Drug delivery for treatment of inner ear disease: current state of knowledge. Ear Hear. 2010;31:156-165. [PMID: 19952751 DOI: 10.1097/aud.0b013e3181c351f2]

Global trend analysis, mechanistic insights and future directions of autoimmune ear diseases: Based on comprehensive findings over the past 20 years

BACKGROUND

In recent years, Autoimmune diseases (ADs) and hearing loss are both significant public health burdens worldwide. An increasing number of studies are focusing on the potential link between these two diseases and exploring how hearing loss can be prevented and treated in the context of autoimmune diseases. In response to this focus, it is very necessary to conduct bibliometric analysis and molecular mechanism exploration to provide guidance for the exploration of basic mechanisms and clinical management.

METHOD

Studies focusing on hearing loss and autoimmune disease were extracted from the Web of Science Core Collection database from 2000 to 2024. Bibliometric and visual analysis of the collected publications was conducted using VOSviewer and CiteSpace. The investigation of molecular pathways associated with diseases was carried out in the GeneCards and STRING databases.

RESULTS

A total of 696 papers met the inclusion and exclusion criteria and were chosen for further research. The number of papers on hearing loss and autoimmune diseases is increasing every year. These papers were mainly from 65 countries, led by the United States, China and Italy. These investigations included 3505 authors in total, with Greco A contributing the most publications. Harvard Medical School and Sapienza University Rome were the two institutions with the highest number of publications. Otology & Neurotology was the journal with the highest number of publications. The most common keywords include " sensorineural hearing loss", "endolymphatic hydrops", "management" and "autoimmune", which represent current and prospective future research trends and target topics in the field. Among them, the highest proportion of hearing loss in autoimmune ear diseases is sensorineural hearing loss, and the highest proportion of primary autoimmune ear diseases is Autoimmune inner ear disease. In addition, A total of 295 potential targets common to both diseases were also identified. Their pathogenesis involves cancer pathways, infectious disease pathways, cell senescence, epithelial and myocyte proliferation, hypoxia response, and inflammatory response.

CONCLUSION

This bibliometric analysis reveals global research trends on hearing loss in the context of autoimmune diseases. Based on this, combined with preliminary bioinformatics analysis, a potential yet close link between the autoimmune diseases and hearing loss has been demonstrated. The current study highlights the need to fully consider the common genetic and pathophysiological mechanisms of these two types of diseases to promote interdisciplinary research and the development of personalized treatments for this clinical focus, with particular attention to the elderly population with comorbidity diseases. A deeper understanding of disease mechanisms has also led to advances in the clinical management of autoimmune ear diseases, including diagnosis and treatment.

Hearing loss during chemotherapy: prevalence, mechanisms, and protection

Ototoxicity is an often-underestimated sequela for cancer patients undergoing chemotherapy, with an incidence rate exceeding 50%, affecting approximately 4 million individuals worldwide each year. Despite the nearly 2,000 publications on chemotherapy-related ototoxicity in the past decade, the understanding of its prevalence, mechanisms, and preventative or therapeutic measures remains ambiguous and subject to debate. To date, only one drug, sodium thiosulfate, has gained FDA approval for treating ototoxicity in chemotherapy. However, its utilization is restricted. This review aims to offer clinicians and researchers a comprehensive perspective by thoroughly and carefully reviewing available data and current evidence. Chemotherapy-induced ototoxicity is characterized by four primary symptoms: hearing loss, tinnitus, vertigo, and dizziness, originating from both auditory and vestibular systems. Hearing loss is the predominant symptom. Amongst over 700 chemotherapeutic agents documented in various databases, only seven are reported to induce hearing loss. While the molecular mechanisms of the hearing loss caused by the two platinum-based drugs are extensively explored, the pathways behind the action of the other five drugs are primarily speculative, rooted in their therapeutic properties and side effects. Cisplatin attracts the majority of attention among these drugs, encompassing around two-thirds of the literature regarding ototoxicity in chemotherapy. Cisplatin ototoxicity chiefly manifests through the loss of outer hair cells, possibly resulting from damages directly by cisplatin uptake or secondary effects on the stria vascularis. Both direct and indirect influences contribute to cisplatin ototoxicity, while it is still debated which path is dominant or where the primary target of cisplatin is located. Candidates for hearing protection against cisplatin ototoxicity are also discussed, with novel strategies and methods showing promise on the horizon.

Biomedical application of materials for external auditory canal: History, challenges, and clinical prospects

Biomaterials play an integral role in treatment of external auditory canal (EAC) diseases. Regarding the special anatomic structure and physiological characteristics of EAC, careful selection of applicable biomaterials was essential step towards effective management of EAC conditions. The bioactive materials can provide reasonable biocompatibility, reduce risk of host pro-inflammatory response and immune rejection, and promote the healing process. In therapeutic procedure, biomaterials were employed for covering or packing the wound, protection of the damaged tissue, and maintaining of normal structures and functions of the EAC. Therefore, understanding and application of biomaterials was key to obtaining great rehabilitation in therapy of EAC diseases. In clinical practice, biomaterials were recognized as an important part in the treatment of different EAC diseases. The choice of biomaterials was distinct according to the requirements of various diseases. As a result, awareness of property regarding different biomaterials was fundamental for appropriate selection of therapeutic substances in different EAC diseases. In this review, we firstly introduced the characteristics of EAC structures and physiology, and EAC pathologies were summarized secondarily. From the viewpoint of biomaterials, the different materials applied to individual diseases were outlined in categories. Besides, the underlying future of therapeutic EAC biomaterials was discussed.

A Benchtop Round Window Model for Studying Magnetic Nanoparticle Transport to the Inner Ear

INTRODUCTION

The round window membrane (RWM) presents a significant barrier to the local application of therapeutics to the inner ear. We demonstrate a benchtop preclinical RWM model and evaluate superparamagnetic iron oxide nanoparticles (SPIONs) as vehicles for magnetically assisted drug delivery.

METHODS

Guinea pig RWM explants were inset into a 3D-printed dual chamber benchtop device. Custom-synthesized 7-nm iron core nanoparticles were modified with different polyethylene glycol chains to yield two sizes of SPIONs (NP-PEG600 and NP-PEG3000) and applied to the benchtop model with and without a magnetic field. Histologic analysis of the RWM was performed using transmission electron microscopy (TEM) and confocal microscopy.

RESULTS

Over a 4-h period, 19.5 ± 1.9% of NP-PEG3000 and 14.6 ± 1.9% of NP-PEG600 were transported across the guinea pig RWM. The overall transport increased by 1.45× to 28.4 ± 5.8% and 21.0 ± 2.0%, respectively, when a magnetic field was applied. Paraformaldehyde fixation of the RWM decreased transport significantly (NP-PEG3000: 7.6 ± 1.5%; NP-PEG600: 7.0 ± 1.6%). Confocal and electron microscopy analysis demonstrated nanoparticle localization throughout all cellular layers and layer-specific transport characteristics within RWM.

CONCLUSION

The guinea pig RWM explant benchtop model allows for targeted and practical investigations of transmembrane transport in the development of nanoparticle drug delivery vehicles. The presence of a magnetic field increases SPION delivery by 45%-50% in a nanoparticle size- and cellular layer-dependent manner.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:3355-3362, 2024.

A Case Report of Sudden Sensorineural Hearing Loss (SSNHL) After Administration of the COVID-19 Vaccine

Since the issuance of the emergency use authorization (EUA) of 3 coronavirus disease 2019 (COVID-19) vaccines, there have been over 180 million individuals fully vaccinated in the United States (US). With the increasing administration of COVID-19 vaccinations, there have been over 550,000 adverse events reported in the Vaccine Adverse Event Reporting System (VAERS) with approximately 230,000 experienced after receipt of the Pfizer-BioNTech COVID-19 Vaccine as of September 23rd 2021. Audio-vestibular symptoms (including Sudden Sensorineural Hearing Loss (SSNHL)) secondary to immunizations has previously been evaluated. However, this report describes the first case of bilateral sudden sensorineural hearing loss potentially due to the Pfizer-BioNTech COVID-19 vaccine. We further review the available literature regarding the treatment of Sudden Sensorineural Hearing Loss, and the association of SSNHL with previous immunizations and COVID-19 infection. Lastly, we hypothesize the underlying potential mechanisms between SSNHL and the Pfizer-BioNTech COVID-19 vaccine.

