Laser irradiation may cause a proliferative response in cartilage leading to new, less invasive treatment modalities for diseases such as osteoarthritis. Our previous studies have shown that laser irradiation causes chondrocytes to proliferate on the periphery of the laser-irradiated region and this effect is dose dependent. In this study, flow cytometry was used for cell counting because the colorimetric assay used previously was relatively insensitive to small proliferative responses. Ex-vivo rabbit nasal septal cartilages were harvested and subjected to one of three treatments: laser irradiation, heating, or mechanical modification. Specimens were irradiated with an Nd:YAG laser (λ=1.32μm, 4-16 sec, 6 W/cm2), heated by immersion in saline or contact heating, and mechanically modified by scoring with a scalpel or crushing with a metal stamp. Specimens were incubated for 7-21 days in growth media containing 10μM Bromodeoxyuridine (BrdU) then chondrocytes were isolated with enzymatic digestion. Cells were incubated with fluorescein conjugated anti-BrdU monoclonal antibody (Roche Diagnostic, Basel, Switzerland) and counterstained with propidium iodide (PI). Fluorescent-activated cell counting was performed by flow cytometry (λ=488 nm, Model BD LSR Flow Cytometer, Becton Dickson) identifying cells with emissions measured at 515 nm (anti-BrdU) and 620 nm (PI). Analysis showed a population of cells in S-phase of the cell cycle indicating these cells had undergone cell division. This provides further evidence that laser irradiation causes a proliferative response in chondrocytes and may lead to new treatments for degenerative articular diseases and disorders.
Much interest has been placed on the permanent reshaping of cartilage for facial reconstructive surgery using lasers. An alternate way to reshape cartilage is to heat the tissue in a water bath while maintaining the specimen in mechanical deformation. The objective of this study was to measure the circular bend angle of a cartilage specimen produced by varying the temperature and immersion time in a water bath. Rectangular cartilage specimens (18 x 4 x 1.5 mm) were bent in a semicircular jig (diameter 11 mm) and then immersed in a saline bath at temperatures between 50 - 80°C. The immersion times were 5, 20, 80, 160 and 320 seconds at each temperature. The distance between the ends of each specimen was measured before reshaping and at 15 minutes and 24 hours after immersion in order to calculate the resulting bend angle. The largest bend angle occurred in the specimen immersed in saline at 74°C for 320 seconds, illustrating a definite thermal influence on the physical shape of the cartilage sample. The critical immersion times and bath temperatures where definite shape change occurred were determined.
Cartilage laser thermoforming, also known as laser reshaping, is a new surgical procedure that allows in-situ treatment of deformities in the head and neck with less morbidity than traditional approaches. During laser irradiation, cartilage becomes sufficiently subtle or deformable for stretching and shaping into new stable configurations. This study describes the experimental and theoretical characterization of the thermal response of porcine cartilage to laser irradiation (Nd:YAG). The surface temperature history of cartilage specimens was monitored during heating and thermal relaxation; using laser exposure times ranging between 1 and 15 s and laser powers of 1 to 10 W. The experimental results were then used to validate a finite element model, which accounts for heat diffusion, light propagation in tissue, and heat loss due to water evaporation. The simultaneous solution of the energy and mass diffusion equations resulted in predictions of temperature distribution in cartilage that were in good agreement with experiments. The model simulations will provide insights to the relationship between the laser treatment parameters (exposure time, laser beam diameter, and power) and the onset of new molecular arrangements and cell thermal injury in the material, thus conceiving basic guidelines of laser thermoforming.
Laser irradiation may stimulate chondrocytes proliferation in the peripheral region surrounding a photothermally-heated area in rabbit nasal septal cartilage. In this study, ex- vivo rabbit nasal septal cartilages maintained in culture were irradiated with an Nd:YAG laser ((lambda) equals1.32 micrometers , 4-16 sec, 10-45 W/cm2) to examine the relationship between the diameter of replicating cells and irradiation time. Also, this study investigated whether proliferation occurs following heating (by immersion in hot saline baths, with a heated metal rod, and a soldering iron) and mechanical modification (crushing with a metal stamp and scoring with a scalpel). Replicating chondrocytes were identified using a Bromodeoxyuridine (BrdU) double antibody detection system in whole mount tissue. Light microscopy was used to confirm the presence of BrdU stained chondrocytes. The mechanical and thermal stressors used failed to produce a proliferative response in chondrocytes as previously seen with laser irradiation. We suspect that chondrocyte proliferation may be induced as a response to alteration in matrix structure produced by photothermal, thermal, or mechanical modification of the matrix. Heat generated by a laser to stimulate chondrocyte proliferation may lead to new treatment options for degenerative articular diseases and disorders. Laser technology can be adapted for use with minimally invasive surgical instrumentation to deliver light into otherwise inaccessible regions of the body.
