Precision removal of uneven skin tissue at the micrometer level via focus-corrected femtosecond-laser ablation

Abstract

Background: From the perspective of aesthetic surgery and regenerative medicine, the precision of surgical instruments is critical for preventing aesthetic complications during procedures such as skin debridement and the removal of unwanted tissues, as well as for better regeneration. Femtosecond lasers (fs-lasers) can achieve micrometer-level tissue removal. However, an uneven skin texture can cause the laser to defocus, leading to iatrogenic injury and hindering clinical application. Overcoming the defocusing tendency of fs-lasers is therefore crucial for their clinical use. Methods: Our self-developed fs-laser microfabrication platform was used to implement a focus-corrected method based on 2D interpolation for uneven skin surfaces, using different laser powers and velocities for linear, planar, and 3D scanning of porcine skin. Leveraging the identified dose–response relationship, the optimized device and parameters were used for precise tissue ablation in an in vivo rat experiment. The structural integrity and viability of the remaining skin were evaluated histologically. Results: Our study revealed that focus-corrected fs-laser ablation enabled controllable micrometer-level removal of target skin tissues. The depth of tissue removal was correlated with the fs-laser single-pulse energy. Unlike other laser devices, the scanning velocity did not affect the ablation depth, as the focusing mechanism of the focus-corrected fs-laser restricts ablation beyond the focal point. Appropriate fs-laser parameters for parallel linear scanning enabled tissue removal in various 3D shapes. Increased depth of field, increased single-pulse energy, and faster scanning velocity enabled precise, rapid, and safe ablation of skin tissue in the rat model. Histological and biochemical analyses demonstrated that focus-corrected fs-laser debridement did not damage the surrounding collagen structure or cell viability of the wound. Conclusions: We demonstrated that focus-corrected fs-laser ablation enables micron-scale skin removal with minimal collateral damage. By selectively adjusting single-pulse energy for depth-specific ablation and operation at the maximum permissible scanning velocity, this technique enables precise skin removal in the desired shape, offering an innovative and ultrahigh-precision surgical approach for skin as well as other tissues or organ surgery.

Keywords

Precision surgery / Debridement / Femtosecond laser / Skin

References

[1] Kwa KAA, Goei H, Breederveld RS, Middelkoop E, van der Vlies CH, van Baar ME et al. A systematic review on surgical and nonsurgical debridement techniques of burn wounds. J Plast Reconstr Aesthet Surg 2019; 72: 1752-62. https://doi.org/10.1016/j.bjps.2019.07.006.

[2] Gurfinkel R, Rosenberg L, Cohen S, Cohen A, Barezovsky A, Cagnano E et al. Histological assessment of tangentially excised burn eschars. Can J Plast Surg 2010; 18: e33-6.

[3] Dal Prà I, Chiarini A, De Santis D, Nocini R, Chang S, Armato U. The quest for the perfect healing of human skin wounds: promising models. Regenesis Repair Rehabilitation 2025; 1: 66-79. https://doi.org/10.1016/j.rerere.2025.03.003.

[4] Vogel A, Venugopalan V. Mechanisms of pulsed laser ablation of biological tissues. Chem Rev 2003; 103: 577-644.

[5] Doizi S, Germain T, Panthier F, Compérat É, Traxer O, Berthe L. Comparison of holmium:YAG and thulium fiber lasers on soft tissue: an ex vivo study. J Endourol 2022; 36: 251-8. https://doi.org/10.1089/end.2021.0263.

[6] Weisberg NK, Kuo T, Torkian B, Reinisch L, Ellis DL. Optimizing fluence and debridement effects on cutaneous resurfacing carbon dioxide laser surgery. Arch Dermatol 1998; 134: 1223-8.

[7] Chopra K, Calva D, Sosin M, Tadisina KK, Banda A, De La Cruz C et al. A comprehensive examination of topographic thickness of skin in the human face. Aesthet Surg J 2015; 35: 1007-13. https://doi.org/10.1093/asj/sjv079.

[8] Dunkin CSJ, Pleat JM, Gillespie PH, Tyler MP, Roberts AH, McGrouther DA. Scarring occurs at a critical depth of skin injury: precise measurement in a graduated dermal scratch in human volunteers. Plast Reconstr Surg 2007; 119: 1722-32. https://doi.org/10.1097/01.prs.0000258829.07399.f0.

[9] Strickland D, Mourou G. Compression of amplified chirped optical pulses. Opt Commun 1985; 56: 447-9. https://doi.org/10.1016/0030-4018(85)90120-8.

[10] He S, Yu J, Hu M. Femtosecond laser high precision fabrication for novel applications. Curr Nanosci 2016; 12: 676-84. https://doi.org/10.2174/1573413712666160530105310.

[11] Kononenko VV, Gololobov VM, Komlenok MS, Konov VI. Nonlinear photooxidation of diamond surface exposed to femtosecond laser pulses. Laser Phys Lett 2015; 12: 96-101. https://doi.org/10.1088/1612-2011/12/9/096101.