Biosafety and potency of high-molecular-weight hyaluronic acid with intratympanic dexamethasone delivery for acute hearing loss

Objective: This study evaluated the potential of high-molecular-weight hyaluronic acid (HHA) as an intratympanic (IT) drug delivery vehicle for dexamethasone (D) in treating acute hearing loss. We compared the efficacy, safety, and residence time of HHA to the standard-of-care IT drug delivery method. Methods: Endoscopic examinations were used to track tympanic membrane (TM) healing post-IT injection. Micro-computed tomography (CT) was used to gauge drug/vehicle persistence in the bulla air space. Histological analyses covered the middle ear, TM, and hair cell counts. Auditory brainstem responses (ABR) were used to measure hearing thresholds, while high-performance liquid chromatography (HPLC) was employed to quantify cochlear perilymph dexamethasone concentrations. Results: The HHA + D group had a notably prolonged drug/vehicle residence time in the bulla (41 ± 27 days) compared to the saline + D group (1.1 ± 0.3 days). Complete TM healing occurred without adverse effects. Histology revealed no significant intergroup differences or adverse outcomes. Hearing recovery trends favored the HHA + D group, with 85.0% of ears showing clinically meaningful improvement. D concentrations in cochlear perilymph were roughly double in the HHA group. Conclusion: HHA is a promising vehicle for IT drug delivery in treating acute hearing loss. It ensures extended residence time, augmented drug concentrations in targeted tissues, and safety. These results highlight the potential for HHA + D to excel beyond existing standard-of-care treatments for acute hearing loss.

Application of lipid and polymeric-based nanoparticles for treatment of inner ear infections via XGBoost

Taking hearing loss as a prevalent sensory disorder, the restricted permeability of blood flow and the blood-labyrinth barrier in the inner ear pose significant challenges to transporting drugs to the inner ear tissues. The current options for hear loss consist of cochlear surgery, medication, and hearing devices. There are some restrictions to the conventional drug delivery methods to treat inner ear illnesses, however, different smart nanoparticles, including inorganic-based nanoparticles, have been presented to regulate drug administration, enhance the targeting of particular cells, and decrease systemic adverse effects. Zinc oxide nanoparticles possess distinct characteristics that facilitate accurate drug delivery, improved targeting of specific cells, and minimized systemic adverse effects. Zinc oxide nanoparticles was studied for targeted delivery and controlled release of therapeutic drugs within specific cells. XGBoost model is used on the Wideband Absorbance Immittance (WAI) measuring test after cochlear surgery. There were 90 middle ear effusion samples (ages = 1-10 years, mean = 34.9 months) had chronic middle ear effusion for four months and verified effusion for seven weeks. In this research, 400 sets underwent wideband absorbance imaging (WAI) to assess inner ear performance after surgery. Among them, 60 patients had effusion Otitis Media with Effusion (OME), while 30 ones had normal ears (control). OME ears showed significantly lower absorbance at 250, 500, and 1000 Hz than controls (p < 0.001). Absorbance thresholds >0.252 (1000 Hz) and >0.330 (2000 Hz) predicted a favorable prognosis (p < 0.05, odds ratio: 6). It means that cochlear surgery and WAI showed high function in diagnosis and treatment of inner ear infections. Regarding the R2 0.899 and RMSE 1.223, XGBoost shows excellent specificity and sensitivity for categorizing ears as having effusions absent or present or partial or complete flows present, with areas under the curve (1-0.944).

Optimization of pharmacological interventions in the guinea pig animal model-a new approach to calculate the perilymph volume of the scala tympani

Objective

The guinea pig serves as a well-established animal model for inner ear research, offering valuable insights into the anatomy, physiology, and therapeutic interventions of the auditory system. However, the heterogeneity of results observed in both in-vivo experiments and clinical studies poses challenges in understanding and optimizing pharmacotherapy outcomes. This heterogeneity may be due to individual differences in the size of the guinea pig cochlea and thus in the volume of the scala tympani (ST), which can lead to different drug concentrations in the ST, a fact that has been largely overlooked thus far. To address this issue, we aimed to develop an approach for calculating the individual volume of perilymph within the ST before and after cochlear implant insertion.

Method

In this study, high-resolution μCT images of a total of n = 42 guinea pig temporal bones were used to determine the volume of the ST. We compared fresh, frozen, and fixed tissues from both colored and albino strains to evaluate the potential influence of tissue condition and strain on the results.

Results

Our findings demonstrate a variability in mean ST volume with a relative standard deviation (RSD) of 14.7%, comparable to studies conducted with humans (range RSD: 5 to 20%). This indicates that the guinea pig cochlea exhibits similar variability to that of the human cochlea. Consequently, it is crucial to consider this variability when designing and conducting studies utilizing the guinea pig as an animal model. Furthermore, we successfully developed a tool capable of estimating ST volume without the need for manual segmentation, employing two geometric parameters, basal diameter (A) and width (B) of the cochlea, corresponding to the cochlear footprint. The tool is available for free download and use on our website.

Conclusion

This novel approach provides researchers with a valuable tool to calculate individual ST volume in guinea pigs, enabling more precise dosing strategies and optimization of drug concentrations for pharmacotherapy studies. Moreover, our study underscores the importance of acknowledging and accounting for inter-individual variability in animal models to enhance the translational relevance and applicability of research outcomes in the field of inner ear investigations.

The Association Between Dehydration and the Prognosis of Sudden Sensorineural Hearing Loss

Background

There is an urgent need to identify undetermined risk factors for sudden sensorineural hearing loss (SSNHL) for the development of effective treatment strategies. SSNHL is likely associated with vascular insufficiency; however, no study has evaluated the relationship between dehydration and SSNHL.

Objective

This study aimed to investigate the role of dehydration in the development and prognosis of sudden sensorineural hearing loss.

Study Design

Retrospective case-control study.

Setting

Secondary referral hospital.

Patients and Interventions

This was a comparative study that compared dehydration parameters between healthy subjects without SSNHL (n = 94) and patients with SSNHL (n = 94). The study also evaluated the effect of dehydrated conditions on the prognosis of SSNHL.

Main Outcome Measures

We compared dehydration parameters, such as the blood urea nitrogen-to-creatinine ratio (BUN/Cre) and plasma osmolality (Posm), between matched healthy subjects without SSNHL and patients with SSNHL. To evaluate the effect of dehydrated conditions on the SSNHL prognosis, the SSNHL patients were divided into 2 groups based on the cutoff value obtained from the receiver operating characteristic analysis: hydrated (n = 50; BUN/Cre <21.4) and dehydrated (n = 44; BUN/Cre ≥21.4) groups. Subsequently, the severity and prognosis of SSNHL were analyzed.

Results

The dehydration parameters, BUN/Cre and Posm, were significantly higher in patients with SSNHL than in healthy subjects. The initial hearing levels and SSNHL grades were worse in the dehydrated group than in the hydrated group. Moreover, a dehydrated condition (BUN/Cre ≥21.4) was associated with a poor SSNHL prognosis in all models of the multiple logistic regression analysis.

Conclusions

The dehydration parameters of BUN/Cre and Posm were higher in patients with SSNHL than in healthy subjects. Additionally, a dehydrated condition (BUN/Cre ≥21.4) was an independent prognostic factor for SSNHL. Level of evidence: Level 4.

A state-of-the-art analysis of pharmacological delivery and artificial intelligence techniques for inner ear disease treatment

Over the last several decades, both the academic and therapeutic fields have seen significant progress in the delivery of drugs to the inner ear due to recent delivery methods established for the systemic administration of drugs in inner ear treatment. Novel technologies such as nanoparticles and hydrogels are being investigated, in addition to the traditional treatment methods. Intracochlear devices, which utilize current developments in microsystems technology, are on the horizon of inner ear drug delivery methods and are designed to provide medicine directly into the inner ear. These devices are used for stem cell treatment, RNA interference, and the delivery of neurotrophic factors and steroids during cochlear implantation. An in-depth analysis of artificial neural networks (ANNs) in pharmaceutical research may be found in ANNs for Drug Delivery, Design, and Disposition. This prediction tool has a great deal of promise to assist researchers in more successfully designing, developing, and delivering successful medications because of its capacity to learn and self-correct in a very complicated environment. ANN achieved a high level of accuracy exceeding 0.90, along with a sensitivity of 95% and a specificity of 100%, in accurately distinguishing illness. Additionally, the ANN model provided nearly perfect measures of 0.99%. Nanoparticles exhibit potential as a viable therapeutic approach for bacterial infections that are challenging to manage, such as otitis media. The utilization of ANNs has the potential to enhance the effectiveness of nanoparticle therapy, particularly in the realm of automated identification of otitis media. Polymeric nanoparticles have demonstrated effectiveness in the treatment of prevalent bacterial infections in pediatric patients, suggesting significant potential for forthcoming therapeutic interventions. Finally, this study is based on a research of how inner ear diseases have been treated in the last ten years (2012-2022) using machine learning.

