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Mishbak, et al.
Where W is the weight after lyophilization (n = 3 for 2% w/v obtained after 24 h of reaction show a clear Bingham
d
each time point). behavior . Results also show a decrease of the equivalent
[34]
viscosity by increasing the alginate concentration for
3. Results and Discussion samples obtained after 24 h of reaction, while no trend
was observed for samples obtained after 8 h of reaction.
3.1 Alginate Functionalization The flow behavior is also closer to a Newtonian fluid for
The alginate modification with MA was performed samples containing high concentrations of alginate. Based
under standard conditions, allowing the introduction of on these results, the system containing 2% w/v of alginate
photo-reactive methacrylate groups into the polymer
backbone, as confirmed by HNMR analysis (Figures 3-5). Table 1. Effect of reaction time on the modification degree of
1
Results indicate the presence of new characteristic alginate methacrylate
peaks of methacrylate (MA) at 5.63 ppm and 6.09 ppm Composition (% w/v) Reaction Degree of
attributed to the methylene group in the vinyl bond, and a time (hours) modification (%)
peak at 1.82 ppm assigned to the methyl group, which are 2% 8 21
not present in the non-modified polymer, showing that the 2% 24 33
polymers were successfully functionalized.
Two different functionalization reaction times (8 and Table 2. Rheological constants for solutions containing 15 mL of
24 h) were also considered and the degree of modification methacrylate and different alginate concentrations, 24 h
determined by dividing the relative integrations of Composition (%w/v) Equivalent Power law
methylene to carbohydrate protons [32,33] . Results, viscosity (Pa. s) constant
presented in Table 1, show that the degree of modification 1 4.36 0.23
increases by increasing the reaction time, reaching a 2 0.54 0.68
maximum value of 33% at 24 h. 3 0.16 0.72
3.2 Rheological Behavior of Pre-polymerized Table 3. Rheological constants for solutions containing 15 mL of
Alginate Methacrylate Systems methacrylate and different alginate concentrations, 8 h
Figures 6-9 showed the stress versus shear rate behavior Composition (%w/v) Equivalent Power law
of solutions containing 1, 2, and 3% (w/v) of alginate viscosity (Pa. s) constant
methacrylate reacted for 8 and 24 h. Key rheological 1 0.09 0.81
parameters are presented in Tables 2 and 3. A non-linear 2 0.48 0.48
behavior is observed for all samples. Samples containing 3 0.08 0.74

Figure 3. (a) Non-functionalized alginate (1% w/v), (b) functionalized alginate (1% w/v) after 8 h of reaction, (c) functionalized alginate
(1% w/v) after 24 h of reaction. The functionalization is confirmed by the presence of new peaks in the spectra at 5.63 ppm and 6.09 ppm
attributed to the methylene group and a peak at 1.82 ppm that corresponds to the methyl group.

International Journal of Bioprinting (2019)–Volume 5, Issue 2 15