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.

Effect of Reticulate Unit Spacing on Microstructure and Properties of Biomimetic 7075 Aluminum Alloy by Laser Cladding

In the context of energy conservation and emission reduction, more and more attention has been paid to the development of lightweight metal materials with both high strength and high toughness. Inspired by the non-smooth surface of natural organisms, a biomimetic surface with various spacing reticulate units of 7075 aluminum alloys was modified by laser cladding. The microstructure, microhardness and tensile properties of the various spacing units with CeO2-SiC-Ni60 were studied. The finer microstructure and the higher microhardness of various spacing units in comparison with that of 7075 aluminum alloys were obtained, no matter the strip-like treated region or the cross-junction region. Moreover, the best combination of strength and toughness of the biomimetic sample with 2.5 mm spacing reticulate unit was discussed. Finally, by combining the microstructure, XRD phase change, thermal gradient effect, thermal expansion coefficient difference and hard phase strengthening mechanism, it was concluded that the 2.5 mm spacing reticulate unit had the best ability to inhibit crack propagation, and the dispersive hard phases of Al₃Ni₂ and SiC played a major role in stress release of the matrix.

Biomimetic Nanopillar Silicon Surfaces Rupture Fungal Spores

The mechano-bactericidal action of nanostructured surfaces is well-documented; however, synthetic nanostructured surfaces have not yet been explored for their antifungal properties toward filamentous fungal species. In this study, we developed a biomimetic nanostructured surface inspired by dragonfly wings. A high-aspect-ratio nanopillar topography was created on silicon (nano-Si) surfaces using inductively coupled plasma reactive ion etching (ICP RIE). To mimic the superhydrophobic nature of insect wings, the nano-Si was further functionalised with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (PFTS). The viability of Aspergillus brasiliensis spores, in contact with either hydrophobic or hydrophilic nano-Si surfaces, was determined using a combination of standard microbiological assays, confocal laser scanning microscopy (CLSM), and focused ion beam scanning electron microscopy (FIB-SEM). Results indicated the breakdown of the fungal spore membrane upon contact with the hydrophilic nano-Si surfaces. By contrast, hydrophobised nano-Si surfaces prevented the initial attachment of the fungal conidia. Hydrophilic nano-Si surfaces exhibited both antifungal and fungicidal properties toward attached A. brasisiensis spores via a 4-fold reduction of attached spores and approximately 9-fold reduction of viable conidia from initial solution after 24 h compared to their planar Si counterparts. Thus, we reveal, for the first time, the physical rupturing of attaching fungal spores by biomimetic hydrophilic nanostructured surfaces.

Geometric Control of Cell Behavior by Biomolecule Nanodistribution

Many dynamic interactions within the cell microenvironment modulate cell behavior and cell fate. However, the pathways and mechanisms behind cell–cell or cell–extracellular matrix interactions remain understudied, as they occur at a nanoscale level. Recent progress in nanotechnology allows for mimicking of the microenvironment at nanoscale in vitro; electron-beam lithography (EBL) is currently the most promising technique. Although this nanopatterning technique can generate nanostructures of good quality and resolution, it has resulted, thus far, in the production of only simple shapes (e.g., rectangles) over a relatively small area (100 × 100 μm), leaving its potential in biological applications unfulfilled. Here, we used EBL for cell-interaction studies by coating cell-culture-relevant material with electron-conductive indium tin oxide, which formed nanopatterns of complex nanohexagonal structures over a large area (500 × 500 μm). We confirmed the potential of EBL for use in cell-interaction studies by analyzing specific cell responses toward differentially distributed nanohexagons spaced at 1000, 500, and 250 nm. We found that our optimized technique of EBL with HaloTags enabled the investigation of broad changes to a cell-culture-relevant surface and can provide an understanding of cellular signaling mechanisms at a single-molecule level.

