Impact of Systemic versus Intratympanic Dexamethasone Administration on the Perilymph Proteome.

Glucocorticoids are the first-line treatment for sensorineural hearing loss, but little is known about the mechanism of their protective effect or the impact of route of administration. The recent development of hollow microneedles enables safe and reliable sampling of perilymph for proteomic analysis. Using these microneedles, we investigate the effect of intratympanic (IT) versus intraperitoneal (IP) dexamethasone administration on guinea pig perilymph proteome. Guinea pigs were treated with IT dexamethasone (n = 6), IP dexamethasone (n = 8), or untreated for control (n = 8) 6 h prior to aspiration. The round window membrane (RWM) was accessed via a postauricular approach, and hollow microneedles were used to perforate the RWM and aspirate 1 µL of perilymph. Perilymph samples were analyzed by liquid chromatography-mass spectrometry-based label-free quantitative proteomics. Mass spectrometry raw data files have been deposited in an international public repository (MassIVE proteomics repository at https://massive.ucsd.edu/) under data set # MSV000086887. In the 22 samples of perilymph analyzed, 632 proteins were detected, including the inner ear protein cochlin, a perilymph marker. Of these, 14 proteins were modulated by IP, and three proteins were modulated by IT dexamethasone. In both IP and IT dexamethasone groups, VGF nerve growth factor inducible was significantly upregulated compared to control. The remaining adjusted proteins modulate neurons, inflammation, or protein synthesis. Proteome analysis facilitated by the use of hollow microneedles shows that route of dexamethasone administration impacts changes seen in perilymph proteome. Compared to IT administration, the IP route was associated with greater changes in protein expression, including proteins involved in neuroprotection, inflammatory pathway, and protein synthesis. Our findings show that microneedles can mediate safe and effective intracochlear sampling and hold promise for inner ear diagnostics.

Risk of Acquiring Perioperative COVID-19 During the Initial Pandemic Peak: A Retrospective Cohort Study.

OBJECTIVE: To determine the risk of acquiring perioperative COVID-19 infection in previously COVID-19 negative patients. SUMMARY OF BACKGROUND DATA: During the initial peak of the COVID-19 pandemic, there was significant concern of hospital acquired COVID-19 infections. Medical centers rapidly implemented systems to minimize perioperative transmission, including routine preoperative testing, patient isolation, and enhanced cleaning. METHODS: In this retrospective cohort study, medical records of all adult patients who underwent surgery at our quaternary, acute care hospital between March 15 and May 15, 2020 were reviewed. The risk of preoperatively negative patients developing symptomatic COVID-19 within 2-14 days postoperatively was determined. Surgical characteristics, outcomes, and complications were compared between those with and without acquired perioperative COVID-19 infection. RESULTS: Among 501 negative patients undergoing index surgeries, 9 (1.8%) developed symptomatic COVID-19 in the postoperative period; all occurred before implementation of routine preoperative testing [9/243, 3.7% vs 0/258, 0%, odds ratio (OR): 0.048, P = 0.036]. No patient who was polymerase-chain-reaction negative on the day of surgery (n = 170) developed postoperative infection. Perioperative infection was associated with preoperative diabetes (OR: 3.70, P = 0.042), cardiovascular disease (OR: 3.69, P = 0.043), angiotensin receptor blocker use (OR: 6.58, P = 0.004), and transplant surgery (OR: 11.00, P = 0.002), and multiple complications, readmission (OR: 5.50, P = 0.029) and death (OR: 12.81, P = 0.001). CONCLUSIONS: During the initial peak of the COVID-19 pandemic, there was minimal risk of acquiring symptomatic perioperative COVID-19 infection, especially after the implementation of routine preoperative testing. However, perioperative COVID-19 infection was associated with poor postoperative outcome.

Perioperative Morbidity and Mortality of Patients With COVID-19 Who Undergo Urgent and Emergent Surgical Procedures.

