Machine Design

Medical coatings with some added "mussel"

A two-sided coating designed by Northwestern University researchers may bring better medical implants and help keep patients safe from infections.

This image shows the ability of the antifouling coating to repel cell attachment. A flat gold surface has been treated in the lower half of the image with an antifouling polymer coating. Fibroblast cells were able to attach themselves to only the unmodified portion of the surface. Cell cytoskeletons are stained green and nuclei blue.

Researchers in the lab at Northwestern University have developed a two-part polymer system to make an antifouling coating for medical implants. The research was supported by the National Institutes of Health.

The coating is made from an adhesive that mimics a protein secreted by mussels and a polymer that repels cells and proteins. It sticks securely to surfaces and prevents bacteria, cells, and proteins from building up or fouling. Previous polymer coatings haven't stopped such buildup. They typically don't last long in-vivo, falling prey to chemical degradation and body's enzymes.

In contrast, the molecular compound developed at Northwestern has effectively prevented fouling for more than five months. This, according to lead investigator Prof. Phillip B. Messersmith, is most likely the longest successful in-vitro antifouling demonstration to date.

The coating has not been tested in humans, but holds promise for use on a variety of medical implants including urinary catheters, cardiac stents, biosensors, and dental implants and devices. The coating also could serve as a biofouling deterrent in waterprocessing equipment, ship hulls, and other man-made marine structures.

To devise a method for increasing the longevity of existing coatings, Messersmith teamed with Prof. Annelise Barron an expert in creating peptoids — synthetic molecules that are closely related to the natural proteins or peptides they mimic but don't degrade in the body.

The team developed a two-part polymer system to make the antifouling coating. One is a short peptide that is the synthetic version of the sticky dihydroxyphenylalanine (DOPA) molecule that gives mussels their adhesive or anchoring strength. The second is a longer peptoid polymer resembling the structure of polyethylene glycol (PEG), a widely studied antifouling polymer.

"Chemical properties of the antifouling component resemble PEG, but the component lasts longer because it resists peptoids and enzymes. Plus, the polymer backbone structure is based on a natural peptide. This structure should make it biocompatible and prevent evoking an immune response in the body," says Messersmith.

The researchers tested the coating on titanium dioxide (a material common in medical implants) in simulated physiologic conditions with fresh serum and cells. The coating anchored itself firmly to the surface and demonstrated and resisted proteins and cells during the five-month experiment. And the coating should resist bacteria for the same reason it is cell and protein resistant, Messersmith says.

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