Shear at Fluid-Fluid Interfaces Affects the Surface Topologies of Alginate Microfibers

Abstract

Hydrogel microfibers have great potential for applications such as tissue engineering or three-dimensional cell culturing. Their favorable attributes can lead to tissue models that can help to reduce or eliminate animal testing, thereby providing an eco-friendly alternative to this unsustainable process. In addition to their highly tunable mechanical properties, this study shows that varying the viscosity and flow rates of the prepolymer core solution and gellator sheath solution within a microfluidic device can affect the surface topology of the resulting microfibers. Higher viscosity core solutions are more resistant to deformation from shear force within the microfluidic device, thereby yielding smoother fibers. Similarly, maintaining a smaller velocity gradient between the fluids within the microfluidic device minimizes shear force and smooths fiber surfaces. This simple modification provides insight into manufacturing microfibers with highly tunable properties.

Behavior of Neural Cells Post Manufacturing and After Prolonged Encapsulation within Conductive Graphene-Laden Alginate Microfibers

“…[20] Since the graphene solutions are significantly more viscous than their alginate counterparts (Figure 1 (A)), it follows that the within the microfluidic device, graphene solutions would be more resistant to deformation by shear force exerted from the sheath fluid. [32] Therefore, the sizes of both wet and dry graphene-alginate microfibers are larger than the corresponding alginate microfibers (Figure 1 (C-D)).…”

“…[8, 29, 30, 31] During fiber fabrication, both core (pre-gel) and sheath (gellator) solutions are used; the core solution will be crosslinked into the resulting microfiber, while the sheath solution helps guide the core solution through the channel, further shaping it and preventing clogging. [6, 30, 32, 33] The viscosities and flow rates used can also affect the shape, size, topography, and mechanical properties of the resulting fibers. [32] In this case, the sheath solution also contains ionic crosslinkers that cause the gellation of the core fluid before it leaves the microfluidic chip; upon exiting the chip, the newly formed microfiber will be introduced into a collection bath that will further strengthen it and allow for easy gathering.…”

“…[6, 30, 32, 33] The viscosities and flow rates used can also affect the shape, size, topography, and mechanical properties of the resulting fibers. [32] In this case, the sheath solution also contains ionic crosslinkers that cause the gellation of the core fluid before it leaves the microfluidic chip; upon exiting the chip, the newly formed microfiber will be introduced into a collection bath that will further strengthen it and allow for easy gathering.…”

“…For this work, the core solution was created with alginate, a commonly used biopolymer derived from the cell walls of brown algea. [7, 32, 34] Alginate features favorable biocompatibility parameters such as cell-safe gelation conditions, high permeability, neutral pH, and low antigenicity. [16] Its structure of M- and G-blocks can be ionically crosslinked in the presence of divalant cations, such as Ca 2+ , Ba 2+ , Sr 2+ , and others; however, calcium crosslinkers are commonly used in biomedical applications because they are readily available and cost effective, and because calcium alginate hydrogels exhibit good swelling properties, which is important to maintain cell viability.…”

“…The viscosities of cell-free pre-polymer solutions were measured using a Cannon-Fenske viscometer, as previously described. [32] The addition of graphene into the 3.5% alginate core solution significantly increased the viscosity of the fluid, which can be seen in Figure 1 (A). This can be attributed to the attachment of alginate chains onto the graphene flakes.…”