Importance Of Nuclear Industry In Health And Sciences

In light of the recent controversy surrounding nuclear power plants and the insistence by many that they can be swapped out without any harmful effects for alternative power sources I figured it’d be refreshing to look at a side of nuclear power plants which isn’t part of public knowledge.

There are two groups of useful radioactive compounds for medical and other examinations and research. These fall into the transuranium (transuranic) elements [1] and other isotopes. Transuranium isotopes are generally only produced artificially as they’re heavier than uranium. Beyond trace elements they do not occur naturally. Similarly, the other isotopes are of the highly radioactive type which consequently have very brief half-lives. These isotopes are all derived or obtained from products of a nuclear reactor.

Of the transuranium elements some of the most remarkable are:

• Californium: high neutron production, extremely useful for treating types of cervical and brain cancers, radiography of aircraft, etc. to detect corrosion, bad welds, trapped moisture, etc. [2]
• Curium: to produce plutonium for radioisotope thermoelectric generators (RTGs) for spacecraft and cardiac pacemakers, source of alpha-particle X-ray spectrometers as installed on the Sojourner, Mars, Mars 96, Spirit, Athena and Opportunity rovers. [3]
• Americium: smoke detectors, RTG fuel in spacecraft, source of gamma rays and alpha particles for medical and industrial use. [4]
• Plutonium: energy source for RTGs. Used in spacecraft and medical pacemakers. [5]

For medical diagnosis, radiation therapy [6], etc. the following isotopes are commonly used:

• Iodine: I-123 is commonly used for medical imaging of the thyroid gland. I-131 is very effective in direct cancer therapy for thyroid cancers. [7]
• Gallium: Ga-67 in the body collects at areas of inflammation and rapid cell division (e.g. tumors), useful for diagnosis and detection. Ga-68 is used as radionuclide with PET-CT scans for cancer diagnosis. Ga-71 is used for neutrino detection in physics experiments. [8]
• Fluorine: F-18 is used in PET imaging for brain glucose metabolism and imaging cancer tumors. F-19 is used in NMR studies of metabolism, protein structures, etc. [9]
• Indium: I-111 is used in indium leukocyte imaging, for assessment of antibiotic therapies. It is useful for monitoring white blood cells and commonly used in drug development. [10]
• Xenon: Xe-133 for imaging of the heart, lungs and brain as well as blood flow. Xe-129 as contrast agent in MRIs for studies of soft issues like the lungs including the gas flow inside the lungs. [11]
• Yttrium: Y-90 is used for the treatment of various cancers including lymphoma, leukemia, ovarian, colorectal, pancreatic and bone cancers in combination with monoclonal antibodies for adhering to cancer cells. Y-90 is also used for needles to sever nerves more precisely than a scalpel would. [12]
• Technetium: Tc-99m is generated via molybdenum-99 and used extensively as a radioactive tracer. It’s used for detection and diagnosis of many tumors. It’s used in well over 20 million diagnostic procedures every year. [13]

Shortages of these isotopes have occurred already when maintenance of the nuclear reactors NRU and HFR (Canada) in 2007 took longer than expected. The repeated shutdowns over a period of 3 years led to a massive world-wide shortage of molybdenum-99. Replacement reactors for these aging reactors were planned but scrapped due to safety issues. At this point the world’s supply of these isotopes is provided mostly by rapidly aging nuclear reactors in addition to cyclotrons.

Solutions to in particular the molybdenum-99 shortages could be found in using the many nuclear power reactors for isotopes, though this would mean changing the way they are being regulated. No technical limitations exist there. Another option is to use cyclotrons for this, but this is an unproven method. [14]

For transuranium elements shortages shouldn’t be underestimated either. Without plutonium for powering our spacecraft we’d have no RTGs and thus be limited with our space exploration to a range not far beyond the Earth’s distance from the sun. It’d make large Mars rovers impossible. Plutonium RTGs for pacemakers aren’t uncommon either even at this point. The potential of new transuranium elements shouldn’t be underestimated either.

