Microbial adhesion to zirconium alloys

Disinfection mechanism of the photocatalytic activity of SnO2 thin films against Candida albicans, proposed from experimental and simulated perspectives

Nosocomial infections are an important health problem and cause of complications and death in hospitalized patients. This problem should be solved from the preventive angle, avoiding the spread of infections by designing disinfection methods based on the photocatalytic activity of semiconductor materials such as tin oxide (SnO₂). The antimicrobial activity of UV light was tested by using inoculation with Candida albicans ATCC10231 on SnO₂ thin films and counting colony forming units (CFU). The interaction of UV light with SnO₂ was analyzed by density functional theory (DFT) and the extension to the Hubbard model (DFT+U) schemes to predict the electron behavior at the subatomic level. After exposure to UV light, C. albicans showed a reduction of 36.5% in viable cells, and when SnO₂ was included, cell viability was reduced by 60.2%. Measurements of the electronic structure obtained by the first-principle calculations under the DFT and DFT+U schemes showed that the O-p orbitals mediate the oxidation process in the bulk semiconductor. By including the surface effects when cleaving the (1 0 0) plane, the three orbitals O-p, Sn-p, and Sn-s are the mediators. SnO₂ films are promising antimicrobial coatings because UV light has a synergic activity with thin films, resulting in faster disinfection.

In vitro adherence of Candida albicans to zirconia surfaces

OBJECTIVES

This study aimed to characterize surface properties such as roughness (Ra) and surface-free energy (SFE) of glazed and polished yttria-stabilized zirconia and to evaluate in vitro adherence of fungus Candida albicans and salivary bacteria, Staphylococcus epidermidis, mixed with C. albicans to these substrata. Additionally, the influence of salivary proteins (albumin, mucin and α-amylase) on yeast adhesion was studied.

MATERIAL AND METHODS

Ra and SFE of glazed and polished zirconia discs were measured. Specimens were wetted with saliva and salivary proteins prior to incubation with C. albicans and mixed suspension of C. albicans and S. epidermidis for 24 hr, respectively. Microbial adhesion was quantified by counting colony-forming units (CFU). Differences in physicochemical properties were proved by t test. "Linear mixed model" with the factors "type of surface" and "wetting media" was applied to analyse the effects on fungal adhesion (p < .05).

RESULTS

SFE and Ra of glazed specimens were significantly higher than corresponding values of polished ones. The wetting media significantly changed the fungal binding (p = .0016). Significantly higher quantities of adhering fungi were found after mucin incubation compared to saliva (p = .004). For the factor "surface" as well as the interaction between "surface" and "wetting media," no statistically significant differences have been found. In mixed suspension, the growth of Candida was completely prevented.

CONCLUSIONS

Glazed and polished zirconia differs in terms of physicochemical surface properties. These differences appear to be modulated by pellicle coating affecting the biomass of adhered Candida. Mucin seems to be good binding sites for adhesion of C. albicans.

Bactericidal activity of the Ti-13Nb-13Zr alloy against different species of bacteria related with implant infection

The Ti-6Al-4V alloy is one of the most commonly used in orthopedic surgery. Despite its advantages, there is an increasing need to use new titanium alloys with no toxic elements and improved biomechanical properties, such as Ti-13Nb-13Zr. Prosthetic joint infections (PJI) are mainly caused by Gram-positive bacteria; however, Gram-negative bacteria are a growing problem due to associated multidrug resistance. In this study, the bacterial adherence and viability on the Ti-13Nb-13Zr alloy have been compared to that of the Ti-6Al-4V alloy using 16 collection and clinical strains of bacterial species related to PJI: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa. When compared with the Ti-6Al-4V alloy, bacterial adherence on the Ti-13Nb-13Zr alloy was significantly higher in most staphylococcal and P. aeruginosa strains and lower for E. coli strains. The proportion of live bacteria was significantly lower for both Gram-negative species on the Ti-13Nb-13Zr alloy than on the Ti-6Al-4V alloy pointing to some bactericidal effect of the Ti-13Nb-13Zr alloy. This bactericidal effect appears to be a consequence of the formation of hydroxyl radicals, since this effect is neutralized when dimethylsulfoxide was added to both the saline solution and water used to wash the stain. The antibacterial effect of the Ti-13Nb-13Zr alloy against Gram-negative bacteria is an interesting property useful for the prevention of PJI caused by these bacteria on this potential alternative to the Ti-6Al-4V alloy for orthopedic surgery.

