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Hydrogels are extensively explored as biomaterials for tissue scaffolds, and their controlled fabrication has been the subject of wide investigation. However, the tedious mechanical property adjusting process through formula control hindered their application for diverse tissue scaffolds. To overcome this limitation, we proposed a two-step process to realize simple adjustment of mechanical modulus over a broad range, by combining digital light processing (DLP) and post-processing steps. UV-curable hydrogels (polyacrylamide-alginate) are 3D printed via DLP, with the ability to create complex 3D patterns. Subsequent post-processing with Fe 3+ ions bath induces secondary crosslinking of hydrogel scaffolds, tuning the modulus as required through soaking in solutions with different Fe 3+ concentrations. This innovative two-step process offers high-precision (10 μm) and broad modulus adjusting capability (15.8–345 kPa), covering a broad range of tissues in the human body. As a practical demonstration, hydrogel scaffolds with tissue-mimicking patterns were printed for cultivating cardiac tissue and vascular scaffolds, which can effectively support tissue growth and induce tissue morphologies.

Metastable β-type titanium alloys are highly suitable for use as structural biomaterials applied to hard tissue, i.e., as cortical bone (hereafter, bone) replacing implants. However, their mechanical biocompatibitities, such as the Young’s modulus, strength and ductility balance, fatigue strength, resistance against fatigue crack propagation and fracture toughness, require improvenent for increased compatibility with bone. Through deformation, the metastable β-phase in a metastable β-type titanium alloy is transformed into various phases, such as α’ martensite, α” martensite, and ω-phases with exact phase depending by metastable β-phase stability. In addition, twinning is also induced by deformation. Deformation twinning effectively enhances the work hardening in the metastable β-type titanium alloy, leading to increased strength and ductility. This improvement is accompanied by with other deformation-induced transformations including the appearance of deformation-induced martensite and ω-phase transformation. The enhancement of the mechanical biocompatibility of various materials using the abovementioned deformation-induced transformation is described in this paper, for both newly developed metastable β-type Ti-Mo and Ti-Cr alloys for biomedical applications.

The MACCEPA (Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator) is an electric actuator of which the compliance and equilibrium position are fully independently controllable and both are set by two dedicated servomotor. In this paper an improvement of the actuator is proposed where the torque-angle curve and consequently the stiffness-angle curve can be modified by choosing an appropriate shape of a profile disk, which replaces the lever arm of the original design. The actuator has a large joint angle, torque and stiffness range and these properties can be made beneficial for safe human robot interaction and the construction of energy efficient walking, hopping and running robots. The benefit of the ability to store and release energy is shown by the 1DOF hopping robot Chobino1D. The achieved hopping height is much higher compared to a configuration in which the same motor is used without a series elastic element. The stiffness of the actuator increases with deflection, more closely resembling the properties shown by elastic tissue in humans.

Currently, intelligent robotics is supplanting traditional industrial applications. It extends to business, service and care industries, and other fields. Stable robot grasping is a necessary prerequisite for all kinds of complex application scenarios. Herein, we propose a method for preparing an elastic porous material with adjustable conductivity, hardness, and elastic modulus. Based on this, we design a soft robot tactile fingertip that is gentle, highly sensitive, and has an adjustable range. It has excellent sensitivity (~1.089 kpa−1), fast response time (~35 ms), and measures minimum pressures up to 0.02 N and stability over 500 cycles. The baseline capacitance of a sensor of the same size can be increased by a factor of 5–6, and graphene adheres better to polyurethane sponge and has good shock absorption. In addition, we demonstrated the application of the tactile fingertip to a two-finger manipulator to achieve stable grasping. In this paper, we demonstrate the great potential of the soft robot tactile finger in the field of adaptive grasping for intelligent robots.

Purpose This paper aims to show a series of hydrogels with adjustable mechanical properties, which can be cured quickly with visible light. The hydrogel is prepared conveniently with hydroxyethyl acrylate, cross-linker, gelatin and photoinitiator, and can be printed into certain 3D patterns with the direct ink write (DIW) 3D printer designed and developed by the research group. Design/methodology/approach In this paper, the authors designed a composite sensitization initiation system that is suitable for hydrogels. The concentration of photoinitiator, gelatin and cross-linker was studied to optimize the curing efficiency and adjust the mechanical properties. A DIW 3D printer was designed for the printing of hydrogel. Pre-gel solution was loaded into printer for printing into established models. The models were made and sliced with software. Findings The hydrogels can be cured efficiently with 405-nm visible light. While adding various content of gelatin and cross-linker, the mechanical properties of hydrogels show from soft and fragile (elastic modulus of 121.18 kPa and work of tension of 218.11 kJ·m−3) to rigid and tough (elastic modulus of 505.15 kPa and work of tension of 969.00 kJ·m−3). The hydrogels have high capacity of water absorption. With the DIW 3D printer, pre-gel hydrogel solution can be printed into objects with certain dimension. Originality/value In this work, a composite sensitization initiation system was designed, and fast curing hydrogels with adjustable mechanical properties had been prepared conveniently, which has high equilibrium water content and 3D printability with the DIW 3D printer.

