A number of applications in nanomedicine - imaging, drug delivery or photo therapy for instance - utilize phenomena called two-photon absorption (TPA). In TPA, the simultaneous absorption of two photons excite a molecule from one state to a higher energy electronic state. TPA initially was used only as a spectroscopic tool but new applications emerged over time. Currently approved two-photon absorption-induced excitation is one of the most promising approaches in photo therapies as it increases light penetration. It enables the use of light in the tissue-transparent window (750-1000 nm), allowing deeper light penetration and reduced risk of laser hyperthermia. An uphill energy conversion through the use of two-photon absorbing chromophores and subsequent energy transfer is a promising scientific frontier.
Cancer researchers are therefore experimenting with nanoparticles as both contrast agent and drug carrier capable of pinpointing and destroying individual cancer cells. Targeted nanoparticles consist of a metallic or organic core conjugated with a biomolecule of interest. To be able to navigate nanoparticles to a desired target (i.e. a specific cancer cell), they need the property of specific target recognition. Depending on the type of cancer that is to be targeted, researchers choose biomolecules that show high affinity toward these specific tumor cells. Think of these biomolecules as a navigation aid to transport nanoparticles to the cancerous site or organ of interest. As part of their overall goal of developing target-specific gold nanoparticles for treatment of cancers, scientists at the University of Missouri have carried out a systematic investigation on the design and development of targeted gold nanorods.
Researchers in Korea have developed a novel platform for intracellular delivery of genetic material and nanoparticles, based on vertically aligned carbon nanosyringe arrays of controllable height. Stem cell research is being pursued in laboratories all over the world in the hope of achieving major medical breakthroughs. Scientists are striving to create therapies that rebuild or replace damaged cells with tissues grown from stem cells and offer hope to people suffering from cancer, diabetes, cardiovascular disease, spinal-cord injuries, and many other disorders. Nanotechnology is increasingly playing a role in how researchers think about delivering stem cell therapies into cells. Cell plasma membranes are a formidable barrier to the delivery of exogenous macromolecules in cellular engineering and labeling and cell therapy. Attempts have been made to breach this barrier, particularly using mechanical means such as microinjectors that deliver genetic material into the cell. However, there is concern about damage to the cell membrane caused by intrinsic invasiveness of the micro- or submicrosized needle used in these procedures.
Millions of people with high cholesterol levels are treated with anti-hypolipidemic drugs based on statins that are commonly used to inhibit cholesterol synthesis and lower its serum level. Unfortunately, statins can have two major side effects, although they occur relatively rarely: raised liver enzymes and skeletal muscle pain or even damage. Pharmaceutical research efforts are therefore underway to develop alternative compounds that avoid these potential problems. A promising drug that works via a different mechanism than statin-based drugs, Probucol (PBC), has several advantages over other drugs - better acceptance, ease of administration, and it is much cheaper. Its downside is that its solubility is extremely poor, which considerably lowers its efficiency to suppress cholesterol. A Japanese-U.S. team has now shown that a nanoparticle processing approach enhances the bioavailability of PBC and they demonstrate the design of a solid dosage form for practical use.
Carbon nanotubes (CNTs) have already been explored as drug carriers into mammalian cells. Compared to nanoparticles, CNTs have a larger inner volume which allows more drug molecules to be encapsulated, and this volume is more easily accessible because the end caps can be easily removed, and they have distinct inner and outer surfaces for functionalization. In addition to nanomedicine applications, plant science research focusing on investigation of plant genomics and gene function as well as improvement of crop species has become a nanotechnology frontier. To what degree nanomaterials can be employed in delivering payloads into plant cells is a subject that has not yet been explored very well although there appears to be demand from plant cell biologists to take advantage of nanomaterials.
The future of tissue and cell engineering depends on the development of next-generation biomaterials that have full control over cell attachment and development into tissue. Since surface topography influences many aspects of cellular and molecular responses, surfaces of implanted devices for instance will one day be engineered to the desired cell shape and cell responses at the point of implantation. The usual techniques of cell patterning are based on passive methods where the intrinsic adhesive properties of the cell are exploited. By creating substrates presenting different areas with particular adhesive characteristics, one can segregate cells on the substrate plane. The main drawback of these techniques is their irreversibility since the differential adhesiveness is permanent. Researchers in France have investigated a new direction for three-dimensional cell patterning that could find applications in tissue engineering. Rather than relying on substrate chemical or physical modifications, they perform the cell patterning using external magnetic forces with which they control the organization of cells on a substrate and create a 3D multicellular assembly.
Ever since doctors started replacing worn or damaged bones and teeth with plastic, metal, or ceramic parts, scientists have been on a quest to develop the perfect material for these orthopedic and dental implants. Initially, the challenge was to overcome the body's response to foreign materials, i.e. the strong tendency to reject them. While a lot of progress has been made, and millions of patients receive implants every year ranging from teeth to hip joints, medical implants still do not achieve the same fit and stability as the original tissue that they replace. Researchers have found that the response of host organisms to nanomaterials is different than that observed to conventional materials and that nanopatterning of the surface of implant materials therefore leads to much more compatible prostheses. One approach to improving the biological performance of implants is by functionalizing a non-physiological metallic implant surface through the application of biologically active coatings. Researchers in The Netherlands are now proposing a simple and cost-effective alternative to traditional biomedical coatings for bone implants.
In previous Spotlights we have addressed the numerous benefits that nanotechnology materials and applications could bring to the field of neural engineering and neural prostheses. Different biomedical devices implanted in the central nervous system, so-called neural interfaces, already have been developed to control motor disorders or to translate willful brain processes into specific actions by the control of external devices. Examples of existing brain implants include brain pacemakers, to ease the symptoms of such diseases as epilepsy, Parkinson's Disease, dystonia and recently depression; retinal implants that consist of an array of electrodes implanted on the back of the retina, a digital camera worn on the user's body, and a transmitter/image processor that converts the image to electrical signals sent to the brain. As promising as these new devices are, the reliability and robustness of neural interfaces is a major challenge due to the way brain tissue responds to the implant.