These polymers have several advantages over existing biodegradable polymers, researchers said. Among them, the polymers called polyketals are biodegradable into Food and Drug Administration-approved compounds, such as food additives. Synthesis is a simple and easily customized process. Degradation of the polymer does not produce inflammation-causing acid, but instead generates membrane-permeable products that allow all of the polymer's byproducts to diffuse outside the cell. That means byproducts shouldn't accumulate in a patient's tissue and cause inflammation.
"We've known for 20 to 30 years that when cells take up particles, they move them to a part of the cell with a low pH -- about 5.0," said Niren Murthy, an assistant professor in the Wallace H. Coulter Department of Biomedical Engineering at the Georgia Institute of Technology and Emory University. "Researchers have been able to successfully exploit this process in cell culture and in animal models, but have done so using materials that generated acid degradation products and that hydrolyzed too slowly for chronic use. Thus, there has been very little clinical activity in this area."
However, polyketal nanoparticles use the cell's acid to hydrolyze into hydrophilic compounds that can release encapsulated therapeutics at an accelerated rate in the acidic environments to which they are targeted, Murthy explained. Also, unlike polyester-based biomaterials, polyketal nanoparticles do not generate acid when they degrade. Researchers don't know yet whether polyketals will be less inflammatory than current polymers used for drug delivery, but expect to evaluate this response within the next year.