Decomposing Organic Molecules on Titanium with Vacuum Ultraviolet Light for Effective and Rapid Photofunctionalization

Abstract

Ultraviolet (UV) photofunctionalization counteracts the biological aging of titanium to increase the bioactivity and osseointegration of titanium implants. However, UV photofunctionalization currently requires long treatment times of between 12 min and 48 h, precluding routine clinical use. Here, we tested the ability of a novel, xenon excimer lamp emitting 172 nm vacuum UV (VUV) to decompose organic molecules coated on titanium as a surrogate of photofunctionalization. Methylene blue as a model organic molecule was coated on grade 4 commercially pure titanium and treated with four UV light sources: (i) ultraviolet C (UVC), (ii) high-energy UVC (HUVC), (iii) proprietary UV (PUV), and (iv) VUV. After one minute of treatment, VUV decomposed 57% of methylene blue compared with 2%, 36%, and 42% for UVC, HUVC, and PUV, respectively. UV dose-dependency testing revealed maximal methylene blue decomposition with VUV within one minute. Equivalent decomposition was observed on grade 5 titanium alloy specimens, and placing titanium specimens in quartz ampoules did not compromise efficacy. Methylene blue was decomposed even on polymethyl methacrylate acrylic specimens at 20–25% lower efficiency than on titanium specimens, indicating a relatively small contribution of titanium dioxide-mediated photocatalytic decomposition to the total decomposition. Load-testing revealed that VUV maintained high efficacy of methylene blue decomposition regardless of the coating density, whereas other UV light sources showed low efficacy with thin coatings and plateauing efficacy with thicker coatings. This study provides foundational data on rapid and efficient VUV-mediated organic decomposition on titanium. In synergy with quartz ampoules used as containers, VUV has the potential to overcome current technical challenges hampering the clinical application of UV photofunctionalization.

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“…The UV light used in this study is new and shows an impressive ability to decompose the hydrocarbon pellicle on titanium and in liquids [88,89]. This UV light is specifically categorized as VUV due to its high energy produced via a short wavelength of 172 nm, in contrast to UVA (400-320 nm), UVB (320-280 nm), and UVC (280-200 nm).…”

“…This UV light is specifically categorized as VUV due to its high energy produced via a short wavelength of 172 nm, in contrast to UVA (400-320 nm), UVB (320-280 nm), and UVC (280-200 nm). The 172 nm wavelength is produced by a xenon excimer lamp, and this wavelength has been shown to induce rapid and maximal pellicle removal in only one minute according to optimization studies [88,89]. The advantage in the pellicle-removing capability of VUV light is explained by its exclusive photochemical decomposition through the production of reactive oxygen species, particularly singlet atomic oxygen, as well as the wider spectrum of direct photophysical decomposition of carbon bonding [88].…”

“…The 172 nm wavelength is produced by a xenon excimer lamp, and this wavelength has been shown to induce rapid and maximal pellicle removal in only one minute according to optimization studies [88,89]. The advantage in the pellicle-removing capability of VUV light is explained by its exclusive photochemical decomposition through the production of reactive oxygen species, particularly singlet atomic oxygen, as well as the wider spectrum of direct photophysical decomposition of carbon bonding [88]. The present study is the first to demonstrate the biological impact of VUV treatment of biomaterials and the first to demonstrate that it is possible to decarbonize zirconia surfaces and induce superhydrophilicity after one minute of VUV treatment.…”

“…Next-generation UV photofunctionalization, or vacuum UV (VUV) photofunctionalization [88,89], may further enhance material bioactivity. A limitation of classical UV photofunctionalization protocols was the UV exposure time-12 or 20 min, or longer up to 48 h-needed to remove the hydrocarbon pellicle [46,66,67,83,[90][91][92].…”

“…Since implants must be treated with UV immediately prior to use to ensure efficacy, these long treatment times were a significant barrier to using the technique during surgery. Recently, high-energy UV light (wavelength < 200 nm), or VUV, was introduced for photofunctionalization [88,89]. VUV can maximally decompose and remove hydrocarbons in the liquid and on titanium surfaces in one minute, drastically improving the exposure time.…”