The rapid development of 3D printing has led to considerable progress in the field of biomedical engineering. Notably, 4D printing provides a potential strategy to achieve a time‐dependent physical ...change within tissue scaffolds or replicate the dynamic biological behaviors of native tissues for smart tissue regeneration and the fabrication of medical devices. The fabricated stimulus‐responsive structures can offer dynamic, reprogrammable deformation or actuation to mimic complex physical, biochemical, and mechanical processes of native tissues. Although there is notable progress made in the development of the 4D printing approach for various biomedical applications, its more broad‐scale adoption for clinical use and tissue engineering purposes is complicated by a notable limitation of printable smart materials and the simplistic nature of achievable responses possible with current sources of stimulation. In this review, the recent progress made in the field of 4D printing by discussing the various printing mechanisms that are achieved with great emphasis on smart ink mechanisms of 4D actuation, construct structural design, and printing technologies, is highlighted. Recent 4D printing studies which focus on the applications of tissue/organ regeneration and medical devices are then summarized. Finally, the current challenges and future perspectives of 4D printing are also discussed.
4D printing is becoming a state‐of‐the‐art research field that holds considerable promise for diverse applications. This article introduces fabrication technologies and transforming strategies in terms of structural design and material composition design. The various 4D inks, actuation mechanisms, and recent advances in tissue regeneration and medical devices are summarized. Finally, the main challenges and future perspectives are presented.
•A novel structural design of the wearable TEG to harvest body heat is developed.•The TEG features excellent flexibility and high power generation for body heat harvesting.•A miniaturized ...accelerometer is powered by the TEG to detect body motion through harvesting wrist heat.
Wearable thermoelectric generators (TEGs) enable the conversion of human body heat into microwatts to milliwatt electricity, which can be utilized to power miniaturized electronic devices for motion detection and healthcare monitoring. This paper presents a novel wearable TEG with 52 pairs of cubic-shaped thermoelectric legs to harvest human body heat. The thermoelectric legs are made of P-type and N-type Bi2Te3-based powder materials, and are connected electrically in series through soldering. The flexible printed circuit board (FPCB) with special holes is designed and used as substrate to enhance the flexibility of the TEG for wearable applications. The performances of the TEG, including the bulk thermoelectric legs, are characterized. The results show that the TEG can generate an open-circuit voltage of 37.2 mV at ΔT = 50 K, and the internal resistance of the TEG is quite low at a value of 1.8 Ω. Then the TEG was worn on a human wrist to harvest body heat and power a 3-axis miniaturized accelerometer for detection of body motion at ΔT = 18 K. The results demonstrate that the developed wearable TEG features high output performance and could be utilized for powering electronics and/or sensors by harvesting human body heat.
This article presents a novel flexible tactile sensor by using skin-like dual-interlocked structure to improve both the sensitivity and force detection range. The fully elastomeric graphene/carbon ...nanotube/silicon rubber nanocomposites are synthesized and used as a sensing material. The sandwich skin-like dual-interlocked structure enables the tactile sensor to easily transform external mechanical stimuli into tensile strain of the sensing material. A low-cost fabrication method and procedure is proposed to fabricate the flexible tactile sensor. The fabricated tactile sensor has <inline-formula> <tex-math notation="LaTeX">3\times3 </tex-math></inline-formula> (= 9) sensing units and features extremely high flexibility. Experimental tests showed that the developed tactile sensor has a linear and high sensitivity of 0.767 N −1 for a wide range of force (0-25 N) characterization. The tactile sensor is also tested with good dynamic response, good repeatability, and long serving life. Then, the flexible tactile sensor was worn on human foot to monitor body standing posture and large force sensing and further served as an extended interface for computer games' application. The results indicated that our developed flexible tactile sensor would have a great potential in human-machine interface of wearable sensors for augmented reality, intelligent robotics, and prosthetics.
