Piezoelectric thin films as artificial sensory epithelium for cochlear prosthetics

The cochlea is a spiral shaped duct located in the inner ear and it represents the receptor organ for hearing allowing the conversion of sound-induced vibration into electrical impulses that are transmitted to the central nervous system. The cochlea is composed of three fluid-filled compartments one of which, the scala media, contains sensory cells called hair cells. These cells are sensitive to a mechanical stimulus and they are innervated by afferent nerve fibers. The hair cells are positioned onto a flexible membrane, the basilar membrane, that vibrates as a sound wave reaches the cochlea. The displacement of the membrane causes the receptor cells to change their potential and this produce a stimulation of the synaptic neurons that transmit an electrical signal to the brain. In this way the characteristics of a sound, such us pitch, loudness and timbre, are perceived and recognized. The cochlear cells survive for life without renewal thus a their damage causes a irreversible loss of the auditory function. In fact if the hair cell are missing, in the presence of an incoming sound, the stimulation of the auditory nerve and the transmission of the electrical signal to the brain does not occur. According to the most recent estimates of the World Health Organization (2011) over 360 million persons (5.3% of the world population) have disabling hearing loss. The main consequences of hearing impairment are the inability to interpret speech sounds that limits the communication with others and causes difficulties in both professional and social life. Furthermore hearing loss also leads to a strong economic impact for a society due to the costs concerning the medical treatments and social services that must be provided by the medical care and welfare system. These represents valid motivations for the search of new medical therapy in order to improve or restore the hearing function of deaf people. At present, for the most severe cases of hearing loss, the only medical therapy to obtain a partial hearing restoration is the use of cochlear implant which function is to bypass the missing inner hair cells providing, in the presence of a sound, an electrical stimulation to the auditory nerve. Although the cochlear implants increase hearing capabilities these devices have many disadvantages, such as high cost, high complexity from both hardware and software point of view, health risks due to surgical insert of many components, need of a battery for working. In the recent years, the idea to use smart materials to mimic the function of the inner hair cells has emerged. In particular, a new approach for obtaining the electrical stimulation of the auditory neurons has been proposed based on the use of piezoelectric materials that provide an electrical charge in response to a mechanical stimulus in a wireless modality. In line with this approach, the study reported in the present thesis work aimed at developing a biomimetic device that could replace a damaged cochlear epithelium and thus provide electrical stimulation of the auditory nerves. To the purpose, thin biocompatible piezoelectric films were prepare having vibrational response similar to the basilar membrane and also capability to generate an electrical signal as a consequence of a deformation provoked by an applied sound. In particular, a new piezoelectric composite material was obtained by dispersing barium titanate nanoparticles (BTNPs) into a matrix of poly(vinyldene fluoride- trifluoroethylene) (P(VDF-TrFE)). This composite was first used to develop a prototype of the basilar membrane which was mechanically characterized in term of its vibrating properties. Then, the biocompatibility of the material and its capability to induce electric stimulation to neural cells were evaluated with in vitro experiments. More in detail, the piezoelectric composite films were used as active substrates on which SH-SY5Y neuroblastoma cells were cultured as a model of cochlear sensory neurons. The effect of the electrical stimulation was evaluated in terms of neurite emission from the cells. The results of the work demonstrated the possibility to obtain, through piezoelectric substrates, an electric stimulation of neuronal cells without an external source of electrical energy but simply by applying a mechanical stimulus that in cochlea is provided by an incoming sound. This is a promising characteristic for the future development of self-powered implantable devices that could be used to bypass a damaged cochlear epithelium

Submillimeter spectroscopy of southern hot cores: NGC6334(I) and G327.3-0.6

High-mass star-forming regions are known to have a rich molecular spectrum from many species. Some of the very highly excited lines are emitted from very hot and dense gas close to the central object(s). The physics and chemistry of the inner cores of two high mass star forming regions, NGC6334(I) and G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX telescope provide spectra which sample many molecular lines at high excitation stages. Partial spectral surveys were obtained, the lines were identified, physical parameters were determined through fitting of the spectra. Both sources show similar spectra that are comparable to that of the only other high mass star forming region ever surveyed in this frequency range}, Orion-KL, but with an even higher line density. Evidence for very compact, very hot sources is found.Comment: APEX A&A special issue, accepte

Complex organic molecules in the interstellar medium: IRAM 30 m line survey of Sagittarius B2(N) and (M)

