Emil Sobol

This paper presents a recently developed variant of phase-resolved Optical Coherence Elastography (OCE) enabling non-contact visualization of transient local strains of various origins in biological tissues and other materials. In this work, we demonstrate the possibilities of this new technique for studying dynamics of osmotically-induced strains in cartilaginous tissue impregnated with optical clearing agents (OCA). For poroelastic water-containing biological tissues, application of non-isotonic OCAs, various contrast additives, as well as drug solutions administration, may excite transient spatially-inhomogeneous strain fields of high magnitude in the tissue bulk, initiating mechanical and structural alterations. The range of the strain reliably observed by OCE varied from ±10⁻³ to ±0.4 for diluted and pure glycerol, correspondingly. The OCE-technique used made it possible to reveal previously inaccessible details of the complex spatio-temporal evolution of alternating-sign osmotic strains at the initial stages of agent diffusion. Qualitatively different effects produced by particular hydrophilic OCAs, such as glycerol and iohexol, are discussed, as well as concentration-dependent differences. Overall, the work demonstrates the unique abilities of the new OCE-modality in providing a deeper insight in real-time kinetics of osmotically-induced strains relevant to a broad range of biomedical applications.

Degenerative disease of the intervertebral discs (DDD) is currently a serious problem facing the world community. The surgical methods and conservative therapy used today, unfortunately, do not stop the pathological process, but serve as a palliative method that temporarily relieves pain and improves the patient’s quality of life. Therefore, at present, there is an active search for new methods of treating DDD. Among new techniques of treatment, biological methods, and minimally invasive surgery, including the use of laser radiation, which, depending on the laser parameters, can cause ablative or modifying effects on the disc tissue, have acquired considerable interest. Here, we analyze a new approach to solving the DDD problem: laser tissue modification. This review of publications is focused on the studies of the physicochemical foundations and clinical applications of a new method of laser reconstruction of intervertebral discs. Thermomechanical action of laser radiation modifies tissue and leads to its regeneration as well as to a long-term restoration of disc functions, elimination of pain and the return of patients to normal life.

We use novel possibilities opened by compressional Optical Coherence Elastography (OCE) to characterize both natural interstitial gaps and laser-irradiation-produced porosity in collagenous tissues (corne and cartilage). Under increasing moderate compression up to strains ~several percent, the current Young modulus of cornea gradually increases from initial values below 100 kPa to values >MPa that are closer to Young's modulus of cartilages in which collagen fibers are much denser packed. The lower stiffness of cornea can reasonably be attributed to the initially looser packed collagenous fiber layers, so that initial high compressibility of cornea is dominated by interlayer voids (gaps). By analogy with geophysics, we apply a model describing the reduction in the tissue elastic modulus due to the presence of a system of nearly parallel, thin "crack-like" voids/pores between the collagenous fiber layers. Initially they are highly compressible, but with increasing compression are getting closed, so that the material gets stiffer. Characterization of such porous component in water-saturated packing of collagenous layers in the natural state is inaccessible to AFM and conventional microscopy, whereas OCE enables earlier unavailable possibility to non-invasively characterize such pores/gaps (their total volume and distribution over the aspect ratio) by analogy with crack characterization in geophysics. Also we apply OCE to characterize spatially-inhomogenous modification of pore characteristics by moderate IR-laser-irradiation in regimes typical of collagenous-tissue reshaping. The obtained results are important for obtaining better insight in the structural modificatons in collagenous packings in the context of the development of novel methods of laser-assisted non-surgical methods of cornea-refraction correction and biologically non-destructive reshaping of cartilaginous samples for fabrication of implants in otolaryngology and maxillofacial surgery.

Laser modelling of costal cartilage implants (grafts) of a given shape is a new promising technology in laser medicine. When the final shape of an implant is formed with a surgical scalpel, residual stresses lead to the distortion of the implant and decrease its survivability after the surgery. Laser-induced relaxation of the interstitial residual stresses without disturbing tissue functionality opens new possibilities for a wide range of implantology problems. This article is devoted to a new laser method of treatment of laryngeal stenosis using laser-modelled costal cartilage grafts for the closure of laryngotracheal defect in patients. The paper discusses the physical ground of the applied laser modes when the stresses at the graft borders are minimal which provides positive impact on the survival of the laser-modelled cartilage. The results of the first clinical application of this method are presented.

In this study, we attempted to determine the critical temperature [T_c] at which accelerated stress relaxation occurred during laser mediated cartilage reshaping. During laser irradiation, mechanically deformed cartilage tissue undergoes a temperature dependent phase transformation which results in accelerated stress relaxation. When a critical temperature is attained, cartilage becomes malleable and may be molded into complex new shapes that harden as the tissue cools. Clinically, reshaped cartilage tissue can be used to recreate the underlying cartilaginous framework of structures such as the ear, larynx, trachea, and nose. The principal advantages of using laser radiation for the generation of thermal energy in tissue are precise control of both the space-time temperature distribution and time- dependent thermal denaturation kinetics. Optimization of the reshaping process requires identification of the temperature dependence of this phase transformation and its relationship to observed changes in cartilage optical, mechanical, and thermodynamic properties. Light scattering, infrared radiometry, and modulated differential scanning calorimetry (MDSC) were used to measure temperature dependent changes in the biophysical properties of cartilage tissue during fast (laser mediated) and slow (conventional calorimetric) heating. Our studies using MDSC and laser probe techniques have identified changes in cartilage thermodynamic and optical properties suggestive of a phase transformation occurring near 60 degrees Celsius.