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* These authors contributed equally
Miniature pigs (mini-pigs) are an ideal large animal model for research into cochlear implants. Cochlear implantation surgery in mini-pigs can be utilized to provide initial evidence of the safety and potential performance of novel electrode arrays and surgical approaches in a living system similar to human beings.
Cochlear implants (CI) are the most effective method to treat people with severe-to-profound sensorineural hearing loss. Although CIs are used worldwide, no standard model exists for investigating the electrophysiology and histopathology in patients or animal models with a CI or for evaluating new models of electrode arrays. A large animal model with cochlea characteristics similar to those of humans may provide a research and evaluation platform for advanced and modified arrays before their use in humans.
To this end, we established standard CI methods with Bama mini-pigs, whose inner ear anatomy is highly similar to that of humans. Arrays designed for human use were implanted into the mini pig cochlea through a round window membrane, and a surgical approach followed that was similar to that used for human CI recipients. Array insertion was followed by evoked compound action potential (ECAP) measurements to evaluate the function of the auditory nerve. This study describes the preparation of the animal, surgical steps, array insertion, and intraoperative electrophysiological measurements.
The results indicated that the same CI used for humans could be easily implanted in mini-pigs via a standardized surgical approach and yielded similar electrophysiological outcomes as measured in human CI recipients. Mini-pigs could be a valuable animal model to provide initial evidence of the safety and potential performance of novel electrode arrays and surgical approaches before applying them to human beings.
According to the World Health Organization (WHO), over 1 billion people are at risk of hearing loss globally, and it is estimated that, by 2050, one out of four people will suffer hearing loss1. Over the last 2 decades, CIs have been the most effective intervention for people with permanent severe and profound sensorineural hearing loss (SNHL). A CI converts physical signals of sound into bioelectrical signals that stimulate the spiral ganglion neurons (SGNs), bypassing hair cells. Over time, the indications for a CI have been broadened so that they now include people with residual hearing, unilateral hearing loss, and very old or young people2,3,4. Meanwhile, totally implantable CIs and advanced arrays have been developed5. There is, however, no economically feasible large animal model for investigating the electrophysiology and histopathology of the inner ear with a CI. This lack of a large animal model limits research seeking to improve CIs and gain insights into the electrophysiological impact of CIs on the inner ear.
Several rodent animal models have been applied in CI research, such as mouse6, gerbil7, rat8, and guinea pig9; however, the characteristics of morphology and electrophysiological responses are different from that in humans. Cochlear structures of animal models traditionally used for CI studies, such as cats, guinea pigs, and other animals, differ greatly from those of human cochlear structures10. Although array insertion has been conducted on cats11 and rabbits12, because of their smaller cochleae, this was done with arrays that were not designed for use in humans. Several large animal models have also been explored for CI. Lambs are well suited as a training model for atraumatic cochlear implantation, but the smaller size of the cochlea makes full array insertion impossible13. Primates might be the most suitable animals for CI research because of their anatomical similarity to humans14,15; however, the sexual maturity of monkeys is delayed (4-5 years), the gestation period is up to about 165 days, and each female usually produces only one offspring per year16. These reasons, and the expensive cost, hinder the extensive application of primates in CI research.
In contrast, pigs reach sexual maturity at 5-8 months and have a gestation period of ~114 days, making pigs more accessible for CI research as a large animal model16. Bama mini pigs (mini-pigs) originated from a small-sized pig species in China in 1985, whose genetic background is well understood. They are characterized by an inherent small size, early sexual maturity, rapid breeding, and ease of management17. The mini-pig is an ideal model for otology and audiology because of its similarity to humans in morphology and electrophysiology18. The scala tympani length of a Bama mini-pig is 38.58 mm, which is close to the 36 mm length in humans10. The mini-pig cochlea has 3.5 turns, which is similar to the 2.5-3 turns seen in humans10. In addition to morphology, the electrophysiology of Bama mini-pigs is also highly similar to that of humans18. Therefore, in the present study, we inserted arrays designed for human use into the mini-pig cochlea via the round window membrane and followed a similar surgical approach to that used in human CI recipients. Intraoperative ECAP measurements were applied to evaluate the procedure. The process we describe herein could be used both for preclinical translational research associated with CIs and as a platform for resident training.
All procedures and animal surgeries were conducted according to the guidelines of the Ethics Committee of the PLA General Hospital and were approved.
1. Anesthesia and surgical preparation
2. Surgical procedure
3. Postoperative care
4. Postoperative CT scan
The integrity (Figure 4A) and impedances (Figure 4B) of the CI were confirmed by MAESTRO Software. ECAP results showed that all 12 electrodes demonstrated good neural responses (Figure 4C), meaning the electrode array was well attached to the cochlear axis and stimulated the auditory nerve. Figure 5 demonstrates postoperative 3D reconstructed electrode coils in the right cochlea. The array did not ...
Around 15% of the world's population have some degree of hearing loss, and over 5% have disabling hearing loss21. CI provision is the most efficient treatment for both adult and pediatric patients with severe and profound sensorineural hearing loss. As the first successful implantable cranial nerve stimulator, over the past 2 decades, CIs have offered thousands of people with hearing loss the opportunity to return to the world of sound and (re)integrate into mainstream society. Even though CIs are...
The authors declare that they have no conflicts of interest.
This study was funded by grants from the National Natural Science Foundation of China (Nos. 81970890) and the Chongqing Scientific Research Institution Performance incentive project (Nos. 19540). We thank Anandhan Dhanasingh and Zhi Shu from the MED-EL company for their support.
Name | Company | Catalog Number | Comments |
0.5 mm diamond burr | |||
1 mm diamond burr | |||
5 mm diamond burr | |||
2-0 suture silk | |||
3D Slicer image computing platform | 3D reconstruction of CT image | ||
Alcohol | |||
Bipolar cautery | |||
Bipolar electrocoagulation | Stop bleeding | ||
CI designed for human use (CONCERTO FLEX28) | MED-EL | Concerto F28 | |
Dressing forceps | |||
ECG monitor | |||
Iodine tincture | |||
Isoflurane | 3.6 mL/h | ||
Laryngoscope | |||
MAESTRO Software | MED-EL | Measure ECAP responses | |
Micro forceps | |||
Micro spatula | |||
Mosquito forceps | |||
Needle holder | |||
Needle probe | |||
Negative pressure suction device | |||
Otological surgical instruments | |||
Respiratory Anesthesia Machine | |||
Scalpel with blade No. 15 | |||
Scissors | |||
Shaver | |||
Stimulation device (MAX Programming Interface) | MED-EL | Measure ECAP responses | |
Surgery microscope | Leica | ||
Surgical drill | |||
Surgical Power Device | |||
Tiletamine and zolazepan | 10-15 mg/kg | ||
Tissue forceps | |||
Trachea cannula |
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