Biomimetic Water-Repelling Surfaces with Robustly Flexible Structures

Biomimetic liquid-repelling surfaces have been the subject of considerable scientific research and technological application. To design such surfaces, a flexibility-based oscillation strategy has been shown to resolve the problem of liquid-surface positioning encountered by the previous, rigidity-based asymmetry strategy; however, its usage is limited by weak mechanical robustness and confined repellency enhancement. Here, we design a flexible surface comprising mesoscale heads and microscale spring sets, in analogy to the mushroomlike geometry discovered on springtail cuticles, and then realize this through three-dimensional projection microstereolithography. Such a surface exhibits strong mechanical robustness against ubiquitous normal and shear compression and even endures tribological friction. Simultaneously, the surface elevates water repellency for impacting droplets by enhancing impalement resistance and reducing contact time, partially reaching an improvement of ∼80% via structural tilting movements. This is the first demonstration of flexible interfacial structures to robustly endure tribological friction as well as to promote water repellency, approaching real-world applications of water repelling. Also, a flexibility gradient is created on the surface to directionally manipulate droplets, paving the way for droplet transport.

Mineralization of Titanium Surfaces: Biomimetic Implants

The surface modification by the formation of apatitic compounds, such as hydroxyapatite, improves biological fixation implants at an early stage after implantation. The structure, which is identical to mineral content of human bone, has the potential to be osteoinductive and/or osteoconductive materials. These calcium phosphates provoke the action of the cell signals that interact with the surface after implantation in order to quickly regenerate bone in contact with dental implants with mineral coating. A new generation of calcium phosphate coatings applied on the titanium surfaces of dental implants using laser, plasma-sprayed, laser-ablation, or electrochemical deposition processes produces that response. However, these modifications produce failures and bad responses in long-term behavior. Calcium phosphates films result in heterogeneous degradation due to the lack of crystallinity of the phosphates with a fast dissolution; conversely, the film presents cracks, which produce fractures in the coating. New thermochemical treatments have been developed to obtain biomimetic surfaces with calcium phosphate compounds that overcome the aforementioned problems. Among them, the chemical modification using biomineralization treatments has been extended to other materials, including composites, bioceramics, biopolymers, peptides, organic molecules, and other metallic materials, showing the potential for growing a calcium phosphate layer under biomimetic conditions.

Fabrication of High Aspect Ratio Micro-Structures with Superhydrophobic and Oleophobic Properties by Using Large-Area Roll-to-Plate Nanoimprint Lithography

Bio-inspired surfaces with superamphiphobic properties are well known as effective candidates for antifouling technology. However, the limitation of large-area mastering, patterning and pattern collapsing upon physical contact are the bottleneck for practical utilization in marine and medical applications. In this study, a roll-to-plate nanoimprint lithography (R2P NIL) process using Morphotonics’ automated Portis NIL600 tool was used to replicate high aspect ratio (5.0) micro-structures via reusable intermediate flexible stamps that were fabricated from silicon master molds. Two types of Morphotonics’ in-house UV-curable resins were used to replicate a micro-pillar (PIL) and circular rings with eight stripe supporters (C-RESS) micro-structure onto polycarbonate (PC) and polyethylene terephthalate (PET) foil substrates. The pattern quality and surface wettability was compared to a conventional polydimethylsiloxane (PDMS) soft lithography process. It was found that the heights of the R2P NIL replicated PIL and C-RESS patterns deviated less than 6% and 5% from the pattern design, respectively. Moreover, the surface wettability of the imprinted PIL and C-RESS patterns was found to be superhydro- and oleophobic and hydro- and oleophobic, respectively, with good robustness for the C-RESS micro-structure. Therefore, the R2P NIL process is expected to be a promising method to fabricate robust C-RESS micro-structures for large-scale anti-biofouling application.

