A Two-Species Drug Delivery Model is Required to Predict Deposition from Drug-Eluting Stents

Mathematical and numerical analysis for PDE systems modeling intravascular drug release from arterial stents and transport in arterial tissue

This paper is concerned with the PDE (partial differential equation) and numerical analysis of a modified one-dimensional intravascular stent model. It is proved that the modified model has a unique weak solution by using the Galerkin method combined with a compactness argument. A semi-discrete finite-element method and a fully discrete scheme using the Euler time-stepping have been formulated for the PDE model. Optimal order error estimates in the energy norm are proved for both schemes. Numerical results are presented, along with comparisons between different decoupling strategies and time-stepping schemes. Lastly, extensions of the model and its PDE and numerical analysis results to the two-dimensional case are also briefly discussed.

Numerical analysis of paclitaxel-eluting coronary stents: Mechanics and drug release properties

Since theoretical models provide data that cannot be otherwise gathered, numerical methods applied to medical devices analysis have emerged as fundamental tool in preclinical development. Large efforts were done to study mechanical and drug-eluting properties in stents but often the coating modelling is neglected. This work presents a finite element framework to calculate mechanical loads and drug distribution in three commercial drug-eluting stents (Palmaz-Schatz, Palmaz Genesis and Multi Link Vision), to check coatings strength and drug distribution maps in biological tissues. The promising copolymer poly(methylmethacrylate-co-n-butylmethacrylate), loaded with paclitaxel, is analyzed. Results demonstrated that the coating undergoes localized plastic phenomena, and calculated stresses are lower than the ultimate stress, ensuring coating integrity. Computed drug concentration depends on stent geometry and its values are in all cases lower than the toxicity level for this drug.

Integrated Stent Models Based on Dimension Reduction: Review and Future Perspectives

Stent modeling represents a challenging task from both the theoretical and numerical viewpoints, due to its multi-physics nature and to the complex geometrical configuration of these devices. In this light, dimensional model reduction enables a comprehensive geometrical and physical description of stenting at affordable computational costs. In this work, we aim at reviewing dimensional model reduction of stent mechanics and drug release. Firstly, we address model reduction techniques for the description of stent mechanics, aiming to illustrate how a three-dimensional stent model can be transformed into a collection of interconnected one-dimensional rods, called a "stent net". Secondly, we review available model reduction methods similarly applied to drug release, in which the "stent net" concept is adopted for modeling of drug elution. As a result, drug eluting stents are described as a distribution of concentrated drug release sources located on a graph that fully represents the stent geometry. Lastly, new results about the extension of these model reduction approaches to biodegradable stents are also discussed.

Improving smooth muscle cell exposure to drugs from drug-eluting stents at early time points: a variable compression approach

The emergence of drug-eluting stents (DES) as a viable replacement for bare metal stenting has led to a significant decrease in the incidence of clinical restenosis. This is due to the transport of anti-restenotic drugs from within the polymer coating of a DES into the artery wall which arrests the cell cycle before restenosis can occur. The efficacy of DES is still under close scrutiny in the medical field as many issues regarding the effectiveness of DES drug transport in vivo still exist. One such issue, that has received less attention, is the limiting effect that stent strut compression has on the transport of drug species in the artery wall. Once the artery wall is compressed, the stents ability to transfer drug species into the arterial wall can be reduced. This leads to a reduction in the spatial therapeutic transfer of drug species to binding sites within the arterial wall. This paper investigates the concept of idealised variable compression as a means of demonstrating how such a stent design approach could improve the spatial delivery of drug species in the arterial wall. The study focused on assessing how the trends in concentration levels changed as a result of artery wall compression. Five idealised stent designs were created with a combination of thick struts that provide the necessary compression to restore luminal patency and thin uncompressive struts that improve the transport of drugs therein. By conducting numerical simulations of diffusive mass transport, this study found that the use of uncompressive struts results in a more uniform spatial distribution of drug species in the arterial wall.

Enhanced drug delivery capabilities from stents coated with absorbable polymer and crystalline drug

Current drug eluting stent (DES) technology is not optimized with regard to the pharmacokinetics of drug delivery. A novel, absorbable-coating sirolimus-eluting stent (AC-SES) was evaluated for its capacity to deliver drug more evenly within the intimal area rather than concentrating drug around the stent struts and for its ability to match coating erosion with drug release. The coating consisted of absorbable poly-lactide-co-glycolic acid (PLGA) and crystalline sirolimus deposited by a dry-powder electrostatic process. The AC-SES demonstrated enhanced drug stability under simulated use conditions and consistent drug delivery balanced with coating erosion in a porcine coronary implant model. The initial drug burst was eliminated and drug release was sustained after implantation. The coating was absorbed within 90 days. Following implantation into porcine coronary arteries the AC-SES coating is distributed in the surrounding intimal tissue over the course of several weeks. Computational modeling of drug delivery characteristics demonstrates how distributed coating optimizes the load of drug immediately around each stent strut and extends drug delivery between stent struts. The result was a highly efficient arterial uptake of drug with superior performance to a clinical bare metal stent (BMS). Neointimal thickness (0.17±0.07 mm vs. 0.28±0.11 mm) and area percent stenosis (22±9% vs. 35±12%) were significantly reduced (p<0.05) by the AC-SES compared to the BMS 30 days after stent implantation in an overlap configuration in porcine coronary arteries. Inflammation was significantly reduced in the AC-SES compared to the BMS at both 30 and 90 days after implantation. Biocompatible, rapidly absorbable stent coatings enable the matching of drug release with coating erosion and provide for the controlled migration of coating material into tissue to reduce vicissitudes in drug tissue levels, optimizing efficacy and reducing potential toxicity.