Structural biomechanics modulate intramuscular distribution of locally delivered drugs.

As local drug delivery continues to emerge as a clinical force, so does understanding of its potentially narrow therapeutic window. Classic molecular transport studies are of value but do not typically account for the local nature of drug transport or the effects of regional dynamic function in target tissues like muscle that may undergo cyclical and variable mechanical motion and loading. We examined the impact of dynamic architecture on intramuscular drug distribution. We designed a tissue mounting technique and mechanical loading system that uniquely enables pharmacokinetics investigations in association with control of muscle biomechanics while preserving physiologic tissue architecture. The system was validated and used to elucidate the influence of architecture and controlled cyclic strain on intramuscular drug distribution. Rat soleus muscles underwent controlled deformations within a drug delivery chamber that preserved in vivo physiology. Penetration of 1mM 20 kDa FITC-dextran at planar surfaces of the soleus axial cross-section increased significantly from 0.52+/-0.09 mm under 80 min of static (0%) strain to 0.81+/-0.09 mm under cyclic (3 Hz, 0-20% peak-to-peak) strain, demonstrating the driving effect of cyclic loading on transport. Penetration at curved margins was 1.57- and 2.53-fold greater than at planar surfaces under static and cyclic strain, respectively, and was enhanced 1.6-fold more by cyclic strain, revealing architecturally dictated spatial heterogeneity in transport and modulation of motion dynamics. Architectural geometry and dynamics modulate the impact of mechanical loading on local drug penetration and intramuscular distribution. Future work will use the biomechanical test system to investigate mechanisms underlying transport effects of specific loading regimens. It is hoped that this work will initiate a broader understanding of intramuscular pharmacokinetics and guide local drug delivery strategies.