Climbing plants: attachment adaptations and bioinspired innovations

The Development of a Stereo Vision System to Study the Nutation Movement of Climbing Plants

Climbing plants, such as common beans (Phaseolus vulgaris L.), exhibit complex motion patterns that have long captivated researchers. In this study, we introduce a stereo vision machine system for the in-depth analysis of the movement of climbing plants, using image processing and computer vision. Our approach involves two synchronized cameras, one lateral to the plant and the other overhead, enabling the simultaneous 2D position tracking of the plant tip. These data are then leveraged to reconstruct the 3D position of the tip. Furthermore, we investigate the impact of external factors, particularly the presence of support structures, on plant movement dynamics. The proposed method is able to extract the position of the tip in 86-98% of cases, achieving an average reprojection error below 4 px, which means an approximate error in the 3D localization of about 0.5 cm. Our method makes it possible to analyze how the plant nutation responds to its environment, offering insights into the interplay between climbing plants and their surroundings.

Investigating Foot Morphology in Rock Climbing Mammals: Inspiration for Biomimetic Climbing Shoes

The sporting goods sector can serve as a proving ground for new technologies. We propose that climbing shoes are an excellent case study for showcasing a systematic approach to bio-inspired design. Foot adaptations to climbing have been described before in some animals and have even been incorporated into bio-inspired products. However, there has not yet been a systematic description of climbing adaptations in mammals, and especially in rock climbing species. We present a description of foot morphology in mammals and compare rock climbing species to those with other locomotion types. Our results show that rock climbing species in our sample had fewer digits and larger anterior pads than arboreal species. Rock climbing species often had hooves or, if they had foot pads, these were relatively smooth. These examples look a bit like current climbing shoe designs, perhaps suggesting convergent evolution. However, there was also variation, with rock climbing species having pads varying in shape, placement and texture. Much of this variation is likely to be dependent on the relatedness of species, with those that are more related having more similar feet. We suggest that incorporation of novel textures and compliant pads might be an interesting focus for future climbing shoe designs.

A Coupled Transport-Adhesion Mechanism Responsible for the Attachment of Adventitious Root Hairs of Climbing Plants to the Surrounding Surface

Biological adhesive systems in both geckoes and climbing plants share similar hierarchical structures, such as the toe-seta-spatula structure in geckoes and the root-rootlet-hair structure in English ivy (Hedera helix). The former operates at a spectrum of length scales that are much smaller than the latter. Consequently, the spatula adhesion in geckoes exhibits a flaw-insensitive behavior, or in other words, the large-scale-bridging characteristics shield the stress singularities at the adhesive contact front. In contrast, adventitious root hairs from commonly seen household climbing plants are of several tens to hundreds of micrometers long, so that the adhesive contact appears to resemble a linear elastic crack and thus would have a very low pulling force for de-adhesion. This apparent contradiction between modeling and observations is resolved in this work by a coupled transport–adhesion mechanism, in which an adhesive layer that carries gluing nanoparticles flows towards the adhesive contact front. This provides an effective way to shield the stress singularity, resulting in a scenario that completely differs from gecko adhesion. Finite element simulations have been conducted to illustrate this proposed mechanism and then compared to available experimental observations in the literature.

Appressed, directed and silicified trichomes of the kudzu climbing vine

Kudzu (Pueraria montana var. lobata) is becoming one of the most prevalent climbing vines in urban forests. Here, surface characteristics of kudzu leaves and stems are investigated using field-emission scanning electron microscopy and X-ray microanalysis. The leaf and stem surfaces were characterized by different types of trichomes. No adhesive pads, modified hooks or tendrils were found on kudzu vines. Trichomes on the leaves and stems of kudzu could be categorized into (i) complex bulbous glandular trichomes and (ii) needle-shaped nonglandular trichomes (NSNGTs). Two morphotypes of the nonglandular trichomes were present on the stems: (i) long hairy nonglandular trichomes and (ii) short NSNGTs. The leaf trichomes were appressed and oriented in an uphill direction, whereas the stem trichomes were appressed and oriented in a downhill direction. This opposite trichome orientation appears to facilitate climbing and prohibits slipping of kudzu vines through differential friction between the plants and the kudzu vines. X-ray microanalysis revealed a distinct accumulation of silicon in the leaf and stem trichomes. These results suggest that appressed, directed and silicified trichomes may contribute to the twining behavior of kudzu vines.

Microspines in tropical climbing plants: a small-scale fix for life in an obstacle course

Many climbing plants have microspines on their stems, which facilitate attachment and prevent slipping and falling from host plant supports. Extending via growth through complex environments and anchoring stems to substrates with minimal contact forces are key benefits for climbing plants. Microspines are also highly desirable features for new technologies and applications in soft robotics. Using a novel sled-like device, we investigated static and sliding attachment forces generated by stems in 10 species of tropical climber from French Guiana differing in size and climbing habit. Eight species showed higher static and sliding forces when their stems were pulled in the basal direction against a standard surface than in the apical direction. This anisotropic behaviour suggests that tropical climbers have evolved different ratchet-like mechanisms that allow easy sliding forwards but are resistant to slipping downwards. The presence of a downwards 'stick-and-slip' phenomenon, where static attachment is not significantly stronger than maximal sliding attachment, was present in most species apart from three showing relatively weak attachment by microspines. This indicates that diverse microspine attachment strategies exist in climbing plants. This diversity of functional properties offers a range of potential design specifications for climbing strategies on different substrates for artificial climbing artefacts.