Surface Design of Antifouling Vascular Constructs Bearing Biofunctional Peptides for Tissue Regeneration Applications

Antifouling polymer layers containing extracellular matrix-derived peptide motifs offer promising new options for biomimetic surface engineering. In this contribution, we report the design of antifouling vascular grafts bearing biofunctional peptide motifs for tissue regeneration applications based on hierarchical polymer brushes. Hierarchical diblock poly(methyl ether oligo(ethylene glycol) methacrylate-block-glycidyl methacrylate) brushes bearing azide groups (poly(MeOEGMA-block-GMA-N₃)) were grown by surface-initiated atom transfer radical polymerization (SI-ATRP) and functionalized with biomimetic RGD peptide sequences. Varying the conditions of copper-catalyzed alkyne-azide “click” reaction allowed for the immobilization of RGD peptides in a wide surface concentration range. The synthesized hierarchical polymer brushes bearing peptide motifs were characterized in detail using various surface sensitive physicochemical methods. The hierarchical brushes presenting the RGD sequences provided excellent cell adhesion properties and at the same time remained resistant to fouling from blood plasma. The synthesis of anti-fouling hierarchical brushes bearing 1.2 × 10³ nmol/cm² RGD biomimetic sequences has been adapted for the surface modification of commercially available grafts of woven polyethylene terephthalate (PET) fibers. The fiber mesh was endowed with polymerization initiator groups via aminolysis and acylation reactions optimized for the material. The obtained bioactive antifouling vascular grafts promoted the specific adhesion and growth of endothelial cells, thus providing a potential avenue for endothelialization of artificial conduits.

Biomimetic Functional Surfaces towards Bactericidal Soft Contact Lenses

The surface with high-aspect-ratio nanostructure is observed to possess the bactericidal properties, where the physical interaction between high-aspect-ratio nanostructure could exert sufficient pressure on the cell membrane eventually lead to cell lysis. Recent studies in the interaction mechanism and reverse engineering have transferred the bactericidal capability to artificial surface, but the biomimetic surfaces mimicking the topographical patterns on natural resources possess different geometrical parameters and surface properties. The review attempts to highlight the recent progress in bactericidal nanostructured surfaces to analyze the prominent influence factors and cell rupture mechanism. A holistic approach was utilized, integrating interaction mechanisms, material characterization, and fabrication techniques to establish inclusive insights into the topographical effect and mechano-bactericidal applications. The experimental work presented in the hydrogel material field provides support for the feasibility of potentially broadening applications in soft contact lenses.

Direct Experimental Evidence of Biomimetic Surfaces with Chemical Modifications Interfering with Adhesive Protein Adsorption

Current approaches to dealing with the worldwide problem of marine biofouling are to impart chemical functionality to the surface or utilize microtopography inspired by nature. Previous reports have shown that only introducing a single method may not resist adhesion of mussels or inhibit biofouling in static forms. While it is promising to integrate two methods to develop an effective antifouling strategy, related basic research is still lacking. Here, we have fabricated engineered shark skin surfaces with different feature heights and terminated with different chemical moieties. Atomic force microscopy (AFM) with a modified colloid probe technique and quartz crystal microbalance with a dissipation n (QCM-D) monitoring method have been introduced to directly determine the interactions between adhesive proteins and functionalized surfaces. Our results indicate that the adhesion strength of probe-surface decreases with increasing feature height, and it also decreases from bare Si surface to alkyl and hydroxyl modification, which is attributed to different contact area domains and interaction mechanisms. Combining biomimetic microtopography and surface chemistry, our study provides a new perspective for designing and developing underwater anti-fouling materials.

Tough Reversible Adhesion Properties of a Dry Self-Cleaning Biomimetic Surface

Geckos have one of the world's most efficient reversible adhesion systems. Even walking in dusty conditions, geckos can dislodge up to 80% of contaminants and recover their adhesion capability after walking as few as four steps. Thus far, artificial dry self-cleaning materials inspired by the geckos' hierarchical fibrillar structure have been only able to remove 55% of collected large particle contaminants with 30 steps. Challenges, including low mechanical strength, low stiffness, and short fatigue time keep these materials from being used in practical applications. This study involves the novel fabrication of dry self-cleaning surfaces with a high mechanical performance and an outstanding dry self-cleaning property. Imposing a load-drag-pull process similar to a gecko's foot adhesion process, our biomimetic surfaces could dislodge up to 59% of microparticles (∼8 μm) with as few as five steps. Furthermore, the surface had an excellent screening ability at low temperatures regardless of the surface roughness similarity. The surfaces were also proven to be scratch resistant. The biomimetic surfaces exhibit enhanced dry self-cleaning and mechanical properties and could be promising in applications such as reusable adhesives, biochips, aerospace satellite waste collection, and screening equipment.

