Piezoelectric Poly L-lactic Acid Research Articles

Application of Braided Piezoelectric Poly-l-Lactic Acid Cord Sensor to Sleep Bruxism Detection System with Less Physical or Mental Stress.

For many years, we have been developing flexible sensors made of braided piezoelectric poly-l-lactic acid (PLLA) fibers that can be tied and untied for practical applications in society. To ensure good quality of sleep, the occurrence of bruxism has been attracting attention in recent years. Currently, there is a need for a system that can easily and accurately measure the frequency of bruxism at home. Therefore, taking advantage of the braided piezoelectric PLLA cord sensor's unique characteristic of being sewable, we aimed to provide a system that can measure the frequency of bruxism using the braided piezoelectric PLLA cord sensor simply sewn onto a bed sheet on which the subject lies down. After many tests using trial and error, the sheet sensor was completed with zigzag stitching. Twenty subjects slept overnight in a hospital room on sheets integrated with a braided piezoelectric PLLA cord. Polysomnography (PSG) was simultaneously performed on these subjects. The results showed that their bruxism could be detected with an accuracy of more than 95% compared with PSG measurements, which can only be performed in a hospital by a physician and are more burdensome for the subjects, with the subjects simply lying on the bed sheet with a braided piezoelectric PLLA cord sensor sewn into it.

Oxygen-producing composite dressing activated by photothermal and piezoelectric effects for accelerated healing of infected wounds

The process of wound healing is often obstructed by the prevalence of bacterial infection at the wound site. Hence, innovative strategies to alleviate infection is extremely necessary to realize effective wound recovery in a timely manner. Here, we report a self-activated composite dressing consisting of piezoelectric and photothermal functional layers for combating wound infection and provide the desired treatment. The synergistic dressing is functionalized with piezoelectric Poly-L-lactic acid (PLLA) which under the effect of ultrasound irradiation controllably generates reactive oxygen species (ROS) for antibacterial activity, thus facilitating the dressing to inhibit the growth of bacteria at the wound bed. Further, the dressing is modified with calcium peroxide (CaO2) which can effectively convert the generated ROS into molecular oxygen (O2) in presence of catalase enzyme for treating chronic hypoxia in the infected wounds. The sustained generation of O2 by the wound dressing augmented the cell proliferation, migration and tissue regeneration aiding in wound healing. By combining the inherent photothermal activity of reduced graphene oxide (rGO), the synergistic dressing under NIR irradiation enhanced the wound recovery by upregulating the heat shock protein 90 (Hsp90) secretion owing to the heat generation on the wounds. The results obtained demonstrate that the self-triggered multifunctional wound dressing is a promising candidate for clinical treatment of infected wounds with a user-friendly interface.

Biodegradable piezoelectric skin-wound scaffold

Electrical stimulation (ES) induces wound healing and skin regeneration. Combining ES with the tissue-engineering approach, which relies on biomaterials to construct a replacement tissue graft, could offer a self-stimulated scaffold to heal skin-wounds without using potentially toxic growth factors and exogenous cells. Unfortunately, current ES technologies are either ineffective (external stimulations) or unsafe (implanted electrical devices using toxic batteries). Hence, we propose a novel wound-healing strategy that integrates ES with tissue engineering techniques by utilizing a biodegradable self-charged piezoelectric PLLA (Poly (l-lactic acid)) nanofiber matrix. This unique, safe, and stable piezoelectric scaffold can be activated by an external ultrasound (US) to produce well-controlled surface-charges with different polarities, thus serving multiple functions to suppress bacterial growth (negative surface charge) and promote skin regeneration (positive surface charge) at the same time. We demonstrate that the scaffold activated by low intensity/low frequency US can facilitate the proliferation of fibroblast/epithelial cells, enhance expression of genes (collagen I, III, and fibronectin) typical for the wound healing process, and suppress the growth of S. aureus and P. aeruginosa bacteria in vitro simultaneously. This approach induces rapid skin regeneration in a critical-sized skin wound mouse model in vivo. The piezoelectric PLLA skin scaffold thus assumes the role of a multi-tasking, biodegradable, battery-free electrical stimulator which is important for skin-wound healing and bacterial infection prevention simultaneuosly.

Application of Piezoelectric PLLA Braided Cord as Wearable Sensor to Realize Monitoring System for Indoor Dogs with Less Physical or Mental Stress.

