Matrices for antibacterial nanoparticles delivery in biomedical implants

Milisav, Ana-Marija (2025) Matrices for antibacterial nanoparticles delivery in biomedical implants. Doctoral thesis, Sveučilište u Zagrebu Fakultet kemijskog inženjerstva i tehnologije.

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Abstract

Implant-associated infections that develop after surgery, together with bacterial resistance to antibiotics, are the main obstacles to the successful use of different types of implants. To combat this, innovative antibacterial implant materials that can release antimicrobial agents locally and have a low potential for causing bacterial resistance are being sought. Among various antimicrobial agents, metal or metal oxide nanoparticles (e.g. AgNP, CuNP, CuONP, ZnONP) are attracting special attention as they offer diverse antibacterial mechanisms to mitigate bacterial resistance. The risk of cytotoxicity of NP can be reduced by immobilizing them in matrices. In this work, three matrices for the delivery of NP were investigated, namely polyelectrolyte multilayers (PEM), magnetron-sputtered ZnO thin films, and alginate hydrogels, some of which were mineralized with calcium phosphates (CaP) to enhance their biocompatibility. These matrices were chosen for their versatility, ease of preparation and the possibility to scale up the coating procedure. All matrices were extensively physico-chemically characterized and their biological properties were investigated to determine their potential for application. PEM were prepared on titanium surfaces using poly(amino acids), poly-L-lysine and poly-L-glutamic acid, with AgNP or CuONP incorporated as part of the multilayer. Compared to AgNP, CuONP was adsorbed in higher amount and formed aggregates on the surface, leading to increased roughness and hydrophilicity, as confirmed by energy dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, atomic force microscopy and water contact angle measurements. Biodegradable magnetron-sputtered ZnO thin films doped with Ag and Cu were prepared by co-deposition in a multi-source magnetron sputtering system, and their properties were compared. X-ray diffraction (XRD) of the prepared thin films revealed the formation of wurtzite structure in all cases. Opposing trends were observed for grain size and water contact angle with increasing Ag and Cu content. The biomimetic CaP deposition led to a partial surface coverage with an apatitic phase, improving surface hydrophilicity. Non-mineralized and mineralized alginate hydrogels with incorporated AgNP, CuONP and ZnONP were prepared at different pH values (7.4 and 9.0). Mineralization was performed in situ using a CaCl2 solution, which initiated both gelation and CaP mineralization in the hydrogels containing Na2HPO4. The influence of pH on mineralization was investigated with XRD and Fourier-transform infrared spectroscopy. It was revealed that the hydrogels prepared at pH 7.4 contained calcium-deficient hydroxyapatite (CaDHA), while amorphous calcium phosphate formed in the hydrogels prepared at pH 9.0 and remained stable over time. The presence of NP influenced mineralization, with larger CaDHA crystals forming in CuONP-containing hydrogels. NP incorporation had negligible effect on the rheological properties of the hydrogels, but mineralization notably influenced the critical strain values, leading to earlier network breakdown in mineralized samples. Ion release patterns were dependent on the type of matrices. The incorporation of NP in PEM prevented ion burst release. Magnetron-sputtered thin films followed a similar trend, with an initial rapid release followed by a slower, sustained release. CaP deposition slightly reduced Cu release and increased Ag release, Zn release remained unaffected. Alginate hydrogels showed the slowest initial release, which increased gradually over time, with variations depending on the type of NP and the pH conditions. Cu release from mineralized hydrogels at pH 7.4 and 9.0 and Zn release from mineralized hydrogels at pH 9.0 was reduced compared to the non-mineralized counterparts. The antibacterial effects of NP varied depending on the matrices in which they were incorporated. Among the NP investigated, CuONP exhibited substantial antibacterial performance in PEM and magnetron-sputtered Cu-doped ZnO, while AgNP were more effective in alginate hydrogels, particularly in those prepared at pH 7.4, where they inhibited Staphylococcus aureus growth by approximately 50 %. Interestingly, despite copper’s enhanced antibacterial activity in the other two matrices, CuONP-incorporated alginate hydrogels unexpectedly promoted the growth of S. aureus. NP-containing hydrogels exhibited lower antibacterial effect for Pseudomonas aeruginosa. Nevertheless, S. aureus was more difficult to inhibit than P. aeruginosa for other matrices. CaP mineralization improved the antibacterial properties of thin films, while its effect on NP-containing hydrogels was negligible. The only significant inhibition was observed for the mineralized CuONP-containing hydrogel prepared at pH 7.4 on P. aeruginosa. Regarding cytotoxicity, PEM matrices were biocompatible regardless of NP incorporation, with MG-63 cell viability exceeding 70 %. In contrast, magnetron-sputtered thin films were cytotoxic. However, this issue was proven to be possible to address with biomimetic CaP deposition. The results obtained confirmed high potential of PEM, magnetron-sputtered ZnO thin films and alginate hydrogels embedded with metal and metal oxide NP for biomedical antibacterial applications, providing a promising approach to developing biocompatible surfaces.

Item Type:

Thesis (Doctoral thesis)

Uncontrolled Keywords:

metal nanoparticles; metal oxide nanoparticles; polyelectrolyte multilayers; magnetron-sputtered thin films; alginate hydrogels; calcium phosphates

Subjects:

NATURAL SCIENCES > Chemistry
NATURAL SCIENCES > Chemistry > Physical Chemistry

Divisions:

Division of Physical Chemistry

Projects: