Cement characterization of Dosima fascicularis Gray, 1825

Many organisms, ranging from microscopic bacteria and fungi to much larger marine and terrestrial vertebrates, use adhesive substances. These biological glues vary widely in structure and components, and often function in ways that differ greatly from conventional man-made adhesives. The synthesis of new and specific biomimetic adhesive polymers is currently one of the hot spots in material science. There is an ongoing need for new tissue adhesive materials for use in wound healing of both soft and hard tissue, as well as for adhesion of medical and dental implants. Cirripedia live attached to hard surfaces by means of extremely strong and permanent cement. This cement is well- characterized and has attracted much attention for the development of new anti-fouling products. While most cirripedes produce just enough cement for attachment on hard substrates the Pedunculate Dosima fascicularis is exceptional in producing excess cement, which is then used as float. So far, not much attention has been paid to the foam-like cement of Dosima. The central objective of this proposed work is to study the morphology of the cement glands and to investigate the structure of the cement ultrastructurally and to analyse its composition histochemically and biochemically. The results of this study are expected to provide the basis for the production of biomimetic adhesives to be used in medicine and to open up new possibilities for application in underwater construction.

Cement is the adhesive of barnacles, sessile marine crustaceans. These animals adhere to any kind of firm natural or artificial substratum. Bonding is extremely strong so that the animals can hardly be removed from their attachment site. These characteristics and the fact that the non-toxic adhesive is secreted under water and polymerizes under wet conditions seemed to make it suitable for medical and industrial application. The first scientists who got interested in the barnacle adhesive were dentists. This is presumably the reason why this substance is called cement.In contrast to all other barnacles which usually adhere to the substratum by a thin layer of cement the stalked barnacle Dosima fascicularis of the family Lepadidae produces a large amount of foam-like cement which has a double function: attachment and floating. The larva of Dosima attaches to any flotsam and if the pieces of algae, bird feathers or tar pellets are small enough the cement of the adult may overgrow these and form a float. With this rafting device Dosima drifts in the water independent of any other natural or artificial floating substratum. It was suspected that the large amount of adhesive with the foam-like structure had chemical qualities and mechanical properties different from those of all other barnacles known so far.In our investigations we first concentrated on a detailed study of the morphology of the cement apparatus and the cement. The cement glands, producing the cement are in the upper part of the stalk. From there the cement is transported through a complex canal system into the attachment disk of the first antenna at the base of the stalk and is secreted through pores to the outside. The animal grows and produces cement in accordance with the moulting cycle throughout its life time. At the same time the pores shift from the base to the lateral side of the stalk. As a result of this the cement forms concentric layers around the stalk and the substratum to which the animal had attached. The outermost layer of cement is the youngest and forms a kind of rind which gives mechanical stability. Our investigations revealed that the cement matrix has a higher density than sea water. The positive static buoyancy of the float is caused gas bubbles enclosed in the cement matrix. The elasticity of the cement is higher, hardness and tensile stress are lower than in all other barnacles investigated so far. Although the overall chemical composition of the cement agrees, as far as it is known, with that of all other barnacles, there are some notable differences: a set of proteins with low homologies to other barnacle cement proteins and no disulfide bridges to stabilize the protein complex. Instead, sulfated polysaccharides may be the potential source of sulfur detected in this cement. The special structure of the Dosima cement make it suitable as scaffolds for cell cultures and its potential damping properties could be used in orthopedics. In industry and technology this kind of adhesive could be applied as strong and durable underwater glue.