**5. Conclusions**

We have successfully demonstrated two platforms for delivery of fluticasone (FTS) for the treatment of eosinophilic esophagitis (EoE). An FTS-eluting string is an innovative approach to drug delivery that is potentially very appealing as it can be swallowed and release drug along the entire length of the esophagus. Additionally, FTS-loaded rings were successfully fabricated using 3D-DLP printing to provide controlled and prolonged drug release, though refinements will be need for more durable implantation. In vitro release studies demonstrated the ability to fine-tune drug release kinetics by changing the crosslink density of resin formulations. Post-printing UV curing improved the mechanical properties of these rings. Additionally, results showed that the process of drug loading into the rings had an effect on drug release kinetics. While there is still room to improve the drug release rate from these rings to achieve the target daily dose of 1 mg/day, and to improve the design for a more durable esophageal implantation, the approaches for esophageal drug delivery overall are very promising. To our knowledge, this is the first report of fabrication and development of string- and ring-based drug delivery devices for the treatment of EoE. Moreover, these drug delivery technologies hold the potential to also serve as a platform

for treatment of other esophageal conditions, ranging from inflammatory to fibrotic to neoplastic diseases.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/2073-436 0/13/4/557/s1.

**Author Contributions:** Conceived and designed the experiments: S.R.B., A.P., A.S., A.B., and E.S.D.; Performed the experiments: A.P., R.S., D.D., P.S.-H., P.M., T.P., A.B., and E.S.D.; Contributed reagents/materials/analysis tools: J.B., S.R.B., A.B., W.Z., and E.S.D.; Wrote the paper: S.R.B., A.P., A.S., and E.S.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** All other data supporting the findings of this manuscript are available from the corresponding author (S.R.B.) upon reasonable request.

**Acknowledgments:** This work was supported by the NC TraCS/NC State Collaborative Translational Research Pilot Grant Award (UNCSUR11602) and the UNC CTSA grant (UL1TR001111), a UNC Center for Health Innovation Pilot Award, and used resources from the Large Animal and Histology Cores of the UNC Center for GI Biology and Disease (P30 DK034987).

**Conflicts of Interest:** The authors declare no conflict of interest.
