Biomimetic Surface Research Articles

Effect of Material Selection and Surface Texture on Tribological Properties of Key Friction Pairs in Water Hydraulic Axial Piston Pumps: A Review

A water hydraulic axial piston pump has become the preferred power component of environmentally friendly water hydraulic transmission systems, due to its advantages of a compact structure, high power density, and so on. The poor friction and wear performance in the water medium, especially under extreme conditions of high speed and high pressure, limit the engineering application of the water hydraulic axial piston pump. In this review, the research progress for key friction pair materials (such as special corrosion-resistant alloys, engineering plastics, and engineering ceramics) for water hydraulic axial piston pumps is, firstly, summarized. Secondly, inspired by nature, the processing methods, lubrication drag-reduction mechanism, and tribological properties of the biomimetic surface textures are discussed. The effects of the surface texture shape, equivalent diameter, depth, and arrangement on the pump’s tribological properties are reviewed in detail. Finally, the application status of, and problems with, surface texture technology in water hydraulic axial piston pumps are summarized. It is suggested that future studies should focus on the multi-field coupling lubrication anti-friction mechanism of the multi-type composite texture under extreme conditions and mixed lubrication; and the anti-wear performance of the texture coupled with a coating modification, to further promote the surface texture in the field of lubrication antifriction engineering applications.

Biomimetic super slippery surface with excellent and durable anti-icing property for immovable heritage conservation

The formation and accumulation of ice on solid surface is not only a potential threat to our daily life, but also a hazard to cultural heritages, such as murals, grottoes, monuments, ancient buildings. Inspired by slippery inner surface of Nepenthes, slippery liquid-infused porous surfaces (SLIPSs) for anti-icing attract a lot of attention recently. In this work, dip-coating approach is utilized to create a hydrophobic silica layer grafted with long-chain organic molecules. After infusing the oil phase, a three-layer Nepenthes-like structure is formed. The SLIPS shows excellent anti-icing property. It reduces the ice-surface adhesion strength to 0 kPa on non-porous surface and 6.83 kPa on porous surface (sandstone from Yungang Grottoes) respectively. After 35 icing/de-icing cycles, the SLIPS still shows good anti-icing ability. Our results show that the middle long-chain organic layer not only enhances the surface hydrophobicity but also increases its affinity with the oil phase to reduce lubricating oil loss, thus increasing its anti-icing durability. When the anti-icing ability decreases with time, simple re-infusing the oil phase can easily restore the anti-icing performance to its original level. The SLIPSs prepared in this work show outstanding hydrophobicity, ice repellency, durability and satisfying water vapor permeability on treated porous sandstones, which makes it potential to protect immovable cultural heritages from ice hazard.

Tribological Properties of Bi2S3/MoS2 Composite Coatings Deposited on Biomimetic Leaf Vein Textured Surfaces

Tribological Properties of Bi2S3/MoS2 Composite Coatings Deposited on Biomimetic Leaf Vein Textured Surfaces

Effect of the Mechanical Properties of Soft Counter-Faces on the Adhesive Capacity of Mushroom-Shaped Biomimetic Microstructures.

The effects of mechanical properties and contact environment conditions on the adhesiveness of the biomimetic adhesive mushroom-shaped micro-structure have been experimentally investigated. The idea is based on the adhesive micro-structures and surfaces inspired by nature after observing the abilities of some animals. Applications are proposed in various fields of engineering and technology. However, to enable unconventional uses of these biomimetic adhesion surfaces, such as in the biomedical field, it is necessary to adjust and optimize their tribological properties (friction, adhesion, and peeling strength) in contact with soft substrates that can simulate the mechanical features of biological tissues. Our work explores the effect of the combinations of the various parameters on the strength of adhesion. Under dry contact conditions, soft counter-faces lead to lower adhesion than hard counter-faces, whereas under wet conditions, soft counter-faces lead to higher adhesion than harder counter-faces.

