Deep, sub-wavelength acoustic patterning of complex and non-periodic shapes on soft membranes supported by air cavities.

Arbitrary patterning of micro-objects in liquid is crucial to many biomedical applications. Among conventional methodologies, acoustic approaches provide superior biocompatibility but are intrinsically limited to producing periodic patterns at low resolution due to the nature of standing waves and the coupling between fluid and structure vibrations. This work demonstrates a near-field acoustic platform capable of synthesizing high resolution, complex and non-periodic energy potential wells. A thin and viscoelastic membrane is utilized to modulate the acoustic wavefront on a deep, sub-wavelength scale by suppressing the structural vibration selectively on the platform. Using 3 MHz excitation (λ∼ 500 µm in water), we have experimentally validated such a concept by realizing patterning of microparticles and cells with a line resolution of 50 µm (one tenth of the wavelength). Furthermore, massively parallel patterning across a 3 × 3 mm2 area has been achieved. This new acoustic wavefront modulation mechanism is powerful for manufacturing complex biologic products.

A novel opto-electromagnetic actuator coupled to the tympanic membrane.

A new type of electromagnetic vibration transducer designed to be placed onto the tympanic membrane was developed. The actuator consisted of two photodiodes, two permanent magnets, an aluminum ring, two opposing wound coils, a latex membrane and a Provil Novo membrane. An optic probe was designed to allow sound and light signals to enter the ear canal, thereby preventing the acoustic occlusion effect of traditional ear molds. Two light-emitting diodes were used for carrying the input signals. The corresponding photodiodes were used for receiving the light signals and generating currents in the actuator. The opto-electromagnetic vibration actuator was fabricated and tested using a Laser Doppler vibrometer. The actuator showed displacements of vibration between 30 and 1 nm from 300 to 6500Hz and reduced in amplitude at higher frequencies. The average gain of the actuator with 140microA on the umbo displacement was about 20 dB relative to 87 dBA at the distance of 6cm from the tympanic membrane and 0microA in actuator.

Optimal graft thickness for different sizes of tympanic membrane perforation in cartilage myringoplasty: a finite element analysis.

OBJECTIVE: The purpose of this study was to determine, using finite element analysis, the optimal graft thickness for cartilage myringoplasty in patients with different sizes of tympanic membrane (TM) perforations. STUDY DESIGN: We developed a cartilage plate-TM-coupled model using high-resolution computed tomography and finite element analysis. The geometric models of the perforated TM were generated using Patran and ANSYS software. METHOD: Three different sizes of TM perforations (15%, 55%, and 85%, representing small, medium, and large perforations, respectively) were created in the pars tensa. A cartilage plate was used to repair the eardrum perforation, and the new TM-cartilage coupled complex was loaded into our three-dimensional biomechanical model for analysis. The frequency-amplitude responses for different cartilage thicknesses were compared with those for natural TM. RESULTS: Our results show that, first, in cases with 85% perforation, the frequency-amplitude responses that were most similar to natural TM at lower frequencies were for graft thicknesses of 0.2 mm and for 0.1 mm at higher frequencies. Second, in cases with 55% posterior perforation of the TM, assessment of the predicted vibration amplitude of different thicknesses of the cartilage plate showed that a cartilage plate of less than 0.2 mm had a frequency response function similar to that of a natural TM in umbo and stapes footplate displacement. Finally, for a central perforation involving 15% of the TM, a cartilage plate of less than 1.0 mm showed a frequency response function similar to that of TM in umbo and stapes-footplate displacement. CONCLUSIONS: On the basis of our biomechanical analysis, the optimal thickness of a cartilage graft for myringoplasty appears to be 0.1 to 0.2 mm for medium and large TM perforations. For small perforations, a cartilage of less than 1.0 mm is a good compromise between mechanical stability and low acoustic transfer loss.

Modeling sound transmission of human middle ear and its clinical applications using finite element analysis.

We have developed a new finite element (FE) model of human right ear, including the accurate geometry of middle ear ossicles, external ear canal, tympanic cavity, and mastoid cavity. The FE model would be suitable to study the dynamic behaviors of pathological middle ear conditions, including changes of stapedial ligament stiffness, tensor tympani ligament (TTL), and tympanic membrane (TM) stiffness and thickness. Increasing stiffness of stapedial ligament has substantial effect on stapes footplate movement, especially at low frequencies, but less effect on umbo movement. Softer TTL will result in increasing umbo and stapes footplate displacement, especially at low frequencies (f<1000Hz). When the TTL was detached, the vibration amplitude of umbo increased by 6dB at 600Hz and two peaks (300 and 600Hz) were found in the vibration amplitude of stapes footplate. Increasing the stiffness of tensor tympani resulted in a slightly decreased umbo amplitude at very low frequencies (f<500Hz) and significantly decreased displacement up to 12dB at middle frequencies (1000Hz1500Hz. As (TM) thickness was increased, the umbo displacement was reduced, especially at very low frequencies (f<600Hz). Otherwise, the stapes displacement was reduced at all frequencies.

