Soft Matter Composites Interfacing with Biomolecules, Cells, and Tissues - Bioinspired Approaches for Human-Centric Technologies - page 42

Fig. 2.4 Photographs of Petri dishes containing heavily populated E. coli bacteria after 48 h
incubation in the presence of (a) 70 wt% NaAlg/30 wt% glycerol film (control film), (b)film
1, (c) film 2, and (d) film 3. The red noncontinuous line indicates the borders of the glass slide.
Photographs of Petri dishes containing C. albicans after 48 h incubation in the presence of (e)70wt%
NaAlg/30 wt% glycerol film, (f) film 1, (g) film 2, and (h) film 3. Film 1, film 2 and film 3 indicate
increasing concentrations of PVPI (Liakos et al. 2013 )
ionic interactions between carboxylic acids and divalent cations such as Ca 2+ ,Mg 2+ ,
and Ba 2+ as depicted in Fig. 2.8 . Applications of alginate hydrogels range from
injecting cells and drugs to wound dressings and dental implants due to their low
toxicity, low cost, and gelling ability by the action of divalent cations.
There is still an active research interest in rendering alginate-based hydrogels
more robust by controlling their mechanical and biophysical properties such as
elastic modulus, swelling ratio, and degradation rate, although control over rapid
ionic cross-linking and rapid loss of ions is still highly challenging. Therefore,
intermolecular cross-linking methods such as conjugating various types of cross-
linkers to the alginate backbone have been developed, but such reagents and
reaction conditions for conjugation and cross-linking are typically toxic to encapsu-
lated cells and can cause denaturation of growth factors or complications in wound
treatment and healing.
The structure and mechanical behavior of gelatin gels have already been widely
studied in the past (Wan et al. 2008 ; Van Vlierberghe et al. 2011 ; Mazzitelli
et al. 2013 ). Gelatin normally dissolves in aqueous solutions at temperatures around
body temperature where it exists as flexible single coils. On cooling down, trans-
parent gels are formed, if the concentration is higher than the critical gelation
concentration. These gels are formed by physical cross-links, also called “junction
zones,” originating from a partial transition to “ordered” triple-helical collagen-like
sequences, separated by peptide residues in the “disordered” conformation.
Because of its unique gelation and biomimetic properties, gelatin is interesting to
use as a hydrogel for biomedical applications (Van Vlierberghe et al. 2011 ). There
exist several methods to cross-link gelatin hydrogels. The disadvantage of most