Flexible and stretchable biosensors have the advantage of enhanced signal validity and patient comfort during physiological signal sensing and biomolecular analysis, crucial for disease diagnosis, treatment and health management. Their lightness, softness and excellent mechanical properties enable effective skin-device interface coupling and skin safety profiles, realizing multi-functional, intelligent real-time sensing. In this review, the basic sensing principles of biosensor systems and their applications are discussed. Moreover, the potential applications and prospective progress of these biosensors are further prospected. Flexible, wearable biosensors have the potential to realize continuous and long-term health monitoring in clinical and daily health care.@en

Modern advanced minimally invasive surgery has been implemented for most of the significant gastrointestinal diseases. However, patients with coagulopathy or unresectable tumors cannot be cured by current treatment methods. Moreover, other existing medical devices for targeted drug release are too large to be applied in gastric endoscope because the diameter of the biopsy channel is smaller than 3 mm. To address it, in this work, we developed a piezoelectric single crystal ultrasonic transducer (the diameter was only 2.2 mm and the mass was 0.076 g) to produce acoustic waves, which could promote the drug release in the designed position of the digestive tract through an endoscope. It exhibited the electromechanical coupling coefficient of 0.36 and the center frequency of 6.9 MHz with the -6-dB bandwidth of 23%. In in vitro sonophoresis experiment, the gastric mucosa permeability to Bovine Serum Albumin increased about 5.6 times when the ultrasonic transducer was activated at 40 ext{V} {{ ext {pp}}} and 60% duty ratio, proving that employment of this transducer could facilitate drug penetration in the gastric mucosa. Meanwhile, the permeability could be adjusted by tuning the duty ratio of the ultrasonic transducer. The corresponding sonophoresis mechanism was related to the acoustic streaming and the thermal effect produced by the transducer. In addition, the measured maximum power density was 128 mW/cm2 and the mechanical index of the ultrasonic transducer was 0.02. The results held a great implication for applications of the transducer for targeted drug release in the gastrointestinal tract. @en

Modern advanced minimally invasive surgery has been implemented for most of the significant gastrointestinal diseases. However, patients with coagulopathy or unresectable tumors cannot be cured by current treatment methods. Moreover, other existing medical devices for targeted drug release are too large to be applied in gastric endoscope because the diameter of the biopsy channel is smaller than 3 mm. To address it, in this work, we developed a piezoelectric single crystal ultrasonic transducer (the diameter was only 2.2 mm and the mass was 0.076 g) to produce acoustic waves, which could promote the drug release in the designed position of the digestive tract through an endoscope. It exhibited the electromechanical coupling coefficient of 0.36 and the center frequency of 6.9 MHz with the -6-dB bandwidth of 23%. In in vitro sonophoresis experiment, the gastric mucosa permeability to Bovine Serum Albumin increased about 5.6 times when the ultrasonic transducer was activated at 40 ext{V} {{ ext {pp}}} and 60% duty ratio, proving that employment of this transducer could facilitate drug penetration in the gastric mucosa. Meanwhile, the permeability could be adjusted by tuning the duty ratio of the ultrasonic transducer. The corresponding sonophoresis mechanism was related to the acoustic streaming and the thermal effect produced by the transducer. In addition, the measured maximum power density was 128 mW/cm2 and the mechanical index of the ultrasonic transducer was 0.02. The results held a great implication for applications of the transducer for targeted drug release in the gastrointestinal tract. @en