High-Precision 3D Printing of Microporous Cochlear Implants for Personalized Local Drug Delivery

Hearing loss is a highly prevalent multifactorial disorder affecting 20% of the global population. Current treatments using the systemic administration of drugs are therapeutically ineffective due to the anatomy of the cochlea and the existing blood-labyrinth barrier. Local drug delivery systems can ensure therapeutic drug concentrations locally while preventing adverse effects caused by high dosages of systemically administered drugs. Here, we aimed to design, fabricate, and characterize a local drug delivery system for the human cochlea. The design was relevant to the size of the human ear, included two different shapes, and incorporated two different microporous structures acting as reservoirs for drug loading and release. The four cochlear implant designs were printed using the two-photon polymerization (2PP) technique and the IP-Q photoresist. The optimized 2PP process enabled the fabrication of the cochlear implants with great reproducibility and shape fidelity. Rectangular and cylindrical implants featuring cylindrical and tapered tips, respectively, were successfully printed. Their outer dimensions were 0.6 × 0.6 × 2.4 mm3 (L × W × H). They incorporated internal porous networks that were printed with high accuracy, yielding pore sizes of 17.88 ± 0.95 μm and 58.15 ± 1.62 μm for the designed values of 20 μm and 60 μm, respectively. The average surface roughness was 1.67 ± 0.24 μm, and the water contact angle was 72.3 ± 3.0°. A high degree of polymerization (~90%) of the IP-Q was identified after printing, and the printed material was cytocompatible with murine macrophages. The cochlear implants designed and 3D printed in this study, featuring relevant sizes for the human ear and tunable internal microporosity, represent a novel approach for personalized treatment of hearing loss through local drug delivery.

Injectable Poloxamer Hydrogel Formulations for Intratympanic Delivery of Dexamethasone

BACKGROUND

In this study, we prepared and evaluated an injectable poloxamer (P407) hydrogel formulation for intratympanic (IT) delivery of dexamethasone (DEX).

METHODS

DEX-loaded P407 hydrogels were characterized in terms of thermogelation, drug loading capacities, particle size, and drug release. The in vivo toxicity and drug absorption of the DEX-loaded P407 formulation after IT injection were evaluated using an animal model by performing histopathological analysis and drug concentration measurements.

RESULTS

The P407 hydrogel effectively solubilized hydrophobic DEX and demonstrated a sustained release compared to the hydrophilic DEX formulation. The in vivo study showed that the hydrogel formulation delivered considerable drug concentrations to the inner ear and displayed a favorable safety profile without apparent cytotoxicity or inflammation.

CONCLUSION

P407 hydrogel can be useful as an injectable inner ear delivery formulation for hydrophobic drugs due to their biocompatibility, drug-solubilizing capacity, thermogelation, and controlled release.

CochleRob: Parallel-Serial Robot to Position a Magnetic Actuator around a Patient's Head for Intracochlear Microrobot Navigation

Our work introduces a new robotic solution named CochleRob, which is used for the administration of super-paramagnetic antiparticles as drug carriers into the human cochlea for the treatment of hearing loss caused by damaged cochlea. This novel robot architecture presents two key contributions. First, CochleRob has been designed to meet specifications pertaining to ear anatomy, including workspace, degrees of freedom, compactness, rigidity, and accuracy. The first objective was to develop a safer mathod to administer drugs to the cochlea without the need for catheter or CI insertion. Secondly, we aimed at developing and validating the mathemathical models, including forward, inverse, and dynamic models, to support the robot function. Our work provides a promising solution for drug administration into the inner ear.

Comparison of Intratympanic Steroid and Hyperbaric Oxygen Salvage Therapy Hearing Outcomes in Idiopathic Sudden Sensorineural Hearing Loss: A Retrospective Study

OBJECTIVES

Systemic steroids are the most common first-line therapy in sudden sensorineural hearing loss (SSNHL), with significant improvement in hearing outcomes in over 60% of patients. It is unknown why 40% of patients do not respond to systemic steroid therapy. Salvage treatment includes intratympanic steroids (ITS) and hyperbaric oxygenation (HBO) therapy, with inconsistent results reported. This study aimed to compare the results of ITS and HBO therapy in patients with SSNHL that previously failed systemic steroid therapy.

DESIGN

This is a comparative retrospective nonrandomized interventional cohort study, enrolling 126 patients with SSNHL. Out of these, 35 patients received HBO therapy, 43 patients received ITS, and 48 patients did not receive any second-line therapy (control group). Pure-tone audiograms were performed before and after the salvage therapy in the IT and HBO groups and at the same time interval in the control group. Study variables included age, time until therapy initiation, tinnitus status, and hearing outcomes, with a cutoff criteria of cumulative >30 dB improvement on all frequencies indicating recovery.

RESULTS

ITS and HBO therapy were associated with statistically significant hearing recovery at all frequencies compared to systemic steroids. The results show an average hearing improvement of 13.6 dB overall frequencies (250 to 8000 Hz) after ITS therapy and 7.4 dB in HBO therapy in comparison to the control group. Presence of significant hearing improvement positively correlated with age, ITS therapy, and HBO therapy. Presence of tinnitus before therapy was negatively correlated with hearing improvement. Patients with tinnitus present at the start of therapy improve 4.67 dB less on average compared to those without tinnitus. ITS therapy significantly reduced tinnitus compared to the other two treatment options. Patients with tinnitus present before therapy significantly improve hearing at low frequencies, compared to the control group.

CONCLUSIONS

ITS and HBO therapy show superior hearing results compared to observation alone after failed oral steroid therapy for SSNHL. ITS shows an additional positive impact on tinnitus reduction and shows superior hearing outcomes after salvage therapy.

Time from sudden sensory neural hearing loss to treatment as a prognostic factor

Introduction

The widely accepted treatment for sudden sensorineural hearing loss (SSNHL) is corticosteroid treatment (oral or intratympanic). The main goal of this work is to define the significance of the time between symptom onset and treatment initiation, as well as other prognostic factors, for hearing improvement.

Methods

This retrospective study included 666 patients treated for SSNHL. Demographic data, audiometry, treatment method, time since symptom onset, and associated symptoms were recorded for each patient. The patients were divided into five groups according to the treatment initiation time-half a week, one week, 2 weeks, 3 weeks, or 4 weeks and over-after symptom onset. The degree of improvement was assessed by comparing the audiometry at the beginning and the end of the treatment.

Results

The average period of hearing loss from symptom onset to treatment initiation was 10.8 days. Significant differences were found between the groups of half a week, one week, and 2 weeks and the groups of 3 weeks and 4 weeks and over (each separately, p < 0.001). No difference was found between the half-week, one-week, and two-week groups, nor was there a difference between the three-week and four-week-and-over groups. A correlation was found between the treatment initiation time in days and the degree of improvement in hearing for both speech recognition threshold (SRT) and discrimination, R = 0.26 p < 0.001 and R = 0.17 p < 0.001, respectively. No correlation was found for gender, age of the patients, comorbidities, or associated symptoms.

Conclusion

The threshold for treatment initiation time is up to 2 weeks, after which the amplitude of hearing improvement decreases significantly. The other prognostic factors measured were not found to be statistically significant predictors.

Pyrolyzed Ultrasharp Glassy Carbon Microneedles

Polymeric microneedles fabricated via two-photon polymerization (2PP) lithography enable safe medical access to the inner ear. Herein, the material class for 2PP-lithography-based microneedles is expanded by pyrolyzing 2PP-fabricated polymeric microneedles, resulting in glassy carbon microneedles. During pyrolysis the microneedles shrink up to 81% while maintaining their complex shape when the exposed surface-area-to-volume ratio (SVR) is 0.025 < SVR < 0.04, for the temperature history protocol used herein. The derived glassy carbon is confirmed with energy-dispersive X-ray spectroscopy and Raman spectroscopy. The pyrolyzed glassy carbon has Young's modulus 9.0 GPa. As a brittle material, the strength is stochastic. Using the two-parameter Weibull distribution, the glassy carbon has Weibull modulus of 3.1 and characteristic strength of 710 MPa. The viscoelastic response has characteristic time scale of about 10000 s. In vitro experiments demonstrate that the glassy carbon microneedles introduce controlled perforations across the guinea pig round window membrane (RWM) from the middle ear space into the inner ear, without damaging the microneedle. The resultant controlled perforation of RWM is known to enhance diffusion of therapeutics across the RWM in a predictable fashion. Hence, the glassy carbon microneedles can be deployed for mediating inner ear delivery.

Prospection of Microfluidics for Local Drug Delivery

Significant endeavors can be made to develop effective drug delivery systems. Nowadays, many of these novel systems have gained attention as they focus primarily on increasing the bioavailability and bioaccessibility of several drugs to finally minimize the side effects, thus improving the treatment's efficacy. Microfluidics systems are unquestionably a superior technology, which is currently revolutionizing the current chemical and biological studies, providing diminutive chip-scale devices that offer precise dosage, target-precise delivery, and controlled release. Microfluidic systems have emerged as a promising delivery vehicle owing to their potential for defined handling and transporting of small liquid quantities. The latest microfabrication developments have been made for application to several biological systems. Here, we review the fundamentals of microfluidics and their application for local drug delivery.

