Self-healing DNA-based injectable hydrogels with reversible covalent linkages for controlled drug delivery

Injectable hydrogels represent a valuable tool for the delivery of therapeutic molecules aimed to restore the functionality of damaged tissues. In this study, we report the design of a nanocomposite DNA-based hydrogel crosslinked with oxidized alginate (OA) via the formation of reversible imine linkages. The formulated hydrogel functioned as an injectable carrier for the sustained delivery of a small molecule drug, simvastatin. The degree of oxidation of alginate and the concentration of silicate-based nanoparticles (nSi) were varied to modulate the rheological properties of the hydrogels. Specifically, the formulations consisting of OA with higher degree of oxidation displayed the highest value of storage moduli, yield stress, yield strain, and rapid recovery after removal of cyclic stress. The hydrogel formulations exhibited self-healing and shear-thinning properties due to the reversible nature of the covalent imine bonds formed between the aldehyde groups of OA and the amine groups present in the DNA nucleotides. Moreover, the incorporation of charged nSi further enhanced the shear strength of the formulated hydrogels by establishing electrostatic interactions with the phosphate groups of the DNA network. The optimized hydrogel was able to promote the sustained release of simvastatin for more than a week. The bioactivity of the released drug was confirmed by testing its ability to induce osteogenic differentiation and migration of human adipose-derived stem cells in vitro. Overall, the results obtained from this study demonstrate that DNA could be used as a natural biopolymer to fabricate self-healing injectable hydrogels with sustained release properties for minimally invasive therapeutic approaches. STATEMENT OF SIGNIFICANCE: Dynamic covalent chemistry, especially Schiff base reactions have emerged as a promising route for the formation of injectable hydrogels. Our study demonstrated the development of a DNA-based self-healing hydrogel formed via Schiff base reaction occurring at physiological conditions. The hydrogels functioned as sustained delivery vehicles for the hydrophobic drug simvastatin, which requires a polymeric carrier for controlled delivery of therapeutic concentrations of the drug without exhibiting cytotoxic effects. Presently available hydrogel-based drug delivery systems encounter major challenges for the delivery of hydrophobic drugs due to the hydrophilic nature of the base matrix. Our strategy presents a platform technology for the design of minimally invasive approaches for the sustained delivery of hydrophobic drugs similar to simvastatin.