OBJECTIVE: To evaluate the perioperative morbidity and mortality of patients with COVID-19 who undergo urgent and emergent surgery. SUMMARY BACKGROUND DATA: Although COVID-19 infection is usually associated with mild disease, it can lead to severe respiratory complications. Little is known about the perioperative outcomes of patients with COVID-19. METHODS: We examined patients who underwent urgent and emergent surgery at 2 hospitals in New York City from March 17 to April 15, 2020. Elective surgical procedures were cancelled throughout and routine, laboratory based COVID-19 screening was instituted on April 1. Mortality, complications, and admission to the intensive care unit were compared between patients with COVID-19 detected perioperatively and controls. RESULTS: Among 468 subjects, 36 (7.7%) had confirmed COVID-19. Among those with COVID-19, 55.6% were detected preoperatively and 44.4% postoperatively. Before the routine preoperative COVID-19 laboratory screening, 7.7% of cases were diagnosed preoperatively compared to 65.2% after institution of screening (P = 0.0008). The perioperative mortality rate was 16.7% in those with COVID-19 compared to 1.4% in COVID-19 negative subjects [aRR = 9.29; 95% confidence interval (CI), 5.68-15.21]. Serious complications were identified in 58.3% of COVID-19 subjects versus 6.0% of controls (aRR = 7.02; 95%CI, 4.96-9.92). Cardiac arrest, sepsis/shock, respiratory failure, pneumonia, acute respiratory distress syndrome, and acute kidney injury were more common in those with COVID-19. The intensive care unit admission rate was 36.1% in those with COVID-19 compared to 16.4% of controls (aRR = 1.34; 95%CI, 0.86-2.09). CONCLUSIONS: COVID-19 is associated with an increased risk for serious perioperative morbidity and mortality. A substantial number of patients with COVID-19 are not identified until after surgery.

Heregulin Activity Assays for Residual Testing of Cell Therapy Products.

BACKGROUND: Heregulin is a ligand for the protooncogene product ErbB/HER that acts as  a key mitogenic factor for human Schwann cells (hSCs). Heregulin is required for sustained hSC growth in vitro but must be thoroughly removed before cell collection for transplantation due to potential safety concerns. The goal of this study was to develop simple cell-based assays to assess the effectiveness of heregulin addition to and removal from aliquots of hSC culture medium. These bioassays were based on the capacity of a ß1-heregulin peptide to elicit ErbB/HER receptor signaling in adherent ErbB2+/ErbB3+ cells. RESULTS: Western blotting was used to measure the activity of three different ß1-heregulin/ErbB-activated kinases (ErbB3/HER3, ERK/MAPK and Akt/PKB) using phospho-specific antibodies against key activating residues. The duration, dose-dependency and specificity of ß1-heregulin-initiated kinase phosphorylation were investigated, and controls were implemented for assay optimization and reproducibility to detect ß1-heregulin activity in the nanomolar range. Results from these assays showed that the culture medium from transplantable hSCs elicited no detectable activation of the aforementioned kinases in independent rounds of testing, indicating that the implemented measures can ensure that the final hSC product is devoid of bioactive ß1-heregulin molecules prior to transplantation. CONCLUSIONS: These assays may be valuable to detect impurities such as undefined soluble factors or factors for which other biochemical or biological assays are not yet available. Our workflow can be modified as necessary to determine the presence of ErbB/HER, ERK, and Akt activators other than ß1-heregulin using native samples, such as fresh isolates from cell- or tissue extracts in addition to culture medium.

SARS-COV-2 transmission rate is low when following a COVID+ patient in the operating room.

PURPOSE: Acquiring SARS-CoV-2 infection for uninfected patients undergoing surgical procedures following a COVID positive (COVID+) patient is of significant concern, both for patients seeking medical care in hospital settings and for management of surgical services during pandemic times. METHODS: Using data identifying all COVID+ surgical patients during the initial pandemic peak in New York City (March 15 to May 15, 2020), we analyzed the rate of postoperative symptomatic SARS-CoV-2 infection in COVID negative (COVID-) patients undergoing surgery in the same operating room within 48 h, thus determining nosocomial symptomatic infection rate attributable to COVID operating room exposure. RESULTS: Five COVID- patients directly followed a COVID+ patient, while 19 patients were exposed to COVID+ operating rooms within 24 h. By 48 h, 21 additional patients were exposed. No exposed patients acquired symptomatic SARS-CoV-2 infection postoperatively. CONCLUSION: With implementation of infection prevention and control procedures in the operating room under local pandemic conditions, our findings suggest that the risk of acquiring SARS-CoV-2 infection, when following a COVID+ patient in the same operating room, is very low.

