Autonomous locomotion and Nastic movements
One area of interest in physiology is to understand autonomous movement and its regulation. Movement requires force production, and its spatiotemporal coordination and control in light of sensory feedback from the environment. The questions any study of coordinated movement raises thus impinge on molecular, cellular and tissue dynamics and neuroscience, and from a mathematical perspective involves ideas from continuum dynamics, control theory, optimization etc. and link to questions in sensory physiology, behavior, ecology etc.
A particular interest is that of locomotion physiology that links systems neuroscience to morphology, mechanics, control and learning. Animals move in diverse manners, and we have studied many of these locomotory gaits – walking, crawling, swimming, slithering, etc. from a theoretical and experimental perspective to understand the neurodynamics of locomotion, as well as their ecodynamics, created theories for the different gaits of long slender animals such as crawling snails, and worms, undulating snakes, flexing fishes etc. and showed that tuning a single parameter suffices to explain the gait transitions from crawling to undulation to inch-worming, explaining how they respond to stimuli in the context of simple behavioral strategies such as thermotaxis etc.
We have shown how one can derive general scaling principles underlying macroscopic aquatic locomotion which capture the essence of locomotion from shrimps to whales, again showing how physical constraints lead to evolutionary convergence, with lessons for robotic swimmers, the evolution of locomotion using robot-like objects, gaits and gait transitions in slender organisms such as snakes, and simple aspects of learning and coordination in primitive organisms.
Animals are not the only living systems capable of autonomous movement. Plants can also move only by growing, except for the odd carnivorous plant, and so respond to environmental changes by very different strategies relative to those deployed by animals. These adaptations and exaptations raise a host of physical and physico-chemical questions that beg for a quantitative treatment from both an experimental and a theoretical perspective. The diversity of plant and fungal life on our planet raises questions from the range of leaf and flower shapes to the ability to silently haul water to the top of a giant Sequoia, the myriad mechanisms for seed and spore dispersal, carnivory and rapid movements, etc. at the interface of biology and physics. Our occasional studies in this area have focused on aspects of hydraulically-driven movements in plants and fungi, the morphometry and morphogenesis of shoots, leaves and flowers, the design principles underlying transpiration, and proprioceptive feedback in growth. We are also interested using plant physiology as an inspiration for engineered devices.
The breakdown of physiology is manifest in a range of disorders and diseases. More than a decade ago, inspired by the early work of Pauling et al. on hemoglobinopathies, we explored the vaso-occlusive dynamics of sickle cell disease in microfluidic devices experimentally and showed that we can capture the phase space of jamming in terms of a set of geometric, physical and biological parameters. This allowed us to construct a theoretical framework for how a single red blood cell gets stuck in a tapering channel, and how the collective dynamics of jamming occurs in pressure-driven flows of soft suspensions of these cells, capturing the dynamics of a vaso-occlusive event. We have recently returned to the question to study how we might create cheap diagnostics for the progression of the disease and deploy these in resource-poor environments.
P. Paoletti and L. Mahadevan, Journal of Fluid Mechanics, 698, 489-516, 2011. [View PDF] [Download PDF]