Smart Collagen Hydrogels Based on 1-Ethyl-3-methylimidazolium Acetate and Microbial Transglutaminase for Potential Applications in Tissue Engineering and Cancer Therapy

For the first time, collagen-based hydrogels were fabricated in the presence of a biocompatible ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM] [Ac]), by a simple biopolymer cross-linking process facilitated by the strong catalytic hydrolysis of microbial transglutaminase (MTGase). Phosphate buffer solution (PBS)-encapsulated human-like collagen (HLC) or fish bone collagen (FBC) for the composite hydrogels was simply prepared by the codissolution of biopolymers in [EMIM] [Ac] or, in the absence of the ionic liquid, by the dispersion of MTGase in the biopolymer solution, leading to the formation of MTGase-aided hydrogels (Gel1 and Gel4) and [EMIM] [Ac]/MTGase-aided hydrogels (Gel2, Gel3, and Gel5). The effects of different contents of [EMIM] [Ac] and collagens of different origins (HLC and FBC) during fabrication on a range of structural and material characteristics, including the synthesis mechanism, three-dimensional structure, swelling behavior, mechanical strength, enzymatic hydrolysis rate, cytotoxicity, fibroblast cell proliferation rate, in vitro inhibition of cancer cells and cell adhesion, and in vivo histocompatibility, were investigated. Surprisingly, fabrication with [EMIM] [Ac] had significant effects on the structure and properties of the collagen/MTGase-based hydrogels. In other words, [EMIM] [Ac] changed the underlying mechanism responsible for the advantageous properties of the hydrogels by changing the three-dimensional structure of HLC or FBC, which improved their effects on fibroblast proliferation (3T3-L1 and L929 cells) and their in vitro inhibition of cancer cells (HepG2 and MKN45 cells). The use of the ionic liquid also imbued the hydrogels with degradation resistance and anti-inflammatory properties after subcutaneous injection into mice (in vivo). The catalytic hydrolysis by MTGase and the [EMIM] [Ac] content were the major factors that influenced the properties of the collagen. This result suggests the potential application of ionic liquid-enzymatic hydrolysis in the fabrication of collagen hydrogels in circumstances where the control of the properties by an ionic liquid is desirable. Therefore, [EMIM] [Ac] could be a promising solvent for the development of collagen into smart biomaterials with controlled biodegradation rates that can meet the needs of specific potential applications, such as tissue engineering and cancer therapy.