Round window membrane intracochlear drug delivery enhanced by induced advection

The caspase-inhibitor Emricasan efficiently counteracts cisplatin- and neomycin-induced cytotoxicity in cochlear cells

Cisplatin is a chemotherapeutic agent widely used to treat solid tumors. However, it can also be highly ototoxic, resulting in high-frequency hearing loss. Cisplatin causes degeneration of hair cells (HCs) and spiral ganglion neurons (SGNs) in the inner ear, which are essential components of the hearing process and cannot be regenerated in mammals. As the affected cells primarily die by apoptosis, we tested several anti-apoptotic small molecules to protect these cells from drug-induced toxicity. We found that the general caspase inhibitor Emricasan could significantly counteract the toxic effects of cisplatin in House Ear Institute-Organ of Corti 1 (HEI-OC1) cells, phoenix auditory cells, and primary SGNs. Importantly, the anti-cytotoxic effect in neuronal cells was even more pronounced than the effect of sodium thiosulfate (STS), which is currently the only approved prevention option for cisplatin-induced ototoxicity. Finally, we tested the protective effect of Emricasan treatment in the context of another ototoxic drug, i.e., the aminoglycoside antibiotic neomycin, and again found a significant increase in cell viability when the cultures were co-treated with Emricasan. These results suggest a promising strategy to prevent ototoxicity in patients by temporarily blocking the apoptotic pathway when applying cisplatin or aminoglycoside antibiotics. KEY MESSAGES: Anti-apoptotic small molecules can reduce cisplatin-induced toxicity. Emricasan can effectively exert its anti-apoptotic effect on cochlear cells. Strong protection from cisplatin- and neomycin-induced cytotoxicity with Emricasan. Sodium thiosulfate and Emricasan provide similar protective effects to cisplatin-treated cells. Emricasan is more potent than sodium thiosulfate in reducing neomycin-induced cytotoxicity.

Polyimide as a biomedical material: advantages and applications

Polyimides (PIs) are a class of polymers characterized by strong covalent bonds, which offer the advantages of high thermal weight, low weight, good electronic properties and superior mechanical properties. They have been successfully used in the fields of microelectronics, aerospace engineering, nanomaterials, lasers, energy storage and painting. Their biomedical applications have attracted extensive attention, and they have been explored for use as an implantable, detectable, and antibacterial material in recent years. This article summarizes the progress of PI in terms of three aspects: synthesis, properties, and application. First, the synthetic strategies of PI are summarized. Next, the properties of PI as a biological or medical material are analyzed. Finally, the applications of PI in electrodes, biosensors, drug delivery systems, bone tissue replacements, face masks or respirators, and antibacterial materials are discussed. This review provides a comprehensive understanding of the latest progress in PI, thereby providing a basis for developing new potentially promising materials for medical applications.

Outer hair cells stir cochlear fluids

Recent observations regarding the non-selective action of outer hair cells contradict frequency-selective cochlear amplification. We hypothesized that active outer hair cells drive cochlear fluid circulation. The hypothesis was tested by delivering a neurotoxin, kainic acid, to the round window of young gerbil cochleae while monitoring auditory responses in the cochlear nucleus. Sounds presented at a modest level significantly expedited kainic acid delivery. When outer-hair-cell motility was suppressed by salicylate, the facilitation effect was compromised. A low-frequency tone was more effective than broadband noise, especially for drug delivery to apical locations. Computational model simulations provided the physical basis for our observation, which incorporated solute diffusion, fluid advection, fluid-structure interaction, and outer-hair-cell motility. Active outer hair cells deformed the organ of Corti like a peristaltic tube to generate apically streaming flows along the tunnel of Corti and basally streaming flows along the scala tympani. Our measurements and simulations coherently indicate that broadband outer-hair-cell action is for cochlear fluid circulation.

Experimental animal models of drug-induced sensorineural hearing loss: a narrative review

Objective

This narrative review describes experimental animal models of sensorineural hearing loss (SNHL) caused by ototoxic agents.

Background

SNHL primarily results from damage to the sensory organ within the inner ear or the vestibulocochlear nerve (cranial nerve VIII). The main etiology of SNHL includes genetic diseases, presbycusis, ototoxic agents, infection, and noise exposure. Animal models with functional and anatomic damage to the sensory organ within the inner ear or the vestibulocochlear nerve mimicking the damage seen in humans are employed to explore the mechanism and potential treatment of SNHL. These animal models of SNHL are commonly established using ototoxic agents.

