Joseph Najem

Biomimetic jellyfish-inspired underwater vehicle actuated by ionic polymer metal composite actuators

This paper presents the design, fabrication, and characterization of a biomimetic jellyfish robot that uses ionic polymer metal composites (IPMCs) as flexible actuators for propulsion. The shape and swimming style of this underwater vehicle are based on the Aequorea victoria jellyfish, which has an average swimming speed of 20 mm s 1 and which is known for its high swimming efficiency. The Aequorea victoria is chosen as a model system because both its bell morphology and kinematic properties match the mechanical properties of IPMC actuators. This medusa is characterized by its low swimming frequency, small bell deformation during the contraction phase, and high Froude efficiency. The critical components of the robot include the flexible bell that provides the overall shape and dimensions of the jellyfish, a central hub and a stage used to provide electrical connections and mechanical support to the actuators, eight distinct spars meant to keep the upper part of the bell stationary, and flexible IPMC actuators that extend radially from the central stage. The bell is fabricated from a commercially available heat-shrinkable polymer film to provide increased shape-holding ability and reduced weight. The IPMC actuators constructed for this study demonstrated peak-to-peak strains of 0.7% in water across a frequency range of 0.1‐1.0 Hz. By tailoring the applied voltage waveform and the flexibility of the bell, the completed robotic jellyfish with four actuators swam at an average speed 0.77 mm s 1 and consumed 0.7 W. When eight actuators were used the average speed increased to 1.5 mm s 1 with a power consumption of 1.14 W. (Some figures may appear in colour only in the online journal)

Activation of bacterial channel MscL in mechanically stimulated droplet interface bilayers.

MscL, a stretch-activated channel, saves bacteria experiencing hypo-osmotic shocks from lysis. Its high conductance and controllable activation makes it a strong candidate to serve as a transducer in stimuli-responsive biomolecular materials. Droplet interface bilayers (DIBs), flexible insulating scaffolds for such materials, can be used as a new platform for incorporation and activation of MscL. Here, we report the first reconstitution and activation of the low-threshold V23T mutant of MscL in a DIB as a response to axial compressions of the droplets. Gating occurs near maximum compression of both droplets where tension in the membrane is maximal. The observed 0.1–3 nS conductance levels correspond to the V23T-MscL sub-conductive and fully open states recorded in native bacterial membranes or liposomes. Geometrical analysis of droplets during compression indicates that both contact angle and total area of the water-oil interfaces contribute to the generation of tension in the bilayer. The measured expansion of the interfaces by 2.5% is predicted to generate a 4–6 mN/m tension in the bilayer, just sufficient for gating. This work clarifies the principles of interconversion between bulk and surface forces in the DIB, facilitates the measurements of fundamental membrane properties, and improves our understanding of MscL response to membrane tension.

Design and development of bio-inspired underwater jellyfish like robot using ionic polymer metal composite (IPMC) actuators

This study presents the design and development of an underwater Jellyfish like robot using Ionic Polymer Metal Composites (IPMCs) as propulsion actuators. For this purpose, IPMCs are manufactured in several variations. First the electrode architecture is controlled to optimize the strain, strain rate, and stiffness of the actuator. Second, the incorporated diluents species are varied. The studied diluents are water, formamide, and 1-ethyl-3-methyimidazolium trifluoromethanesulfonate (EmI-Tf) ionic liquid. A water based IPMC demonstrates a fast strain rate of 1%/s, but small peak strain of 0.3%, and high current of 200mA/cm2, as compared to an IL based IPMC which has a slow strain rate of 0.1%/s, large strain of 3%, and small current of 50mA/cm2. The formamide is proved to be the most powerful with a strain rate of approximately 1%/s, peak strain larger than 5%, and a current of 150mA/cm2. The IL and formamide based samples required encapsulation for shielding the diluents from being dissolved in the surrounding water. Two Jellyfish like robots are developed each with an actuator with different diluents. Several parameters on the robot are optimized, such as the input waveform to the actuators, the shape and material of the belly. The finesse ratio of the shape of the robotic belly is compared with biological jellyfish such as the Aurelia-Aurita..

A bio-inspired bell kinematics design of a jellyfish robot using ionic polymer metal composites actuators

This paper presents the re-creation of the bell deformation cycle of the Aequorea victoria jellyfish. It focuses on the design, fabrication, and characterization of the bio-inspired bell kinematics of an IPMC actuated robotic jellyfish. The shape and bell kinematics of this underwater vehicle are based on the Aequorea victoria jellyfish. This medusa is chosen as a model system based on a comparative bell kinematics study that is conducted among different jellyfish species. Aequorea victoria is known by its low swimming frequency, small bell deformation, and high Froude efficiency (95%). Different methods of implementing the actuators underneath the bell with smaller IPMC actuators are investigated to replicate the natural jellyfishs bell deformation. Results demonstrates that proper placement of the IPMC actuators results in bell configuration that more accurately represents the deformation properties of the natural jellyfish. Smaller IPMC actuators are used to achieve the desired deformation and thus the power consumption is reduced by 70% compared to previous generations. A biomimetic jellyfish robot prototype is built, and its ability to swim and produce thrust with smaller IPMC actuators is shown. The robot swam with four actuators swam at an average speed 0.77 mm/s and consumed 0.7 W. When eight actuators were used the average speed increased to 1.5 mm/s with a power consumption of 1.14 W.