Introduction: Over the decades, tendon adhesion has become a major health problem threatening the rehabilitation of patients after tendon surgery. Injury of the flexor tendon leads to rupture of the synovial sheath, which causes tendon exposure and adhesion with subcutaneous tissue. Current conservative therapies can promote chronic healing of tendon adhesion but have mixed success rates. Objectives: To reduce the degree of tendon adhesion, the need for a new non-invasive and accurate treatment method is substantial. Methods: A concave spherical ultrasonic phased array was fabricated by a fast 3D printing method. We generated a set of delayed square wave pulse sequences by Field Programmable Gate Arrays (FPGA) to excite the ultrasonic array, creating an ultrasonic focal area. Then we put flexor tendon phantoms, which were constructed by chitosan hydrogel and fibrous membrane using electrospinning, into the preset focal region and injected nano drugs in them. Finally, we measured the pulling force of tendon phantoms with a tensile tester. Results: The pulling force of three experimental groups were measured by a tensile tester. Compared to the “untreated group” (0.96 N), the phantom pulling force of the “ultrasound + drug group” is 0.15 N, which is reduced by 85%. Furthermore, with the driving voltage increased from 5 V to 20 V, the pulling force can be reduced by 60%; with the duty ratio increased from 20% to 60%, the pulling force can be reduced by 50%; with treatment time increased from 1 min to 5 min, the pulling force can be reduced by 64%. Conclusion: Utilizing an ultrasonic array combined with nano drugs, our phase compensation control method can reduce the degree of tendon adhesion and hold a great implication for applications of rehabilitation treatment for postoperative patients.@en

Introduction: Over the decades, tendon adhesion has become a major health problem threatening the rehabilitation of patients after tendon surgery. Injury of the flexor tendon leads to rupture of the synovial sheath, which causes tendon exposure and adhesion with subcutaneous tissue. Current conservative therapies can promote chronic healing of tendon adhesion but have mixed success rates. Objectives: To reduce the degree of tendon adhesion, the need for a new non-invasive and accurate treatment method is substantial. Methods: A concave spherical ultrasonic phased array was fabricated by a fast 3D printing method. We generated a set of delayed square wave pulse sequences by Field Programmable Gate Arrays (FPGA) to excite the ultrasonic array, creating an ultrasonic focal area. Then we put flexor tendon phantoms, which were constructed by chitosan hydrogel and fibrous membrane using electrospinning, into the preset focal region and injected nano drugs in them. Finally, we measured the pulling force of tendon phantoms with a tensile tester. Results: The pulling force of three experimental groups were measured by a tensile tester. Compared to the “untreated group” (0.96 N), the phantom pulling force of the “ultrasound + drug group” is 0.15 N, which is reduced by 85%. Furthermore, with the driving voltage increased from 5 V to 20 V, the pulling force can be reduced by 60%; with the duty ratio increased from 20% to 60%, the pulling force can be reduced by 50%; with treatment time increased from 1 min to 5 min, the pulling force can be reduced by 64%. Conclusion: Utilizing an ultrasonic array combined with nano drugs, our phase compensation control method can reduce the degree of tendon adhesion and hold a great implication for applications of rehabilitation treatment for postoperative patients.@en

Introduction: Over the decades, tendon adhesion has become a major health problem threatening the rehabilitation of patients after tendon surgery. Injury of the flexor tendon leads to rupture of the synovial sheath, which causes tendon exposure and adhesion with subcutaneous tissue. Current conservative therapies can promote chronic healing of tendon adhesion but have mixed success rates. Objectives: To reduce the degree of tendon adhesion, the need for a new non-invasive and accurate treatment method is substantial. Methods: A concave spherical ultrasonic phased array was fabricated by a fast 3D printing method. We generated a set of delayed square wave pulse sequences by Field Programmable Gate Arrays (FPGA) to excite the ultrasonic array, creating an ultrasonic focal area. Then we put flexor tendon phantoms, which were constructed by chitosan hydrogel and fibrous membrane using electrospinning, into the preset focal region and injected nano drugs in them. Finally, we measured the pulling force of tendon phantoms with a tensile tester. Results: The pulling force of three experimental groups were measured by a tensile tester. Compared to the “untreated group” (0.96 N), the phantom pulling force of the “ultrasound + drug group” is 0.15 N, which is reduced by 85%. Furthermore, with the driving voltage increased from 5 V to 20 V, the pulling force can be reduced by 60%; with the duty ratio increased from 20% to 60%, the pulling force can be reduced by 50%; with treatment time increased from 1 min to 5 min, the pulling force can be reduced by 64%. Conclusion: Utilizing an ultrasonic array combined with nano drugs, our phase compensation control method can reduce the degree of tendon adhesion and hold a great implication for applications of rehabilitation treatment for postoperative patients.@en

