Functional principles of steerable multi-element probes in insects

Terebra steering in chalcidoid wasps

Various chalcidoid wasps can actively steer their terebra (= ovipositor shaft) in diverse directions, despite the lack of terebral intrinsic musculature. To investigate the mechanisms of these bending and rotational movements, we combined microscopical and microtomographical techniques, together with videography, to analyse the musculoskeletal ovipositor system of the ectoparasitoid pteromalid wasp Lariophagus distinguendus (Förster, 1841) and the employment of its terebra during oviposition. The ovipositor consists of three pairs of valvulae, two pairs of valvifers and the female T9 (9th abdominal tergum). The paired 1st and the 2nd valvulae are interlocked via the olistheter system, which allows the three parts to slide longitudinally relative to each other, and form the terebra. The various ovipositor movements are actuated by a set of nine paired muscles, three of which (i.e. 1st valvifer-genital membrane muscle, ventral 2nd valvifer-venom gland reservoir muscle, T9-genital membrane muscle) are described here for the first time in chalcidoids. The anterior and posterior 2nd valvifer-2nd valvula muscles are adapted in function. (1) In the active probing position, they enable the wasps to pull the base of each of the longitudinally split and asymmetrically overlapping halves of the 2nd valvula that are fused at the apex dorsally, thus enabling lateral bending of the terebra. Concurrently, the 1st valvulae can be pro- and retracted regardless of this bending. (2) These muscles can also rotate the 2nd valvula and therefore the whole terebra at the basal articulation, allowing bending in various directions. The position of the terebra is anchored at the puncture site in hard substrates (in which drilling is extremely energy- and time-consuming). A freely steerable terebra increases the chance of contacting a potential host within a concealed cavity. The evolution of the ability actively to steer the terebra can be considered a key innovation that has putatively contributed to the acquisition of new hosts to a parasitoid's host range. Such shifts in host exploitation, each followed by rapid radiations, have probably aided the evolutionary success of Chalcidoidea (with more than 500,000 species estimated).

Biomimetics with Trade-Offs

Our knowledge of physics and chemistry is relatively well defined. Results from that knowledge are predictable as, largely, are those of their technical offspring such as electrical, chemical, mechanical and civil engineering. By contrast, biology is relatively unconstrained and unpredictable. A factor common to all areas is the trade-off, which provides a means of defining and quantifying a problem and, ideally, its solution. In order to understand the anatomy of the trade-off and how to handle it, its development (as the dialectic) is tracked from Hegel and Marx to its implementation as dialectical materialism in Russian philosophy and TRIZ, the Theory of Invention. With the ready availability of mathematical techniques, such as multi-objective analysis and the Pareto set, the trade-off is well-adapted to bridging the gaps between the quantified and the unquantifiable, allowing modelling and the transfer of concepts by analogy. It is thus an ideal tool for biomimetics. An intracranial endoscope can be derived with little change from the egg-laying tube of a wood wasp. More complex transfers become available as the technique is developed. Most important, as more trade-offs are analyzed, their results are stored to be used again in the solution of problems. There is no other system in biomimetics which can do this.

Tsetse fly inspired steerable bone drill-a proof of concept

The fixation strength of pedicle screws could be increased by fixating along the much stronger cortical bone layer, which is not possible with the current rigid and straight bone drills. Inspired by the tsetse fly, a single-plane steerable bone drill was developed. The drill has a flexible transmission using two stacked leaf springs such that the drill is flexible in one plane and can drill along the cortical bone layer utilizing wall guidance. A proof-of-principle experiment was performed which showed that the Tsetse Drill was able to successfully drill through 5, 10 and 15 PCF cancellous bone phantom which has similar mechanical properties to severe osteoporotic, osteoporotic and healthy cancellous bone. Furthermore, the Tsetse Drill was able to successfully steer and drill along the cortical wall utilizing wall guidance for an insertion angle of 5°, 10° and 15°. The experiments conclude that the tsetse fly-inspired drilling method is successful and even allows the drilling along the cortical bone layer. The Tsetse Drill can create curved tunnels utilizing wall guidance which could increase the fixation strength of bone anchors and limit the risk of cortical breach and damage to surrounding anatomy.

Comparative Material and Mechanical Properties among Cicada Mouthparts: Cuticle Enhanced with Inorganic Elements Facilitates Piercing through Woody Stems for Feeding

Adult cicadas pierce woody stems with their mouthparts to feed on xylem, suggesting the presence of cuticular adaptations that could increase hardness and elastic modulus. We tested the following hypotheses: (a) the mouthpart cuticle includes inorganic elements, which augment the mechanical properties; (b) these elements are abundant in specific mouthpart structures and regions responsible for piercing wood; (c) there are correlations among elements, which could provide insights into patterns of element colocalization. We used scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to investigate mouthpart morphology and quantify the elemental composition of the cuticle among four cicada species, including periodical cicadas (Magicicada sp.). Nanoindentation was used to quantify hardness and elastic modulus of the mandibles. We found 12 inorganic elements, including colocalized manganese and zinc in the distal regions of the mandible, the structure most responsible for piercing through wood; nanoindentation determined that these regions were also significantly harder and had higher elastic modulus than other regions. Manganese and zinc abundance relates to increased hardness and stiffness as in the cuticle of other invertebrates; however, this is one of the first reports of cuticular metals among insects with piercing-sucking mouthparts (>100,000 described species). The present investigation provides insight into the feeding mechanism of cicadas, an important but understudied component of their life traits.

