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

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).

Synthesis, characterization & cytocompatibility of poly (diol-co-tricarballylate) based thermally crosslinked elastomers for drug delivery & tissue engineering applications

The aim of this study was to investigate the synthesis and in vitro characterization of thermoset biodegradable poly (diol-co-tricarballylate) (PDT) elastomeric polymers for the purpose of their use in implantable drug delivery and tissue engineering applications. The synthesis was based on thermal crosslinking technique via a polycondensation reaction of tricarballylic acid with aliphatic diols of varying chain lengths (C6-C12). PDT prepolymers were synthesized at 140 °C for 20 min. After purification, the prepolymers were molded and kept at 120 °C for 18 h under vacuum to complete the crosslinking process. PDT prepolymers were characterized by DSC, FT-IR, ¹H NMR and GPC. The PDT elastomers were also subjected to thermal and structural analysis, as well as sol content, mechanical testing, in vitro degradation and cytocompatibility studies. The mechanical properties and sol content were found to be dependent on synthesis conditions and can be controlled by manipulating the crosslinking density and number of methylene groups in the chain of precursor aliphatic diol. The family of thermally crosslinked PDT biodegradable polyesters were successfully prepared and characterized; besides they have promising use in drug delivery and other biomedical tissue engineering applications.

Design of super-elastic biodegradable scaffolds with longitudinally oriented microchannels and optimization of the channel size for Schwann cell migration

We newly designed super-elastic biodegradable scaffolds with longitudinally oriented microchannels for repair and regeneration of peripheral nerve defects. Four-armed poly(ε-caprolactone-co-D,L-lactide)s (P(CL-co-DLLA)s) were synthesized by ring-opening copolymerization of CL and DLLA from terminal hydroxyl groups of pentaerythritol, and acryloyl chloride was then reacted with the ends of the chains. The end-functionalized P(CL-co-DLLA) was crosslinked in a cylindrical mold in the presence of longitudinally oriented silica fibers as the templates, which were later dissolved by hydrofluoric acid. The elastic moduli of the crosslinked P(CL-co-DLLA)s were controlled between 10^-1 and 10² MPa at 37 °C, depending on the composition. The scaffolds could be elongated to 700% of their original size without fracture or damage ('super-elasticity'). Scanning electron microscopy images revealed that well-defined and highly aligned multiple channels consistent with the mold design were produced in the scaffolds. Owing to their elastic nature, the microchannels in the scaffolds did not collapse when they were bent to 90°. To evaluate the effect of the channel diameter on Schwann cell migration, microchannels were also fabricated in transparent poly(dimethylsiloxane), allowing observation of cell migration. The migration speed increased with channel size, but the Young's modulus of the scaffold decreased as the channel diameter increased. These findings may serve as the basis for designing tissue-engineering scaffolds for nerve regeneration and investigating the effects of the geometrical and dimensional properties on axonal outgrowth.

Shape-memory surface with dynamically tunable nano-geometry activated by body heat

Shape-memory surfaces with on-demand, tunable nanopatterns are developed to observe time dependent changes in cell alignment using temperature-responsive poly(ϵ-caprolactone) (PCL) films. Temporary grooved nanopatterns are easily programmed on the films and triggered to transition quickly to permanent surface patterns by the application of body heat. A time-dependent cytoskeleton remodeling is also observed under biologically relevant conditions.