By Liz Stevens, writer, UV+EB Technology
The medical and biomedical fields increasingly are benefiting from the advanced technologies made possible by UV-cured 3D printing. Additive-manufactured bolus for use during cancer treatment and 3D-printed dental aligners are some fairly recent developments in this area. Maddiy Segal, a Ph.D. candidate in Mechanical Engineering & Materials Science at the Becker Lab for Functional Biomaterials at Duke University, has pushed the technology envelope in another new direction – 3D printing of biocompatible, biodegradable medical implants.
Drawbacks in existing materials
Resin-based medical implant design and production have been complicated by a host of problems. Highly viscous resins have yielded poor resolution. Low viscosity solvent-based resins tend to shrink and warp after production. Short-term implants produced with existing materials are not biodegradable and so generally require surgery at the end of treatment to remove the implant. Long-term implants made with existing materials often trigger reactions in the body that can stop the implant’s functionality. And, with all implants created with existing materials, the body’s defenses attack the implants via foreign body reaction (FBR). FBR takes a toll on a possibly already-compromised patient’s body, and the reaction can hamper or stop an implant’s functionality. FBR includes acute FBR – the body’s first reactions to a foreign object, and chronic FBR – the body’s long-term reactions for persistent foreign bodies.
Biocompatible polymer resin materials
To address these drawbacks found in existing materials, Segal has focused her research on producing polymer resin materials with superior strength, non-shrinking/warping character and other attributes. “I wanted to create an inherently thin, low-viscosity material,” said Segal. “Through much research and trial-and-error, I identified optimal monomers and a synthetic technique to create a solvent-free polymer that can be used without any dilution.” With this material, Segal also has reached her goal to engineer a material with biocompatibility that allows for implant use with decreased concerns of chronic foreign body reaction, and with biodegradable properties that eliminate the need for post-treatment surgical removal of implants.
Segal uses poly(allyl glycidyl ether succinate) (PAGES), a low-viscosity, degradable polyester that is synthesized by ring-opening copolymerization. Used in combination with degradable thiol crosslinkers, this is a solvent-free resin that can be used for additive manufacturing with Digital Light Processing (DLP) and Carbon, Inc.’s Continuous Liquid Interface Production (CLIP) technology. Segal has used a variety of 3D printers while developing the unique resin. “I have used several printers, both commercial and ‘homemade,’” she said. “The printers I primarily use are an unmodified, commercial D4K Pro EnvisionTEC printer (DLP) and a Carbon M2 printer (CLIP). The UV wavelength I use to print typically is 385 nm.” Segal’s thiol crosslinkers can be cured under UV light, just as those made with the more common (meth)acrylate crosslinkers.
Segal explained some of the factors for gauging biocompatibility. “To assess biocompatibility,” she said, “we first test materials with cells, then move to small animals, and then to large animals if each prior step shows promising results. An important aspect to consider when designing degradable materials is how the body will respond to not only the material itself, but also how the body will respond to any byproducts that result from the breakdown of the material. As such, we design materials whose breakdown byproducts are either small molecules found in natural body processes, like the Kreb’s cycle, or derivatives of those.”
Engineering for degradability in the case of medical implants draws on the nature of the polymer and crosslinker chosen. “Degradability of a material is determined by the type of chemical bonds present,” Segal explained. “PAGES polymer and the thiol crosslinker that I selected contain ester bonds, which react with water to break down, making the entire material degradable in water or aqueous-based solutions (like acids, bases, salt water or body fluids).”
Engineering for the timing of degradability, likewise, relies on the choice of chemical bonds. “The rate of degradation can be adjusted by changing the bonds present in the polymer or crosslinker,” said Segal. “For example, incorporating more degradable bonds will make the material break down more quickly. When trying to design a material that breaks down in a certain timeframe, we typically design a library of materials that should have a range of degradability, and we then do real-time degradation testing with all materials until we find one with the right degradation profile.”
The supple nature of PAGES polyester is ideal for producing implants that cause much less tissue trauma than can occur with hard or stiff implants. “Since PAGES is a soft material with mechanical properties similar to vasculature or muscle,” Segal said, “we are focusing on using it to make degradable implants for applications with those tissue types. This promotes less inflammation than hard or inflexible implants whose mechanical properties don’t match those of the tissue being treated. We have advanced PAGES material through both small and large animal models with promising results.”
Maddiy Segal is a RadTech 2025 RadLaunch Award Winner. For more information, visit https://www.linkedin.com/in/maddison-segal/.