Biomimetic surfaces with patterned wettability for high-efficiency dehumidification and fog harvesting

In this paper, by studying the characteristics of the bionic surface with pattern wettability, the process of its efficient dehumidification and atomization is explored. This paper briefly introduces the importance of dehumidification and physicochemical and the market demand, and also introduces the properties of superhydrophobic materials. The theoretical part mainly describes the basic principle of superhydrophobicity and the Wenzel and Cassie-Baxter models. Subsequently, natural and synthetic superhydrophobic surfaces are introduced, involving Namib beetles, butterfly wings, and so on. The final article points out that superhydrophobic surfaces can be used in numerous fields, especially in fog collection. However, the improvement of durability is the focus of attention for superhydrophobic surfaces. In future research, attention needs to be paid to the use of materials and the efficiency of fog collection.

Natural and biomimetic superhydrophobic surface: Review of the manufacturing techniques

Nature has produced many materials, things, and processes at all scales, from the large to the tiny. The newly growing area of biomimicry enables the development of materials, tools, and techniques with desired features by mimicking biology or nature. Consequently, the traits of animals, plants, and insects in nature have drawn much attention. Because of its surface roughness and epicuticular waxes, the lotus leaf, for instance, has a superhydrophobic surface. These surfaces feature a water-repellent effect and high and low-contact angle hysteresis. This essay briefly introduces the theoretical wetting process before describing some of the traits of several naturally occurring species. Next, a thorough analysis of artificial superhydrophobic surfaces made in the last five years utilizing the most popular fabrication methods is provided.

Biomimetic surface engineering for sustainable water harvesting systems

Biomimetic surface engineering for sustainable water harvesting systems

Layer-by-layer-assembled biomimetic microstructure surface with multiple synergistic antifouling performance

With the ecological crisis and serious problems of marine biofouling, the bionic antifouling strategy of natural organisms is explored for the construction of antifouling coating and replacement of the traditional toxic antifouling coating. In this work, inspired by Laminaria japonica's ability to inhibit marine fouling by the combination with physical micromorphology, chemical composition and bioactive substances, a novel PDMS-based antifouling coating with multiple synergistic antifouling properties is fabricated by layer by layer (LbL) self-assembly method. Firstly, the natural active substance (capsaicin) is introduced into the nanocapsule by the microemulsion method (CAP@CS). Subsequently, the nanocapsules are stably deposited on PDMS surface modified by the guanidine-hexamethylenediamine-PEI / sodium alginate (GHPEI/ALG)*n films through LbL assembly method to prepare the (GHPEI/ALG-CAP@CS-x)*n films with multiple antifouling properties. Our study indicates that this biomimetic surface has excellent antifouling ability against bacteria (99.2 ± 0.6 %) and diatoms (0.08 ± 0.05 %), which proves the great potential applications of this synergistic antifouling strategy demonstrated in marine engineering in the future.

3D-printing-assisted fabrication of hierarchically structured biomimetic surfaces with dual-wettability for water harvesting

Freshwater acquisition methods under various environments are required because water scarcity has intensified worldwide. Furthermore, as water is an essential resource for humans, a freshwater acquisition method that can be utilized even under harsh conditions, such as waterless and polluted water environments, is highly required. In this study, a three-dimensional (3D) printing-assisted hierarchically structured surface with dual-wettability (i.e., surface with both hydrophobic and hydrophilic region) for fog harvesting was developed by mimicking the biological features (i.e., cactus spines and elytra of Namib Desert beetles) that have effective characteristics for fog harvesting. The cactus-shaped surface exhibited self-transportation ability of water droplet, derived from the Laplace pressure gradient. Additionally, microgrooved patterns of the cactus spines were implemented using the staircase effect of 3D printing. Moreover, a partial metal deposition method using wax-based masking was introduced to realize the dual wettability of the elytra of the Namib Desert beetle. Consequently, the proposed surface exhibited the best performance (average weight of 7.85 g for 10 min) for fog harvesting, which was enhanced by the synergetic effect between the Laplace pressure gradient and surface energy gradient. These results support a novel freshwater production system that can be utilized even in harsh conditions, such as waterless and polluted water environments.

