Arachnid locomotion is the various means by which arachnids walk, run, or jump; they make use of more than muscle contraction, employing additional methods like hydraulic compression. [1] [2] Another adaptation seen especially in larger arachnid variants is inclusion of elastic connective tissues.
In most arachnids, hydraulic compression acts as the primary means of extension in several of their hinged leg joints, namely the femur–patella joint and tibia–metatarsus joints or second and third leg joints respectively. [3] Instead of blood, hemolymph is used to move nutrients around inside of the arachnid, and has the secondary function of acting as a hydraulic fluid. When compressed by the body of the arachnid, the hemolymph applies compressive force through channels in the limbs that cause them to extend. [4] This motion is then balanced by flexor muscle to retract the leg joints as needed. Due to hydraulics being used for extension, the flexor muscle is able to be significantly larger than would otherwise be possible without impacting size or weight. [5] Measurable core body volume change can occur during periods of higher compression to the legs, as the sinuses of the body contract to achieve pressurization in specific legs. [6] Aside from the normal gait of the arachnid, in some variants, extremely high pressures are used as a means of jumping, propelling rear legs and allowing for much greater and more sudden motion. [6]
In larger variants of arachnids, such as the tarantulas and hairy desert spiders, another mechanism used for locomotion is an elastic sclerite. [6] These sclerites are semi-rigid connectors between leg segments that allow storage and expending of potential energy. This is used as a supplement or in conjunction with the hydraulics normally employed in those joints, allowing for greater weights to be carried, more rapid and sudden movement when combined with the already pronounced flexor muscle acting in those joints, as well as fine motor control with reduced sudden disruption of hemolymph flow. [6] At higher compression of the joint the stiffness of the sclerite has been found to increase significantly, denoting support even outside of normal tension. [6]
Hydraulic locomotion in arachnids has acted as an inspiration for many modern biomimetic concepts in robotics intended for use by or with people, especially in the field of soft robotics. The use of hydraulics in robotic joints is aimed at replacing the more control heavy nature of modern robotics with a more passive system developed in soft actuation. [7] Various forms of actuation and force transmission can be achieved through these inspired designs, including rotation, lifting, and even damping effects. [8] The passive nature of the hydraulic and elastic extensor mechanisms employed have found use in orthotics projects aimed at assisting joints weakened by age or disease. [8]
An additional method used by some arachnids to improve locomotion is to secrete fluids, characterized by a hydrophobic effect, through the pads on the ends of their legs that are in contact with the walking surface. [9] It has been shown that the arachnid is capable of using the adhesive fluid selectively, meaning it can choose to not secrete the fluid in certain circumstances where it would be unwarranted such as in moist conditions. [9] The use of fluids allow the arachnid better traction through improved shear force for both standard locomotion and also sudden movements such as in jumping and leaping.
Modelling the hydraulic system used by arachnids has been a challenge in the past due to scale and complexity. Simplified models focusing on individual joints and flow channels using modern imaging such as Micro-CT has allowed for mathematical expressions of pressure and flow acting on the joints. [3] Visualizing the flow of hemolymph in small bodies directly has been difficult due to resolution constraints and lack of contrast causing fluid and soft tissue being indistinguishable, but techniques have been employed using a combination of injected microbubbles as tracers in the hemolymph and synchrotron x-ray contrast imaging to track them. [10]
A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal frame to which the organs and soft tissues attach; and the hydroskeleton, a flexible internal structure supported by the hydrostatic pressure of body fluids.
Jumping or leaping is a form of locomotion or movement in which an organism or non-living mechanical system propels itself through the air along a ballistic trajectory. Jumping can be distinguished from running, galloping and other gaits where the entire body is temporarily airborne, by the relatively long duration of the aerial phase and high angle of initial launch.
Arachnida is a class of joint-legged arthropods, in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.
Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph cells called hemocytes are suspended. In addition to hemocytes, the plasma also contains many chemicals. It is the major tissue type of the open circulatory system characteristic of arthropods. In addition, some non-arthropods such as mollusks possess a hemolymphatic circulatory system.
An actuator is a component of a machine that produces force, torque, or displacement, usually in a controlled way, when an electrical, pneumatic or hydraulic input is supplied to it in a system. An actuator converts such an input signal into the required form of mechanical energy. It is a type of transducer. In simple terms, it is a "mover".
