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Table 2 Compression tests on gels with different guluronate content with or without treatment with additional calcium

From: Rheological characterization of an injectable alginate gel system

  ~45% guluronate, no treatment ~70% guluronate, no treatment ~45% guluronate, Ca-treated ~70% guluronate, Ca-treated
Number of tests (n) 6 8 4 6
Young’s modulus (E, kPa) 20 ± 3 21 ± 1 90 ± 10  120 ± 10
Maximal stress (σ c,u , kPa) 6.4 ± 0.2 9.8 ± 0.4 59.0 ± 0.8 85 ± 4
Hencky strain at maximal stress (ε h,u ) 0.39 ± 0.01 0.62 ± 0.01 1.08 ± 0.04 0.92 ± 0.09
  1. Compression tests were performed on gels made from 1.5 ml 2% sodium alginate solution with a guluronate content of ~45% or ~70% and 1.5 ml of 2% calcium alginate dispersion. Gels were either left in the mold for approx. 3 hrs or left in the mold for 1.5 hrs and subsequently incubated in 0.55% w/w CaCl2 and 0.61% w/w NaCl for 2 hrs. Engineering stress (σ eng ) and strain (ε eng ) values were converted to corrected stress (σ c ) and Hencky’s strain (ε h ) according to eqs. 2 and 3. Young’s modulus was calculated as the initial linear slope of the resultant stress–strain plot. Ultimate stress was calculated as the upper inflection point of the stress–strain curve. In the case of Ca2+-treated gels, the inflection point, rather than an abrupt break, was the top of a plateau. All values are given as mean ± standard error, with the number of parallels given in the first row. There is no statistically significant difference between the Young’s moduli of gels having received the same treatment. Gels of similar composition (containing ~45% and ~70% guluronate in the sodium alginate component) but treated differently, show a statistically significant difference at the p < 0.01 and p < 0.001 level (based on corrected readings). For each formulation and treatment, maximal stress was statistically different from the others at p < 0.005. For untreated gels, the strain at maximal stress was statistically different at the p < 10−7 level for both corrected and uncorrected measurements. There was no such difference for treated gels (p = 0.37 and p = 0.15, respectively).