COVID-19 survivorship: How otolaryngologist-head and neck surgeons can restore quality of life after critical illness.

Mortality from COVID-19 has obscured a subtler crisis - the swelling ranks of COVID-19 survivors. After critical illness, patients often suffer post-intensive care syndrome (PICS), which encompasses physical, cognitive, and/or mental health impairments that are often long-lasting barriers to resuming a meaningful life. Some deficits after COVID-19 critical illness will require otolaryngologic expertise for years after hospital discharge. There are roles for all subspecialties in preventing, diagnosing, or treating sequelae of COVID-19. Otolaryngologist leadership in multidisciplinary efforts ensures coordinated care. Timely tracheostomy, when indicated, may shorten the course of intensive care unit stay and thereby potentially reduce the impairments associated with PICS. Otolaryngologists can provide expertise in olfactory disorders; thrombotic sequelae of hearing loss and vertigo; and laryngotracheal injuries that impair speech, voice, swallowing, communication, and breathing. In the aftermath of severe COVID-19, otolaryngologists are poised to lead efforts in early identification and intervention for impairments affecting patients' quality of life.

Hearing Loss Is Associated with Increased Variability in Double Support Period in the Elderly.

Hearing loss is a disabling condition that increases with age and has been linked to difficulties in walking and increased risk of falls. The purpose of this study is to investigate changes in gait parameters associated with hearing loss in a group of older adults aged 60 or greater. Custom-engineered footwear was used to collect spatiotemporal gait data in an outpatient clinical setting. Multivariable linear regression was used to determine the relationship between spatiotemporal gait parameters and high and low frequency hearing thresholds of the poorer hearing ear, the left ear, and the right ear, respectively, adjusting for age, sex, race/ethnicity, and the Dizziness Handicap Inventory-Screening version score. Worsening high and low frequency hearing thresholds were associated with increased variability in double support period. Effects persisted after adjusting for the effects of age and perceived vestibular disability and were greater for increases in hearing thresholds for the right ear compared to the left ear. These findings illustrate the importance of auditory feedback for balance and coordination and may suggest a right ear advantage for the influence of auditory feedback on gait.

Simulation assisted design for microneedle manufacturing: Computational modeling of two-photon templated electrodeposition.

Fully metallic micrometer-scale 3D architectures can be fabricated via a hybrid additive methodology combining multi-photon lithography with electrochemical deposition of metals. The methodology - referred to as two-photon templated electrodeposition (2PTE) - has significant design freedom that enables the creation of complicated, traditionally difficult-to-make, high aspect ratio metallic structures such as microneedles. These complicated geometries, combined with their fully metallic nature, can enable precision surgical applications such as inner ear drug delivery or fluid sampling. However, the process involves electrochemical deposition of metals into complicated 3D lithography patterns thicker than 500 µm. This causes potential and chemical gradients to develop within the 3D template, creating limitations to what can be designed. These limitations can be explored, understood, and overcome via numerical modeling. Herein we introduce a numerical model as a design tool that can predict growth for manufacturing complicated 3D metallic geometries. The model is successful in predicting the geometric result of 2PTE, and enables extraction of insights about geometric constraints through exploration of its mechanics.

In-vitro perforation of the round window membrane via direct 3-D printed microneedles.

The cochlea, or inner ear, is a space fully enclosed within the temporal bone of the skull, except for two membrane-covered portals connecting it to the middle ear space. One of these portals is the round window, which is covered by the Round Window Membrane (RWM). A longstanding clinical goal is to reliably and precisely deliver therapeutics into the cochlea to treat a plethora of auditory and vestibular disorders. Standard of care for several difficult-to-treat diseases calls for injection of a therapeutic substance through the tympanic membrane into the middle ear space, after which a portion of the substance diffuses across the RWM into the cochlea. The efficacy of this technique is limited by an inconsistent rate of molecular transport across the RWM. A solution to this problem involves the introduction of one or more microscopic perforations through the RWM to enhance the rate and reliability of diffusive transport. This paper reports the use of direct 3D printing via Two-Photon Polymerization (2PP) lithography to fabricate ultra-sharp polymer microneedles specifically designed to perforate the RWM. The microneedle has tip radius of 500 nm and shank radius of 50 µ m, and perforates the guinea pig RWM with a mean force of 1.19 mN. The resulting perforations performed in vitro are lens-shaped with major axis equal to the microneedle shank diameter and minor axis about 25% of the major axis, with mean area 1670 µ m2. The major axis is aligned with the direction of the connective fibers within the RWM. The fibers were separated along their axes without ripping or tearing of the RWM suggesting the main failure mechanism to be fiber-to-fiber decohesion. The small perforation area along with fiber-to-fiber decohesion are promising indicators that the perforations would heal readily following in vivo experiments. These results establish a foundation for the use of Two-Photon Polymerization lithography as a means to fabricate microneedles to perforate the RWM and other similar membranes.

