Pardis Keikhosravani

The development of antibacterial coatings is a promising approach to preventing biofilm formation and reducing the overuse of systemic antibiotics. However, widespread antibiotic use has resulted in antibiotic‐resistant bacteria, limiting the efficacy of antibiotic‐based coatings. Herein, an antibacterial coating is developed by layer‐by‐layer (LbL) assembly of two polymers namely PDLG (poly (D,L‐lactide‐co‐glycolide)) and gelatin methacryloyl (GelMA) while chicken cathelicidin‐2 (CATH‐2), a cationic and amphipathic peptide, is loaded between these polymer layers. The electrospray method is used to apply the coatings to achieve efficient peptide loading and durability. The CATH‐2 bactericidal concentration ranges are first identified, followed by a study of their cytotoxicity to human mesenchymal stem cells (hMSCs) and macrophage cell lines. Later, different LbL electrospray coating assemblies loaded with the optimal peptide concentration are sought. Various coating strategies are investigated to identify an LbL coating that exhibits prolonged and biocompatible CATH‐2 release. The resulting CATH‐2‐coated titanium surfaces exhibit strong antibacterial activity against both Staphylococcus aureus and Escherichia coli bacteria for 4 days and are biocompatible with hMSCs and macrophage cells. This coating can be considered as a versatile delivery system platform for the delivery of CATH‐2 peptides while avoiding cytotoxicity, particularly for the prevention of infections associated with implants.

The material for bone scaffold replacement should be biocompatible and antibacterial to prevent scaffold-associated infection. We biofunctionalized the hydroxyapatite (HA) properties by doping it with lithium (Li). The HA and 4 Li-doped HA (0.5, 1.0, 2.0, 4.0 wt.%) samples were investigated to find the most suitable Li content for both aspects. The synthesized nanoparticles, by the mechanical alloying method, were cold-pressed uniaxially and then sintered for 2 h at 1250 °C. Characterization using field-emission scanning electron microscopy (FE-SEM) revealed particle sizes in the range of 60 to 120 nm. The XRD analysis proved the formation of HA and Li-doped HA nanoparticles with crystal sizes ranging from 59 to 89 nm. The bioactivity of samples was investigated in simulated body fluid (SBF), and the growth of apatite formed on surfaces was evaluated using SEM and EDS. Cellular behavior was estimated by MG63 osteoblast-like cells. The results of apatite growth and cell analysis showed that 1.0 wt.% Li doping was optimal to maximize the bioactivity of HA. Antibacterial characteristics against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were performed by colony-forming unit (CFU) tests. The results showed that Li in the structure of HA increases its antibacterial properties. HA biofunctionalized by Li doping can be considered a suitable option for the fabrication of bone scaffolds due to its antibacterial and unique bioactivity properties.

In the present work, hydroxyapatite (HA)‐titanium (Ti, 20 wt%) composite coating was coated on NiTi alloy substrate by EPD (electrophoretic deposition) process. Before applying the coating, the HA powder was composed with Ti powder using a ball milling process. Influence of the ball milling time on morphology and phase structure of HA‐Ti powder was evaluated using TEM and XRD analysis. After composing the HA particles with Ti, the HA‐Ti composite powders were coated on the NiTi substrate by the EPD process in an n‐butanol medium for 2 min, with the applied voltage of 60 V. XRD and SEM analysis were utilized to evaluate the phase analysis and morphology of the coatings. Mechanical and electrochemical characteristic of the coatings were also assessed using the micro‐indentation, micro‐scratch, and polarization tests, respectively. The results revealed that the milling process time had a significant influence on reaction bonds and optimum mixing time was 4 hr. Micro‐hardness of the HA‐Ti composite coating (304 HV) was substantially higher than the HA coating (72 HV). Also, as the HA coating was composed with Ti particles, the amount of force (in the micro‐scratch test) required for detaching the coating from the NiTi substrate increased from 7.1 to 17.8 N. The polarization results showed that the HA‐Ti composite coating had a higher electrochemical resistance compared with the HA coating. Corrosion resistance of the NiTi alloy coated with HA increased from 133 kΩ.cm² to 2,720 kΩ.cm² after composed with the Ti particles.