Wearable tactile sensors can be used for haptic perception and are widely utilized in soft robotics, intelligent prosthetics, and other human interfaced/interface applications. The development of ...tactile sensors with for multifunctional tactile sensing capacity remains a challenge. This article presents the design and fabrication of a wearable tactile sensor based on galinstan liquid metal for the simultaneous sensing of temperature and contact force independently. The decoupling of temperature and contact force sensing, which is based on the measured output voltage signals, is achieved by a designed Wheatstone bridge circuit and by the structural design of the fingerprint-patterned microfluidic channels and the top oval-shaped protrusion. Characterization tests show that the fabricated tactile sensor has a relatively high force sensing sensitivity of 0.32 N −1 and its temperature sensing sensitivities are 0.41% °C −1 at 20~50 °C and 0.21% °C −1 at 50~80 °C. Two wearable tactile sensors are worn on the index finger and thumb of the human hand and are used to detect temperature changes and contact forces during grasping applications. The results show that the developed liquid metal-based tactile sensor has a high flexibility and durability, and can accurately measure the contact forces and temperatures simultaneously. Thus, the developed wearable tactile sensor has great potential for robotic manipulation and healthcare condition sensing in humans.
This paper presents a highly sensitive and flexible tactile sensor based on 3D microstructure graphene sponges. The graphene sponges are fabricated in a dip-coating process that stacks the graphene ...layers onto the polyimide scaffolds in a homogeneous graphene solution with graphene oxide serving as the dispersant. The tactile sensor has <inline-formula> <tex-math notation="LaTeX">3 \times 3 </tex-math></inline-formula> sensing units and is fabricated through photoetching, magnetron sputtering, and screen-printing processes. The graphene sponge has relatively low Young's modulus of 16 kPa and is capable of enduring large strains over 60%. Furthermore, the sensor unit with the graphene sponge has a high sensitivity of 0.046 kPa<inline-formula> <tex-math notation="LaTeX">^{-1} </tex-math></inline-formula> at 0.3 ~ 10 kPa, a lower sensitivity of 0.007 kPa<inline-formula> <tex-math notation="LaTeX">^{-1} </tex-math></inline-formula> at 10 ~ 40 kPa, and shows good reproducibility and dynamic response. The increase in the contact areas of the graphene cell walls inside the graphene sponge and the overlapping areas in the laminated graphene flakes synergistically contribute to the high piezoresistive sensitivity. Body wearing experiments to detect wrist bending and muscle vibration demonstrate that the tactile sensor has potential for monitoring body motion and other biomedical applications. 2018-0189
Black inorganic materials with low infrared absorption/emission (or IR white) are rare in nature but highly desired in numerous areas, such as solar–thermal energy harvesting, multispectral ...camouflage, thermal insulation, and anti‐counterfeiting. Due to the lack of spectral selectivity in intrinsic materials, such counter‐intuitive properties are generally realized by constructing complicated subwavelength metamaterials with costly nanofabrication techniques. Here, the intrinsically low mid‐IR emissivity (down to 10%) of the 2D Ti3C2Tx MXene is reported. Associated with a high solar absorptance (up to 90%), it embraces the best spectral selectivity among the reported intrinsic black solar‐absorbing materials. Its appealing potential in several of the aforementioned areas is experimentally demonstrated. First‐principles calculations reveal that the IR emissivity of MXene relies on both the nanoflake orientations and terminal groups, indicating great tunability. The calculations also suggest more potential low‐emissivity MXenes including Ti2CTx, Nb2CTx, and V2CTx. This work opens the avenue to further exploration of a family of intrinsically low‐emissivity materials with over 70 members.
The ultralow infrared emissivity of the 2D Ti3C2Tx MXene is experimentally demonstrated. First‐principles calculations confirm this discovery and reveal other MXenes such as Ti2CTx, Nb2CTx, and V2CTx are also low‐emissivity materials. Such intrinsically visible black but infrared white materials that are rare in nature show great potential in solar–thermal conversion, multispectral camouflage, thermal insulation, and anti‐counterfeiting applications.
Summary
Methanol steam reforming can convert methanol solution into hydrogen rich steam, which can be used to supply for the proton exchange membrane fuel cell (PEMFC). The carbon monoxide (CO) in ...the produced hydrogen rich steam will be poison to the PEMFC and limits the application of this technic. This study develops a new methanol fuel processing system (MFPS) with incorporated methanol steam reforming and CO selective methanation modules for production of hydrogen rich steam with a low concentration of CO, and used to directly supply for the PEMFC. The core component of the MFPS is a highly layer‐packed microreactor, wherein methanol steam reforming, methanol combustion, and CO selective methanation reactions can occur. For the developed MFPS, an optimized methanol supply strategy is proposed to startup the MFPS, the fastest startup time is about 15.8 minutes. Experimental tests showed that the MFPS can be continuously operated for more than 100 hours with CO concentration below 10 ppm. The produced hydrogen rich steam was directly supplied for a PEMFC to generate 100 W electricity. Results obtained in this study demonstrated that the developed MFPS can produce CO‐free hydrogen rich stream for the supply of PEMFC, the generated electricity can be used to power mobile device and/or electronics.
A novel methanol fuel processing system with methanol steam reforming and CO methanation modules is proposed to generate low CO concentration reformate steadily and efficiently. Experimental results show that the system can be operated for 100 hours with CO concentration below 10 ppm at the reformate flow rate of 2.5 g/min. With airbleed technology PEMFC integrated with the system can generate 100 W of electricity for 200 minutes.
The visual servoing control extends the potential application of cable-driven hyper-redundant manipulators (CDHRM) to automatically execute tasks by sensing the visual information of environment. ...However, the high proportion of feature point mismatching and visual occlusion may occur in the complex and narrow environment that CDHRM works in, which make the traditional image-based visual servoing (IBVS) system hard to work or even cause instability. In this article, a novel IBVS system is proposed for CDHRM with eye-in-hand configuration, where the ability of mismatching resistance is improved by optimizing the vector of feature points, while the stability and tracking performance are still guaranteed. The maximum likelihood estimation random sample consensus (MLESAC) algorithm is designed to estimate the inlier model that resists mismatching and extracts well-matched feature points (namely the inliers) for the first captured image. Since the inliers may become mismatched in the newly captured image, the inliers and inlier model are both updated according to the feature quality weights. As a result, the newly mismatched feature points are excluded so that the weighted feature vector with less mismatching and higher quality can be generated. Subsequently, the weighted IBVS control law based on this vector is designed to achieve the mismatching resistance as well as guarantee the asymptotic stability and tracking performance of system. Comparative experiments are implemented for the proposed MLESAC algorithm and novel IBVS system, and the results verify that our method has better adaptability to the environment when applied in CDHRM, even with partial visual occlusion.
This paper presents a flexible capacitive tactile sensor array embedded with a truncated polydimethylsiloxane pyramid array as a dielectric layer. The proposed sensor array has been fabricated with 4 ...× 4 sensor units. The measurement ranges of forces in the x-axis, y-axis, and z-axis are 0-0.5, 0-0.5, and 0-4 N, respectively. In the range of 0-0.5 N, the sensitivities of the sensor unit are 58.3%/N, 57.4%/N, and 67.2%/N in the x-axis, y-axis, and z-axis, respectively. In the range of 0.5-4 N, the sensitivity in the z-axis is 7.7%/N. Three-axis force measurement has been conducted for all the sensor units. The average errors between the applied and calculated forces are 11.8% ± 6.4%. The sensor array has been mounted on a prosthetic hand. A paper cup and a cube are grasped by the prosthetic hand and the three-axis contact force is measured in real time by the sensor array. Results show that the sensor can capture the three-axis contact force image both in light and tight grasping. The proposed capacitive tactile sensor array can be utilized in robotics and prosthetic hand applications.
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