Microfabrication refers to the creation of products through the use of nano-machinery or other microscopic devices. Once thought to be the realm of science fiction, scientists and engineers have already created simple machines and even microscopic motors at the nanoscale. While these tools may not yet be ready for implementation, the tremendous potential of this technology  is becoming more and more apparent each day.

"Every industry that involves manufactured items will be impacted by nanotechnology research. Everything can be made in some way better—stronger, lighter, cheaper, easier to recycle—if it’s engineered and manufactured at the nanometer scale."  Stan Williams.

In general, there are two methods for fabricating structures at the molecular scale: addition of materials (one molecule at a time), or, conversely, removing molecules to create precise structures. Aspects of these types of microfabrication are described in the "Nanotools" section (above links).

One of the best ways to examine the concept of micro-fabrication is to first consider the requirements of traditional manufacturing:

Traditional Manufacturing:  

1. In general terms, manufacturing is "the transformation of raw materials into a higher-value finished product"
2. Manufacturing adds or removes material to assemble products
3. There are many techniques: a traditional manufacturing process applies heat, molds / casts, bends, cuts, grinds, welds, etc. to create a new product
4. Traditional manufacture employs tools and materials which may be  automated or user-directed
5. Traditional manufacturing has significant space requirements: manufacturing locations have a large "footprint" requiring space and resources adequate to both the quality and quantity requirements of the task.
6. The traditional manufacturing process is limited in scale: larger size products are easiest to manufacture
7. The difficulty of manufacturing process increases as size of product is reduced - traditional technologies have considerable limitations at the molecular scale (think about trying to manipulate a golf ball using only a pickup truck - possible, but very difficult)

Overall the concept is simple: regular "top down" manufacturing means you start big and make things out of large parts or components. In "bottom-up" manufacturing you start with nano-scale components (molecules and atoms) and assemble them as required to make larger products.  How do these  concepts relate to nano / molecular manufacturing?

Molecular Manufacturing:

1. Molecular-level manufacturing involves two concepts: first the design and creation of, and secondly the usage of molecular tools / machines.
2. Molecular manufacturing allows assembly of the fundamental components - molecules - with an unprecedented level of precision  (i.e. molecule by molecule / atom by atom)
3. Molecular manufacturing is far closer to the assembly mechanisms employed by living systems: assembly of individual components with molecular precision - like amino acids to make proteins or individual nucleotide assembly to make DNA.

http://nanoarchitecture.net/images/720.jpgTechniques of Molecular Manufacturing

1. Biodesign - the creation and/or use of nanomachinery based on the successful design strategies employed by nature. After all, millennia of natural selection have undoubtedly resulted in the most effective molecular tools possible for living systems).   Enzymes, (physically active  proteins which bring components together to make products and drive reactions) are an obvious model system. In  molecular biology, for example, there is extensive use of specific enzymes to cut, insert, repair and alter DNA / RNA at the molecular level.

2. Miniaturization - simply making tools and devices smaller until (eventually) they are capable of manufacturing at the nano level. Many groups are actively pursuing this model and there have been successful outcomes with microscopic motors and lithography tools capable of working at the molecular level.

There is a certain amount of irony in the current pursuit of molecular manufacturing and nanotechnology.  Life itself, even at the level of single-celled organisms has been successfully employing molecular machinery for years. The current nanotech revolution will borrow heavily from the techniques used by living systems to manipulate, assemble, alter and repair biomolecules at the molecular level.

In living systems there is both "cost efficiency" and functionality: energy in cellular manufacture is conserved and reused wherever possible and energy-deficient steps are typically linked to energy-consuming reactions. Living systems manufacture complex structures and polymers with absolute precision: correct components, accurate three-dimensional structures, sub-units and other assembly requirements conducted efficiently. Examples of molecular manufacture in living systems are endless:

1. Proteins (amino acids assembled one-by-one)

2. Carbohydrates (individual carbon molecules added as required)

3. Lipids (complex polymers made from individual components)

4. DNA / RNA (addition of individual nucleotides with flawless  precision - structural assembly even includes a "proofreading" function to assure accurate assembly)

To a certain extent living cellular systems are already independent, self-sufficient and self-replicating nano-machines which produce countless products in response to changing needs and environmental conditions. 

