Surface Finish Analysis of Gradient Voltage Electrochemical Polishing of 316L Stainless Steel Parts Forming by Laser Powder Bed Fusion.

Laser powder bed fusion (LPBF) of complex-structure 316L stainless steel (316L ss) parts has a wide application prospects in aerospace, biomedical, and defense industry fields. However, the surface roughness (Ra) of the LPBF sample is unsatisfactory due to the process characteristics of layer-by-layer selective melting and cumulative forming, which limits its applications in the engineering field. Herein, a gradient voltage electrochemical polishing strategy is proposed based on the characteristics of electrochemical polishing technology, which can polish complex structures. The mechanisms of polishing process parameters and polishing strategy on the surface finish of LPBF parts are investigated. The gradient voltage polishing strategy is extended to complex structures, and the Ra of the inner surfaces of square and round tubes are successfully reduced to about 1 µm. The gradient electrochemical polishing process for surface finish post-treatment of LPBF parts can broaden the engineering applications of complex-structure metal parts.

Non-invasive in vivo study of morphology and mechanical properties of the median nerve.

The current literature studied the median nerve (MN) at specific locations during joint motions. As only a few particular parts of the nerve are depicted, the relevant information available is limited. This experiment investigated the morphological and biomechanical properties of the MN. The effects of the shoulder and wrist motions on MN were explored as well. Eight young healthy female individuals were tested with two-dimensional ultrasound and shear wave elastography (SWE). The morphological and biomechanical properties were examined in limb position 1, with the wrist at the neutral position, the elbow extended at 180°, and the shoulder abducted at 60°. In addition, the experiment assessed the differences among the wrist, forearm, elbow, and upper arm with Friedman's test and Bonferroni post hoc analysis. Two groups of limb positions were designed to explore the effects of shoulder movements (shoulder abducted at 90° and 120°) and wrist movements (wrist extended at 45° and flexed at 45°) on the thickness and Young's modulus. Differences among the distributions of five limb positions were tested as well. The ICC3, 1 values for thickness and Young's modulus were 0.976 and 0.996, respectively. There were differences among the MN thicknesses of four arm locations in limb position 1, while Young's modulus was higher at the elbow and wrist than at the forearm and upper arm. Compared to limb position 1, only limb position 4 had an effect on MN thickness at the wrist. Both shoulder and wrist motions affected MN Young's modulus, and the stiffness variations at typical locations all showed a downward trend proximally in all. The distributions of MN thickness and Young's modulus showed fold line patterns but differed at the wrist and the pronator teres. The MN in the wrist is more susceptible to limb positions, and Young's modulus is sensitive to nerve changes and is more promising for the early diagnosis of neuropathy.

Soft Actuator with Biomass Porous Electrode: A Strategy for Lowering Voltage and Enhancing Durability.

Electroactive artificial muscles with deformability have attracted widespread interest in the field of soft robotics. However, the design of artificial muscles with low-driven voltage and operational durability remains challenging. Herein, novel biomass porous carbon (BPC) electrodes are proposed. The nanoporous BPC enables the electrode to provide exposed active surfaces for charge transfer and unimpeded channels for ion migration, thus decreasing the driving voltage, enhancing time durability, and maintaining the actuation performances simultaneously. The proposed actuator exhibits a high displacement of 13.6 mm (bending strain of 0.54%) under 0.5 V and long-term durability of 99.3% retention after 550,000 cycles (∼13 days) without breaks. Further, the actuators are integrated to perform soft touch on a smartphone and demonstrated as bioinspired robots, including a bionic butterfly and a crawling robot (moving speed = 0.08 BL s-1). This strategy provides new insight into the design and fabrication of high-performance electroactive soft actuators with great application potential.

An Improved Extreme Learning Machine (ELM) Algorithm for Intent Recognition of Transfemoral Amputees With Powered Knee Prosthesis.

