Search

Traditional robot designs typically employ rigid body parts and high-torque servo motors. This helps to obtain simple reproducible models and, therefore, to facilitate control. Soft robotics is a new research field that deliberately expands the design toolbox to a wide range of smart and, often, soft materials. This approach is generally inspired by the remarkable performance of biological systems, which use soft structures to interact successfully with noisy and hard-to-model environments and, as a result, outperform state-of-the-art robots in open-world scenarios. However, using soft bodies comes with a significant disadvantage. Soft materials often have complex and nonlinear dynamics, which makes them hard to model and therefore difficult to control. To fulfill the potential of soft robotics to achieve performances close to biological systems, this control problem has to be solved. A promising solution is another bioinspired principle called morphological computation, which proposes to outsource functionality directly to the body morphology. From this point of view, the seemingly undesired nonlinear dynamics become a resource for implementing nonlinear functionalities. This extends the control design problem to the question of how to design the body morphology of the robot. While there exist proofs of concept that demonstrate the potential of this approach, the existing work (for the most part) is lacking mathematical rigor and a general framework. We believe that the control community has the right set of tools to support the development of a design framework for morphological computation. The goal of this article (see “Summary”) is to provide an introduction to the concepts of soft robotics and morphological computation, explain how they can work together, and (with the help of examples) illustrate their potential for control. The hope is to inspire members of the control community to develop novel control frameworks for the next generation of soft robots.

Designing locomotive mechanisms for micro-scale robotic systems could enable new approaches to tackling problems such as transporting cargos, or self-assembling into pre-programmed architectures. Morphological factors often play a crucial role in determining the behaviour of micro-systems, yet understanding how to design these aspects optimally is a challenge. This paper explores how the morphology of a multi-cellular micro-robotic agent can be optimised for reliable locomotion using artificial evolution in a stochastic environment. We begin by establishing the theoretical mechanisms that would allow for collective locomotion to emerge from contractile actuations in multiple connected cells. These principles are used to develop a Cellular Potts model, in order to explore the locomotive performance of morphologies in simulation. Evolved morphologies yield significantly better performance in terms of the reliability of the travel direction and the distance covered, compared to random morphologies. Finally, we demonstrate that patterns in evolved morphologies are robust to small imperfections and generalise well to larger morphologies.

The ability to optically interact with cells on both an individual and collective level has applications from wound healing to cancer treatment. Building systems that can facilitate both localised light illumination and visualisation of cells can, however, be challenging and costly. This work takes the Dynamic Optical MicroEnvironment (DOME), an existing platform for the closed-loop optical control of microscale agents, and adapts the design to support live-cell imaging. Through modifications made to the imaging and projection systems within the DOME, a significantly higher resolution, alternative imaging channels and the ability to customise light wavelengths are achieved (Bio-DOME). This is accompanied by an interactive calibration procedure that is robust to changes in the hardware configuration and provides fluorescence imaging (Fluoro-DOME). These alterations to the fundamental design allow for long-term use of the DOME in an environment of higher temperature and humidity. Thus, long-term imaging of living cells in a wound, with closed-loop control of real-time frontier illumination via projected light patterns, is facilitated.

In recent years, researchers have investigated different methods to quantify embodiment for a variety of robotic systems including robotic arms, grippers and legged robots. This paper will discuss some of these methods, focusing on their potential contribution to designing robotic systems based on muscle-driven models. We start with the definition of embodiment based on the relational dynamics between the system and its environments by drawing upon the idea of mutual perturbation and structural coupling between the two. We will discuss how such an understanding can provide potential approaches to quantify embodiment. These includes two information-theoretic measures which are particularly suitable for muscle-driven models. The two methods are based on (i) comparing the controller and behaviour complexity and (ii) Conditional Mutual Information, which compares the difference in distribution of the action conditional on the actuated state and purely on its morphological properties. These methods were used on muscle-driven, biologically realistic hopping models to quantify embodiment at different stages of the hopping gait. The results clearly demonstrate the contribution of morphology of the muscle fibers at different points in the hopping cycle. Furthermore, these methods have been used in latter studies to measure the contribution of embodiment across different levels in a hierarchical control system of a neuro-musculoskeletal model and also to quantify the effects of information cost during various actions in a muscle-driven robotic system. We discuss the practical implications as well as limitations and the future work in the application of these quantification methods.

Soft robotics is a new and fast-growing field of robotics [1], [2]. It proposes to extend conventional robotics by going beyond the default building blocks, that is, rigid body parts and high-torque servo motors. Soft robotics also uses soft materials like silicone, hydrogels, and polymers. It also includes a wide range of smart materials that are able to change physical properties when stimulated, therefore outsourcing computational functionality directly to the body of the robot (this concept is often referred to as morphological computation [3], [4]). In addition, soft robotics considers partially rigid structures like tensegrity designs, foldable robots, origami-based mechanisms, and many others [5]. This expansion of the design space enriches robotics in general and opens the space for radically novel sensing and actuation systems and, consequently, for new applications that were previously out of reach for conventional robotic systems.