The response of cartilage tissue to thermal stress can be investigated indirectly by measuring changes in optical properties during heating. Temperature distributions in cartilage depend on the mode of heating. Laser irradiation of thick cartilage specimens results in non-uniform heating, causing asynchronous stress relaxation in different regions of the tissue. In contrast, slow heating of cartilage in a Rose chamber results in more uniform temperature profiles. In addition, the heating of tissue in a saline- (or mineral oil) filled Rose chamber eliminates dehydration effects that are commonly encountered during laser heating. The purpose of this investigation was to measure diffuse reflectance and diffuse transmittance of porcine septal cartilage tissue during slow heating. Diffuse reflectance and transmittance were measured using integrating sphere and lock-in detection techniques. Cartilage surface temperatures were estimated using a thermocouple and cold-junction compensator. Diffusely transmitted light was observed to decrease, plateau, and then increase, whereas diffusely reflected light was observed to increase, plateau, and then decrease. The change in slope for both transmitted and reflected light occurred at cartilage front surface temperatures of between 45 and 50 degree(s)C. The results suggest that changes in the optical properties of cartilage tissue occur due to a phase transformation during heating.
KEYWORDS: Cartilage, In vivo imaging, Tissues, Surgery, Bone, Temperature metrology, Laser vision correction, Laser therapeutics, Nd:YAG lasers, Data modeling
Laser cartilage reshaping has become of clinic interest due to its potential applications for facial plastic surgery. Although the temperature dependent phase transformation oflaser mediated cartilage reshaping has been well described, few studies have examined the reshaping process in an in vivo model and correlated shape change with laser dosimetry in a rigorous fashion. We report preliminary findings of Nd:YAG laser mediated cartilage reshaping ofthe New Zealand White rabbit nasal septum. Four New Zealand white rabbits (3.5 -4.0 kg) underwent submucous resection ofthe nasal septum via a novel surgical approach under anesthesia. The septal cartilage was removed and cut into two equal sized slabs (5 x 1 5 mm); one used as a control, while other was reshaped using an Nd:YAG laser (?=1.32µm, 25W/cm2). Both the control and irradiated cartilages were reimplanted into a subcutaneous pocket in the rabbit's back. All four rabbits survived the submucous resection procedure, with no post-operative complications at 3 months post op. Cartilage reshaping was seen to take place at the thermal range 60-70°C. Further study on the long term viability oflaser reshaped cartilage will be performed by serial biopsies ofthe control and irradiated cartilage grafts at 6 and 12 month intervals for histological and viability assays. The preliminary results are promising thus far, and suggest the feasibility of utilizing the rabbit model in studying laser mediated cartilage reshaping.
Internal stress σ(t), diffuse transmitted light intensity I(t) from a He-Ne probe laser (λ= 632.8 nm), and radiometric surface temperature Ts(t) were measured during the photothermal heating of porcine septal cartilage using a pulsed Nd:YAG laser (λ= 1.32 μm). Rectangular specimens, 1-4 mm thick, were secured to a tensile force testing rig and laser irradiated. Force measurements during heating showed significant variation in the rate of deformation, which were found to be strong dependent on tissue orientation; revealing the anisotropic nature of its thermo-mechanical properties. These finding suggest that the collagen and proeoglycan networks lie in a preferential orientation within the extracellular matrix, which must be addressed before this procedure can be used on a wider basis.
In this study, the rheological and phase behavior of porcine nasal cartilage were determined using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry, and thermogravimetric analysis and the principles of thermal analysis (TA). The results were then incorporated in a finite element analysis used to estimate thermal residual stress and temperature distributions during laser irradiation. The finite element analysis was conducted by using a commercially available code ABAQUS (Hibbitt, Karlsson & Sorensen, Inc, USA) to solve the fully coupled thermo-mechanical equations. Arrhenius kinetics were used to obtain the activation energy associated with the phase transition as determined using DMTA and the results were compared with the energy of the phase transformation calculated using DSC. Laser-induced stress relaxation produced an increase in the von Mises stress within the simulation. The values generated during photo thermal heating were calculated assuming cartilage as an isotropic linear visoelastic material. The advantages and limitations of this approach technique are discussed, in particular with relevance to optimizing this procedure for use in clinical settings.
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