LECTURE 10. NANOTECHNOLOGY, NANOMEDICINE AND NANOSURGERY

Nanomedicine is the medical application of nanotechnology. Nanomedicine ranges from the medical applications of nanomaterials, to nanoelectronic biosensors, and even possible future applications of molecular nanotechnology. Current problems for nanomedicine involve understanding the issues related to toxicity and environmental impact of nanoscale materials. One nanometer is one-millionth of a millimeter.

Nanomedicine research is receiving funding from the US National Institutes of Health. Of note is the funding in 2005 of a five-year plan to set up four nanomedicine centers. In April 2006, the journalNature Materials estimated that 130 nanotech-based drugs and delivery systems were being developed worldwide

Cancer

A schematic illustration showing how nanoparticles or other cancer drugs might be used to treat cancer.

The small size of nanoparticles endows them with properties that can be very useful in oncology, particularly in imaging. Quantum dots (nanoparticles with quantum confinement properties, such as size-tunable light emission), when used in conjunction with MRI (magnetic resonance imaging), can produce exceptional images of tumor sites. These nanoparticles are much brighter than organic dyes and only need one light source for excitation. This means that the use of fluorescent quantum dots could produce a higher contrast image and at a lower cost than today's organic dyes used ascontrast media. The downside, however, is that quantum dots are usually made of quite toxic elements.

Another nanoproperty, high surface area to volume ratio, allows many functional groups to be attached to a nanoparticle, which can seek out and bind to certain tumor cells. Additionally, the small size of nanoparticles (10 to 100 nanometers), allows them to preferentially accumulate at tumor sites (because tumors lack an effective lymphatic drainage system). Research into multifunctional nanoparticles that would detect, image, and then proceed to treat a tumor is under way. A promising new cancer treatment that may one day replace radiation and chemotherapy is edging closer to human trials. Kanzius RF therapy attaches microscopic nanoparticles to cancer cells and then "cooks" tumors inside the body with radio waves that heat only the nanoparticles and the adjacent (cancerous) cells.

Sensor test chips containing thousands of nanowires, able to detect proteins and other biomarkers left behind by cancer cells, could enable the detection and diagnosis of cancer in the early stages from a few drops of a patient's blood.

The basic point to use drug delivery is based upon three facts: a) efficient encapsulation of the drugs, b) successful delivery of said drugs to the targeted region of the body, and c) successful release of that drug there.

Researchers at Rice University under Prof. Jennifer West, have demonstrated the use of 120 nm diameter nanoshells coated with gold to kill cancer tumors in mice. The nanoshells can be targeted to bond to cancerous cells by conjugating antibodies or peptides to the nanoshell surface. By irradiating the area of the tumor with an infrared laser, which passes through flesh without heating it, the gold is heated sufficiently to cause death to the cancer cells.

Limitations to conventional cancer chemotherapy include drug resistance, lack of selectivity, and lack of solubility. Nanoparticles have the potential to overcome these problems.

Nanoparticles of cadmium selenide (quantum dots) glow when exposed to ultraviolet light. When injected, they seep into cancer tumors. The surgeon can see the glowing tumor, and use it as a guide for more accurate tumor removal.

In photodynamic therapy, a particle is placed within the body and is illuminated with light from the outside. The light gets absorbed by the particle and if the particle is metal, energy from the light will heat the particle and surrounding tissue. Light may also be used to produce high energy oxygen molecules which will chemically react with and destroy most organic molecules that are next to them (like tumors). This therapy is appealing for many reasons. It does not leave a "toxic trail" of reactive molecules throughout the body (chemotherapy) because it is directed where only the light is shined and the particles exist. Photodynamic therapy has potential for a noninvasive procedure for dealing with diseases, growth and tumors.

Surgery

At Rice University, a flesh welder is used to fuse two pieces of chicken meat into a single piece. The two pieces of chicken are placed together touching. A greenish liquid containing gold-coated nanoshells is dribbled along the seam. An infrared laser is traced along the seam, causing the two sides to weld together. This could solve the difficulties and blood leaks caused when the surgeon tries to restitch the arteries that have been cut during a kidney or heart transplant. The flesh welder could weld the artery perfectly.

