Bioadhesives

Bioadhesives are natural polymeric materials that act as adhesives. The term is sometimes used more loosely to describe a glue formed synthetically from biological monomers such as sugars, or to mean a synthetic material designed to adhere to biological tissue.

Bioadhesives may consist of a variety of substances, but proteins and carbohydrates feature prominently. Proteins such as gelatin and carbohydrates such as starch have been used as general purpose glues by man for many years, but typically their performance shortcomings have seen them superseded by synthetic alternatives. Highly effective adhesives found in the natural world are currently under investigation but not yet in widespread commercial use. For example, bioadhesives secreted by microbes and by marine molluscs and crustaceans are being researched with a view to biomimicry.

Bioadhesives are of commercial interest because they tend to be biocompatible, i.e., useful for biomedical applications involving skin or other body tissue. Some work in wet environments and under water, while others can stick to low surface energy or nonpolar surfaces such as plastics. In recent years, the synthetic adhesives industry has been impacted by environmental concerns and by health and safety issues relating to hazardous ingredients, volatile organic compound emissions, and difficulties in recycling or remediating adhesives derived from petrochemical feedstocks. Rising oil prices may also stimulate commercial interest in biological alternatives to synthetic adhesives.

Commercial Applications

Some commercial applications exist currently, and still others are in development.

• Commodity wood adhesive is based on a bacterial exopolysaccharide.
• USB PRF/Soy 2000 is a commodity wood adhesive that is 50% soy hydrolysate and that excels at finger-jointing green lumber.
• Mussel adhesive proteins can assist in attaching cells to plastic surfaces in laboratory cell and tissue culture experiments.
• The Notaden frog glue is under development for biomedical uses, e.g., as a surgical glue for orthopedic applications or as a hemostat, to hasten clotting.
• Films of mussel adhesive protein give comparable mucoadhesion to polycarbophil, a synthetic hydrogel used to achieve effective drug delivery at low drug doses.

Several commercial methods of production are being researched:

• direct chemical synthesis, e.g., incorporation of L-DOPA groups in synthetic polymers
• fermentation of transgenic bacteria or yeasts that express bioadhesive protein genes
• farming of natural organisms (small and large) that secrete bioadhesive materials