Development and in vivo validation of small interfering RNAs targeting NOX3 to prevent sensorineural hearing loss

The reactive oxygen species (ROS)-generating enzyme NOX3 has recently been implicated in the pathophysiology of several acquired forms of sensorineural hearing loss, including cisplatin-, noise- and age-related hearing loss. NOX3 is highly and specifically expressed in the inner ear and therefore represents an attractive target for specific intervention aiming at otoprotection. Despite the strong rationale to inhibit NOX3, there is currently no specific pharmacological inhibitor available. Molecular therapy may represent a powerful alternative. In this study, we developed and tested a collection of small interfering (si) RNA constructs to establish a proof of concept of NOX3 inhibition through local delivery in the mouse inner ear. The inhibitory potential of 10 different siRNA constructs was first assessed in three different cells lines expressing the NOX3 complex. Efficacy of the most promising siRNA construct to knock-down NOX3 was then further assessed in vivo, comparing middle ear delivery and direct intracochlear delivery through the posterior semi-circular canal. While hearing was completely preserved through the intervention, a significant downregulation of NOX3 expression in the mouse inner ear and particularly in the spiral ganglion area at clinically relevant levels (>60%) was observed 48 h after treatment. In contrast to successful intracochlear delivery, middle ear administration of siRNA failed to significantly inhibit Nox3 mRNA expression. In conclusion, intracochlear delivery of NOX3-siRNAs induces a robust temporal NOX3 downregulation, which could be of relevance to prevent predictable acute insults such as cisplatin chemotherapy-mediated ototoxicity and other forms of acquired hearing loss, including post-prevention of noise-induced hearing loss immediately after trauma. Successful translation of our concept into an eventual clinical use in humans will depend on the development of atraumatic and efficient delivery routes into the cochlea without a risk to induce hearing loss through the intervention.

Local Delivery of Therapeutics to the Cochlea Using Nanoparticles and Other Biomaterials

Hearing loss negatively impacts the well-being of millions of people worldwide. Systemic delivery of ototherapeutics has limited efficacy due to severe systemic side effects and the presence of the blood-labyrinth barrier that selectively limits or enables transfer of molecules between plasma and inner ear tissues and fluids. Local drug delivery into the middle and inner ear would be preferable for many newly emerging classes of drugs. Although the cochlea is a challenging target for drug delivery, recent technologies could provide a safe and efficacious delivery of ototherapeutics. Local drug delivery routes include topical delivery via the external auditory meatus, retroauricular, transtympanic, and intracochlear delivery. Many new drug delivery systems specifically for the inner ear are under development or undergoing clinical studies. Future studies into these systems may provide a means for extended delivery of drugs to preserve or restore hearing in patients with hearing disorders. This review outlines the anatomy of the (inner) ear, describes the various local delivery systems and routes, and various quantification methodologies to determine the pharmacokinetics of the drugs in the inner ear.

An Evaluation of the Drug Permeability Properties of Human Cadaveric In Situ Tympanic and Round Window Membranes

It is estimated that hearing loss currently affects more than 1.5 billion people, or approximately 20% of the global population; however, presently, there are no Food and Drug Administration-approved therapeutics or prophylactics for this condition. While continued research on the development of otoprotective drugs to target this clear unmet need is an obvious path, there are numerous challenges to translating promising therapeutic candidates into human clinical testing. The screening of promising drug candidates relies exclusively on preclinical models. Current models do not permit the rapid high-throughput screening of promising drug candidates, and their relevance to clinical scenarios is often ambiguous. With the current study, we seek to understand the drug permeability properties of the cadaveric tympanic and round window membranes with the goal of generating knowledge that could inform the design and/or evaluation of in vitro organotypic models. The development of such models could enable the early high-throughput screening of topical therapeutic candidates and should address some of the limitations of currently used animal models.

Injectable glycol chitosan thermogel formulation for efficient inner ear drug delivery

We prepared a new injectable thermogel to enhance the efficiency of inner ear delivery of dexamethasone (DEX). Hexanoyl glycol chitosan (HGC) was synthesized and evaluated as an amphiphilic thermogel (T_gel ~ 32 °C) for use as a solubilizing agent as well as an injectable carrier for intratympanic delivery of the hydrophilic and hydrophobic forms of DEX. Various thermogel formulations with different drug types and concentrations were prepared, and their physicochemical and thermogelling properties were characterized by ¹H NMR, ATR-FTIR, and rheometer. They exhibited versatile release kinetics from several hours to more than 2 weeks, depending on drug type and concentration. Our formulations further showed good residual stability for more than 21 days without any cytotoxicity or inflammation in the middle and inner ear and could deliver a considerably high drug concentration into the inner ear. Therefore, HGC thermogel has great potential as an effective and safe formulation for inner ear drug delivery.

Application of Nanomedicine in Inner Ear Diseases

The treatment of inner ear disorders always remains a challenge for researchers. The presence of various physiological barriers, primarily the blood–labyrinth barrier (BLB), limits the accessibility of the inner ear and hinders the efficacy of various drug therapies. Yet despite recent advances in the cochlea for repair and regeneration, there are currently no pharmacological or biological interventions for hearing loss. Current research focuses on the localized drug-, gene-, and cell-based therapies. Drug delivery based on nanotechnology represents an innovative strategy to improve inner ear treatments. Materials with specific nanostructures not only exhibit a unique ability to encapsulate and transport therapeutics to the inner ear but also endow specific targeting properties to auditory hair cells as well as the stabilization and sustained drug release. Along with this, some alternative routes, like intratympanic drug delivery, can also offer a better means to access the inner ear without exposure to the BLB. This review discusses a variety of nano-based drug delivery systems to the ear for treating inner ear diseases. The main factors affecting the curative efficacy of nanomaterials are also discussed. With a deeper understanding of the link between these crucial factors and the clinical effect of nanomaterials, it paves the way for the optimization of the therapeutic activity of nanocarriers.

Stereolithography 3D printed implants: A preliminary investigation as potential local drug delivery systems to the ear

The current study is a preliminary investigation on the use of stereolithography 3D printing technology in the field of personalized medicines and specifically for delivering drugs locally, which can for example usefully be applied to ear infections. The main aim is the development of drug-loaded implants for the treatment of ear diseases, to improve patient compliance and to overcome the limitations of current delivery approaches. Multiple prototypes of implant geometries have been created and printed using a flexible resin containing 0.5% w/v of Levofloxacin. Physicochemical characterization of the printed implants was carried out using a variety of techniques (e.g., microscopic, spectroscopic, and mechanical analysis). Finally, preliminary in vitro tests were performed to evaluate the release profile of Levofloxacin, the prototype implant's stability, and their antimicrobial property. The results obtained show that there is no interaction between the resin and the drug, which is perfectly solubilized in the device. In addition, the results of the mechanical tests show that the material used resists compression without compromising the design itself, and the diffusion test has shown that the drug diffused through the matrix prototype at 50% over 3 weeks. The selected designs showed higher antimicrobial activity on E. coli than on S. aureus.

Characterizing the Access of Cholinergic Antagonists to Efferent Synapses in the Inner Ear

Stimulation of cholinergic efferent neurons innervating the inner ear has profound, well-characterized effects on vestibular and auditory physiology, after activating distinct ACh receptors (AChRs) on afferents and hair cells in peripheral endorgans. Efferent-mediated fast and slow excitation of vestibular afferents are mediated by α4β2*-containing nicotinic AChRs (nAChRs) and muscarinic AChRs (mAChRs), respectively. On the auditory side, efferent-mediated suppression of distortion product otoacoustic emissions (DPOAEs) is mediated by α9α10nAChRs. Previous characterization of these synaptic mechanisms utilized cholinergic drugs, that when systemically administered, also reach the CNS, which may limit their utility in probing efferent function without also considering central effects. Use of peripherally-acting cholinergic drugs with local application strategies may be useful, but this approach has remained relatively unexplored. Using multiple administration routes, we performed a combination of vestibular afferent and DPOAE recordings during efferent stimulation in mouse and turtle to determine whether charged mAChR or α9α10nAChR antagonists, with little CNS entry, can still engage efferent synaptic targets in the inner ear. The charged mAChR antagonists glycopyrrolate and methscopolamine blocked efferent-mediated slow excitation of mouse vestibular afferents following intraperitoneal, middle ear, or direct perilymphatic administration. Both mAChR antagonists were effective when delivered to the middle ear, contralateral to the side of afferent recordings, suggesting they gain vascular access after first entering the perilymphatic compartment. In contrast, charged α9α10nAChR antagonists blocked efferent-mediated suppression of DPOAEs only upon direct perilymphatic application, but failed to reach efferent synapses when systemically administered. These data show that efferent mechanisms are viable targets for further characterizing drug access in the inner ear.

Nanocarriers for Inner Ear Disease Therapy

Hearing loss is a common disease due to sensory loss caused by the diseases in the inner ear. The development of delivery systems for inner ear disease therapy is important to achieve high efficiency and reduce side effects. Currently, traditional drug delivery systems exhibit the potential to be used for inner ear disease therapy, but there are still some drawbacks. As nanotechnology is developing these years, one of the solutions is to develop nanoparticle-based delivery systems for inner ear disease therapy. Various nanoparticles, such as soft material and inorganic-based nanoparticles, have been designed, tested, and showed controlled delivery of drugs, improved targeting property to specific cells, and reduced systemic side effects. In this review, we summarized recent progress in nanocarriers for inner ear disease therapy. This review provides useful information on developing promising nanocarriers for the efficient treatment of inner ear diseases and for further clinical applications for inner ear disease therapy.

