Engineers in the US have turned to nature to develop an adhesive that is biocompatible and can be tuned for specific applications.
The non-toxic glue, which is modelled after adhesive proteins produced by mussels and other creatures, is said to have out-performed commercially available products, pointing toward potential surgical glues to replace sutures and staples.
Over 12 million traumatic wounds are treated every years in the United States alone and about 60 per cent of those wounds are closed using sutures and staples that can cause discomfort, higher risk of infection and damage to surrounding healthy tissue.
Most adhesives don’t work well in moist environments because water interferes with the adhesion process. While developing adhesives that overcome this problem is challenging, glues for medical applications must also be non-toxic and biocompatible.
“We designed a bioinspired protein system that shows promise to achieve biocompatible underwater adhesion coupled with environmentally responsive behaviour that is ‘smart,’ meaning it can be tuned to suit a specific application,” said Julie Liu, an associate professor of chemical engineering and biomedical engineering at Purdue University.
In efforts to develop better alternatives, researchers have been inspired by natural glues. Specifically, underwater application and bonding has been demonstrated with materials based on organisms such as sandcastle worms and mussels. Both produce proteins containing the amino acid 3,4- dihydroxyphenylalanine (DOPA), which has been shown to provide adhesion strength, even in wet environments.
Research findings were detailed in a research paper published in April in Biomaterials. The paper was authored by graduate student M. Jane Brennan; undergraduate Bridget F. Kilbride; Jonathan Wilker, a professor of chemistry and materials engineering; and Liu.
Current FDA-approved adhesives and sealants face several challenges: many exhibit toxic characteristics, some can only be applied topically because they degrade into carcinogenic products; some are derived from blood sources and carry the potential for blood-borne pathogen transmission such as hepatitis and HIV; and others cause inflammation and irritation.
“More important, however, is that most of these adhesives do not possess sufficient adhesion in an excessively wet environment and are not approved for application in wound closure,” Liu said.
The Purdue researchers created a new adhesive material called ELY16, an elastin-like polypeptide (ELP). It contains elastin, a highly elastic protein found in connective tissue, and tyrosine, an amino acid. The ELY16 was modified by adding the enzyme tyrosinase, converting tyrosine into the adhesive DOPA molecule and forming mELY16.
Both ELY16 and mELY16 are not toxic to cells and are said to work well under dry conditions. Modification with DOPA increases adhesion strength in highly humid conditions. Moreover, the modified version is “tuneable” to varying environmental conditions and might be engineered to match the properties of different tissue types.
“To our knowledge, mELY16 provides the strongest bonds of any engineered protein when used completely underwater, and its high yields make it more viable for commercial application compared to natural adhesive proteins,” she said. “So it shows great potential to be a new smart underwater adhesive.”
The adhesive is also claimed to possess outstanding biocompatibility due to the use of human elastin.
“Our goal was to mimic the type of adhesion that mussel adhesive proteins have, and much other work has focused on the DOPA molecule as being critical to that adhesion,” said Liu. “We found that when the adhesive materials were exposed to large amounts of moisture, proteins containing DOPA had a much higher adhesion strength compared to unconverted proteins containing only tyrosine. So, DOPA conferred much stronger adhesion in wet environments.”