Methods

A literature search of PubMed, Embase, and Web of Science was performed for research articles on hearing loss and ototoxic agents in animal models of hearing loss.

Conclusions

Common ototoxic medications such as aminoglycoside antibiotics (AABs) and platinum antitumor drugs are extensively used to induce SNHL in experimental animals. The effect of ototoxic agents in vivo is influenced by the chemical mechanisms of the ototoxic agents, the species of animal, routes of administration of the ototoxic agents, and the dosage of ototoxic agents. Animal models of drug-induced SNHL contribute to understanding the hearing mechanism and reveal the function of different parts of the auditory system in humans.

Dexamethasone-loaded cochlear implants: How to provide a desired "burst release"

Cochlear implants containing iridium platinum electrodes are used to transmit electrical signals into the inner ear of patients suffering from severe or profound deafness without valuable benefit from conventional hearing aids. However, their placement is invasive and can cause trauma as well as local inflammation, harming remaining hair cells or other inner ear cells. As foreign bodies, the implants also induce fibrosis, resulting in a less efficient conduction of the electrical signals and, thus, potentially decreased system performance. To overcome these obstacles, dexamethasone has recently been embedded in this type of implants: into the silicone matrices separating the metal electrodes (to avoid short circuits). It has been shown that the resulting drug release can be controlled over several years. Importantly, the dexamethasone does not only act against the immediate consequences of trauma, inflammation and fibrosis, it can also be expected to be beneficial for remaining hair cells in the long term. However, the reported amounts of drug released at “early” time points (during the first days/weeks) are relatively low and the in vivo efficacy in animal models was reported to be non-optimal. The aim of this study was to increase the initial “burst release” from the implants, adding a freely water-soluble salt of a phosphate ester of dexamethasone. The idea was to facilitate water penetration into the highly hydrophobic system and, thus, to promote drug dissolution and diffusion. This approach was efficient: Adding up to 10% dexamethasone sodium phosphate to the silicone matrices substantially increased the resulting drug release rate at early time points. This can be expected to improve drug action and implant functionality. But at elevated dexamethasone sodium phosphate loadings device swelling became important. Since the cochlea is a tiny and sensitive organ, a potential increase in implant dimensions over time must be limited. Hence, a balance has to be found between drug release and implant swelling.

Microtechnologies for inner ear drug delivery

PURPOSE OF REVIEW

Treatment of auditory dysfunction is dependent on inner ear drug delivery, with microtechnologies playing an increasingly important role in cochlear access and pharmacokinetic profile control. This review examines recent developments in the field for clinical and animal research environments.

RECENT FINDINGS

Micropump technologies are being developed for dynamic control of flow rates with refillable reservoirs enabling timed delivery of multiple agents for protection or regeneration therapies. These micropumps can be combined with cochlear implants with integral catheters or used independently with cochleostomy or round window membrane (RWM) delivery modalities for therapy development in animal models. Sustained release of steroids with coated cochlear implants remains an active research area with first-time-in-human demonstration of reduced electrode impedances. Advanced coatings containing neurotrophin producing cells have enhanced spiral ganglion neuron survival in animal models, and have proven safe in a human study. Microneedles have emerged for controlled microperforation of the RWM for significant enhancement in permeability, combinable with emerging matrix formulations that optimize biological interaction and drug release kinetics.

SUMMARY

Microsystem technologies are providing enhanced and more controlled access to the inner ear for advanced drug delivery approaches, alone and in conjunction with cochlear implants.

Drug distribution along the cochlea is strongly enhanced by low-frequency round window micro vibrations

The cochlea’s inaccessibility and complex nature provide significant challenges to delivering drugs and other agents uniformly, safely and efficiently, along the entire cochlear spiral. Large drug concentration gradients are formed along the cochlea when drugs are administered to the middle ear. This undermines the major goal of attaining therapeutic drug concentration windows along the whole cochlea. Here, utilizing a well-known physiological effect of salicylate, we demonstrate a proof of concept in which drug distribution along the entire cochlea is enhanced by applying round window membrane low-frequency micro vibrations with a probe that only partially covers the round window. We provide evidence of enhanced drug influx into the cochlea and cochlear apical drug distribution without breaching cochlear boundaries. It is further suggested that ossicular functionality is not required for the effective drug distribution we report. The novel method presented here of local drug delivery to the cochlea could be implemented when ossicular functionality is absent or impeded and can be incorporated in clinically approved auditory protheses for patients who suffer with conductive, sensorineural or mixed hearing loss.