The value of having an initial word recognition score for a precise prognosis of idiopathic sudden sensorineural hearing loss

OBJECTIVE

Although the hearing thresholds of patients with idiopathic sudden sensorineural hearing loss (ISSNHL) closely relate to the prognosis that results in progressive floor effects, many studies have usually used hearing thresholds as the main outcome of the measurement of prognostic factors. The present study aimed to identify the prognostic factors related to initial hearing tests and speculates the effects of word recognition score (WRS) on the prognoses for patients with ISSNHL.

METHODS

Between March 2011 and November 2020, we retrospectively reviewed chart profiles of 2,636 ISSNHL patients. The 180 patients who met the inclusion criteria were asked to participate in the present study. Based on their initial WRS, all these patients were divided into good WRS (GW) and poor WRS (PW) groups with 52% as the cut-off points. Demographic, clinical, and audiological variables, such as age, onset time, duration of treatment, gender, ear side, comorbidities (i.e., hypertension, diabetes mellitus, tinnitus, dizziness), hearing configuration (i.e., ascending, descending, flat, irregular, and profound), treatment options (i.e., systemic corticosteroid therapy per oral, intratympanic steroid injection, and hyperbaric oxygen therapy), and WRS were analyzed as being underlying prognostic factors.

RESULTS

Both groups showed significantly different distributions for hearing thresholds and hyperbaric oxygen therapy (HBOT) as general characteristics. The results of a multivariate logistic regression analysis showed that the odds ratio (OR) of age (OR: 0.96, 95% CI: 0.59 - 24.25), duration of treatment (OR: 0.98, 95% CI: 0.96 - 1.00), ascending configuration (OR: 4.97, 95% CI: 1.64 - 16.62), irregular configuration (OR: 4.58, 95% CI: 1.62 - 13.79), and WRS (OR: 1.01, 95% CI: 1.00 - 1.02) were the significant prognostic factors for all the patients. Further analysis of those patients with WRS under 52% cut-off points showed that an ascending configuration (OR: 5.87, 95% CI: 1.18 - 35.99), irregular configuration (OR: 8.03, 95% CI: 1.69 - 46.30), and WRS (OR: 1.05, 95% CI: 1.01 - 1.10) significantly affected the prognosis. As the initial WRS of ISSNHL patients decreased, the OR of the WRS itself increased. These results suggested that the importance of WRS as the prognostic factor was stressed for PW patients.

CONCLUSION

The age, duration of treatment, initial hearing configuration (ascending and irregular types), and WRS were the significant prognostic factors for patients with ISSNHL. It was learned that WRS could be a remarkable prognostic factor to consider, especially for ISSNHL patients with poor WRS.

Drug Delivery across Barriers to the Middle and Inner Ear

The prevalence of ear disorders has spurred efforts to develop drug delivery systems to treat these conditions. Here, recent advances in drug delivery systems that access the ear through the tympanic membrane (TM) are reviewed. Such methods are either non-invasive (placed on the surface of the TM), or invasive (placed in the middle ear, ideally on the round window [RW]). The major hurdles to otic drug delivery are identified and highlighted the representative examples of drug delivery systems used for drug delivery across the TM to the middle and (crossing the RW also) inner ear.

Promising Applications of Nanoparticles in the Treatment of Hearing Loss

Hearing loss is one of the most common disabilities affecting both children and adults worldwide. However, traditional treatment of hearing loss has some limitations, particularly in terms of drug delivery system as well as diagnosis of ear imaging. The blood–labyrinth barrier (BLB), the barrier between the vasculature and fluids of the inner ear, restricts entry of most blood-borne compounds into inner ear tissues. Nanoparticles (NPs) have been demonstrated to have high biocompatibility, good degradation, and simple synthesis in the process of diagnosis and treatment, which are promising for medical applications in hearing loss. Although previous studies have shown that NPs have promising applications in the field of inner ear diseases, there is still a gap between biological research and clinical application. In this paper, we aim to summarize developments and challenges of NPs in diagnostics and treatment of hearing loss in recent years. This review may be useful to raise otology researchers’ awareness of effect of NPs on hearing diagnosis and treatment.

Fused deposition modelling 3D printing proof-of-concept study for personalised inner ear therapy

OBJECTIVES

There is a requirement within ear therapeutics for a delivery system capable of safely delivering controlled doses to the inner ear. However, the anatomy and sensitivity of the inner ear make current delivery systems problematic and often ineffective. Therefore, a new delivery system is required to overcome these issues and provide a more efficacious system in the treatment of inner ear disease. This study assesses the potential of 3D printing (3DP) as a fabrication method for an implantable drug delivery system (DDS) to the inner ear.

KEY FINDINGS

Three implantable designs of varying geometry were produced with fused deposition modelling (FDM) 3DP, each loaded with 0.25%, 0.5% and 1% levofloxacin; filaments prepared by hot-melt extrusion. Each implant was effective in providing sustained, therapeutic release of levofloxacin for at least 4 days and as such would be effective in therapeutic treatment of many common inner ear diseases, such as otitis media or Ménière's disease.

CONCLUSIONS

This proof-of-concept research was successful in utilising FDM as a fabrication method for a DDS capable of providing prolonged release directly to the inner ear and highlights the viability of 3DP in the fabrication of an inner ear DDS.

Evaluation of the Efficacy of Dexamethasone-Eluting Electrode Array on the Post-Implant Cochlear Fibrotic Reaction by Three-Dimensional Immunofluorescence Analysis in Mongolian Gerbil Cochlea

Cochlear implant is the method of choice for the rehabilitation of severe to profound sensorineural hearing loss. The study of the tissue response to cochlear implantation and the prevention of post-cochlear-implant damages are areas of interest in hearing protection research. The objective was to assess the efficacy of dexamethasone-eluting electrode array on endo canal fibrosis formation by three-dimensional immunofluorescence analysis in implanted Mongolian gerbil cochlea. Two trials were conducted after surgery using Mongolian gerbil implanted with dexamethasone-eluting or non-eluting intracochlear electrode arrays. The animals were then euthanised 10 weeks after implantation. The cochleae were prepared (electrode array in place) according to a 29-day protocol with immunofluorescent labelling and tissue clearing. The acquisition was carried out using light-sheet microscopy. Imaris software was then used for three-dimensional analysis of the cochleae and quantification of the fibrotic volume. The analysis of 12 cochleae showed a significantly different mean volume of fibrosis (2.16 × 10⁸ μm³ ± 0.15 in the dexamethasone eluting group versus 3.17 × 10⁸ μm³ ± 0.54 in the non-eluting group) (p = 0.004). The cochlear implant used as a corticosteroid delivery system appears to be an encouraging device for the protection of the inner ear against fibrosis induced by implantation. Three-dimensional analysis of the cochlea by light-sheet microscopy was suitable for studying post-implantation tissue damage.

Reducing Auditory Nerve Excitability by Acute Antagonism of Ca2+-Permeable AMPA Receptors

Hearing depends on glutamatergic synaptic transmission mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). AMPARs are tetramers, where inclusion of the GluA2 subunit reduces overall channel conductance and Ca²⁺ permeability. Cochlear afferent synapses between inner hair cells (IHCs) and auditory nerve fibers (ANFs) contain the AMPAR subunits GluA2, 3, and 4. However, the tetrameric complement of cochlear AMPAR subunits is not known. It was recently shown in mice that chronic intracochlear delivery of IEM-1460, an antagonist selective for GluA2-lacking AMPARs [also known as Ca²⁺-permeable AMPARs (CP-AMPARs)], before, during, and after acoustic overexposure prevented both the trauma to ANF synapses and the ensuing reduction of cochlear nerve activity in response to sound. Surprisingly, baseline measurements of cochlear function before exposure were unaffected by chronic intracochlear delivery of IEM-1460. This suggested that cochlear afferent synapses contain GluA2-lacking CP-AMPARs alongside GluA2-containing Ca²⁺-impermeable AMPA receptors (CI-AMPARs), and that the former can be antagonized for protection while the latter remain conductive. Here, we investigated hearing function in the guinea pig during acute local or systemic delivery of CP-AMPAR antagonists. Acute intracochlear delivery of IEM-1460 or systemic delivery of IEM-1460 or IEM-1925 reduced the amplitude of the ANF compound action potential (CAP) significantly, for all tone levels and frequencies, by > 50% without affecting CAP thresholds or distortion product otoacoustic emissions (DPOAE). Following systemic dosing, IEM-1460 levels in cochlear perilymph were ~ 30% of blood levels, on average, consistent with pharmacokinetic properties predicting permeation of the compounds into the brain and ear. Both compounds were metabolically stable with half-lives >5 h in vitro, and elimination half-lives in vivo of 118 min (IEM-1460) and 68 min (IEM-1925). Heart rate monitoring and off-target binding assays suggest an enhanced safety profile for IEM-1925 over IEM-1460. Compound potency on CAP reduction (IC₅₀ ~ 73 μM IEM-1460) was consistent with a mixture of GluA2-lacking and GluA2-containing AMPARs. These data strongly imply that cochlear afferent synapses of the guinea pig contain GluA2-lacking CP-AMPARs. We propose these CP-AMPARs may be acutely antagonized with systemic dosing, to protect from glutamate excitotoxicity, while transmission at GluA2-containing AMPARs persists to mediate hearing during the protection.