Introduction: Over the decades, tendon adhesion has become a major health problem threatening the rehabilitation of patients after tendon surgery. Injury of the flexor tendon leads to rupture of the synovial sheath, which causes tendon exposure and adhesion with subcutaneous tissue. Current conservative therapies can promote chronic healing of tendon adhesion but have mixed success rates. Objectives: To reduce the degree of tendon adhesion, the need for a new non-invasive and accurate treatment method is substantial. Methods: A concave spherical ultrasonic phased array was fabricated by a fast 3D printing method. We generated a set of delayed square wave pulse sequences by Field Programmable Gate Arrays (FPGA) to excite the ultrasonic array, creating an ultrasonic focal area. Then we put flexor tendon phantoms, which were constructed by chitosan hydrogel and fibrous membrane using electrospinning, into the preset focal region and injected nano drugs in them. Finally, we measured the pulling force of tendon phantoms with a tensile tester. Results: The pulling force of three experimental groups were measured by a tensile tester. Compared to the “untreated group” (0.96 N), the phantom pulling force of the “ultrasound + drug group” is 0.15 N, which is reduced by 85%. Furthermore, with the driving voltage increased from 5 V to 20 V, the pulling force can be reduced by 60%; with the duty ratio increased from 20% to 60%, the pulling force can be reduced by 50%; with treatment time increased from 1 min to 5 min, the pulling force can be reduced by 64%. Conclusion: Utilizing an ultrasonic array combined with nano drugs, our phase compensation control method can reduce the degree of tendon adhesion and hold a great implication for applications of rehabilitation treatment for postoperative patients.@en

Micro robots, due to their light weight, small size and high mobility, can explore narrow space or hazardous locations that humans or larger robots cannot reach. Consequently, both academia and industry are concerned with the development of advanced microrobots. In this paper, we design a steerable miniature legged robot (SMLR) which possesses light weight and controllable linear/steerable motion by using two piezoelectric bending actuators. Its dimensions are 35 mm × 30 mm × 9 mm (length × width × height) and mass is 9 g. User can modulate the speed, turning radius, and load capacity of the robot by simply tuning the driving voltage. The robot exhibits a speed of 330 mm s-1 and a turning radius of 102 mm upon a driving voltage of 200 V and a frequency of 8.67 kHz. Moreover, it is capable of driving a 55 g embedded mass at a speed of 20 mm s-1 under a voltage of 200 V, and its simple design is ideal for down-sizing. Further, we establish a series of open-loop control programs in a virtual instrument through LabVIEW to accurately control the behavior of the SMLR (the location error is less than 5 mm), demonstrating its great potential in practical applications such as movement in a narrow space.@en

Micro robots, due to their light weight, small size and high mobility, can explore narrow space or hazardous locations that humans or larger robots cannot reach. Consequently, both academia and industry are concerned with the development of advanced microrobots. In this paper, we design a steerable miniature legged robot (SMLR) which possesses light weight and controllable linear/steerable motion by using two piezoelectric bending actuators. Its dimensions are 35 mm × 30 mm × 9 mm (length × width × height) and mass is 9 g. User can modulate the speed, turning radius, and load capacity of the robot by simply tuning the driving voltage. The robot exhibits a speed of 330 mm s-1 and a turning radius of 102 mm upon a driving voltage of 200 V and a frequency of 8.67 kHz. Moreover, it is capable of driving a 55 g embedded mass at a speed of 20 mm s-1 under a voltage of 200 V, and its simple design is ideal for down-sizing. Further, we establish a series of open-loop control programs in a virtual instrument through LabVIEW to accurately control the behavior of the SMLR (the location error is less than 5 mm), demonstrating its great potential in practical applications such as movement in a narrow space.@en