Non-transuranium isotopes used in medical diagnostics are crucial enough that without their wide availability cancer diagnosis and treatment would become difficult to impossible depending on the type of cancer. The presence of nuclear reactors to generate these is paramount.

It should be clear that the impact of the nuclear industry as it has developed over the past decade and into this decade goes far beyond mere generating of electricity. Lives literally depend on it.

Maya

1. http://en.wikipedia.org/wiki/Transuranium_element
2. http://en.wikipedia.org/wiki/Californium
3. http://en.wikipedia.org/wiki/Curium
4. http://en.wikipedia.org/wiki/Americium
5. http://en.wikipedia.org/wiki/Plutonium
6. http://en.wikipedia.org/wiki/Nuclear_medicine
7. http://en.wikipedia.org/wiki/Iodine
8. http://en.wikipedia.org/wiki/Gallium
9. http://en.wikipedia.org/wiki/Fluorine
10. http://en.wikipedia.org/wiki/Indium
11. http://en.wikipedia.org/wiki/Xenon
12. http://en.wikipedia.org/wiki/Yttrium
13. http://en.wikipedia.org/wiki/Technetium-99m
14. http://physicsworld.com/cws/article/news/2010/dec/03/medical-isotope-shortages-could-become-commonplace

Filed under: Analysis, General Science, Nuclear Technology, anti-nuclear, health, isotopes, medical, medicine, nuclear medicine, radio isotopes, radiotherapy, rtg, science

Protein Synthesis; Polymer Design

To the average person ‘polymer’ brings to mind images of rubbers and plastics. They are indeed polymers [1], but only a small number of examples. One of the most intricate collections of polymers has to be biological life forms like you, me, animals in general as well as plants and single-celled biological systems. Proteins form most of the solid mass of a human body and every single one of them is a protein.

The way a single cell functions is that it stores the information needed to form protein polymers in the form of deoxyribonucleic acid  (DNA). DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. Attached to each sugar is one of four types of molecules called nucleobases, cytosine, guanine, adenine and thymine (C, G, A, T respectively).

During transcription of active (uncovered) genes in the DNA these nucleobases are transcribed into strings of ribonucleic acid (RNA), whereby the thymine is exchanged for uracil (U). These RNA strings are referred to as messenger RNA (mRNA). These mRNA strings are used as the template by the polymer synthesis engines of the cell: the ribosomes [2]. This process is known as translation.

Each three nucleobases in mRNA, called a codon, encode one type of amino acid, or monomer. The thus encoded monomers will be assembled in the specified order by the ribosome. It first latches on to the mRNA string, then runs across it whereby it uses transfer RNA (tRNA) which has a complimentary anti-codon on one end and the matching amino acid on the other end to assemble the resulting polymer string.

After translation the polymer string usually undergoes structural changes (folding) as well as some chemical modifications. This results in the final, functional protein.

It’s quite a nice example of how to construct a storage and translation/synthesis unit out of only polymers. It also contains the basics of where medical science is taking us. More and more often we end up fixing issues in medicine on a protein level, whether it concerns cancer, Alzheimer’s or similar diseases whereby something went wrong during the above process.

Protein synthesis and design of custom proteins also forms the basis of two exciting new developments, namely in improving an existing body and in creating a cell and ultimately a body from scratch. Additionally there is the possibility of tapping into this system and modifying it to link it up with, say, a computer.

Imagine if the polymer structure wasn’t stored in DNA, but in a computer, and didn’t use mRNA, ribosomes and the like for translation into proteins. What if a different unit than a ribosome was used to assemble the amino acids, for example by presenting the proper receptor at the right time to coax the two amino acids to be matched together? It could thus simulate the functioning of the tRNA molecules while presenting a direct link between the digital design and the resulting string of amino acids. It could be used universally for any type of monomer, really.

Designing a protein is hard because its functioning is based on its 3-dimensional structure and functional units presented to external receptors and molecules. The polymer design language I’m working on at this point has to find the proper links and simulation accuracy to allow one to describe a functional 3D polymer which can then be unfolded into a 2D string and sent to the aforementioned translation unit.

