Making Channels: Polymer Nanotubes.

The Coaxial electrospinning process needn’t only line the inside of nanofibers with drug delivery media or structural elements, they can also hold apart the walls of a tube! This can be done by electrospinning a core of mineral oil (large-molecule distillates of petrol) inside a shell of immiscible polymer solution. This core can then be removed through various treatments, either heating the part-ceramic shell material to vaporise the core away, or by applying pressure to the tubes.

Electrospun nanotubes are very different from pure carbon nanotubes. They have a far greater (sometimes microscale) diameter, and as electrospun products, they are versatile and readily modifiable, offering some exciting properties in themselves.

A nanofiber filled with round, hollow cores will not only have more surface area, and more mechanical strength per unit mass, but it will also have more solid-air interfaces, making it the basis of an excellent heat insulator if the fibers are aligned en masse. Since it is relatively easy to adjust parallel core sizes by adjusting the inflow of space-filling fluids into the nozzle, multi-channel nanofibers have been produced {1}. Their channels have areas that can be tuned by input pressure or flow rate. These channels are maintained along the length of the fiber, all of whose arrangements are mechanically strong, and reminiscent of natural forms.

Numerous protein receptors in the natural world have strong, and highly specific responses to trace chemicals. Where they are part of a cell, these receptors are strictly produced according to the cell’s needs, and their signal output is generally drowned out by other cellular activity. Biosensors are being developed to amplify these specialised receptor's responses by placing them out of their cellular context and onto high surface area, parallel, and linear fibers whose electrical conductance will be changed by these receptors' stimulation{2}. Polymer nanotubes not only near-double the surface area available an immobilised receptor, but they also offer the possibility of placing biologically active receptors across a cellular membrane engineered on the tube tip. This allows a wider range of delicate receptors, which are desensitised by polymer immobilisation, to be incorporated into biosensor technology.

A continuous polymer nanotube could be an excellent capillary, able both to rigidly direct the movement of fluids down the desired direction, and to chemically alter the contents with immobilised enzymatic, nanoparticle-encapsulated or mineral catalysts along the way. But electrospun nanotubes in particular may be produced continuously from different shell solutions that contain different chemical agents {3}. The resulting tube will visit a sequence of different catalytic environments on the fluids that pass through it. This way, multiple chemical processes can be quickly and compactly enacted on bespoke material, possibly allowing the multiple enzymatic steps in biochemistry to be emulated artificially.


References

  1. doi: 10.5772/8166
  2. doi: 10.1088/0957-4484/20/30/305501
  3. doi: 10.1039/C3TB21232G