Optimization of sapphire capillary needles for interstitial and percutaneous laser medicine

Abstract

Sapphire capillary needles fabricated by edge-defined film-fed growth (EFG) technique hold strong potential in laser thermotherapy and photodynamic therapy, thanks to the advanced physical properties of sapphire. These needles feature an as-grown optical quality, their length is tens of centimeters, and they contain internal capillary channels, with open or closed ends. They can serve as optically transparent bearing elements with optical fibers introduced into their capillary channels in order to deliver laser radiation to biological tissues for therapeutic and, in some cases, diagnostic purposes. A potential advantage of the EFG-grown sapphire needles is associated with an ability to form the tip of a needle with complex geometry, either as-grown or mechanically treated, aimed at controlling the output radiation pattern. In order to examine a potential of the radiation pattern shaping, we present a set of fabricated sapphire needles with different tips. We studied the radiation patterns formed at the output of these needles using a He-Ne laser as a light source, and used intralipid-based tissue phantoms to proof the concept experimentally and the Monte-Carlo modeling to proof it numerically. The observed results demonstrate a good agreement between the numerical and experimental data and reveal an ability to control within wide limits the direction of tissue exposure to light and the amount of exposed tissue by managing the sapphire needle tip geometry.

Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review

“…Other delivery devices such as fibre-focusing types have been benchmarked for oral surgery [ 117 ]. Recently, the use of sapphire capillary needles coupling optical fibres inside the needles with different tips and light patterns has been demonstrated [ 51 , 118 , 119 ]. Figure 6 a depicts an example of such advanced capillary sapphire needles incorporating several types of needle tips with different geometry to control the direction of tissue light exposure and the amount of exposed tissue [ 119 ].…”

Microfocusing sapphire capillary needle for laser surgery and therapy: Fabrication and characterization

“…The radiation patterns formed at the output needle end were studied numerically by means of the ray tracing approach, since previously it demonstrated a good agreement with experimental results [23], and since the analysis of light‐needle interaction is implemented at the scales much larger than the wavelength, where approximations of geometrical optics are relevant. In this study, the radiation wavelength λ is set to 1.06 μm; the refractive index n and the absorption coefficient (by power) μ a of sapphire are considered to be 1.78 and 10 −6 mm −1 , respectively, at the chosen wavelength; the corresponding modeling parameters of silica fiber are n = 1.54 and μ a = 3 × 10 −6 mm −1 .…”

“…Sapphire forms a favorable material platform for medical instruments applied for laser surgery, light delivery, optical diagnosis and their combinations [18][19][20][21][22][23][24][25]. It possesses the aforementioned features, admits multiple sterilization and combination with magnetic resonance imaging (MRI) for additional control of laser treatments [26].…”

“…It possesses the aforementioned features, admits multiple sterilization and combination with magnetic resonance imaging (MRI) for additional control of laser treatments [26]. In order to overcome the considerable difficulties of sapphire instruments' manufacturing, arised mainly due to its high hardness, the edge-define film-fed (EFG) crystal growth technique [27][28][29] was proposed for fabrication of such instruments with a complex shape, including needles for LTT and PDT [23,30]. This approach does not require essential mechanical processing [31,32], and allows production of rather thin (1 mm) needles with small capillary channels along the whole length directly during the crystal growth process.…”

“…The absence of junctions and other materials in the sapphire needle design admits its application for a high‐power coagulation and ablation. Moreover, the significantly different radiation patterns for interstitial and superficial exposure can be formed by the optimized shape of a needle tip [23].…”