3D Printing Inspires Artificial Blood Vessel Engineering Process in Teeth to Reimagine Root Canals

Over the last few years, there has been a lot of research conducted on how to 3D print artificial blood vessels. In December, live 3D printed blood vessels were successfully implanted in Rhesus monkeys, and even more recently, researchers were able to get a 3D printed blood vessel network to survive and function within laboratory mice. Most of the time, this innovative work centers around procedures like bypass surgery and transplants, but researchers at the Oregon Health & Science University (OHSU) in Portland are interested in 3D printed artificial blood vessels for a different type of procedure: root canals.

According to the American Association of Endontics, over 15 million root canals are conducted each year in the US; that’s over 41,000 procedures daily. During the procedure, infected dental tissues are removed and replaced with synthetic biomaterials, which are covered by a protective crown. While root canals can save infected or decayed teeth, the procedure can have some unfortunate side effects – it may cause teeth to become brittle, which makes them more likely to fracture over time.

Luiz Bertassoni, DDS, PhD [Image: OHSU/Kristyna Wentz-Graff]

“This process eliminates the tooth’s blood and nerve supply, rendering it lifeless and void of any biological response or defense mechanism,” explained Luiz Bertassoni, DDS, PhD, assistant professor of restorative dentistry in the OHSU School of Dentistry, assistant professor of biomedical engineering in the OHSU School of Medicine, and the principal investigator for the root canal research. “Without this functionality, adult teeth may be lost much sooner, which can result in much greater concerns, such as the need for dentures or dental implants.”

Bertassoni and his other OHSU researchers developed a process, inspired by 3D printing and based on previous research working to fabricate artificial capillaries, that enables them to engineer new blood vessels in teeth, which creates better long-term root canal outcomes for clinicians and patients. The team is saying that its use of prefabricated blood vessels in the lab may actually revolutionize root canals.

The OHSU researchers recently published their findings online in Scientific Reports; co-authors of the paper, titled “A Novel Strategy to Engineer Pre-Vascularized Full-Length Dental Pulp-like Tissue Constructs,” include Bertassoni, fellow OHSU colleagues Avathamsa Athirasala, Jack Ferracane, Monica Hinds, Fernanda Lins, Christine Sedgley, and Anthony Tahayeri, and Anthony J. Smith from the University of Birmingham.

Schematic diagram illustrating the basic steps of the proposed strategy to engineer pre-vascularized full-length dental pulp-like tissue constructs. (A) The root canal is prepared following common endodontic procedure using endodontic files. (B) A pre-made sacrificial fiber is positioned in the root canal. A cell-laden hydrogel is loaded into the canal and photopolymerized. (C) After the hydrogel photopolymerization, the sacrificial fiber is removed, creating a hollow microchannel that traverses the entire length of the canal, from the apex through the pulp chamber. (D) Endothelial cells are seeded in the fabricated microchannel to engineer the core vascular capillary in the dental pulp, thus resulting in a pre-vascularized full-length dental pulp-like tissue construct.

The abstract for the paper reads:

“The requirement for immediate vascularization of engineered dental pulp poses a major hurdle towards successful implementation of pulp regeneration as an effective therapeutic strategy for root canal therapy, especially in adult teeth. Here, we demonstrate a novel strategy to engineer pre-vascularized, cell-laden hydrogel pulp-like tissue constructs in full-length root canals for dental pulp regeneration. We utilized gelatin methacryloyl (GelMA) hydrogels with tunable physical and mechanical properties to determine the microenvironmental conditions (microstructure, degradation, swelling and elastic modulus) that enhanced viability, spreading and proliferation of encapsulated odontoblast-like cells (OD21), and the formation of endothelial monolayers by endothelial colony forming cells (ECFCs). GelMA hydrogels with higher polymer concentration (15% w/v) and stiffness enhanced OD21 cell viability, spreading and proliferation, as well as endothelial cell spreading and monolayer formation. We then fabricated pre-vascularized, full-length, dental pulp-like tissue constructs by dispensing OD21 cell-laden GelMA hydrogel prepolymer in root canals of extracted teeth and fabricating 500 µm channels throughout the root canals. ECFCs seeded into the microchannels successfully formed monolayers and underwent angiogenic sprouting within 7 days in culture. In summary, the proposed approach is a simple and effective strategy for engineering of pre-vascularized dental pulp constructs offering potentially beneficial translational outcomes.”

Representative images of pre-vascularized pulp-like tissue construct. (A) Longitudinal and (B) cross-sectional views of GelMA hydrogels loaded with green fluorescent microparticles showing the fabricated microchannel after being perfused with a red fluorescent microparticle solution. The channels cross the entire length of the root. (C,D) Photographs of GelMA hydrogels from longitudinal and occlusal perspectives inside a full-length root fragment. Root fragments were stabilized prior to hydrogel loading and microchannel fabrication, and were separated to retrieve the constructs and illustrate the position of the hydrogel inside the tooth. Microchannels were perfused with red food dye.

The vascularization process relies on biological events that are complexly orchestrated, the researchers explain. Other studies have focused on how vascularized pulp regenerates by culturing stem and/or endothelial cells on flat substrates, in 3D scaffold matrices, and in tissue constructs with no scaffolds. But, these strategies require lengthy biological processes, as it takes time for interconnected vasculature to form. So the OHSU team set out to develop a simpler biofabrication strategy with greater clinical potential.

In the OHSU study, the team placed a fiber mold, made out of sugar molecules, across the root canal of extracted human teeth. A gel-like material, not dissimilar to proteins in the human body and filled with dental pulp cells, was then injected into the mold. In order to make a long microchannel in the root canal, the team removed the fiber and inserted endothelial cells, which were isolated from the synthetic blood vessels’ interior lining.

“To fabricate the microchannels, 500 µm diameter 6% (w/v) sacrificial agarose fibers were prepared using a glass capillary fitted with a metallic piston inside, using a 3D printing-inspired method we have developed recently,” the researchers wrote.

After one week, dentin-producing cells began to proliferate near the walls of the tooth, while artificial blood vessels formed inside it.

Bertassoni said, “This result proves that fabrication of artificial blood vessels can be a highly effective strategy for fully regenerating the function of teeth. We believe that this finding may change the way that root canal treatments are done in the future.”

The Medical Research Foundation of Oregon and the National Institute of Dental and Craniofacial Research of the National Institutes of Health (NIH) provided funding for this study. Discuss in the 3D Printed Blood Vessels forum at 3DPB.com.