Visualization

Tracking movement can help determine how well drugs are being distributed or how substances are metabolized. It is difficult to track a small group of cells throughout the body, so scientists used to dye the cells. These dyes needed to be excited by light of a certain wavelength in order for them to light up. While different color dyes absorb different frequencies of light, there was a need for as many light sources as cells. A way around this problem is with luminescent tags. These tags are quantum dots attached to proteins that penetrate cell membranes. The dots can be random in size, can be made of bio-inert material, and they demonstrate the nanoscale property that color is size-dependent. As a result, sizes are selected so that the frequency of light used to make a group of quantum dots fluoresce is an even multiple of the frequency required to make another group incandesce. Then both groups can be lit with a single light source. They have also found a way to insert nanoparticles into the affected parts of the body so that those parts of the body will glow showing the tumor growth or shrinkage or also organ trouble.

Tissue engineering

Nanotechnology may be able to help reproduce or repair damaged tissue. “Tissue engineering” makes use of artificially stimulated cell proliferation by using suitable nanomaterial-based scaffolds and growth factors. For example, bones could be regrown on carbon nanotube scaffolds. Tissue engineering might replace today's conventional treatments like organ transplants or artificial implants. Advanced forms of tissue engineering may lead to life extension.^] Artificial bone composites are also being manufactured from nanocrystalline calcium phosphates.

Antibiotic resistance

Nanoparticles can be used in combination therapy for decreasing antibiotic resistance. It has been shown that Zinc Oxide nanoparticlescan decrease the antibiotic resistance and enhance the antibacterial activity of Ciprofloxacin against microorganism in Vitro. Nanoparticles can interfere with the different proteins which are interacting in the antibiotic resistance or pharmacologic mechanisms of drugs.

Immune response

Buckyballs have been investigated for the ability to "interrupt" the allergy/immune response by preventing mast cells (which cause allergic response) from releasing histamine into the blood and tissues, by binding to free radicals "dramatically better than any anti-oxidant currently available, such as vitamin E".

Arthroscope

Nanotechnology is helping to advance the use of arthroscopes, which are pencil-sized devices that are used in surgeries with lights and cameras so surgeons can do the surgeries with smaller incisions. The smaller the incisions the faster the healing time which is better for the patients. It is also helping to find a way to make an arthroscope smaller than a strand of hair.

Diagnostic and medical devices

Nanotechnology-on-a-chip is one more dimension of lab-on-a-chip technology. Magnetic nanoparticles, bound to a suitable antibody, are used to label specific molecules, structures or microorganisms. Gold nanoparticles tagged with short segments of DNA can be used for detection of genetic sequence in a sample. Multicolor optical coding for biological assays has been achieved by embedding different-sized quantum dots into polymeric microbeads. Nanopore technology for analysis of nucleic acids converts strings of nucleotides directly into electronic signatures.

· C-dots (Cornell dots) are the smallest silica-based nanoparticles with the size <10 nm. The particles are infused with organic dye which will light up with fluorescence. Clinical trial is underway since 2011 to use the C-dots as diagnostic tool to assist surgeons to identify the location of tumor cells.

Nanotechnology is also opening up new opportunities in implantable delivery systems, which are often preferable to the use of injectable drugs, because the latter frequently display first-order kinetics (the blood concentration goes up rapidly, but drops exponentially over time). This rapid rise may cause difficulties with toxicity, and drug efficacy can diminish as the drug concentration falls below the targeted range.

An exciting revolution in health care and med- ical technology looms large on the horizon. Yet the agents of change will be microscopically small, future products of a new discipline known as nanotechnology. Nanotechnology is the engineer- ing of molecularly precise structures e typically 0.1 mm or smaller e and, ultimately, molecular machines.

Nanomedicine is the application of nanotechnology to medicine. It is the preservation and improvement of human health, using molecu- lar tools and molecular knowledge of the human body. Present-day nanomedicine exploits carefully structured nanoparticles such as dendrimers, carbon, fullerenes (buckyballs) and nanoshells to target specific tissues and organs. These nanopar- ticles may serve as diagnostic and therapeutic an- tiviral, antitumor or anticancer agents. But as this technology matures in the years ahead, complex nanodevices and even nanorobots will be fabri- cated, first of biological materials but later using more durable materials such as diamond to achieve the most powerful results.

Early vision

Can it be that someday nanorobots will be able to travel through the body searching out and clearing up diseases, such as an arterial atheromatous plaque The first and most famous scientist to voice this possibility was the late Nobel physicist Richard P. Feynman. In his remarkably prescient 1959 talk ‘‘There’s Plenty of Room at the Bottom,’’ Feynman proposed employing machine tools to make smaller machine tools, these are to be used in turn to make still smaller machine tools, and so on all the way down to the atomic level, noting that this is ‘‘a development which I think cannot be avoided.’’