Protein scaffolds in human clinics

Fundamental clinical areas such as drug delivery and regenerative medicine require biocompatible materials as mechanically stable scaffolds or as nanoscale drug carriers. Among the wide set of emerging biomaterials, polypeptides offer enticing properties over alternative polymers, including full biocompatibility, biodegradability, precise interactivity, structural stability and conformational and functional versatility, all of them tunable by conventional protein engineering. However, proteins from non-human sources elicit immunotoxicities that might bottleneck further development and narrow their clinical applicability. In this context, selecting human proteins or developing humanized protein versions as building blocks is a strict demand to design non-immunogenic protein materials. We review here the expanding catalogue of human or humanized proteins tailored to execute different levels of scaffolding functions and how they can be engineered as self-assembling materials in form of oligomers, polymers or complex networks. In particular, we emphasize those that are under clinical development, revising their fields of applicability and how they have been adapted to offer, apart from mere mechanical support, highly refined functions and precise molecular interactions.

Discovery of spatial pattern of prickles on stem of Rosa hybrida 'Red Queen' and mathematical model of the pattern

The developmental patterns of many organisms are orchestrated by the diffusion of factors. Here, we report a novel pattern on plant stems that appears to be controlled by inhibitor diffusion. Prickles on rose stems appear to be randomly distributed, but we deciphered spatial patterns of prickles on Rosa hybrida cv. ‘Red Queen’ stem. The prickles primarily emerged at 90 to 135 degrees from the spiral phyllotaxis that connected leaf primordia. We proposed a simple mathematical model that explained the emergence of the spatial patterns and reproduced the prickle density distribution on rose stems. We confirmed the model can reproduce the observed prickle patterning on stems of other plant species using other model parameters. These results indicated that the spatial patterns of prickles on stems of different plant species are organized by similar systems. Rose cultivation by humans has a long history. However, prickle development is still unclear and this is the first report of prickle spatial pattern with a mathematical model. Comprehensive analysis of the spatial pattern, genome, and metabolomics of other plant species may lead to novel insights for prickle development.

Hooked on mushrooms: Preparation and mechanics of a bioinspired soft probabilistic fastener

Probabilistic fasteners are known to provide strong attachment onto their respective surfaces. Examples are Velcro® and the "3M dual lock" system. However, these systems typically only function using specific counter surfaces and are often destructive to other surfaces such as fabrics. Moreover, the design parameters to optimize their functionality are not obvious. Here, we present a surface patterned with soft micrometric features inspired by the mushroom shape showing a nondestructive mechanical interlocking and thus attachment to fabrics. We provide a scalable experimental approach to prepare these surfaces and quantify the attachment strength with rheometric and video-based analysis. In these "probabilistic fasteners," we find that higher feature densities result in higher attachment force; however, the individual feature strength is higher on a low feature density surface. We interpret our results via a load-sharing principle common in fiber bundle models. Our work provides new handles for tuning the mechanical attachment properties of soft patterned surfaces that can be used in various applications including soft robotics.

The Bio-Engineering Approach for Plant Investigations and Growing Robots. A Mini-Review

It has been 10 years since the publication of the first article looking at plants as a biomechatronic system and as model for robotics. Now, roboticists have started to look at plants differently and consider them as a model in the field of bioinspired robotics. Despite plants have been seen traditionally as passive entities, in reality they are able to grow, move, sense, and communicate. These features make plants an exceptional example of morphological computation - with probably the highest level of adaptability among all living beings. They are a unique model to design robots that can act in- and adapt to- unstructured, extreme, and dynamically changing environments exposed to sudden or long-term events. Although plant-inspired robotics is still a relatively new field, it has triggered the concept of growing robotics: an emerging area in which systems are designed to create their own body, adapt their morphology, and explore different environments. There is a reciprocal interest between biology and robotics: plants represent an excellent source of inspiration for achieving new robotic abilities, and engineering tools can be used to reveal new biological information. This way, a bidirectional biology-robotics strategy provides mutual benefits for both disciplines. This mini-review offers a brief overview of the fundamental aspects related to a bioengineering approach in plant-inspired robotics. It analyses the works in which both biological and engineering aspects have been investigated, and highlights the key elements of plants that have been milestones in the pioneering field of growing robots.