I hope to present more details on this Polymer Design Language (PDL) and the associated synthesis tools soon, including hopefully some examples and simulation results in GROMACS [3] or similar. Until then.

Maya

[1] http://en.wikipedia.org/wiki/Polymer
[2] http://en.wikipedia.org/wiki/Ribosome
[3] http://www.gromacs.org/

Filed under: Polymers, Synthesis, dna, polymer, protein, protein design, rna, synthesis

Making Things Move: Muscles As A Fundamental Requirement

Whether we’re talking biological lifeforms or robotic creations, there is one fundamental property they all share: the ability to displace themselves. Bacteria and similar propel themselves forward using flagellum, thin, whip-like structures, directly driven using molecular motors. Larger, multi-celled creatures begin to use muscle-like structures. Robots use electric motors, steppers, servos and sometimes pneumatic artificial muscles [1] or electroactive polymers [2].

For a system like that of the mammalian body including that of humans, there is the option to use a rotational actuator, such as an electric motor or equivalent, implanted in the joints so as to directly move the joint. The major disadvantage of this is that it takes a lot more energy to move the joint this way than to use the approach used in biological systems: the very familiar lever system. As the muscle is attached on two points a fair distance on opposing from the joint, the exerted force when the muscle contracts is multiplied by the distance from the joint, effectively making it much stronger. The only disadvantage is that the muscle has to work over a long distance to generate this force. With pneumatic and electroactive polymer muscles this actuator system is emulated.

While many robots feature wheels and thus are fine with non-linear actuators, the use of wheels and propulsion methods based upon these have a lot of disadvantages, such as navigating non-flat terrain, ascending and descending stairs and ultimately a lack of sheer speed and versatility. For any universal body, the type used by primates including humans has proven to be the most versatile and universal, as its ability to interact with its environment is unparalleled. This is the body type I would pick for an advanced artificial human project.

Moving on, we have established that linear actuators akin to muscles are a definite requirement for advanced movement and maneuvering. We have mentioned pneumatic and electroactive polymer muscles as possible options. We will look at these two options as an alternative for biological muscles in our theoretical artificial human body.

Pneumatic artificial muscles (PAMs) are the oldest form of linear actuator emulating the function of the biological muscle (BM). Both shorten in length when activated, resulting in a pulling force across a certain distance. Main difference is that in a BM this shortening force is generated by the many myofibrils, which form the fundamental units of muscle fibers. A myofibril consists out of long proteins including actin, myosin and titin. The basic organization is into thick and thin filaments, repeated along the length of the myofibril in sections called sarcomeres. During contraction the thin (actin/nebulin) and thick (myosin/titin) filaments slide along each other. This contraction is triggered through the active provision of energy to the myofibril and the contraction is reversed upon ceasing this energy provision (neutral state).

A PAM is essentially a bladder made out of rubber or similar material with an inflexible net-like material surrounding it. When air (pneumatic) or a fluid (hydraulic) is pumped into the bladder it will swell up, shortening the length of the bladder as it draws both ends together. As a BM replacement PAMs come pretty close, as their compliant behaviour and simplicity of construction makes them both safe and cheap. They are however also bulky due to the required valves and air compressor. As the elastic material of the bladder’s membrane is constantly stressed, failures often occur here, in the form of ruptured bladders.

Electroactive polymers (EAPs) are a much newer invention. They’re polymers which exhibit a change in size or shape when exposed to an electric field. There is a large number of very different EAPs, but we’ll just focus on the ones relevant to our theoretical body build. These are Dielectric EAPs and Ionic EAPs.

Dielectric EAPs (DE-EAPs) [4] are based on the electrostatic force [5] and is similar in construction to a capacitor [6]. It has two electrodes with an insulating elastomer film between them. Applying a voltage to the electrodes causes the Coulomb forces between both sides to move the electrodes together, a movement allowed by the flexible elastomer film sandwiched between both sides. This results in an elongated movement. As this configuration is a capacitor the elongation doesn’t reverse on its own when an external voltage is no longer applied. This makes it very power-efficient. As with all polymers durability is an issue, however, even if DE-EAPs are otherwise an almost perfect albeit inversed approximation of BMs.

