One-Dimensional Radial Diffusion of Small Molecules (376 Da) in Bone Tissue

The flow of nutrients through any biological tissue is important to maintain homeostasis. If the transport process is understood, medical research teams can better design medications, prosthetic implants, and tissue scaffolds. Additionally, transport rates help physicians to better understand disease states and wound healing, including minor injuries such as breaks and sprains, which will aid in better diagnoses. We developed a novel method that measures the rate of diffusion in vitro, of fluorescein sodium salt. Samples were incubated at 37°C in a 5 CO2 atmosphere for various periods of time. Samples were sliced and analyzed using Image-Pro Plus and MATLAB to obtain concentration profiles. The diffusivity was estimated from the data using the model equation for one-dimensional transport in a finite medium. We found that radial diffusivity in canine bone in 1-dimension was 1.27 x 10-7±177 1.96 x 10-8 cm2/s. As a point of reference, the diffusivity of fluorescein sodium salt in PBS is 2.7 x 10-6 cm2/s. Given the average distance between a Haversian canal and an osteon radius is 250 um, our data shows it would take approximately 20 minutes for a nutrient of a weight of 376 Da to travel between the two locations. This indicates that the diffusion time of key nutrients, such as vitamin D, with molecular weight of 384 Da, would be about 20 minute