[12] Latz C, Asshauer T, Rathjen C, Mirshahi A. Femtosecond-laser assisted surgery of the eye: overview and impact of the low-energy concept. Micromachines 2021; 12: 122. https://doi.org/10.3390/mi12020122.

[13] Loganathan S, Santhanakrishnan S, Bathe R, Arunachalam M. Physiochemical characteristics: a robust tool to overcome teeth heterogeneity on predicting laser ablation profile. J Biomed Mater Res B Appl Biomater 2021; 109: 486-95. https://doi.org/10.1002/jbm.b.34717.

[14] Teichman JMH. Femtosecond laser lithotripsy: feasibility and ablation mechanism. J Biomed Opt 2010; 15: 028001. https://doi.org/10.1117/1.3368998.

[15] Andrus L, Mau T, Ben-Yakar A. Scattering properties and femtosecond laser ablation thresholds of human and canine vocal folds at 776-nm wavelength. J Biomed Opt 2019; 24: 085005. https://doi.org/10.1117/1.JBO.24.8.085005.

[16] Gemini L, Al-Bourgol S, Machinet G, Bakkali A, Faucon M, Kling R. Ablation of bone tissue by femtosecond laser: a path to high-resolution bone surgery. Materials (Basel) 2021; 14: 2429. https://doi.org/10.3390/ma14092429.

[17] Hu B, Zhao X, Lu Y, Zhu Y, He H. A transient photoactivation of epidermal stem cells by femtosecond laser promotes skin wound healing. J Biophotonics 2022; 15: e202200217. https://doi.org/10.1002/jbio.202200217.

[18] Nicolodelli G, Angarita DPR, Inada NM, Tirapelli LF, Bagnato VS. Effect of photodynamic therapy on the skin using the ultrashort laser ablation. J Biophotonics 2014; 7: 631- 7. https://doi.org/10.1002/jbio.201300024.

[19] Santos MOD, Latrive A, De Castro PAA, De Rossi W, Z TMT, Samad RE et al. Multimodal evaluation of ultra-short laser pulses treatment for skin burn injuries. Biomed Opt Express 2017; 8: 1575-88. https://doi.org/10.1364/BOE.8.001575.

[20] Garvie Cook H, Stone JM, Yu F, Guy RH, Gordeev SN. Femtosecond pulsed laser ablation to enhance drug delivery across the skin. J Biophotonics 2016; 9: 144-54. https://doi.org/10.1002/jbio.201500120.

[21] Jia M, Huang J, Chen Y, Jincheng L, Wang K. Experimental study on the effect of scanning path on skin tissue properties of femtosecond laser welding. J Biophotonics 2023; 16:e202300205. https://doi.org/10.1002/jbio.202300205.

[22] He X, Ma Y, Li J, Yuan MZ, Yin MF, Meng LM et al. Method and application of femtosecond laser processing on non-flat surfaces. Laser Optoelectron P 2023; 60: 1714009.

[23] Gibson ALF, Shatadal S. A simple and improved method to determine cell viability in burn-injured tissue. J Surg Res 2017; 215: 83-7. https://doi.org/10.1016/j.jss.2017.03.064.

[24] Zhang X, Chen X, Chen T, Ma G, Zhang W, Huang L. Influence of pulse energy and defocus amount on the mechanism and surface characteristics of femtosecond laser polishing of SiC ceramics. Micromachines 2022; 13: 1118. https://doi.org/10.3390/mi13071118.

[25] Gill RK, Smith ZJ, Lee C, Wachsmann-Hogiu S. The effects of laser repetition rate on femtosecond laser ablation of dry bone: a thermal and LIBS study. J Biophotonics 2016; 9: 171-80. https://doi.org/10.1002/jbio.201500144.

[26] Dmitriev AK, Konovalov AN, Kortunov VN, Ulyanov VA. Evaporation peculiarities of soft biological tissues in the process of automated 2D-scanning of CO2 laser radiation. J Biomed Photonics Eng 2024; 10: 040307. https://doi.org/10.18287/JBPE24.10.040307.

[27] Lin Z, Hong M. Femtosecond laser precision engineering: from Micron, submicron, to nanoscale. Ultrafast Sci 2021; 2021: 9783514. https://doi.org/10.34133/2021/9783514.

[28] Wang B, Wang X, Zheng H, Lam YC. Thermal effect of femtosecond laser polystyrene processing. Opt Laser Technol 2019; 117: 244-50. https://doi.org/10.1016/j.optlastec.2019.04.033.

[29] Yin M, Li Y, Luo Y, Yuan M, Armato U, Prà ID et al. A novel method for objectively, rapidly and accurately evaluating burn depth via near infrared spectroscopy. Burns Trauma 2021; 9: tkab014. https://doi.org/10.1093/burnst/tkab014.