홍합 족사 내구력 단백질의 이해 및 생체공학적인 인터페이스로써의 응용 연구

Abstract

Achieving robust attachment between living tissues and inert materials comes with the main challenge of mitigating contact damage due to mismatches in properties such as stiffness, hardness, strength and Poisson’s ratio. There appear to be two common strategies in biology for mitigating contact damage between mismatched loadbearing materials: (i) creating an interface that relies on molecular gradients (ii) using a strong interfacial adhesion over an increased surface area of contact (thereby reducing the load per unit area).

Marine mussels use the load bearing byssal thread (byssus) to attach themselves to a variety kind of surfaces and to anchor themselves by overcoming aforementioned mechanical mismatches. These byssal threads have elastic and shock absorbing properties with stiffness as well as the ability for self-healing. Load bearing mechanisms byssus of each mussel differs according to its natural habitat. Blue mussels (Mytilus species) optimize their byssus to adapt to intertidal zone by using the molecular gradient, and byssi of fan mussels (Pinna and Atrina species) have optimized to wetlands and sea-mud by utilizing a strong interfacial adhesion. Here, investigations on the attachment mechanisms of two different marine mussels (Mytilus edulis & Atrina pectinata) with load bearing byssus were performed to understand strategies to overcome the mechanical mismatches by mimicking the naturally occured load bearing systems.

Marine organism, Mytilus is able to achieve such robust attachment where its load bearing byssus uses Proximal Thread Matrix Protein 1 (PTMP1) to create such interface that relies on molecular gradients. PTMP1 interacts with a class of collagen protein, preCol-P and loosen their molecular structure, whereby this formation enables the mussels through its load bearing byssus to attach themselves to hard surfaces without been washed away under the strong wave. The loosening of the molecular structure of collagen has resulted in the formation of the mechanical stiffness gradient, which has been attributed to be the key feature in many load bearing components incurred by mechanical mismatch. The ability to exploit the variation in stiffness gradient through manipulating the physiology of the collagen structure with its relevant interacting protein has vast potential in expediting its application to the area of tissue engineering. As such, in this thesis, investigations on several factors that affects the interaction between PTMP1 and collagen; pH condition, contact time, effect of cofactor and the effect of mechanical shearing, were performed to gain insights on the byssus molecular gradients in mytilus species.

Byssal threads of the fan shell Atrina pectinata are non-living functional materials intimately associated with in most living tissues of Atrina, which provide an intriguing paradigm of bionic interface for robust load-bearing device, which does not create an interface that relies on molecular gradients. It was found that Atrina foot protein 1 (apfp-1) is localized at the stiff byssus and by immunochemical staining implying that apfp-1 is an interfacial linker between the byssus and soft tissue. apfp-1 has two domains — (i) 3,4 dihydroxyphenylalanine (DOPA), a postranslationally modified amino acid from tyrosine, containing metal binding domain that interacts with the stiff byssus (ii) the mannose-binding domain (C-LECT)that interacts with the soft tissue and cell membranes. Both the DOPA-metal ion andhe sugar-mediated bindings were reversible and robust under wet conditions, which is strong enough to mitigate the mechanical mismatch between soft living tissues and stiff byssus. This work shows the combination of sugar and DOPA chemistries at asymmetric interfaces is unprecedented and highly relevant to bionic interface design for tissue engineering and bionic devices.