Gepu Guo

Ultrasound-assisted permeability improvement and acoustic characterization for solid-state fabricated PLA foams.

In the present study, power ultrasound is applied to improve the permeability of the solid-state fabricated PLA foams with different cell sizes. It is experimentally proved that cell interconnection and the permeability is improved with the increasing of power ultrasound radiation intensity. Furthermore, an insert-substitution testing approach is put forward to perform acoustic measurement and property characterization for the PLA foams before and after ultrasound radiation. The experimental results indicate that the attenuation coefficient of the close-celled PLA foams decreases exponentially with respect to the saturation pressure and it shows linear behavior with respect to the ultrasound radiation intensity. The favorable results suggest the feasibility of the proposed technologies of ultrasound-assisted permeability improvement and acoustic characterization for the application of the solid-state foamed PLA foams in tissue engineering.

Investigation on the thermo-mechanical properties and thermal stability of polylactic acid tissue engineering scaffold material

Thermogravimetric analysis and dynamic mechanical analysis were combined with scanning electron microscopy to analyze the thermo-mechanical properties and thermal stability of polylactic acid (PLA) foams fabricated using a solvent-free solid-state gas foaming method. The dependence of decomposition time and the lifetime on the PLA cell size was evaluated based on the thermal decomposition kinetic analyses. The results show that PLA specimens with larger cell sizes can be made at lower saturation gas pressures, which will ensure that the fabricated PLA foams have a shorter decomposition time, better flexibility, and are more satisfactory for medical requirements of tissue engineering scaffold (TES) material. The current work may help to optimize the PLA foaming parameters and precisely design PLA foams with different decomposition times according to specific TES requirements of different organ structures.

Near-field multiple traps of paraxial acoustic vortices with strengthened gradient force generated by sector transducer array

In order to improve the capability of particle trapping close to the source plane, theoretical and experimental studies on near-field multiple traps of paraxial acoustic vortices (AVs) with a strengthened acoustic gradient force (AGF) generated by a sector transducer array were conducted. By applying the integration of point source radiation, numerical simulations for the acoustic fields generated by the sector transducer array were conducted and compared with those produced by the circular transducer array. It was proved that strengthened AGFs of near-field multiple AVs with higher peak pressures and smaller vortex radii could be produced by the sector transducer array with a small topological charge. The axial distributions of the equivalent potential gradient indicated that the AGFs of paraxial AVs in the near field were much higher than those in the far field, and the distances at the near-field vortex antinodes were also proved to be the ideal trapping positions with relatively higher AGFs. With the ...

Magneto-acousto-electrical Measurement Based Electrical Conductivity Reconstruction for Tissues

Objective: Based on the interaction of ultrasonic excitation and magnetoelectrical induction, magneto-acousto-electrical (MAE) technology was demonstrated to have the capability of differentiating conductivity variations along the acoustic transmission. By applying the characteristics of the MAE voltage, a simplified algorithm of MAE measurement based conductivity reconstruction was developed. Methods: With the analyses of acoustic vibration, ultrasound propagation, Hall effect, and magnetoelectrical induction, theoretical and experimental studies of MAE measurement and conductivity reconstruction were performed. The formula of MAE voltage was derived and simplified for the transducer with strong directivity. MAE voltage was simulated for a three-layer gel phantom and the conductivity distribution was reconstructed using the modified Wiener inverse filter and Hilbert transform, which was also verified by experimental measurements. Results: The experimental results are basically consistent with the simulations, and demonstrate that the wave packets of MAE voltage are generated at tissue interfaces with the amplitudes and vibration polarities representing the values and directions of conductivity variations. With the proposed algorithm, the amplitude and polarity of conductivity gradient can be restored and the conductivity distribution can also be reconstructed accurately. Conclusion: The favorable results demonstrate the feasibility of accurate conductivity reconstruction with improved spatial resolution using MAE measurement for tissues with conductivity variations, especially suitable for nondispersive tissues with abrupt conductivity changes. Significance: This study demonstrates that the MAE measurement based conductivity reconstruction algorithm can be applied as a new strategy for nondestructive real-time monitoring of conductivity variations in biomedical engineering.

Accurate acoustic power measurement for low-intensity focused ultrasound using focal axial vibration velocity

Low-intensity focused ultrasound is a form of therapy that can have reversible acoustothermal effects on biological tissue, depending on the exposure parameters. The acoustic power (AP) should be chosen with caution for the sake of safety. To recover the energy of counteracted radial vibrations at the focal point, an accurate AP measurement method using the focal axial vibration velocity (FAVV) is proposed in explicit formulae and is demonstrated experimentally using a laser vibrometer. The experimental APs for two transducers agree well with theoretical calculations and numerical simulations, showing that AP is proportional to the square of the FAVV, with a fixed power gain determined by the physical parameters of the transducers. The favorable results suggest that the FAVV can be used as a valuable parameter for non-contact AP measurement, providing a new strategy for accurate power control for low-intensity focused ultrasound in biomedical engineering.

Noninvasive treatment efficacy monitoring and dose control for high-intensity focused ultrasound therapy using relative electrical impedance variation

As an effective therapeutic modality, high-intensity focused ultrasound (HIFU) can destroy tumour tissues by thermocoagulation with less metastasis, but it is still limited by inaccurate non-invasive temperature monitoring and efficacy evaluation. A model of electrical impedance measurement during HIFU therapy was established using the temperature-impedance relationship. Based on the simulations of acoustic pressure, temperature, and electrical conductivity, the impedance of the phantom was calculated and experimentally demonstrated for different values of acoustic power values and treatment time. We proved that the relative impedance variation (RIV) increases linearly with the increasing treatment time at a fixed acoustic power, and the relative impedance variation rate shows a linear relationship with the acoustic power. The RIV and treatment time required for HIFU treatment efficacy are inversely proportional to the acoustic power and the square of acoustic power, respectively. The favourable results suggest that RIV can be used as an efficient indicator for noninvasive temperature monitoring and efficacy evaluation and may provide new strategy for accurate dose control of HIFU therapy.

