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Diamond pillars are all ears
doi:10.1038/nmat4422]. The nanoparticles, which are typically just under 100 nm in diameter, comprise a polylactic acid (PLA) core and a surface of hyperbranched polyglycerol (HPG). The UV filter is held in the core of the nanoparticle and the hydroxyl surface is converted to one rich in aldehyde groups, which stick to biological molecules like proteins. ‘‘The bioadhesive nanoparticles adhere strongly to the skin and retain UV filter molecules within the core,’’ explains Saltzman. In mouse models, the team found that the UV filter-containing BNPs remain on the surface and do not penetrate into the skin, in marked contrast to nonbioadhesive nanoparticles or padimate-O alone. Moreover, a much lower
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concentration of active sunscreen has a comparable anti-UV effect when applied in combination with BNPs compared with commercial formulations. In fact, the researchers found that just 5% of the amount of UV filter used in commercial sunscreens is needed to achieve the same level of protection in their nanoparticlebased formulation. The BNP-based sunscreen has an additional practical advantage—while it is water resistant, it can be readily wiped off with a towel or left to slough off with dead skin cells without any harmful effect. Encapsulating padimate-O in nanoparticles appears to have another benefit, as well. In the researchers’ study, the BNP-based formulation significantly reduces a type of DNA damage called double-strand breaks.
‘‘We have taken UV agents that are known to be effective, combined them with materials that are known to be safe, and produced a better sunblock,’’ says Saltzman. ‘‘[Our] sunblock is more effective, longer-lasting, and less toxic than any previously described.’’ Saltzman believes the tactic should work with other UV filters too, and is now planning the first tests of the BNPbased formulation on human volunteers. ‘‘This is a promising approach that could protect against the collateral damage potentially inflicted by the penetration of active sunscreen agents into cells,’’ says Peter J. McHugh of the University of Oxford. This paper was originally published in Nano Today (2015), doi:10.1016/j.nantod. 2015.10.003. Cordelia Sealy
cally have only 12–22 electrodes, so there is some inevitable shortcoming in fine hearing and the ability to resolve speech or music. Many patients also lack excitable neurons altogether. Now, Mikael Karlsson, Hao Li, and Helge Rask-Andersen, along with co-workers, have found that human inner-ear ganglion neurites attach preferentially to micro-textured nanocrystalline diamond deposited on silicon pillars. The 5 5 micron nailhead-shaped pillars, spaced 4–9 microns apart, were fabricated using sputtering,
photolithography, and plasma etching techniques. Samples of human and mouse inner ear ganglion tissue were then placed on the textured surface and cultured in growth medium for two weeks. Ganglion cells appear to adhere readily to the micro-textured nanocrystalline diamond surface, even without the usually required extracellular matrix coating. Moreover, auditory neurons grow preferentially wherever there is micro-textured nanocrystalline diamond, forming a fine network of regenerated axons. But when the growing
Diamond pillars are all ears Diamond-coated micro-sized pillars could sharpen up cochlear implants by acting as a guide for regrowing auditory neurons, according to researchers from Uppsala University in Sweden [Cai, et al., Acta Biomater. (2015), doi:10.1016/j.actbio.2015.11.021]. Cochlear implants are now widely used to treat patients – especially children – with profound hearing loss. The devices make up for the lack of neural stimulation from vibration-receptor hair cells by providing an artificial stimulus. But the ear has some 3400 inner hairs cells, while devices typi-
Scanning electron micrograph of micrometer-sized nanocrystalline diamond before culturing with mouse ganglion cells (left) and after (right).
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Materials Today Volume 19, Number 2 March 2016
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axons come to the edge of the textured nanocrystalline diamond, they halt and do not migrate further. Since the axons grow in an ordered manner along the nanocrystalline diamond pillars, the researchers believe the approach could be used for neural guidance and to create new neural materials. Together with its antibacterial and electrical properties, textured nanocrystalline diamond could make an ideal electrode for cochlear implants, providing electrical stimulation signals of nerve NEWS 68
Materials Today Volume 19, Number 2 March 2016
cells and facilitating the regeneration of new neurons. In theory, several or small groups of nanocrystalline diamond pillars could make up individual electrodes, vastly increasing the number of stimulation points in an implant and improving the resolution of sound though a cochlear implant. ‘‘After an organized network of neurites is achieved, it becomes possible to stimulate the neurons selectively,’’ explains Li.
