Chitin nanofibrils modulate mechanical response in tympanic membrane replacements.

The tympanic membrane (TM), is a thin tissue lying at the intersection of the outer and the middle ear. TM perforations caused by traumas and infections often result in a conductive hearing loss. Tissue engineering has emerged as a promising approach for reconstructing the damaged TM by replicating the native material characteristics. In this regard, chitin nanofibrils (CN), a polysaccharide-derived nanomaterial, is known to exhibit excellent biocompatibility, immunomodulation and antimicrobial activity, thereby imparting essential qualities for an optimal TM regeneration. This work investigates the application of CN as a nanofiller for poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) copolymer to manufacture clinically suitable TM scaffolds using electrospinning and fused deposition modelling. The inclusion of CN within the PEOT/PBT matrix showed a three-fold reduction in the corresponding electrospun fiber diameters and demonstrated a significant improvement in the mechanical properties required for TM repair. Furthermore, in vitro biodegradation assay highlighted a favorable influence of CN in accelerating the scaffold degradation over a period of one year. Finally, the oto- and cytocompatibility response of the nanocomposite substrates corroborated their biological relevance for the reconstruction of perforated eardrums.

Neuron Compatibility and Antioxidant Activity of Barium Titanate and Lithium Niobate Nanoparticles.

The biocompatibility and the antioxidant activity of barium titanate (BaTiO3) and lithium niobate (LiNbO3) were investigated on a neuronal cell line, the PC12, to explore the possibility of using piezoelectric nanoparticles in the treatment of inner ear diseases, avoiding damage to neurons, the most delicate and sensitive human cells. The cytocompatibility of the compounds was verified by analysing cell viability, cell morphology, apoptotic markers, oxidative stress and neurite outgrowth. The results showed that BaTiO3 and LiNbO3 nanoparticles do not affect the viability, morphological features, cytochrome c distribution and production of reactive oxygen species (ROS) by PC12 cells, and stimulate neurite branching. These data suggest the biocompatibility of BaTiO3 and LiNbO3 nanoparticles, and that they could be suitable candidates to improve the efficiency of new implantable hearing devices without damaging the neuronal cells.

Immune Response After Cochlear Implantation.

A cochlear implant (CI) is an electronic device that enables hearing recovery in patients with severe to profound hearing loss. Although CIs are a successful treatment for profound hearing impairment, their effectivity may be improved by reducing damages associated with insertion of electrodes in the cochlea, thus preserving residual hearing ability. Inner ear trauma leads to inflammatory reactions altering cochlear homeostasis and reducing post-operative audiological performances and electroacoustic stimulation. Strategies to preserve residual hearing ability led to the development of medicated devices to minimize CI-induced cochlear injury. Dexamethasone-eluting electrodes recently showed positive outcomes. In previous studies by our research group, intratympanic release of dexamethasone for 14 days was able to preserve residual hearing from CI insertion trauma in a Guinea pig model. Long-term effects of dexamethasone-eluting electrodes were therefore evaluated in the same animal model. Seven Guinea pigs were bilaterally implanted with medicated rods and four were implanted with non-eluting ones. Hearing threshold audiograms were acquired prior to implantation and up to 60 days by recording compound action potentials. For each sample, we examined the amount of bone and fibrous connective tissue grown within the scala tympani in the basal turn of the cochlea, the cochleostomy healing, the neuronal density, and the correlation between electrophysiological parameters and histological results. Detection of tumor necrosis factor alpha, interleukin-6, and foreign body giant cells showed that long-term electrode implantation was not associated with an ongoing inflammation. Growth of bone and fibrous connective tissue around rods induced by CI was reduced in the scala tympani by dexamethasone release. For cochleostomy sealing, dexamethasone-treated animals showed less bone tissue growth than negative. Dexamethasone did not affect cell density in the spiral ganglion. Overall, these results support the use of dexamethasone as anti-inflammatory additive for eluting electrodes able to protect the cochlea from CI insertion trauma.

Lithium niobate nanoparticles as biofunctional interface material for inner ear devices.

