Selective Proteolytic Degradation of Guest-Host Assembled, Injectable Hyaluronic Acid Hydrogels.

There have been significant advances in the past decades toward the engineering of materials with biomimetic properties. In particular, hydrogels covalently cross-linked with protease degradable peptides have demonstrated the importance of protease mediated degradation for targeted therapeutic cargo delivery and controlling cell-material interactions. However, the incorporation of such degradation mechanisms into synthetic shear-thinning hydrogels has yet to be accomplished. Herein, we utilize supramolecular self-assembly mediated by the guest-host interaction of hyaluronic acid (HA) separately modified by adamantane (Ad) or cyclodextrin (CD) to form shear-thinning and self-healing hydrogels. In this design, Ad is bound to HA via a proteolytically degradable peptide tether (attached via Michael-addition of a cysteine residue in an Ad-terminated peptide with maleimide modified HA), enabling subsequent proteolytic degradation of the assembly. Upon mixing of the Ad-peptide modified HA and the CD modified HA, a supramolecular hydrogel was formed (' ≈ 300 Pa at 1 Hz), which displayed shear-thinning (>80% viscosity reduction at 0.5 s) and near-instantaneous self-healing properties. Rational, selective modification of amino acid residues near the proteolytic site enabled control over peptide cleavage kinetics, specifically with either collagenases or MMP-2. Hydrogel degradation, mediated by a combination of stochastically governed erosion and proteolytic degradation, was influenced by peptide susceptibility to proteolysis both in vitro and in vivo (>2 fold difference at 3 weeks in vivo) when injected subcutaneously. This material system provides unique opportunities for therapeutic delivery (e.g., growth factors, cells) through facile material formation, ease of injection, and bioresponsive material degradation.