Human Schwann cells exhibit long-term cell survival, are not tumorigenic and promote repair when transplanted into the contused spinal cord.

The transplantation of rodent Schwann cells (SCs) provides anatomical and functional restitution in a variety of spinal cord injury (SCI) models, supporting the recent translation of SCs to phase 1 clinical trials for human SCI. Whereas human (Hu)SCs have been examined experimentally in a complete SCI transection paradigm, to date the reported behavior of SCs when transplanted after a clinically relevant contusive SCI has been restricted to the use of rodent SCs. Here, in a xenotransplant, contusive SCI paradigm, the survival, biodistribution, proliferation and tumorgenicity as well as host responses to HuSCs, cultured according to a protocol analogous to that developed for clinical application, were investigated. HuSCs persisted within the contused nude rat spinal cord through 6 months after transplantation (longest time examined), exhibited low cell proliferation, displayed no evidence of tumorigenicity and showed a restricted biodistribution to the lesion. Neuropathological examination of the CNS revealed no adverse effects of HuSCs. Animals exhibiting higher numbers of surviving HuSCs within the lesion showed greater volumes of preserved white matter and host rat SC and astrocyte ingress as well as axon ingrowth and myelination. These results demonstrate the safety of HuSCs when employed in a clinically relevant experimental SCI paradigm. Further, signs of a potentially positive influence of HuSC transplants on host tissue pathology were observed. These findings show that HuSCs exhibit a favorable toxicity profile for up to 6 months after transplantation into the contused rat spinal cord, an important outcome for FDA consideration of their use in human clinical trials.

Gene Therapy for Leber Hereditary Optic Neuropathy: Initial Results.

PURPOSE: Leber hereditary optic neuropathy (LHON) is a disorder characterized by severe and rapidly progressive visual loss when caused by a mutation in the mitochondrial gene encoding NADH:ubiquinone oxidoreductase subunit 4 (ND4). We have initiated a gene therapy trial to determine the safety and tolerability of escalated doses of an adeno-associated virus vector (AAV) expressing a normal ND4 complementary DNA in patients with a G to A mutation at nucleotide 11778 of the mitochondrial genome. DESIGN: In this prospective open-label trial (NCT02161380), the study drug (self-complementary AAV [scAAV]2(Y444,500,730F)-P1ND4v2) was intravitreally injected unilaterally into the eyes of 5 blind participants with G11778A LHON. Four participants with visual loss for more than 12 months were treated. The fifth participant had visual loss for less than 12 months. The first 3 participants were treated at the low dose of vector (5 × 10(9) vg), and the fourth participant was treated at the medium dose (2.46 × 10(10) vg). The fifth participant with visual loss for less than 12 months received the low dose. Treated participants were followed for 90 to 180 days and underwent ocular and systemic safety assessments along with visual structure and function examinations. PARTICIPANTS: Five legally blind patients with G11778A LHON. MAIN OUTCOME MEASURES: Loss of visual acuity. RESULTS: Visual acuity as measured by the Early Treatment Diabetic Retinopathy Study (ETDRS) eye chart remained unchanged from baseline to 3 months in the first 3 participants. For 2 participants with 90-day follow-up, acuity increased from hand movements to 7 letters in 1 and by 15 letters in 1, representing an improvement equivalent to 3 lines. No one lost vision, and no serious adverse events were observed. Minor adverse events included a transient increase of intraocular pressure (IOP), exposure keratitis, subconjunctival hemorrhage, a sore throat, and a transient increase in neutralizing antibodies (NAbs) against AAV2 in 1 participant. All blood samples were negative for vector DNA. CONCLUSIONS: No serious safety problems were observed in the first 5 participants enrolled in this phase I trial of virus-based gene transfer in this mitochondrial disorder. Additional study follow-up of these and additional participants planned for the next 4 years is needed to confirm these preliminary observations.

