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Piezoelectric ultrasonic-assisted precision machining (PUAPM) technology is considered to be an efficient and environmentally friendly machining strategy by virtue of cutting force reduction, ductile cutting promotion, tool wear and machining noise reduction. Piezoelectric ultrasonic transducer (PUT) provides ultrasonic energy for PUAPM system, which is the core component to ensure the normal operation of the system. PUTs for PUAPM devices have emerged endlessly in recent decades and have been successfully applied in many fields, such as MEMS, biomedicine, optoelectronics, aerospace, etc. However, there is no comprehensive classification and analysis of the basic configurations, excitation principles, typical structures, performance analyses and control strategies for PUT. This work gives a critical review of research on PUT in recent years, especially the structural optimization, application expansion and ultrasonic energy stabilization in PUAPM. The influence mechanism of excitation mode, modal type, modal combination, horn structure and ceramic arrangement on the optimization of PUT structure is summarized. The improvement effect and mechanism of PUT vibration dimension, amplitude, frequency and structural characteristics on surface roughness, surface texture and cutting force are discussed. In addition, the causes of PUT amplitude fluctuation, and the influence of sensing and control methods on PUT amplitude regulation and system integration are analyzed. This review will help in understanding the current development and diversified applications of PUT and will promote the application of ultrasonic technology in more fields., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Macrophages play crucial roles in host tissue reaction to biomaterials upon implantation in vivo. However, the complexity of biomaterial degradation-related macrophage subpopulations that accumulate around the implanted biomaterials in situ is not fully understood. Here, using single cell RNA-seq, we analyze the transcriptome profiles of the various cell types around the scaffold to map the scaffold-induced reaction, in an unbiased approach. This enables mapping of all biomaterial degradation-associated cells at high resolution, revealing distinct subpopulations of tissue-resident macrophages as the major cellular sources of biomaterial degradation in situ. We also find that scaffold architecture can affect the mechanotransduction and catabolic activity of specific material degradation-related macrophage subpopulations in an Itgav-Mapk1-Stat3 dependent manner, eventually leading to differences in scaffold degradation rate in vivo. Our work dissects unanticipated aspects of the cellular and molecular basis of biomaterial degradation at the single-cell level, and provides a conceptual framework for developing functional tissue engineering scaffolds in future., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Ultrasonic welding (USW) has been receiving more and more attentions in material joining field due to its advantages of cleanness and high efficiency. The knurl tooth angle (KTA), as a key factor of horn knurl geometry (HKG), has significant influences on the contact and friction behavior of the joint formation. Although there have been some researches on the simulation of ultrasonic welding, the 3D finite element (FE) model considering the influence of KTA has not been reported. In this study, the FE models of different KTAs are established to reveal the effects of KTA on joint formation. The simulation result shows that the KTA greatly influences the process parameters of the USW after 0.025 s. The gaps of the faying interface and local stress concentration in the sonotrode-workpiece contact area, caused by KTAs less than 120°, are the main reasons for the strength reduction of the joint. The higher average equivalent plastic strain and temperature of the welding area, formed by KTAs greater than 130°, are turned out to be the main reasons for the formation of more bonds. The simulation has been verified by experiments, and the results provide guidance to improve the quality of the joint., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The temperature characteristics of a T-shaped linear ultrasonic motor using longitudinal vibration transducers are reported. When the ultrasonic motor is excited by different voltages, the surface temperatures at the driving foot, PZT ceramic and end cap are tested by a thermal imager for obtaining the thermal characteristics of the motor under no-load condition. PZT ceramic shows the maximum temperature increase. Then, the variations of resonant frequencies, electromechanical coupling factors and mechanical Q-factors versus time, as well as the effect of the temperature on the resonance frequencies, electromechanical coupling factors and mechanical Q-factors, is measured and analysed under the long-term running. It is found that all the resonance frequencies and electromechanical coupling factors decrease as the increase of the temperature, as well as the mechanical Q-factors. In addition, the change of the output speed over temperature is tested and the obtained result shows the trend of decline. This work can provide useful guidelines for the design and optimization of linear ultrasonic motor operating in wide temperature range., (Copyright © 2019 Elsevier B.V. All rights reserved.)