Micro robots, due to their light weight, small size and high mobility, can explore narrow space or hazardous locations that humans or larger robots cannot reach. Consequently, both academia and industry are concerned with the development of advanced microrobots. In this paper, we design a steerable miniature legged robot (SMLR) which possesses light weight and controllable linear/steerable motion by using two piezoelectric bending actuators. Its dimensions are 35 mm × 30 mm × 9 mm (length × width × height) and mass is 9 g. User can modulate the speed, turning radius, and load capacity of the robot by simply tuning the driving voltage. The robot exhibits a speed of 330 mm s-1 and a turning radius of 102 mm upon a driving voltage of 200 V and a frequency of 8.67 kHz. Moreover, it is capable of driving a 55 g embedded mass at a speed of 20 mm s-1 under a voltage of 200 V, and its simple design is ideal for down-sizing. Further, we establish a series of open-loop control programs in a virtual instrument through LabVIEW to accurately control the behavior of the SMLR (the location error is less than 5 mm), demonstrating its great potential in practical applications such as movement in a narrow space.@en

Micro actuators have been used to realize the arrival of digestive tract lesions for the local targeted application of drugs in endoscopes. However, there still exists a key safety issue that casts a shadow over the practical and safe implementation of actuators in the human body, namely an overheated environment caused by actuators' operation. Herein, with the aim of solving the temperature rising problem of a piezoelectric micro actuator operating in an endoscopic biopsy channel (OLYMPUS, Tokyo, Japan), a thermal finite element method (FEM) based on COMSOL Multiphysics software is proposed. The temperature distribution and its rising curves are obtained by the FEM method. Both the simulated and experimental maximum temperatures are larger than the safety value (e.g., 42 °C for human tissues) when the driving voltage of the actuator is 200 Vpp, which proves that the overheating problem really exists in the actuator. Furthermore, the results show that the calculated temperature rising curves correspond to the experimental results, proving the effectiveness of this FEM method. Therefore, we introduce a temperature control method through optimizing the duty ratio of the actuator. In comparison with a 100% duty ratio operation condition, it is found that a 60% duty ratio with a driving voltage of 200 Vpp can more effectively prevent the temperature rising issue in the first 3 min, as revealed by the corresponding temperatures of 44.4 and 41.4 °C, respectively. When the duty ratio is adjusted to 30% or less, the temperature rise of the actuator can be significantly reduced to only 36.6 °C, which is close to the initial temperature (36.4 °C). Meanwhile, the speed of the actuator can be well-maintained at a certain level, demonstrating its great applicability for safe operation in the human body.@en

Low frequency sonophoresis (LFS) is currently being attempted as a transdermal drug delivery method in clinical areas. However, it lacks both an effective control method and the equipment to satisfy the varying drug dosage requirements of individual patients. Herein, a novel method aimed at controlling permeability is proposed and developed, using a pressure control strategy which is based on an accurate, adjustable and non-invasive ultrasound transdermal drug delivery system in in vitro LFS. The system mainly consists of a lead screw linear ultrasonic motor and an ultrasonic transducer, in which the former offers pressure and the latter provides ultrasound wave in the liquid. The ultrasound can enhance non-invasive permeation and the pressure from the motor can control the permeability. The calculated and experimental results demonstrate that the maximum pressure on artificial skin is under the area with the maximum vibration amplitude of the ultrasonic transducer, and the total pressure consists of acoustic pressure from the transducer and approximate static pressure from the motor. Changing the static pressure from the ultrasonic motor can effectively control the non-invasive permeability, by adjusting the duty ratio or the amplitude of the motor's driving voltage. In addition, the permeability control of calcein by thrust control is realized in 15 min, indicating the suitability of this method for application in accurate medical technology. The obtained results reveal that the issue of difficult permeability control can be addressed, using this control method in in vitro LFS to open up a route to the design of accurate drug delivery technology for individual patients.@en

