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.