Narrow response temperature range with excellent reversible shape memory effect for semi-crystalline networks as soft actuators

Micropatterned shape-memory polymer substrate containing hydrogen bonds creates a long-term dynamic microenvironment for regulating nerve-cell fate

Peripheral nerve injuries (PNIs) caused by mechanical contusion are frequently encountered in clinical practice, using nerve guidance conduits (NGCs) is now a promising therapy. An NGC creates a microenvironment for cell growth and differentiation, thus understanding physical and biochemical cues that can affect nerve-cell fate is a prerequisite for rationally designing NGCs. However, most of the previous works were focused on some static cues, the dynamic nature of the nerve microenvironment has not yet been well captured. Herein, we develop a micropatterned shape-memory polymer as a programmable substrate for providing a dynamic cue for nerve-cell growth. The shape-memory properties enable temporal programming of the substrate, and a dynamic microenvironment is created during standard cell culturing at 37 °C. Unlike most of the biomedical shape-memory polymers that recover rapidly at 37 °C, the proposed substrate shows a slow recovery process lasting 3-4 days and creates a long-term dynamic microenvironment. Results demonstrate that the vertically programmed substrates provide the most suitable dynamic microenvironment for PC12 cells as both the differentiation and maturity are promoted. Overall, this work provides a strategy for creating a long-term dynamic microenvironment for regulating nerve-cell fate and will inspire the rational design of NGCs for the treatment of PNIs.

Solvent Content Controlling Strategy for Cocrystallizable Polyesters Enables a Stress-Free Two-Way Shape Memory Effect with Wider Service Temperatures

It is challenging to enhance the stress-free two-way shape memory (stress-free TWSM) effect to obtain a wide range of response temperatures. Herein, a polycaprolactone (PCL)/poly(ω-pentadecalactone) (PPDL) is photocured under UV light irradiation in the solvent of 1,1,2-trichloroethane (TCA), to obtain a series of cross-linked polyesters (CPES). Controlling solvent content (SC) which is removed after the polymerization allows the yielded CPES to perform a regulatable thermodynamic and stress-free TWSM properties. High SC is beneficial to reduce the degree of chain overlap (C/C* ) of PPDL chain segments in the PCL-based CPES network, then causes the cocrystallization of PCL and PPDL and yielding an additional melting-transitions (Tm ). An enhanced stress-free TWSM is obtained in high SC samples (CPES-15-90), reflected in the attainment of a wide range of response temperature, which means a wider service temperature. The enhancement is reflected in higher reversible strain of high SC samples compared with the samples prepared with low SC when varying high trigger temperature (Thigh ). Even at high Thigh , the high SC sample still has reversible strain. Therefore, controlling SC strategy for photocuring copolyester not only provides a new preparation approach for high-performance shape memory (SM) polymers, but also offers new condensed polymer structure to explore.

Bio-Inspired Hydrogel-Elastomer Actuator with Bidirectional Bending and Dynamic Structural Color

In nature, some creatures can change their body shapes and surface colors simultaneously to respond to the external environments, which greatly inspired researchers in the development of color-tunable soft actuators. In this work, we present a facile method to prepare a smart hydrogel actuator that can bend bidirectionally and change color simultaneously, just like an octopus. The actuator is fabricated by elastomer/hydrogel bilayer and the hydrogel layer was decorated with thermoresponsive microgels as the photonic crystal blocks. Compared with the previously reported poly(N-isopropylacrylamide) hydrogel-based bilayer hydrogel actuators, which are generally limited to one-directional deformation, the elastomer/hydrogel bilayer actuator prepared in our work exhibits unique bidirectional bending behavior in accordance with the change of structural color. The bending degrees can be changed from -360° to 270° in response to solution temperatures ranging from 20 °C to 60 °C. At the same time, the surface color changes from red to green, and then to blue, covering the full visible light spectrum. The bending direction and degree of the hydrogel actuator can easily be adjusted by tuning the layer thickness ratio of the elastomer/hydrogel or the composition of the hydrogel. The color-tunable hydrogel-elastomer actuator reported in this work can achieve both programmable deformations and color-changing highly resembling the natural actuating behaviors of creatures.