Anomalous Loss of Stiffness with Increasing Reinforcement in a Photo-Activated Nanocomposite.

Hydrogels are commonly doped with stiff nanoscale fillers to endow them with the strength and stiffness needed for engineering applications. Although structure-property relations for many polymer matrix nanocomposites are well established, modeling the new generation of hydrogel nanocomposites requires the study of processing-structure-property relationships because subtle differences in chemical kinetics during their synthesis can cause nearly identical hydrogels to have dramatically different mechanical properties. The authors therefore assembled a framework to relate synthesis conditions (including hydrogel and nanofiller mechanical properties and light absorbance) to gelation kinetics and mechanical properties. They validated the model against experiments on a graphene oxide (GO) doped oligo (ethylene glycol) diacrylate (OEGDA), a system in which, in apparent violation of laws from continuum mechanics, doping can reduce rather than increase the stiffness of the resulting hydrogel nanocomposites. Both model and experiment showed a key role light absorbance-dominated gelation kinetics in determining nanocomposite mechanical properties in conjunction with nanofiller reinforcement, with the nanofiller's attenuation of chemical kinetics sometimes outweighing stiffening effects to explain the observed, anomalous loss of stiffness. By bridging the chemical kinetics and mechanics of nanocomposite hydrogels, the authors' modeling framework shows promise for broad applicability to design of hydrogel nanocomposites.

A polycationic antimicrobial and biocompatible hydrogel with microbe membrane suctioning ability.

Despite advanced sterilization and aseptic techniques, infections associated with medical implants have not been eradicated. Most present coatings cannot simultaneously fulfil the requirements of antibacterial and antifungal activity as well as biocompatibility and reusability. Here, we report an antimicrobial hydrogel based on dimethyldecylammonium chitosan (with high quaternization)-graft-poly(ethylene glycol) methacrylate (DMDC-Q-g-EM) and poly(ethylene glycol) diacrylate, which has excellent antimicrobial efficacy against Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus and Fusarium solani. The proposed mechanism of the antimicrobial activity of the polycationic hydrogel is by attraction of sections of anionic microbial membrane into the internal nanopores of the hydrogel, like an 'anion sponge', leading to microbial membrane disruption and then microbe death. We have also demonstrated a thin uniform adherent coating of the hydrogel by simple ultraviolet immobilization. An animal study shows that DMDC-Q-g-EM hydrogel coating is biocompatible with rabbit conjunctiva and has no toxicity to the epithelial cells or the underlying stroma.

Engineering the Cell Microenvironment Using Novel Photoresponsive Hydrogels.

In vivo, cells are located in a dynamic, three-dimensional (3D) cell microenvironment, and various biomaterials have been used to engineer 3D cell microenvironments in vitro to study the effects of the cell microenvironment on the regulation of cell fate. However, conventional hydrogels can only mimic the static cell microenvironment without any synchronous regulations. Therefore, novel hydrogels that are capable of responding to specific stimuli (e.g., light, temperature, pH, and magnetic and electrical stimulations) have emerged as versatile platforms to precisely mimic the dynamic native 3D cell microenvironment. Among these novel hydrogels, photoresponsive hydrogels (PRHs) that are capable of changing their physical and chemical properties after exposure to light irradiation enable the dynamic, native cell microenvironment to be mimicked and show great promise in deciphering the unknown mechanisms of the 3D cell microenvironment in regulating the cell fate. Several reviews have already summarized the advances of PRHs and have focused on specific photosensitive chemical groups and photoresponsive elements or on the reaction categories and mechanism of PRHs. However, a holistic view of novel PRHs, which highlights the multiple physical and chemical properties that can be tuned by remote light activation, as well as their applications in engineering a dynamic cell microenvironment for the regulation of cell behaviors in vitro is still missing and is the focus of this review.