Feynman was clearly aware of the potential medical applications of this new technology. He offered the first known proposal for a nanorobotic surgical procedure to cure heart disease: ‘‘A friend of mine (Albert R. Hibbs) suggests a very interest- ing possibility for relatively small machines. He says that, although it is a very wild idea, it would be interesting in surgery if you could swallow the surgeon. You put the mechanical surgeon inside the blood vessel and it goes into the heart and looks around. (Of course the information has to be fed out.) It finds out which valve is the faulty one and takes a little knife and slices it out, that we can manufacture an object that maneuvers at that level!. Other small machines might be permanently incorporated in the body to assist some inadequately functioning organ.’’

Medical microrobotics

There are ongoing attempts to build microrobots for in vivo medical use. In 2002, Ishiyama et al. at Tohoku University developed tiny magnetically driven spinning screws intended to swim along veins and carry drugs to infected tissues or even to burrow into tumors and kill them with heat. In 2003, the ‘‘MR-Sub’’ project of Martel’s group at the NanoRobotics Laboratory of Ecole Polytechni- que in Montreal tested using variable MRI magnetic fields to generate forces on an untethered micro- robot containing ferromagnetic particles, develop- ing sufficient propulsive power to direct the small device through the human body. Brad Nelson’s team at the Swiss Federal Institute of Technology in Zurich continued this approach. In 2005, they reported the fabrication of a microscopic robot small enough (w200 mm) to be injected into the body through a syringe. They hope that this device or its descendants might someday be used to de- liver drugs or perform minimally invasive eye surgery. Nelson’s simple microrobot has success- fully maneuvered through a watery maze using ex- ternal energy from magnetic fields, with different frequencies that are able to vibrate different me- chanical parts on the device to maintain selective control of different functions. Gordon’s group at the University of Manitoba has also proposed mag- netically controlled ‘‘cytobots’’ and ‘‘karyobots’’ for performing wireless intracellular and intranu- clear surgery.

Manufacturing medical nanorobots

The greatest power of nanomedicine will emerge, perhaps in the 2020s, when we can design and construct complete artificial nanorobots using rigid diamondoid nanometer-scale parts like molecular gears (Fig. 1) and bearings. These nanorobots will possess a full panoply of autonomous subsys- tems including onboard sensors, motors, manipula- tors, power supplies, and molecular computers. But getting all these nanoscale components to spontaneously self-assemble in the right sequence will prove increasingly difficult as machine struc- tures become more complex. Making complex nanorobotic systems requires manufacturing techniques that can build a molecular structure by what is called positional assembly. This will in- volve picking and placing molecular parts one by one, moving them along controlled trajectories much like the robot arms that manufacture cars on automobile assembly lines. The procedure is then repeated over and over with all the different parts until the final product, such as a medical nanorobot, is fully assembled.

Figure 1 A molecular planetary gear is a mechanical component that might be found inside a medical nanoro- bot. The gear converts shaft power from one angular fre- quency to another. The casing is a strained silicon shell with predominantly sulfur termination, with each of the nine planet gears attached to the planet carrier by a carbonecarbon single bond. The planetary gear shown here has not been built experimentally but has been modeled computationally. Copyright 1995 Institute for Molecular Manufacturing (IMM).

The positional assembly of diamondoid struc- tures, some almost atom by atom, using molecular feedstock has been examined theoretically via computational models of diamond mechanosyn- thesis (DMS). DMS is the controlled addition of car- bon atoms to the growth surface of a diamond crystal lattice in a vacuum-manufacturing environ- ment. Covalent chemical bonds are formed one by one as the result of positionally constrained me- chanical forces applied at the tip of a scanning probe microscope apparatus, following a pro- grammed sequence. Mechanosynthesis using sili- con atoms was first achieved experimentally in 2003. Carbon atoms should not be far behind.

To be practical, molecular manufacturing must also be able to assemble very large numbers of medical nanorobots very quickly. Approaches un- der consideration include using replicative manufacturing systems or massively parallel fabri- cation, employing large arrays of scanning probe tips all building similar diamondoid product struc- tures in unison.

