gms | German Medical Science

Objective: Spinal instrumentation in neurosurgery has giant popularity for the treatment of spondylodiscitis. Thereby most of the implants are made of titanium alloys (Ti), which is associated with artefacts on postoperative imaging. However, for patients with suspected relapse of the infection these artefacts render these imaging modalities to be useless. Recently, carbon fiber-reinforced polyetheretherketone (CFRP) implants became available for posterior instrumentation with the aim to reduce imaging artifacts by implants. The aim of this study was to compare the bacterial adhesion by numbers on titanium with CFRP, in order to evaluate the material-associated property to facilitate such infections.

Methods: A bacterial adhesion assay was conducted with the main surgical site infection bacterial strains - S. aureus (ATCC® 25923™), S. epidermidis (ATCC® 35984™) and methicillin-resistant S. aureus (ATCC® 43300™). Within the adhesion assay, both types of implants polished titanium discs and CFRP discs were incubated in bacterial suspensions (1.3 x 105 cfu/ml) over 24 hours. Then, viable adhered bacteria on implant surfaces were determined quantitatively after sample sonication and plating of supernatants on agar. Colonies were counted for each sample. Moreover, to characterize material surfaces the average roughness (Ra in µm) was measured with a stylus surface profilometer Dektak 8 (Veeco Inc., US). Additionally, contact angles were measured with the sessile drop method using standardized fluids, followed by calculating the surface free energy for each sample type.

Results: Incubation in bacterial suspensions resulted in numbers of adhered bacteria on CFRP (MRSA: 8.7 x 106 cfu; S.aureus: 7.6 x 106 cfu; S.epidermidis: 6.4 x 106 cfu), and on Ti controls (MRSA: 3.3 x 106 cfu; S.aureus: 3.6 x 106 cfu; S.epidermidis: 4.0 x 106 cfu). Each cfu-value per sample is the average of at least 8 samples. There are no significant differences between cfu numbers of adhered bacteria on CRRP and Ti materials. Surface profilometry showed Ra values for titanium at 0.20±0.04 µm and 0.38±0.10 µm for CFRP. Both materials showed a similar hydrophilic wettability by water (contact angels: 83° for Ti and 73° for CFRP). Completely different surface energy values were measured (overall/polar/disperse), for titanium (39.0/38.9/0.1 in mJ/m²) and CFRP (12.4/12.4/~0 in mJ/m²).

Conclusion: Despite CFRP has a roughness double as titanium, there were no significant differences in bacterial adherence of MRSA, S.aureus or S.epidermidis between CFRP- and Ti-implants. Possibly, because of CFRP’s low surface free energy, the bacterial adhesion could be determined at a comparably low level as for polished titanium. The application of carbon/PEEK (CFRP) in neurosurgical instrumentations is a promising approach to combine the properties of titanium, possibly without increasing infection rates and the benefit of reducing imaging artefacts.