Assessment of Titanium Modification for Coloring the Backplate of Boston Keratoprosthesis

Abstract

 

Purpose

 

Recent use of a titanium (Ti) backplate has improved the design and biocompatibility of the Boston Keratoprosthesis (BKPro). Titanium’s shiny metallic appearance, however, makes it cosmetically less favorable. The purpose of this study was to develop and test a coloring, surface modification of Ti.

 

Methods

 

Ti coloring was achieved electrochemically by controlled anodization of the Ti surface, which creates an oxide film on the Ti. Biocompatibility was assessed in vitro by co-culture of the modified Ti with human corneal limbal epithelial cells (HCLE) followed by assays of cell proliferation, cytotoxicity and migration, and in vivo by histologic appearance (H&E staining) and presence of inflammation (immunolocalization of CD45 positive cells) in rabbit corneal tissues 50 days after an intralamellar implant of the modified Ti. Surface characterization of the modified Ti included assessment by scanning electron microscopy (SEM), X-ray diffraction crystallography (XRD), Fourier transform infrared spectroscopy (FTIR) and chemical/color stability was determined after exposure to 70% alcohol for three months.

 

Results

 

Blue and brown coloration of Ti was achieved by anodization at 33 and 13.4 volts, respectively with a current supply of 3 Amps, (Figure 1). The in vitro biocompatibility assays showed no significant differences in cell proliferation, cytotoxicity or migration between HCLE cells co-cultured with surface modified or non-modified Ti (p> 0.745 for all group comparisons. Analysis of corneal tissues that had harbored the Ti implants showed normal cell appearance, and lack of CD45 or TUNEL positive cells. SEM showed the presence of a nano porous surface and similar crystallographic prints were observed with XRD and FTIR for the non-coated and the modified Ti, (Figure 2). Three months exposure to alcohol had no effect on the color or color homogeneity of the oxidized surface.

 

Conclusions

 

Ti backplate coloring was achieved by altering the voltage of the electrochemical anodization and controlling the thickness of the Ti oxidation. In vitro and in vivo results suggest that the modified Ti is equally biocompatible and as safe as the standard non-coated Ti. The color modification of the BKpro may improve the cosmesis and acceptance of the KPro by patients. *Supported by The Boston Keratoprosthesis Fund at the Massachusetts Eye and Ear Infirmary.

 

 

 

Keywords: 575 keratoprostheses • 480 cornea: basic science • 467 clinical laboratory testing