Outcomes of 2-Level Versus 3- or 4-Level Anterior Cervical Discectomy and Fusion Using a Biomimetic Surface Titanium Cage: Multicenter Experience

Interbody cages for spinal fusions are primarily constructed from polyetheretherketone or titanium compositions. However, these crude macroscopic materials pose limitations for improving the rates of bony fusions. The authors aimed to compare the fusion rates and postoperative complications in patients who underwent 2-level or 3-or 4-level anterior cervical discectomy and fusion (ACDF) performed with the use of a novel biomimetic surface titanium cage. A retrospective, multicenter study was conducted that included all patients who underwent multilevel ACDF with this cage between January 2017 and April 2021. Patient demographics and procedure-related, radiographic, and postoperative complication data were collected. A total of 124 patients were identified; 69 (55.6%) had a 3-or 4-level fusion and 55 (44.4%) had a 2-level fusion. The demographics of the two groups differed significantly only in terms of age (p=.01). At 3 months, a significantly higher solid fusion rate was found for 2-level fusions than 3-or 4-level fusions (83.7% vs. 56.3%, p=.004); however, significance was lost at 6-months (98.2% vs. 88.4%, respectively; p=.08). No patients required posterior supplemental fixation. Transient dysphagia was the only postoperative complication that was significantly increased in the 3-or 4-level fusion group compared to the 2-level group (27.5% vs. 9.1%, p=.02). Radiographic and clinical outcomes were equivalent in 3-or 4-level and 2-level ACDFs in which these biomimetic surface titanium cages were used. Furthermore, the use of this technology led to high fusion rates with no requirement for posterior supplemental fusions.

Cortical facilitation of tactile afferents during the preparation of a body weight transfer when standing on a biomimetic surface.

Self-generated movement shapes tactile perception, but few studies have investigated the brain mechanisms involved in the processing of the mechanical signals related to the static and transient skin deformations generated by forces and pressures exerted between the foot skin and the standing surface. We recently found that standing on a biomimetic surface (i.e., inspired by the characteristics of mechanoreceptors and skin dermatoglyphics), that magnified skin-surface interaction, increased the sensory flow to the somatosensory cortex and improved balance control compared to standing on control (e.g., smooth) surfaces. In this study, we tested whether the well-known sensory suppression that occurs during movements is alleviated when the tactile afferent signal becomes relevant with the use of a biomimetic surface. Eyes-closed participants (n = 25) self-stimulated their foot cutaneous receptors by shifting their body weight toward one of their legs while standing on either a biomimetic or a control (smooth) surface. In a control task, similar forces were exerted on the surfaces (i.e., similar skin-surface interaction) by passive translations of the surfaces. Sensory gating was assessed by measuring the amplitude of the somatosensory-evoked potential over the vertex (SEP, recorded by EEG). Significantly larger and shorter SEPs were found when participants stood on the biomimetic surface. This was observed whether the forces exerted on the surface were self-generated or passively generated. Contrary to our prediction, we found that the sensory attenuation related to the self-generated movement did not significantly differ between the biomimetic and control surfaces. However, we observed an increase in gamma activity (30-50 Hz) over centroparietal regions during the preparation phase of the weight shift only when participants stood on the biomimetic surface. This result might suggest that gamma-band oscillations play an important functional role in processing behaviorally relevant stimuli during the early stages of body weight transfer.

RGD and rhBMP-7 immobilized on zirconia scaffold with interweaved human dental pulp stem cells for promoting bone regeneration

Biomimetic surface modification of scaffolds with osteoinductive molecules is a promising strategy for improving the bioactivity of scaffold and stimulating stem cell signals in bone tissue engineering. Zirconia (ZrO2) offers excellent mechanical properties and biocompatibility, but its bio-inert nature hinders its use in bone regeneration applications. Recombinant human bone morphogenetic protein 7 (rhBMP-7) and arginine-glycine-aspartate (RGD) peptide were investigated for their potential use as surface-modifying biomolecules on the ZrO2 scaffold. Our results showed that human dental pulp stem cells (hDPSCs) were induced to osteogenic differentiation by rhBMP-7 and RGD in a dose-dependent manner. Significantly enhanced alkaline phosphatase activity and up-regulated expression of osteogenic genes in hDPSCs were associated with rhBMP-7 and RGD grafting onto the ZrO2 scaffold. Western blot analysis revealed that rhBMP-7 and RGD grafting led to activation of the SMAD1/5, p38 MARK, and ERK signaling pathways during hDPSCs differentiation. After 4 and 8 weeks of transplantation, the hDPSCs-seeded ZrO2-RGD-BMP-7 scaffold facilitated osteogenic differentiation and enhanced in vivo bone formation in critical-sized calvarial bone defects. The results support the simultaneous use of rhBMP-7 and RGD as surface-modifying biomolecules and hDPSCs as a source of osteogenic stem cells in conjugation with ZrO2-based porous scaffold for bone tissue engineering.

