Nano News: 02/13/15

Nanotechnology in dentistry - applications, hazards, benefits

There appears to be many potential benefits to patient outcome from using nanotechnology in dentistry. The benefits include new materials for preventative health care using dentifrices that are either antimicrobial and/or have some restorative properties for the enamel and dentine. A new review paper in ("Review of Nanomaterials in Dentistry: Interactions with the Oral Microenvironment, Clinical Applications, Hazards, and Benefits") aims to detail the ultrafine structure, chemical composition, and reactivity of dental tissues in the context of interactions with ENMs, including the saliva, pellicle layer, and oral biofilm; then describes the applications of ENMs in dentistry in context with beneficial clinical outcomes versus potential risks. nanomaterials in dentistry

The use of engineered nanomaterials (ENMs) to enhance themechanical and physiological functions of the tooth via new nanofillers and composites should provide an enhanced capability for some areas of restorative dentistry. The use of ENMs to improve osseointegration, infection control, and biocompatibility of dental implants may reduce the rejection rates in some invasive procedures. There are also completely new frontiers in dental treatment such as the use of ENMs to control and direct pulp stem cells in order to regenerate the tooth. These potential benefits should be balanced against the risks. For the patient the exposure to ENMs will be controlled by the planned dental treatment, and thus, the main concern is on the hazard of the ENMs in dental materials. The data so far indicates that oral toxicity for ENMs is low, but some ENMs are translocated across the gut to cause systemic disturbances, perhaps with organ pathology. However, the matrix in which the ENM is incorporated will be important, and oral toxicity studies have yet to be done with dental materials containing EMNs. Overall, however, the information so far indicates that the oral hazard is low or manageable and should not be a barrier to the safe innovation of nanotechnology in dentistry. The safety assessment processes in place for medicines and medical devices remain robust, and although individual toxicity tests may need modifications to work well with ENMs, the overall safety strategy is appropriate. Nonetheless, there are some improvements in health and safety that can be made. For example, better guidance to practitioners on nano-incorporated products with respect to patient safety and occupational health. For the public and patients, the nanospecific labeling on the many personal care products in dentistry could be improved to clearly identify the nanoingredient(s). Thus, giving clarity on whether a product actually contains an ENM and what the proposed mode of action or benefit of the new product might be to the consumer.

Scientists establish the source of the peculiar stability of the structures forming carbon nanotubes

The source of the peculiar stability of the structures forming carbon nanotubes has been established by researchers from the RIKEN Elements Chemistry Laboratory ("n-Plane Aromaticity in Cycloparaphenylene Dications: A Magnetic Circular Dichroism and Theoretical Study"). Carbon nanotubes are made of hoop-like macrocycles called cycloparaphenylenes (CPPs), which themselves are formed by the interlinking of six-carbon benzene rings. Ever since the first synthesis of a molecule in this family in 2008, researchers have been racing to make different sized rings and to explore their chemistry.

A cycloparaphenylene consisting of eight benzene rings displays rare aromatic stability in its dication (2+) state. (Image: Atsuya Muranaka, RIKEN Elements Chemistry Laboratory) A dication (2+) form of cycloparaphenylene consisting of eight benzene rings (Fig. 1) had previously been found to be unexpectedly stable, but the reason for this stability was unclear. Atsuya Muranaka and Masanobu Uchiyama from RIKEN with co-workers from the University of Tokyo and Kyoto University have now discovered that the stability originates from aromatic stabilization. The team first made the dication [8]CPP2+ by treating the neutral macrocycle [8]CPP with a strong antimony-based oxidizing agent. They then probed its electronic structure using a technique known as magnetic circular dichroism spectroscopy. Through extensive theoretical studies based on the acquired data, the team eventually found that in the dication [8]CPP2+, certain atomic orbitals—the envelope in which the atom’s electrons circulate—overlap both inside and outside the ring to create a stable planar ring arrangement called aromaticity. As predicted, the neutral [8]CPP macrocycle displayed no evidence of aromaticity. The team then probed the electronic structure of the radical cation [8]CPP•+, which had also shown anomalous stability in earlier studies. The radical cation is not aromatic, as it lacks the correct number of electrons. “Instead,” notes Muranaka, “the stability of the radical cation may be associated with spin delocalization over the nanohoop.” In-plane aromaticity is rare, having been reported in only a few molecules. “To date, molecules with in-plane aromaticity have been limited to highly substituted fullerene derivatives such as C60Cl30,” says Muranaka. Further calculations led the team to predict that all the dications and dianions of cycloparaphenylenes containing between five and ten benzene rings possess in-plane aromaticity. They also found, unexpectedly, that a linear relationship exists between the ring size and its aromatic character. “We did not expect that the aromatic character would increase with decreasing size of cycloparaphenylene rings,” Muranaka says. One reason for the interest in these molecules is their large range of potential applications. Neutral CPPs, for example, could be used as seeds or templates for growing carbon nanotubes, while the strong infrared absorption of the dication could find use in organic dyes and pigments.