A novel aerosol-mediated drug delivery system for inner ear therapy: intratympanic aerosol methylprednisolone can attenuate acoustic trauma.

We developed a novel aerosol-mediated drug delivery system for inner ear therapy by using a silicon-based multiple-Fourier horn nozzle. Intratympanic aerosol (ITA) methylprednisolone (MP) delivery can protect hearing after acoustic trauma. The highest concentration of MP (38.9 ± 5.47 ppm) appeared at 2 h and declined rapidly within 10 h. The concentrations of MP remained at a relatively low level for more than 10 h. Compared to the baseline, the auditory brainstem response (ABR) thresholds shifted markedly at 1 h after noise exposure in all groups (p < 0.05). From the cochleograms, it can be noted that the main lesions encompassed the 2-20 kHz frequency range. Significant differences ( ) were observed for the range between 5 and 8 kHz in the cell loss of outer hair cells (OHCs). The losses for IHCs were lower than for OHCs. The MP movement in the middle ear was simulated by a convection diffusion equation with a relaxation time. The relaxation time was 0.5 h, and the concentration threshold of MP on the round window membrane (RWM) in the middle ear (C T) was 8900 ppm. Using the unit hydrograph (UH) method, we obtained a proper boundary concentration on the RWM at the cochlea, which resulted in a well-fit concentration. Finally, a linking mechanism between the middle ear and the cochlea was established by the RWM. The adjustable permeability and concentration threshold provide the flexibility to match the peak times and peak values of the concentration on the RWM in the middle ear and the cochlea.

Novel device to measure critical point "Onset" of capillary wave and interpretation of Faraday instability wave by numerical analysis.

A capillary wave was created on a surface by vibrating from the bottom of a container. When the amplitude of the container vibration approached the critical point, called the onset state, the surface broke up and bursted into very small drops on the air. The numerical analysis was used to determine the amplitude of the onset. The onset point was found to be 0.349µm at f=500kHz. The critical amplitude h(cr) was determined by using a multi-Fourier horn nozzle (MFHN) device. The onset point was measured to be 0.37µm using a laser Doppler vibrometer (LDV) with the MFHN at f=486kHz. These drops indicate that particle size distributions of 10.8µm and 7.0µm were produced by the MFHN at f=289kHz and f=486kHz, respectively. These results agreed with those obtained using Kelvin's equation, which predicted D=0.34λ.

Registration of micro-computed tomography and histological images of the guinea pig cochlea to construct an ear model using an iterative closest point algorithm.

We present a practical and systematic method to reconstruct accurate physical models of the guinea pig ear (n = 1). The method uses a semi-automatic technique to create three-dimensional (3-D) models of the guinea pig cochlea by registration of micro-computed tomography (CT) and histological images. An iterative closest point algorithm was employed to minimize the sum of square errors with respect to the closest histological model and corresponding micro-CT model. This allowed creation of an accurate geometric ear model including external ear canal, tympanic membrane, middle ear cavity, auditory ossicles, and the cochlea. The characteristic cross-sectional areas of scala tympani, scala vestibuli, and scala media were measured. The length, thickness, and apex width of the guinea pig's basilar membrane were compared to the data found in literature. Some shape parameters were also compared among different species. The results confirmed that the geometric model created by this method was accurate. This method provides an effective way to visualize the 3-D structure and the detailed information about ear geometry required for finite element and multibody dynamic analysis.

Biomechanical modeling and design optimization of cartilage myringoplasty using finite element analysis.

The purpose of this study was to determine the acoustic transfer characteristics of cartilage for optimal cartilage myringoplasty. In order to do so, we developed a cartilage plate/tympanic membrane-coupled model using finite element analysis. Cartilage specimens of the tragus were obtained from fresh human cadavers, and the parameters of the tragus were determined by curve fitting and cross-calibration. A cartilage plate was used to repair an eardrum perforation, and the new coupled tympanic membrane-cartilage complex was loaded into our 3-dimensional biomechanical model of the middle ear for analysis. Our results show that first the beta-damping value of the cartilage plate depends on frequency. The value of beta damping was close to 3 x 10(-4) s at lower frequencies and 5 x 10(-6) s at higher frequencies. Secondly, reducing cartilage thickness leads to an improvement of its acoustic transfer qualities. From an acoustics point of view, the 0.1- to 0.2-mm cartilage plate seems to be most preferable with regard to tympanic membrane vibration. Furthermore, thicknesses of 0.2 mm at lower frequencies and 0.1 mm at higher frequencies were regarded as good compromises between sufficient mechanical stability and low acoustic transfer loss.