Ultrafast laser surgery probe for sub-surface ablation to enable biomaterial injection in vocal folds

Abstract

Creation of sub-epithelial voids within scarred vocal folds via ultrafast laser ablation may help in localization of injectable therapeutic biomaterials towards an improved treatment for vocal fold scarring. Several ultrafast laser surgery probes have been developed for precise ablation of surface tissues; however, these probes lack the tight beam focusing required for sub-surface ablation in highly scattering tissues such as vocal folds. Here, we present a miniaturized ultrafast laser surgery probe designed to perform sub-epithelial ablation in vocal folds. The requirement of high numerical aperture for sub-surface ablation, in addition to the small form factor and side-firing architecture required for clinical use, made for a challenging optical design. An Inhibited Coupling guiding Kagome hollow core photonic crystal fiber delivered micro-Joule level ultrashort pulses from a high repetition rate fiber laser towards a custom-built miniaturized objective, producing a 1/e2 focal beam radius of 1.12 ± 0.10 μm and covering a 46 × 46 μm2 scan area. The probe could deliver up to 3.8 μJ pulses to the tissue surface at 40% transmission efficiency through the entire system, providing significantly higher fluences at the focal plane than were required for sub-epithelial ablation. To assess surgical performance, we performed ablation studies on freshly excised porcine hemi-larynges and found that large area sub-epithelial voids could be created within vocal folds by mechanically translating the probe tip across the tissue surface using external stages. Finally, injection of a model biomaterial into a 1 × 2 mm2 void created 114 ± 30 μm beneath the vocal fold epithelium surface indicated improved localization when compared to direct injection into the tissue without a void, suggesting that our probe may be useful for pre-clinical evaluation of injectable therapeutic biomaterials for vocal fold scarring therapy. With future developments, the surgical system presented here may enable treatment of vocal fold scarring in a clinical setting.

Ultrafast Laser Microlaryngeal Surgery for In Vivo Subepithelial Void Creation in Canine Vocal Folds

“…2B), similar to ex vivo studies in porcine VF. 31 Figure 2C shows a histological cross section of the void shown in Figure 2B. The void has a width close to the 3-mm scanning width and is located just deep to the epithelium, agreeing well with the probe's working distance of $105 μm.…”

“…Ultrashort 5 ps pulses at 500 kHz were used for all experiments described herein. The rationale for pulse width and repetition rate selection was described previously 31 …”

Optimization of laser parameters for ultrashort-laser spinal surgeries

“…More in-depth characterization of the fiber in delivering high laser pulse energies, considering the non-linearities, has been reported by Andrus et. al 28 . The fiber was scanned across the desired field-of-view (FOV) using a piezo that was attached at the proximal end of the probe.…”

“…The primary consideration in designing the experimental setup is the feasibility of miniaturization of the probe such that it can be easily translated to a clinical setting. The experimental setup is based on in-line architecture where the fiber delivering the high-energy laser pulses is scanned using a piezo 3,27,28 . However, the only major distinguishable characteristic is the use of off-the-shelf optics to focus the laser pulses at the tissue end.…”

“…Our simulation also predicts the number of overlapping pulses, which then dictates the ablation depth and, thereby, MRR. The details of the Lissajous scanning simulation may be found in our previous work 27,28 . To characterize the tissue ablation properties of our experimental setup, we performed experiments on cortical bone samples.…”