Large-area preparation strategy and anti-erosion mechanism for morphology-material coupled biomimetic anti-erosion functional surface

A novel morphology-material coupled biomimetic anti-erosion surface was presented in this paper. The coupled biomimetic principle was utilized to design a biomimetic model inspired by the anti-erosion characteristics of Parabuthus transvaalicus and Tamarisk. Furthermore, a large-area preparation technology was developed based on the specific engineering requirements, enabling the accurate preparation of the morphology-material coupled biomimetic anti-erosion functional surface. The results of the sandblasting experiment demonstrated that the morphology-material coupled biomimetic anti-erosion functional surface enhanced the anti-erosion performance from various impact angles due to the synergistic effect of biomimetic surface morphology and multilayer material in different stages.

Biomimetic surfaces: Insights on the role of surface topography and wetting properties in bacterial attachment and biofilm formation

The study explores the impact of biomimetic surfaces on bacterial attachment and biofilm formation. Specifically, it investigates the effects of topographic scale and wetting behavior on the attachment and growth of Staphylococcus aureus and Escherichia coli on four different biomimetic surfaces: rose petals, Paragrass leaves, shark skin, and goose feathers. Using soft lithography, epoxy replicas with surface topographies similar to those of the natural surfaces were created. The static water contact angles of the replicas exceeded the hydrophobic threshold of 90°, while the hysteresis angles were found to be in the order of goose feathers, shark skin, Paragrass leaves, and rose petals. The results showed that bacterial attachment and biofilm formation were the lowest on rose petals and the highest on goose feathers, regardless of the bacterial strain. Additionally, the study revealed that surface topography had a significant impact on biofilm formation, with smaller feature sizes inhibiting biofilm formation. Hysteresis angle, rather than static water contact angle, was identified as a critical factor to consider when evaluating bacterial attachment behavior. These unique insights have the potential to lead to the development of more effective biomimetic surfaces for the prevention and eradication of biofilms, ultimately improving human health and safety.

Biomimetic high water adhesion superhydrophobic surface via UV nanoimprint lithography

Imitating nature and comprehending its workings is a means for human beings to advance the development of functional materials. In this study, UV nanoimprint lithography technology was utilized to successfully replicate the micro-nano hierarchical structure (micro-papillae and nano-wax tube crystals) present on the surface of the natural fresh lotus leaf. A series of UV-curable waterborne polyurethane acrylate (UV-WPUA) surfaces with special wetting and superhydrophobic properties were obtained. The polydimethylsiloxane negative stamp with lotus leaf’s structure was obtained through a stamp replica molding method, and then the UV-WPUA resin covered with the negative stamp was exposed to 172 nm Xe2* excimer and medium-pressure mercury lamps to mimic the micro-nano hierarchical structure of the lotus leaf. The UV-WPUA surfaces displayed high water adhesion superhydrophobic properties, with a water contact angle reaching 160.8° and water adhesive force of 140.0 μN, and exhibiting excellent self-cleaning performance. The results indicate that higher the UV intensity, the more accurately the surface replicates the micro-nano hierarchical structure of the lotus leaf, resulting in larger water contact angle and higher adhesive force. This study paves the way for the advancement of functional surfaces through the simulation of natural materials.

Novel femur-like multimodal ultrahigh strength structure with superb freedom based on the improvement strategy of curvature fabricated by additive manufacturing

Based on the microstructure of biological femur, the femur-like multimodal surface structures are designed. But they exhibit fracture behavior when the porosity changes, resulting in structural failure. The high curvature surface factor is introduced to improve the fracture behavior of the biomimetic surface structure. Combine the high curvature surface factor to construct novel biomimetic homogenized surface structures. Novel radial gradient surface structures and axial gradient surface structures are designed based on the construction concept of cone functions and linear functions gradients. Theoretical, experimental and numerical methods are used to investigate the mechanical properties of novel biomimetic multimodal surface structures. Euler theory states that the properties of lattice structures are determined by the relative density of structures. The load distribution in the radially gradient structure is uniform, and the deformation mode presents overall failure, which can achieve better resistance and dissipation of the load. The deformation modes of axial gradient structures present layered failure. The underlying mechanism of the difference in mechanical properties of biomimetic multimodal structures is explained in detail. It’s very important significance for targeted application in protective engineering.