To learn more about how the step of cholesterol uptake into the brush border membrane (BBM) of enterocytes influences overall cholesterol absorption, we measured cholesterol absorption 4 and 24 h after administration of an intragastric bolus of radioactive cholesterol in mice with scavenger receptor class B, type 1 (SR-BI) and/or cluster determinant 36 (CD36) deleted. The cholesterol absorption efficiency is unaltered by deletion of either one or both of the receptors. In vitro determinations of the cholesterol uptake specific activity of the BBM from the mice reveal that the scavenger receptors facilitate cholesterol uptake into the proximal BBM. It follows that cholesterol uptake into the BBM is not normally rate-limiting for the cholesterol absorption process in vivo; a subsequent step, such as NPC1L1-mediated transfer from the BBM into the interior of the enterocyte, is rate-limiting. The absorption of dietary cholesterol after 4 h in mice lacking SR-BI and/or CD36 and fed a high-fat/high-cholesterol diet is delayed to more distal regions of the small intestine. This effect probably arises because ATP binding cassette half transporters G5 and G8-mediated back flux of cholesterol from the BBM to the lumen of the small intestine limits absorption and causes the local cholesterol uptake facilitated by SR-BI and CD36 to become rate-limiting under this dietary condition.

To learn more about how the step of cholesterol uptake into the brush border membrane (BBM) of enterocytes influences overall cholesterol absorption, we measured cholesterol absorption 4 and 24 h after administration of an intragastric bolus of radioactive cholesterol in mice with scavenger receptor class B, type 1 (SR-BI) and/or cluster determinant 36 (CD36) deleted. The cholesterol absorption efficiency is unaltered by deletion of either one or both of the receptors. In vitro determinations of the cholesterol uptake specific activity of the BBM from the mice reveal that the scavenger receptors facilitate cholesterol uptake into the proximal BBM. It follows that cholesterol uptake into the BBM is not normally rate-limiting for the cholesterol absorption process in vivo; a subsequent step, such as NPC1L1-mediated transfer from the BBM into the interior of the enterocyte, is rate-limiting. The absorption of dietary cholesterol after 4 h in mice lacking SR-BI and/or CD36 and fed a high-fat/high-cholesterol diet is delayed to more distal regions of the small intestine. This effect probably arises because ATP binding cassette half transporters G5 and G8-mediated back flux of cholesterol from the BBM to the lumen of the small intestine limits absorption and causes the local cholesterol uptake facilitated by SR-BI and CD36 to become rate-limiting under this dietary condition.

No Abstract

No Abstract

The phospholipids of lipoproteins can be transferred to cells by an endocytosis-independent uptake pathway. We analyzed the role of scavenger receptor BI (SR-BI) for the selective cellular phospholipid import. Human monocytes rapidly acquired the pyrene (py)-labeled phospholipids sphingomyelin (SM), phosphatidylcholine, and phosphatidylethanolamine from different donors (low and high density lipoproteins (LDL, HDL), lipid vesicles). The anti-SR-BI antibody directed against the extracellular loop of the membrane protein lowered the cellular import of the phospholipids by 40–80%. The phospholipid transfer from the lipid vesicles into the monocytes was suppressed by LDL, HDL, and apoprotein AI. Transfection of BHK cells with the cDNA for human SR-BI enhanced the cellular import of the vesicle-derived py-phospholipids by 5–6-fold. In the case of the LDL donors, transfer of py-SM to the transfected cells was stimulated to a greater extent than the uptake of the other py-phospholipids. Similar differences were not observed when the vesicles and HDL were used as phospholipid donors. The concentration of LDL required for the half-maximal phospholipid import was close to the previously reported apparent dissociation constant for LDL binding to SR-BI. The low activation energy of the SR-BI-mediated py-phospholipid import indicated that the transfer occurs entirely in a hydrophobic environment. Disruption of cell membrane caveolae by cyclodextrin treatment reduced the SR-BI-catalyzed incorporation of py-SM, suggesting that intact caveolae are necessary for the phospholipid uptake. In conclusion, SR-BI mediates the selective import of the major lipoprotein-associated phospholipids into the cells, the transfer efficiency being dependent on the structure of the donor lipoprotein.

