High-tough hydrogels formed via Schiff base reaction between PAMAM dendrimer and Tetra-PEG and their potential as dual-function delivery systems

One way to form tough hydrogels is to create structures with homogeneous networks, such as Tetra-PEG hydrogels. In the current work, Poly(amidoamine) (PAMAM) dendrimers were introduced into Tetra-PEG hydrogels via Schiff base reaction between NH2 groups on PAMAM and CHO groups on 4arm-PEG-aldehyde. The results indicated that the mechanical properties of PAMAM-Tetra-PEG hydrogels were very dependent on the generation of PAMAM. When PAMAM-G1 was introduced, nearly all of the formed hydrogels tended to be mucilage-like semisolids, while PAMAM-G3 or PAMAM-G5 was introduced, no matter what molecular weight or ratio of 4arm-PEG was paired with, the formed hydrogels tended to be solid elastomers, showing high compression strength (0.8722 MPa), and excellent fatigue resistance (~300 cycles of loading-unloading under strain of 90%). The swelling properties of the PAMAM-Tetra-PEG hydrogels were mainly affected by the 4arm-PEG molecular weight, PAMAM generation, and component ratio between PAMAM and 4arm-PEG, reaching to the highest swelling capacity of 1008%. SEM and SAXS confirmed that the formed PAMAM-Tetra-PEG hydrogels were comprised of very uniform networks. Additionally, because of well-defined hydrophobic empty cavities in high-generation PAMAM, the PAMAM-G5-Tetra-PEG hydrogels showed dual-embedding capacity for both hydrophilic and hydrophobic substances, and had potential as dual-function delivery systems.