The Bright Side of the Tiger: Autofluorescence Patterns in Aedes albopictus (Diptera, Culicidae) Male and Female Mosquitoes

Light-based events in insects deserve increasing attention for various reasons. Besides their roles in inter- and intra-specific visual communication, with biological, ecological and taxonomical implications, optical properties are also promising tools for the monitoring of insect pests and disease vectors. Among these is the Asian tiger mosquito, Aedes albopictus, a global arbovirus vector. Here we have focused on the autofluorescence characterization of Ae. albopictus adults using a combined imaging and spectrofluorometric approach. Imaging has evidenced that autofluorescence rises from specific body compartments, such as the head appendages, and the abdominal and leg scales. Spectrofluorometry has demonstrated that emission consists of a main band in the 410–600 nm region. The changes in the maximum peak position, between 430 nm and 500 nm, and in the spectral width, dependent on the target structure, indicate the presence, at variable degrees, of different fluorophores, likely resilin, chitin and melanins. The aim of this work has been to provide initial evidence on the so far largely unexplored autofluorescence of Ae. albopictus, to furnish new perspectives for the set-up of species- and sex-specific investigation of biological functions as well as of strategies for in-flight direct detection and surveillance of mosquito vectors.

Penetration mechanics of elongated female and male genitalia of earwigs

We unveiled the penile penetration mechanics of two earwig species, Echinosoma horridum, whose intromittent organ, termed virga, is extraordinarily long, and E. denticulatum, whose virga is conversely short. We characterised configuration, geometry, material and bending stiffness for both virga and spermatheca. The short virga of E. denticulatum has a material gradient with the stiffer base, whereas the long virga of E. horridum and the spermathecae of both species are homogeneously sclerotised. The long virga of E. horridum has a lower bending stiffness than the spermatheca. The virga of E. denticulatum is overall less flexible than the spermatheca. We compared our results to a previous study on the penetration mechanics of elongated beetle genitalia. Based on the comparison, we hypothesised that the lower stiffness of the male intromittent organ comparing to the corresponding female structure is a universal prerequisite for the penetration mechanics of the elongated intromittent organ in insects.

Biologically Inspired Surgical Needle Steering: Technology and Application of the Programmable Bevel-Tip Needle

Percutaneous interventions via minimally invasive surgical systems can provide patients with better outcomes and faster recovery times than open surgeries. Accurate needle insertions are vital for successful procedures, and actively steered needles can increase system precision. Here, we describe how biology inspired the design of a novel Programmable Bevel-Tip Needle (PBN), mimicking the mechanics and control methods of certain insects ovipositors. Following an overview of our unique research and development journey, this paper explores our latest, biomimetic control of PBNs and its application to neurosurgery, which we validate within a simulated environment. Three modalities are presented, namely a Direct Push Controller, a Cyclic Actuation Controller, and a newly developed Hybrid Controller, which have been integrated into a surgical visual interface. The results of open loop, expert human-in-the-loop and a non-expert user study show that the Hybrid Controller is the best choice when considering system performance and the ability to lesson strain on the surrounding tissue which we hypothesis will result in less damage along the insertion tract. Over representative trajectories for neurosurgery using a Hybrid Controller, an expert user could reach a target along a 3D path with an accuracy of 0.70±0.69 mm, and non-expert users 0.97±0.72 mm, both clinically viable results and equivalent or better than the state-of-the-art actively steered needles over 3D paths. This paper showcases a successful example of a biologically inspired, actively steered needle, which has been integrated within a clinical interface and designed for seamless integration into the neurosurgical workflow.

Lepidopteran mouthpart architecture suggests a new mechanism of fluid uptake by insects with long proboscises

Proboscises of many fluid-feeding insects share a common architecture: they have a partially open food canal along their length. This feature has never been discussed in relation to the feeding mechanism. We formulated and solved a fluid mechanics model of fluid uptake and estimated the time required to completely fill the food canal of the entire proboscis through the openings along its length. Butterflies and moths are taken as illustrative and representative of fluid-feeding insects. We demonstrated that the proposed mechanism of filling the proboscis with fluid through permeable lengthwise bands, in association with a thin film of saliva in the food canal, offers a competitive pathway for fluid uptake. Compared with the conventional mechanism of fluid uptake through apically restricted openings, the new mechanism provides a faster rate of fluid uptake, especially for long-tongued insects. Accordingly, long-tongued insects with permeable lengthwise bands would be able to more rapidly exploit a broader range of liquids in the form of films, pools, and discontinuous columns, thereby conserving energy and minimizing exposure to predators, particularly for hovering insects.

