Image of the immobilised antibodies.
Credit: University of Sydney
BRISTOL: New cloaking technology may prevent an unwanted immune response to biomedical implants, say researchers.
When medical devices, such as cardiovascular stents, are implanted in the body, it triggers an abnormal immune response known as the foreign body response. For the patient, this can mean extended inflammation, higher risk of infection, and tissue build-up that may cause complications as well as discomfort. This slows patient recovery and often means further medical intervention.
A multi-disciplinary group of researchers from the University of Sydney have developed a surface that binds biomolecules, such as proteins and peptides, without affecting their function. This means medical devices could be coated in a layer of the patient's own protein - essentially cloaking it - avoiding any adverse response to the implant.
"When proteins land on surfaces currently used in implants they unfold and distort, losing their biological function," said Marcela Bilek, lead author on the paper published recently in Proceedings of the National Academy of Science. "When our surface is immersed in a fluid containing protein, the protein is bound by reacting with free radicals that are trapped in the surface's under-layer. The radicals do not harm the proteins but tether them gently to the surface".
Hard to tie down a working protein
For decades the biomedical field has been searching for elegant methods of immobilising biomolecules onto surfaces while retaining their function. Such surfaces have far reaching applications, including cloaking medical implants and diagnostic assays for early disease detection.
However, the field has had to overcome some challenges. First, the biomolecules need to be tethered with sufficient strength that they resist any processing of the surface, such as chemical washes.
Second, the orientation of the molecules needs to be controlled so they function in a desired way, such as antibodies binding antigens. Third, the natural bioactivity of the molecule needs to be retained.
Reservoir of free radicals
In this study, Bilek and her colleagues describe how their technology overcomes two of these challenges.
The team developed a chemical process, using energetic ions, which creates a hydrophilic surface with a reservoir of free radicals below the surface. The hydrophilic surface preserves the function of the biomolecules, while the free radicals form covalent bonds that tightly bind the biomolecules.
"Unpaired electrons are looking to lower their energy state by pairing up and they have some mobility within the network. So, if a protein comes in contact with the surface, there is a high probability that a free electron will come free and form a covalent bond with that protein" explained Bilek.
