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Picosecond Infrared Laser for Scarfree Surgery<br/>with Preservation of the Tissue Structure and Recognition of Tissue Type and Boundaries

Final Report Summary - SUREPIRL (Picosecond Infrared Laser for Scarfree Surgerywith Preservation of the Tissue Structure and Recognition of Tissue Type and Boundaries)

Within the SUREPIRL project, the expected potential of the innovative laser as a surgical and diagnostic instrument has been proven. A wide range of advancements from proof of principle experiments for demonstrating the capabilities of the laser system to highly integrated methods closing in on established medical application scenarios have been achieved.
With respect to surgical applications, results from experiments on the vocal cord were of fundamental relevance for the prospective use of the laser in phonosurgery. Böttcher et al. and Hess et al. demonstrated nearly complete absence of thermal injury and much narrower cutting gaps with the PIRL-scalpel in comparison to the CO2 laser and the cold steel scalpel [1,2]. Infrared thermography showed a significantly lower temperature rise during PIRL irradiation compared to the Er:YAG-laser [3]. This was also observed on skin and bone tissue [4,5]. Experiments in stapes surgery to induce footplate perforation on human cadaver tissue have been resulted in a clear superiority of the PIRL in comparison to the Er:YAG laser regarding the procedure’s outcomes, promising a solution for previous problems of laser stapedotomy [14].
In eye surgery experiments, Linke et al. demonstrated that PIRL enables minimization of optical scattering while permitting very good-quality incisions deep into the corneal stroma. As the only laser system enabling contact-free penetrating cuts in corneal tissue, PIRL seems to be an effective tool for corneal incisional surgery, such as cornea transplantation. Also regarding sclerostomy, a procedure to establish a stable connection channel to the eye’s anterior chamber, successful proof of principle experiments for Picosecond infrared laser - fibre-assisted-sclerostomy (“PIRL-FAST”) were carried out [6,7,13].
In an in-vivo animal model on rat skin, wound healing of incisions made by PIRL, an electrocautery and a scalpel were compared [12]. After 21 days of wound healing the incisions made by PIRL showed significantly less scar tissue formation compared to the electrocautery and the scalpel (PIRL < scalpel < electrocautery). These results support a widespread usage of the PIRL in dermatology to remove different kinds of skin pathologies as it is done routinely with the Er:YAG or the CO2 laser. Based on this study, the first use of the (fiber coupled) PIRL on an in-vivo wound healing model based on pigs was successfully employed. Aspects of the wound healing study on a rat-model lead to a study of ablation rates in the laser applications of PIRL and in comparison Er:YAG, that bring significant data to compare the ablation mechanisms with well-established literature values and studies (Maier et. al., submitted to Biomedical Optics Express, 2017). In conclusion it is already possible to cut “fast enough” for procedures like eye-surgery (i.e. cornea transplantation cuts), while for starched out skin cuts the speed will need to be enhanced still.
Taking steps towards robotic integration of the PIRL, an OCT imaging system and the fiber coupled laser were coupled with a robotic arm. It was shown successfully that navigation via imaging and review by OCT is possible in different scan – ablation – rescan approaches. With the integration of a suction tube and the collection of ablation plume products during the procedure, important steps towards a combined OCT and biomolecular information imaging are done.
This constitutes the second main focus of the project, to enable characterization of molecules ablated by the picosecond infrared laser (PIRL) from tissues. Advancements could be realized with respect to the different involved fields of biomolecular “omics” analyses like proteomics and peptidomics. A differential proteome analysis of human primary tumors and matched spontaneous distant metastases in an in-vivo mouse model (Lange et. al., submitted to Nature Scientific Reports, 2018) was performed. It showed that the distant metastases mainly represent the protein expression patterns of the matched primary tumors, but still enables identifying novel candidate proteins that contribute to spontaneous metastasis formation in-vivo.
We demonstrated the efficient transfer of biomolecules, viruses and even whole cells from tissues into the gas phase by direct DIVE ablation from several different tissue types, cell cultures, aqueous solutions, and of viruses from their natural environment, virtually without any additional preparation steps [8, 9]. For a direct transfer of the aerosols to mass spectrometry, charge states and sensitivity are equivalent or higher than those produced in optimized nano-electrospray ionization conditions, which is the standard method in the field. PIRL-DIVE condensates of different brain tissues directly sprayed into the mass spectrometer yielded significantly different spectra, demonstrating the possibility to discriminate between tissues. In comparison to classical homogenization PIRL-DIVE homogenization of tissues offers qualitative and quantitative advantages. This development represents a breakthrough in analysis of biomolecules from tissues [11].

In order to increase the range of possible applications in the surgical and bioanalytical fields, the research projects were constantly accompanied by technical developments. Investigations of alternative 3 µm laser sources (as seed or low power ablation laser directly) have shown clear disadvantages of Erbium doped materials as direct 3 µm pulsed laser radiation gain media. Instead, new approaches towards 1 µm radiation amplification and conversion have been undertaken. As indicated above, a fiber delivery of the PIRL system’s 3 µm laser beam was investigated. First fiber application trials showed most promising results for puncturing soft tissue (i.e. porcine cadaver eyes) and cutting surface tissues of various sorts (i.e. porcine cadaver vocal fold). While it was obvious in these experiments that precise motion and position control is important, further trials without robotic integration lead to another important invention, a new contact laser scalpel. It makes use of local impulsive heating of the water in the tissue to reduce tissue shear stress thresholds for cutting to near zero, and simultaneously employs such minimal shear force as to locally cut the tissue without exceeding thermal or mechanical damage thresholds to adjacent tissue.
In the process of marker identification, which can be used as reliable markers for the detection of different types of tissue to reach the goal of a real time mass spectrometry assisted guidance of the PIRL scalpel, an ablation chamber and two trapping systems (cooling trap and membrane trap) were developed for collecting the PIRL ablation products for further analysis.
These are important steps towards marker identification, leading to reliable detection of different tissue types to reach the goal of a real time mass spectrometry assisted guidance of the PIRL scalpel. In conclusion, the DIVE-driven PIRL applications prove to enable a number of advantageous methods in surgery and bio-diagnostic fields.