Titanium-copper-nitride coated spacers for two-stage revision of infected total hip endoprostheses

Copper as an alternative antimicrobial coating for implants - An in vitro study

AIM

To investigate osteoconductive and antimicrobial properties of a titanium-copper-nitride (TiCuN) film and an additional BONIT^® coating on titanium substrates.

METHODS

For micro-structuring, the surface of titanium test samples was modified by titanium plasma spray (TPS). On the TPS-coated samples, the TiCuN layer was deposited by physical vapor deposition. The BONIT^® layer was coated electrochemically. The concentration of copper ions released from TiCuN films was measured by atomic absorption spectrometry. MG-63 osteoblasts on TiCuN and BONIT^® were analyzed for cell adhesion, viability and spreading. In parallel, Staphylococcus epidermidis (S. epidermidis) were cultivated on the samples and planktonic and biofilm-bound bacteria were quantified by counting of the colony-forming units.

RESULTS

Field emission scanning electron microscopy (FESEM) revealed rough surfaces for TPS and TiCuN and a special crystalline surface structure on TiCuN + BONIT^®. TiCuN released high amounts of copper quickly within 24 h. These release dynamics were accompanied by complete growth inhibition of bacteria and after 2 d, no planktonic or adherent S. epidermidis were found on these samples. On the other hand viability of MG-63 cells was impaired during direct cultivation on the samples within 24 h. However, high cell colonization could be found after a 24 h pre-incubation step in cell culture medium simulating the in vivo dynamics closer. On pre-incubated TiCuN, the osteoblasts span the ridges and demonstrate a flattened, well-spread phenotype. The additional BONIT^®coating reduced the copper release of the TiCuN layer significantly and showed a positive effect on the initial cell adhesion.

CONCLUSION

The TiCuNcoating inhibits the formation of bacterial biofilms on orthopedic implants by influencing the “race for the surface” to the advantage of osteoblasts.

Antibacterial and Biocompatible Titanium-Copper Oxide Coating May Be a Potential Strategy to Reduce Periprosthetic Infection: An In Vitro Study

BACKGROUND

Periprosthetic infections are devastating for patients and more efficacious preventive strategies are needed. Surface-modified implants using antibacterial coatings represent an option to cope with this problem; however, manufacturing limitations and cytotoxicity have curbed clinical translation. Among metals with antibacterial properties, copper has shown superior in vitro antibacterial performance while maintaining an acceptable cytotoxicity profile. A thin film containing copper could prevent early biofilm formation to limit periprosthetic infections. This pilot study presents the in vitro antibacterial effect, cytotoxicity, and copper ion elution pattern of a thin film of titanium-copper oxide (TiCuO).

QUESTIONS/PURPOSES

(1) Do titanium alloy (Ti6Al4V) discs coated with a thin film of TiCuO reduce Staphylococcus epidermidis biofilm and planktonic cell density compared with uncoated discs? (2) Do Ti6Al4V discs coated with a thin film of TiCuO affect normal human osteoblast viability compared with untreated cells? (3) Is copper ion concentration generated by coated discs lower than previously published copper ion concentrations that cause 50% toxicity in similar human cell lines in vitro (TC50)?

METHODS

Ninety Ti6Al4V discs (12.5 mm diameter; 1.25 mm thick) were used in this study. Seventy-two Ti6Al4V discs were coated with a thin film of either titanium oxide (TiO) or TiCuO containing 20%, 40%, or 80% copper using high-power impulse magnetron sputtering (HiPIMS). Eighteen Ti6Al4V discs remained uncoated for control purposes. We tested antibacterial properties of S epidermidis grown on discs in wells containing growth medium. After 24 hours, planktonic bacteria as well as biofilms removed by sonication were quantitatively cultured. Annexin/Pi staining was used to quantify in vitro normal human osteoblast cell viability at 24 hours and Day 7, respectively. Copper elution was measured at Days 1, 2, 3, 7, 14, and 28 using an inductively coupled plasma mass spectrometer to analyze aliquots of culture medium. Copper ion concentration achieved at 24 hours was compared with previously published TC50 for gingival fibroblast, a phenotypically similar cell line with available data regarding copper ion exposure.

RESULTS

Discs coated with TiCuO 80% copper showed greater biofilm and planktonic cell density reduction when compared with other tested compositions (analysis of variance [ANOVA]; p < 0.001). Discs coated with TiCuO 80% copper showed mean biofilm and planktonic cell density of 4.0 log₁₀ (SD = 0.4) and 5.7 log₁₀ (SD = 0.2). Discs coated with TiCuO 80% showed a mean difference in biofilm and planktonic cell density of 2.5 log₁₀ (95% confidence interval [CI], 1.9-3.1 log_10; p < 0.001) and 1.2 (95% CI, 0.6-1.8; p < 0.001), respectively, when compared with uncoated discs. Normal human osteoblast viability did not differ among all groups at 24 hours (ANOVA; p = 0.2) and Day 7 (ANOVA; p = 0.7). Discs coated with TiCuO 80% copper showed a mean difference (95% CI) in relative cell viability (%) at 24 hours and Day 7 of 31.1 (95% CI, -19.4 to 81.7; p = 0.4) and -5.0 (95% CI, -7.8 to 17.9; p = 0.9), respectively, when compared with untreated cells. For all TiCuO-coated discs, copper ion elution peaked at 24 hours and slowly decreased in a curvilinear fashion to nearly undetectable levels by Day 28. Discs coated with TiCuO 80% copper showed mean copper ion concentration at 24 hours of 269.4 µmol/L (SD = 25.2 µmol/L) and this concentration was lower than previously published TC50 for similar human cell lines at 24 hours (344 µmol/L, SEM = 44 µmol/L).

CONCLUSIONS

This pilot study demonstrates a proof of concept that a thin-film implant coating with TiCuO can provide a potent local antibacterial environment while remaining relatively nontoxic to a human osteoblast cell line. Further research in an animal model will be necessary to establish efficacy and safety of this technique and whether it might be useful in the design of implants.

CLINICAL RELEVANCE

A thin film coating with TiCuO demonstrates high antibacterial activity and low cellular cytotoxicity to human osteoblasts in vitro. Taken together, these properties represent a potential strategy for preventing periprosthetic infection if further work in animal models can confirm these results in vivo.