A Wirelessly Controlled Scalable 3D-Printed Microsystem for Drug Delivery

Here we present a 3D-printed, wirelessly controlled microsystem for drug delivery, comprising a refillable microreservoir and a phase-change peristaltic micropump. The micropump structure was inkjet-printed on the back of a printed circuit board around a catheter microtubing. The enclosure of the microsystem was fabricated using stereolithography 3D printing, with an embedded microreservoir structure and integrated micropump. In one configuration, the microsystem was optimized for murine inner ear drug delivery with an overall size of 19 × 13 × 3 mm3. Benchtop results confirmed the performance of the device for reliable drug delivery. The suitability of the device for long-term subcutaneous implantation was confirmed with favorable results of implantation of a microsystem in a mouse for six months. The drug delivery was evaluated in vivo by implanting four different microsystems in four mice, while the outlet microtubing was implanted into the round window membrane niche for infusion of a known ototoxic compound (sodium salicylate) at 50 nL/min for 20 min. Real-time shifts in distortion product otoacoustic emission thresholds and amplitudes were measured during the infusion, demonstrating similar results with syringe pump infusion. Although demonstrated for one application, this low-cost design and fabrication methodology is scalable for use in larger animals and humans for different clinical applications/delivery sites.

Opposite Roles of NT-3 and BDNF in Synaptic Remodeling of the Inner Ear Induced by Electrical Stimulation

With the development of neural prostheses, neural plasticity including synaptic remodeling under electrical stimulation is drawing more and more attention. Indeed, intracochlear electrical stimulation used to restore hearing in deaf can induce the loss of residual hearing and synapses of the inner hair cells (IHCs). However, the mechanism under this process is largely unknown. Considering that the guinea pig is always a suitable and convenient choice for the animal model of cochlea implant (CI), in the present study, normal-hearing guinea pigs were implanted with CIs. Four-hour electrical stimulation with the intensity of 6 dB above electrically evoked compound action potential (ECAP) threshold (which can decrease the quantity of IHC synapses and the excitability of the auditory nerve) resulted in the upregulation of Bdnf (p < 0.0001) and downregulation of Nt-3 (p < 0.05). Intracochlear perfusion of exogenous NT-3 or TrkC/Fc (which blocks NT-3) can, respectively, resist or aggravate the synaptic loss induced by electrical stimulation. In contrast, local delivery of exogenous BDNF or TrkB/Fc (which blocks BDNF) to the cochlea, respectively, exacerbated or protected against the synaptic loss caused by electrical stimulation. Notably, the synaptic changes were only observed in the basal and middle halves of the cochlea. All the findings above suggested that NT-3 and BDNF may play opposite roles in the remodeling of IHC synapses induced by intracochlear electrical stimulation, i.e. NT-3 and BDNF promoted the regeneration and degeneration of IHC synapses, respectively.

Local Drug Delivery to the Entire Cochlea without Breaching Its Boundaries

The mammalian cochlea is one of the least accessible organs for drug delivery. Systemic administration of many drugs is severely limited by the blood-labyrinth barrier. Local intratympanic administration into the middle ear would be a preferable option in this case, and the only option for many newly emerging classes of drugs, but it leads to the formation of drug concentration gradients along the extensive, narrow cochlea. The gradients are orders of magnitude and well outside the therapeutic windows. Here we present an efficient, quick, and simple method of cochlear pumping, through large-amplitude, low-frequency reciprocal oscillations of the stapes and round window, which can consistently and uniformly deliver drugs along the entire length of the intact cochlea within minutes without disrupting the cochlear boundaries. The method should facilitate novel ways of approaching the treatment of inner ear disorders because it overcomes the challenge of delivering therapeutics along the entire cochlear length.

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Systemic delivery of drugs to the inner ear is limited by the blood-labyrinth barrier

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Middle ear administration results in pronounced drug gradients along the cochlea

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Cochlear pumping distributes drugs evenly along the entire cochlea within minutes

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.

