Journal of The Royal Society Interface最新文献

Bond graphs provide an energy-based methodology for modelling complex systems hierarchically; at the moment, the method allows biological systems with both chemical and electrical subsystems to be modelled. Herein, the bond graph approach is extended to include chemomechanical transduction thus extending the range of biological systems to be modelled. Actin filament polymerization and force generation is used as an example of chemomechanical transduction, and it is shown that the TF (transformer) bond graph component provides a practical, and conceptually simple, alternative to the Brownian ratchet approach of Peskin, Odell, Oster and Mogilner. Furthermore, it is shown that the bond graph approach leads to the same equation as the Brownian ratchet approach in the simplest case. The approach is illustrated by showing that flexibility and non-normal incidence can be modelled by simply adding additional bond graph components and that compliance leads to non-convexity of the force-velocity curve. Energy flows are fundamental to life; for this reason, the energy-based approach is utilized to investigate the power transmission by the actin filament and its corresponding efficiency. The bond graph model is fitted to experimental data by adjusting the model physical parameters.

Achieving a comprehensive understanding of animal intelligence demands an integrative approach that acknowledges the interplay between an organism's brain, body and environment. Insects, despite their limited computational resources, demonstrate remarkable abilities in navigation. Existing computational models often fall short in faithfully replicating the morphology of real insects and their interactions with the environment, hindering validation and practical application in robotics. To address these gaps, we present I2Bot, a novel simulation tool based on the morphological characteristics of real insects. This tool empowers robotic models with dynamic sensory capabilities, realistic modelling of insect morphology, physical dynamics and sensory capacity. By integrating gait controllers and computational models into I2Bot, we have implemented classical embodied navigation behaviours and revealed some fundamental navigation principles. By open-sourcing I2Bot, we aim to accelerate the understanding of insect intelligence and foster advances in the development of autonomous robotic systems.

Many swimmers, especially small- to medium-sized animals, use intermittent locomotion that differs from continuous swimming of large species. This type of locomotion, called burst and coast, is often associated with an energetic advantage. In this work, we investigate the intermittent locomotion inspired by fish locomotion but applied to a propeller. The energy consumption of burst-and-coast cycles is measured and compared to the continuous rotation regime. We show that a substantial drag ratio between the active and passive phases of the motion, as observed in fish, is critical for energy savings. Such a contrast can be obtained using a folding propeller that passively opens and closes as the propeller starts and stops rotating. For this reconfigurable propeller, intermittent propulsion is found to be energetically advantageous, saving up to 24% of the energy required to cruise at a given speed. Using an analytical model, we show that intermittent motion is more efficient than continuous motion when the drag reduction in the coast phase exceeds 65%. For fish-like locomotion, this threshold seems to be closer to 30%. A formal analogy allows us to explain the difference between propeller propulsion and fish locomotion.

As SARS-CoV-2 has transitioned from a novel pandemic-causing pathogen into an established seasonal respiratory virus, focus has shifted to post-acute sequelae of COVID-19 (PASC, colloquially 'long COVID'). We use compartmental mathematical models simulating emergence of new variants to help identify key sources of uncertainty in PASC trajectories. Some parameters (such as the duration and equilibrium prevalence of infection, as well as the fraction of infections that develop PASC) matter more than others (such as the duration of immunity and secondary vaccine efficacy against PASC). Even if newer variants carry the same risk of PASC as older types, the dynamics of selection can give rise to greater PASC prevalence. However, identifying plausible PASC prevalence trajectories requires accurate knowledge of the transmission potential of COVID-19 variants in the endemic phase. Precise estimates for secondary vaccine efficacy and duration of immunity will not greatly improve forecasts for PASC prevalence. Researchers involved with Living Evidence Synthesis, or other similar initiatives focused on PASC, are well advised to ascertain primary efficacy against infection, duration of infection and prevalence of active infection in order to facilitate predictions.

Nitric oxide (NO) is an important vasodilator responsible for maintaining vascular tone in the human body. Its production in endothelial cells (ECs) is regulated by the rise of cytoplasmic Ca²⁺ concentration and shear stress perceived by blood flow. The increase in cytoplasmic Ca²⁺ concentration is mainly activated by adenosine triphosphate (ATP) released from red blood cells (RBCs) and ECs. However, RBCs, which act as NO scavengers, can affect the bioavailability of NO in blood vessels. In this study, we developed a model that incorporates ATP and shear stress-dependent NO production, integrating various biochemical pathways. The model results are qualitatively consistent with the experimental findings. Given that ATP concentration and shear stress vary spatially within blood circulation, influenced by factors such as vessel width, flow strength and RBC concentration, these variations can significantly affect NO bioavailability. Here, we study RBC flow, ATP release from RBCs and ECs, and [Formula: see text] and NO dynamics in a two-dimensional channel using the immersed boundary lattice Boltzmann method. The main findings from the study include: (i) an increase in RBC concentration leads to a rise in ATP and cytoplasmic Ca²⁺ concentrations for all variation in channel widths, while NO concentration exhibits a decrease; (ii) NO bioavailability is significantly influenced by RBC distribution, particularly in strongly confined channels; and (iii) two phases of NO bioavailability are observed in different regions of the blood vessels: one with a significant concentration change at low RBC concentration and another with a minimal concentration change at high RBC concentration, across all confinements. The outcomes of this study may provide valuable insights into the mechanisms of NO-dependent vasodilation and the transport of oxygen by RBCs within microvascular networks for future studies.