Design and Development of a Biomimetic Jellyfish Robot That Features Ionic Polymer Metal Composites Actuators

This paper presents the design, fabrication, and characterization of a second generation biomimetic jellyfish robot that uses ionic polymer metal composites (IPMCs) as flexible actuators for propulsion. The shape and swimming style of this underwater vehicle are based on the Aurelia aurita jellyfish, which has an average swimming speed of 13 mm/s and which is known for a high swimming efficiency. The critical components of the vehicle include the flexible bell that provides the overall shape and dimensions of the jellyfish, a central hub used to provide electrical connections and mechanical support to the actuators, and flexible IPMC actuators that extend radially from the central hub. In order to provide increased shape holding ability and reduced weight, the bell is fabricated from a commercially available heat-shrinkable polymer film. A new lightweight hub has been designed and was fabricated by 3D printing using ABS plastic material. The hub features internal electrical contacts for providing voltage to the individual IPMC actuators. Finally, a new set of IPMC actuators are manufactured using the Direct Assembly Process (DAP). The IPMC actuators constructed for this study demonstrated peak-to-peak strains of ∼ 0.7% in water across a frequency range of 0.1–1.0Hz. By tailoring the applied voltage waveform and the flexibility of the bell, the completed robotic jellyfish swam at maximum speed of 1.5 mm/s.Copyright

A Hydrogel-Based Droplet Interface Lipid Bilayer Network

In this work, we present a process for the fabrication of meso-scale hydrogel-based lipid bilayer arrays. The hydrogels support lipid monolayers at an oil-water interface, and when brought together, form stable bilayers. The substrates are formed using 3D printed molds and include built-in, customizable circuits patterned with silver paint. The system can be adapted to varying network sizes and circuit designs, and new arrays are fabricated quickly and inexpensively using common laboratory techniques. An enclosed 3×3 array with 3 mm spacing between neighboring hydrogels and electrodes to individually examine each bilayer has been created using this method. An alternative test setup was also developed to better observe the formation of bilayers in a small array. Using this setup, two bilayers were formed simultaneously, demonstrating the feasibility of this type of system and providing valuable information for expanding and improving the enclosed network. Many of the design concepts presented here can be adapted for use at smaller scales using microfabrication techniques.Copyright

Biomolecular Hydrogel-Based Lipid Bilayer Array System

This work investigates the fabrication of hydrogel based lipid bilayers arrays using micro fabrication technologies that enable high precision in controlling the cell-scale droplets. Arrays of hydrogels that support curved aqueous lenses are deposited on two parallel substrates using lithography techniques on top of a network of Ag/AgCl electrodes. The first step in the fabrication process is to deposit silver electrodes using silver paint through a mask, a layer of silver chloride is then formed around the silver channels using another mask with the desired geometry. The hydrogel arrays are then achieved by exposing a thin film of photocrosslinkable hydrogel to UV light through a mask. Hydrogel arrays are fabricated using this technique, which is represents a relatively accurate and inexpensive method. The hydrogel structures can host a thin aqueous curved lenses containing phospholipids . Bilayer arrays can be formed by using a technique similar to the regulated attachment method, where mechanical force is used to bring adjacent aqueous lenses in contact.

The voltage-dependence of MscL has dipolar and dielectric contributions and is governed by local intramembrane electric field

Channels without canonical voltage sensors can be modulated by voltage acting on other domains. Here we show that besides protein dipoles, pore hydration can be affected by electric fields. In patches, both WT MscL and its V23T mutant show a decrease in the tension midpoint with hyperpolarization. The mutant exhibits a stronger parabolic dependence of transition energy on voltage, highly consistent with the favourable dielectric contribution from water filling the expanding pore. Purified V23T MscL in DPhPC droplet interface bilayers shows a similar voltage dependence. When reconstituted in an asymmetric DOPhPC/DPhPC bilayer carrying a permanent bias of ~130 mV due to a dipole potential difference between the interfaces, the channel behaved as if the local intramembrane electric field sets the tension threshold for gating rather than just the externally applied voltage. The data emphasize the roles of polarized water in the pore and interfacial lipid dipoles in channel gating thermodynamics.