3D Printing With Synthetic Scaffolds
Researchers in China have used the concept of 3D printing for biomedical purposes, specifically fabrication of an artificial vertebral body.
The role of three-dimensional (3D) printing with synthetic carriers was presented by Alan Dang, MD. Dr. Dang is an Assistant Professor in the Department of Orthopaedic Surgery at the University of California at San Francisco. His presentation was made during the North American Spine Foundation's Biologic Interventions for Spinal Pathologies: Stem Cells, Growth Factors and Novel Therapeutics course.
3D printing is a new technology and, at this time, the literature is very limited. 3D printing is called additive manufacturing, and is categorized as rapid prototyping. "This is technology that can quickly fabricate a physical object using 3D imaging data," stated Dr. Dang.
The imaging data is translated using computer software, computerized numerical control (CNC) machinery or a 3D printer. Software has evolved to support generation of 3D models, to convert and slide 3D models into cross-sections, generate supporting structures, control the movement of the printer, and optimize placement of the model on the build plate.
Additive manufacturing is created when successive layers of material are added generating an object. Technically speaking, 3D object fabrication is also called fused deposition modeling (FDM). FDM machines work similarly. "There is a build plate that can move up and down on the Z-axis. A print head, or an extruder moves along with X and Y axis," Dr. Dang explained. Since build plates are flat, temporary supports are needed to build objects that are not self-supporting, and these can then be removed or broken off by hand.
Structural Spinal Scaffolds
In China, researchers have used the concept of 3D printing for biomedical purposes, specifically fabrication of an artificial vertebral body. Using titanium powder, they a custom-fit a vertebral implant for use in a patient's thoracic spine surgery.
BTS-7 is a bioglass from Korea that is a mechanically strong and forms an apatite-like surface with bone. It is not designed to be replaced by new bone formation; rather, it is an inert object for bony ongrowth and/or ingrowth. There is clinical data that, unfortunately is only available from the manufacturer, and has not yet been published.
The Korean study was a randomized, one-year, single-blind, non-inferiority trial. Dr. Dang explained, "They developed a titanium clip with local autograph using pedicle screws, and then used the bioglass clip with pedicle screws. Fusion was assessed using CT scans and flexion/extension x-rays." At 12-months, the imaging was compared and both groups had ~90% success rates.
3D Printing Repurposed
Currently, 3D printing scaffolds involves using a powder or other appropriate substance. The rollers spread the powder on the build plate (Z-axis). An inkjet printer can move in the Z and Y axis—but instead of injecting colored inks, different drugs, devices or binder solutions can be used to build the scaffold. Thus, there are potential other applications for the technology.
Dr. Dang likened it to building a sandcastle. "A sandcastle is a network of sand grains glued together by very thin bridges of water. Without any water, sand would flow, and a perfectly dry sandcastle would collapse. But too much water doesn't work either, so it has to be just right."
Dr. Dang pointed out that hybrid scaffolds have much to do with the preservation of the bioactive agent(s) during the fabrication process. Heat is a mechanical property of this type of manufacturing, and not all technologies allow for 3D printing at other temperatures.