Expanding the range of available isoelectric points of highly methacryloylated gelatin

Cross-linkable gelatin methacryloyl (GM) is widely used for the generation of artificial extracellular matrix in tissue engineering. However, so far, isoelectric points (IEPs) of highly methacryloylated GM derivatives are limited to IEPs below 7 due to the consumption of amino groups in the modification reaction. In this contribution, the synthesis of a new GM derivative, gelatin methacryloyl-aminoethyl (GME), with an IEP above 7 similar to the gelatin type A (GA) starting material is reported, together with a high degree of methacryloylation. GME is obtained by reacting GM with ethylenediamine (EDA). The impact of the EDA functionalization on the properties of GM and GME derivatives is characterized thoroughly via 1H-NMR, 1H-13C-HSQC-NMR, IEP, solution viscosity, gel point, and physico-chemical properties of resulting hydrogels. The second functionalization step results in amino group concentrations similar to GA and with that in an IEP of 9.9. The data suggest that amino functionalization with EDA prevents physical cross-linking in the same way as described before for acetyl functionalization. Therefore, GME hydrogels are less stiff than GM hydrogels from GMs with a comparable amount of methacrylic functions. With GME, a gelatin derivative is available that is positively charged at neutral pH without being limited to low methacryl modifications.