ADVANCED MANUFACTURING NOW `Lauralyn McDaniel
3D Printing Adds the Fourth Dimension (Time) a D
esigning and printing a device to change over time— 4D printing—helped the University of Michigan’s CS Mott Children’s Hospital save three very young lives.
Born with tracheobronchimalacia (TBM), which causes the windpipe to collapse and prevent breathing, all three faced what could have been a short, diffi cult life. Using a combination of medical and engineering skills, the Michigan team built a splint that would hold the airway open, prevent outside compression of the airway, and bend and change as the child grew. Eventually, the splint would be ab- sorbed when its crucial job was completed. Using 3D printing, each splint was designed specifi cally for each patient. Designing the splint to change over time makes these the fi rst 4D-printed devices not only used in a patient, but shown over three years to successfully do exactly what they were designed to do. With TBM, if the child can be supported through the fi rst 24–36 months, growth generally results in a natural resolution of the disease. Using the US Food and Drug Administration’s emergency exemption for devices, the Michigan team set about developing a device that would meet all performance requirements while not causing adverse tissue reaction. The concept device was an open, bellowed cylinder with 10 design variables allowing placement of the splint around the collapsed airway via sutures through small holes. To personalize the device for each patient, the team began with multidetector CT imaging of each patient. The images and parameters were input to proprietary software to generate the bellow waves and design to submillimeter ac- curacy. The splint design was placed over a 3D model of the patient’s airway for validation. Mechanical performance of the design was ensured through fi nite element analysis. Splints were manufactured using laser sintering of two
FDA-approved materials: 96% polycaprolactone (PCL), a bio- compatible, bioresorbable polyester, and 4% hydroxyapatite (HA), a calcium phosphate, as a fl ow agent. Multiples of each splint were printed in the same build. This allowed some to be sterilized in preparation of surgery while others underwent mechanical testing to further validate performance.
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AdvancedManufacturing.org | July 2015
According to Glenn Green, MD, associate professor, otolaryngology, “This engineering design has worked as in- tended…the fi rst child to receive this implant three years ago appears to be cured of tracheobronchomalacia with a splint that has now functionally degraded.” He added, “Today, our fi rst patient Kaiba is an active, healthy 3-year-old in pre- school with a bright future.” The three case studies provide the groundwork for more use of the device. “The next step is to evaluate the airway splint in a clinical trial,” said Robert Morrison, MD, otolaryn- gology-head & neck surgery resident. “However, a clinical trial would not be possible without the design control process and initial results.”
Splints were manufactured using laser sintering of two FDA-approved materials, including a biocompatible, bioresorbable polyester.
The combination of 3D printing, bioresorbable materials, and design becomes 4D printing. Particularly for pediatrics, the ability of a device to change over time and adapt to growth could provide many opportunities for new ways to treat patients. “The splint engineering process illustrates the power of integrated patient-specifi c digital design and 3D printing, the ability to customize devices, or even develop entirely new devices for a patient’s specifi c need,” said Scott Hollister, PhD, professor of biomedical engineering and me- chanical engineering and associate professor of surgery. While 3D printing and medicine have always made sense to develop devices specifi c to a patient, the fi rst 3D-printed devices have generally been applied to rare diseases and dis- orders. The FDA is aggressively looking to develop guidance for 3D printed devices. Together with the splint case studies, expected clinical trials, the development of biomaterials, and enhanced imaging techniques may set the framework for the next era of truly personalized medicine.
SME Industry Manager, Medical Manager:
Innovation Watch, SME Technology Interchange, Medical Manufacturing Innovations
LMcDaniel@sme.org
MODERN MANUFACTURING PROCESSES, SOLUTIONS & STRATEGIES
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