Plant Bioinspired Ecological Robotics

Plants are movers, but the nature of their movement differs dramatically from that of creatures that move their whole body from point A to point B. Plants grow to where they are going. Bio-inspired robotics sometimes emulates plants' growth-based movement; but growing is part of a broader system of movement guidance and control. We argue that ecological psychology's conception of "information" and "control" can simultaneously make sense of what it means for a plant to navigate its environment and provide a control scheme for the design of ecological plant-inspired robotics. In this effort, we will outline several control laws and give special consideration to the class of control laws identified by tau theory, such as time to contact.

Plant Complexity and Cosmetic Innovation

Plants have been used in cosmetic products since ancient times and are the subject of scientific investigation even nowadays. During the years, a deeper understanding of both the behavior of skin and of plants have become available drawing increasingly complex pictures. Plants are complex organisms that produce different metabolites responding to the environment they live in. Applied to the skin, phytomolecules interact with skin cells and affect the skin well-being and appearance. Ethnobotanical studies on the one hand and physico-chemical analyses on the other have pictured a rich inventory of plants with potential to enrich modern cosmetic products.

Mechanical Innovations of a Climbing Cactus: Functional Insights for a New Generation of Growing Robots

Climbing plants are being increasingly viewed as models for bioinspired growing robots capable of spanning voids and attaching to diverse substrates. We explore the functional traits of the climbing cactus Selenicereus setaceus (Cactaceae) from the Atlantic forest of Brazil and discuss the potential of these traits for robotics applications. The plant is capable of growing through highly unstructured habitats and attaching to variable substrates including soil, leaf litter, tree surfaces, rocks, and fine branches of tree canopies in wind-blown conditions. Stems develop highly variable cross-sectional geometries at different stages of growth. They include cylindrical basal stems, triangular climbing stems and apical star-shaped stems searching for supports. Searcher stems develop relatively rigid properties for a given cross-sectional area and are capable of spanning voids of up to 1 m. Optimization of rigidity in searcher stems provide some potential design ideas for additive engineering technologies where climbing robotic artifacts must limit materials and mass for curbing bending moments and buckling while climbing and searching. A two-step attachment mechanism involves deployment of recurved, multi-angled spines that grapple on to wide ranging surfaces holding the stem in place for more solid attachment via root growth from the stem. The cactus is an instructive example of how light mass searchers with a winged profile and two step attachment strategies can facilitate traversing voids and making reliable attachment to a wide range of supports and surfaces.

Taking inspiration from climbing plants: methodologies and benchmarks-a review

One of the major challenges in robotics and engineering is to develop efficient technological solutions that are able to cope with complex environments and unpredictable constraints. Taking inspiration from natural organisms is a well-known approach to tackling these issues. Climbing plants are an important, yet innovative, source of inspiration due to their ability to adapt to diverse habitats, and can be used as a model for developing robots and smart devices for exploration and monitoring, as well as for search and rescue operations. This review reports the main methodologies and approaches used by scientists to investigate and extract the features of climbing plants that are relevant to the artificial world in terms of adaptation, movement, and behaviour, and it summarizes the current available climbing plant-inspired engineering solutions.

Boston Ivy Disk-Inspired Pressure-Mediated Adhesive Film Patches

Boston ivy (Parthenocissus tricuspidata) climbs brick walls using its tendril disks, which excrete a sticky substance to perform binding and attachment. While the cellular structures and adhesive substances involved have been identified for decades, their practical applicability as an adhesive has not yet been demonstrated. A Boston ivy disk-inspired adhesive film patch system is reported in which structural and compositional features of the Boston ivy disk are mimicked with a form of thin adhesive film patches. In analogy to the sticky disk of a mature ivy in which porous microchannels are occupied by catechol-containing microgranules on the bound site, 3,4-dihydroxylphenylalanine bolaamphiphile nanoparticle (DOPA-C7 NP)-coated alginate microgels are two-dimensionally positioned into the cylindrical holes that are periodically micropatterned on the flexible stencil film. Finally, it is demonstrated that the pressurization of the patch breaks the microgels filled in the holes, releasing the polysaccharides and leading to crosslinking with DOPA-C7 NPs via ligandation with combined Ca²⁺ and Fe³⁺ ions, thus enabling development of a pressure-mediated adhesion technology.

Autonomously shaping natural climbing plants: a bio-hybrid approach

Plant growth is a self-organized process incorporating distributed sensing, internal communication and morphology dynamics. We develop a distributed mechatronic system that autonomously interacts with natural climbing plants, steering their behaviours to grow user-defined shapes and patterns. Investigating this bio-hybrid system paves the way towards the development of living adaptive structures and grown building components. In this new application domain, challenges include sensing, actuation and the combination of engineering methods and natural plants in the experimental set-up. By triggering behavioural responses in the plants through light spectra stimuli, we use static mechatronic nodes to grow climbing plants in a user-defined pattern at a two-dimensional plane. The experiments show successful growth over periods up to eight weeks. Results of the stimuli-guided experiments are substantially different from the control experiments. Key limitations are the number of repetitions performed and the scale of the systems tested. Recommended future research would investigate the use of similar bio-hybrids to connect construction elements and grow shapes of larger size.