Time-Dependent Liquid Transport on a Biomimetic Topological Surface

Liquid drops impacting on a solid surface is a familiar phenomenon. On rainy days, it is quite important for leaves to drain off impacting raindrops. Water can bounce off or flow down a water-repellent leaf easily, but with difficulty on a hydrophilic leaf. Here, we show an interesting phenomenon in which impacting drops on the hydrophilic pitcher rim of Nepenthes alata can spread outward to prohibit water filling the pitcher tank. We mimic the peristome surface through a designed 3D printing and replicating way and report a time-dependently switchable liquid transport based on biomimetic topological structures, where surface curvature can work synergistically with the surface microtextures to manipulate the switchable spreading performance. Motived by this strange behavior, we construct a large-scaled peristome-mimetic surface in a 3D profile, demonstrating the ability to reduce the need to mop or to squeegee drops that form during the drop impacting process on pipes or other curved surfaces in food processing, moisture transfer, heat management, etc.

Screening Platform for Cell Contact Guidance Based on Inorganic Biomaterial Micro/nanotopographical Gradients

High-throughput screening (HTS) methods based on topography gradients or arrays have been extensively used to investigate cell-material interactions. However, it is a huge technological challenge to cost efficiently prepare topographical gradients of inorganic biomaterials due to their inherent material properties. Here, we developed a novel strategy translating PDMS-based wrinkled topography gradients with amplitudes from 49 to 2561 nm and wavelengths between 464 and 7121 nm to inorganic biomaterials (SiO2, Ti/TiO2, Cr/CrO3, and Al2O3) which are frequently used clinical materials. Optimal substratum conditions promoted human bone-marrow derived mesenchymal stem cell alignment, elongation, cytoskeleton arrangement, filopodia development as well as cell adhesion in vitro, which depended both on topography and interface material. This study displays a positive correlation between cell alignment and the orientation of cytoskeleton, filopodia, and focal adhesions. This platform vastly minimizes the experimental efforts both for inorganic material interface engineering and cell biological assessments in a facile and effective approach. The practical application of the HTS technology is expected to aid in the acceleration of developments of inorganic clinical biomaterials.

Graphene Sheet-Induced Global Maturation of Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) can proliferate infinitely. Their ability to differentiate into cardiomyocytes provides abundant sources for disease modeling, drug screening and regenerative medicine. However, hiPSC-derived cardiomyocytes (hiPSC-CMs) display a low degree of maturation and fetal-like properties. Current in vitro differentiation methods do not mimic the structural, mechanical, or physiological properties of the cardiogenesis niche. Recently, we present an efficient cardiac maturation platform that combines hiPSCs monolayer cardiac differentiation with graphene substrate, which is a biocompatible and superconductive material. The hiPSCs lines were successfully maintained on the graphene sheets and were able to differentiate into functional cardiomyocytes. This strategy markedly increased the myofibril ultrastructural organization, elevated the conduction velocity, and enhanced both the Ca²⁺ handling and electrophysiological properties in the absence of electrical stimulation. On the graphene substrate, the expression of connexin 43 increased along with the conduction velocity. Interestingly, the bone morphogenetic proteins signaling was also significantly activated during early cardiogenesis, confirmed by RNA sequencing analysis. Here, we reasoned that graphene substrate as a conductive biomimetic surface could facilitate the intrinsic electrical propagation, mimicking the microenvironment of the native heart, to further promote the global maturation of hiPSC-CMs. Our findings highlight the capability of electrically active substrates to influence cardiomyocyte development. We believe that application of graphene sheets will be useful for simple, fast, and scalable maturation of regenerated cardiomyocytes.

