ideal for other sophisticated uses, Since 2006, two open-source 3D printers have become avail- such as drug delivery and gene transfection during tissue able to the public, Fab@Home (www.fabathome.org) and construction.10 RepRap (www.reprap.org/wiki/RepRap).6,9 The availability of these open-source printers greatly lowered the barrier of Fused Deposition Modeling entry for people who want to explore and develop new ideas FDM printers are much more common and inexpensive for 3D printing.9 These open-source systems allow anyone than the SLS type.11 An FDM printer uses a printhead similar with a budget of about $1,000 to build a 3D printer and start to an inkjet printer.11 However, instead of ink, beads of heated experimenting with new processes and materials.9 plastic are released from the printhead as it moves, building This low-cost hardware and growing interest from hobbyists the object in thin layers.4,11 This process is repeated over and has spurred rapid growth in the consumer 3D printer market.11 over, allowing precise control of the amount and location of A relatively sophisticated 3D printer costs about $2,500 to each deposit to shape each layer.4 Since the material is heated $3,000, and simpler models can be purchased for as little as as it is extruded, it fuses or bonds to the layers below.4 As each $300 to $400.8,11 For consumers who have difficulty printing layer of plastic cools, it hardens, gradually creating the solid 3D models themselves, several popular 3D printing services object as the layers build.11 Depending on the complexity and have emerged, such as Shapeways, (www.shapeways.com), cost of an FDM printer, it may have enhanced features such Thingiverse (www.thingiverse.com), MyMiniFactory (www. as multiple printheads.11 FDM printers can use a variety of myminifactory.com), and Threeding (www.threeding.com).11 plastics.11 In fact, 3D FDM printed parts are often made from the same thermoplastics that are used in traditional injection COMMON TYPES OF 3D PRINTERS molding or machining, so they have similar stability, durability, All 3D printing processes offer advantages and disadvan- and mechanical properties.4 tages.3 The type of 3D printer chosen for an application often depends on the materials to be used and how the layers in the BENEFITS OF 3D PRINTING finished product are bonded.11 The three most commonly used IN MEDICAL APPLICATIONS 3D printer technologies in medical applications are: selective Customization and Personalization laser sintering (SLS), thermal inkjet (TIJ) printing, and fused The greatest advantage that 3D