Functionalization of titanium with chitosan via silanation: evaluation of biological and mechanical performances

Abstract

Complications in dentistry and orthopaedic surgery are mainly induced by peri-implant bacterial infections and current implant devices do not prevent such infections. The coating of antibacterial molecules such as chitosan on its surface would give the implant bioactive properties. The major challenge of this type of coating is the attachment of chitosan to a metal substrate. In this study, we propose to investigate the functionalization of titanium with chitosan via a silanation. Firstly, the surface chemistry and mechanical properties of such coating were evaluated. We also verified if the coated chitosan retained its biocompatibility with the peri-implant cells, as well as its antibacterial properties. FTIR and Tof-SIMS analyses confirmed the presence of chitosan on the titanium surface. This coating showed great scratch resistance and was strongly adhesive to the substrate. These mechanical properties were consistent with an implantology application. The Chitosan-coated surfaces showed strong inhibition of Actinomyces naeslundii growth; they nonetheless showed a non significant inhibition against Porphyromonas gingivalis after 32 hours in liquid media. The chitosan-coating also demonstrated good biocompatibility to NIH3T3 fibroblasts. Thus this method of covalent coating provides a biocompatible material with improved bioactive properties. These results proved that covalent coating of chitosan has significant potential in biomedical device implantation.

Figure 1. Reaction scheme allowing the covalent bonding of chitosan to titanium surface.

Figure 2. FTIR-ATR spectra.

(A) chitosan. (B) chitosan–coated sample.

Figure 3. Graphs displaying the evolution of the Vickers Hardness (HV) versus inverse of the diagonal of the indent (1/l).

(A) Measurements on the composite (HVc) and on the substrate (HVs). (B) Scheme of the theoretical curves. HVs represents the curve of a hard substrate and HVf the curve of a soft film. HVc is the curve of the composite film-substrate: for high load (l → ∞), HVc ∼ HVs, for very low load (l → 0), HVc ∼ HVf.

Figure 4. Optical micrographs of scratches observed on chitosan-coated surfaces.

Figure 5. Optical micrograph of scratch observed on chitosan-coated surface.

The image is a detail of Figure 4 for a applied load of 5,5 N.

Figure 6. Graph displaying the evolution of the groove diameter (d) versus the applied force (F).

Figure 7. Schemes displaying coating behavior under tip contact with an applied load (F).

(A) the burial depth (h) is less than the thickness of the coating (e). (B) the burial depth (h) is greater than the thickness of the coating (e).

Figure 8. The effects of chitosan coated Ti.

on Porphyromonas gingivalis and on Actinomyces naeslundii in liquid medium for 32 hours. Data are expressed in % of bacteria in contact with coated sample compared to the bacteria in contact with control (or percentage of bacterial inhibition). Data represent the means ± SD of three independent experiments. * p<0.01.

Figure 9. Diagram displaying % of resazurin reduction for uncoated and Chitosan-coated samples.

Data are given after 2, 4 and 7 days of NIH3T3 fibroblasts culture. Data are presented as means ± SD.

Figure 10. Confocal images of fibroblasts proliferated.

(A) 2 days on chitosan-coated surface. (B) 2 days on titanium surface. (C) 4 days on chitosan-coated surface. (D) 7 days on chitosan-coated surface. Actin filaments (green) and nuclei (red) were stained.