A dual wedge microneedle for sampling of perilymph solution via round window membrane.

Precision medicine for inner-ear disease is hampered by the absence of a methodology to sample inner-ear fluid atraumatically. The round window membrane (RWM) is an attractive portal for accessing cochlear fluids as it heals spontaneously. In this study, we report on the development of a microneedle for perilymph sampling that minimizes the size of RWM perforation, facilitates quick aspiration, and provides precise volume control. Here, considering the mechanical anisotropy of the RWM and hydrodynamics through a microneedle, a 31G stainless steel pipe was machined into wedge-shaped design via electrical discharge machining. The sharpness of the needle was evaluated via a surface profilometer. Guinea pig RWM was penetrated in vitro, and 1 µL of perilymph was sampled and analyzed via UV-vis spectroscopy. The prototype wedge shaped needle was successfully fabricated with the tip curvature of 4.5 µm and the surface roughness of 3.66 µm in root mean square. The needle created oval perforation with minor and major diameter of 143 and 344 µm (n = 6). The sampling duration and standard deviation of aspirated volume were 3 s and 6.8 % respectively. The protein concentration was 1.74 mg/mL. The prototype needle facilitated precise perforation of RWMs and rapid aspiration of cochlear fluid with precise volume control. The needle design is promising and requires testing in human cadaveric temporal bone and further optimization to become clinically viable.

Hearing Aid Use is Associated with Better Mini-Mental State Exam Performance.

OBJECTIVE: Hearing loss is associated with cognitive decline in the elderly. However, it is unknown if the use of hearing aids (HAs) is associated with enhanced cognitive function. METHODS: In a cross-sectional study at an academic medical center, participants underwent audiometric evaluation, the Mini-Mental State Exam (MMSE), and the Trail Making Test, Part B (TMT-B). The impact of use versus disuse of HAs was assessed. Performance on cognitive tests was then compared with unaided hearing levels. RESULTS: HA users performed better on the MMSE (1.9 points; rank-sum, p = 0.008) despite having worse hearing at both high frequencies (15.3-dB hearing level; t test, p < 0.001) and low frequencies (15.7-dB hearing level; t test p < 0.001). HA use had no effect TMT-B performance. Better performance on the MMSE was correlated with both low frequency (ρ = -0.28, p = 0.021) and high frequency (ρ = -0.21, p = 0.038) hearing level, but there was no correlation between performance on the TMT-B and hearing at any frequency. CONCLUSION: Despite having poorer hearing, HA users performed better on the MMSE. Better performance on cognitive tests with auditory stimuli (MMSE) but not visual stimuli (TMT-B) suggests that hearing loss is associated with sensory-specific cognitive decline rather than global cognitive impairment. Because hearing loss is nearly universal in those older than 80 years, HAs should be strongly recommended to minimize cognitive impairment in the elderly.

Physiologic Effects of Microneedle-Mediated Intracochlear Dexamethasone Injection in the Guinea Pig.

OBJECTIVES: Oral or intratympanic corticosteroids are commonly used to treat sudden sensorineural hearing loss (SSHL), tinnitus, and Meniere disease. Direct intracochlear delivery has been proposed to overcome the variability in bioavailability and efficacy of systemic or middle ear delivery. In this study, we aim to characterize the physiologic consequences of microneedle-mediated direct intracochlear injection of dexamethasone through the round window membrane (RWM). METHODS: In Hartley guinea pigs (n = 5), a post-auricular incision followed by bullostomy was made to access the round window membrane. Using 100 µm diameter hollow microneedles, 1.0 µl of 10 mg/ml dexamethasone was injected through the RWM over 1 min. Compound action potential (CAP) and distortion product otoacoustic action emissions (DPOAE) were measured before perforation, at 1 h, and at 5 h following injection. CAP hearing thresholds were measured from 0.5 to 40 kHz, and DPOAE f2 frequencies ranged from 1.0 and 32 kHz. Repeated measures ANOVA followed by pairwise t-tests were used for statistical analysis. RESULTS: ANOVA identified significant CAP threshold shifts at four frequencies (4, 16, 36, and 40 kHz) and differences in DPOAE at 1 frequency (6 kHz). Paired t-tests revealed differences between the pre-perforation and 1 h time point. By 5 h post injection, both CAP hearing thresholds and DPOAE recover and are not significantly different from baseline thresholds. CONCLUSION: Direct intracochlear delivery of dexamethasone via microneedles results in temporary shifts in hearing thresholds that resolve by 5 hours, thus supporting microneedle technology for the treatment of inner ear disorders. LEVEL OF EVIDENCE: NA Laryngoscope, 134:388-392, 2024.

