Necrobotics: Biotic Materials as Ready-to-Use Actuators

Abstract

Designs perfected through evolution have informed bioinspired animal-like robots that mimic the locomotion of cheetahs and the compliance of jellyfish; biohybrid robots go a step further by incorporating living materials directly into engineered systems. Bioinspiration and biohybridization have led to new, exciting research, but humans have relied on biotic materials-non-living materials derived from living organisms-since their early ancestors wore animal hides as clothing and used bones for tools. In this work, an inanimate spider is repurposed as a ready-to-use actuator requiring only a single facile fabrication step, initiating the area of "necrobotics" in which biotic materials are used as robotic components. The unique walking mechanism of spiders-relying on hydraulic pressure rather than antagonistic muscle pairs to extend their legs-results in a necrobotic gripper that naturally resides in its closed state and can be opened by applying pressure. The necrobotic gripper is capable of grasping objects with irregular geometries and up to 130% of its own mass. Furthermore, the gripper can serve as a handheld device and innately camouflages in outdoor environments. Necrobotics can be further extended to incorporate biotic materials derived from other creatures with similar hydraulic mechanisms for locomotion and articulation.

Keywords: biohybrids; bioinspiration; grippers; pneumatic actuators; soft robotics; spiders.

Figure 1

Fabrication of the necrobotic gripper. a) A spider is euthanized by application of cold temperature. The patellofemoral joint of the spider was visualized with a scanning electron microscope (SEM) to show the articular membrane at the joint with the stroller sun shade geometry. b) A 25‐gauge hypodermic needle is inserted into the prosoma of the spider and sealed with glue. The SEM image shows the glue forming an airtight seal around the needle and the cuticle (or exoskeleton). We performed the same procedure with blue‐dyed glue on a similar needle to illustrate the self‐sealing mechanism. c) After the glue has cured, a syringe (or any suitable pressure source) is connected to the needle, completing the fabrication of the necrobotic gripper.

Figure 2

a) Experimental sequence employed to determine the gripping force of the necrobotic gripper by using a universal testing machine to control the displacement and an analytical balance to measure the gripping force of the gripper. a‐i) The necrobotic gripper is pressurized to open, and approaches the “weight” (i.e., the red bead). a‐ii) After the necrobotic gripper almost contacts the weight, a‐iii) the necrobotic gripper is depressurized to grip onto the weight. a‐iv) The universal testing machine raises the necrobotic gripper at a constant, quasi‐static velocity, and the analytical balance displays the effective gripping force exerted on the weight by the necrobotic gripper. a‐v) The gripping force is zero when the necrobotic gripper is no longer in contact with the weight. b) The gripping force for the same spider was characterized at eight different gripping pressures, P _grip, and plotted against displacement. We performed three trials at P _grip = 0 kPa and found that, while minor variability in the gripping force appears at a given pressure, the overall performance remains consistent and follows a monotonic trend (higher F _grip at lower P _grip). The colored stars in (a) correspond to the force at each displacement in (b) to provide additional context for the characterization process. c) The maximum gripping force exerted by the necrobotic gripper at each gripping pressure is plotted, showing that an increase in gripping pressure results in a decrease in maximum gripping force.

Figure 3

a) Joint angles of the spider leg in the gripper's neutral state and at two elevated actuation pressures. The leg that we characterized is outlined with dashes, and the two joints, (i) trochanter and (ii) patellofemoral, are indicated with red and blue arrows, respectively. b) We determined the change in joint angle for both joints, Δθ, with respect to the joint angle in the neutral state (0 kPa) for different P _grip. The data on the plot emphasized with colored stars correspond to the joint angles in (a). c) Cyclic testing was performed by opening and closing the necrobotic gripper for 1000 cycles, and the change in the neutral state joint angle with respect to the neutral state joint angle at the zeroth cycle was measured every 100 cycles.

Figure 4

We highlight the ability of the necrobotic gripper to grasp various objects with different masses, m _obj, and geometries. a) We show a closed circuit (LED on) which was then disconnected (LED off) when the necrobotic gripper removed a jumper wire that was affixed to the electric breadboard. The jumper wire is 0.64 times the mass of the necrobotic gripper and requires additional force to overcome friction when removing it from the breadboard. b) The necrobotic gripper also successfully grasps a spider which is 1.34 times the gripper's mass and has an irregular shape. c) We demonstrate that the necrobotic gripper can pick up objects with larger volumes by picking up a block of red‐dyed polyurethane foam (2.6 times the volume and 0.92 times the mass of the gripper). d) Furthermore, we show an untethered configuration for the necrobotic gripper by directly connecting a handheld pressure source to the needle of the necrobotic gripper, thereby converting it into a portable device. The handheld necrobotic gripper is able to transport a white polyurethane foam block (0.45 times the mass of the necrobotic gripper) from one location to another, and is not tethered to bulky control infrastructure.

Figure 5

Scaling analysis of the gripper force compared to the weight of the gripper. We show a range of potential spider masses from 0.1 mg to 1 kg and predict the gripping force to gripper weight ratio. We present two models: (i) a muscle model where the gripping force, F _grip, scales with L ², and (ii) a spring model where the gripping force, F _grip, scales with L.