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/e2focal beam radius of 1.12 ± 0.10 μm and covering a 46 × 46 μm2scan 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 mm2void 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.
We present a miniaturized ultrafast laser surgery probe with improved miniaturized optics to deliver higher peak powers and enable higher surgical speeds than previously possible. A custom-built miniaturized CaF2objective showed no evidence of the strong multiphoton absorption observed in our previous ZnS-based probe, enabling higher laser power delivery to the tissue surface for ablation. A Kagome fiber delivered ultrashort pulses from a high repetition rate fiber laser to the objective, producing a focal beam radius of 1.96 μm and covering a 90×90 μm2scan area. The probe delivered the maximum available fiber laser power, providing fluences >6 J/cm2at the tissue surface at 53% transmission efficiency. We characterized the probe’s performance through a parametric ablation study on bovine cortical bone and defined optimal operating parameters for surgery using an experimental- and simulation-based approach. The entire opto-mechanical system, enclosed within a 5-mm diameter housing with a 2.6-mm diameter probe tip, achieved material removal rates >0.1 mm3/min, however removal rates were ultimately limited by the available laser power. Towards a next generation surgery probe, we simulated maximum material removal rates when using a higher power fiber laser and found that removal rates >2 mm3/min could be attained through appropriate selection of laser surgery parameters. With future development, the device presented here can serve as a precise surgical tool with clinically viable speeds for delicate applications such as spinal decompression surgeries.
more » « less- NSF-PAR ID:
- 10274645
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Biomedical Optics Express
- Volume:
- 12
- Issue:
- 8
- ISSN:
- 2156-7085
- Page Range / eLocation ID:
- Article No. 4779
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Ultrafast Laser Microlaryngeal Surgery for In Vivo Subepithelial Void Creation in Canine Vocal Foldsmore » « less
Background/Objectives Tightly‐focused ultrafast laser pulses (pulse widths of 100 fs–10 ps) provide high peak intensities to produce a spatially confined tissue ablation effect. The creation of sub‐epithelial voids within scarred vocal folds (VFs) via ultrafast laser ablation may help to localize injectable biomaterials to treat VF scarring. Here, we demonstrate the feasibility of this technique in an animal model using a custom‐designed endolaryngeal laser surgery probe.
Methods Unilateral VF mucosal injuries were created in two canines. Four months later, ultrashort laser pulses (5 ps pulses at 500 kHz) were delivered via the custom laser probe to create sub‐epithelial voids of ~3 × 3‐mm2in both healthy and scarred VFs. PEG‐rhodamine was injected into these voids. Ex vivo optical imaging and histology were used to assess void morphology and biomaterial localization.
Results Large sub‐epithelial voids were observed in both healthy and scarred VFs immediately following in vivo laser treatment. Two‐photon imaging and histology confirmed ~3‐mm wide subsurface voids in healthy and scarred VFs of canine #2. Biomaterial localization within a void created in the scarred VF of canine #2 was confirmed with fluorescence imaging but was not visualized during follow‐up two‐photon imaging. As an alternative, the biomaterial was injected into the excised VF and could be observed to localize within the void.
Conclusions We demonstrated sub‐epithelial void formation and the ability to inject biomaterials into voids in a chronic VF scarring model. This proof‐of‐concept study provides preliminary evidence towards the clinical feasibility of such an approach to treating VF scarring using injectable biomaterials.
Level of Evidences N/A
Laryngoscope , 133:3042–3048, 2023 -
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