Optical coherence elastography with osmotically induced strains: Preliminary demonstration for express detection of cartilage degradation.

Optical coherence elastography (OCE) demonstrated impressive abilities for diagnosing tissue types/states using differences in their biomechanics. Usually, OCE visualizes tissue deformation induced by some additional stimulus (e.g., contact compression or auxiliary elastic-wave excitation). We propose a new variant of OCE with osmotically induced straining (OIS-OCE) and demonstrate its application to assess various stages of proteoglycan content degradation in cartilage. The information-bearing signatures in OIS-OCE are the magnitude and rate of strains caused by the application of osmotically active solutions onto the sample surface. OCE examination of the induced strains does not require special tissue preparation, the osmotic stimulation is highly reproducible, and strains are observed in noncontact mode. Several minutes suffice to obtain a conclusion. These features are promising for intraoperative method usage when express assessment of tissue state is required during surgical operations. The "waterfall" images demonstrate the development of cumulative osmotic strains in control and degraded cartilage samples.

Spatio-Temporal Dynamics of Diffusion-Associated Deformations of Biological Tissues and Polyacrylamide Gels Observed with Optical Coherence Elastography.

In this work, we use the method of optical coherence elastography (OCE) to enable quantitative, spatially resolved visualization of diffusion-associated deformations in the areas of maximum concentration gradients during diffusion of hyperosmotic substances in cartilaginous tissue and polyacrylamide gels. At high concentration gradients, alternating sign, near-surface deformations in porous moisture-saturated materials are observed in the first minutes of diffusion. For cartilage, the kinetics of osmotic deformations visualized by OCE, as well as the optical transmittance variations caused by the diffusion, were comparatively analyzed for several substances that are often used as optical clearing agents, i.e., glycerol, polypropylene, PEG-400 and iohexol, for which the effective diffusion coefficients were found to be 7.4 ± 1.8, 5.0 ± 0.8, 4.4 ± 0.8 and 4.6 ± 0.9 × 10-6 cm2/s, respectively. For the osmotically induced shrinkage amplitude, the influence of the organic alcohol concentration appears to be more significant than the influence of its molecular weight. The rate and amplitude of osmotically induced shrinkage and dilatation in polyacrylamide gels is found to clearly depend on the degree of their crosslinking. The obtained results show that observation of osmotic strains with the developed OCE technique can be applied for structural characterization of a wide range of porous materials, including biopolymers. In addition, it may be promising for revealing alterations in the diffusivity/permeability of biological tissues that are potentially associated with various diseases.

Optical Coherence Elastography as a Tool for Studying Deformations in Biomaterials: Spatially-Resolved Osmotic Strain Dynamics in Cartilaginous Samples.

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.

Infrared Laser Effect on Healthy and Ossified Costal Cartilage: The Development of Stable Load-Bearing Autoimplants.

BACKGROUND AND OBJECTIVE: The laser-induced stress relaxation provides new prospects to obtain stable long fragments of costal cartilage for autoimplantation avoiding the risk of spontaneous deformation and poor engraftment. However, the age-related alterations of cartilage may sufficiently influence its interaction with infrared (IR) laser radiation and disrupt the effectiveness and safety of the technique. The aim of the work is to study the influence of the structural quality of costal cartilage on its interaction with IR laser and efficiency of obtaining of curved implants for trachea surgery. STUDY DESIGN/MATERIALS AND METHODS: Healthy costal cartilage was taken from pigs and human. Ossified costal cartilage was taken from humans of age 65 ± 7. The cartilage slices with a mean thickness of 3 mm were mechanically curved and processed to stress relaxation by laser irradiation with the wavelength 1.56 µm. The structure and mineral content were studied by X-ray microtomography and element analysis. The optical measurements included the study of the propagation of IR radiation, speckle interferometry, and IR radiometry. RESULTS: The aged cartilage demonstrates a high level of heterogeneity in structure and properties and decreased water content. The presence of dense inclusions consisting of amorphous calcined volumes makes the tissue more fragile and less elastic. The IR radiation propagation intensity for aged cartilage is at least twice higher than that for healthy cartilage. The thermal-induced motion of scatterers in aged cartilage is slower. X-ray microtomography showed the cartilage-like and the bone-like structures within the ossified samples. CONCLUSIONS: The main challenge for laser reshaping of aged cartilage is the presence of ossifications. However, the new stable curvature can be obtained with adjustment of laser power. To obtain the satisfying stable curvature of an implant the ossified volumes should be avoided The laser-induced stress-relaxation mechanism for aged cartilage can be particularly different from that of healthy tissue and the optimal laser regimes should be specified. Lasers Surg. Med. © 2020 Wiley Periodicals, Inc.

