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

Abstract

A sapphire shaped capillary needle designed for collimating and focusing of laser radiation was proposed and fabricated by the edge-defined film-fed growth technique. It features an as-grown surface quality, high transparency for visible and near-infrared radiation, high thermal and chemical resistance and the complex shape of the tip, which protects silica fibers. The needle's geometrical parameters can be adjusted for use in various situations, such as type of tissue, modality of therapy and treatment protocol. The focusing effect was demonstrated numerically and observed experimentally during coagulation of the ex vivo porcine liver samples. This needle in combination with 0.22NA optical fiber allows intensive and uniform coagulation of 150 mm 3 volume interstitially and 30 mm 3 superficially by laser exposure with 280 J without tissue carbonization and fiber damaging along with delicate treatment of small areas. The demonstrated results reveal the perspectives of the proposed sapphire microfocusing needle for laser surgery and therapy.

Proof of concept for the sapphire scalpel combining tissue dissection and optical diagnosis

“…At the same time, the third channel could be applied for the coagulation of the adjacent tissues and vessels during the surgery, as well as for photodynamic therapy. Since the sapphire demonstrated high thermal resistance, such application would not lead to the damages of its surface; moreover, the quartz fiber would be protected from destruction since the closed internal channel of the scalpel prevents the direct contact of fiber with tissue during coagulation 36 . We should add that sapphire scalpel withstands multiple dissections and sterilization cycles without decreasing its bulk and surface quality, allowing different types of cleaning.…”

“…The approaches for growing sapphire shaped crystals, in particular ribbons, with longitudinal capillary channels, are based on the EFG technique, which implies the crystal growth from a melt formed on the top of a capillary die. [34][35][36] One of the main problems in growing sapphire crystals with capillary channels of small diameter is the possibility of channel collapse due to an increase in Laplace pressure in the melt meniscus with a decrease in the radius of the mean curvature of the meniscus surface (decrease in the channel diameter) and an increase in the meniscus height. 48 To mitigate this challenge, we optimized the growth rates and temperature regimes in the crystallization zone, as well as applied new approaches to the die design and a system for monitoring the crystallization front state.…”

“…In contrast, inorganic monocrystals, such as sapphire and diamond, are free from these drawbacks 44 and demonstrate high biocompatibility and chemical resistance along with mechanical strength, approving strong potential for medical applications. 36,[45][46][47] Sapphire medical instruments can withstand multiple applications without considerable losses of mechanical and optical performance. Furthermore, they can be sterilized using any conventional techniques, including high temperature, chemical, or plasma treatments.…”

“…This paper describes the feasibility of a sapphire scalpel to be applied for optical diagnosis during tissue dissection. Sapphire shaped crystal used for its fabrication is grown by the edge-defined film-fed growth (EFG) technique [34][35][36] and then mechanically processed by grinding and polishing with further chemical etching of the cutting edge. EFG technique yields the growth of crystals with complex geometry and high optical quality, which is ideally suitable for the fabrication of different optical waveguides, fibers, and high-tech medical tools.…”

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

“…In this line, micro-focusing needles, allowing for lower energy required for treatment have also been developed. Such sapphire needles are advantageous because they can avoid degradation of their properties for multiple applications and sterilisation [ 120 ].…”