Development of thermosensitive poloxamer 407-based microbubble gel with ultrasound mediation for inner ear drug delivery

ABSTRACTSOur previous study first investigated feasibility of applying ultrasound (US) and microbubbles (MBs) via external auditory canal to facilitate drug delivery into inner ear. However, most drugs are in aqueous formulae and eliminated via Eustachian tubes after drug application. In this study, feasibility of sustained release of thermosensitive poloxamer 407 (P407)-based MB gel for US mediation-enhanced inner ear drug (dexamethasone, DEX) delivery was investigated. The sol-to-gel transition temperature showed that mixture of DEX and only 10% and 12.5% P407 in MBs can be used for in vitro and in vivo drug delivery experiments. In in vitro Franz diffusion experiments, the release rates of 12.5% P407-MBs + US groups in the model using DEX as the delivered reagent at 3 h resulted in values 1.52 times greater than those of 12.5% P407-MBs groups. In guinea pigs, by filling tympanic bulla with DEX in 12.5% P407-MBs (DEX-P407-MBs), USMB applied at post-treatment days 1 and 7 induced 109.13% and 66.67% increases in DEX delivery efficiencies, respectively, compared to the group without US. On the 28th day after US-mediated P407-MB treatment, the safety assessment showed no significant changes in the hearing thresholds and no damage to the integrity of cochlea or middle ear. These are the first results to demonstrate feasibility of US-modified liquid form DEX-P407-MB cavitation for enhancing permeability of round window membrane. Then, a gel form of DEX-P407-MBs was generated and thus prolonged the release of DEX in middle ear to maintain the therapeutic DEX level in inner ear for at least 7 days.

Nanoparticles for the Treatment of Inner Ear Infections

The inner ear is sensitive to various infections of viral, bacterial, or fungal origin, which, if left untreated, may lead to hearing loss or progress through the temporal bone and cause intracranial infectious complications. Due to its isolated location, the inner ear is difficult to treat, imposing an acute need for improving current therapeutic approaches. A solution for enhancing antimicrobial treatment performance is the use of nanoparticles. Different inorganic, lipidic, and polymeric-based such particles have been designed, tested, and proven successful in the controlled delivery of medication, improving drug internalization by the targeted cells while reducing the systemic side effects. This paper makes a general presentation of common inner ear infections and therapeutics administration routes, further focusing on newly developed nanoparticle-mediated treatments.

Modulating surface charge of dexamethasone non-spherical microcrystals for improved inner ear delivery

It is important to achieve precise surface charge manipulation of non-spherical drug microcrystals using facile and time-efficient methods for local drug delivery. In this study, silk-coated dexamethasone (DEX) non-spherical microcrystals were synthesized by precipitation technique followed by alternate deposition of poly(allylamine hydrochloride) (PAH) (or PAH-coated Fe₃O₄) and silk fibroin (SF) via layer-by-layer assembly. EDC and glutaraldehyde were employed to manipulate positive or negative charge of particles by simple chemical cross-linking reactions, respectively. In vivo assessment was carried out by intratympanic (IT) injection of DEX non-spherical microcrystals in guinea pigs. In vivo pharmacokinetic results demonstrate that negatively charged DEX microcrystals appeared to improve outcomes of inner ear delivery in comparison to positively-charged counterparts. This is partly because of the adhesive features of the SF. The present study may provide new ideas to construct surface charge-tunable drug delivery vehicles that are capable of crossing biological barriers, especially for inner ear delivery due to the simple and practical strategy.

Determination of the Round Window Niche Anatomy Using Cone Beam Computed Tomography Imaging as Preparatory Work for Individualized Drug-Releasing Implants

Modern therapy of inner ear disorders is increasingly shifting to local drug delivery using a growing number of pharmaceuticals. Access to the inner ear is usually made via the round window membrane (RWM), located in the bony round window niche (RWN). We hypothesize that the individual shape and size of the RWN have to be taken into account for safe reliable and controlled drug delivery. Therefore, we investigated the anatomy and its variations. Cone beam computed tomography (CBCT) images of 50 patients were analyzed. Based on the reconstructed 3D volumes, individual anatomies of the RWN, RWM, and bony overhang were determined by segmentation using 3D Slicer^TM with a custom build plug-in. A large individual anatomical variability of the RWN with a mean volume of 4.54 mm³ (min 2.28 mm³, max 6.64 mm³) was measured. The area of the RWM ranged from 1.30 to 4.39 mm² (mean: 2.93 mm²). The bony overhang had a mean length of 0.56 mm (min 0.04 mm, max 1.24 mm) and the shape was individually very different. Our data suggest that there is a potential for individually designed and additively manufactured RWN implants due to large differences in the volume and shape of the RWN.

Drug delivery device for the inner ear: ultra-sharp fully metallic microneedles

Drug delivery into the inner ear is a significant challenge due to its inaccessibility as a fluid-filled cavity within the temporal bone of the skull. The round window membrane (RWM) is the only delivery portal from the middle ear to the inner ear that does not require perforation of bone. Recent advances in microneedle fabrication enable the RWM to be perforated safely with polymeric microneedles as a means to enhance the rate of drug delivery from the middle ear to the inner ear. However, the polymeric material is not biocompatible and also lacks the strength of other materials. Herein we describe the design and development of gold-coated metallic microneedles suitable for RWM perforation. When developing microneedle technology for drug delivery, we considered three important general attributes: (1) high strength and ductility material, (2) high accuracy and precision of fabrication, and (3) broad design freedom. We developed a hybrid additive manufacturing method using two-photon lithography and electrochemical deposition to fabricate ultra-sharp gold-coated copper microneedles with these attributes. We refer to the microneedle fabrication methodology as two-photon templated electrodeposition (2PTE). We demonstrate the use of these microneedles by inducing a perforation with a minimal degree of trauma in a guinea pig RWM while the microneedle itself remains undamaged. Thus, this microneedle has the potential literally of opening the RWM for enhanced drug delivery into the inner ear. Finally, the 2PTE methodology can be applied to many different classes of microneedles for other drug delivery purposes as well the fabrication of small scale structures and devices for non-medical applications. Graphical Abstract Fully metallic ultra-sharp microneedle mounted at end of a 24-gauge stainless steel blunt syringe needle tip: (left) Size of microneedle shown relative to date stamp on U.S. one-cent coin; (right) Perforation through guinea pig round window membrane introduced with microneedle.

Steady streaming as a method for drug delivery to the inner ear

The inner ear, or cochlea, is a fluid-filled organ housing the mechanosensitive hair cells. Sound stimulation is relayed to the hair cells through waves that propagate on the elastic basilar membrane. Sensorineural hearing loss occurs from damage to the hair cells and cannot currently be cured. Although drugs have been proposed to prevent damage or restore functionality to hair cells, a difficulty with such treatments is ensuring adequate drug delivery to the cells. Because the cochlea is encased in the temporal bone, it can only be accessed from its basal end. However, the hair cells that are responsible for detecting speech-frequency sounds reside at the opposite, apical end. In this paper we show that steady streaming can be used to transport drugs along the cochlea. Steady streaming is a nonlinear process that accompanies many fluctuating fluid motions, including the sound-evoked waves in the inner ear. We combine an analytical approximation for the waves in the cochlea with computational fluid dynamic simulations to demonstrate that the combined steady streaming effects of several different frequencies can transport drugs from the base of the cochlea further towards the apex. Our results therefore show that multi-frequency sound stimulation can serve as a non-invasive method to transport drugs efficiently along the cochlea.

Cochlear protein biomarkers as potential sites for targeted inner ear drug delivery

The delivery of therapies to the cochlea is notoriously challenging. It is an organ protected by a number of barriers that need to be overcome in the drug delivery process. Additionally, there are multiple sites of possible damage within the cochlea. Despite the many potential sites of damage, acquired otologic insults preferentially damage a single location. While progress has been made in techniques for inner ear drug delivery, the current techniques remain non-specific and our ability to deliver therapies in a cell-specific manner are limited. Fortunately, there are proteins specific to various cell-types within the cochlea (e.g., hair cells, spiral ganglion cells, stria vascularis) that function as biomarkers of site-specific damage. These protein biomarkers have potential to serve as targets for cell-specific inner ear drug delivery. In this manuscript, we review the concept of biomarkers and targeted- inner ear drug delivery and the well-characterized protein biomarkers within each of the locations of interest within the cochlea. Our review will focus on targeted drug delivery in the setting of acquired otologic insults (e.g., ototoxicity, noise-induce hearing loss). The goal is not to discuss therapies to treat acquired otologic insults, rather, to establish potential concepts of how to deliver therapies in a targeted, cell-specific manner. Based on our review, it is clear that future of inner ear drug delivery is a discipline filled with potential that will require collaborative efforts among clinicians and scientists to optimize treatment of otologic insults.