Nanotopography-Induced Structural Anisotropy and Sarcomere Development in Human Cardiomyocytes Derived from Induced Pluripotent Stem Cells

Understanding the phenotypic development of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is a prerequisite to advancing regenerative cardiac therapy, disease modeling, and drug screening applications. Lack of consistent hiPSC-CM in vitro data can be largely attributed to the inability of conventional culture methods to mimic the structural, biochemical, and mechanical aspects of the myocardial niche accurately. Here, we present a nanogrid culture array comprised of nanogrooved topographies, with groove widths ranging from 350 to 2000 nm, to study the effect of different nanoscale structures on the structural development of hiPSC-CMs in vitro. Nanotopographies were designed to have a biomimetic interface, based on observations of the oriented myocardial extracellular matrix (ECM) fibers found in vivo. Nanotopographic substrates were integrated with a self-assembling chimeric peptide containing the Arg-Gly-Asp (RGD) cell adhesion motif. Using this platform, cell adhesion to peptide-coated substrates was found to be comparable to that of conventional fibronectin-coated surfaces. Cardiomyocyte organization and structural development were found to be dependent on the nanotopographical feature size in a biphasic manner, with improved development achieved on grooves in the 700-1000 nm range. These findings highlight the capability of surface-functionalized, bioinspired substrates to influence cardiomyocyte development, and the capacity for such platforms to serve as a versatile assay for investigating the role of topographical guidance cues on cell behavior. Such substrates could potentially create more physiologically relevant in vitro cardiac tissues for future drug screening and disease modeling studies.

Bioinspired Surface for Surgical Graspers Based on the Strong Wet Friction of Tree Frog Toe Pads

Soft tissue damage is often at risk during the use of a surgical grasper, because of the strong holding force required to prevent slipping of the soft tissue in wet surgical environments. Improvement of wet friction properties at the interface between the surgical grasper and soft tissue can greatly reduce the holding force required and, thus, the soft tissue damage. To design and fabricate a biomimetic microscale surface with strong wet friction, the wet attachment mechanism of tree frog toe pads was investigated by observing their epithelial cell structure and the directionally dependent friction on their toe pads. Using these observations as inspiration, novel surface micropatterns were proposed for the surface of surgical graspers. The wet friction of biomimetic surfaces with various types of polygon pillar patterns involving quadrangular pillars, triangular pillars, rhomboid pillars, and varied hexagonal pillars were tested. The hexagonal pillar pattern exhibited improved wet frictional performance over the modern surgical grasper jaw pattern, which has conventional macroscale teeth. Moreover, the deformation of soft tissue in the bioinspired surgical grasper with a hexagonal pillar pattern is decreased, compared with the conventional surgical grasper.

The Biomimetic Shark Skin Optimization Design Method for Improving Lubrication Effect of Engineering Surface

Nature has long been an important source of inspiration for mankind to develop artificial ways to mimic the remarkable properties of biological systems. In this work, a new method was explored to fabricate a biomimetic engineering surface comprising both the shark-skin, the shark body denticle, and rib morphology. It can help reduce water resistance and the friction contact area as well as accommodate lubricant. The lubrication theory model was established to predict the effect of geometric parameters of a biomimetic surface on tribological performance. The model has been proved to be feasible to predict tribological performance by the experimental results. The model was then used to investigate the effect of the grid textured surface on frictional performance of different geometries. The investigation was aimed at providing a rule for deriving the design parameters of a biomimetic surface with good lubrication characteristics. Results suggest that: (i) the increase in depression width ratio [Formula: see text] decreases its corresponding coefficient of friction, and (ii) the small coefficient of friction is achievable when [Formula: see text] is beyond 0.45. Superposition of depth ratio Γ and angle's couple under the condition of [Formula: see text] < 0.45 affects the value of friction coefficient. It shows the decrease in angle decreases with the increase in dimension depth [Formula: see text].