Fluid Dynamics of Ballistic Strategies in Nematocyst Firing
Fluid Dynamics of Ballistic Strategies in Nematocyst Firing
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DOI：
10.3390/fluids5010020
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发表时间：
2020-03-01
期刊：
影响因子：
1.9
通讯作者：
Miller, Laura
中科院分区：
文献类型：
--
作者：
Hamlet, Christina;Strychalski, Wanda;Miller, Laura
刺丝囊是刺胞动物门（例如水母、海葵、水螅虫类）的成员所使用的具有刺细胞的细胞器，具有多种重要功能，包括捕获猎物和防御。刺丝囊是动物界中已知加速最快的结构。其微小的尺寸（微米级）加上快速的加速度（超过500万g）给成像带来了重大挑战，阻碍了对其运动学的详细描述。浸入边界法被用于数值模拟一种类似倒钩的结构在二维空间中朝着一个被动弹性目标在雷诺数从0.9到900的范围内短距离加速的动力学过程。结果表明，在较低雷诺数下先加速然后滑行不足以使刺丝囊到达其目标。刺丝囊类似倒钩的射弹需要高加速度才能过渡到惯性状态，并克服在细胞小尺度下通常会遇到的粘性阻尼效应。倒钩在惯性状态下的时间越长，当它接触到目标时射弹的最终速度就越高。我们发现，对于足够大的雷诺数，目标猎物的大小并不会显著影响倒钩的接近方式，然而较长的倒钩能够加速更多的周围流体，这反过来又使倒钩能够在惯性状态下保持更长的时间。由于最终速度与刺穿猎物细胞膜的可用力成正比，使系统能够在惯性状态下持续的高加速度对刺丝囊刺穿细胞膜甚至甲壳类动物表皮等表面的能力具有影响。
Nematocysts are stinging organelles used by members of the phylum Cnidaria (e.g., jellyfish, anemones, hydrozoans) for a variety of important functions including capturing prey and defense. Nematocysts are the fastest-known accelerating structures in the animal world. The small scale (microns) coupled with rapid acceleration (in excess of 5 million g) present significant challenges in imaging that prevent detailed descriptions of their kinematics. The immersed boundary method was used to numerically simulate the dynamics of a barb-like structure accelerating a short distance across Reynolds numbers ranging from 0.9-900 towards a passive elastic target in two dimensions. Results indicate that acceleration followed by coasting at lower Reynolds numbers is not sufficient for a nematocyst to reach its target. The nematocyst's barb-like projectile requires high accelerations in order to transition to the inertial regime and overcome the viscous damping effects normally encountered at small cellular scales. The longer the barb is in the inertial regime, the higher the final velocity of the projectile when it touches its target. We find the size of the target prey does not dramatically affect the barb's approach for large enough values of the Reynolds number, however longer barbs are able to accelerate a larger amount of surrounding fluid, which in turn allows the barb to remain in the inertial regime for a longer period of time. Since the final velocity is proportional to the force available for piercing the membrane of the prey, high accelerations that allow the system to persist in the inertial regime have implications for the nematocyst's ability to puncture surfaces such as cellular membranes or even crustacean cuticle.