The self-healing hydrogels are extremely attractive in biological and biomedical fields. The imine bond obtained by the Schiff base reaction is a commonly used dynamic covalent bond to fabricate self-healing hydrogels. Gelatin is a commonly used natural macromolecule in the biomedical field with excellent biocompatibility, biodegradability, and nonimmunogenicity. However, the gelatin-based hydrogels with self-healing ability are rarely reported based on imine bonds. Herein, we present a facile approach to fabricate a gelatin hydrogel with self-healing ability based on the Schiff base reaction. The gelatin was first reacted with ethylenediamine to increase the content of amino groups. Then dialdehyde carboxymethyl cellulose was used to cross-link amino-gelatin to fabricate the self-healing hydrogel. The results showed that the fabricated hydrogel exhibited good self-healing ability as expected because of the formed dynamic imine bonds between amino-gelatin and dialdehyde carboxymethyl cellulose. The hydrogel also presented good fatigue resistance and self-recovery capacity. Moreover, the self-healing hydrogel possessed ideal hemocompatibility and cytocompatibility. In sum, the fabricated self-healing hydrogel has application prospects in biomedical fields, such as injectable cell and drug carrier and injectable tissue engineering scaffold.

The self-healing hydrogel and conductive hydrogel have attracted extensive attention in tissue engineering. The selfhealing hydrogel can restore its original structure and functionality after damage. The conductive hydrogel is beneficial to the differentiation and proliferation of electrical-stimuli-responsive cells. It is significant to integrate the self-healing ability and the electrical conductivity into a single hydrogel system. Herein we present polypyrrole-grafted gelatin-based hydrogels with combined conductive, self-healing and injectable properties. Methacrylic anhydride was first grafted onto gelatin to form double-bond-functionalized gelatin. Then, the commonly used conductive polymer polypyrrole was grafted onto gelatin by reacting with the double bond. Finally, the polypyrrole-grafted gelatin was mixed with ferric ions to construct the hydrogels. As revealed by the results, the hydrogels possess good conductivity owing to the incorporated polypyrrole and ferric ions. The reversible ionic interactions of ferric ions with gelatin and polypyrrole endow the hydrogels with selfhealing abilities. It is interesting that the hydrogels exhibit good injectable properties attributed to their self-healing abilities. Moreover, the hydrogels show a controllable porous structure, an inhibited swelling ability, and good cytocompatibility and blood compatibility.

The porous microstructure of scaffolds is an essential consideration for tissue engineering, which plays an important role for cell adhesion, migration, and proliferation. It is crucial to choose optimum pore sizes of scaffolds for the treatment of various damaged tissues. Therefore, the proper porosity is the significant factor that should be considered when designing tissue scaffolds. Herein, we develop an improved emulsion template method to fabricate gelatinbased scaffolds with controllable pore structure. Gelatin droplets were first prepared by emulsification and then solidified by genipin to prepare gelatin microspheres. The microspheres were used as a template for the fabrication of porous scaffolds, which were gathered and tightened together by dialdehyde amylose. The results showed that emulsification can produce gelatin microspheres with narrow size distribution. The size of gelatin microspheres was easily controlled by adjusting the concentration of gelatin and the speed of mechanical agitation. The gelatin-based scaffolds presented macroporous and interconnected structure. It is interesting that the pore size of scaffolds was directly related to the size of gelatin microspheres, displaying the same trend of change in size. It indicated that the gelatin microspheres can be used as the proper template to fabricate gelatin-based scaffold with a desired pore structure. In addition, the gelatin-based scaffolds possessed good blood compatibility and cytocompatibility. Overall, the gelatin-based scaffolds exhibited great potential in tissue engineering.

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The increasing molecular weight of PEG can increase the water dispersion but decrease the photocatalytic activity of PEG-capped TiO2.

Guided bone regeneration (GBR) has been regarded as a valuable way to effectively induce bone remodeling. The key factor of GBR is to place a barrier membrane between the soft tissue and bone defect, preventing the untimely intrusion of fibroblasts and permitting the prior settlement of internal osteoblasts. Notably, heterogeneous double-layer GBR membranes with a compact upper layer and a loose lower layer exhibit enhanced effectiveness in blocking fibroblasts and promoting the growth of osteoblasts. Herein, we present porous and interconnected collagen-based sponges with controllable pore size for the fabrication of absorbable GBR membranes with a heterogeneous double-layer structure. Dialdehyde carboxymethyl cellulose was used to fix collagen-based sponges. The pore size of the sponges can be well controlled by adjusting the cross-linking degree, which is decreased with an increase of cross-linking degree. The sponges show enhanced mechanical properties, inhibited swelling ability and biodegradation, good blood compatibility, and good cytocompatibility. The sponges are feasible to form a heterogeneous double-layer structure with a loose lower layer and a compact upper layer. Interestingly, the lower layer with the pore size of 200–300 μm can promote the adhesion, proliferation, and differentiation of osteoblasts MC3T3-E1 cells, while the upper layer with the pore size of 20–50 μm makes a great contribution to the growth of myoblast C2C12 cells. Overall, the collagen-based sponges have the potential to be used to fabricate heterogeneous double-layer bone barrier membranes for bone remodeling.

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Osteosarcoma is a common malignant bone tumor that tends to occur in adolescents, with surgical resection of the tumor tissue as its standard treatment. After surgery, long-term chemotherapy should be performed to prevent patients from recrudescence. However, conventional chemotherapy drugs impose many serious side effects on patients. It is significant to optimize a chemotherapy drug delivery system. Herein, we present an injectable self-healing hydrogel carrying curcumin with pH-responsive drug release and selective toxicity for osteosarcoma therapy. Amino-gelatin and oxidized starch were synthesized and used as substrates to prepare hydrogels based on imine linkages. Polymerized β-CD was synthesized to encapsulate curcumin and incorporate it into hydrogels. As a dynamic covalent bond, imine linkages endowed the hydrogel with injectability and self-healing properties. Under acidic conditions, the hydrogel presented a pH-responsive curcumin release property due to instable imine linkages, showing a higher cumulative release of curcumin at pH 6.5 than at pH 7.4. Moreover, hydrogels could continuously release curcumin for more than 28 days, featuring a sudden early release and a slow late release. Interestingly, differentiated from healthy osteoblasts, the hydrogel showed selective cytotoxicity to osteosarcoma cells and could even accelerate the differentiation of osteoblasts owing to the incorporation of curcumin. Briefly speaking, as a drug delivery system, the composite hydrogel can be widely applied for osteosarcoma treatment.