Introduction: Fibers have drawn particular attention in tissue engineering as they can be used as building blocks for the fabrication of three dimensional (3D) scaffolds using well-established textile techniques such as weaving. Fibers have been made from different materials including synthetic polymers and hydrogels[1],[2]. However, the fabrication process of synthetic fibers generally requires harsh environments that are not suitable for cellular encapsulation. On the other hand, hydrogel fibers have low mechanical strength which hampers their assembly using current textile technologies. We have recently developed a novel strategy that combines the advantages of synthetic fibers and hydrogels to create composite living fibers[3]. However, since alginate lacked cell binding moieties and was not able to absorb serum proteins, cellular viability and function was dramatically reduced over time. In this work, composite living fibers made from a collagen-based core material and an interpenetrating network (IPN) of alginate:GelMA. We observed better cellular viability while the composite fibers compared to fibers made from pure alginate.
Experimental: Composite fibers were fabricated by coating a flexible biocompatible and mechanically strong collagen-based fiber by a cell-laden hydrogel layer from alginate and gelatin methacrylate (GelMA) hybrid. A motorized spool drew the core fiber through a mixed solution of alginate, GelMA, and cells and then through a solution of CaCl2 to crosslink the alginate part and form a polymeric network template (Fig. 1A). GelMA part was crosslinked by UV irradiation. Cellular viability and metabolic activity were assessed by a standard live/dead assay and PrestoBlue assay. Cellular morphology and alignment were monitored by immunostaining of α-actin and nuclei.
Results and Discussion: Composite fibers containing fibroblasts were created with the hydrogel layer ranging from 20µm to 600µm. We analyzed the effect of incorporating GelMA in the alginate matrix on cellular viability. Addition of GelMA to alginate significantly improved the cellular viability and activity in the hydrogel layer compared to pure alginate (Fig. 1B). In addition, the existence of GelMA in the alginate matrix provided binding sites for the cells to attach and spread in the 3D matrix of the hydrogel. The feasibility of making complex structures using bioactive composite fibers was assessed. We showed that these fibers can be assembled into woven and braided structures without losing the hydrogel integrity. Moreover, patterning cells on surgical fabrics and hydrogel sheets were also studied. Complex patterns were made using the composite fibers in a process that was not harmful to the cells (Fig. 1C).
Conclusion: In this work, we developed bioactive composite fibers from a core collagen-based thread coated with an IPN hydrogel. The fibers were continuously generated using a dipping system that enables controlling the hydrogel thickness around the core thread. A two-step crosslinking approach including chemically and photo crosslinking steps was utilized to create the IPN hydrogel around the core threads. We showed that the CLFs made from IPN hydrogel exhibited better cell compatibility could be assembled into higher order constructs using textile approaches. Future studies may include the incorporation of more clinically relevant cells and biomaterials to create complex tissue-like constructs.
References:
[1] Onoe H, Okitsu T, Itou A, Kato-Negishi M, Gojo R, Kiriya D, et al. Metre-long cell-laden microfibres exhibit tissue morphologies and functions. Nat Mater. 2013;12(6):584-90.
[2] Hwang CM, Khademhosseini A, Park Y, Sun K, Lee S-H. Microfluidic chip-based fabrication of PLGA microfiber scaffolds for tissue engineering. Langmuir. 2008;24(13):6845-51.
[3] Akbari M, Tamayol A, Laforte V, Annabi N, Najafabadi AH, Khademhosseini A, et al. Composite Living Fibers for Creating Tissue Constructs Using Textile Techniques. Advanced Functional Materials. 2014;24:4060-7.