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褐藻胶显示，我们在海中还有更多的配方思想

来源：林中祥胶粘剂技术信息网2011年05月04日

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Alginate Adhesives Show There are Plenty More Formulation Ideas in the Sea

Mussels have long been discussed as inspiration for new adhesive systems, but directly extracting 1 kg of their natural adhesive would need five to ten million of them.Yet alongside algae and more recently oysters, their ability to bond securely in salt-water is one that man has struggled to match. As well as making assembling structures exposed to marine environments easier, that ability could help withstand physiological fluids such as blood or saline. Now, in targeting these latter environments for lucrative biomedical applications, researchers look to have developed a practical way to bring such aquatic adhesives to market.

Beyond the ability to hold in wet environments, naturally-derived adhesives could offer advantages in enhancing tissue closure techniques such as sutures and staples. While synthetic adhesives improve medical sealing capabilities they have low biocompatibility and can be toxic. Biological glues are costly, often show relatively poor mechanical and tissue-bonding properties and are potentially immunogenic. Its to resolve these issues that researchers at the Technion-Research & Development Foundation in Haifa, Israel have turned to marine-inspired adhesion.

Figure 1: : Phenolic compounds that create adhesives when mixed with alginate carbohydrate polymers

The common feature shared by mussels and other watery species are proteins featuring high proportions of amino acids with phenolic hydroxyl chemical groups.² Its thought that the adhesion is therefore mediated by hydrogen bonding or interacting with metal ions. Many efforts to recreate this therefore seek to synthesize "biomimetic" random block copolymers featuring a similar proportion of phenolic components.

Yet there are ways to deliver adhesives closer to those produced by nature than these synthetic options without resorting to massive ocean harvests. The lead comes from an adhesive based on red and brown algae, which produce phenolic compounds that exhibit adhesive properties and extraordinarily high cohesive strength. Consequently adhesives have been made by activating algae-derived phloroglucinol derivatives so that they form polymeric chains, and then cross-linking those chains with the algal carbohydrate alginate.

While this method still requires extracting tons of a specific species, it also suggests a way to avoid that practical challenge. Phoroglucinol is the simplest tri-substituted phenol around, and synthetic versions are readily available. Likewise, there are many commercially-available polyphenols that could be used to formulate an adhesive. Alginate is already produced in large volumes commercially from the extraction of seaweed for use in food, pharmaceuticals and cosmetics.

Consequently, the Israeli scientists have developed adhesives similar to those made from red and brown algae, but with materials obtained from commercial sources. They can use commercial polyphenols in their monomeric forms or polymerise them, for example using an enzyme like haloperoxidase. The polyphenol is added to the alginate carbohydrate in an aqueous mixture to form a "pre-gel", before cross-linking the carbohydrate into a gel form. This gelation is induced by the addition of multivalent ions, typically in the form of soluble CaCl₂ or insoluble CaCO₃. All of their inventions demonstrated a higher tensile strength in bonding to porcine tissue than a commercial fibrin sealant.

Figure 2: Tensile strength of adhesives made by combining different polyphenol compounds and alginate carbohydrates, plus a fibrin sealant, in bonding porcine tissue

The resulting adhesive can be used by spreading a layer of pre-gel onto tissue, before applying the ion solution to it by spraying, dripping or other wetting. Including insoluble CaCO₃ with alginate creates a one-part tissue adhesive, where calcium ions are only slowly released. Either approach can also be used after soaking the pre-gel into a solid support, made of plastic, knitted synthetic or natural polymer mesh, or natural cellulose gauze, to produce a bandage. Another method for producing a bandage is to air- or freeze-dry the pre-gel into a film, and then incorp