Sensorineural hearing loss (SNHL) affects the inner ear compartment and can be caused by different factors. Usually, the lack, death, or malfunction of sensory cells deputed to transduction of mechanic-into-electric signals leads to SNHL. To date, the therapeutic option for patients impaired by severe or profound SNHL is the cochlear implant (CI), a high-tech electronic device replacing the entire cochlear function. Piezoelectric materials have catalyzed attention to stimulate the auditory neurons by simply mimicking the function of the cochlear sensory epithelium. In this study, the authors investigated lithium niobate (LiNbO3) as a potential candidate material for next generation CIs. LiNbO3 nanoparticles resulted otocompatible with inner ear cells in vitro, had a pronounced immunomodulatory activity, enhanced human beta-defensin in epithelial cells, and showed direct antibacterial activity against P. aeruginosa. Moreover, LiNbO3 nanoparticles were incorporated into poly(vinylidene fluoride-trifluoro ethylene) fibers via electrospinning, which enhanced the piezoelectric response. Finally, the resulting fibrous composite structures support human neural-like cell growth in vitro, thus showing promising features to be used in new inner ear devices.

Biocompatibility of glycerol monooleate nanoparticles as tested on inner ear cells.

Sensorineural hearing loss due to aging, noise exposure, trauma or drug ototoxicity is irreversible because cochlear hair cells and neurons cannot regenerate. Recently, therapeutic strategies involving nanoparticles have been developed as innovative drug delivery systems. Thermodynamically stable liquid crystalline nanoparticles based on the polar lipid glycerol monooleate (GMO NP, cubosomes), nontoxic and able to encapsulate both hydrophilic and hydrophobic compounds, were produced and tested for biocompatibility in an immortalized Organ of Corti derived cell line (OC-k3), through cell viability and cytomorphological assays, and Western blot expression profiles of apoptotic markers. Overall, the GMO NP were biocompatible in OC-k3 at the doses and time tested, supporting previous data obtained in a neuronal cell line (PC12). The results encourage further tests on GMO NP-mediated drug release with improved target specificity and could be useful to develop innovative therapies against sensorineural hearing loss.

Cisplatin-Induced Ototoxicity: Updates on Molecular Targets.

Cis-diamminedichloridoplatinum (II) (cisplatin) is a chemotherapeutic drug currently prescribed for the treatment of many types of human cancer, but its use is associated with numerous adverse effects, one of which is ototoxicity. Cisplatin-induced hearing loss is mainly attributed to oxidative stress, but recent data suggest that inflammation could be the trigger event leading to inner ear cell death through endoplasmic reticulum (ER) stress, autophagy, necroptosis, and then intrinsic apoptosis. In this review, we look at the molecular targets of cisplatin, and the intracellular pathways underlying its ototoxicity. Special attention is devoted to signal transduction processes involving cisplatin that may promote the development of new strategies to prevent cisplatin-induced hearing loss, an adverse event with severe social impacts.

Polydimethylsiloxanes biocompatibility in PC12 neuronal cell line.

Cochlear implants, the only way to recover from severe/profound hearing loss, may cause adverse effects, among which reactions to silicone materials coating implant electrodes, leading to apoptosis and necrosis of spiral ganglion cells. Our aim was to evaluate whether three polydimethylsiloxane (PDMS) compounds (hexadimethylsiloxane, octamethyltrisiloxane, decamethylcyclopentasiloxane) used in silicone rods could exert toxic effects on an in vitro neuronal cell model (PC12). Cell viability, morphology and mRNA expression levels of apoptotic markers were evaluated on PC12 cells at different PDMS dilutions up to 6 days of exposure. The results showed that at the highest concentrations tested cell viability was reduced by hexadimethylsiloxane and octamethyltrisiloxane at all times of exposure, but only from 72 h onwards by decamethylcyclopentasiloxane. The number of neurites per cell was not affected by hexadimethylsiloxane, but was significantly reduced from 24 h onwards by octamethyltrisiloxane and decamethylcyclopentasiloxane. Neurite length was reduced by hexadimethylsiloxane only at 24 h, and by octamethyltrisiloxane and decamethylcyclopentasiloxane at all exposure intervals. In controls exposed to silicone or glass rods cell viability was reduced only after 24 h, but neurite number and length was never reduced at any exposure interval. Biomolecular investigations showed that apoptotic markers did not change in any experimental condition, suggesting that PDMS are biocompatible. The reduction of cell viability and neurite number and length caused by exposure to these compounds was probably caused by a PDMS surface film formed over the cell medium, preventing air exchange, and not by the release of cytotoxic molecules.