Shear-Activated Drug Release from Red Blood Cell Carriers in Arterial Stenosis

Introduction: : Red blood cells (RBCs) hold exceptional promise as innovative drug carriers, offering unique advantages due to their natural abundance, biocompatibility, and prolonged circulation time in the bloodstream. Designed by nature to efficiently transport oxygen throughout the body, RBCs provide an ideal, non-immunogenic vehicle for therapeutic delivery. Recently, cellular hitchhiking, where nanoparticles are attached to the surface of RBCs, has shown auspicious results for first-pass delivery to target organs. Another approach involves loading therapeutic agents directly into RBCs, either in their free form or as particles. Recently, transient pore formation due to membrane stretching while flowing in constricted microchannels has been exploited to load therapeutic agents into RBCs and other cell types. However, mechanical disruption of cells, particularly RBCs, has not been explored to trigger drug release at disease sites.
Several cardiovascular disease conditions, including stenotic arteries, are associated with pathologically elevated shear stress beyond normal shear stress. Leveraging this biophysical pathological feature, we propose using RBCs as mechanosensitive drug carriers for stenotic arteries based on the high shear at these sites. Here we study the drug release mechanism in which RBC carriers release their cargo at stenotic arteries via transient pore opening in their membrane, induced by the hemodynamic forces at these sites. Complementing our simulations, we establish a correlation between experimental shear release findings and coarse-grained simulations of RBC deformation kinetics, under flow in stenotic vessels.

Materials and

Methods: : A multiscale computational method for simulating cellular and molecular blood flow has been developed and validated to capture realistic cell mechanics and hemorheology. A time-varying shear rate is imposed to drive the flow of RBCs along the x-direction, where the transient WSR is obtained from macroscopic hemodynamic simulations of flow through stenotic arteries of various stenosis%. The computational studies are validated experimentally by 3D models that were connected to a closed-circuit perfusion system that mimics arterial flow. A damper was attached after the peristaltic pump to dampen the peristaltic pulse to ensure a constant flow profile. Loaded RBCs, resuspended in PBS (-/-) solution, were perfused for one hour through a system containing stenotic models of varying severity. Samples were collected before and after perfusion to measure the percentage of FITC-Dextran (DEX) released from the RBCs using FACS.

Results, Conclusions, and Discussions:: The shear rate exerted on the RBC carriers was extracted under different stenotic flow simulations as shown in Fig. 1a. The snapshot in Fig. 1b illustrates the region of extensional areal strain (AS>0) in red and compressional AS (AS < 0) in blue. Fig. 1c represents time histories of the averaged extensional AS for RBCs flowing through different stenoses. Experimental drug release correlates well with the extensional AS averaged along the stenotic throat region, as shown in Fig. 1d (empty bars: experimental drug release (%), solid bars: quantified extensional AS (%)).

RBC undergoes tank-treading motion (TTM) at high shear generated by high % stenosis. Fig. 2a illustrates the local oscillating AS of an RBC membrane patch moving tangentially to the RBC surface from t1 to t2, as shown in the inset, due to the TTM. The membrane patch clearly undergoes expansion and compression deformation as a result of the RBC TTM. The extensional AS rate determined from Fig. 2a in the extending direction on an RBC membrane patch as a function of arterial stenosis (Fig. 2c). Local membrane strain (Fig. 2b) and strain rate synergistically control transient pore opening at high shear conditions. The pore opening states predicted by our simulation are plotted on the RBC membrane pore opening phase diagram, and correlated well with the in vitro drug release results (Fig. 2d).
Our multiscale in silico simulations of RBC deformation and dynamics demonstrate an RBC tank-treading-governed pore-opening mechanism controlled by the local membrane strain and strain rate synergistically, leading to transient pore formation at high shear conditions. Our in vitro perfusion studies support our computational studies, which revealed a shear-dependent release profile, where drug release increased with stenosis severity.
Our work establishes RBCs as a promising high shear-activated drug delivery platform for targeted release at arterial stenosis. By integrating advanced biomaterials, rheological strategies, and computational modeling, RBC carriers could be designed with enhanced loading capacities, tunable release profiles, and precision targeting capabilities. Mechanoresponsive drug delivery strategies like RBC-based drug carriers can potentially transform the treatment of cardiovascular diseases by enabling site-specific therapy, long circulating time, with minimal off-target effects.

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