Control of optical transparency and infrared laser heating of costal cartilage via injection of iohexol.

Infrared (IR) laser impact has no analogues for rapid and safe cartilage reshaping. For better penetration of radiation optical clearing agents (OCAs) can be applied. In present work, the effect of low-osmolality agent iohexol on costal cartilage is studied. Specifically, it is shown that ½ of total increase of optical transparency occurs in 20 minutes of immersion. Maximally, cartilage transparency on 1560 nm can be increased in 1.5 times. Injection of iohexol results in increased tissue hygroscopicity, lower drying rate and higher percentage of bound water. Effective diffusion coefficients of water liberation at 21°C are (5.3 ± 0.4) × 10-7 and (3.3 ± 0.1) × 10-7 cm2 /s for untreated and iohexol-modified tissue, respectively. Raman spectroscopy of irradiated iohexol solution reveals its photo and thermo-stability under clinically used IR laser energies up to 350 W/cm2 for exposure times of several seconds. At energies higher than 500 W/cm2 [Correction added on 5 September 2018, after first online publication: This unit has been changed] decomposition of iohexol occurs rapidly through formation of molecular iodine and fluorescent residue.

Controlling the near-infrared transparency of costal cartilage by impregnation with clearing agents and magnetite nanoparticles.

Penetration depth of near-infrared laser radiation to costal cartilage is controlled by the tissue absorption and scattering, and it is the critical parameter to provide the relaxation of mechanical stress throughout the whole thickness of cartilage implant. To enhance the penetration for the laser radiation on 1.56 µm, the optical clearing solutions of glycerol and fructose of various concentrations are tested. The effective and reversible tissue clearance was achieved. However, the increasing absorption of radiation should be concerned: 5°C-8°C increase of tissue temperature was detected. Laser parameters used for stress relaxation in cartilage should be optimized when applying optical clearing agents. To concentrate the absorption in the superficial tissue layers, magnetite nanoparticle (NP) dispersions with the mean size 95 ± 5 nm and concentration 3.9 ± 1.1 × 1011 particles/mL are applied. The significant increase in the tissue heating rate was observed along with the decrease in its transparency. Using NPs the respective laser power can be decreased, allowing us to obtain the working temperature locally with reduced thermal effect on the surrounding tissue.

Laser-induced micropore formation and modification of cartilage structure in osteoarthritis healing.

Pores are vital for functioning of avascular tissues. Laser-induced pores play an important role in the process of cartilage regeneration. The aim of any treatment for osteoarthritis is to repair hyaline-type cartilage. The aims of this study are to answer two questions: (1) How do laser-assisted pores affect the cartilaginous cells to synthesize hyaline cartilage (HC)? and (2) How can the size distribution of pores arising in the course of laser radiation be controlled? We have shown that in cartilage, the pores arise predominately near chondrocytes, which promote nutrition of cells and signal molecular transfer that activates regeneration of cartilage. In vivo laser treatment of damaged cartilage of miniature pig joints provides cellular transformation and formation of HC. We propose a simple model of pore formation in biopolymers that paves the way for going beyond the trial-and-error approach when choosing an optimal laser treatment regime. Our findings support the approach toward laser healing of osteoarthritis.