The applications of hydrogels are severely limited by their weak mechanical properties. Despite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high stretchability, toughness, and recoverability at the same time in a hydrogel. Herein, we develop a novel class of dual physically cross-linked (DPC) hydrogels, which are triggered by clay nanosheets and iron ions (Fe 3+ ) as cross-linkers. First, clay nanosheets induce the formation of the first cross-linking points through the interaction of hydrogen bonds with poly(acrylamide-co-acrylic acid) (PAm-co-Ac) chains. Then the secondary cross-linking points are introduced by ionic coordinates between Fe 3+ and −COO− groups of PAm-co-Ac polymer chains. The mechanical properties of DPC hydrogels can be tuned readily by varying preparation parameters such as clay concentration, Fe 3+ concentration, and molar ratio of Ac/Am. More importantly, the optimal DPC hydrogels possess high tensile strength (ca. 3.5 MPa), large elongation (ca. 21 times), remarkable toughness (ca. 49 MJ m −3 ), and good self-recoverability (ca. 65% toughness recovery within 4 h without any external stimuli). Thus, this work provides a promising strategy for the fabrication of novel tough hydrogel containing a dual physical cross-linked network.

Biocompatible and biodegradable porous scaffolds with adjustable pore structure have aroused increasing interest in bone tissue engineering. Here, we report a facile method to fabricate hierarchical macroporous biocompatible (HmPB) scaffolds by combining Pickering high internal phase emulsion (HIPE) templates with three-dimensional (3D) printing. HmPB scaffolds composed of a polymer matrix of poly(l-lactic acid), PLLA, and poly(ε-caprolactone), PCL, are readily fabricated by solvent evaporation of 3D printed Pickering HIPEs which are stabilized by hydrophobically modified silica nanoparticles (h-SiO). The pore structure of HmPB scaffolds is easily tailored to be similar to natural extracellular matrix (ECM) by varying the fabrication conditions of the Pickering emulsion or adjusting the printing parameters. In addition, in vivo drug release studies which employ enrofloxacin (ENR) as a model drug indicate the potential of HmPB scaffolds as a drug carrier. Furthermore, in vivo cell culture assays prove that HmPB scaffolds that possess good biocompatibility as mouse bone mesenchymal stem cells (mBMSCs) can adhere and proliferate well on them. All the results suggest that HmPB scaffolds hold great potential in bone tissue engineering applications.

Shape-memory polymers (SMPs) are synthesized with adjustable glass transition temperature (T g ) ranging from 299 to 322 °C, higher than those reported previously. The polyimide containing thermal stable but flexible linkages within the backbone act as reversible phase, and high molecular weight (M n ) is necessary to form physical cross-links as fixed phase of thermoplastic shape-memory polyimide. The critical M n is 21.3 kg/mol, and the relationship between M n and T g is explored. Thermoset polyimides show higher storage modulus and better shape-memory effects than thermoplastic counterparts due to covalent cross-linking, and the effective cross-link density with the influence on their physical properties is studied. The mechanism of high-temperature shape-memory effect of polyimide on the basis of chain flexibility, molecular weight, and cross-link density is proposed, which will benefit further research on high-temperature SMPs.

Porous scaffolds consisting of bioactive inorganic nanoparticles and biodegradable polymers have gained much interest in bone tissue engineering. We report here a facile approach to fabricating poly(l-lactic acid)-grafted hydroxyapatite (g-HAp)/poly(lactide-co-glycolide) (PLGA) nanocomposite (NC) porous scaffolds by solvent evaporation of Pickering high internal phase emulsion (HIPE) templates, where g-HAp nanoparticles act as particulate stabilizers. The resultant porous scaffolds exhibit an open and rough pore structure. The pore structure and mechanical properties of the scaffolds can be tuned readily by varying the g-HAp nanoparticle concentration and internal phase volume fraction of the emulsion templates. With increasing the g-HAp concentration or decreasing the internal phase volume fraction, the pore size and the porosity decrease, while the Young's modulus and the compressive stress enhance. Moreover, the in vitro mineralization tests show that the bioactivity of the scaffolds increases with increasing the g-HAp concentration. Furthermore, the anti-inflammatory drug ibuprofen (IBU) is loaded into the scaffolds, and the drug release studies indicate that the loaded-IBU exhibits a sustained release profile. Finally, in vitro cell culture assays prove that the scaffolds are biocompatible because of supporting adhesion, spreading, and proliferation of mouse bone mesenchymal stem cells. All the results indicate that the solvent evaporation based on Pickering HIPE templates is a promising alternative method to fabricate NC porous scaffolds for potential bone tissue engineering applications.