Biological skin plug system - Characterization of the attachment cement in ticks

Numerous organisms produce adhesive substances which fulfil different functions like the attachment to a substratum, catching of prey or defence from predators. A firm attachment is also known for ectoparasitic ticks which secrete a hardening substance called cement to support the attachment by their mouthparts in the hosts skin and seal the feeding lesion to the exterior. Despite these interesting characteristics for the field of biomaterials and biomimetics a detailed knowledge on the chemical composition of the cement in ticks is largely lacking and also the hardening process of this adhesive is unclear. In the present research project the cementitious secretions of the two tick species Dermacentor marginatus and Amblyomma hebraeum shall be visualised structurally and its components characterized biochemically. Additionally, biocompatibility tests will serve to address the potential use of tick cement as medical adhesive and sealant. These analyses will contribute to the knowledge on the nature of the cement material and allow the comparison with already given adhesive systems, especially those of mussels, polychaetes and barnacles.

Tissue adhesives are important tools in wound care and surgical interventions. However, the products currently in clinical use are inadequate because they either have a weak adhesive force (e.g. fibrin) or contain toxic substances (e.g. Histoacryl) which damage the surrounding cells when they come into contact with tissue. Thus, there is an urgent need for new, strongly adhesive and at the same time biocompatible substances. Nature has produced many mechanisms for successful gluing in dry and humid environments. One example are ticks that produce a secretion when they anchor the mouthparts in the skin. This secretion is of particular interest to biomedical research because it is naturally designed to adhere to tissue. In this project, the largely unknown substance was investigated using two types of tick. The tick secretion, also called cement, was obtained from tick cultures in artificial feeding units in order to avoid contamination of the secretion through the skin of host animals and to avoid animal experiments. For the subsequent analyzes, several methods were adapted to the material properties and the small size or quantity of the tick cement. One of the research questions was the adhesive force, which was previously unexplored. The aim was to find out whether it was a purely mechanical dowel effect or an adhesion based on molecular interactions. Adhesion tests showed that both mechanisms are involved and that the molecular forces are higher than those of clinical fibrin glue. Biomechanical studies have shown viscoelastic deformability with a wide range of stiffness within the hardened secretion, material properties that would be well suited for certain applications as clinical tissue adhesives. Analysis of the cement composition have shown that the tick secretion of the examined species is a protein-based substance. An amino acid DOPA, known from the mussel as an adhesive, was not detectable, which means that ticks have a DOPA-independent adhesive mechanism. The large proportion of the amino acid glycine and glycine rich proteins are common in biological adhesives suggesting a connection with the adhesive mechanism. Although some proteins have been identified (e.g. antimicrobial proteins or blood components), most of them are unknown and are currently investigated in more detail by analyzing the cement cells of the salivary glands. It was also noticeable that the cement is very lipid-rich, which suggests that the hydrophobic properties contribute to the adhesive mechanism. The long-term goal of this project is to identify the adhesive substances and to develop a biotechnologically producible adhesive that simplifies surgical techniques and ensures faster regeneration of tissue damage.