Page 134 - Nanotechnology an introduction

of physiological parameters. The autonomous robot (“nanobot”) is still some way in the future. Superior nanostructured tissue scaffolds will enhance
the ability to regenerate tissue for repair purposes.
In medicine, scrutinizing the world from the viewpoint of the atom or molecule amounts to finding the molecular basis of disease, which has been
underway ever since biochemistry became established, and which now encompasses all aspects of disease connected with the DNA molecule
and its relatives. There can be little doubt about the tremendous advance of knowledge that it represents. It, however, is part of the more general
scientific revolution that began in the European universities founded from the 11th century onwards—and which is so gradual and ongoing that it
never really constitutes a perceptible revolution. Furthermore, it is always necessary to counterbalance the reductionism implicit in the essentially
analytical atomic (or nano) viewpoint by insisting on a synthetic systems approach at the same time. Nanotechnology carried through to productive
nanosystems could achieve this, because the tiny artifacts produced by an individual assembler have somehow to be transformed into something
macroscopic enough to be serviceable for mankind.
The application of nanotechnology to human health is usually called nanomedicine, and is thus a subset of nanobiotechnology. To recall the
dictionary definition, medicine is “the science and art concerned with the cure, alleviation and prevention of disease, and with the restoration and
preservation of health, by means of remedial substances and the regulation of diet, habits, etc.” Therefore, in order to arrive at a more detailed
definition of nanomedicine, one needs to simply ask which parts of nanotechnology (e.g., as represented by Figure 1.1) have a possible medical
application.
Much of nanomedicine is concerned with materials. Quantum dots and other nano-objects, surface-functionalized in order to confer the capability of
specific binding to selected biological targets, are used for diagnostic purposes in a variety of ways, including imaging and detection of pathogens.
Certain nano-objects such as nanosized hollow spheres are used as drug delivery vehicles. Based on the premise that many biological surfaces
are structured in the nanoscale, and hence it might be effective to intervene at that scale, nanomaterials are being used in regenerative medicine
both as scaffolds for constructing replacement tissues and directly as artificial prostheses. Nanomaterials are also under consideration as high-
capacity absorbents for kidney replacement dialysis therapy. Other areas in which materials are important and which can be considered to be
sufficiently health-related to be part of nanomedicine include the design and fabrication of bactericidal surfaces (e.g., hospital paints incorporating
silver nanoparticles).

The advantages of miniaturized analytical devices for medicine (“labs-on-chips”), especially for low-cost point-of-care devices, are already
apparent at the microscale. Further miniaturization would continue some of these advantageous trends, resulting inter alia in the need for even
smaller sample volumes and even lower power consumption, although some of the problems associated with miniaturization such as unwanted
nonspecific binding to the internal surfaces of such devices would be exacerbated. However, whereas microscale point-of-care devices rely on the
patient (or his or her physician) to take a sample and introduce it into the device, miniaturization down to the nanoscale would enable such devices
to be implanted in the body and, hence, able to monitor a biomarker continuously. The apotheosis of this trend is represented by the nanobot, a
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more or less autonomous robotic device operating in large swarms of perhaps as many as 10 in the bloodstream.
As well as analysis, synthesis (especially of high-value pharmaceuticals) is also an area where microtechnology is contributing through microscale
mixers. This technology is very attractive to the pharmaceutical manufacturing industry. Enough evidence has accumulated for it to be generally
recognized that many drugs are typically efficacious against only part of the population. This may partly be due to genetic diversity, and partly to
other factors, which have not yet been characterized in molecular detail. In the case of genetic diversity, it is possible that almost all the
pharmaceutically relevant DNA sequence variants occur in haplotype blocks, regions of 10,000 to 100,000 nucleotides in which a few sequence
variants account for nearly all the variation in the world human population (typically, five or six sequence variants account for nearly all the variation).
If a drug that has been found to be efficacious against the majority haplotype variant can be made to be efficacious against the others by small
chemical modifications, then the task of the drug developer would not be insuperable.
At present, clinical trials do not generally take account of haplotype variation. Advances in sequencing, which nanotechnology is helping both
through the development of nanobiotechnological analytical devices (although it seems that microtechnological “labs-on-chips” may be adequate to
fulfil needs) and through more powerful information processing, should make it possible in the fairly near future for haplotype determination to
become routine. It is, however, not known whether (and perhaps rather improbable that) small modifications to a drug would adapt its efficacity to
other haplotype variants. At any rate, different drugs will certainly be needed to treat different groups of patients suffering from what is clinically
considered to be the same disease. Micromixers represent a key step in making custom synthesis of drugs for groups of patients, or even for
individual patients, economically viable.
The precise control of the hydrodynamic regime that is attainable (see Section 2.4) typically enables reactions that normally run to what are
considered to be quite good yields of 90%, say, to proceed at the microscale without by-products; that is, a yield of 100%. The advantages for the
complicated multistep syntheses typically required for pharmaceuticals are inestimable. Added to that advantage is the ease of scaling up the
volume of synthesis from a laboratory experiment to that of full-scale industrial production simply by scaleout; that is, multiplication of output by the
addition of identical parallel reactors.
It is not, however, obvious that further miniaturization down to the nanoscale will further enhance performance. Similar problems to those afflicting
nanoscale analytical labs-on-chips would become significant, especially the unwanted adsorption of reagents to the walls of the mixers and their
connecting channels.
Two further aspects of nanomedicine deserve a mention. One is automated diagnosis. It is an inevitable corollary of the proliferation of diagnostic
devices enabled by their miniaturization that the volume of data that needs to be integrated in order to produce a diagnosis becomes overwhelming
for a human being. Interestingly, according to a University of Illinois study by Miller and McGuire (quoted by Fabb [49]), about 85% of medical
examination questions require only recall of isolated bits of factual information. This suggests that automated diagnosis to at least the level currently
attainable by a human physician would be rather readily realizable. The program would presumably be able to determine when the situation was too
complicated for its capabilities and would still be able to refer the case to one or more human agents in that case. Indeed, medicine has already
become accustomed to depending on heavy computations in the various tomographies that are now routine in large hospitals. Diagnosis is
essentially a problem of pattern recognition: an object (in this case, the disease) must be inferred from a collection of features. Although there have
already been attempts to ease the work of the physician by encapsulating his or her knowledge in an expert system that makes use of the
physician's regular observations, significant progress is anticipated when measurements from numerous implanted biosensors are input to the