Soft wearable ionic polymer sensors for palpatory pulse-rate extraction

IPMC (Ionic-Polymer-Metal-Composites) based sensing applications are gaining momentum owing to their flexible structure as well as bio-compatible attributes. The present article explores the domain of bio-potential measurements by using a soft-wearable IPMC-sensing unit to record natural auscultations of the wrist artery. The sensing capabilities are validated by characterizing the same through periodic impact loading over the polymer surface. The composite is installed on 10 healthy individuals, while the generated pulse-tracks are recorded simultaneously using a configured digital stethoscope used as reference. The experiments conducted on the selected experimental-set, in diverse physiological states reveal the potence of the proposed scheme in offering a novel material alternate to prevalent practices in pulse-bit sensing. The marked simplicity paves way for its induction as a potential smart sensor interface for pulse-rate monitoring

An iteratively optimized resolution to hyper redundancy for dissimilarly doped compliant IPMC actuators

Soft-robotics is gradually emerging as one of the promising fields of research and innovation. Owing to the blend of material-chemistry and conventional mechanics, complex motions have been successfully generated by flexible polymeric composites that act upon external activation stimuli. However, lack of robust deterministic models which can command reliable actuator performance, hinder their widespread deployments in diverse paradigms. The present article seeks to address the argument by modelling Ionic Polymer Metal Composites (IPMC) as multi-segmented chains of connected rigid bodies. A Cyclic-Coordinate-Descent (CCD) based Inverse Kinematic solver is employed to resolve the redundancy, by minimizing an objective function in joint space at gradual iterative steps. The algorithm is validated for its ability to model dissimilarly doped polymeric curvatures bearing distinct spatial postures. The 2-D shape estimation problem is addressed to generate patterns akin to original IPMCs for deployment on potential applications that anticipate a foresight of actuator geometry

Development of two jaw compliant gripper based on hyper-redundant approximation of IPMC actuators

Ionic Polymer Metal Composites (IPMC) have emerged as an actuator for gripping soft as well as rigid objects, owing to their compliance and good scalability. Their use in precision gripping necessitates the absence of any ambivalence in its characterization to ensure grasp stability. This article proposes an alternative approach to model IPMCs, contrary to prior attempts that have employed cantilever deflection theories. The bending patterns of the actuator soaked in distilled water and LiCl solution are studied using a Tractrix based hyper-redundant kinematic algorithm. Two distinct gripper designs comprising of a conventional two jaw as well as a modified passive jaw gripper have been investigated to ascertain their traversed workspaces in the aforementioned mediums. A prior knowledge of this working-area ensures an effective design of target-specific gripper configurations adept to negotiate objects with varied surface profiles. The results obtained after experiments indicate that IPMCs infused in LiCl solution exhibit a characteristic curvilinearity, suited for ensuring surface contact with the object. However the ones hydrated in de-ionized water demonstrate linear bending, apt for generating point contact. Though the passive-jaw gripper showcases a smaller workspace with respect to the active ones, yet it conveys a vital information regarding the contact force exerted on an object surface by the polymer jaw

Molecular Dynamics Simulations Reveal the HIV-1 Vpu Transmembrane Protein to Form Stable Pentamers

<div><p>The human immunodeficiency virus type I (HIV-1) Vpu protein is 81 residues long and has two cytoplasmic and one transmembrane (TM) helical domains. The TM domain oligomerizes to form a monovalent cation selective ion channel and facilitates viral release from host cells. Exactly how many TM domains oligomerize to form the pore is still not understood, with experimental studies indicating the existence of a variety of oligomerization states. In this study, molecular dynamics (MD) simulations were performed to investigate the propensity of the Vpu TM domain to exist in tetrameric, pentameric, and hexameric forms. Starting with an idealized α-helical representation of the TM domain, a thorough search for the possible orientations of the monomer units within each oligomeric form was carried out using replica-exchange MD simulations in an implicit membrane environment. Extensive simulations in a fully hydrated lipid bilayer environment on representative structures obtained from the above approach showed the pentamer to be the most stable oligomeric state, with interhelical van der Waals interactions being critical for stability of the pentamer. Atomic details of the factors responsible for stable pentamer structures are presented. The structural features of the pentamer models are consistent with existing experimental information on the ion channel activity, existence of a kink around the Ile17, and the location of tetherin binding residues. Ser23 is proposed to play an important role in ion channel activity of Vpu and possibly in virus propagation.</p> </div

Shape estimation of IPMC actuators in ionic solutions using hyper redundant kinematic modeling

Ionic Polymer Metal Composites (IPMCs) has established itself as an ionomer rendering wide-ranging applications spanning the paradigm of robotics to medical appliances, thereby drawing significant research interests. Prior studies to characterize IPMCs have been conducted over several years but efforts on its kinematic modeling have remained inchoate. The bending profile of IPMC changes when placed in different ionic solutions. The IPMC trace along with its tip location characterizes its complete behavior upon low level actuation. This article aims at identifying the bending patterns of an IPMC actuator, decomposing it as a 20-link hyper-redundant serial manipulator. The Tractrix based inverse kinematics engine is used to study the polymer profile in distilled water, 1.5 N LiCl and NaCl solutions respectively. The proposed algorithm yields a natural curve (Tractrix) which resembles the profile traced by an actuated IPMC strip — enabling its use in potential applications which would require a foresight of the actuator workspace

Representative structures.

<p>The structures for the different oligomeric states before (top row) and after (bottom row) 10 ns simulation in an implicit membrane environment are shown.</p

Replica-exchange molecular dynamics in an implicit membrane environment.

<p>(A) Probability distribution of the tilt angle for the conformations sampled at 300 K from the last 9 ns of replica-exchange molecular dynamics. (B) Average potential energy and (C) free energy of the different oligomeric states over the last 9 ns of replica-exchange molecular dynamics. The values shown are relative to the monomer. (D) RMSD of the tetramer, the pentamer, and the hexamer in the REX/MD simulations.</p

Interhelical distance and protein-lipid interactions.

<p>(A) Probability distribution of interhelical distance for tetramer, pentamer and hexamer. The distance between the centres-of-mass of adjoining helices was calculated. Only the helical backbone was considered, and the top three and bottom three residues were neglected. (B) Average number of hydrogen bonds between lipid headgroups and polar residues for Arg30 and headgroup (left panel), and Tyr29 and headgroup (right panel). The cutoffs used were 3.5 Å for the donor-acceptor distance, and 45° for the donor-hydrogen-acceptor angle.</p

Pore profile.

<p>(A) View along the pore axis from the C-terminal showing the Ser23 residue in “licorice” representation. Serine faces the interior of the channel in the pentamer model. (B) Side view of the pentamer model showing the location of the Ser23 residue (in “licorice” representation) and water molecules in the pore. The N-terminal side is on the top and the C-terminal is at the bottom. (C) Pore radius across the axis of the pentamer model. The pore is constricted towards the N-terminal side (top half).</p

Molecular dynamics in an explicit membrane environment.

<p>(A) Models for the tetramer, pentamer and hexamer after simulation in a fully hydrated lipid bilayer. The images for the pentamer are after 30 ns, and those for the tetramer and hexamer are after 10 ns. The lipid bilayer and solvent molecules have been omitted for clarity. The pentamer retained a channel-like structure in both the simulations. (B) RMSD of the different oligomeric states.</p