Synthesis of quaternary ammonium coated surfaces: Physico-chemistry, bacterial killing and phagocytosis

The number one cause of failure of biomaterial implants and devices is the occurrence of biomaterial-associated infection. A universal method to create biomaterial implants and devices with intrinsic antimicrobial functionalities is difficult. Immobilizing antimicrobial coatings on existing biomaterials is, on the other hand, relatively simple. In this work we prepared a coating with quaternary ammonium surface groups that kill bacteria upon contact and evaluated the ability of such coating against bacterial adhesion and biofilm formation.
The prepared coating is shape-adaptive and contact-killing and able to kill more than 99.99% of the adhering Staphylococcus epidermidis bacteria. Also, the adhesion forces between the bacteria and the coating were extremely high. These strong adhesion forces are lethal in nature and caused removal of membrane lipids and therefore eventually lead to bacterial death. Upon studying the surface in detail we found a new and easy parameter which can be used to predict the contact killing properties of a novel coating using employing quaternary ammonium compounds to kill bacteria.

In literature different methods are described to evaluate bacterial contact killing. However, the results of the different methods are often conflicting. We compared five methods to evaluate contact killing using our coating. Similar to the literature, the obtained results were highly depending on the used method.

This study also involved the behavior of macrophages upon adhesion to this highly energetic coating and was compared this to poly(ethylene)glycol-hydrogels, stainless steel and several other common biomaterials, in order to identify changes in the ability to clear bacteria. Hereby we identified crucial parameters which should be taken into account by next-generation biomaterials, in order to enhance the ability of these materials to resist infections.