chapter  5
From Sand Tube to Test Tube: The Adhesive Secretion From Sabellariid Tubeworms
Pages 20

Polychaetes of the family Sabellariidae are tube-dwelling marine worms commonly called honeycomb worms or sandcastle worms because they can build large colonies made up of thousands of tubes placed side by side. Tubes are composed of sand grains or shell fragments assembled with spots of cement released at the level of a bilobed building organ located near the mouth. This building organ is the visible external part of a complex secretory machinery made up of bouquets of cement cells located deep within the anterior part of the animal’s body. Two main types of cement cells can been distinguished: cells with homogeneous granules and cells with

heterogeneous granules containing inclusions. After secretion, the granules mix partially and form porous cement discs in which the pores derive from the swelling of the intragranular inclusions. The cement consists of several proteins, a sulphated polysaccharide, and magnesium and calciumions. Five major proteins were identified which are characterized by highly repetitive and blocky primary structures. DOPA and phosphoserine, two posttranslationally modified amino acids, were detected in some of the adhesive proteins. Biomimetic molecules have been produced in the form of recombinant preparations of the adhesive proteins, of chemically synthesized peptides, or by the functionalization of (meth)acrylate polymers with reactive DOPA groups. The bio-inspired polymers were condensed into a liquid complex coacervate exhibiting ideal features for effective underwater adhesion, allowing them to be tested in medical applications. 5.1 IntroductionSabellariids are tube-dwelling marine polychaetes which live in the intertidal zone [1,2]. They are commonly called honeycomb worms or sandcastle worms because some species are gregarious and the tubes from a huge number of individuals are closely imbricated to form large reef-like mounds (Fig. 5.1a). To build the tube in which they live, they use their tentacles to collect particles such as sand grains, mollusc shell fragments or broken sea urchin spines from the water column and sea bottom, and convey them to the so-called building organ. This organ is a pulpy crescent-shaped bilobed structure located near the mouth (Fig. 5.1b). It selects the particles, dabs them with spots of cement, and adds them at the growing edge of the tube [3-5].The stonemason abilities of sabellariids have been known for centuries [6], but it is only recently that some of the secrets of their cement have been unravelled, due to its potential to inspire the development of novel biomimetic underwater adhesives [see, e.g., Ref. 7]. As of today, the cement of sabellariid tubeworm is one of the best characterized marine bioadhesive together with those of mussels and barnacles [8,9]. Two species have attracted most of the attention in terms of tube building: Sabellaria alveolata, a common species along European coasts occurring from Cornwall to the south of Morocco [10]; and Phragmatopoma californica, which

is found on the west coast of North America, from California to Mexico [11]. These species were investigated extensively in terms of building organ morphology, tube structure, and micro-and nanostructure as well as composition of the cement [3-5,12-18].