This work presents a general optimum frequency tracking scheme for an ultrasonic motor, which no longer requires the amplitudes of the applied voltages to keep identical. The proposed scheme here greatly extends the application of the optimum frequency in comparison to the existing studies. The mechanical quality factor of an ultrasonic motor is initially derived to describe the loss, which further is also in proportion to the temperature rise. The optimum frequency from the loss reduction viewpoint is then obtained, at which frequency the ultrasonic motor maintains the minimum loss and subsequently the minimum temperature rise. The optimum-frequency tracking scheme is subsequently constructed. Experiments are carried out to verify the existence of the optimum frequency and the reduction of the temperature-rise under the applied voltages in the general form, whose amplitudes and phase difference are all adjustable. The results have inferred that the optimum frequency still exists even though the applied voltages are in the general form, at which frequency the temperature-rise is obviously reduced in the absence of any external cooling equipment. The optimum frequency of the ultrasonic motor now gets closer to the industrial applications, especially when the applications require the velocity adjustment in a wide range., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A bi-directional standing wave linear piezoelectric ultrasonic actuator with four driving feet is proposed in this work. Two sandwich type transducers operated in longitudinal-bending hybrid modes are set parallelly. The working mode of the transducer is not simple hybrid vibrations of a longitudinal one and a bending one, but a special coupling vibration mode contained both longitudinal and bending components. Two transducers with the same structure and unsymmetrical boundary conditions are set parallelly to accomplish the bi-directional driving: the first transducer can push the runner forward, while the other one produces the backward driving. In the experiments, two voltages with different amplitudes are applied on the two transducers, respectively: the one with higher voltage serves as the actuator, whereas the other one applied with lower voltage is used to reduce the frictional force. The prototype achieves maximum no-load speed and thrust force of 244 mm/s and 9.8 N. This work gives a new idea for the construction of standing wave piezoelectric ultrasonic actuator with bi-directional driving ability., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A new type of multiple-degree-of-freedom (multi-DOF) ultrasonic motor was developed aiming at high output torque and compact structure. To reach this purpose, a ring type composite stator was proposed with four driving feet uniformly arranged in the inner circumference of the ring stator. The stator employs two orthogonal axial bending modes and a radial bending mode, by exciting two of them simultaneously, to generate elliptic trajectories on driving feet tips and to push sphere rotor around x, y and z axis respectively. Based on the deduced criteria, a specific combination of the A(0,5) axial bending modes and R(0,2) radial bending mode were chosen to realize that the rotating directions of the elliptical driving trajectories on four feet tips can push the sphere rotor to spin in the same direction consistently, thus the efficiency and output performance will be improved by decreasing the slip between feet and rotor. FEM was used to design the motor including selecting key parameters to tune the resonant frequencies by sensitivity analysis, and a prototype was fabricated and tested. The experiment results showed that the maximum output torque of the motor is 0.118Nm and the maximum speed is 55r/min., (Copyright © 2017 Elsevier B.V. All rights reserved.)

This paper presents a new-type linear ultrasonic motor which takes advantage of the combination of two orthogonal bending vibration modes. The proposed ultrasonic motor consists of eight pieces of PZT ceramic plates and a metal beam that includes two cone-shaped horns and a cylindrical driving foot. The finite element analyses were finished to verify the working principle of the proposed motor. The mode shapes of the motor were obtained by modal analysis; the elliptical trajectories of nodes on the driving foot were obtained by time-domain analysis. Based on the analyses, a prototype of the proposed motor was fabricated and measured. The mechanical output characteristics were obtained by experiments. The maximal velocity of the proposed motor is 735mm/s and the maximal thrust is 1.1N., (Copyright © 2016 Elsevier B.V. All rights reserved.)

