Table II.
Variables Used in D-optimal Response Surface Design
| Independent variables (factors) | Levels | |||
| −1 | +1 | |||
| Numeric factors | Polymer pH (X 1) | 3.0 | 6.5 | |
| Concentration ratio of polymer/insulin (X 2) | 0.5 | 2.0 | ||
| Categorical factor | Polymer type (X 3) | A | B | C |
| Methylated N-(4-N,N-dimethylaminobenzyl) chitosan | Methylated N-(4-pyridin) chitosan | Methylated N-(benzyl) chitosan | ||
| Dependent variables (responses) | Constrains | |||
| Y 1 = size (nm) | Minimize | |||
| Y 2 = zeta potential (mV) | 20 < Y 2 < 30 | |||
| Y 3 = PdI | Minimize | |||
| Y 4 = EE% | Maximize | |||
EE% entrapment efficiency