The discovery of amino acids in meteorites and the detection of glycine in samples returned from a comet to Earth suggest that the interstellar chemistry is capable of producing such complex organic molecules. Our goal is to investigate the degree of chemical complexity that can be reached in the ISM. We performed an unbiased, spectral line survey toward Sgr B2(N) and (M) with the IRAM 30m telescope in the 3mm window. The spectra were analyzed with a simple radiative transfer model that assumes LTE but takes optical depth effects into account. About 3675 and 945 spectral lines with a peak signal-to-noise ratio higher than 4 are detected toward N and M, i.e. about 102 and 26 lines per GHz, respectively. This represents an increase by about a factor of 2 over previous surveys of Sgr B2. About 70% and 47% of the lines detected toward N and M are identified and assigned to 56 and 46 distinct molecules as well as to 66 and 54 less abundant isotopologues of these molecules, respectively. We also report the detection of transitions from 59 and 24 catalog entries corresponding to vibrationally or torsionally excited states of some of these molecules, respectively. Excitation temperatures and column densities were derived for each species but should be used with caution. Among the detected molecules, aminoacetonitrile, n-propyl cyanide, and ethyl formate were reported for the first time in space based on this survey, as were 5 rare isotopologues of vinyl cyanide, cyanoacetylene, and hydrogen cyanide. We also report the detection of transitions from within 12 new vib. or tors. excited states of known molecules. Although the large number of unidentified lines may still allow future identification of new molecules, we expect most of these lines to belong to vib. or tors. excited states or to rare isotopologues of known molecules for which spectroscopic predictions are currently missing. (abridged)Comment: Accepted for publication in A&A. 266 pages (39 pages of text), 111 tables, 8 figure

High-resolution study of a star-forming cluster in the Cep-A HW2 region

Due to its relatively small distance (725 pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes. Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. Goal of our work is to ascertain the nature of this structure. We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On the 1-arcsecond (about 725 AU) scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out, but such structure is likely to be detected on a smaller spatial scale, or using different molecular tracers.Comment: 6 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

First interstellar detection of OH+

The Atacama Pathfinder Experiment (APEX) 12m telescope was used to observe the N=1-0, J=0-1 ground state transitions of OH+ at 909.1588 GHz with the CHAMP+ heterodyne array receiver. Two blended hyperfine structure transitions were detected in absorption against the strong continuum source Sagittarius B2(M) and in several pixels offset by 18". Both, absorption from Galactic center gas as well as absorption from diffuse clouds in intervening spiral arms in a velocity range from -116 to 38.5 km/s is observed. The total OH+ column density of absorbing gas is 2.4 \times 10^15 cm-2. A column density local to Sgr B2(M) of 2.6 \times 10^14 cm-2 is found. On the intervening line-of-sight the column density per unit velocity interval are in the range from 1 to 40 \times 10^12 cm-2/(km/s). OH+ is found to be on average more abundant than other hydrides such as SH+ and CH+. Abundance ratios of OH and atomic oxygen to OH+ are found to be in the range of 10^1-2 and 10^3-4, respectively. The detected absorption of a continuous velocity range on the line-of-sight shows OH+ to be an abundant component of diffuse clouds.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy and Astrophysic

Molecular line survey of the high-mass star-forming region NGC 6334I with Herschel/HIFI and the SMA

We aim at deriving the molecular abundances and temperatures of the hot molecular cores in the high-mass star-forming region NGC 6334I and consequently deriving their physical and astrochemical conditions. In the framework of the Herschel guaranteed time key program CHESS, NGC 6334I is investigated by using HIFI aboard the Herschel Space Observatory. A spectral line survey is carried out in the frequency range 480-1907 GHz, and auxiliary interferometric data from the SMA in the 230 GHz band provide spatial information for disentangling the different physical components contributing to the HIFI spectrum. The spectral lines are identified with the aid of former surveys and spectral line catalogs. The observed spectrum is then compared to a simulated synthetic spectrum with XCLASS, assuming local thermal equilibrium, and best fit parameters are derived using the model optimization package MAGIX. A total of 46 molecules are identified, with 31 isotopologues, resulting in about 4300 emission and absorption lines. High- energy levels of the dominant emitter methanol and vibrationally excited HCN are detected. The number of unidentified lines remains low with 75, or less than 2 percent of the lines detected. The modeling suggests that several spectral features need two or more components to be fitted properly. Other components could be assigned to cold foreground clouds or to outflows, most visible in the SiO emission. A chemical variation between the two embedded hot cores is found, with more N-bearing molecules identified in SMA1 and O-bearing molecules in SMA2. Spectral line surveys give powerful insights into the study of the interstellar medium. Different molecules trace different physical conditions like the inner hot core, the envelope, the outflows or the cold foreground clouds. The derived molecular abundances provide further constraints for astrochemical models.Comment: 30 pages including appendix, 49 figures, accepted for publication in Astronomy and Astrophysic