Reversible hydrogel formation driven by protein-peptide-specific interaction and chondrocyte entrapment.

We developed a hydrogel self-assembling method driven by the interaction between recombinant tax-interactive protein-1 (TIP1) with the PDZ domain in a molecule, which is fused to each end of the triangular trimeric CutA protein (CutA-TIP1), and a PDZ domain-recognizable peptide which is covalently bound to each terminus of four-armed poly(ethylene glycol) (PDZ-peptide-PEG). Genetic manipulation based on molecular-dynamic simulation generated a cell-adhesive RGD tripeptidyl sequence in the CutA loop region [CutA(RGD)-TIP1]. Spontaneous viscoelastic hydrogel formation occurred when either CutA-TIP1- or CutA(RGD)-TIP1-containing buffer solution and PDZ-peptide-PEG-containing buffer solutions were stoichiometrically mixed. Dynamic viscoelasticity measurement revealed shear stress-dependent reversible-phase transformation: a spontaneous viscoelastic hydrogel was formed at low shear stress, but it was transformed into a sol at high shear stress. Upon the cessation of shear, hydrogel was restored. When chondrocytes were pre-mixed with one of these two components containing buffer solutions, the stoichiometric mixed solution was also spontaneously gelled. Individual rounded cells and multicellular aggregates were entrapped within both hydrogels without substantial cellular impairment regardless of the presence or absence of RGD motif in the CutA-TIP1 molecule. The potential use of such a shear-sensitive hydrogel for injectable cell delivery into diseased or lost cartilage tissue is discussed.