PhD ceremony Ms. L.A.T.W. Asri: Immobilized hyperbranched polyureas coatings with antibacterial performance

PhD ceremony: Ms. L.A.T.W. Asri

Dissertation: Immobilized hyperbranched polyureas coatings with antibacterial performance

Promotor(s): prof. J.A. Loontjens

Faculty: Mathematics and Natural Sciences

Biomedical implants, such as hip, knee and hearth valve prosthesis, play an increasing role in modern health care. However, one of the major problems in their application is still the risk of infection. Chemically anchored coatings comprising immobilized antibacterial compounds that kill bacteria upon contact are perhaps the most promising approach to provide implants with sterile surfaces. We have developed an enabling technology to fix chemically antibacterial coatings onto surfaces, based on our hyperbranched polyurea, modified with quaternary ammonium ions. The hyperbranched polyurea coatings were fabricated by heating AB2 monomers on substrates. The B-groups were blocked isocyanates, which resulted in coatings comprising numerous blocked isocyanates. These blocked isocyanates groups allow fixation of various potent antibacterial compounds comprising amino or hydroxyl functional groups, such as polyoxazolines, ethoquad C/25 and (quaternized) polyethyleneimines. Among these compounds, hyperbranched polyureas coating, decorated with chemically anchored quaternized polyethyleneimines showed highly effective antibacterial efficacies, in which bacteria were killed on contact. It is, however, difficult to envisage that the contact killing mechanism of immobilized quaternary ammonium compounds was the same as with releasing biocides that are currently used. Therefore we proposed a novel mechanism. High charge densities,of immobilized cationic species, that appeared to be critical, exert such strong electrostatic attraction forces that the bacteria cells deform and anionic species are pulled out of the cell membrane, leading to high stresses and finally to cell death.