Intra-operative tensioning of the posterior cruciate ligament (PCL) in total knee arthroplasty (TKA) is commonly based on the surgeon's experience, resulting in a possibly loose or overly tight PCL. To date, the consequences of different PCL tensioning scenarios for the post-operative biomechanics of the knee remain unclear. Using a comprehensive musculoskeletal modelling approach that allows predictive joint kinematic and kinetic balance, we assessed variations in the movement and loading patterns of the knee as well as changes in ligament and muscle forces during walking in response to systematic variations in the PCL reference strain. The results indicate only small differences in the tibiofemoral and patellofemoral kinematics and kinetics for scenarios involving up to 10% release of the PCL (relative to the baseline reference scenario with 2% residual strain). These observations remain valid for simulations performed with high- as well as with low-conformity implant designs. However, over-tensioning of the ligament was found to considerably overload the tibiofemoral joint, including altered contact mechanics, and may therefore shorten the implant longevity. Finally, no meaningful impact of the PCL reference strain on the muscle force patterns was observed. This study therefore favours balancing the knee with a slightly loose rather than tense PCL, if appropriate intra-operative PCL tension cannot be objectively achieved.

For sustained swimming and flights, vertebrates and insects oscillate their propulsors periodically within a narrow range of Strouhal number (St), a dimensionless quantity describing the rate and density of the motion, suggesting a close relationship between the range and cruising optimality. The persistence of this range across size and fluids has puzzled biologists and engineers, resulting in multiple interpretations of its cause. Here, we propose that the optimal St range is largely constrained by power output efficiency of the trailing edge of the caudal fin. A mathematical model of the periodic wake of the trailing edge, which defines the proportion of power lost without contributing to propulsion, predicts that such energy loss is minimal in the observed range of St preferred by fish. The constraints apply across a range of Reynolds number in cruising fish. The same constraints dictate the optimal speed across a wide range of swimmers, in combination with morphological characteristics. Other factors such as drag properties also affect the optimal swimming speed, but probably to a smaller extent. The result that the geometry of periodic waveforms is key to cruising optimality provides an additional angle to study animal locomotion in fluids and related bioinspired robotics.

Soft tissue at the human-exoskeleton interface can deform under load to absorb, return and dissipate the mechanical energy generated by the exoskeleton. These soft tissue effects are often not accounted for and may mislead researchers on the actual joint assistance an exoskeleton provides. We assessed the effects of soft tissue by quantifying the performance and energy distribution of a knee exoskeleton under different assistance strategies using a synthetic lower limb phantom. The phantom emulated knee kinematics and soft tissue deformation at the exoskeleton interface. We loaded the exoskeleton on the phantom under six different spring stiffness conditions. Motion capture marker and load cell data from the phantom-exoskeleton assembly allowed us to estimate the moments, stiffness and energy contributions of the exoskeleton and physical interface. We found that soft tissue caused interface power to increase and exoskeleton power to decrease with increasing spring stiffness. Despite similar joint kinematics, our findings show that increasing exoskeleton assistance did not notably change power transfer to the targeted joint, as soft tissue compressed under high forces. Our methodology improves exoskeleton design process by estimating energy distribution and transfer for exoskeletons while accounting for the effects of soft tissue deformation before human testing.

Directly transmitted infectious diseases spread through social contacts that change over time, but outbreak models typically make simplifying assumptions about network structure and dynamics. To assess how common assumptions relate to real-world interactions, we analysed 11 networks from five settings and developed metrics, capturing crucial epidemiological features of these networks. We developed a novel metric, the 'retention index', to characterize the distribution of retained contacts over consecutive time steps relative to fully static and dynamic networks. In workplaces and schools, contacts in the same department formed most of the retained contacts. In contrast, no clear contact type dominated the retained contacts in hospitals, thus reducing overall risk of disease introduction would be more effective than control targeted at departments. We estimated the contacts repetition over multiple days and showed that simple resource planning models overestimate the number of unique contacts by 20%-70%. We distinguished the difference between 'superspreader' and infectious individuals driving 'superspreading events' by measuring how often the individual represents the top 80% of contacts in the time steps over the study duration. We showed an inherent difficulty in identifying 'superspreaders' reliably: less than 20% of the individuals in most settings were highly connected for multiple time steps.