Cochlear pharmacokinetics - Micro-computed tomography and learning-prediction modeling for transport parameter determination

Inner ear disorders such as sensorineural deafness and genetic diseases may one day be treated with local drug delivery to the inner ear. Current pharmacokinetic models have been based on invasive methods to measure drug concentrations, limiting them in spatial resolution, and restricting the research to larger rodents. We developed an intracochlear pharmacokinetic model based on an imaging, learning-prediction (LP) paradigm for learning transport parameters in the murine cochlea. This was achieved using noninvasive micro-computed tomography imaging of the cochlea during in vivo infusion of a contrast agent at the basal end of scala tympani through a cochleostomy. Each scan was registered in 3-D to a cochlear atlas to segment the cochlear regions with high accuracy, enabling concentrations to be extracted along the length of each scala. These spatio-temporal concentration profiles were used to learn a concentration dependent diffusion coefficient, and transport parameters between the major scalae and to clearance. The LP model results are comparable to the current state of the art model, and can simulate concentrations for cases involving different infusion molecules and different drug delivery protocols. Forward simulation results with pulsatile delivery suggest the pharmacokinetic model can be used to optimize drug delivery protocols to reduce total drug delivered and the potential for toxic side effects. While developed in the challenging murine cochlea, the processes are scalable to larger animals and different drug infusion paradigms.

Drug Diffusion Along an Intact Mammalian Cochlea

Intratympanic drug administration depends on the ability of drugs to pass through the round window membrane (RW) at the base of the cochlea and diffuse from this location to the apex. While the RW permeability for many different drugs can be promoted, passive diffusion along the narrowing spiral of the cochlea is limited. Earlier measurements of the distribution of marker ions, corticosteroids, and antibiotics demonstrated that the concentration of substances applied to the RW was two to three orders of magnitude higher in the base compared to the apex. The measurements, however, involved perforating the cochlear bony wall and, in some cases, sampling perilymph. These manipulations can change the flow rate of perilymph and lead to intake of perilymph through the cochlear aqueduct, thereby disguising concentration gradients of the delivered substances. In this study, the suppressive effect of salicylate on cochlear amplification via block of the outer hair cell (OHC) somatic motility was utilized to assess salicylate diffusion along an intact guinea pig cochlea in vivo. Salicylate solution was applied to the RW and threshold elevation of auditory nerve responses was measured at different times and frequencies after application. Resultant concentrations of salicylate along the cochlea were calculated by fitting the experimental data using a mathematical model of the diffusion and clearing of salicylate in a tube of variable diameter combined with a model describing salicylate action on cochlear amplification. Concentrations reach a steady-state at different times for different cochlear locations and it takes longer to reach the steady-state at more apical locations. Even at the steady-state, the predicted concentration at the apex is negligible. Model predictions for the geometry of the longer human cochlea show even higher differences in the steady-state concentrations of the drugs between cochlear base and apex. Our findings confirm conclusions that achieving therapeutic drug concentrations throughout the entire cochlear duct is hardly possible when the drugs are applied to the RW and are distributed via passive diffusion. Assisted methods of drug delivery are needed to reach a more uniform distribution of drugs along the cochlea.

A nanoliter resolution implantable micropump for murine inner ear drug delivery

Advances in protective and restorative biotherapies have created new opportunities to use site-directed, programmable drug delivery systems to treat auditory and vestibular disorders. Successful therapy development that leverages the transgenic, knock-in, and knock-out variants of mouse models of human disease requires advanced microsystems specifically designed to function with nanoliter precision and with system volumes suitable for implantation. Here we present results for a novel biocompatible, implantable, scalable, and wirelessly controlled peristaltic micropump. The micropump configuration included commercially available catheter microtubing (250 μm OD, 125 μm ID) that provided a biocompatible leak-free flow path while avoiding complicated microfluidic interconnects. Peristaltic pumping was achieved by sequentially compressing the microtubing via expansion and contraction of a thermal phase-change material located in three chambers integrated adjacent to the microtubing. Direct-write micro-scale printing technology was used to build the mechanical components of the micropump around the microtubing directly on the back of a printed circuit board assembly (PCBA). The custom PCBA was fabricated using standard commercial processes providing microprocessor control of actuation and Bluetooth wireless communication through an Android application. The results of in vitro characterization indicated that nanoliter resolution control over the desired flow rates of 10-100 nL/min was obtained by changing the actuation frequency. Applying 10× greater than physiological backpressures and ± 3 °C ambient temperature variation did not significantly affect flow rates. Three different micropumps were tested on six mice for in vivo implantation of the catheter microtubing into the round window membrane niche for infusion of a known ototoxic compound (sodium salicylate) at 50 nL/min for 20 min. Real-time shifts in distortion product otoacoustic emission thresholds and amplitudes were measured during the infusion. There were systematic increases in distortion product threshold shifts during the 20-min perfusions; the mean shift was 15 dB for the most basal region. A biocompatibility study was performed to evaluate material suitability for chronic subcutaneous implantation and clinical translational development. The results indicated that the micropump components successfully passed key biocompatibility tests. A micropump prototype was implanted for one month without development of inflammation or infection. Although tested here on the small murine cochlea, this low-cost design and fabrication methodology is scalable for use in larger animals and for clinical applications in children and adults by appropriate scaling of the microtubing diameter and actuator volume.

