Researchers tested how a sleep‑related peptide (DSIP) can be trapped in different kinds of PVA‑based gels and how fast it comes out. The porous gels let the peptide spill out quickly (within minutes to a few hours), while the dense, non‑porous gels kept the peptide locked in even after two days.

The aim of the study was to entrap delta-sleep inducing peptide (DSIP) in cross-linked poly(vinyl alcohol)-based hydrogels of different structures and to evaluate peptide release kinetics from these hydrogels using an in vitro model. Isotropic and macroporous hydrogels on the basis of poly(vinyl alcohol) acrylic derivative (Acr-PVA) as well as macroporous hydogels containing epoxy groups which were synthesized by copolymerization of this monomer with glycidyl methacrylate. The isotropic hydrogels were fabricated at positive temperatures while the macroporous hydrogels (cryogels) were prepared at the temperatures below zero. The peptide was entrapped into macroporous modified PVA hydrogels by addition of a peptide solution on previously fabricated matrices, while into PVA-GMA hydrogels containing epoxy groups peptide immobilization was carried out by incubation of hydrogel matrices in the peptide solution. In the case of isotropic hydrogels the peptide was added into the polymer mixture at a hydrogel formation reaction. The peptide release kinetics was studied by incubation of hydrogels in PBS (pH 7.4), in physiological solution (0.9% NaCl) and in water. DSIP concentration in supernatants was determined by phase-reverse HPLC. DSIP release from the macroporous PVA hydrogel after 30 min incubation was 74, 70 and 64% in water, PBS and 0.9% NaCl, relatively, and it was completed in 3 hs. From the isotropic hydrogel the release neither peptide nor products of its degradation was not observed even after 48 hs of incubation. For freshly prepared hydrogel the release kinetics was as follows: 27 and 78% in 30 and 33 hs, relatively. In the case of the lyophilized hydrogel samples the peptide release was 63% in 30 min incubation while drying patterns at room temperature for 3 days resulted in significant peptide loss because its structure damage.