Investigating the Potential of Phosphatidylcholine-Based Nano-Sized Carriers in Boosting the Oto-Topical Delivery of Caroverine: in vitro Characterization, Stability Assessment and ex vivo Transport Studies

Purpose

Drug delivery into the inner ear across the intact tympanic membrane (TM) has been a challenge in the treatment of inner ear disorders. In this study, nano-sized carriers were formulated for improving the non- invasive oto-topical delivery of caroverine for the treatment of tinnitus.

Methods

Caroverine was loaded into two types of phospholipid-containing systems, namely, nano elastic vesicles (EVs) and phosphatidylcholine-based liquid crystalline nano-particles (PC-LCNPs). The prepared formulations were characterized for their drug loading, particle size, polydispersity index, zeta potential, morphological features by transmission electron microscopy (TEM), and physicochemical stability. In addition, comparative ex vivo transport study was carried out using rabbits’ TM for both types of formulations.

Results

The findings show a significant superiority of PC-LCNPs over the EVs formulations in the drug payload (1% and 0.25%, respectively), physical stability and the efficiency of permeation across rabbits’ TM. The results showed a more than twofold increase in the cumulative drug flux values of PC-LCNPs (699.58 ± 100 µg/cm²) compared to the EVs (250 ± 45 µg/cm²) across the TM.

Conclusion

The current study revealed the smart physicochemical properties of PC-LCNPs demonstrating the potential of this carrier as a new attractive candidate for improving the non-invasive oto-topical delivery of caroverine.

A metal-organic framework based inner ear delivery system for the treatment of noise-induced hearing loss

Noise-induced hearing loss (NIHL) is associated with both acute and chronic noise exposure. The application of steroid hormones is the first-line treatment for NIHL. However, a high dose of steroid hormone in the body is necessary to maintain its efficacy and causes side effects, such as headache and osteoporosis. In this work, we prepared a zeolitic imidazolate framework (ZIF)-based system for steroid hormone delivery in the inner ear. Methylprednisolone (MP), a typical steroid hormone, was encapsulated into ZIF-90 nanoparticles (NPs) using one-pot synthesis method. The obtained MP@ZIF-90 NPs are negatively charged and 120 nm in size and showed good biocompatibility and stability at a pH value of 7.4. After intraperitoneal injection, ZIF-90 could efficiently protect drugs during peripheral blood circulation, enter the inner ear via the blood labyrinthine barrier (BLB) and slowly release the drugs. Auditory brainstem response (ABR) tests indicated that MP@ZIF-90 exhibits better protection of mice from noise than those using the free MP and ZIF-8 with encapsulated MP (MP@ZIF-8). More importantly, MP@ZIF-90 showed no defects to the inner ear after being treated for noise and low nephrotoxicity during therapy, which demonstrates the biocompatibility of this material. We believe the ZIF-90 based delivery system is an efficient strategy for inner ear therapy of NIHL.

Prospects and Opportunities for Microsystems and Microfluidic Devices in the Field of Otorhinolaryngology

Microfluidic systems can be used to control picoliter to microliter volumes in ways not possible with other methods of fluid handling. In recent years, the field of microfluidics has grown rapidly, with microfluidic devices offering possibilities to impact biology and medicine. Microfluidic devices populated with human cells have the potential to mimic the physiological functions of tissues and organs in a three-dimensional microenvironment and enable the study of mechanisms of human diseases, drug discovery and the practice of personalized medicine. In the field of otorhinolaryngology, various types of microfluidic systems have already been introduced to study organ physiology, diagnose diseases, and evaluate therapeutic efficacy. Therefore, microfluidic technologies can be implemented at all levels of otorhinolaryngology. This review is intended to promote understanding of microfluidic properties and introduce the recent literature on application of microfluidic-related devices in the field of otorhinolaryngology.

Biocompatibility and Therapeutic Effect of 3 Intra-Tympanic Drug Delivery Vehicles in Acute Acoustic Trauma

INTRODUCTION

The aim of this study was to assess the biocompatibility of several intra-tympanic (IT) drug delivery vehicles and to compare hearing outcomes.

MATERIALS AND METHODS

After acute acoustic trauma, rats were treated with IT 10 mg/mL dexamethasone phosphate (D) and divided into the following groups for drug delivery: saline + D (n = 15), hyaluronic acid (HA) + D (n = 17), and methoxy polyethylene glycol-b-polycaprolactone block copolymer (MP) + D (n = 24).

RESULTS

No inflammation was found in the saline + D or HA + D groups. The duration of vehicle/drug persistence in the bulla was significantly longer for the MP + D (47.5 days) and HA + D groups (1.8 days) than for the saline + D group (<1 day). The tympanic membrane was significantly thicker in the MP + D group than in the saline + D and HA + D groups. The proportion of ears with good hearing outcome was significantly higher (63.6%) in the HA + D group than in the MP + D group. The number of hair cells in the hearing loss (HL) control group was significantly lower than in the MP + D group.

DISCUSSION/CONCLUSION

HA shows great potential as a biocompatible vehicle for D delivery via the IT route, without an inflammatory reaction and with better hearing outcomes. Considering inflammation and hearing, MP may not be a good candidate for IT drug delivery.

Efficacy of the additional effect of hyperbaric oxygen therapy in combination of systemic steroid and prostaglandin E1 for idiopathic sudden sensorineural hearing loss

PURPOSE

The efficacies of hyperbaric oxygen therapy (HBO), systemic steroid, prostaglandin E₁, or the combination of any two modalities have been reported in patients with idiopathic sudden sensorineural hearing loss (ISSNHL). However, little is known about the combined efficacy of HBO, systemic steroid, and prostaglandin E₁ for this disorder. We aimed to investigate the efficacy of HBO combined with systemic steroids and prostaglandin E₁ as triple therapy in patients with ISSNHL.

MATERIALS AND METHODS

We retrospectively evaluated the records of 67 patients with ISSNHL who were treated with systemic steroid and prostaglandin E₁, with (n = 38) or without (n = 29) HBO. The inclusion criteria included a diagnosis of ISSNHL within 14 days of symptom onset, age ≥15 years, treatment according to the protocol, and clinical follow-up of at least 1 month. The patients' hearing levels were evaluated 1 month after hearing loss onset. The primary outcome was hearing improvement on pure tone audiometry. We also evaluated the demographic profiles of patients.

RESULTS

Patients treated with triple therapy showed significantly greater hearing improvement (p < 0.01) than those treated without HBO, despite some differences between the two treatment groups. Multivariate logistic regression analysis revealed a significant positive correlation between pure tone audiometry improvement and hyperbaric oxygen therapy, after adjustment for confounding factors (odds ratio = 7.42; 95% and confidence interval = 2.37-23.3; p = 0.001).

CONCLUSION

HBO with systemic steroid and prostaglandin E₁ administration conferred significant therapeutic benefits for ISSNHL. Therefore, routine use of triple therapy is recommended for patients with ISSNHL.

State-of-the-art methods in clinical intracochlear drug delivery

PURPOSE OF REVIEW

Increasing awareness and prevalence of disorders in hearing and balance have placed emphasis on treatment strategies. With the rapid evolution in molecular, gene, and nanotechnology, alternate delivery methods have advanced intracochlear drug delivery. This review aims to raise awareness of recent developments in technologies to augment current clinical practices.

RECENT FINDINGS

Intracochlear drug delivery research has expanded with the familiarity and accessibility to cochlear implantation. Various therapeutics are closely studied for both safety and efficacy as well as biologic effect. Agents including neurotrophins, antiapoptotics, cell therapy, gene therapy, and anti-inflammatory drugs are on the forefront of preclinical research. Cochlear implant electrode modification and drug administration at the time of implantation is a major focus of research. Improvements in study design have focused on overcoming barriers including elucidating the role of the blood-perilymph barrier.

SUMMARY

Inner ear drug delivery methods include systemic, intratympanic, and intracochlear administration. Therapeutic technologies aim to overcome delivery barriers and to improve overall biologic effect while minimizing toxicity. Precision of drug application through intratympanic and intracochlear administration with minimal trauma is the future of inner ear drug development.

