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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.

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Collagen is a favorable candidate in the field of biomaterials as a wound dressing. However, it cannot be ignored that the application of collagen is limited to its poor physicochemical and perishable properties. It is significant to endow collagen with antibacterial activity and simultaneously improve its physicochemical properties. Here, we present a simple method to fabricate antibacterial collagen-based wound dressing with appropriate physicochemical properties. First, dialdehyde xanthan gum (DXG) was used as an environmentally friendly reducing agent and stabilizer to synthesize silver nanoparticles (AgNPs). Then, collagen/DXG-AgNP composite dressings were fabricated by directly immersing a collagen sponge in the obtained DXG-AgNP aqueous solutions. Our results showed that the spherical AgNPs with diameters of 12–35 nm were successfully synthesized. The presence of DXG effectively prevented aggregation and precipitation of AgNPs in aqueous solution. By the simple one-step solution-immersion approach, AgNPs were homogeneously introduced into the collagen matrix and collagen was simultaneously cross-linked by the existent DXG. Robust antibacterial activity was endowed to collagen as expected while the physicochemical properties of collagen were effectively improved. It is interesting that collagen/DXG-AgNP composite dressings possessed the properties of shape memory, good blood compatibility, and cytocompatibility. In addition, collagen/DXG-AgNP composite dressings could accelerate the deposition of collagen and thereby effectively promote full-thickness burn healing without scar formation.

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The denaturation of collagen solution in acetic acid has been investigated by using ultra-sensitive differential scanning calorimetry (US-DSC), circular dichroism (CD), and laser light scattering (LLS). US-DSC measurements reveal that the collagen exhibits a bimodal transition, i.e., there exists a shoulder transition before the major transition. Such a shoulder transition can recover from a cooling when the collagen is heated to a temperature below 35 degrees C. However, when the heating temperature is above 37 degrees C, both the shoulder and major transitions are irreversible. CD measurements demonstrate the content of triple helix slowly decreases with temperature at a temperature below 35 degrees C, but it drastically decreases at a higher temperature. Our experiments suggest that the shoulder transition and major transition arise from the defibrillation and denaturation of collagen, respectively. LLS measurements show the average hydrodynamic radius R(h), radius of gyration R(g)of the collagen gradually decrease before a sharp decrease at a higher temperature. Meanwhile, the ratio R(g)/R(h) gradually increases at a temperature below approximately 34 degrees C and drastically increases in the range 34-40 degrees C, further indicating the defibrillation of collagen before the denaturation.

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