Introduction: For over four decades, commercially pure titanium (Ti) and titanium alloys have been used for implant therapy due to their remarkable mechanical properties, low density, and biocompatibility[1]. Regrettably, despite accumulating evidence regarding the positive role played by implant surface modification on bone integration[2], the risk of infection, and thus early implant loss, still embodies a major clinical concern[3]. In this study, tetracycline (TCH), a protein synthesis inhibitor that acts at the ribosomal level was selected due to its antimicrobial properties and potential bone induction effects. No single dental implant that conjugates antimicrobial and bone promoting surface properties is currently available. Here, it was hypothesized that the surface modification of Ti with TCH-incorporated fibers could inhibit the growth of peri-implantitis-related pathogens and more effectively induce osteoprecursor cell differentiation when compared to un-modified Ti.
Materials and Methods: TCH was added to the polymer solution at different concentrations (5, 10, and 25 wt.%) and electrospun into fibers. Morphological (scanning electron microscopy, SEM), mechanical strength, antimicrobial activity against various pathogens, and cytocompatibility with osteoprecursor cells (MC3T3-E1) were evaluated. Commercially pure Ti discs were procured from United Titanium, Inc. (Wooster, OH, USA), cleaned, mounted on a aluminum foil-covered mandrel, and modified by TCH-incorporated electrospun fibers. The antimicrobial activity of the TCH-incorporated fiber-modified Ti (n=3/group) was evaluated using agar diffusion assays. Cell proliferation (n=4/group) was assessed (WST-1®, Roche, IN, USA) after 1, 3, 5, and 7 days. Additional samples were included to qualitatively evaluate cell morphology via SEM. MC3T3-E1 cells osteogenic differentiation on the TCH-incorporated nanofiber-modified Ti was quantitatively (n=4/group) determined by alkaline phosphatase (ALP) activity at days 1, 3, 7, and 14 using an ALP assay kit (SensoLyte pNPP, AnaSpec, CA, USA).
Results and Discussion: TCH was successfully incorporated into the submicron-sized and cytocompatible polymer fibers. Regarding mechanical performance, there was a significant (p≤0.001) interaction between electrospun mats and storage condition, except for tensile strength. All TCH-incorporated mats presented significant antimicrobial activity. The antimicrobial potential of the TCH-incorporated fibers-modified Ti was influenced by both the TCH concentration and bacteria tested.
At days 5 and 7, a significant increase in MC3T3-E1 cell number was observed for TCH-incorporated nanofibers-modified Ti discs when compared to that of TCH-free nanofibers-modified Ti-discs and bare Ti. Meanwhile, there was a significant increase in alkaline phosphatase (ALP) levels on the Ti discs modified with TCH-incorporated nanofiber on days 7 and 14, suggesting that the proposed surface modification promotes early osteogenic differentiation.
No visible sign of fiber detachment from the Ti was noticed.
Conclusion: Collectively, the data suggests that TCH-incorporated polymer fibers could function as an antimicrobial surface modifier and might enhance peri-implant bone formation upon implantation.
This research project was partially supported by a Delta Dental Foundation Grant. M.C.B. also acknowledges start-up funds from IUSD and funding from NIH/NIDCR (Grant#DE023552).
References:
[1] Adell R, Lekholm U, Rockler B, Branemark PI. 1981. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg. 10(6):387–416.
[2] Adell R, Lekholm U, Rockler B, Branemark PI. 1981. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg. 10(6):387–416.
[3] Chrcanovic BR, Albrektsson T, Wennerberg A. 2014. Periodontally compromised vs. periodontally healthy patients and dental implants: a systematic review and meta-analysis. J Dent. 42(12):1509-27.