Unveiling Quick-Release Mechanism of Mussels

The same bundle of non-living filaments that mussels use to anchor themselves within their environment – to withstand crushing waves, for example – can also be jettisoned on demand. Mussels create this quick-release interface, a new study finds, by way of a neurochemically-mediated junction, where billions of motile cilia hold fast to interlinked biopolymer sheets. "[The study's] findings could be informative about how nonliving materials can be dynamically interfaced with living tissue, as in the case of detachable biosensors and medical implants," write Guoqing Pan and Bin Li in a related Perspective. The ability to produce stable and strong connections between living tissues and nonliving surfaces – while also being easily removed on demand – is crucial for a wide range of advanced biomaterials applications. Engineering such biointerfaces has proven difficult, mainly due to the large differences in mechanical properties between soft biotic tissues and abiotic materials. Here, taking inspiration from an example of a strong biointerface in nature, Jenaes Sivasundarampillai and colleagues investigated the connections between the byssus stem root and the foot of Mytilus mussels. More colloquially known as the "beard," a byssus is a bundle of non-living filaments that mussels use to anchor themselves. The stem root of the byssus is connected to the living tissue of the mussel foot. While the connection between the byssus stem root and foot is strong, Mytilus mussels can inexplicably jettison their entire byssus on demand, suggesting that the byssus biointerface must also be dynamically tunable to enable quick release. To better understand the mechanism underlying this ability, Sivasundarampillai et al. leveraged a suite of imaging and spectroscopic approaches, only to discover a sophisticated biointerface junction consisting of non-living biopolymer sheets interlocked between layers of living tissue covered in nearly six billion soft, motile cilia. The high surface contact between the cilia on the foot tissue and the lamellar byssus stem root provides a way to counteract the mechanical mismatch between the two surfaces, and the oscillating motion of the cilia helps with both the strength and rapid release of the biointerface. Sivasundarampillai et al. also show that this cilial movement is influenced by neurotransmitters, suggesting that dopamine and serotonin control the mechanical interaction between the living and non-living tissues.