The biomolecular interface and the definition of living

Definitional and classification issues often arise in any field of heightened focus and progress (e.g.; what is a planet?). For the many fields integrating organic and inorganic materials, an interesting issue comes up as to what is the definition of life. Many different gradations of living things are emerging.

Some interesting new cases of living materials are the idea of organic sensors made of biomaterial placed on buildings, self-replicating crystals and biological scaffolding for stem cell grown organs and 3D tissue printing.

De novo materials synthesis
One exciting aspect of the living/non-living classification is the new synthesis of both organic and inorganic materials. Scientists are creating de novo engineered proteins and other biological materials, non-naturally occurring inorganic materials with superior properties using molecular manufacturing techniques and hybrid organic-inorganic materials, with the best of organic and inorganic properties in one object, for example rotaxanes which could be used in quantum computing.

Definition of integration
Not just the definition of what is living arises, but also the definition of the integration of organic and inorganic materials. Alan H. Goldstein proposes that a true integration of organic and inorganic material involves communicating back and forth, not just a system which has properties or components of both organic and inorganic systems.

The future of biomolecular interfaces

The future of biomolecular interfaces is probably a further blurring of the underlying substrates as the focus is more relevantly on the properties and requirements of any challenge at hand.

The future of computing – rotaxanes?

One of the great human endeavors at the moment is being able to work at the molecular scale (e.g.; 1-100 nm), using organic and inorganic materials for a variety of purposes ranging from basic materials to computing to electronics to life sciences therapeutics to energy. This includes the designed direction of existing molecular processes (e.g.; biology) and the synthesis of novel materials, structures and dynamic behavior.

Three of the most interesting advances in working at the molecular scale and examples of bio-infotech convergence are described below…

1) Hybrid organic-inorganic rotaxanes
First is the March 2009 work of David Leigh’s lab at the University of Edinburgh in creating hybrid organic-inorganic rotaxanes. A rotaxane (rota/wheel + axis) is a mechanically-interlocked molecular structure, essentially a dumbbell shape with a ring around its middle (Figure 1), often man-made but occasionally existing in nature. In this case, the dumbbell portion of the hybrid organic-inorganic rotaxane is an organic amine, the ring around the middle is a metal.

Figure 1: Rotaxane graphical schematic and crystal structure (source)

The benefit of metal-organic frameworks is that they have the properties of both organic and inorganic materials; structural and functional properties from organic materials and electronic, magnetic and catalytic properties from inorganic materials. This rotaxane molecule has directed shuttle-like behavior, where the metal ring around the center can be pushed to bind at either end, with its biggest potential application being in quantum computing.

2) Bio-inorganic interfaces
A second interesting example of molecular scale work and bio-infotech convergence is biocomposites/GEPIs (genetically-engineered peptides for inorganics) which regulate cell behavior and improve binding at bio-inorganic interfaces by modifying surface chemistry and immobilizing infection-causing bioactive molecules. Candan Tamerler’s lab at the University of Washington is doing some interesting work in this area. Improved bio-inorganic interfaces are needed for reduced infection and seamless interaction between human wetware and implants: heart, hip, prosthetics, eye, brain, etc.

3) DNA nanotechnology
The third interesting bio-infotech convergence example is DNA nanotechnology, the notion of using DNA as a structural building material (for example, for self-directed rapid templating) rather than as an information carrier. One key use is employing DNA as a programmable scaffolding for the self-assembly of nanoscale electronic components, meaning that scaffolds comprised of self-assembled DNA serve as templates for the targeted deposition of ordered nanoparticles and molecular arrays. DNA is formed into tubes and then metallized in solution to produce ultra-thin metal wires. John Reif’s lab at Duke University, Erik Winfree’s lab at Caltech and many other groups are working on DNA nanotechnology. Moving to the molecular scale for electronics manufacture is imperative for maintaining Moore’s Law computing performance improvements.

Future implications
It seems likely that working at the molecular scale and bio-infotech convergence will continue to grow. Organic-inorganic hybridization approaches could proliferate to exploit the full suite of properties afforded by organic and inorganic inputs, and as researchers suggest, lead to novel properties and the ability to harness molecular dynamics for human use.