OBJECTIVE To evaluate the biochemical and biomechanical properties of native and decellularized superficial digital flexor tendons (SDFTs) and deep digital flexor tendons (DDFTs) harvested from the pelvic limbs of orthopedically normal dogs. SAMPLE 22 commercially supplied tendon specimens (10 SDFT and 12 DDFT) harvested from the pelvic limbs of 13 canine cadavers. PROCEDURES DNA, glycosaminoglycan, collagen, and protein content were measured to biochemically compare native and decellularized SDFT and DDFT specimens. Mechanical testing was performed on 4 groups consisting of native tendons (5 SDFTs and 6 DDFTs) and decellularized tendons (5 SDFTs and 6 DDFTs). All tendons were preconditioned, and tension was applied to failure at 0.5 mm/s. Failure mode was video recorded for each tendon. Load-deformation and stress-strain curves were generated; calculations were performed to determine the Young modulus and stiffness. Biochemical and biomechanical data were statistically compared by use of the Wilcoxon rank sum test. RESULTS Decellularized SDFT and DDFT specimens had significantly less DNA content than did native tendons. No significant differences were identified between native and decellularized specimens with respect to glycosaminoglycan, collagen, or protein content. Biomechanical comparison yielded no significant intra- or intergroup differences. All DDFT constructs failed at the tendon-clamp interface, whereas nearly half (4/10) of the SDFT constructs failed at midsubstance. CONCLUSIONS AND CLINICAL RELEVANCE Decellularized commercial canine SDFT and DDFT specimens had similar biomechanical properties, compared with each other and with native tendons. The decellularization process significantly decreased DNA content while minimizing loss of extracellular matrix components. Decellularized canine flexor tendons may provide suitable, biocompatible graft scaffolds for bioengineering applications such as tendon or ligament repair.

OBJECTIVE To measure penetration efficiencies of low-level laser light energy through equine skin and to determine the fraction of laser energy absorbed by equine digital flexor tendons (superficial [SDFT] and deep [DDFT]). SAMPLE Samples of skin, SDFTs, and DDFTs from 1 metacarpal area of each of 19 equine cadavers. PROCEDURES A therapeutic laser with wavelength capabilities of 800 and 970 nm was used. The percentage of energy penetration for each wavelength was determined through skin before and after clipping and then shaving of hair, through shaved skin over SDFTs, and through shaved skin, SDFTs, and DDFTs (positioned in anatomically correct orientation). Influence of hair color; skin preparation, color, and thickness; and wavelength on energy penetration were assessed. RESULTS For haired skin, energy penetration was greatest for light-colored hair and least for dark-colored hair. Clipping or shaving of skin improved energy penetration. Light-colored skin allowed greatest energy penetration, followed by medium-colored skin and dark-colored skin. Greatest penetration of light-colored skin occurred with the 800-nm wavelength, whereas greatest penetration of medium- and dark-colored skin occurred with the 970-nm wavelength. As skin thickness increased, energy penetration of samples decreased. Only 1% to 20% and 0.1% to 4% of energy were absorbed by SDFTs and DDFTs, respectively, depending on skin color, skin thickness, and applied wavelength. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that most laser energy directed through equine skin was absorbed or scattered by the skin. To achieve delivery of energy doses known to positively affect cells in vitro to equine SDFTs and DDFTs, skin preparation, color, and thickness and applied wavelength must be considered.