Animal locomotion, in ethology, is any of a variety of methods that animals use to move from one place to another. Some modes of locomotion are (initially) self-propelled, e.g., running, swimming, jumping, flying, hopping, soaring and gliding. There are also many animal species that depend on their environment for transportation, a type of mobility called passive locomotion, e.g., sailing, kiting (spiders), rolling or riding other animals (phoresis).
Robot locomotion is the collective name for the various methods that robots use to transport themselves from place to place.
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa, trochanter, femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus, patella.
Opiliones are an order of arachnids and share many common characteristics with other arachnids. However, several differences separate harvestmen from other arachnid orders such as spiders. The bodies of opiliones are divided into two tagmata : the abdomen (opisthosoma) and the cephalothorax (prosoma). Unlike spiders, the juncture between the abdomen and cephalothorax is often poorly defined. Harvestmen have chelicerae, pedipalps and four pairs of legs. Most harvestmen have two eyes, although there are eyeless species.
Arthropods are covered with a tough, resilient integument, cuticle or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. This happens in parts of the body where there is a need for rigidity or elasticity. Typically the mineral crystals, mainly calcium carbonate, are deposited among the chitin and protein molecules in a process called biomineralization. The crystals and fibres interpenetrate and reinforce each other, the minerals supplying the hardness and resistance to compression, while the chitin supplies the tensile strength. Biomineralization occurs mainly in crustaceans. In insects and arachnids, the main reinforcing materials are various proteins hardened by linking the fibres in processes called sclerotisation and the hardened proteins are called sclerotin. The dorsal tergum, ventral sternum, and the lateral pleura form the hardened plates or sclerites of a typical body segment.
A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element capable of changing length and rotating about an omnidirectional "hip" joint.
Insect morphology is the study and description of the physical form of insects. The terminology used to describe insects is similar to that used for other arthropods due to their shared evolutionary history. Three physical features separate insects from other arthropods: they have a body divided into three regions, three pairs of legs, and mouthparts located outside of the head capsule. This position of the mouthparts divides them from their closest relatives, the non-insect hexapods, which include Protura, Diplura, and Collembola.
Neuromechanics of orthoses refers to how the human body interacts with orthoses. Millions of people in the U.S. suffer from stroke, multiple sclerosis, postpolio, spinal cord injuries, or various other ailments that benefit from the use of orthoses. Insofar as active orthoses and powered exoskeletons are concerned, the technology to build these devices is improving rapidly, but little research has been done on the human side of these human-machine interfaces.
As humans move through their environment, they must change the stiffness of their joints in order to effectively interact with their surroundings. Stiffness is the degree to a which an object resists deformation when subjected to a known force. This idea is also referred to as impedance, however, sometimes the idea of deformation under a given load is discussed under the term "compliance" which is the opposite of stiffness . In order to effectively interact with their environment, humans must adjust the stiffness of their limbs. This is accomplished via the co-contraction of antagonistic muscle groups.
Proportional myoelectric control can be used to activate robotic lower limb exoskeletons. A proportional myoelectric control system utilizes a microcontroller or computer that inputs electromyography (EMG) signals from sensors on the leg muscle(s) and then activates the corresponding joint actuator(s) proportionally to the EMG signal.
The two palpal bulbs – also known as palpal organs and genital bulbs – are the copulatory organs of a male spider. They are borne on the last segment of the pedipalps, giving the spider an appearance often described as like wearing boxing gloves. The palpal bulb does not actually produce sperm, being used only to transfer it to the female. Palpal bulbs are only fully developed in adult male spiders and are not completely visible until after the final moult. In the majority of species of spider, the bulbs have complex shapes and are important in identification.
Soft robotics is a subfield of robotics that concerns the design, control, and fabrication of robots composed of compliant materials, instead of rigid links. In contrast to rigid-bodied robots built from metals, ceramics and hard plastics, the compliance of soft robots can improve their safety when working in close contact with humans.
Necrobotics is the practice of using biotic materials as robotic components. In July 2022, researchers in the Preston Innovation Lab at Rice University in Houston, Texas published a paper in Advanced Science introducing the concept and demonstrating its capability by repurposing dead spiders as robotic grippers and applying pressurized air to activate their gripping arms.
A peristaltic robot, also known as a worm-bot, is a robot that uses peristaltic locomotion to move, mimicking the movement of earthworms. Peristaltic locomotion relies on compressions and expansions of the metameres, or body segments, of earthworms. This method of movement is especially effective in navigating through narrow and intricate surfaces, making it particularly suitable for small millimeter-scale robots. Peristaltic robots have a wide range of applications, including endoscopy, mining operations, and pipe inspections.