Low-Cost Advanced Hydrogels of Calcium Alginate/Carbon Nanofibers with Enhanced Water Diffusion and Compression Properties

Abstract

A series of alginate films was synthesised with several calcium chloride cross-linker contents (from 3 to 18% w/w) with and without a very low amount (0.1% w/w) of carbon nanofibers (CNFs) in order to reduce the production costs as much as possible. The results of this study showed a very significant enhancement of liquid water diffusion and mechanical compressive modulus for high calcium chloride contents when this minuscule amount of CNFs is incorporated into calcium alginate hydrogels. These excellent results are attributed to a double cross-linking process, in which calcium cations are capable of cross-linking both alginate chains and CNFs creating a reinforced structure exhibiting ultrafast water diffusion through carbon nanochannels. Thus, these excellent results render these new alginate composites very promising for many bioengineering fields in need of low-cost advanced hydrogels with superior water diffusion and compression properties.

Keywords: Raman spectroscopy; calcium alginate; carbon nanofibers; composite hydrogels; compression performance; electron microscopy; water diffusion.

Figure 1

Water contents (grams of absorbed water per grams of dry sample) at 24 ± 0.5 °C represented as mean ± standard deviation for alginate hydrogels synthesised with several calcium chloride contents (a) and with also the addition of 0.1% w/w of CNFs (b).

Figure 2

Apparent diffusion coefficients (D) of liquid water in the alginate hydrogels (grey columns) and in the composite alginate hydrogels with 0.1% w/w of CNFs (black columns) with the indicated cross-linker contents (3, 6, 12 and 18% w/w). Data are represented as mean ± standard deviation.

Figure 3

HR-TEM of the CNFs at two magnifications (a,b) and TEM of A18-CNFs (c).

Figure 4

Elementary composition of the carbon nanofibers with and without cross-linking with Ca²⁺ measured by EDS at 20 kV.

Figure 5

Raman spectra of CNFs and CNFs cross-linked with calcium cations.

Figure 6

Mechanical compressive modulus (mean ± standard deviation) of alginate hydrogels (grey columns) and alginate composite hydrogels with 0.1% w/w of CNFs (black columns) cross-linked with increasing amounts of calcium chloride (3, 6, 12 and 18% w/w).