The transport of Fe2+ and other divalent transition metal ions across the intestinal brush border membrane (BBM) was investigated using brush border membrane vesicles (BBMVs) as a model. This transport is an energy-independent, protein-mediated process. The divalent metal ion transporter of the BBM is a spanning protein, very likely a protein channel, that senses the phase transition of the BBM, as indicated by a break in the Arrhenius plot. The transporter has a broad substrate range that includes Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+. Under physiological conditions the transport of divalent metal ions is proton-coupled, leading to the acidification of the internal cavity of BBMVs. The divalent metal ion transporter can be solubilized in excess detergent (30mM diheptanoylphosphatidylcholine or 1% Triton X-100) and reconstituted into an artificial membrane system by detergent removal. The reconstituted membrane system showed metal ion transport characteristics similar to those of the original BBMVs. The properties of the protein described here closely resemble those of the proton-coupled divalent cation transporter (DCT1, Nramp2) described by Gunshin et al. (1997, Nature. 388:482–488). We may conclude that a protein of the Nramp family is present in the BBM, facilitating the transport of Fe2+ and other divalent transition metal ions.

The determination of the NMR structure of the sterol carrier protein-2 (SCP2), analysis of backbone 15N spin relaxation parameters and NMR studies of nitroxide spin-labeled substrate binding are presented as a new basis for investigations of the mode of action of SCP2. The SCP2 fold is formed by a five-stranded β-sheet and four α-helices. Fatty acid binding to a hydrophobic surface area formed by amino acid residues of the first and third helices, and the β-sheet, which are all located in the polypeptide segment 8-102, was identified with the use of the spin-labeled substrate 16-doxylstearic acid. In the free protein, the lipid-binding site is covered by the C-terminal segment 105-123, suggesting that this polypeptide segment, which carries the peroxisomal targeting signal (PTS1), might be involved in the regulation of ligand binding.

Selective lipid transport through the brush-border membrane in the small intestine of mammals is mediated by membrane-bound proteins, the so-called scavenger receptors of class B, type I or II (SR-BI or -BII). These, in turn, are inhibited by certain proteins and synthetic α-peptides that have an amphipathic helix as the binding motif (Fig. 1). In whole cells (test with human colonic carcinoma cells, CaCo-2), on the other hand, the inhibitors are subject to proteolysis. We have now tested six β-peptides (hexa-, hepta-, and nonamers 1 – 6), each carrying one to seven water-solubilizing side chains of either Ser or Lys, with a brush-border-membrane (BBM) vesicle model system (rate and IC50 values in Figs. 2 and 3) and with a tightly packed monolayer of CaCo-2 cells (rate in Fig. 4), to find that the rate of transport of cholesterol can be reduced to what may be considered the passive diffusion (`background') level. There is a correlation between the ability of the β-peptides to form an amphipathic-type 314-helical secondary structure in MeOH and their inhibitory effect (Table 1 and Fig. 5). Although the inhibitory activity of the β-peptides is in only the mM range (Table 2), it is to be compared with no activity at all of previously tested α-peptides and proteins (built of L-amino acids) in CaCo-2 cells. Furthermore, these active β-peptides (1, 5, and 6) contain only seven or nine residues and must be considered simple, first-generation models capable of mimicking the biological activity of amphipathic α-peptide helices in living whole cells.

Summary Na+ and sugar permeabilities of egg lecithin bilayers were measured using curved bilayers and planar bilayers as represented by single-bilayer vesicles and black lipid films, respectively. The Na+ permeability coefficient measured with single-bilayer vesicles at 25°C is (2.1±0.6)×10-13 cm sec-1. Because of technical difficulties it has been impossible to measure ionic permeabilities of values lower than about 10-10 cm sec-1 in planar (black) lipid bilayers using tracer methods. Thed-glucose andd-fructose permeabilities were measured with both curved and planar bilayers. The permeability coefficients measured with vesicles at 25°C are (0.3±0.2)×10-10 cm sec-1 for glucose and (4±1)×10-10 cm sec-1 ford-fructose; these are in reasonable agreement with the corresponding values obtained for planar (black) lipid bilayers which are (1.1±0.3)×10-10 cm sec-1 ford-glucose and (9.3±0.3)×10-10 cm sec-1 ford-fructose, respectively.