The most practical ionic EAP is an ionic polymer-metal composite [7], yet they aren’t nearly as universal as DE-EAPs, displaying only a deflection actuation (bending), making it far less useful.

In the end it seems that biological systems are more practical and versatile here. Although the actual energy to force conversion of BMs is fairly low, their ruggedness and self-repairing qualities make them quite unmatched at this point. Our best bet may lie in a type of artificial muscle which actually mimics the functioning of BMs on a molecular level. Call them neo-biological muscles, if you wish. I would like to discuss this option in another article.

Until then,

Maya

[1] http://en.wikipedia.org/wiki/Pneumatic_artificial_muscle
[2] http://en.wikipedia.org/wiki/Electroactive_polymers
[3] http://en.wikipedia.org/wiki/Myofibril
[4] http://en.wikipedia.org/wiki/Dielectric_elastomers
[5] http://jnaudin.free.fr/lfpt/html/bubble.htm
[6] http://en.wikipedia.org/wiki/Capacitor
[7] http://en.wikipedia.org/wiki/Ionic_polymer-metal_composite

Filed under: Actuators, electroactive polymers, muscles

The Many Interpretations Of ‘Artificial Human’

Welcome to the very first article on this blog. I would like to introduce my goals with this blog as well as my views on a lot of areas related to humanity’s foray into the big, exciting world which lies beyond the world as we currently know it. Recent developments in science and society are showing us already which way we are heading, and it is nothing short of exciting.

First of all, as the title of this article infers, there are a lot of ways to interpret the words ‘artificial human’. From (partial) human-like, pre-programmed robots to robots possessing intelligence akin to or superior to that of a human, to artificial organs and limbs aimed at replacing sick or missing biological ones. The first category isn’t so terribly controversial, as simple robots have embedded themselves deeply into every day life. From a microwave to a washing machine to the industrial robots which assemble entire cars for us, they’re an essential part of society. Their arrival was inevitable with the birth of the Industrial Revolution.

This leaves us with the two types of changes which are already occurring. That of building intelligent ‘life’ from scratch, and replacing biological components in humans with artificial ones. Both are exciting areas of research, with the promise to make life even better for everyone.

Building new lifeforms is hard. There’s no doubt about that. Basic structures which nature figured out ages ago using biochemical evolution such as muscles and biological power sources are still baffling us while we search for replacement. For the former we may have found the solution in active polymers, structures which respond to electrical impulses much like biological muscles do. For the latter we still have a long way to go, as the chemical energy storage used by the body is quite hard to replicate, let alone use for our own purposes.

Replacing parts of an existing, biological body is in some ways easier, and in some ways harder. The requirements are already known, the only challenge is implementing it in such a way that it fulfills those requirements and isn’t rejected by the body. The first steps have been taken here already with the use of artificial hearts, which in itself is one of the more basic organs in the body, as it doesn’t produce any hormones or provide any regulatory functions beyond adjusting its pumping rhythm to the oxygen/carbon dioxide levels in the blood.

As an aside, I’m not here to judge whether any of these changes are ‘good’ or ‘evil’. I see them as an inevitable change, with many positive uses. Naturally there will be people who will oppose violating the ‘sanctity’ of the human body, but by trying to stop progress, they will violate that which is most fundamental to humans: the drive to explore and understand. Ensuring that everyone who needs a new heart, arm, or other organ or limb can get one within a week and have it function perfectly for the rest of their natural lifespan is something completely noble in my eyes.

Moving on, I intend to post articles the coming time features analyses of various organs, tissues and so on with possible artificial replacement strategies. I’ll also post articles on AI, robotics and other relevant topics. Hopefully in the near future I’ll also be able to showcase something more concrete than just a bunch of loose parts or semi-useful AIs. The future just can’t arrive quickly enough, can it?

Maya

Filed under: Analysis, Introductions