An electromechanical coupling model of a bending vibration type piezoelectric ultrasonic transducer is proposed. The transducer is a Langevin type transducer which is composed of an exponential horn, four groups of PZT ceramics and a back beam. The exponential horn can focus the vibration energy, and can enlarge vibration amplitude and velocity efficiently. A bending vibration model of the transducer is first constructed, and subsequently an electromechanical coupling model is constructed based on the vibration model. In order to obtain the most suitable excitation position of the PZT ceramics, the effective electromechanical coupling coefficient is optimized by means of the quadratic interpolation method. When the effective electromechanical coupling coefficient reaches the peak value of 42.59%, the optimal excitation position (L1=22.52 mm) is found. The FEM method and the experimental method are used to validate the developed analytical model. Two groups of the FEM model (the Group A center bolt is not considered, and but the Group B center bolt is considered) are constructed and separately compared with the analytical model and the experimental model. Four prototype transducers around the peak value are fabricated and tested to validate the analytical model. A scanning laser Doppler vibrometer is employed to test the bending vibration shape and resonance frequency. Finally, the electromechanical coupling coefficient is tested indirectly through an impedance analyzer. Comparisons of the analytical results, FEM results and experiment results are presented, and the results show good agreement., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A cylindrical traveling wave ultrasonic motor using bonded-type composite beam is proposed in this work. In this new design, a new exciting mode for L-B (longitudinal-bending) hybrid vibrations using bonded-type is adopted, which requires only two pieces of PZT ceramic plates and a single metal beam. In the new motor, the traveling wave of a cylinder can be excited by the L-B vibrations of a bonded-type beam. When two alternating voltages with phase difference are applied, the longitudinal and bending vibrations of the beam can be generated synchronously based on the new exciting mode for L-B hybrid vibrations, and the temporal phase difference of the two vibrations is always 90°. Finite element method is adopted to realize the modal degeneration in order to confirm the final structural parameters of the motor, and analyze the motion trajectory of the driving tip. After the fabrication of a prototype, the vibration characteristics and mechanical output ability are measured. The maximum no-load speed and maximum output torque of the prototype are 342 rpm and 6.26 mN m at a voltage of 100 Vrms., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A new T-shape piezoelectric motor using the hybrid of two orthogonal longitudinal vibrations is proposed in this work. Six pieces of PZT ceramic plates are bonded on the upside and downside surfaces of a T-shape duralumin alloy base respectively to form the proposed motor. Elliptical movement can be generated on the driving tip by applying sine and cosine voltages to the PZT elements. The horizontal displacement of the driving tip will push the runner while the vertical displacement can overcome the preload. Finite element method is used to accomplish the design and analysis process. The resonance frequencies of the two vibration modes are tuned to be close by modal analysis, while the motion trajectory of the driving tip is observed by transient analysis. After the fabrication of a prototype, the vibration characteristics and mechanical output ability are measured. The no-load speed and the maximum output thrust force of the proposed motor are tested to be 718 mm/s and 3.5 N under an exciting frequency of 53.1 kHz. The proposed T-shape piezoelectric motor exhibits merits of simple structure, easy to realize miniaturization, easy to be fabricated, and high power-to-weight ratio., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Anterior cruciate ligament (ACL) is difficult to heal after injury due to the dynamic fluid environment of joint. Previously, we have achieved satisfactory regeneration of subcutaneous tendon/ligament with knitted silk-collagen sponge scaffold due to its specific "internal-space-preservation" property. This study aims to investigate the long-term effects of knitted silk-collagen sponge scaffold on ACL regeneration and osteoarthritis prevention. The knitted silk-collagen sponge scaffold was fabricated and implanted into a rabbit ACL injury model. The knitted silk-collagen sponge scaffold was found to enhance migration and adhesion of spindle-shaped cells into the scaffold at 2 months post-surgery. After 6 months, ACL treated with the knitted silk-collagen sponge scaffold exhibited increased expression of ligament genes and better microstructural morphology. After 18 months, the knitted silk-collagen sponge scaffold-treated group had more mature ligament structure and direct ligament-to-bone healing. Implanted knitted silk-collagen sponge scaffolds degraded much more slowly compared to subcutaneous implantation. Furthermore, the knitted silk-collagen sponge scaffold effectively protected joint surface cartilage and preserved joint space for up to 18 months post-surgery. These findings thus demonstrated that the knitted silk-collagen sponge scaffold can regenerate functional ACL and prevent osteoarthritis in the long-term, suggesting its clinical use as a functional bioscaffold for ACL reconstruction., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A cylindrical standing wave ultrasonic motor using bending vibration transducer was proposed in this paper. The proposed stator contains a cylinder and a bending vibration transducer. The two combining sites between the cylinder and the transducer locate at the adjacent wave loops of bending vibration of the transducer and have a distance that equal to the half wave length of bending standing wave excited in the cylinder. Thus, the bending mode of the cylinder can be excited by the bending vibration of the transducer. Two circular cone type rotors are pressed in contact to the end rims of the teeth, and the preload between the rotors and stator is accomplished by a spring and nut system. The working principle of the proposed motor was analyzed. The motion trajectories of teeth were deduced. The stator was designed and analyzed with FEM. A prototype motor was fabricated and measured. Typical output of the prototype is no-load speed of 165rpm and maximum torque of 0.45Nm at an exciting voltage of 200V(rms)., (Copyright © 2010 Elsevier B.V. All rights reserved.)

This study developed a bioactive knitted silk-collagen sponge scaffold by incorporation of exogenous SDF-1 alpha, to enable selective migration and homing of cells for in situ tendon regeneration. With in vitro studies, it was observed that CXCR4 gene expression and migration of bone mesenchymal stromal cells and hypo-dermal fibroblasts were more sensitive to exogenous SDF-1 alpha, while expression of tendon repair gene markers by hypo-dermal fibroblasts and Achilles tendon fibroblasts were more sensitive to exogenous SDF-1 alpha. With a rat Achilles tendon injury model, exogenous SDF-1 alpha was shown to reduce infiltration of inflammatory cells and enhance migration of fibroblast-like cells into the scaffold at 4 days and 1 week post-surgery. After 4 weeks, SDF-1 alpha treated tendon had increased expression of tendon repair gene markers and endogenous SDF-1 alpha, exhibited more physiological microstructures with larger diameter collagen fibrils, and had better biomechanical properties than the control group. Hence, our bioactive scaffold improved efficacy of tendon regeneration by increasing the recruitment of fibroblast-like cells, enhancing local endogenous SDF-1 alpha and tendon extracellular matrix production, and decreasing accumulation of inflammatory cells. Incorporation of SDF-1 alpha within a knitted silk-collagen sponge scaffold can therefore be a practical application for tendon tissue engineering.

This paper deals with the control of a transducer to realize low speed. A new PWM control is proposed to fit the transducer. By this control method, the transducer is directly excited by pulses whose width can be modulated. The noise induced by conventional PWM control is eliminated and the motor works more steadily and more quietly. Instead of the general method of decreasing vibrating amplitude of ultrasonic motor to realize low speed, in this paper, two fast contrary elliptical vibrations of the transducer's two Langevin vibrators are excited to restrain skip-slip influence on ultrasonic motor's low speed performance and the driven is realized by the difference of the two vibrators' vibrating amplitudes. Experiments had been carried out by driving an aerostatic guide and fuzzy control is applied. The controlled speed reached 0.1 mm/s.