Frst successful demonstration of the biomedical use of gold nanotubes in human cancer model

Scientists have shown that gold nanotubes have many applications in fighting cancer: internal nanoprobes for high-resolution imaging; drug delivery vehicles; and agents for destroying cancer cells. The study, published today in the journal ("Engineering Gold Nanotubes with Controlled Length and Near-Infrared Absorption for Theranostic Applications"), details the first successful demonstration of the biomedical use of gold nanotubes in a mouse model of human cancer.

Pulsed near infrared light (shown in red) is shone onto a tumour (shown in white) that is encased in blood vessels. The tumour is imaged by multispectral optoacoustic tomography via the ultrasound emission (shown in blue) from the gold nanotubes. (Image: Jing Claussen (Ithera Medical, Germany) Study lead author Dr Sunjie Ye, who is based in both the School of Physics and Astronomy and the Leeds Institute for Biomedical and Clinical Sciences at the University of Leeds, said: "High recurrence rates of tumours after surgical removal remain a formidable challenge in cancer therapy. Chemo- or radiotherapy is often given following surgery to prevent this, but these treatments cause serious side effects. Gold nanotubes - that is, gold nanoparticles with tubular structures that resemble tiny drinking straws - have the potential to enhance the efficacy of these conventional treatments by integrating diagnosis and therapy in one single system." The researchers say that a new technique to control the length of nanotubes underpins the research. By controlling the length, the researchers were able to produce gold nanotubes with the right dimensions to absorb a type of light called 'near infrared'. The study's corresponding author Professor Steve Evans, from the School of Physics and Astronomy at the University of Leeds, said: "Human tissue is transparent for certain frequencies of light - in the red/infrared region. This is why parts of your hand appear red when a torch is shone through it. "When the gold nanotubes travel through the body, if light of the right frequency is shone on them they absorb the light. This light energy is converted to heat, rather like the warmth generated by the Sun on skin. Using a pulsed laser beam, we were able to rapidly raise the temperature in the vicinity of the nanotubes so that it was high enough to destroy cancer cells." In cell-based studies, by adjusting the brightness of the laser pulse, the researchers say they were able to control whether the gold nanotubes were in cancer-destruction mode, or ready to image tumours. In order to see the gold nanotubes in the body, the researchers used a new type of imaging technique called 'multispectral optoacoustic tomography' (MSOT) to detect the gold nanotubes in mice, in which gold nanotubes had been injected intravenously. It is the first biomedical application of gold nanotubes within a living organism. It was also shown that gold nanotubes were excreted from the body and therefore are unlikely to cause problems in terms of toxicity, an important consideration when developing nanoparticles for clinical use. Study co-author Dr James McLaughlan, from the School of Electronic & Electrical Engineering at the University of Leeds, said: "This is the first demonstration of the production, and use for imaging and cancer therapy, of gold nanotubes that strongly absorb light within the 'optical window' of biological tissue. "The nanotubes can be tumour-targeted and have a central 'hollow' core that can be loaded with a therapeutic payload. This combination of targeting and localised release of a therapeutic agent could, in this age of personalised medicine, be used to identify and treat cancer with minimal toxicity to patients." The use of gold nanotubes in imaging and other biomedical applications is currently progressing through trial stages towards early clinical studies.