Subjecting rabbit small intestinal brush border membrane vesicles (BBMV) to freeze-thaw cycles releases water-soluble lipid exchange (transfer) proteins into the supernatant. They differ widely in apparent molecular weight and catalyze cholesterol, phosphatidylcholine, and phosphatidylinositol exchange between two populations of small unilamellar lipid vesicles. In order to determine their interrelations, the smallest water-soluble lipid exchange protein was purified to homogeneity by gel filtration on Sephadex G-75 and cation exchange chromatography on Mono S. It is a basic protein of apparent molecular mass of 13 ± 0.5 kDa. The purified protein was used to raise polyclonal antibodies. Polyclonal antibodies were also produced against a lipid exchange protein of apparent molecular mass of 100-120 kDa. By comparing lipid exchange, lipid binding, and immunological properties of the water-soluble lipid exchange proteins it can be shown that the 13-kDa (peak 3) protein is related to the 100-120 kDa (peak 1) protein; the properties of these two proteins are different from those of the peak 2 lipid exchange protein of apparent molecular mass of 22 kDa. Based on the immunological cross-reactivity observed between the 13 and 100-120 kDa and the lipid binding properties of these two proteins, a working hypothesis is proposed: both proteins are probably part of an intergral membrane protein of the brush border membrane that facilitates cholesterol and phosphatidylcholine absorption in this membrane. Evidence derived from immunogold labeling of BBMV supports the notion that this protein is located on the external (luminal) side of the brush border membrane. The analogous behavior of rabbit and human small intestinal brush border membrane in terms of lipid absorption and the release of water-soluble lipid exchange proteins is discussed.

The uptake of free and esterified cholesterol at the brush border membrane is protein‐mediated. Here we show that this sterol uptake is effectively inhibited by exchangeable serum apolipoproteins. Binding of the apolipoprotein to the brush border membrane mediates the inhibitory effect. Evidence is presented to show that the structural motif responsible for the inhibition is the amphipathic α‐helix.

The potential of ESR spin labeling in determining hexagonal amphiphilic phases is assessed. Spin labeled hexagonal phases in which the motional averaging about the cylinder axis is rapid on the ESR time scale can be readily identified by their ESR spectrum. The lineshape is distinctly different from that of smectic lamellar phases. The same ESR lineshape which is characteristic of the hexagonal phase is also obtained with spin labeled rodlike micelles provided that the motional averaging about their cylinder axis is rapid. If, however, this averaging is slow both hexagonal phases and rodlike micelles give ESR spectra which are indistinguishable from smectic phases (disclike micelles).

Dilute (>10% w/v) unsonicated phosphatidylserine dispersions in H2O contain spherical particles of a wide size distribution (0.1 to 15 µm). The majority have diameters between 0.1 to 2 µm and lack the multilamellar arrangement of bilayers typical of unsonicated lecithin dispersions. Sonication produces small thermodynamically unstable vesicles surrounded by a single closed bilayer with an average vesicle diameter of 160 A (range 125 to 250 A). The vesicles are more homogeneous with respect to size and their curvature is significantly greater than that of vesicles prepared from lecithins of similar chain length. While phosphatidylserine forms inverted micelles in organic solvent, no micelles were detected in sonicated, aqueous dispersions. Increasing the ionic strength leads to an increase in particle size and to the formation of multilamellar structures both with sonicated and unsonicated dispersions and eventually flocculation of a metal-phosphatidylserine complex occurs. Unsonicated phosphatidylserine dispersions give no high resolution spectrum. Proton nuclear magnetic resonance measurements on sonicated dispersions in 2H2O show that the molecular motion in the polar group of the molecule is sufficient for all protons, including those of the glycerol group, to contribute to the high resolution spectrum. Increasing the ionic strength leads to a closer packing of the polar groups and of the hydrocarbon chain CH2groups close to the glycerol group without significantly affecting the correlation times of motion of most of the protons along the hydrocarbon chains. However, the anisotropy of the hydrocarbon chain motion and thus the degree of order within the bilayer increases significantly.

Sterol carrier protein 2 (SCP2) is a basic intracellular protein which facilitates the in vitrointermembrane transfer of cholesterol, phospholipids and glycolipids. SCP2 was expressed in Escherichia coli, purified to apparent electrophoretic homogeneity and crystallized. Single crystals were obtained by hanging‐drop vapour diffusion using ammonium sulfate as precipitant. These crystals belong to space group P41212 or its enantiomorph, with unit‐cell parameters a= b= 57.5, c= 86.5 Å, and have one molecule in the crystallographic asymmetric unit. Intensity data to 1.8 Å resolution were collected from native SCP2 crystals using synchrotron radiation, were processed and scaled with an Rlinear= 4.9%.

Robust locomotion in a wide range of environments is still beyond the capabilities of robots. In this article, we explore how exploiting the soft morphology can be used to achieve stability in the commonly used spring-loaded inverted pendulum model. We evolve adaption rules that dictate how the attack angle and stiffness of the model should be changed to achieve stability for both offline and online learning over a range of starting conditions. The best evolved rules, for both the offline and online learning, are able to find stability from a significantly wider range of starting conditions when compared to an un-adapting model. This is achieved through the interplay between adapting both the control and the soft morphological parameters. We also show how when using the optimal online rule set, the spring-loaded inverted pendulum model is able to robustly withstand changes in ground level of up to 10 m downwards step size.