Unconstrained recovery characterization of shape-memory polymer networks for cardiovascular applications

Abstract

Shape-memory materials have been proposed in biomedical device design due to their ability to facilitate minimally invasive surgery and recover to a predetermined shape in vivo. Use of the shape-memory effect in polymers is proposed for cardiovascular stent interventions to reduce the catheter size for delivery and offer highly controlled and tailored deployment at body temperature. Shape-memory polymer networks were synthesized via photopolymerization of tert-butyl acrylate and poly(ethylene glycol) dimethacrylate to provide precise control over the thermomechanical response of the system. The free recovery response of the polymer stents at body temperature was studied as a function of glass transition temperature (T(g)), crosslink density, geometrical perforation, and deformation temperature, all of which can be independently controlled. Room temperature storage of the stents was shown to be highly dependent on T(g) and crosslink density. The pressurized response of the stents is also demonstrated to depend on crosslink density. This polymer system exhibits a wide range of shape-memory and thermomechanical responses to adapt and meet specific needs of minimally invasive cardiovascular devices.

Figure 1

Recovery of a 20 wt% crosslinked SMP stent with T_g=52°C delivered via an 18Fr. catheter into a 22 mm ID glass tube containing body temperature water at 37°C. Black rings were drawn to facilitate deployment visualization.

Figure 2

Example of a glass transition curve measured by DMA with thermomechanical properties labeled on the curve. The DMA 3-point bending setup is also shown.

Figure 3

Design of solid and 50% perforated shape-memory polymer stents.

Figure 4

Example of free recovery measurements of a shape-memory polymer stent.

Figure 5

a). Glass transition curves of materials with T_g~52°C and differing amounts of wt% crosslinker. b). Glass transition curves of materials with 20 wt% crosslinker and different T_g’s.

Figure 5

a). Glass transition curves of materials with T_g~52°C and differing amounts of wt% crosslinker. b). Glass transition curves of materials with 20 wt% crosslinker and different T_g’s.

Figure 6

Performance of solid stents. a). Recovery of stents deformed at room temperature and recovered at body temperature. b). Recovery of a 10 wt% crosslinked stent with a T_g of 52°C deformed at room and body temperature and recovered at body temperature. c). Recovery of a 10 wt% crosslinked stent with a T_g of 52°C deformed and recovered at both body temperature and ~5°C above body temperature.

Figure 6

Performance of solid stents. a). Recovery of stents deformed at room temperature and recovered at body temperature. b). Recovery of a 10 wt% crosslinked stent with a T_g of 52°C deformed at room and body temperature and recovered at body temperature. c). Recovery of a 10 wt% crosslinked stent with a T_g of 52°C deformed and recovered at both body temperature and ~5°C above body temperature.

Figure 6

Performance of solid stents. a). Recovery of stents deformed at room temperature and recovered at body temperature. b). Recovery of a 10 wt% crosslinked stent with a T_g of 52°C deformed at room and body temperature and recovered at body temperature. c). Recovery of a 10 wt% crosslinked stent with a T_g of 52°C deformed and recovered at both body temperature and ~5°C above body temperature.

Figure 7

Comparison of solid vs. perforated stents for a recovery temperature of 37 °C. a). Stents made from the 10 wt% crosslinked polymer with a T_g of 52°C. b). Stents made from Networks 2, 4, and 5.

Figure 7

Comparison of solid vs. perforated stents for a recovery temperature of 37 °C. a). Stents made from the 10 wt% crosslinked polymer with a T_g of 52°C. b). Stents made from Networks 2, 4, and 5.

Figure 8

Storage diameter of packaged stents as a function of time. a). Crosslinked stents with a T_g of 52°C. b). Crosslinked stents with a T_g of 55°C.

Figure 8

Storage diameter of packaged stents as a function of time. a). Crosslinked stents with a T_g of 52°C. b). Crosslinked stents with a T_g of 55°C.

Figure 9

Stents with a Tg=52°C gradually cycled twice between 55–160 mm·Hg