Biomimetic catheter surface with dual action NO-releasing and generating properties for enhanced antimicrobial efficacy.

Infection of indwelling catheters is a common healthcare problem, resulting in higher morbidity and mortality. The vulnerable population reliant on catheters post-surgery for food and fluid intake, blood transfusion, or urinary incontinence or retention is susceptible to hospital-acquired infection originating from the very catheter. Bacterial adhesion on catheters can take place during the insertion or over time when catheters are used for an extended period. Nitric oxide-releasing materials have shown promise in exhibiting antibacterial properties without the risk of antibacterial resistance which can be an issue with conventional antibiotics. In this study, 1, 5, and 10 wt % selenium (Se) and 10 wt % S-nitrosoglutathione (GSNO)-incorporated catheters were prepared through a layer-by-layer dip-coating method to demonstrate NO-releasing and NO-generating capability of the catheters. The presence of Se on the catheter interface resulted in a 5 times higher NO flux in 10% Se-GSNO catheter through catalytic NO generation. A physiological level of NO release was observed from 10% Se-GSNO catheters for 5 d, along with an enhanced NO generation via the catalytic activity as Se was able to increase NO availability. The catheters were also found to be compatible and stable when subjected to sterilization and storage, even at room temperature. Additionally, the catheters showed a 97.02% and 93.24% reduction in the adhesion of clinically relevant strains of Escherichia coli and Staphylococcus aureus, respectively. Cytocompatibility testing of the catheter with 3T3 mouse fibroblast cells supports the material's biocompatibility. These findings from the study establish the proposed catheter as a prospective antibacterial material that can be translated into a clinical setting to combat catheter-related infections.

Surface Functionalization of 4D Printed Substrates Using Polymeric and Metallic Wrinkles.

Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well.

Luminal Surface Plasma Treatment of Closed Cylindrical Microchannels: A Tool toward the Creation of On-Chip Vascular Endothelium.

On-chip vascular microfluidic models provide a great tool to study aspects of cardiovascular diseases in vitro. To produce such models, polydimethylsiloxane (PDMS) has been the most widely used material. For biological applications, its hydrophobic surface has to be modified. The major approach has been plasma-based surface oxidation, which has been very challenging in the case of channels enclosed within a microfluidic chip. The preparation of the chip combined a 3D-printed mold with soft lithography and commonly available materials. We have introduced the high-frequency low-pressure air-plasma surface modification of seamless channels enclosed within a PDMS microfluidic chip. The plasma treatment modified the luminal surface more uniformly than in previous works. Such a setup enabled a higher degree of design freedom and a possibility of rapid prototyping. Further, plasma treatment in combination with collagen IV coating created a biomimetic surface for efficient adhesion of vascular endothelial cells as well as promoted long-term cell culture stability under flow. The cells within the channels were highly viable and showed physiological behavior, confirming the benefit of the presented surface modification.

Polymer-induced adhesion of endothelial cells

The effects of neutral dextran concentration and molecular mass on the adhesion of endothelial cells (EC) to siliclad-covered glass surfaces were studied using interference reflection microscopy (IRM). Results indicate that close contact of the EC to the glass slides is markedly enhanced in the presence of 500 kDa dextran, with this increase reflected by both the speed of forming close contact as well as the size of the contact area. This increased adhesion is attributed to the reduction in surface concentrations of large polymers and, therefore, to the attractive forces caused by depletion interaction. Our findings suggest that depletion could play an important role in cell-cell or cell-surface interactions via accelerating and enhancing close contacts. This interaction should thus be considered in vivo and in vitro for specific potential applications, such as cell culture and cell adhesion to biomimetic surfaces. It should therefore be of particular interest in a wide range of biomedical applications.