Animal model studies yield translational solutions for cochlear drug delivery

The field of hearing and deafness research is about to enter an era where new cochlear drug delivery methodologies will become more innovative and plentiful. The present report provides a representative review of previous studies where efficacious results have been obtained with animal models, primarily rodents, for protection against acute hearing loss such as acoustic trauma due to noise overexposure, antibiotic use and cancer chemotherapies. These approaches were initiated using systemic injections or oral administrations of otoprotectants. Now, exciting new options for local drug delivery, which opens up the possibilities for utilization of novel otoprotective drugs or compounds that might not be suitable for systemic use, or might interfere with the efficacious actions of chemotherapeutic agents or antibiotics, are being developed. These include interesting use of nanoparticles (with or without magnetic field supplementation), hydrogels, cochlear micropumps, and new transtympanic injectable compounds, sometimes in combination with cochlear implants.

Age-related hearing loss: prevention of threshold declines, cell loss and apoptosis in spiral ganglion neurons

Age-related hearing loss (ARHL) -presbycusis - is the most prevalent neurodegenerative disease and number one communication disorder of our aged population; and affects hundreds of millions of people worldwide. Its prevalence is close to that of cardiovascular disease and arthritis, and can be a precursor to dementia. The auditory perceptual dysfunction is well understood, but knowledge of the biological bases of ARHL is still somewhat lacking. Surprisingly, there are no FDA-approved drugs for treatment. Based on our previous studies of human subjects, where we discovered relations between serum aldosterone levels and the severity of ARHL, we treated middle age mice with aldosterone, which normally declines with age in all mammals. We found that hearing thresholds and suprathreshold responses significantly improved in the aldosterone-treated mice compared to the non-treatment group. In terms of cellular and molecular mechanisms underlying this therapeutic effect, additional experiments revealed that spiral ganglion cell survival was significantly improved, mineralocorticoid receptors were upregulated via post-translational protein modifications, and age-related intrinsic and extrinsic apoptotic pathways were blocked by the aldosterone therapy. Taken together, these novel findings pave the way for translational drug development towards the first medication to prevent the progression of ARHL.

Emerging Gene Therapies for Genetic Hearing Loss

Gene therapy, or the treatment of human disease using genetic material, for inner ear dysfunction is coming of age. Recent progress in developing gene therapy treatments for genetic hearing loss has demonstrated tantalizing proof-of-principle in animal models. While successful translation of this progress into treatments for humans awaits, there is growing interest from patients, scientists, clinicians, and industry. Nonetheless, it is clear that a number of hurdles remain, and expectations for total restoration of auditory function should remain tempered until these challenges have been overcome. Here, we review progress, prospects, and challenges for gene therapy in the inner ear. We focus on technical aspects, including routes of gene delivery to the inner ear, choice of vectors, promoters, inner ear targets, therapeutic strategies, preliminary success stories, and points to consider for translating of these successes to the clinic.

