Polycaprolactone is a semicrystalline polymer with five non-polar methylene groups -CH2- and one polar ester group -COO- on its repeating structural unit. The C-C bonds and C-O bonds in the molecular chain can rotate freely. This structure makes polycaprolactone very flexible and processable, and it can be extruded, injection molded, wire drawn, blown, etc.
Conductive hydrogels have good biocompatibility, conductivity and mechanical properties, bringing unprecedented opportunities to the emerging field of bioelectronics, such as wearable flexible electronic devices, health monitoring and medical devices, and soft robots. The biggest advantage of conductive hydrogels is that they can maintain excellent conductivity while ensuring excellent mechanical properties, thereby achieving seamless integration of biology and electronics. Nanoadditives provide conductivity and mechanical properties to the matrix material. However, the current preparation of nanoadditives usually adopts traditional methods, which makes it difficult to precisely control the size of nanoassemblies, resulting in uneven distribution of composite materials and loss of control of microstructure at the submicron scale, which leads to poor dispersion of nanoadditives in the matrix and ultimately deterioration of various properties of composite materials. Therefore, it is still challenging to improve the conductivity and mechanical strength of hydrogels. The precise preparation of uniform nanostructures from the bottom up can replace the above-mentioned uneven nanoassemblies, making it possible to explore the structure-activity relationship of nanocomposites and facilitating the preparation of nanocomposites with controllable properties.
Researchers have proposed an innovative method for preparing nanocomposite hydrogels with excellent mechanical properties and electrical conductivity. The researchers preassembled polycaprolactone block copolymer nanosheets with uniform size and used these polyanionic nanosheets as fillers to significantly enhance the conductivity and mechanical properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/nanosheet composite conductive hydrogels. First, PCL-b-PSS diblock copolymers (BCPs) rich in sulfonic acid groups were designed and synthesized. Through a crystallization-driven bottom-up self-assembly method, these block copolymers were assembled into uniform two-dimensional polyanionic nanosheets, in which the PSS block was located on the surface of the nanosheet as a solvent-philic part. Therefore, these negatively charged nanosheets, as counteranions, can further participate in the polymerization reaction of 3,4-ethylenedioxythiophene to prepare PEDOT:PSS/nanosheet composite organic semiconductors from the bottom up. Conductivity studies showed that the conductivity of PEDOT films containing polyanionic nanosheets was significantly improved. Nanocomposite calcium alginate conductive hydrogels with excellent mechanical properties were successfully prepared by further mixing the PEDOT:PSS/nanosheet complex with alginate. Mechanical strength comparison studies showed that uniform nanosheets as additives can significantly improve the shear resistance of nanocomposite hydrogels. The results of this study show that the preparation of nanocomposite hydrogels by a bottom-up approach can not only improve the mechanical properties and conductivity of hydrogels, but also provide an important reference for exploring the structure-activity relationship of nanocomposites and preparing nanocomposites with controllable properties.
