(M1230-06-33) 4D Printed Temperature Responsive Drug-Eluting Biodegradable Stent for Coronary Artery Disease

Purpose: Coronary Artery Disease remains the most common cause of death in the United States. It is associated with the deposition of plaque resulting in toughening and narrowing of arteries. Coronary stenting is usually performed to restore proper blood flow. However, no biodegradable and bioresorbable stents exist in the market. Hence, the aim of this project was to synthesize a biodegradable stimuli-responsive shape memory polymer which on account of its shape recovery can exert pressure on arteries to prevent them from clogging again2. A polymer with temperature responsive shape memory effect was utilized to fabricate cardiac stents. Subsequently, the thermal and mechanical characterization of the polymer was performed.

Methods: A temperature responsive shape memory polymer was utilized to fabricate a cardiac stent using additive manufacturing techniques. The polymer employed Polylactic acid as the shape fixity and Polycaprolactone as shape recovery component. In order to optimize the shape recovery performance, different batches of polymer with Polylactic acid and Polycaprolactone percentages  between 0 and 100% were studied. The polymer obtained was subjected to different spectroscopic tests including Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H-NMR) for structure elucidation. The thermal properties of the polymer were studied by thermal characterization techniques including differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Subsequently, X-ray diffraction was used to study the nature of the polymer and its crystalline structure. Following this shape recovery tests were performed to study shape retention and shape fixity properties. Further tests of mechanical characterization and drug release are currently underway.

Results: A hollow cylindrical cardiac stent was 3D printed with Polylactic acid and Polycaprolactone based shape memory polymer. DSC confirmed that the  polymer has a transition temperature close to physiological temperature and hence body temperature can act as a stimulus. FTIR analysis was utilized to study the functional groups in the final polymer while the XRD results towards the crystalline nature of the polymer. Shape recovery tests illustrated that a sample molded to a temporary shape by heat and mechanical conditioning can recover its shape on heating. 

Conclusion: The thermo-responsive polymer can act as a biodegradable filament that will serve as the building material for the cardiac stent. Given its transition temperature, the stent should expand after it is inserted into the body and hold onto the artery walls. The stent can be used for localized delivery of aspirin and simvastatin to the artery walls.

References: 1. Cassar A, Holmes DR, Rihal CS, Gersh BJ. Chronic Coronary Artery Disease: Diagnosis and Management. Mayo Clinic Proceedings. 2009;84(12):1130-1146. doi:10.4065/mcp.2009.0391
2. Behl M, Lendlein A. Shape-memory polymers. Materials Today. 2007;10(4):20-28. doi:10.1016/S1369-7021(07)70047-0

Acknowledgments: Joon Kim would like to acknowledge Undergraduate Research Fellowship (URF-2020), offered by the University of Texas at Austin, for supporting and funding this research.

Figure 1: FTIR spectra for PLA/PCL film



Figure 2: Differential Scanning Calorimetry for PLA/PCL film



Figure 3: Illustration demonstrating shape memory test showing programming and recovery stage