Schematic of gilled fiber scaffold fabrication (from top left): polymer pellets are fed to separate extruders, melted, and forced through a spinnerette; filaments are collected in a bundle and wound onto a collector roll; fibers are crimped into a zig-zag pattern and converted to a tangled ‘web’ via a series of specialized combed rollers; web structure is locked into place via needle punching using barbed needles entangle the fibers; finally, the material is washed and dried. Scanning electron microscope image of gilled fiber cross-section.
Schematic of gilled fiber scaffold fabrication (from top left): polymer pellets are fed to separate extruders, melted, and forced through a spinnerette; filaments are collected in a bundle and wound onto a collector roll; fibers are crimped into a zig-zag pattern and converted to a tangled ‘web’ via a series of specialized combed rollers; web structure is locked into place via needle punching using barbed needles entangle the fibers; finally, the material is washed and dried. Scanning electron microscope image of gilled fiber cross-section.

Polymer fibers with ‘gills’ that resemble the underside of a mushroom could improve tissue engineering approaches to bone repair by giving cells more space to grow and better access to nutrients, according to researchers at the University of Missouri and North Carolina State University [Tuin et al., Acta Biomaterialia (2016), doi: 10.1016/j.actbio.2016.03.025].

Creating scaffolds that encourage the transformation of stem cells into bone cells – known as osteoblasts – is a promising approach for repairing diseased or damaged bone. Differentiation of stem cells into the right kind of specialized cell depends on getting the right chemical cues. But as well as chemical cues, the mechanical environment can have an effect too. If nutrients cannot reach deep inside the scaffold structure, for example, stem cells cannot survive.

To build a scaffold that enables better distribution of nutrients, Elizabeth G. Loboa and her team created novel fibers from biodegradable a poly(lactic acid) (PLA) shell covered with multiple gill-like projections. The novel fibers are produced using a conventional meltspinning technique but using a modified winged spinnerette. The hollow gilled fibers are made into nonwoven fabrics using a technique known as ‘carding’ in which rollers covered with barbed needles tangle the fibers into a web-like mesh, rather like making felt.

“This is the first time that the formation of gilled fibers has been described,” say Loboa and first author of the paper, Stephen Tuin. “The hollow gilled internal structure results in reduced fiber density, leading to lighter weight scaffolding materials, and greatly enhanced surface area compared to solid fibers (1500% increase).”

When stem cells taken from fat deposits in the human body (human adipose-derived stem cells or hASCs) were seeded onto the carded scaffolds, the researchers found much higher levels of attachment, proliferation, and differentiation of cells, as well as fewer dead cells after a week, compared with conventional round PLA fibers.

The researchers believe that the gilled structure of the fibers improves the transport of nutrients and oxygen through the scaffold via capillary action, as well as providing routes for the removal of waste products.

“Future work to validate this hypothesis is needed,” say Loboa and Tuin, “but if it is true, it may offer strategies for full thickness tissue engineering scaffolds that are not limited to cell growth on the surface.”

The fiber spinning process, which requires only heat and water, could be readily scaled up for commercial manufacturing, add the researchers, with the potential to produce both nonwoven and woven materials for tissue engineering applications.