Effects on Mass Transfer in the Bone Lacunar-Canalicular System under Different Radial Extracorporeal Shock Waves

The bone lacunar-canalicular system (LCS) is an important microscopic infrastructure for signaling and solute transport in bone tissue, which guarantees the normal physiological processes of bone tissue, and there is a direct relationship between osteoporosis and intrabody mass transfer; however, the mass transfer pattern of the LCS has not yet been clarified under different intensities of in extracorporeal shock waves. The present study aims to assess the effect of extracorporeal shock waves on mass transfer in LCS.

Sodium fluorescein tracer was taken as the transport substance, and the fluorescence intensities of osteocytes at lacuna in bovine cortical bone were used to indicate the mass transfer effect. The free diffusion and different extracorporeal shock waves were performed in LCS experiments and the fluorescence intensities of the superficial, shallow, middle, and deep layers of osteocytes, which were arranged in a proximity-to-distant order away from the Haversian canal, were detected by laser scanning confocal microscopy.

The results showed that, under different shock waves, the fluorescence intensities of superficial lacunae were the highest in an osteon, followed by shallow and middle layers, and the fluorescence intensities of deep lacunae furthest from the Haversian canal were the lowest, with a decreasing trend and a decreased range of 44.75-97.11%. Relative to free diffusion, the fluorescence intensities of the lacunae in each layer increased by 33.16%, 20.56%, 16.11%, and 26.64% in the superficial, shallow, middle, and deep layers of osteocytes, respectively, under the effect of the extracorporeal shock waves at 1 bar; the fluorescence intensities of the middle layer increased by 100.03% when the intensity was 5 bar, and average fluorescence intensities increased the most with an incremental value of 81.34% in all different shock waves; the fluorescence intensities of the lacunae of each layer was enhanced with a range of 110.93-161.03% by 8 bar.

Extracorporeal shock waves promoted tracer mass transfer within the LCS, and the higher the shock wave magnitudes, the larger the mass transfer in LCS. The transport of solute molecules, nutrients, and signaling molecules within the LCS was facilitated by the extracorporeal shock waves, which may help to address bone diseases such as osteoporosis from the direction of mass transfer in LCS.