We attempted to realize a prototype system that monitors the living condition of indoor dogs without physical or mental burden by using a piezoelectric poly-l-lactic acid (PLLA) braided cord as a wearable sensor. First, to achieve flexibility and durability of the piezoelectric PLLA braided cord used as a sensor for indoor dogs, the process of manufacturing the piezoelectric PLLA fiber for the piezoelectric braided cord was studied in detail and improved to achieve the required performance. Piezoelectric PLLA braided cords were fabricated from the developed PLLA fibers, and the finite element method was used to realize an e-textile that can effectively function as a monitoring sensor. As a result, we realized an e-textile that feels similar to a high-grade textile and senses the complex movements of indoor dogs without the use of a complex computer system. Finally, a prototype system was constructed and applied to an actual indoor dog to demonstrate the usefulness of the e-textile as a sensor for indoor dog monitoring.

A Prototype Sensor System Using Fabricated Piezoelectric Braided Cord for Work-Environment Measurement during Work from Home.

We proposed a new prototype sensor system to understand the workload of employees during telework. The goal of sensing using such a system is to index the degree of stress experienced by employees during work and recognize how to improve their work environment. Currently, to realize this, image processing technology with a Web camera is generally used for vital sign sensing. However, it creates a sense of discomfort at work because of a strong sense of surveillance. To truly evaluate a working environment, it is necessary that an employee be unaware of the sensor system and for the system to be as unobtrusive as possible. To overcome these practical barriers, we have developed a new removable piezoelectric sensor incorporated in a piezoelectric poly-L-lactic acid (PLLA) braided cord. This cord is soft and flexible, and it does not cause any discomfort when attached to the cushion cover sheet. Thus, it was possible to measure the workload of an employee working from home without the employee being aware of the presence of a sensor. Additionally, we developed a system for storing data in a cloud system. We succeeded in acquiring continuous long-term data on the vital signs of employees during telework using this system. The analysis of the data revealed a strong correlation between behavior and stress.

Application of a piezoelectric braided cord to sense vital signs during sleep

The final goal of this study is to provide a sleep-monitoring device that indexes sleep status and allows users to measure their sleep status and easily recognize how to improve their sleep. As a first step toward achieving this, we have developed a prototype system with a simple structure consisting of a bed sheet and a pillow case embraided with a piezoelectric poly-L-lactic acid (PLLA) braided cord, enabling in situ observation of sensing body movements and vital signs during sleep. A PLLA braided cord as a material for a new wearable sensor is flexible and feels soft, which can sense complex human motion without using a complex computer system. As a preliminary experiment, the pulse wave and breathing were observed in situ using the prototype system when the subject lay awake on a bed, where the subject first lay on their back and then lay on their side. Optimization of the piezoelectric PLLA embroidery was performed only on selected patterns. It was found that the pulse wave could usually be measured by in situ observation using a pillow case embraided with piezoelectric PLLA embroidery, and breathing could usually be measured using a bed sheet with piezoelectric PLLA embroidery. On the basis of this experimental result, we measured breathing and pulse waves during sleep for eight hours. We successfully measured breathing and pulse waves using the optimized system with a bed sheet and a pillow case embroidered with piezoelectric PLLA embroidery even though the subject, who wore pajamas, often turned over in his sleep.

Biodegradable Nanofiber Bone-Tissue Scaffold as Remotely-Controlled and Self-Powering Electrical Stimulator.

Electrical stimulation (ES) has been shown to induce and enhance bone regeneration. By combining this treatment with tissue-engineering approaches (which rely on biomaterial scaffolds to construct artificial tissues), a replacement bone-graft with strong regenerative properties can be achieved while avoiding the use of potentially toxic levels of growth factors. Unfortunately, there is currently a lack of safe and effective methods to induce electrical cues directly on cells/tissues grown on the biomaterial scaffolds. Here, we present a novel bone regeneration method which hybridizes ES and tissue-engineering approaches by employing a biodegradable piezoelectric PLLA (Poly(L-lactic acid)) nanofiber scaffold which, together with externally-controlled ultrasound (US), can generate surface-charges to drive bone regeneration. We demonstrate that the approach of using the piezoelectric scaffold and US can enhance osteogenic differentiation of different stem cells in vitro, and induce bone growth in a critical-sized calvarial defect in vivo. The biodegradable piezoelectric scaffold with applied US could significantly impact the field of tissue engineering by offering a novel biodegradable, battery-free and remotely-controlled electrical stimulator.