A Comparative Study of Drug Delivery Methods Targeted to the Mouse Inner Ear: Bullostomy Versus Transtympanic Injection

We present two minimally invasive microsurgical techniques in rodents for specific drug delivery into the middle ear so that it may reach the inner ear. The first procedure consists of perforation of the tympanic bulla, termed bullostomy; the second one is a transtympanic injection. Both emulate human clinical intratympanic procedures. Chitosan-glycerophosphate (CGP) and Ringer´s Lactate buffer (RL) were used as biocompatible vehicles for local drug delivery. CGP is a nontoxic biodegradable polymer widely used in pharmaceutical applications. It is a viscous liquid at RT but it congeals to a semi solid phase at body temperature. RL is an isotonic solution used for intravenous administrations in humans. A small volume of this vehicle is precisely placed on the Round Window (RW) niche by means of a bullostomy. A transtympanic injection fills the middle ear and allows less control but broader access to the inner ear. The safety profiles of both techniques were studied and compared by using functional and morphological tests. Hearing was evaluated by registering the Auditory Brainstem Response (ABR) before and several times after microsurgery. The cytoarchitecture and preservation level of cochlear structures were studied by conventional histological techniques in paraformaldehyde-fixed and decalcified cochlear samples. In parallel, unfixed cochlear samples were taken and immediately frozen to analyze gene expression profiles of inflammatory markers by quantitative Reverse Transcriptase Polymerase Chain Reaction (qRT-PCR). Both procedures are suitable as drug delivery methods into the mouse middle ear, although transtympanic injection proved to be less invasive compared to bullostomy.

Protein transduction therapy into cochleae via the round window niche in guinea pigs

Cell-penetrating peptides (CPPs) are short sequences of amino acids that facilitate the penetration of conjugated cargoes across mammalian cell membranes, and as such, they may provide a safe and effective method for drug delivery to the inner ear. Simple polyarginine peptides have been shown to induce significantly higher cell penetration rates among CPPs. Herein, we show that a peptide consisting of nine arginines ("9R") effectively delivered enhanced green fluorescent protein (EGFP) into guinea pig cochleae via the round window niche without causing any deterioration in auditory function. A second application, 24 hours after the first, prolonged the presence of EGFP. To assess the feasibility of protein transduction using 9R-CPPs via the round window, we used "X-linked inhibitor of apoptosis protein" (XIAP) bonded to a 9R peptide (XIAP-9R). XIAP-9R treatment prior to acoustic trauma significantly reduced putative hearing loss and the number of apoptotic hair cells loss in the cochleae. Thus, the topical application of molecules fused to 9R-CPPs may be a simple and promising strategy for treating inner ear diseases.

Towards an Implantable, Low Flow Micropump That Uses No Power in the Blocked-Flow State

Low flow rate micropumps play an increasingly important role in drug therapy research. Infusions to small biological structures and lab-on-a-chip applications require ultra-low flow rates and will benefit from the ability to expend no power in the blocked-flow state. Here we present a planar micropump based on gallium phase-change actuation that leverages expansion during solidification to occlude the flow channel in the off-power state. The presented four chamber peristaltic micropump was fabricated with a combination of Micro Electro Mechanical System (MEMS) techniques and additive manufacturing direct write technologies. The device is 7 mm × 13 mm × 1 mm (<100 mm³) with the flow channel and exterior coated with biocompatible Parylene-C, critical for implantable applications. Controllable pump rates from 18 to 104 nL/min were demonstrated, with 11.1 ± 0.35 nL pumped per actuation at an efficiency of 11 mJ/nL. The normally-closed state of the gallium actuator prevents flow and diffusion between the pump and the biological system or lab-on-a-chip, without consuming power. This is especially important for implanted applications with periodic drug delivery regimens.

Persistence, distribution, and impact of distinctly segmented microparticles on cochlear health following in vivo infusion

Delivery of pharmaceuticals to the cochleae of patients with auditory dysfunction could potentially have many benefits from enhancing auditory nerve survival to protecting remaining sensory cells and their neuronal connections. Treatment would require platforms to enable drug delivery directly to the cochlea and increase the potential efficacy of intervention. Cochlear implant recipients are a specific patient subset that could benefit from local drug delivery as more candidates have residual hearing; and since residual hearing directly contributes to post-implantation hearing outcomes, it requires protection from implant insertion-induced trauma. This study assessed the feasibility of utilizing microparticles for drug delivery into cochlear fluids, testing persistence, distribution, biocompatibility, and drug release characteristics. To allow for delivery of multiple therapeutics, particles were composed of two distinct compartments; one containing polylactide-co-glycolide (PLGA), and one composed of acetal-modified dextran and PLGA. Following in vivo infusion, image analysis revealed microparticle persistence in the cochlea for at least 7 days post-infusion, primarily in the first and second turns. The majority of subjects maintained or had only slight elevation in auditory brainstem response thresholds at 7 days post-infusion compared to pre-infusion baselines. There was only minor to limited loss of cochlear hair cells and negligible immune response based on CD45+ immunolabling. When Piribedil-loaded microparticles were infused, Piribedil was detectable within the cochlear fluids at 7 days post-infusion. These results indicate that segmented microparticles are relatively inert, can persist, release their contents, and be functionally and biologically compatible with cochlear function and therefore are promising vehicles for cochlear drug delivery. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1510-1522, 2016.