But, the researchers caution, there are still many obstacles to resolve first, such as the stiffness of diamond and the ability to connect it up to external platinum wires. The researchers are now working on micro multi-electrode array chips based on textured nanocrystalline diamond, says Karlsson, which will be tested in vitro and animal studies. Cordelia Sealy
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concentration of active sunscreen has a comparable anti-UV effect when applied in combination with BNPs compared with commercial formulations. In fact, the researchers found that just 5% of the amount of UV filter used in commercial sunscreens is needed to achieve the same level of protection in their nanoparticlebased formulation. The BNP-based sunscreen has an additional practical advantage—while it is water resistant, it can be readily wiped off with a towel or left to slough off with dead skin cells without any harmful effect. Encapsulating padimate-O in nanoparticles appears to have another benefit, as well. In the researchers’ study, the BNP-based formulation significantly reduces a type of DNA damage called double-strand breaks.
‘‘We have taken UV agents that are known to be effective, combined them with materials that are known to be safe, and produced a better sunblock,’’ says Saltzman. ‘‘[Our] sunblock is more effective, longer-lasting, and less toxic than any previously described.’’ Saltzman believes the tactic should work with other UV filters too, and is now planning the first tests of the BNPbased formulation on human volunteers. ‘‘This is a promising approach that could protect against the collateral damage potentially inflicted by the penetration of active sunscreen agents into cells,’’ says Peter J. McHugh of the University of Oxford. This paper was originally published in Nano Today (2015), doi:10.1016/j.nantod. 2015.10.003. Cordelia Sealy
cally have only 12–22 electrodes, so there is some inevitable shortcoming in fine hearing and the ability to resolve speech or music. Many patients also lack excitable neurons altogether. Now, Mikael Karlsson, Hao Li, and Helge Rask-Andersen, along with co-workers, have found that human inner-ear ganglion neurites attach preferentially to micro-textured nanocrystalline diamond deposited on silicon pillars. The 5 5 micron nailhead-shaped pillars, spaced 4–9 microns apart, were fabricated using sputtering,
photolithography, and plasma etching techniques. Samples of human and mouse inner ear ganglion tissue were then placed on the textured surface and cultured in growth medium for two weeks. Ganglion cells appear to adhere readily to the micro-textured nanocrystalline diamond surface, even without the usually required extracellular matrix coating. Moreover, auditory neurons grow preferentially wherever there is micro-textured nanocrystalline diamond, forming a fine network of regenerated axons. But when the growing
Diamond pillars are all ears Diamond-coated micro-sized pillars could sharpen up cochlear implants by acting as a guide for regrowing auditory neurons, according to researchers from Uppsala University in Sweden [Cai, et al., Acta Biomater. (2015), doi:10.1016/j.actbio.2015.11.021]. Cochlear implants are now widely used to treat patients – especially children – with profound hearing loss. The devices make up for the lack of neural stimulation from vibration-receptor hair cells by providing an artificial stimulus. But the ear has some 3400 inner hairs cells, while devices typi-
Scanning electron micrograph of micrometer-sized nanocrystalline diamond before culturing with mouse ganglion cells (left) and after (right).
67
NEWS
Materials Today Volume 19, Number 2 March 2016
NEWS
axons come to the edge of the textured nanocrystalline diamond, they halt and do not migrate further. Since the axons grow in an ordered manner along the nanocrystalline diamond pillars, the researchers believe the approach could be used for neural guidance and to create new neural materials. Together with its antibacterial and electrical properties, textured nanocrystalline diamond could make an ideal electrode for cochlear implants, providing electrical stimulation signals of nerve NEWS 68
Materials Today Volume 19, Number 2 March 2016
cells and facilitating the regeneration of new neurons. In theory, several or small groups of nanocrystalline diamond pillars could make up individual electrodes, vastly increasing the number of stimulation points in an implant and improving the resolution of sound though a cochlear implant. ‘‘After an organized network of neurites is achieved, it becomes possible to stimulate the neurons selectively,’’ explains Li.
But, the researchers caution, there are still many obstacles to resolve first, such as the stiffness of diamond and the ability to connect it up to external platinum wires. The researchers are now working on micro multi-electrode array chips based on textured nanocrystalline diamond, says Karlsson, which will be tested in vitro and animal studies. Cordelia Sealy