Conductive heart stent matched with mechanical anisotropy of human heart muscle

Contributed by Meng Zijie and He Jianjian
Contributed by: State Key Laboratory of Mechanical Manufacturing System Engineering

Myocardial stent is a promising method to treat myocardial infarction. The ideal heart stent should be seamlessly integrated with the myocardium and satisfy its stretched and relaxed state. But so far, it is still a challenge to manufacture a conductive stent that can meet the biomechanical needs of human heart muscle.

Researchers at Trinity College Dublin designed and fabricated a conductive heart stent that conforms to the mechanics of the human heart muscle. Through the melt electrodynamic printing technology (EHD Printing) and degradable polycaprolactone, a new type of stent that overcomes the limited elastic range of the traditional square stent design is manufactured [1]. By adjusting the geometry of the stent, the anisotropic mechanical properties can be well controlled to adapt to the tension and stress exhibited by the human heart muscle during relaxation and contraction. In addition, in this study, polypyrrole (PPy) was polymerized in situ on the stent, making its electrical conductivity close to that of the reported human myocardium.

 
The researchers designed the vanishing rib model as shown in Figure 1a. The element of the disappearing rib model is to selectively cut the connecting rib from the diamond grid, and the design parameters mainly include the diamond internal angle θ. Rotation is the main deformation mechanism of the vanishing rib model, and the deformation of the elastic network under tension can be achieved only by changing the angle θ. For example, stretching the transverse corrugated ribs causes the longitudinal corrugated ribs to open around the connection point, and increasing the angle θ will increase the lateral expansion of the structure (Figure 1b). When unloading, the outward folding and rotating processes are reversed (Figure 1b). Therefore, by adjusting the size of the angle θ to control the shape of the missing rib model, the anisotropic mechanical properties of the stent can be adjusted to simulate the anisotropic biomechanical properties of myocardial tissue.

 
The researchers went on to obtain conductive myocardial scaffolds through in-situ chemical oxidation polymerization of pyrrole (Py). The current-voltage characteristic curve of the square and anisotropic PPy-coated myocardial stent is shown in Fig. 3a. These curves have a linear relationship, indicating that their internal resistance is constant within the range of the test voltage (3v). The conductivity of the stent (2–2.5 S m −1) is higher than that of the human myocardium (≈0.57 S m −1), and it can be used to transmit electrical signals between biological tissues. The results of cell experiments show that compared with the non-polymerized polypyrrole polycaprolactone scaffold, the conductive scaffold of polymerized polypyrrole has good biological activity and is more easily attached by cells.

In summary, this study proposes a vanishing rib model. By adjusting the design parameters of the vanishing rib model, the mechanical properties of the anisotropy of the stent can be adjusted to meet the biomechanical properties of the human myocardium, and the conductive polymer polypyrrole is polymerized in situ The preparation of the conductive myocardial stent with good biocompatibility is realized, and it is expected to be used for the treatment of myocardial infarction in the future.

references:
D. Olvera, M. Sohrabi Molina, G. Hendy, M.G. Monaghan, Electroconductive Melt Electrowritten Patches Matching the Mechanical Anisotropy of Human Myocardium, Advanced Functional Materials (2020).