Regulation of multiple off-axis acoustic vortices with a centered quasi-plane wave

In treating a circular point-source array using the phase-coded method, a composite acoustic field of multiple off-axis acoustic vortices (AVs) with a centered quasi-plane wave is proposed which is superimposed by an AV beam and a co-axial non-AV beam generated by the even- and odd-numbered source arrays, respectively. The acoustic pressure and the phase of the composite acoustic field are derived using explicit formulae and demonstrated by numerical simulations. Off-axis sub-AVs (SAVs) are shown to be formed at the intersections of the radial pressure distributions of the AV and non-AV beams for the same pressure amplitude and opposite phases. Off-axis SAVs can be generated on a circumference centered with a regular polygon of quasi-plane waves. The radii and azimuthal angles of the off-axis AVs and the radius of the centered quasi-plane wave are determined by the topological charge and the initial phase difference of the acoustic beams. With the established 16-source experimental system, the generation ...

Non-invasive treatment efficacy evaluation for high-intensity focused ultrasound therapy using magnetically induced magnetoacoustic measurement

Although the application of high intensity focused ultrasound (HIFU) has been demonstrated to be a non-invasive treatment technology for tumor therapy, the real-time temperature monitoring is still a key issue in the practical application. Based on the temperature-impedance relation, a fixed-point magnetically induced magnetoacoustic measurement technology of treatment efficacy evaluation for tissue thermocoagulation during HIFU therapy is developed with a sensitive indicator of critical temperature monitoring in this study. With the acoustic excitation of a focused transducer in the magnetoacoustic tomography with the magnetic induction system, the distributions of acoustic pressure, temperature, electrical conductivity, and acoustic source strength in the focal region are simulated, and the treatment time dependences of the peak amplitude and the corresponding amplitude derivative under various acoustic powers are also achieved. It is proved that the strength peak of acoustic sources is generated by tissue thermocoagulation with a sharp conductivity variation. The peak amplitude of the transducer collected magnetoacoustic signal increases accordingly along with the increase in the treatment time under a fixed acoustic power. When the temperature in the range with the radial and axial widths of about ±0.46 mm and ±2.2 mm reaches 69 °C, an obvious peak of the amplitude derivative can be achieved and used as a sensitive indicator of the critical status of treatment efficacy. The favorable results prove the feasibility of real-time non-invasive temperature monitoring and treatment efficacy evaluation for HIFU ablation using the magnetically induced magnetoacoustic measurement, and might provide a new strategy for accurate dose control during HIFU therapy.Although the application of high intensity focused ultrasound (HIFU) has been demonstrated to be a non-invasive treatment technology for tumor therapy, the real-time temperature monitoring is still a key issue in the practical application. Based on the temperature-impedance relation, a fixed-point magnetically induced magnetoacoustic measurement technology of treatment efficacy evaluation for tissue thermocoagulation during HIFU therapy is developed with a sensitive indicator of critical temperature monitoring in this study. With the acoustic excitation of a focused transducer in the magnetoacoustic tomography with the magnetic induction system, the distributions of acoustic pressure, temperature, electrical conductivity, and acoustic source strength in the focal region are simulated, and the treatment time dependences of the peak amplitude and the corresponding amplitude derivative under various acoustic powers are also achieved. It is proved that the strength peak of acoustic sources is generated by tis...

Acoustic radiation torque of an acoustic-vortex spanner exerted on axisymmetric objects

Based on the analysis of the wave vector of an acoustic-vortex (AV) spanner, the radiation torque of object rotation is investigated. It is demonstrated that the rotation of an axisymmetric disk centered on the AV spanner is mainly driven by the acoustic radiation force. The radiation torque exerted on a small-radius object is inversely associated with the topological charge in the center AV, and it is enhanced significantly for a larger AV with a higher topological charge. With the sixteen-source experimental setup, radius dependencies of radiation torque for AV spanners with different topological charges are verified by quantitative laser-displacement measurements using disks with different radii. The favorable results demonstrate that the radiation torque is more applicable than the orbital angular momentum in describing the driving capability of an AV spanner and can be used as an effective tool in clinical applications to manipulate objects with a feature size at the wavelength-scale inside body.

Enhanced chondrocytes growth in 3-D alginate scaffolds with improved porosity and permeability induced by low intensity pulse ultrasound

Recent development in applications of new biomaterials and biomedical engineering enable the tissue engineering to become a promising cartilage repair technique. Here, a 3-D alginate scaffold was fabricated by a cross-linked method. Experiments were performed to investigate how the porosity and permeability of the 3-D scaffold, as well as the proliferation rate of seeded cells, were affected by the ultrasound exposure parameters. The scanning electron microscopy and fluorescence imaging were used to examine the micro-structure, porosity, and permeability of the scaffolds, and biochemical analyses were applied to assess the cell growth in the scaffold. The optimum low intensity pulsed ultrasound (LIPU) driving parameters that benefit the enhancement of scaffold porosity and cell proliferation were also explored. The results suggest that, for the scaffold exposed to LIPU, its porosity and permeability could be significantly enhanced by the increasing LIPU amplitude, which might be induced by the microstream...