(426c) Reinforced Hydrogel Fibers for Cell Encapsulation and Organ Printing

Introduction: Assembling cells into long fiber like structures have a great potential for building complex higher order 3D tissues and organoids. Cell laden fibers have been made using microfluidics by encapsulating cells in a continuous stream of hydrogels such as Ca-Alginate and gelatin. However such fibers are very delicate with poor mechanical properties and handling them is challenging. In this work we present a novel method to fabricate cell-laden alginate fibers reinforced with polymeric or metallic filament core. These reinforced fibers have superior mechanical strength combined with the advantaged of the hydrogel shell.

Materials and Methods: The fibers are made by custom made 3D printed nozzle that coaxially injects a steady stream of alginate over a spooling polymeric thread (which forms the core). The spooling system consisted of a 3D printed spool-drum rotated though a stepper motor driven at a precise predetermined rate by a microcontroller. The alginate flow rate together with the spooling rate determined the final dimension of the composite fiber. For encapsulating cells, cells were suspended in 1.4% alginate and introduced into the nozzle, while the alginate was crosslinked in a bath having 20mM Ba++ for 10 min. Cell loaded fibers were cultured in petridishes using normal medial and imaged after 3 weeks to observe cell growth.

Results: Reinforced fibers were made using braided nylon suture (diameter 150um) as the core and alginate shell. The fibers showed excellent mechanical properties with good adhesion of the hydrogel to the polymeric core. No peeling of the hydrogel was observed even upon bending of the fibers. SEM analysis of the fibers reveled the core-shell structure of the composite fibers with the polymeric core concentric to the shell. The thickness of the hydrogel shell could be precisely controlled by varying the flowrate or the spooling speed, and had excellent agreement with theoretical predictions. Hela cells laden reinforced fibers supported cell survival and growth for at least 3 weeks in vitro. Curiously, cells proliferated within the alginate shell forming linear ‘string’ like patterns travelling from within the core towards the surface having uncanny resemblance to the fluidic streamlines formed within the alginate just before crosslinking.

Conclusion: In this work we have demonstrated a new fabrication method for creating composite hydrogel fibers. These fibers would not only be useful in creating higher order cellular constructs but also as implantable systems for in vivo applications.