Interpenetrating polymer network (IPN) is generally considered to be one of the most effective methods for imparting high-strength mechanical properties to hydrogel materials. To broaden the application of alginate hydrogel in skeletal muscle or muscle tissue engineering, the interpenetrating network technology and layer-by-layer (LBL) electrostatic assembly were proposed to fabricate the homogeneous alginate/polyacrylamide-chitosangelatin (Alg/PAAM-CS-GT) composite hydrogel scaffolds, using the hydroxyapatite/D-glucono-δ-lactone (HAP/GDL) complex as the gelling system. The effects of different components of alginate/polyacrylamide (Alg/PAAM) on the morphology, mechanical properties, swelling, degradability, and cytocompatibility of the hydrogel scaffolds were comparatively characterized. Experimental results showed that the as-prepared Alg/PAAM-CS-GT composite hydrogel scaffolds exhibited sharp edges and regular 3D structures. Their pore structure could be regulated by changing the content of PAAM in Alg/PAAM-CS-GT composite hydrogel scaffolds. And the filling of PAAM reduced the pores and thickened the pore walls, which obviously enhanced the mechanical properties of Alg/PAAM-CS-GT composite hydrogel scaffolds. FT-IR and thermogravimetric analysis showed that O‧‧‧N hydrogen bonding between COOH of SA and NH 2 of PAAM could be helpful to improve the thermal stability of the composite hydrogel scaffolds. The swelling and biodegradation measurements indicated that the swelling and degradation of Alg/PAAM-CS-GT composite hydrogel scaffolds could be effectively regulated by changing the component content of the composite hydrogel. In addition, the in vitro cytocompatibility analysis showed that the Alg/PAAM-CS-GT composite hydrogel scaffolds could support the growth of MC3T3-E1 cells and promote cell proliferation and differentiation. According to the in vitro cytocompatibility test results, the optimum PAAM content for the Alg/PAAM-CS-GT composite hydrogel scaffolds was 60%. Because of good morphology, well-developed pores, excellent mechanical properties, and high

Oxidized sodium alginate (OSA) is selected as an appropriate material to be extensively applied in regenerative medicine, 3D-printed/composite scaffolds, and tissue engineering for its excellent physicochemical properties and biodegradability. However, few literatures have systematically investigated the structure and properties of the resultant OSA and the effect of the oxidation degree (OD) of alginate on its biodegradability and gelation ability. Herein, we used NaIO4 as the oxidant to oxidize adjacent hydroxyl groups at the C-2 and C-3 positions on alginate uronic acid monomer to obtain OSA with various ODs. The structure and physicochemical properties of OSA were evaluated by Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and thermogravimetric analysis (TGA). At the same time, gel permeation chromatography (GPC) and a rheometer were used to determine the hydrogel-forming ability and biodegradation performance of OSA. The results showed that the two adjacent hydroxyl groups of alginate uronic acid units were successfully oxidized to form the aldehyde groups; as the amount of NaIO4 increased, the OD of OSA gradually increased, the molecular weight decreased, the gelation ability continued to weaken, and degradation performance obviously rose. It is shown that OSA with various ODs could be prepared by regulating the molar ratio of NaIO4 and sodium alginate (SA), which could greatly broaden the application of OSA-based hydrogel in tissue engineering, controlled drug release, 3D printing, and the biomedical field.

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In this work, the hydrophobically modified alginate derivative (HMAD) was synthesized by using sodium alginate, cyclohexyl isocyanide, octylamine and propionaldehyde instead of formaldehyde, based on previous explorations of the Ugi reaction for the modification of alginate. Experimental results revealed that the successful grafting of the hydrophobic chains onto the alginate molecular backbone via the Ugi reaction had weakened and destroyed the intramolecular hydrogen bonds, thus enhancing the molecular flexibility of alginate, which endowed the HMAD with good amphiphilic property with the critical aggregation concentration (CAC) of 0.44 g/L. Moreover, the resultant HMAD could form the stable self-aggregated micelles with the spherical shape due to the intra or intermolecular hydrophobic associations. Its average hydrodynamic diameter and zeta potential were 458 nm (PDI = 0.26) and À 61.4 mV, respectively, which was able to achieve the loading and sustained-release of hydrophobic ibuprofen. Meanwhile, HMAD had no significant cytotoxicity to the murine macrophage RAW264.7 cells. Based on the above merits, the synthesized HMAD could exhibit great potential for the development of hydrophobic pharmaceutical formulations.

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