Low frequency sonophoresis (LFS) is currently being attempted as a transdermal drug delivery method in clinical areas. However, it lacks both an effective control method and the equipment to satisfy the varying drug dosage requirements of individual patients. Herein, a novel method aimed at controlling permeability is proposed and developed, using a pressure control strategy which is based on an accurate, adjustable and non-invasive ultrasound transdermal drug delivery system in in vitro LFS. The system mainly consists of a lead screw linear ultrasonic motor and an ultrasonic transducer, in which the former offers pressure and the latter provides ultrasound wave in the liquid. The ultrasound can enhance non-invasive permeation and the pressure from the motor can control the permeability. The calculated and experimental results demonstrate that the maximum pressure on artificial skin is under the area with the maximum vibration amplitude of the ultrasonic transducer, and the total pressure consists of acoustic pressure from the transducer and approximate static pressure from the motor. Changing the static pressure from the ultrasonic motor can effectively control the non-invasive permeability, by adjusting the duty ratio or the amplitude of the motor's driving voltage. In addition, the permeability control of calcein by thrust control is realized in 15 min, indicating the suitability of this method for application in accurate medical technology. The obtained results reveal that the issue of difficult permeability control can be addressed, using this control method in in vitro LFS to open up a route to the design of accurate drug delivery technology for individual patients.@en

Low frequency sonophoresis (LFS) is currently being attempted as a transdermal drug delivery method in clinical areas. However, it lacks both an effective control method and the equipment to satisfy the varying drug dosage requirements of individual patients. Herein, a novel method aimed at controlling permeability is proposed and developed, using a pressure control strategy which is based on an accurate, adjustable and non-invasive ultrasound transdermal drug delivery system in in vitro LFS. The system mainly consists of a lead screw linear ultrasonic motor and an ultrasonic transducer, in which the former offers pressure and the latter provides ultrasound wave in the liquid. The ultrasound can enhance non-invasive permeation and the pressure from the motor can control the permeability. The calculated and experimental results demonstrate that the maximum pressure on artificial skin is under the area with the maximum vibration amplitude of the ultrasonic transducer, and the total pressure consists of acoustic pressure from the transducer and approximate static pressure from the motor. Changing the static pressure from the ultrasonic motor can effectively control the non-invasive permeability, by adjusting the duty ratio or the amplitude of the motor's driving voltage. In addition, the permeability control of calcein by thrust control is realized in 15 min, indicating the suitability of this method for application in accurate medical technology. The obtained results reveal that the issue of difficult permeability control can be addressed, using this control method in in vitro LFS to open up a route to the design of accurate drug delivery technology for individual patients.@en

Low frequency sonophoresis (LFS) is currently being attempted as a transdermal drug delivery method in clinical areas. However, it lacks both an effective control method and the equipment to satisfy the varying drug dosage requirements of individual patients. Herein, a novel method aimed at controlling permeability is proposed and developed, using a pressure control strategy which is based on an accurate, adjustable and non-invasive ultrasound transdermal drug delivery system in in vitro LFS. The system mainly consists of a lead screw linear ultrasonic motor and an ultrasonic transducer, in which the former offers pressure and the latter provides ultrasound wave in the liquid. The ultrasound can enhance non-invasive permeation and the pressure from the motor can control the permeability. The calculated and experimental results demonstrate that the maximum pressure on artificial skin is under the area with the maximum vibration amplitude of the ultrasonic transducer, and the total pressure consists of acoustic pressure from the transducer and approximate static pressure from the motor. Changing the static pressure from the ultrasonic motor can effectively control the non-invasive permeability, by adjusting the duty ratio or the amplitude of the motor's driving voltage. In addition, the permeability control of calcein by thrust control is realized in 15 min, indicating the suitability of this method for application in accurate medical technology. The obtained results reveal that the issue of difficult permeability control can be addressed, using this control method in in vitro LFS to open up a route to the design of accurate drug delivery technology for individual patients.@en