There are strengths and weaknesses to both the biodesign and miniaturization strategies for microfabrication, but whether a system is natural or synthetic it must still operate following relevant laws of science, despite the question of scale.

Regardless of size, all materials have core fundamental properties:

1. Three-dimensional shape
2. Volume occupied
3. Rigidity / flexibility
4. Elasticity
5. Textural properties, etc...

Since materials both large and small share these (and other) properties, they are subject to the same general laws of nature.

Micro-machines

Enzymes (proteins) accomplish their molecular-level work by physically holding one component and bringing it into precise contact with another component (enzyme-substrate systems). The accuracy of these natural micro-machines is uncanny - correct positioning of bond angles down to the angstrom level.  One aspect of development is to harness the existing capabilities of enzyme systems (as in their extensive usage in molecular biology) and apply it to the creation of synthetic micro-machines. The idea is simple: use existing natural systems as a "head start" in the fabrication of microscopic tools and devices.

http://www.richardbanks.com/trends/wp-content/uploads/2007/09/image40.pngMicro-machines Building Micro-machines

Natural  synthesis and assembly functions of enzymes tends to involve repetitive synthesis such as creation of various polymers through the addition of a number of monomeric subunits. This type of assembly is very much like making a string of beads.  Nanotechnology seeks to create synthetic mechano-chemical assemblers which will also function at the molecular level but allow a far greater degree of control.  This first wave of nano-devices will be used to fabricate the next generation of micro-machines. Each successive generation becoming more capable and focused on more complex tasks.

This generation-by-generation enhancement will mimic the same events that have occurred in other industrial revolutions:

1. Iron age - metal tools used to fabricate better  metal tools
2. Steam power - engines and designs based on progressive development
3. Computer age - computers used to design and implement new IT systems

Thus it will continue: microscopic tools used to create more and  more effective micro-machines. Physical construction may include metals, proteins, ceramics, silica/silicon, graphite, diamonds and many other materials.  Eventually, there will likely be an interface between synthetic materials - physical consistency and strength of synthetic materials  combined with the flexibility and manipulation capabilities of enzymatic systems. 

Example Impact of Microfabrication

1. Precision: consider the capability of micro-machines capable of manipulating single molecules with absolute precision. Accurate, reproducible microfabrication of microscopic devices to a level of precision never even imagined. This precision will have a profound impact on medicine - allowing remarkable selectivity in the diagnosis and treatment of medical conditions.  (please refer to the linked section on nanomedicine).

2. Reduction of Mass: one of the great challenges of the industrial production of machines and devices is the limitations created by the mass of the product. Airplanes, cars, space  computers - virtually any modern machine has certain limitations based on both size and mass. Vehicles of nano-fabricated polymers will be able to enjoy enormous weight reductions.  Savings in size and scale, fuel costs and even reduced  ecological footprints will be achieved. The relationship between strength and weight will be altered significantly - greater strength with significant reductions in  size and mass.

3. Self-Replication of Nano-machines:  probably the single greatest cost in establishing a successful production-based business is to build a facility and acquire the machinery / hardware required for operations. To expand the business, this cycle of spiking costs and purchasing must be repeated for each new location.

4. Computing: currently there are physical and manufacturing limitations on computer technologies. Current computer manufacturing uses ltithographic-based methods (photo-lithography). Nano-assembly and molecular level memory will significantly reduce the size and dramatically increase the capacity of computing systems.

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Nanotechnology will also provide extremely powerful computers with which to guide both those ships and a wide range of other activities in space. Today, computer chips are made using photolithography, our finest manufacturing technology. However, there are fundamental limits in how much smaller we can make chips using photolithography. If the computer hardware revolution is to continue at its current pace, in a decade or so we'll have to move beyond lithography to nanoassembly.

5. Knowledge: the potential for nano-disasseblers to take apart samples / specimens atom by atom - vastly increasing our knowledge of science, engineering and medicine. Rather than using grossly oversized tools (at the atomic level) microscopic disassemblers will allow researchers a level of control and precision that will be invaluable in the study and understanding of both biological and  electro-mechanical systems.