Imaging of slow deformations in biological tissues may contribute to study and reveal many complex processes, such as fluid flow, mechanical stress growth and relaxation, formation of interstitial pores caused by application of external force. Here the new method of strain mapping based on analysis of complex-valued OCT signal for real-time cartilage visualization is presented. Cartilaginous tissue is modified with laser radiation, immersion agent glycerol and on air drying. The evolution of strain caused by the modifying effects is analyzed. For the non-equilibrium diffusion regime, it was shown that the tissue experiences intensive alternate-sign strain with the amplitudes up to 0.4. The extensive dehydration within 1 mm thickness of the tissue and pronounced subsurface swelling are detected. The strains caused by osmotically-induced and on air dehydration are compared.
Laser-assisted relaxation of internal stresses can be used to stabilize the new shape of cartilaginous implants. The ability of cartilage tissue to experience irreversible deformation under certain conditions, as well as to restore its original configuration after external mechanical stress, is studied in near real time using a new method of optical coherent elastography (OCE), developed to visualize slow deformation. The OCE technique allows one to monitor the efficiency of laser-induced stress relaxation at 1–2 minute intervals using 2D subsurface strain mapping. It has been shown that the redistribution of the interstitial fluid due to the applied load is an important factor for the mechanism of "shape memory" of the cartilage. Deviations in the behavior of cartilage from the usual elastic properties of homogeneous materials, such as subsurface dilatation opposing the applied load, are identified and analyzed.
Cartilage is the best nature material for transplantation. Laser reshaping of cartilage allows obtaining any desirable shape of the implant. This work continues the interdisciplinary studies on laser-induced development of stable costal cartilage implants, the most promising biological object for the manufacture of implants (grafts) used in otolaryngology and maxillofacial surgery, in particular, in recovering tracheal defects for the treatment of larynx stenosis. We used 1560 nm fiber laser with feedback control system measuring tissue temperature in the course of laser irradiation.
The thermomechanical IR-laser effect on reshaping process for ENT is studied. The possibility and conditions of the laser reshaping of costal cartilage for stable human implants are investigated. The causes of nonlinear thermomechanical behavior of cartilage and its influence on controlled reshaping and stability of costal cartilage for ENT are discussed. Clinical trials for 5 patients with one and a half year follow-up observation demonstrate stable positive results.
KEYWORDS: Cartilage, Transplantation, Surgery, Laser stabilization, Medical laser equipment, Anisotropy, Collagen, Tissues, In vivo imaging, Temperature metrology
As cartilage is an ideal natural material for transplantation, its use in the ENT surgery is limited by a difficulty to get
proper shape of cartilage implants. Aim of the work is to make ring-shaped cartilage implants, to check their stability
after laser reshaping and to perform transplantation into rabbits in vivo. We experimented with costal cartilages of 1-2
mm in thickness obtained from 3rd and 4rd ribs of a rabbit. 1.56 μm laser (Arcuo Medical Inc.) was used for cartilage
reshaping. The laser settings were established taking into account anisotropy of cartilage structure for different
orientation of the implants. The reshaped cartilage implants were surgically sewn to rib cartilages of the other rabbits.
The rabbits were slaughtered in 3.5-4 months after surgery. The results have shown that (1) all reshaped implants kept
circular form, and (2) the implants were adhered to the native rabbit cartilage sites (3) pronounced signs of regeneration
in the intermediate zones were observed. The prospects of the cartilage implants use in larynx stenosis surgery are
discussed.
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