Stabilization of costal cartilage graft warping using infrared laser irradiation in a porcine model

Abstract

Objective: To develop a method to rapidly stabilize the shape change process in peripheral slices of costal cartilage by using infrared laser irradiation in a porcine model.

Methods: Forty peripheral porcine costal cartilage specimens (40 × 10 × 2 mm) were harvested. Thirty of these specimens were immediately irradiated with an Nd:YAG laser (λ = 1.32 μm; spot size, 2-mm diameter) using 1 of 3 exposure treatments: 6 W, 2 seconds, and 4 spots; 8 W, 3 seconds, and 4 spots; or 6 W, 2 seconds, and 8 spots. Ten control specimens were only immersed in 0.9% saline solution. Angle of curvature was measured from photographs taken at 0 minutes, immediately after irradiation, and at 30 minutes, 1 hour, 5 hours, and 24 hours. Infrared imaging was used to measure surface temperatures during irradiation. Cell viability after irradiation was determined using a live/dead assay in conjunction with fluorescent confocal microscopy.

Results: Compared with the untreated controls, the irradiated grafts underwent accelerated shape change within the first 30 minutes to reach a stable geometry. Thereafter, irradiated grafts underwent little or no shape change, whereas the control group exhibited significant change in curvature from 30 minutes to 24 hours (P < .001). The average peak irradiated spot temperatures ranged from 76°C to 82°C. Cell viability measurements at the laser spot sites demonstrated a hemispherically shaped region of dead cells with a depth of 0.8 to 1.2 mm and a surface diameter of 1.9 to 2.7 mm.

Conclusions: Laser irradiation of peripheral costal cartilage slices provides an effective method for rapidly stabilizing acute shape change by accelerating the warping process. The temperature elevations necessary to achieve this are spatially limited and well within the limits of tolerable tissue injury.

Figure 1

Costal cartilage was harvested from porcine ribs 2 through 5.

Figure 2

Laser irradiation patterns for groups 1 through 3. Diagram drawn to scale.

Figure 3

Warping angle (Ø) is calculated using the equation arctangent (2×H/L), in which H represents height and L indicates length.

Figure 4

Warping over time for cartilage grafts from the control group (A) and laser exposure group 2 (B).

Figure 5

Warping angle vs time for all grafts in the control and laser exposure groups. Grafts in the control group (A) continued to warp beyond 30 minutes. In comparison, laser-irradiated grafts for exposure group 1 (B), exposure group 2 (C), and exposure group 3 (D) achieved near-steady-state geometry after 30 minutes.

Figure 6

Mean warping angles at 0 minutes, 30 minutes, and 24 hours for the control and laser exposure groups.

Figure 7

Confocal images of cartilage stained with a cell viability assay (LIVE/DEAD; Molecular Probes, Eugene, Oregon). A, Cartilage after irradiation at 6 W for 2 seconds. B, Cartilage after irradiation at 8 W for 3 seconds.