Inspired by the mechanism of touch and pain in human skin, we integrated two ion-sensing films and a polydimethylsiloxane (PDMS) layer together to achieve a bionic artificial receptor with the capacity of distinguishing touch or pain perception through ion-electrical effect. The ion-sensing film provides the carrier of touch or pain perception, while the PDMS layer as a soft substrate is used to regulate the perception ability of receptor. Through a series of experiments, we investigated the effects of physical properties of the PDMS layer on the sensing ability of an artificial receptor. Further, contact area tests were performed in order to distinguish touch or pain under a sharp object. It is revealed that the pressure threshold triggering the touch and pain feedback of the artificial receptor presented an increasing trend when the elastic modulus and thickness of the PDMS substrate increase. The distinction ability of touch and pain becomes more pronounced under higher elastic modulus and larger thickness. Furthermore, the induced pain feedback becomes more intense with the decrease of the loading area under the same load, and the threshold of pain drops down from 176.68 kPa to 54.57 kPa with the decrease of the radius from 3 mm to 1 mm. This work potentially provides a new strategy for developing electronic skin with tactile sensing and pain warning. The pressure threshold and sensing range can be regulated by changing the physical properties of the middle layer, which would be advantageous to robotics and healthcare fields.

Adjustable compliant actuators are being designed and implemented in robotic devices because of their ability to minimize large forces due to impacts, to safely interact with the user, and to store and release energy in passive elastic elements. Conceived as a new force-controlled compliant actuator, an adjustable rigidity with embedded sensor and locking mechanism actuator (ARES-XL) is presented in this paper. This compliant system is intended to be implemented in a gait exoskeleton for children with neuro muscular diseases (NMDs) to exploit the intrinsic dynamics during locomotion. This paper describes the mechanics and initial evaluation of the ARES-XL, a novel variable impedance actuator (VIA) that allows the implementation of an add-on locking mechanism to this system, and in combination with its zero stiffness capability and large deflection range, provides this novel joint with improved properties when compared to previous prototypes developed by the authors and other state-of-the-art (SoA) devices. The evaluation of the system proves how this design exceeds the main capabilities of a previous prototype as well as providing versatile actuation that could lead to its implementation in multiple joints.

Polyurethane (PU) and other plastic foams are widely used as passive acoustic absorbers. For optimal design, it is often necessary to know the viscoelastic properties of these materials in the frequency range relevant to their application. An experimental/numerical technique has been implemented to determine the Young and shear dynamic moduli and loss factor of poroelastic materials under low-frequency 40–520Hz random excitation. The method consists of measuring the dynamic response of the sample at its surface, and matching the response with the predictions from a finite element model in which the two complex elastic moduli are the adjustable parameters. Results are presented for measurements made in air, under standard pressure and temperature conditions, and compared with predictions based on Okuno’s model. The dependence of elastic moduli on the dimension of the sample and its boundary conditions is also studied.

In this research, composites of polypropylene (PP) and a relatively small concentrations of iron ferrite (Fe3O4) nanopowder equal to 2, 5 and 10 wt.% have been made. An methacrylate monomer 2,2'-bis-[4-(2-methylprop-2-enoyloxy)phenyl]-propane (BAD) was added at a small amount (3 wt.%) to part of the composites during the thermoplastic mixing. The BAD has been used as a compatibilizing agent on the phase interaction between the filler and the matrix of polypropylene. It has been found that composites have adjustable mechanical, structural and magnetic properties dependent on the content of magnetic filler. Increase of concentration of ferrite particles affects a notable increase of elastic modulus and reduces the deformability in comparison to pure polypropylene, whereas the modification with BAD has mainly a plasticizing effect, affecting a small decrease on stiffness but a notable increase of strain at break. An important role of Fe3O4 adhesion in polymer matrix and interphase effects on the changes of crystallinity and magnetic properties has been found.

The theory of balancing of frequency-independent, alternating-current bridges for the measurement of the parameters of three-element RC two-terminal networks is considered. The theory supports the creation of fast algorithms designed to achieve balance with respect to three adjustable parameters.[PUBLICATION ABSTRACT]