Exploring Inner Ear and Brain Connectivity through Perilymph Sampling for Early Detection of Neurological Diseases: A Provocative Proposal.

Recent evidence shows that it is possible to identify the elements responsible for sensorineural hearing loss, such as pro-inflammatory cytokines and macrophages, by performing perilymph sampling. However, current studies have only focused on the diagnosis of such as otologic conditions. Hearing loss is a feature of certain neuroinflammatory disorders such as multiple sclerosis, and sensorineural hearing loss (SNHL) is widely detected in Alzheimer's disease. Although the environment of the inner ear is highly regulated, there are several communication pathways between the perilymph of the inner ear and cerebrospinal fluid (CSF). Thus, examination of the perilymph may help understand the mechanism behind the hearing loss observed in certain neuroinflammatory and neurodegenerative diseases. Herein, we review the constituents of CSF and perilymph, the anatomy of the inner ear and its connection with the brain. Then, we discuss the relevance of perilymph sampling in neurology. Currently, perilymph sampling is only performed during surgical procedures, but we hypothesize a simplified and low-invasive technique that could allow sampling in a clinical setting with the same ease as performing an intratympanic injection under direct visual check. The use of this modified technique could allow for perilymph sampling in people with hearing loss and neuroinflammatory/neurodegenerative disorders and clarify the relationship between these conditions; in fact, by measuring the concentration of neuroinflammatory and/or neurodegenerative biomarkers and those typically expressed in the inner ear in aging SNHL, it could be possible to understand if SNHL is caused by aging or neuroinflammation.

Community Health Worker Intervention for Newborns Not Passing Initial Universal Hearing Screening.

BACKGROUND: Universal newborn hearing screening (UNHS) is effective in identifying newborns with possible hearing loss (HL). Outpatient follow-up for newborns referred after hospital-based screening remains a potential area of improvement. In this study, we evaluate the efficacy of a community health worker (CHW) intervention in promoting adherence to outpatient rescreening for newborns referred after initial UNHS. METHODS: A mixed prospective-retrospective cohort study was performed to evaluate a CHW intervention at an academic medical center. Caregivers of referred newborns were contacted by CHWs prior to discharge and educated about HL and the importance of follow-up screening. The CHW outreach intervention was performed for 297 referred newborns between May 2020 and June 2021 and compared to a cohort of 238 newborns without the CHW intervention between March 2019 and June 2021. Statistical analyses were conducted using 2 × 2 Chi-square tests, two-tailed unpaired t-tests, multinomial logistic regression, and multiple linear regression. RESULTS: In the intervention group, 236 of 297 newborns (79.5%) completed their outpatient follow-up rescreening; in the comparison group, 170 of 238 newborns (71.4%) completed their follow-up rescreening (P = .031, OR = 1.55 with regression P = .04). In the intervention group, the average time to follow-up was 13.4 days versus 12.5 days for the comparison group (P = .449, multiple R2 = .02 with P = .78). CONCLUSIONS: CHW outreach intervention may increase adherence to outpatient follow-up rescreening for newborns referred after initial, hospital-based UNHS. Expansion of nursery teams to include CHWs may thus improve completion of recommended follow-up hearing screens.

Musical hallucinations associated with pontine lacunar lesions.

Three elderly patients experienced musical hallucinations (MH) in the context of hearing loss. In at least two of the cases, the onset was sudden. All three patients had pontine T2/FLAIR hyperintense foci on MR scan after the onset of the MH.

Microneedles Facilitate Small-Volume Intracochlear Delivery Without Physiologic Injury in Guinea Pigs.

