**8. Conclusion**

320 Biomedical Science, Engineering and Technology

Fig. 6. Axial drug concentrations at 25% of the artery wall depth, illustrated in Fig 4 Model 1 by the 25% WT concentration line. Concentrations are measured after 30 minutes (solid line)

Fig. 7. Axial drug concentrations at 50% of the artery wall depth, illustrated in Fig 4 Model 1 by the 50% WT concentration line. Concentrations are measured after 30 minutes (solid line)

and 60 minutes (dashed line) respectively.

and 60 minutes (dashed line) respectively.

Understanding the behaviour of DES in the pursuit of improving device functionality is of great importance to clinicians and researchers alike. The modern application of computational techniques have greatly aided in achieving this goal, with researchers continuingly adding to the global understanding of drug mass transport from these devices. However, computational modelling isn't the complete solution because exact recreation of DES deployment and ensuing mass transport is not feasible for a number of reasons. No two patients will have identical stenosis of the coronary artery and therefore a single computational model will not provide the information required to comprehensively assess the viability of a single stent design. Instead a variety of models that will cover the spectrum of DES deployment scenarios is required and to computationally recreate these like for like with *in vivo* stenting conditions would be too computationally demanding for the same rewards that one could yield with a simplified analysis.

However, one must be mindful when simplifying the problem. The computational models developed in this chapter were created as 2-D axis-symmetric models as the study was intent on analysing the influence of relatively simple geometries. However, this may not always be the case and the need may arise where it would be necessary to model the problem in 3-D. The pitfalls of over simplification can be seen in the computational Model 1 where failure to model BSMT results in drug concentrations that are higher than that of the more realistic case, Model 2, that includes the luminal blood flow and mass transport therein.

Computational models where DES struts are flush against a bare artery wall have their merits but a greater degree of complexity needs to be implemented if an improved insight into DES mass transport within the coronary artery environment is to be gained. These arteries are heavily diseased and even a thin layer of plaque between the stent strut and the wall can inhibit WSMT. The compression of the porous artery wall upon stent expansion has an interesting effect on drug concentration within the wall. The reduction in artery wall diffusivity results in higher peak concentrations beneath the stent strut compared to the models where artery wall compression is not present. This pooling of drugs close to the stent strut is undesirable as it retards the early penetration of drugs into the wall, demonstrated in Figure 5 as the uncompressed artery wall of Model 2 recorded concentrations higher than that of Models 4 and 5 from a depth of approximately 50*µ*m through the rest of the artery wall. There is also the danger of potential toxicity due to prolonged exposure of high drug concentrations close to the strut.

Analysis of mass transport from DES requires a multifaceted approach in order to predict behaviour of these devices and subsequently their response to *in vivo* arterial conditions. Future research that is mindful of preoperative DES design and postoperative environmental conditions will increase our knowledge of the second generation DES and enable us as a community to prepare for the advent of biodegradable DES.

## **9. Acknowledgements**

The authors would like to thank the Irish Research Council for Science, Engineering and Technology (IRCSET), Grant no. RS/2005/159, for funding this body of work. The authors would also like to thank the members of CABER and the MSSI.

### **10. References**


through the rest of the artery wall. There is also the danger of potential toxicity due to

Analysis of mass transport from DES requires a multifaceted approach in order to predict behaviour of these devices and subsequently their response to *in vivo* arterial conditions. Future research that is mindful of preoperative DES design and postoperative environmental conditions will increase our knowledge of the second generation DES and

The authors would like to thank the Irish Research Council for Science, Engineering and Technology (IRCSET), Grant no. RS/2005/159, for funding this body of work. The authors

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**10. References** 

enable us as a community to prepare for the advent of biodegradable DES.

