Fig. 2. Characterization of BA hydrogel. (A) NIR spectra. The BA and BA hydrogel (BA : B = 100 mM : 200 mM) were freeze-dried under pH 9.0 solution. (B) ¹H-NMR spectra; the BA, Na₂B₄O₇, were dissolved in D₂O under pH 9.0 to prepare the NMR-sample. (C) Photography of hydrogel made in different shapes.