Intravenously delivered aminoglycoside antibiotics, tobramycin and amikacin, are not ototoxic in mice

Many drugs on the World Health Organization's list of critical medicines are ototoxic, destroying sensory hair cells within the ear. These drugs preserve life, but patients can experience side effects including permanent hearing loss and vestibular dysfunction. Aminoglycoside ototoxicity was first recognised 80 years ago. However, no preventative treatments have been developed. In order to develop such treatments, we must identify the factors driving hair cell death. In vivo, studies of cell death are typically conducted using mouse models. However, a robust model of aminoglycoside ototoxicity does not exist. Previous studies testing aminoglycoside delivery via intraperitoneal or subcutaneous injection have produced variable ototoxic effects in the mouse. As a result, surgical drug delivery to the rodent ear is often used to achieve ototoxicity. However, this technique does not accurately model clinical practice. In the clinic, aminoglycosides are administered to humans intravenously (i.v.). However, repeated i.v. delivery has not been reported in the mouse. This study evaluated whether repeated i.v. administration of amikacin or tobramycin would induce hearing loss. Daily i.v. injections over a two-week period were well tolerated and transient low frequency hearing loss was observed in the aminoglycoside treatment groups. However, the hearing changes observed did not mimic the high frequency patterns of hearing loss observed in humans. Our results indicate that the i.v. delivery of tobramycin or amikacin is not an effective technique for inducing ototoxicity in mice. This result is consistent with previously published reports indicating that the mouse cochlea is resistant to systemically delivered aminoglycoside ototoxicity.

Clinical Practice Guideline: Sudden Hearing Loss (Update)

OBJECTIVE

Sudden hearing loss is a frightening symptom that often prompts an urgent or emergent visit to a health care provider. It is frequently but not universally accompanied by tinnitus and/or vertigo. Sudden sensorineural hearing loss affects 5 to 27 per 100,000 people annually, with about 66,000 new cases per year in the United States. This guideline update provides evidence-based recommendations for the diagnosis, management, and follow-up of patients who present with sudden hearing loss. It focuses on sudden sensorineural hearing loss in adult patients aged ≥18 years and primarily on those with idiopathic sudden sensorineural hearing loss. Prompt recognition and management of sudden sensorineural hearing loss may improve hearing recovery and patient quality of life. The guideline update is intended for all clinicians who diagnose or manage adult patients who present with sudden hearing loss.

PURPOSE

The purpose of this guideline update is to provide clinicians with evidence-based recommendations in evaluating patients with sudden hearing loss and sudden sensorineural hearing loss, with particular emphasis on managing idiopathic sudden sensorineural hearing loss. The guideline update group recognized that patients enter the health care system with sudden hearing loss as a nonspecific primary complaint. Therefore, the initial recommendations of this guideline update address distinguishing sensorineural hearing loss from conductive hearing loss at the time of presentation with hearing loss. They also clarify the need to identify rare, nonidiopathic sudden sensorineural hearing loss to help separate those patients from those with idiopathic sudden sensorineural hearing loss, who are the target population for the therapeutic interventions that make up the bulk of the guideline update. By focusing on opportunities for quality improvement, this guideline should improve diagnostic accuracy, facilitate prompt intervention, decrease variations in management, reduce unnecessary tests and imaging procedures, and improve hearing and rehabilitative outcomes for affected patients.

METHODS

Consistent with the American Academy of Otolaryngology-Head and Neck Surgery Foundation's "Clinical Practice Guideline Development Manual, Third Edition" (Rosenfeld et al. Otolaryngol Head Neck Surg. 2013;148[1]:S1-S55), the guideline update group was convened with representation from the disciplines of otolaryngology-head and neck surgery, otology, neurotology, family medicine, audiology, emergency medicine, neurology, radiology, advanced practice nursing, and consumer advocacy. A systematic review of the literature was performed, and the prior clinical practice guideline on sudden hearing loss was reviewed in detail. Key Action Statements (KASs) were updated with new literature, and evidence profiles were brought up to the current standard. Research needs identified in the original clinical practice guideline and data addressing them were reviewed. Current research needs were identified and delineated.

RESULTS

The guideline update group made strong recommendations for the following: (KAS 1) Clinicians should distinguish sensorineural hearing loss from conductive hearing loss when a patient first presents with sudden hearing loss. (KAS 7) Clinicians should educate patients with sudden sensorineural hearing loss about the natural history of the condition, the benefits and risks of medical interventions, and the limitations of existing evidence regarding efficacy. (KAS 13) Clinicians should counsel patients with sudden sensorineural hearing loss who have residual hearing loss and/or tinnitus about the possible benefits of audiologic rehabilitation and other supportive measures. These strong recommendations were modified from the initial clinical practice guideline for clarity and timing of intervention. The guideline update group made strong recommendations against the following: (KAS 3) Clinicians should not order routine computed tomography of the head in the initial evaluation of a patient with presumptive sudden sensorineural hearing loss. (KAS 5) Clinicians should not obtain routine laboratory tests in patients with sudden sensorineural hearing loss. (KAS 11) Clinicians should not routinely prescribe antivirals, thrombolytics, vasodilators, or vasoactive substances to patients with sudden sensorineural hearing loss. The guideline update group made recommendations for the following: (KAS 2) Clinicians should assess patients with presumptive sudden sensorineural hearing loss through history and physical examination for bilateral sudden hearing loss, recurrent episodes of sudden hearing loss, and/or focal neurologic findings. (KAS 4) In patients with sudden hearing loss, clinicians should obtain, or refer to a clinician who can obtain, audiometry as soon as possible (within 14 days of symptom onset) to confirm the diagnosis of sudden sensorineural hearing loss. (KAS 6) Clinicians should evaluate patients with sudden sensorineural hearing loss for retrocochlear pathology by obtaining magnetic resonance imaging or auditory brainstem response. (KAS 10) Clinicians should offer, or refer to a clinician who can offer, intratympanic steroid therapy when patients have incomplete recovery from sudden sensorineural hearing loss 2 to 6 weeks after onset of symptoms. (KAS 12) Clinicians should obtain follow-up audiometric evaluation for patients with sudden sensorineural hearing loss at the conclusion of treatment and within 6 months of completion of treatment. These recommendations were clarified in terms of timing of intervention and audiometry and method of retrocochlear workup. The guideline update group offered the following KASs as options: (KAS 8) Clinicians may offer corticosteroids as initial therapy to patients with sudden sensorineural hearing loss within 2 weeks of symptom onset. (KAS 9a) Clinicians may offer, or refer to a clinician who can offer, hyperbaric oxygen therapy combined with steroid therapy within 2 weeks of onset of sudden sensorineural hearing loss. (KAS 9b) Clinicians may offer, or refer to a clinician who can offer, hyperbaric oxygen therapy combined with steroid therapy as salvage therapy within 1 month of onset of sudden sensorineural hearing loss.

DIFFERENCES FROM PRIOR GUIDELINE

Incorporation of new evidence profiles to include quality improvement opportunities, confidence in the evidence, and differences of opinion Included 10 clinical practice guidelines, 29 new systematic reviews, and 36 new randomized controlled trials Highlights the urgency of evaluation and initiation of treatment, if treatment is offered, by emphasizing the time from symptom occurrence Clarification of terminology by changing potentially unclear statements; use of the term sudden sensorineural hearing loss to mean idiopathic sudden sensorineural hearing loss to emphasize that >90% of sudden sensorineural hearing loss is idiopathic sudden sensorineural hearing loss and to avoid confusion in nomenclature for the reader Changes to the KASs from the original guideline: KAS 1-When a patient first presents with sudden hearing loss, conductive hearing loss should be distinguished from sensorineural. KAS 2-The utility of history and physical examination when assessing for modifying factors is emphasized. KAS 3-The word "routine" is added to clarify that this statement addresses nontargeted head computerized tomography scan that is often ordered in the emergency room setting for patients presenting with sudden hearing loss. It does not refer to targeted scans, such as temporal bone computerized tomography scan, to assess for temporal bone pathology. KAS 4-The importance of audiometric confirmation of hearing status as soon as possible and within 14 days of symptom onset is emphasized. KAS 5-New studies were added to confirm the lack of benefit of nontargeted laboratory testing in sudden sensorineural hearing loss. KAS 6-Audiometric follow-up is excluded as a reasonable workup for retrocochlear pathology. Magnetic resonance imaging, computerized tomography scan if magnetic resonance imaging cannot be done, and, secondarily, auditory brainstem response evaluation are the modalities recommended. A time frame for such testing is not specified, nor is it specified which clinician should be ordering this workup; however, it is implied that it would be the general or subspecialty otolaryngologist. KAS 7-The importance of shared decision making is highlighted, and salient points are emphasized. KAS 8-The option for corticosteroid intervention within 2 weeks of symptom onset is emphasized. KAS 9-Changed to KAS 9A and 9B. Hyperbaric oxygen therapy remains an option but only when combined with steroid therapy for either initial treatment (9A) or salvage therapy (9B). The timing of initial therapy is within 2 weeks of onset, and that of salvage therapy is within 1 month of onset of sudden sensorineural hearing loss. KAS 10-Intratympanic steroid therapy for salvage is recommended within 2 to 6 weeks following onset of sudden sensorineural hearing loss. The time to treatment is defined and emphasized. KAS 11-Antioxidants were removed from the list of interventions that the clinical practice guideline recommends against using. KAS 12-Follow-up audiometry at conclusion of treatment and also within 6 months posttreatment is added. KAS 13-This statement on audiologic rehabilitation includes patients who have residual hearing loss and/or tinnitus who may benefit from treatment. Addition of an algorithm outlining KASs Enhanced emphasis on patient education and shared decision making with tools provided to assist in same.