To overcome the challenges posed by the complex structure and large parameter requirements of existing classification models, the authors propose an improved extreme learning machine (ELM) classifier for human locomotion intent recognition in this study, resulting in enhanced classification accuracy. The structure of the ELM algorithm is enhanced using the logistic regression (LR) algorithm, significantly reducing the number of hidden layer nodes. Hence, this algorithm can be adopted for real-time human locomotion intent recognition on portable devices with only 234 parameters to store. Additionally, a hybrid grey wolf optimization and slime mould algorithm (GWO-SMA) is proposed to optimize the hidden layer bias of the improved ELM classifier. Numerical results demonstrate that the proposed model successfully recognizes nine daily motion modes including low-, mid-, and fast-speed level ground walking, ramp ascent/descent, sit/stand, and stair ascent/descent. Specifically, it achieves 96.75% accuracy with 5-fold cross-validation while maintaining a real-time prediction time of only 2 ms. These promising findings highlight the potential of onboard real-time recognition of continuous locomotion modes based on our model for the high-level control of powered knee prostheses.

Multi-Level Structural Enhancement Mechanism of the Excellent Mechanical Properties of Dung Beetle Leg Joint.

The multi-level structure is a strategy to enhance the mechanical properties of dung beetle leg joints. Under external loads, the microstructure facilitates energy dissipation and prevents crack extension. The macrostructure aids in transferring the load to more reliable parts. The connection established by the two hemispheres is present in the dung beetle leg joint. The micron-layered and nanoscale crystal structures further constitute the leg joint with excellent mechanical properties. The maximum compression fracture force is ≈101000 times the weight of the leg. Here, the structural design within the dung beetle leg joints and reveal the resulting mechanical response and enhancement mechanisms is determined. A series of beetle leg joints where the macrostructure and microstructure of the dung beetle leg provide mechanical strength at critical strains while avoiding catastrophic failure by transferring the load from the joint to the exoskeleton of the femur is highlighted. Nanocrystalline structures and fiber layers contribute to crack propagation of the exoskeleton. Based on this, the bionic joint with multi-level structures using resin and conducted a series of tests to verify their effectiveness is prepared. This study provides a new idea for designing and optimizing high-load joints in engineering.

Flexible Multimodal Sensing System Based on a Vertical Stacking Strategy for Efficiently Decoupling Multiple Signals.

Multisensory integration enables the simultaneous perception of multiple environmental stimuli while minimizing size and energy consumption. However, conventional multifunctional integration in flexible electronics typically requires large-scale horizontal sensing arrays (such as flexible printed circuit boards), posing decoupling complexities, tensile strain limitation, and spatial constraints. Herein, a fully flexible multimodal sensing system (FMSS) is developed by coupling biomimetic stretchable conductive films (BSCFs) and strain-insensitive communication interfaces using a vertical stacking integration strategy. The FMSS achieves vertical integration without additional adhesives, and it can incorporate individual sensing layers and stretchable interconnects without any essential constraint on their deformations. Accordingly, the temperature and pressure are precisely decoupled simultaneously, and tensile stress can be accurately discerned in different directions. This vertical stacking integration strategy is expected to offer a new approach to significantly streamline the design and fabrication of multimodal sensing systems and enhance their decoupling capabilities.

Bio-Inspired Interlocking Structures for Enhancing Flexible Coatings Adhesion.

The flexible protective coatings and substrates frequently exhibit unstable bonding in industrial applications. For strong interfacial adhesion of heterogeneous materials and long-lasting adhesion of flexible protective coatings even in harsh corrosive environments. Inspired by the interdigitated structures in Phloeodes diabolicus elytra, a straightforward magnetic molding technique is employed to create an interlocking microarray for reinforced heterogeneous assembly. Benefiting from this bio-inspired microarrays, the interlocking polydimethylsiloxane (PDMS) coating recorded a 270% improvement in tensile adhesion and a 520% increase in shear resistance, approaching the tensile limitation of PDMS. The elastic polyurethane-polyamide (PUPI) coating equipped with interlocking structures demonstrated a robust adhesion strength exceeding 10.8 MPa and is nearly unaffected by the corrosion immersion. In sharp contrast, its unmodified counterpart exhibited low initial adhesion and maintain ≈20% of its adhesion strength after 30 d of immersion. PUPI coating integrated with microarrays exhibits superior resistance to corrosion (30 d, |Z|0.01HZ ≈1010  Ω cm2 , Rct ≈108  Ω cm2 ), cavitation and long-term adhesion retention. These interlocking designs can also be adapted to curved surfaces by 3D printing and enhances heterogeneous assembly of non-bonded materials like polyvinylidene fluoride (PTFE) and PDMS. This bio-inspired interlocking structures offers a solution for durably bonding incompatible interfaces across varied engineering applications.

Novel-Ink-Based Direct Ink Writing of Ti6Al4V Scaffolds with Sub-300 µm Structural Pores for Superior Cell Proliferation and Differentiation.

