The Boston Keratoprosthesis (BKpro, Massachusetts Eye and Ear Infirmary) is an artificial cornea that is applicable for a broad array of corneal conditions not amenable to standard corneal transplantation.
1 The device is designed like a collar button, with a plastic stem and a backplate supporting the donor corneal tissue. In the initial prototype, the BKpro was manufactured exclusively from medical-grade polymethyl methacrylate (PMMA). Following its Food and Drug Administration (FDA) approval for marketing in 1992, incremental steps and significant improvements have been made to the BKpro.
2,3 It is now the most commonly used prosthetic cornea in the world, with approximately 7500 devices implanted worldwide to date (Dohlman CH, personal oral communication, 2013). Of those, roughly 5000 devices have been used in the United States. Although aesthetically acceptable due to its transparency, the PMMA design of the backplate can be associated with the formation of a retroprosthetic membrane and the congestion of the anterior chamber. The medical-grade titanium (Ti) backplate, introduced in 2005 at the Massachusetts Eye and Ear Infirmary, was found to be more biologically inert than PMMA.
4 The Ti backplate implementation also resulted in marked improvement in retroprosthetic membrane formation
5 and has enhanced the device by providing higher tensile strength, corrosion resistance, bio-inertness, ductility, and lightness (4.5 g/cm
3). This new design contains a medical-grade Ti that is identical to the one used in orthopedic and dental prosthetics. However, despite the apparent advantages of Ti over PMMA, its metallic shiny silver appearance makes it less aesthetically desirable and socially acceptable by patients.
This study presents a surface modification technique of coloring the Ti backplates with an inert and biocompatible oxide layer. This modification was assessed in vitro using cell proliferation, cytotoxicity, and cell-coverage assays, as well as in vivo with histological morphology and immunohistochemistry of explanted rabbit corneas. Moreover, the Ti surface was characterized by scanning electron microscopy, x-ray diffraction crystallography (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and chemical/color stability.