Conjugation of zwitterionic polymer with dopamine is a promising approach to endow the surface with antifouling properties for medical devices, biosensors and marine coating applicationsetc. Zwitterionic polymers can be conjugated with dopamine by mostly four methods.

Boronic ester, one typical example of dynamic covalent bonds, has presented great potential to prepare self-healing hydrogels. However, most of currently reported hydrogels based on boronic esters are formed at pH > 8, which impeded their further use in physiological conditions. In this study, we designed two kinds of zwitterionic copolymers with benzoxaborole and catechol pendant groups, respectively. Owing to the lower pK_a value of benzoxaborole (7.2), gelation can happen easily at pH 7.4 PBS after mixing these two copolymers due to efficient formation of benzoxaborole-catechol complexations. The resulting hydrogels exhibited excellent self-healing property as well as dual pH/sugar responsiveness due to the dynamic nature of boronic ester. Moreover, benefiting from the cell membrane bioinspired 2-methacryloyloxyethyl phosphorylcholine (MPC)-based polymeric matrix, the hydrogel was further investigated for 3D cell encapsulation. The combination of biocompatible zwitterionic polymers with dynamic benzoxaborole-catechol complexation makes the hydrogels a promising platform for diverse potential bioapplications like drug delivery and tissue engineering.

Thermo-responsive hydrogels containing poly(N-isopropylacrylamide) (PNIPAAm), reinforced both with covalent and non-covalent interactions with cellulose nanocrystals (CNC), were synthesized via free-radical polymerization in the absence of any additional cross-linkers. The properties of PNIPAAm-CNC hybrid hydrogels were dependent on the amounts of incorporated CNC. The thermal stability of the hydrogels decreased with increasing CNC content. The rheological measurement indicated that the elastic and viscous moduli of hydrogels increased with the higher amounts of CNC addition, representing stronger mechanical properties of the hydrogels. Moreover, the hydrogel injection also supported the hypothesis that CNC reinforced the hydrogels; the increased CNC content exhibited higher structural integrity upon injection. The PNIPAAm-CNC hybrid hydrogels exhibited clear thermo-responsive behavior; the volume phase transition temperature (VPTT) was in the range of 36 to 39 °C, which is close to normal human body temperature. For wound dressing purposes, metronidazole, an antibiotic and antiprotozoal often used for skin infections, was used as a target drug to study drug-loading and the release properties of the hydrogels. The hydrogels showed a good drug-loading capacity at room temperature and a burst drug release, which was followed by slow and sustained release at 37 °C. These results suggested that newly developed drugs containing injectable hydrogels are promising materials for wound dressing.

Introduction: Hydrogels are of special importance, owing to their high-water content and various applications in biomedical and bio-engineering research. Self-healing properties is a common phenomenon in living organisms. Their endowed property of being able to self-repair after physical/chemical/mechanical damage to fully or partially its original properties demonstrates their prospective therapeutic applications. Due to complicated preparation and selection of suitable materials, the application of many host–guest supramolecular polymeric hydrogels are so limited. Thus, the design and construction of self-repairing material are highly desirable for effectively increase in the lifetime of a functional material. However, recent advances in the field of materials science and bioengineering and nanotechnology have led to the design of biologically relevant self-healing hydrogels for therapeutic applications. This review focuses on the recent development of self-healing hydrogels for biomedical application. Areas covered: The strategies of making self-healing hydrogels and their healing mechanisms are discussed. The significance of self-healing hydrogel for biomedical application is also highlighted in areas such as 3D/4D printing, cell/drug delivery, as well as soft actuators. Expert opinion: Materials that have the ability to self-repair damage and regain the desired mechanical properties, have been found to be excellent candidate materials for a range of biomedical uses especially if their unique characteristics are similar to that of soft-tissues. Self-healing hydrogels have been synthesized and shown to exhibit similar characteristics as human tissues, however, significant improvement is required in the fabrication process from inexpensive and nontoxic/non-hazardous materials and techniques, and, in addition, further fine-tuning of the self-healing properties are needed for specific biomedical uses.

The development of stimuli responsive polymers has progressed significantly with novel preparation techniques, which has allowed access to new materials with unique properties. Dual thermoresponsive (double temperature responsive) block copolymers are particularly of interest as their properties can change depending on the lower critical solution temperature (LCST) or upper critical solution temperature (UCST) of each segment. For instance, these block copolymers can change from being hydrophilic, to amphiphilic or to hydrophobic simply by changing the solution temperature without any additional chemicals and the block copolymers can change from being fully solubilized to self-assembled structures to macroscopic aggregation/precipitation. Based on the unique solution properties, these dual thermo-responsive block copolymers are expected to be suitable for biomedical applications. This review is divided into three parts; LCST-LCST types of block copolymers, UCST-LCST types of block copolymers, and their potential as biomedical applications.