Gelatin-Based Colloidal Versus Monolithic Gels to Regulate Macrophage-Mediated Inflammatory Response

• Published in: Tissue engineering. Part C, Methods Methods, 2022-07, Vol.28 (7), p.351-362
• Main Authors: Zhuang, Zhumei, Sun, Shengnan, Chen, Kaiwen, Zhang, Yue, Han, Xiaoman, Zhang, Yang, Sun, Kai, Cheng, Fang, Zhang, Lijun, Wang, Huanan
• Format: Article
• Language: English
• Subjects: Biocompatible Materials - chemistry; Gelatin - chemistry; Gelatin - pharmacology; Hydrogels - chemistry; Hydrogels - pharmacology; Macrophages; Methacrylates; Methods; Methods Articles
• ISSN: 1937-3384; 1937-3392
• DOI: 10.1089/ten.tec.2022.0044

Unlike conventional monolithic hydrogels with covalent cross-linkage that are typically elastic, colloidal gels assembled by reversibly assembled particles as building blocks have shown fascinating viscoelastic properties. They follow a gel-sol transition upon yielding and recover to the initial state upon the release of the shear force (so-called shear-thinning and self-healing behavior); this makes them an ideal candidate as injectable and moldable biomaterials for tissue regeneration. The immune response provoked by the implantation of the colloidal gels with special viscoelastic and structural features is critical for the successful integration of the implants with the host tissues, which, however, remains little explored. Since macrophages are known as the primary immune cells in determining the inflammatory response against the implants, we herein investigated in vitro macrophage polarization and in vivo inflammatory response induced by gelatin-based colloidal gels as compared to monolithic gels. Specifically, self-healing colloidal gels composed of pure gelatin nanoparticles, or methacrylate gelatin (GelMA) nanoparticles to allow secondary covalent cross-linkage were compared with GelMA bulk hydrogels. We demonstrated that hydrogel's elasticity plays a more dominant role rather than the structural feature in determining in vitro macrophage polarization evidenced by the stiffer gels inducing pro-inflammation M2 macrophage phenotype as compared to soft gels. However, subcutaneous implantation revealed a significantly alleviated immune response characterized by less fibrous capsule formation for the colloidal gels as compared to bulk gels of similar matrix elasticity. We speculated this can be related to the improved permeability of the colloidal gels for cell penetration, thereby leading to less fibrosis. In general, this study provided in-depth insight into the biophysical regulator of hydrogel materials on macrophage behavior and related inflammatory response, which can further direct future implant design and predict biomaterial–host interactions for immunotherapy and regenerative medicine.