Low frequency sonophoresis (LFS) is currently being attempted as a transdermal drug delivery method in clinical areas. However, it lacks both an effective control method and the equipment to satisfy the varying drug dosage requirements of individual patients. Herein, a novel method aimed at controlling permeability is proposed and developed, using a pressure control strategy which is based on an accurate, adjustable and non-invasive ultrasound transdermal drug delivery system in in vitro LFS. The system mainly consists of a lead screw linear ultrasonic motor and an ultrasonic transducer, in which the former offers pressure and the latter provides ultrasound wave in the liquid. The ultrasound can enhance non-invasive permeation and the pressure from the motor can control the permeability. The calculated and experimental results demonstrate that the maximum pressure on artificial skin is under the area with the maximum vibration amplitude of the ultrasonic transducer, and the total pressure consists of acoustic pressure from the transducer and approximate static pressure from the motor. Changing the static pressure from the ultrasonic motor can effectively control the non-invasive permeability, by adjusting the duty ratio or the amplitude of the motor's driving voltage. In addition, the permeability control of calcein by thrust control is realized in 15 min, indicating the suitability of this method for application in accurate medical technology. The obtained results reveal that the issue of difficult permeability control can be addressed, using this control method in in vitro LFS to open up a route to the design of accurate drug delivery technology for individual patients.@en

Unresectable tumors in the gastrointestinal tract are difficult to treat, and traditional radiotherapy combined with chemotherapy can easily induce severe side-effects due to the toxicities of anticancer drugs. Effective methods to enhance the concentration of local drug release in the narrow and hollow organs of the gastrointestinal tract are unavailable. To address this shortcoming, we propose a method to thermally trigger the release of Nile Red from temperature-sensitive liposomes (TSLs) in an in vitro hydrogel phantom of the gastric mucosa through ultrasound treatment by using a small, piezoelectric, single-crystal ultrasonic transducer with a diameter of 2.2 mm. To control the rise in temperature, we establish a model for ultrasound thermal calculation according to Helmholtz's equation, the equations of heat transfer, and the Navier-Stokes equations and validate it through an in vitro experiment. The results show that the temperature reached the melting-phase transition temperature of TSL (40-42 °C) when the duty ratio of the driving voltage of the ultrasonic transducer was 60%, and the amplitude was greater than 40 Vpp and less than 60 Vpp. Furthermore, the maximum rate of release of Nile Red was 2.9 × 10−3 mg/min when the ultrasonic transducer was activated with a driving voltage of 60 Vpp and a duty ratio of 60%. Thus, the proposed method for temperature control can be applied to improve local drug concentration in the gastrointestinal tract and reduce the number of anticancer drugs in the body.@en

To realize an efficient translation in a narrow space, a surface milli-walker based on linear piezoelectric actuation is proposed, fabricated, and tested in this paper. Operating at the second-order out-of-plane flexural vibration mode, the proposed surface walker is able to realize a linear movement on demand. The surface walker has a weight of 0.135 g with package size of 6 × 2 × 2 mm. Experimental results show that the maximum velocity and drag force of the walker can reach up to 200 mm/s and 10 mN, respectively. The velocity of the walker can be smoothly adjusted over a range of 0.15–200 mm/s. In addition, its startup time is as quick as 6 ms. The milli-walker holds great promises for numerous potential applications in precise instruments.@en

Friction materials form a critical component of piezoelectric actuators, and wear of the material affects output and service life of the actuator. This paper examines the influence of polyimide (PI) composites when used as a friction material on the performance of a legged piezoelectric bending actuator. We design and manufacture demountable shoe soles, made of a novel PI-based friction material, for an actuator. A Coulomb friction model is also established to determine the behavior resulting from contact-induced friction between the surface and the actuator. Reciprocating wear tests involving an insulation rubber pad against phosphor bronze and PI composites as friction materials yielded average friction coefficients of 0.21 and 0.28, respectively. We also found that PI composites have higher wear resistance than phosphor bronze, with a specific wear rate of 1.36 × 10-4 mm3/N m. The results of experiments and simulations indicate that the shoe soles made of PI composites reduced the actuator's driving frequency and vibrational amplitude, but they did not affect the principle of locomotion of the actuator. Furthermore, the operational stability of the actuator improved by 46.8% by using the demountable shoe soles made of PI composites, albeit at the cost of its velocity and load capacity. This work has guiding significance for the design and selection of friction materials for piezoelectric actuators. @en