HYPOTHESIS: Microneedle-mediated intracochlear injection through the round window membrane (RWM) will facilitate intracochlear delivery, not affect hearing, and allow for full reconstitution of the RWM within 48 hours. BACKGROUND: We have developed polymeric microneedles that allow for in vivo perforation of the guinea pig RWM and aspiration of perilymph for diagnostic analysis, with full reconstitution of the RWM within 48 to 72 hours. In this study, we investigate the ability of microneedles to deliver precise volumes of therapeutics into the cochlea and assess the subsequent consequences on hearing. METHODS: Volumes of 1.0, 2.5, or 5.0 µL of artificial perilymph were injected into the cochlea at a rate of 1 µL/min. Compound action potential (CAP) and distortion product otoacoustic emission were performed to assess for hearing loss (HL), and confocal microscopy was used to evaluate the RWM for residual scarring or inflammation. To evaluate the distribution of agents within the cochlea after microneedle-mediated injection, 1.0 µL of FM 1-43 FX was injected into the cochlea, followed by whole mount cochlear dissection and confocal microscopy. RESULTS: Direct intracochlear injection of 1.0 µL of artificial perilymph in vivo , corresponding to about 20% of the scala tympani volume, was safe and did not result in HL. However, injection of 2.5 or 5.0 µL of artificial perilymph into the cochlea produced statistically significant high-frequency HL persisting 48 hours postperforation. Assessment of RWMs 48 hours after perforation revealed no inflammatory changes or residual scarring. FM 1-43 FX injection resulted in distribution of the agent predominantly in the basal and middle turns. CONCLUSION: Microneedle-mediated intracochlear delivery of small volumes relative to the volume of the scala tympani is feasible, safe, and does not cause HL in guinea pigs; however, injection of large volumes induces high-frequency HL. Injection of small volumes of a fluorescent agent across the RWM resulted in significant distribution within the basal turn, less distribution in the middle turn, and almost none in the apical turn. Microneedle-mediated intracochlear injection, along with our previously developed intracochlear aspiration, opens the pathway for precision inner ear medicine.

Anatomic, physiologic, and proteomic consequences of repeated microneedle-mediated perforations of the round window membrane.

BACKGROUND: We have developed 3D-printed microneedle technology for diagnostic aspiration of perilymph and intracochlear delivery of therapeutic agents. Single microneedle-mediated round window membrane (RWM) perforation does not cause hearing loss, heals within 48-72 h, and yields sufficient perilymph for proteomic analysis. In this study, we investigate the anatomic, physiologic, and proteomic consequences of repeated microneedle-mediated perforations of the same RWM at different timepoints. METHODS: 100-µm-diameter hollow microneedles were fabricated using two-photon polymerization (2PP) lithography. The tympanic bullae of Hartley guinea pigs (n = 8) were opened with adequate exposure of the RWM. Distortion product otoacoustic emissions (DPOAE) and compound action potential (CAP) were recorded to assess hearing. The hollow microneedle was introduced into the bulla and the RWM was perforated; 1 µL of perilymph was aspirated from the cochlea over the course of 45 s. 72 h later, the above procedure was repeated with aspiration of an additional 1 µL of perilymph. 72 h after the second perforation, RWMs were harvested for confocal imaging. Perilymph proteomic analysis was completed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). RESULTS: Two perforations and aspirations were performed in 8 guinea pigs. In six, CAP, DPOAE, and proteomic analysis were obtained; in one, only CAP and DPOAE results were obtained; and in one, only proteomics results were obtained. Hearing tests demonstrated mild hearing loss at 1-4 kHz and 28 kHz, most consistent with conductive hearing loss. Confocal microscopy demonstrated complete healing of all perforations with full reconstitution of the RWM. Perilymph proteomic analysis identified 1855 proteins across 14 samples. The inner ear protein cochlin was observed in all samples, indicating successful aspiration of perilymph. Non-adjusted paired t-tests with p < 0.01 revealed significant changes in 13 of 1855 identified proteins (0.7%) between the first and second aspirations. CONCLUSIONS: We demonstrate that repeated microneedle perforation of the RWM is feasible, allows for complete healing of the RWM, and minimally changes the proteomic expression profile. Thus, microneedle-mediated repeated aspirations in a single animal can be used to monitor the response to inner ear treatments over time.