The Rowland Institute at Harvard, 100 Edwin H. Land Blvd, Cambridge, MA 02142, USA.
Bioinspir Biomim. 2012 Mar;7(1):016010. doi: 10.1088/1748-3182/7/1/016010. Epub 2012 Feb 16.
To explore the interplay between muscle function and propulsor shape in swimming animals, we built a robotic foot to mimic the morphology and hind limb kinematics of Xenopus laevis frogs. Four foot shapes ranging from low aspect ratio (AR = 0.74) to high (AR = 5) were compared to test whether low-AR feet produce higher propulsive drag force resulting in faster swimming. Using feedback loops, two complementary control modes were used to rotate the foot: force was transmitted to the foot either from (1) a living plantaris longus (PL) muscle stimulated in vitro or (2) an in silico mathematical model of the PL. To mimic forward swimming, foot translation was calculated in real time from fluid force measured at the foot. Therefore, bio-robot swimming emerged from muscle-fluid interactions via the feedback loop. Among in vitro-robotic trials, muscle impulse ranged from 0.12 ± 0.002 to 0.18 ± 0.007 N s and swimming velocities from 0.41 ± 0.01 to 0.43 ± 0.00 m s(-1), similar to in vivo values from prior studies. Trends in in silico-robotic data mirrored in vitro-robotic observations. Increasing AR caused a small (∼10%) increase in peak bio-robot swimming velocity. In contrast, muscle force-velocity effects were strongly dependent on foot shape. Between low- and high-AR feet, muscle impulse increased ∼50%, while peak shortening velocity decreased ∼50% resulting in a ∼20% increase in net work. However, muscle-propulsion efficiency (body center of mass work/muscle work) remained independent of AR. Thus, we demonstrate how our experimental technique is useful for quantifying the complex interplay among limb morphology, muscle mechanics and hydrodynamics.
为了探究游泳动物中肌肉功能和推进器形状之间的相互作用，我们制造了一个机器脚来模拟非洲爪蟾的形态和后肢运动学。我们比较了四种从低长宽比（AR=0.74）到高长宽比（AR=5）的脚型，以测试低长宽比的脚是否能产生更高的推进阻力，从而使游泳速度更快。我们使用反馈回路，采用两种互补的控制模式来旋转脚：（1）通过体外刺激的比目鱼肌（PL）肌肉或（2）PL 的计算机数学模型向脚传递力。为了模拟向前游泳，根据脚处测量到的流体力实时计算脚的平移。因此，生物机器人游泳通过反馈回路从肌肉-流体相互作用中产生。在体外机器人试验中，肌肉脉冲范围为 0.12±0.002 至 0.18±0.007 N s，游泳速度范围为 0.41±0.01 至 0.43±0.00 m s(-1)，与先前研究中的体内值相似。在计算机机器人数据中的趋势与体外机器人观察结果相吻合。长宽比的增加导致生物机器人游泳速度的峰值略有增加（约 10%）。相比之下，肌肉力-速度效应强烈依赖于脚的形状。在低长宽比和高长宽比的脚之间，肌肉脉冲增加了约 50%，而峰值缩短速度下降了约 50%，导致净功增加了约 20%。然而，肌肉推进效率（质心工作/肌肉工作）与长宽比无关。因此，我们展示了我们的实验技术如何有助于量化肢体形态、肌肉力学和水动力学之间的复杂相互作用。