Ti6Al4V scaffolds with pore sizes between 300 and 600 µm are deemed suitable for bone tissue engineering. However, a significant proportion of human bone pores are smaller than 300 µm, playing a crucial role in cell proliferation, differentiation, and bone regeneration. Ti6Al4V scaffolds with these small-sized pores are not successfully fabricated, and their cytocompatibility remains unknown. The study presents a novel ink formula specifically tailored for fabricating Ti6Al4V scaffolds featuring precise and unobstructed sub-300 µm structural pores, achieved by investigating the rheological properties and printability of five inks containing 60-77.5 vol% Ti6Al4V powders and bisolvent binders. Ti6Al4V scaffolds with 50-600 µm pores are fabricated via direct ink writing and subjected to in vitro assays with MC3T3-E1 and bone marrow mesenchymal stem cells. The 100 µm pore-sized scaffolds exhibit the highest cell adhesion and proliferation capacity based on live/dead assay, FITC-phalloidin/4',6-diamidino-2-phenylindole staining, and cell count kit 8 assay. The alizarin red staining, real-time quantitative PCR assay, and immunocytochemical staining demonstrate the superior osteogenic differentiation potential of 100 and 200 µm pore-sized scaffolds. The importance of sub-300 µm structrual pores is highlighted, redefining the optimal pore size for Ti6Al4V scaffolds and advancing bone tissue engineering and clinical medicine development.

Underwater Bionic Self-Healing Superhydrophobic Coating with the Synergetic Effect Of Hydrogen Bonds and Self-Formed Bubbles.

The self-healing ability of superhydrophobic surfaces in air has attracted tremendous additions in recent years. Once the superhydrophobic surface is damaged underwater, water seeps into gaps among micro/nano structures. The air film diffuses into water and eventually disappears during immersion without actively replenishing the gas, which results in the impossible of self-healing. Here, an underwater self-healing superhydrophobic coating with the synergetic effect of hydrogen bonds and self-formed bubbles via the spraying method is fabricated. The movement of hydrogen bonds of the prepared polyurethane enables microstructures to reconstruct at room temperature and self-formed bubbles of effervescent materials underwater actively replenish gas before microstructures completely self-healing, achieving the self-healing property of the superhydrophobic coating. Moreover, the hydrophilic effervescent material is sprayed along with unmodified micron-scaled particles because modified nano-scale particles are key factors for the realization of superhydrophobic coating. An underwater stable superhydrophobic surface with pressure resistance (4.9 kPa) is demonstrated. This superhydrophobic coating also shows excellent drag reduction, anti-icing, and anti-corrosion properties. This facile and scalable method offers a new route that an underwater self-healing superhydrophobic coating executes the gas film recovery.

High-Fidelity, Low-Hysteresis Bionic Flexible Strain Sensors for Soft Machines.

Stretchable flexible strain sensors based on conductive elastomers are rapidly emerging as a highly promising candidate for popular wearable flexible electronic and soft-mechanical sensing devices. However, due to the intrinsic limitations of low fidelity and high hysteresis, existing flexible strain sensors are unable to exploit their full application potential. Herein, a design strategy for a successive three-dimensional crack conductive network is proposed to cope with the uncoordinated variation of the output resistance signal arising from the conductive elastomer. The electrical characteristics of the sensor are dominated by the successive crack conductive network through a greater resistance variation and a concise sensing mechanism. As a result, the developed elastomer bionic strain sensors exhibit excellent sensing performance in terms of a smaller overshoot response, a lower hysteresis (∼2.9%), and an ultralow detection limit (0.00179%). What's more, the proposed strategy is universal and applicable to many conductive elastomers with different conductive fillers (including 0-D, 1-D, and 2-D conductive fillers). This approach improves the sensing signal accuracy and reliability of conductive elastomer strain sensors and holds promising potential for various applications in the fields of e-skin and soft robotic systems.

Study on Osseointegration Capability of ß-Type Ti-Nb-Zr-Ta-Si Alloy for Orthopedic Implants.