Extraoral digestion: outsourcing the role of the hemipteran midgut

Extraoral digestion allows for breakdown of dietary components before they reach the midgut for final enzymatic degradation and absorption. In the Hemiptera, this is achieved by the secretion of enzyme-rich fluids from the salivary gland, with the combination of protein and mRNA from these tissues termed the sialome. Separate channels within the hemipteran stylets allow for secretion of saliva and ingestion of predigested material in a non-reflux mechanism. Both feeding mode and diet type influence the composition of the hemipteran sialome, as illustrated by 1) differences in protease abundance between hematophagous and predatory heteropteran sialomes, 2) diet specific aminopeptidase-N genes among aphid biotypes, and 3) adaptation-induced sialome variation in related cicada populations. Despite challenges associated with incomplete genome annotation, -omics analysis of the sialomes of diverse hemipteran species will enhance understanding of both sialome function and the evolution of extraoral digestion within the order.

Structure and function of the stylets of hematophagous Triatominae (Hemiptera: Reduviidae), with special reference to Dipetalogaster maxima

Kissing bugs (Hemiptera: Reduviidae: Triatominae) are able to bend their rod-like maxillae while searching for blood vessels in the tissue of their vertebrate hosts. Little is known about the working mechanisms of these bending movements and the distal opening of the food channel. We compared the morphological structure of the stylets (mandibles and maxillae) of four triatomine species and analyzed the feeding process of Dipetalogaster maxima (Uhler, 1894). The maxillae of triatomine bugs are interlocked by a tongue-and-groove system, allowing longitudinal sliding. While penetrating the host tissue, the animals perform rapid alternate back and forth movements of the maxillae. The resistance of the surrounding tissue pushes the asymmetric apex of the maxillae away from its straight path, i.e., if one individual maxilla is protracted alone, its tip curves inwards, and the other maxilla follows. Once a blood vessel is tapped, the spine-like tip of the left maxilla splays outwards. Apically, each of the maxillae features an abutment, the left one exhibiting a notch that presumably facilitates splaying. The mechanical interaction of the two maxillary abutments enables the distal opening of the food channel but might also support the movements of the maxillary bundle attributable to different bending moment distributions.

The ovipositor actuation mechanism of a parasitic wasp and its functional implications

Parasitic wasps use specialized needle‐like structures, ovipositors, to drill into substrates to reach hidden hosts. The external ovipositor (terebra) consists of three interconnected, sliding elements (valvulae), which are moved reciprocally during insertion. This presumably reduces the required pushing force on the terebra and limits the risk of damage whilst probing. Although this is an important mechanism, it is still not completely understood how the actuation of the valvulae is achieved, and it has only been studied with the ovipositor in rest position. Additionally, very little is known about the magnitude of the forces generated during probing. We used synchrotron X‐ray microtomography to reconstruct the actuation mechanism of the parasitic wasp Diachasmimorpha longicaudata (Braconidae) in four distinct phases of the probing cycle. We show that only the paired first valvulae of the terebra move independently, while the second valvula moves with the metasoma (‘abdomen’). The first valvula movements are initiated by rotation of one chitin plate (first valvifer) with respect to another such plate (second valvifer). This is achieved indirectly by muscles connecting the non‐rotating second valvifer and the abdominal ninth tergite. Contrary to previous reports, we found muscle fibres running inside the terebra, although their function remains unclear. The estimated maximal forces that can be exerted by the first valvulae are small (protraction 1.19 mN and retraction 0.874 mN), which reduces the risk of buckling, but are sufficient for successful probing. The small net forces of the valvulae on the substrate may still lead to buckling of the terebra; we show that the sheaths surrounding the valvulae prevent this by effectively increasing the diameter and second moment of area of the terebra. Our findings improve the comprehension of hymenopteran probing mechanisms, the function of the associated muscles, and the forces and damage‐limiting mechanism that are involved in drilling a slender terebra into a substrate.

Experimental evaluation of a self-propelling bio-inspired needle in single- and multi-layered phantoms

In percutaneous interventions, reaching targets located deep inside the body with minimal tissue damage and patient pain requires the use of long and thin needles. However, when pushed through a solid substrate, a structure with a high aspect ratio is prone to buckle. We developed a series of multi-element needles with a diameter smaller than 1 mm and a length larger than 200 mm, and we experimentally evaluated the performance of a bio-inspired insertion mechanism that prevents needle buckling of such slender structures. The needles consisted of Nitinol wires and advance into a substrate by pushing the wires forward one after the other, followed by pulling all the wires simultaneously backward. The resulting net push force is low, allowing the needles to self-propel through the substrate. We investigated the effect of the needle design parameters (number of wires and their diameter) and substrate characteristics (stiffness and number of layers) on the needle motion. Three needle prototypes (consisting of six 0.25-mm wires, six 0.125-mm wires, and three 0.25-mm wires, respectively) were inserted into single- and multi-layered tissue-mimicking phantoms. The prototypes were able to move forward in all phantoms without buckling. The amount of needle slip with respect to the phantom was used to assess the performance of the prototypes. The six-wire 0.25-mm prototype exhibited the least slip among the three prototypes. Summarizing, we showed that a bio-inspired motion mechanism prevents buckling in very thin (diameter <1 mm), long (length >200 mm) needles, allowing deep insertion into tissue-mimicking phantoms.