Hybrid gelation processes in enzymatically gelled gelatin: impact on nanostructure, macroscopic properties and cellular response
F Bode and MA da Silva and P Smith and CD Lorenz and S McCullen and MM Stevens and CA Dreiss, SOFT MATTER, 9, 6986-6999 (2013).
Physical, chemical and hybrid tilapia fish gelatin hydrogels were investigated by small-angle neutron scattering (SANS), molecular dynamic simulations and their biological effect in cell cultures studied; results from the different experimental techniques were then correlated and linked to the rheological properties of the gels (F. Bode et al., Biomacromolecules, 2011, 12, 3741-3752). Hydrogels were obtained by cross-linking with the microbial enzyme transglutaminase (mTGase) under two conditions: above and below gelatin physical gelation temperature (ca. 23 degrees C). Hydrogels cross-linked at 37 degrees C, from the sol-state, are referred to as 'chemical' gels (C); hydrogels cross- linked at 21 degrees C, thus with concurrent physical gelation, are referred to as 'physical-co-chemical' gels (PC). The SANS data were appropriately described by a combination of a Lorentzian and a power law model. For physical gels, the correlation length (xi) obtained from the fits decreased linearly with gelatin concentration, from 42 to 26 angstrom for 3.5 to 10% w/w gelatin, respectively. Independently of gelation temperature, all physical gels at a given concentration showed a similar correlation length xi (26 +/- 2 angstrom), with no significant difference with the sol-state (23 +/- 2 angstrom). In both C and PC gels, xi increased with mTGase concentration over the range studied: 40 to 167 angstrom for 10 and 40 U mTGase per g gelatin in C gels (after 120 min cross-linking) and 40 to 82 angstrom for 10 and 40 U mTGase per g gelatin for PC gels. xi reached a plateau at the highest mTGase concentration studied for both types of gels. In addition, kinetic studies on C gels revealed that x increased linearly with time in the first two hours and grew faster with increasing mTGase concentration. xi values in the PC gels were smaller than in the corresponding C gels. Cell proliferation studies showed that the gels were compatible with cell growth and indicated no statistically relevant dependence on mTGase concentration for C gels. For PC gels, cell proliferation decreased with increases in mTGase concentration, by approximately 80% from 10 to 40 U mTGase per g gelatin. With the exception of the highest mTGase concentration studied, PC gels overall showed a slightly (but statistically significant) higher cell proliferation than the corresponding chemical gels.
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