Scientists from the US Department of Energy's National Laboratory have "forced" polymers to weave themselves into tiny nanometer ropes - materials approaching the structural complexity of biological materials.
This research is the latest development in the effort to develop self-organizing nanomaterials that mimic the complexity and functionality of natural systems, and at the same time, are stable enough to withstand extreme conditions such as heat and dryness.
Although the research is in its infancy, its results could lead to new applications that combine the best of both worlds. It is possible and possible to use the new materials as scaffolding structures that direct the construction of nanowires and other nanoscale structures. Or maybe they could be used in the development of carriers to deliver drugs that affect the disease at the molecular level, or to develop molecular sensors and filter devices that separate molecules from one another.
Practically, the scientists found the conditions under which synthetic polymers, called "polypeptoids", organize themselves into much more complex structures: first into a structure of sheets, then into stacks of those sheets, which in turn fold into double helices resembling a braided rope with a diameter of 600 nanometers only.
"This graded self-organization is a hallmark of many biological materials, such as collagen (the term in Wikipedia), but designing and developing synthetic structures that do this has so far been a serious challenge," says Ron Zuckermann, who is director of the lab's Biological Nanostructures Facility.
In addition, and unlike ordinary polymers, the scientists can control the arrangement of the nanorope structure at the level of a single atom. They can also produce coils of specified lengths and sequences to order. This "tuning" ability opens the hatch to development possibilities of synthetic structures that mimic the ability of biological materials to perform highly precise tasks, such as the nesting on defined molecules.
"Nature uses precise lengths and sequences in order to produce structures with the highest functional capacity. An antibody, for example, is able to recognize one form of a protein and not another, and we are interested in imitating this ability," the researcher points out. The research findings were published in the scientific journal Journal of the American Chemical Society.
The scientists used chains of polymers that are similar to natural polymers, and which are called peptoids The term on Wikipedia). Peptoids are structures that mimic the composition of peptides, the same building blocks that nature uses to create proteins - the heart of biology. Instead of using peptides to build proteins, scientists aim to use peptoids to build synthetic structures that behave like proteins.
The scientists began the research by using block co-polymers, polymers composed of two or more different types of monomers (building blocks).
"Simple block copolymers do self-organize into nanoscale structures, but we wanted to examine how the exact sequence and function of biology-mimicking units can be used to prepare more complex structures," notes one of the researchers. In light of this, the peptoid units are automatically synthesized, processed and then added to the solution that promotes self-assembly.
The result was a variety of independently created shapes and structures, with the intertwined coils being the most fascinating of them all. The staggered structure of the coil, as well as the ability to affect each and every atom in it individually, means that this material can be used as a template for preparing complex structures on a nanometer scale.
"The idea is to prepare nanometric shapes with complex structures with a minimal investment," notes one of the researchers. The scientists' next research step will be to examine the effects of small chemical changes on the helix structure.
Says the lead researcher: "The interlaced coils are the first step in the automatic preparation of block copolymers defined to order. The idea is to create something that to our mind looks like plastic, but it can adapt to itself more complex and functional structures than usual, such as structures for molecular recognition, which proteins do so good."