Osseointegration is the basic condition for orthopedic implants to maintain long-term stability. In order to achieve osseointegration, a low elastic modulus is the most important performance indicator. It is difficult for traditional titanium alloys to meet this requirement. A novel ß-titanium alloy (Ti-35Nb-7Zr-5Ta)98Si2 was designed, which had excellent strength (a yield strength of 1296 MPa and a breaking strength 3263 MPa), an extremely low elastic modulus (37 GPa), and did not contain toxic elements. In previous in vitro studies, we confirmed the good biocompatibility of this alloy and similar bioactivity to Ti-6Al-4V, but no in vivo study was performed. In this study, Ti-6Al-4V and (Ti-35Nb-7Zr-5Ta)98Si2 were implanted into rabbit femurs. Imaging evaluation and histological morphology were performed, and the bonding strength and bone contact ratio of the two alloys were measured and compared. The results showed that both alloys remained in their original positions 3 months after implantation, and neither imaging nor histological observations found inflammatory reactions in the surrounding bone. The bone-implant contact ratio and bonding strength of (Ti-35Nb-7Zr-5Ta)98Si2 were significantly higher than those of Ti-6Al-4V. The results confirmed that (Ti-35Nb-7Zr-5Ta)98Si2 has a better osseointegration ability than Ti-6Al-4V and is a promising material for orthopedic implants.

Bioinspired Structural Composite Flexible Material with High Cushion Performance.

Impacts occur everywhere, and they pose a serious threat to human health and production safety. Flexible materials with efficient cushioning and energy absorption are ideal candidates to provide protection from impacts. Despite the high demand, the cushioning capacity of protective materials is still limited. In this study, an integrated bionic strategy is proposed, and a bioinspired structural composite material with highly cushioning performance is developed on the basis of this strategy. The results demonstrated that the integrated bionic material, an S-spider web-foam, has excellent energy storage and dissipation as well as cushioning performance. Under impact loading, S-spider web-foam can reduce peak impact forces by a factor of 3.5 times better than silicone foam, achieving unprecedented cushioning performance. The results of this study deepen the understanding of flexible cushioning materials and may provide new strategies and inspiration for the preparation of high-performance flexible cushioning materials.

Effect of Strontium-Substituted Calcium Phosphate Coatings Prepared by One-Step Electrodeposition at Different Temperatures on Corrosion Resistance and Biocompatibility of AZ31 Magnesium Alloys.

As potential degradable biomaterials, magnesium (Mg) alloys have development prospects in the field of orthopedic load-bearing, whereas the clinical application has encountered a bottleneck due to a series of problems caused by its rapid corrosion. In this study, strontium-substituted calcium phosphate (CaP) coatings with different structures were prepared on the surface of the Mg matrix by a simple one-step electrodeposition method at different temperatures, which enhanced the poor corrosion resistance of the Mg matrix. The coated sample prepared at 65 °C reduced the corrosion current density by 3 orders of magnitude and increased the impedance by nearly 2 orders of magnitude compared with bare Mg alloy, thanks to its dense fibrous structure similar to that of natural bones. Although the coating composition varies with different preparation temperatures, CaP, as an inorganic component similar to natural bone, has good cytocompatibility. Doping the right amount of strontium, which is a trace element in human bones, is beneficial to stimulate osteoblast differentiation, inhibit the activity of osteoclasts, and induce the formation of bone tissues. This provides a new option for modifying the Mg alloy with CaP coatings as a base.

Bio-inspired copper ion-chelated chitosan coating modified UHMWPE fibers for enhanced interfacial properties of composites.

Ultra-high molecular weight polyethylene (UHMWPE) fibers are broadly applied in lightweight and high-strength composite fiber materials. However, the development of UHMWPE fibers is limited by their smooth and chemically inert surfaces. To address the issues, a modified UHMWPE fibers material has been fabricated through the chelation reaction between Cu2+ and chitosan coatings within the surface of fibers after plasma treatment, which is inspired by the hardening mechanism, a crosslinked network between metal ions and proteins/polysaccharides of the tips and edges in arthropod-specific cuticular tools. The coatings improve the surface wettability and interfacial bonding ability, which are beneficial in extending the application range of UHMWPE fibers. More importantly, compared to the unmodified UHMWPE fiber cloths, the tensile property of the modified fiber cloths is increased by 18.89% without damaging the strength, which is infrequent in modified UHMWPE fibers. Furthermore, the interlaminar shear strength and fracture toughness of the modified fibers laminate are increased by 37.72% and 135.90%, respectively. These improvements can be attributed to the synergistic effects between the surface activity and the tiny bumps of the modified UHMWPE fibers. Hence, this work provides a more straightforward and less damaging idea of fiber modification for manufacturing desirable protective and medical materials.