Piezoelectric “Kumihimo-gumi” sensor fabricated by braiding method using piezoelectric poly-L-lactic acid fiber

We have developed a piezoelectric braided cord consisting of a conducting fiber yarn core, piezoelectric poly-l-lactic acid (PLLA) fiber yarn and a polyethylene terephthalate (PET) middle sheath, and a conducting fiber outer shield (piezoelectric PLLA braided cord). Actually, we made various types of piezoelectric PLLA braided cords using Japanese traditional braiding method called as Kumihimo-gumi in Japanese. Furthermore, by optimization based on the calculation results for each type of piezoelectric PLLA Kumihimo-gumi obtained by the finite element method (FEM), we were able to develop a new type of piezoelectric PLLA braided cord with a sensing function for complex motion (piezoelectric PLLA Kumihimo-gumi). Finally, we developed a new wearable sensor for a selfie stick which is a popular smartphone accessory, fabricated from a piezoelectric PLLA Kumihimo-gumi.

New wearable sensor in the shape of a braided cord (Kumihimo)

A new piezoelectric sensor was developed in the shape of a traditional Japanese braided cord known as a Kumihimo by weaving piezoelectric poly-l-lactic acid (PLLA) fibers (piezoelectric PLLA braided cord). We found that the piezoelectric PLLA braided cord tied in various decorative knots, and worn as an accessory such as a choker or necklace, can detect pulse waves, swallowing, and coughing in a systematic way in one's daily life. To demonstrate this, we developed a system for measuring pulse waves with a Wi-Fi communication system using a piezoelectric PLLA braided cord with decorative knots.

Piezoelectric poly-L-lactic acid fabric and its application to control of humanoid robot

ABSTRACTWe report the potential of a system that enables the monitoring of complex human movements via new smart fabrics based on a piezoelectric poly-L-lactic acid (PLLA) fabric that have the function of sensing complex human motion. In particular, piezoelectric PLLA fabrics with plain, twill, and satin weaves were produced by Teijin Limited, Japan, a joint research company. First, a smart fabric was developed that consisted of pieces of the piezoelectric PLLA fabric with satin, plain, and twill weaves joined in the horizontal direction. The smart fabric, designed to accurately detect the twisting, bending, and elongation of the smart fabric itself was fabricated using a technique for sewing Japanese kimonos. Finally, we developed a prototype system that allows simple human motion to be detected through the motion sensing of clothes capable of being worn on the joints, such as the elbows, shoulders, knees, and waist, obtained by sewing together pieces of the smart fabric. This motion was linked with that of a humanoid robot.

Smart piezoelectric fabric and its application to control of humanoid robot

ABSTRACTWe have developed a piezoelectric fabric for sensing applied stress and strain using piezoelectric poly-l-lactic acid (PLLA) fibers, and tailored smart clothing having the function of sensing complex human motion using the piezoelectric PLLA fabric. To provide a high-quality PLLA fabric with large piezoelectricity, simultaneously satisfying the characteristics of softness, stretchability, and wearability, we first attempted the to improve the balance of the physical properties of PLLA fibers. We investigated the use of an acrylic copolymer as a plastic additive for improving the piezoelectric and mechanical properties of PLLA fibers, since the acrylic copolymer has extremely high dispersibility and compatibility, and the optimized furthermore the PLLA fiber fabrication conditions to improve the physical properties. To realize a piezoelectric fabric with the ability of sensing complex human motion, plain, twill, and satin weaves with improved the piezoelectricity, softness, stretchability, and wearability were produced using the PLLA fibers by Teijin Limited, Japan, a joint research company. Moreover, we developed a prototype system that allows human movement, detected through the motion sensing of smart clothing obtained by sewing together pieces of piezoelectric fabric, to be linked with that of a humanoid robot. At present, simple procedures such as bending of the arms and twisting of the wrists can be replicated by the humanoid robot but not complex movements of the arms.

Sensing Complicated Motion of Human Body Using Piezoelectric Chiral Polymer Fiber

Toward sensing the complicated motion of the human body, we have developed a new soft and flexible fiber sensor assembled from piezoelectric poly-L-lactic acid (PLLA) fibers (PLLA fiber sensor). As an early stage of this study, we attempted to detect the pulse rate and observe the motion of a human arm using the PLLA fiber sensor. First, we prepared left-hand and right-hand helical torsion coils (PLLA fiber left-hand and right-hand coils), which were formed by drawing a PLLA fiber with a drawing ratio of ten. As a result, we found that the pulse rate could be measured with extremely high accuracy by the PLLA fiber sensor. At the same time, we were able to detect the rotation of the forearm and upper arm using PLLA fiber sensors.