Antibacterial surface coatings for biomedical applications

Licentiate thesis, 2016

Over the past decades there has been a significant increase in the diversity and function of biomaterials. Today, medical practices utilize a large number of biomaterials in the form of medical devices and implants. However, one major obstacle that limits the efficiency of biomaterials is their susceptibility to develop infection. Biomaterials associated infection caused by adherent biofilms is usually difficult to hinder by means of systemic antibiotic therapy. In addition, the rapid emergence and growth of antibiotic resistant bacterial strains is further limiting the potency of available antibiotics used to treat infections. To address these limitations, different surface modifications are considered to be an effective solution to improve antibacterial performance of biomaterials by hindering biofilm formation. In this thesis, two different strategies to create surfaces with pronounced antibacterial properties have been developed and evaluated. In both methods, the antibacterial modification has been deposited onto bioactive surface coatings to further improve their future clinical performance. In the first approach, mesoporous titania (MPT) surface coatings were used as antibiotic carriers to investigate the effect of local delivery of the antibiotics Vancomycin, Gentamicin and Daptomycin on the attachment and growth of  S. aureus and P. aeruginosa. MPT thin films with pore diameters of 4, 6, and 7 nm were formed using the evaporation-induced self-assembly method. Reduced bacterial adhesion was observed on the antibiotic loaded surfaces. It was also shown that presence of the pores alone had a desired hampering effect on bacterial colonization. In the second approach, an antimicrobial peptide (AMP), RRPRPRPRPWWWW-NH2 (RRP9W4N), was used to covalently modify elastin like polypeptide (ELP) surface coatings having cell adhesive sequences in its structure. RRP9W4N was immobilized onto ELP surfaces using EDC-NHS coupling chemistry. It was shown that the AMP could retain its antibacterial activity against S. epidermidis, S. aureus and P. aeruginosa when covalently bonded to ELP. RRP9W4N stability in human blood serum was studied and the results suggested that the AMP could preserve its antibacterial activity up to 24 hours. The overall results from both surface modification techniques developed in this thesis suggest that they can be considered as promising candidates for the development of antimicrobial surfaces for future biomedical applications.