A Selective-Response Hypersensitive Bio-Inspired Strain Sensor Enabled by Hysteresis Effect and Parallel Through-Slits Structures.

Flexible strain sensors are promising in sensing minuscule mechanical signals, and thereby widely used in various advanced fields. However, the effective integration of hypersensitivity and highly selective response into one flexible strain sensor remains a huge challenge. Herein, inspired by the hysteresis strategy of the scorpion slit receptor, a bio-inspired flexible strain sensor (BFSS) with parallel through-slit arrays is designed and fabricated. Specifically, BFSS consists of conductive monolayer graphene and viscoelastic styrene-isoprene-styrene block copolymer. Under the synergistic effect of the bio-inspired slit structures and flexible viscoelastic materials, BFSS can achieve both hypersensitivity and highly selective frequency response. Remarkably, the BFSS exhibits a high gage factor of 657.36, and a precise identification of vibration frequencies at a resolution of 0.2 Hz through undergoing different morphological changes to high-frequency vibration and low-frequency vibration. Moreover, the BFSS possesses a wide frequency detection range (103 Hz) and stable durability (1000 cycles). It can sense and recognize vibration signals with different characteristics, including the frequency, amplitude, and waveform. This work, which turns the hysteresis effect into a "treasure," can provide new design ideas for sensors for potential applications including human-computer interaction and health monitoring of mechanical equipment.

Adhesion Behavior in Fish: From Structures to Applications.

In nature, some fish can adhere tightly to the surface of stones, aquatic plants, and even other fish bodies. This adhesion behavior allows these fish to fix, eat, hide, and migrate in complex and variable aquatic environments. The adhesion function is realized by the special mouth and sucker tissue of fish. Inspired by adhesion fish, extensive research has recently been carried out. Therefore, this paper presents a brief overview to better explore underwater adhesion mechanisms and provide bionic applications. Firstly, the adhesion organs and structures of biological prototypes (e.g., clingfish, remora, Garra, suckermouth catfish, hill stream loach, and goby) are presented separately, and the underwater adhesion mechanisms are analyzed. Then, based on bionics, it is explained that the adhesion structures and components are designed and created for applications (e.g., flexible gripping adhesive discs and adhesive motion devices). Furthermore, we offer our perspectives on the limitations and future directions.

Effects of extreme cyclic loading on the cushioning performance of human heel pads under engineering test condition.

Human heel pads commonly undergo cyclic loading during daily activities. Low cyclic loadings such as daily human walking tend to have less effect on the mechanical properties of heel pads. However, the impact of cyclic loading on cushion performance, a vital biomechanical property of heel pads, under engineering test condition remains unexplored. Herein, dynamic mechanical measurements and finite element (FE) simulations were employed to explore this phenomenon. It was found that the wavy collagen fibers in the heel pad will be straightened under cycle compression loading, which resulted in increased stiffness of the heel pad. The stiffness of the heel pads demonstrated an inclination to escalate over a span of 50,000 loading cycles, consequently resulting in a corresponding increase in peak impact force over the same loading cycles. Sustained cyclic loading has the potential to result in the fracturing of the straightened collagen fibers, this collagen breakage may diminish the stiffness of the heel pad, leading to a reduction in peak impact force. This work enhances understanding of the biomechanical functions of human heel pad and may provide potential inspirations for the innovative development of healthcare devices for foot complex.

Golden section criterion to achieve droplet trampoline effect on metal-based superhydrophobic surface.

Clarifying the consecutive droplet rebound mechanisms can provide scientific inspirations to regulate dynamic wettability of superhydrophobic surface, which facilitates the practical applications on efficient heat control and active anti-icing. Generally, droplet rebound behaviors are directly affected by surface structure and Weber number. Here, we report a novel "golden section" design criterion to regulate the droplet rebound number determined by the structure spacing, subverting conventional knowledge. Especially, the droplet can continuously rebound for 17 times on the metal-based surface, exhibiting an amazing phenomenon of "droplet trampoline". The droplet rebound number has been experimentally revealed to be closely related to Weber number. We propose novel quantitative formulas to predict droplet rebound number and clarify the coupling effect of the structure spacing and the Weber number on the rebound mechanisms, which can be utilized to establish the regulation criteria of rebound numbers and develop novel metal-based superhydrophobic materials.