The Mouse Round-window Approach for Ototoxic Agent Delivery: A Rapid and Reliable Technique for Inducing Cochlear Cell Degeneration

Investigators have utilized a wide array of animal models and investigative techniques to study the mammalian auditory system. Much of the basic research involving the cochlea and its associated neural pathways entails exposure of model cochleae to a variety of ototoxic agents. This allows investigators to study the effects of targeted damage to cochlear structures, and in some cases, the self-repair or regeneration of those structures. Various techniques exist for delivery of ototoxic agents to the cochlea. When selecting a particular technique, investigators must consider a number of factors, including the induction of inadvertent systemic toxicity, the amount of cochlear damage produced by the surgical procedure itself, the type of lesion desired, animal survivability, and reproducibility/reliability of results. Currently established techniques include parenteral injection, intra-peritoneal injection, trans-tympanic injection, endolymphatic sac injection, and cochleostomy with perilymphatic perfusion. Each of these methods has been successfully utilized and is well described in the literature; yet, each has various shortcomings. Here, we present a technique for topical application of ototoxic agents directly to the round window niche. This technique is non-invasive to inner ear structures, produces rapid onset of reliably targeted lesions, avoids systemic toxicity, and allows for an intra-animal control (the contra-lateral ear). Results stemming from this approach have helped deeper understanding of auditory pathophysiology, cochlear cell degeneration, and regenerative capacity in response to an acute injury. Future investigations may use this method to conduct interventional studies involving gene therapy and stem cell transplantation to combat hearing loss.

Hyaluronic acid pretreatment for Sendai virus-mediated cochlear gene transfer

Gene therapy with viral vectors is one of the most promising strategies for sensorineural hearing loss. However, safe and effective administration of the viral vector into cochlear tissue is difficult because of the anatomical isolation of the cochlea. We investigated the efficiency and safety of round window membrane (RWM) application of Sendai virus, one of the most promising non-genotoxic vectors, after pretreatment with hyaluronic acid (HA) on the RWM to promote efficient viral translocation into the cochlea. Sendai virus expressing the green fluorescent protein reporter gene was detected throughout cochlear tissues following application combined with HA pretreatment. Quantitative analysis revealed that maximum expression was reached 3 days after treatment. The efficiency of transgene expression was several 100-fold greater with HA pretreatment than that without. Furthermore, unlike the conventional intracochlear delivery methods, this approach did not cause hearing loss. These findings reveal the potential utility of gene therapy with Sendai virus and HA for treatment of sensorineural hearing loss.

Auditory brainstem gap responses start to decline in mice in middle age: a novel physiological biomarker for age-related hearing loss

The auditory function of the CBA/CaJ mouse strain is normal during the early phases of life and gradually declines over its lifespan, much like human age-related hearing loss (ARHL) but within the "time frame" of a mouse life cycle. This pattern of ARHL is similar to that of most humans: difficult to diagnose clinically at its onset and currently not treatable medically. To address the challenge of early diagnosis, we use CBA mice to analyze the initial stages and functional onset biomarkers of ARHL. The results from Auditory Brainstem Response (ABR) audiogram and Gap-in-noise (GIN) ABR tests were compared for two groups of mice of different ages, namely young adult and middle age. ABR peak components from the middle age group displayed minor changes in audibility but had a significantly higher prolonged peak latency and decreased peak amplitude in response to temporal gaps in comparison with the young adult group. The results for the younger subjects revealed gap thresholds and recovery rates that were comparable with previous studies of auditory neural gap coding. Our findings suggest that age-linked degeneration of the peripheral and brainstem auditory system begins in middle age, allowing for the possibility of preventative biomedical or hearing protection measures to be implemented in order to attenuate further damage to the auditory system attributable to ARHL.