Dual ions implantation of zirconium and nitrogen into magnesium alloys for enhanced corrosion resistance, antimicrobial activity and biocompatibility

Biodegradable magnesium-based alloys have shown great potential for medical applications due to their superior biological performances and mechanical properties. However, on one hand, some side effects including inferior biocompatibility, a local high-alkaline environment and gas cavities caused by a rapid corrosion rate, hinder their clinical application. On the other hand, it is also necessary to endow Mg alloys with antibacterial properties, which are crucial for clinic orthopedic applications. In this study, Zr and N ions are simultaneously implanted into AZ91 Mg alloys by plasma immersion ion implantation (PIII). A modified layer with a thickness of approximately 80nm is formed on the surface of AZ91 Mg alloys, and the hydrophobicity and roughness of these AZ91 Mg alloys obviously increase after Zr and N implantation. The in vitro evaluations including corrosion resistance tests, antimicrobial tests and cytocompatibility and alkaline phosphatase (ALP) activity tests, revealed that the dual ions implantation of Zr and N not only enhanced the corrosion resistance of the AZ91 Mg alloy but also provided better antimicrobial properties in vitro. Furthermore, the formation of biocompatible metal nitrides and metal oxides layer in the near surface of the Zr-N-implanted AZ91 Mg alloy provided a favorable implantation surface for cell adhesion and growth, which in return further promoted the bone formation in vivo. These promising results suggest that the Zr-N-implanted AZ91 Mg alloy shows potential for future application in the orthopedic field.

The antimicrobial and osteoinductive properties of silver nanoparticle/poly (DL-lactic-co-glycolic acid)-coated stainless steel

Implant-associated bacterial infections are one of the most serious complications in orthopedic surgery. Treatment of these infections often requires multiple operations, device removal, long-term systemic antibiotics, and extended rehabilitation, and is frequently ineffective, leading to worse clinical outcomes and increased financial costs. In this study, we evaluated silver nanoparticle/poly(DL-lactic-co-glycolic acid) (PLGA)-coated stainless steel alloy(SNPSA) as a potential antimicrobial implant material. We found that SNPSA exhibited strong antibacterial activity in vitro and ex vivo, and promoted MC3T3-E1 pre-osteoblasts proliferation and maturation in vitro. Furthermore, SNPSA implants induced osteogenesis while suppressing bacterial survival in contaminated rat femoral canals. Our results indicate that SNPSA has simultaneous antimicrobial and osteoinductive properties that make it a promising therapeutic material in orthopedic surgery.

Antibacterial effect of 317L stainless steel contained copper in prevention of implant-related infection in vitro and in vivo

Bone and intramedullary bacterial infections are one of the most serious complications of the surgical repair of fractures. To reduce the incidence of implant-related infections, several biomaterial surface treatments with integrated antibiotics, antiseptics, or metal ions have been developed for implants. In this study, we evaluated the antibacterial activity and biocompatibility of 317L stainless steel containing 4.5% copper alloy (317L-Cu) in vitro and in vivo using an animal model. Common pathogens of implant-related infections are Staphylococcus aureus and Escherichia coli, which were injected into implant materials to study their antimicrobial potential. We compared antimicrobial potential of 317L-Cu with 317L stainless steel (317L) and titanium (Ti-6Al-4V) alloys as controls. Compared with controls, 317L-Cu materials inhibited colonization by both bacteria in vitro and in vivo. Compared with 317L and Ti-6Al-4V controls, 317L-Cu showed no significant difference in colony formation of osteoblast-like cells on metal surfaces after 72 h of incubation in vitro. Metal screws containing these materials were also made for our vivo study in a rabbit model. Tissue-implants were analyzed for infection and inflammatory changes by hematoxylin-eosin staining of implants in bone. The screw tract inflammation and infection of 317L-Cu was minimal, although some inflammatory cells gathered at acutely infected sites. In addition, after materials had been implanted for 14 days in vivo, the expression of insulin-like growth factor-1 (IGF-1) in osteoblasts around 317L-Cu screws tracts had increased compared with 317L and Ti-6Al-4V controls. Overall, 317L-Cu demonstrated strong antimicrobial activity and biocompatibility in vitro and in vivo and may be used as a biomaterial to reduce implant-related infections.

Modified implant surfaces show different biofilm compositions under in vivo conditions

OBJECTIVE

Plaque accumulation on implant surfaces can result in peri-implantitis with potential implant loss. The aim of the present study was to examine the influence of zirconium nitride (ZrN) as a potential implant surface on the biofilm composition and diversity in vivo.

MATERIAL AND METHODS

ZrN- or titanium (Ti)-coated glass specimens and ZrN or roughened Ti discs were used as substrates. Pure glass and polished titanium served as controls. The specimens were mounted on removable intraoral splints in five adults. After 24 h of intraoral exposure, the biofilms were analyzed applying single-strand conformation polymorphism (SSCP analysis) of 16S rRNA genes. Sequence analysis of the dominant bands excised from the SSCP fingerprints allowed to taxonomically describe bacteria derived from biofilm samples.

RESULTS

The highest number of bands was counted on pure glass and Ti 800. ZrN-coated glass and ZrN-coated titanium discs showed the lowest values for species richness. However, no significant differences were observed regarding the diversity of the identified bacterial species among all the surfaces examined. A total of 46 different bacteria were identified. The dominant bands within the fingerprints indicated bacteria belonging to the Streptococcus group as identified by their 16S rDNA sequence.

CONCLUSION

A coating of glass surfaces with ZrN significantly reduced the species richness in early bacterial colonization but the diversity was not significantly changed. In consideration of the results obtained by this and former studies a ZrN coating appears to rather modify the quantity of early bacterial adherence than the quality of the microbial community structure.