For example, simple mechanical ciliary arrays consisting of 10,000 independent microactuators on a 1-cm2 chip have been made at the Cornell Nation- al Nanofabrication Laboratory for microscale parts transport applications, and similarly at IBM for me- chanical data storage applications. Active probe arrays of 10,000 independently actuated micro- scope tips have been developed by Mirkin’s group at Northwestern University for dip-pen nanolithog- raphy using DNA-based ‘‘ink’’. Almost any desired 2D shape can be drawn using 10 tips in concert. An- other microcantilever array manufactured by Proti- veris Corp. has millions of interdigitated cantilevers on a single chip. Martel’s group has investigated using fleets of independently mobile wireless in- strumented microrobot manipulators called Nano- Walkers to collectively form a nanofactory system that might be used for positional manufacturing operations. Zyvex Corp. (www.zyvex.com) of Richardson, TX has a $25 million, five-year, National Institute of Standards and Technology (NIST) con- tract to develop prototype microscale assemblers using microelectromechanical systems. This re- search may eventually lead to prototype nanoscale assemblers using nanoelectromechanical systems.

Respirocytes and microbivores

The ability to build complex diamondoid medical nanorobots to molecular precision, and then to build them cheaply enough in sufficiently large numbers to be useful therapeutically, will revolu- tionize the practice of medicine and surgery. The first theoretical design study of a complete medi- cal nanorobot ever published in a peer-reviewed journal (in 1998) described a hypothetical artificial mechanical red blood cell or ‘‘respirocyte’’ made of 18 billion precisely arranged structural atoms.

The respirocyte is a bloodborne spherical 1-mm di- amondoid 1000-atmosphere pressure vessel with reversible molecule-selective surface pumps pow- ered by endogenous serum glucose. This nanorobot would deliver 236 times more oxygen to body tis- sues per unit volume than natural red cells and would manage carbonic acidity, controlled by gas concentration sensors and an onboard nanocom- puter. A 5-cc therapeutic dose of 50% respirocyte saline suspension containing 5 trillion nanorobots could exactly replace the gas carrying capacity of the patient’s entire 5.4 l of blood.

Nanorobotic artificial phagocytes called ‘‘micro-bivores’’ (Fig. 2) could patrol the bloodstream, seeking out and digesting unwanted pathogens in- cluding bacteria, viruses, or fungi. Microbivores would achieve complete clearance of even the most severe septicemic infections in hours or less. This is far better than the weeks or months needed for antibiotic-assisted natural phagocytic defenses. The nanorobots do not increase the risk of sepsis or septic shock because the pathogens are completely digested into harmless sugars, ami- no acids and the like, which are the only effluents from the nanorobot.

Figure 2 Nanorobotic artificial phagocytes called ‘‘mi- crobivores’’ could patrol the bloodstream, seeking out and digesting unwanted pathogens. Surgical nanorobotics

Surgical nanorobots could be introduced into the body through the vascular system or at the ends of catheters into various vessels and other cavities in the human body. A surgical nanorobot, pro- grammed or guided by a human surgeon, could act as a semi-autonomous on-site surgeon inside the human body. Such a device could perform various functions such as searching for pathology and then diagnosing and correcting lesions by nanomanipulation, coordinated by an onboard computer while maintaining contact with the supervising surgeon via coded ultrasound signals. The earliest forms of cellular nanosurgery are already being explored today. For example, a rap- idly vibrating (100 Hz) micropipette with a <1-mm tip diameter has been used to completely cut den- drites from single neurons without damaging cell viability. Axotomy of roundworm neurons was performed by femtosecond laser surgery, after which the axons functionally regenerated. A femtolaser acts like a pair of ‘‘nano-scissors’’ by vaporizing tissue locally while leaving adjacent tis- sue unharmed. Femtolaser surgery has performed the following: (1) localized nanosurgical ablation of focal adhesions adjoining live mammalian epi- thelial cells, (2) microtubule dissection inside yeast cells, (3) noninvasive intratissue nanodis- section of plant cell walls and selective destruction of intracellular single plastids or selected parts of them, and even (4) the nanosurgery of individual chromosomes (selectively knocking out genomic nanometer-sized regions within the nu- cleus of living Chinese hamster ovary cells). These procedures do not kill the cells upon which the nanosurgery was performed. Atomic force mi- croscopes have also been used for bacterium cell wall dissection in situ in aqueous solution, with 26 nm thick twisted strands revealed inside the cell wall after mechanically peeling back large patches of the outer cell wall.

Future nanorobots equipped with operating instruments and mobility will be able to perform precise and refined intracellular surgeries which are beyond the capabilities of direct manipulation by the human hand. We envision biocompatible surgical nanorobots that can find and eliminate isolated cancerous cells, remove microvascular obstructions and recondition vascular endothelial cells, perform ‘‘noninvasive’’ tissue and organ transplants, conduct molecular repairs on trauma- tized extracellular and intracellular structures, and even exchange new whole chromosomes for old ones inside individual living human cells.

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