Smart Shape‐Memory Polymeric String for the Contraction of Blood Vessels in Fetal Surgery of Sacrococcygeal Teratoma

Abstract

Shape-memory polymers (SMPs) are promising materials in numerous emerging biomedical applications owing to their unique shape-memory characteristics. However, simultaneous realization of high strength, toughness, stretchability while maintaining high shape fixity (R f ) and shape recovery ratio (R r ) remains a challenge that hinders their practical applications. Herein, a novel shape-memory polymeric string (SMP string) that is ultra-stretchable (up to 1570%), strong (up to 345 MPa), tough (up to 237.9 MJ m −3 ), and highly recoverable (R f averagely above 99.5%, R r averagely above 99.1%) through a facile approach fabricated solely by tetra-branched poly(𝝐-caprolactone) (PCL) is reported. Notably, the shape-memory contraction force (up to 7.97 N) of this SMP string is customizable with the manipulation of their energy storage capacity by adjusting the string thickness and stretchability. In addition, this SMP string displays a controllable shape-memory response time and demonstrates excellent shape-memory-induced contraction effect against both rigid silicone tubes and porcine carotids. This novel SMP string is envisioned to be applied in the contraction of blood vessels and resolves the difficulties in the restriction of blood flow in minimally invasive surgeries such as fetoscopic surgery of sacrococcygeal teratoma (SCT).

Influences of Crystallinity and Crosslinking Density on the Shape Recovery Force in Poly(ε-Caprolactone)-Based Shape-Memory Polymer Blends

“…The shape recovery force of the 4b100PCL homopolymer greatly enhanced from 0.061 N at 50% strain to 0.894 N at 800% strain. These results are in accordance with the previous conclusion that an almost linear enhancement in shape recovery force that correlates with the energy storage capacity in response to the increase of the stretched strains occurs [ 19 , 31 ]. Moreover, evidence suggests that crosslinking density is among the most important factors for tuning the shape-memory properties [ 28 ].…”

“…Low molecular weight 4b10PCL is theoretically amorphous after crosslinking, resulting from the short chain length between crosslinking points, which can contribute to a higher crosslinking density and usually results in difficulty forming crystal regions [ 26 ]. Contrarily, high molecular weight 4b100PCL is highly crystalline and possesses excellent mechanical properties, as reported in our previous study [ 19 ]. By simply blending different ratios of amorphous 4b10PCL with highly crystalline 4b100PCL, we could obtain a series of polymer blends that could help distinguish the influence of crystallinity and crosslinking density on macroscopic thermal, mechanical, and shape-memory properties such as elastic modulus, stretchability, T m , and shape recovery force, as shown in Figure 1 c. With a better understanding of the influences of crystallinity and crosslinking density on the shape recovery force of semicrystalline SMPs, we can expect great convenience and precision in the future design of soft robotics, actuators, and biomedical devices.…”

“…In our previous study, we reported that the increase in stretched strains could give rise to a stronger shape recovery force and better contraction effect [ 19 ]. In support of this conclusion, the shape recovery forces and energy storage capacities at different stretched strains of 4b100PCL are depicted in Figure 5 a.…”

“…The obtained films were then washed with methanol for 2 h before being dried under reduced pressure overnight. Dried SMPB films were annealed at 60 °C in an oven for 10 min and collected after cooling down at room temperature [ 19 ].…”

“…Kumar et al [ 18 ] demonstrated an SMP-based smart compression device that utilizes the shape recovery-induced contraction force for the treatment of chronic venous disorder. In our previous study, we designed a novel shape-memory string capable of occluding the feeding vessels of fetal tumors in minimally invasive fetoscopic surgery contributed by the laser-actuatable shape-memory contraction [ 19 ]. The aforementioned shape recovery force is a pivotal function of SMPs, which are commonly utilized in wide range of applications.…”