In vivo and in vitro release of lysozyme from cross-linked gelatin hydrogels: a model system for the delivery of antibacterial proteins from prosthetic heart valves

Prosthetic valve endocarditis may be reduced by the local delivery of antib acterial proteins from the Dacron sewing ring of a prosthetic heart valve. Dacron discs were treated with a carbon dioxide gas plasma to improve the h ydrophilicity and thereby enabling homogeneous impregnation with gelatin ty pe B. The gelatin samples were cross-linked to different degrees using vari ous amounts of water-soluble carbodiimide (EDC) and N-hydroxysuccinimide (N HS). Lysozyme, a model protein for antibacterial proteins, was loaded into (non)-cross-linked gelatin gels incorporated in Dacron, or adsorbed onto no n-treated and gas plasma-treated Dacron. The in vivo lysozyme release was m easured after subcutaneous implantation of lysozyme-loaded samples in rats. The lysozyme content of the samples, and the lysozyme level of the surroun ding tissue were determined at different explantation times (ranging from 6 h up to 1 week). For cross-linked gelatin gels, the lysozyme tissue level was elevated up to 2 days after implantation. In vitro release was measured using agarose medium or phosphate buffer. Lysozyme release in buffer solut ion under sink conditions was in good agreement with the in vivo lysozyme r elease profiles, and therefore considered a good model to describe in vivo release characteristics. The release was modelled with a solution of Fick's second law of diffusion using the appropriate boundary conditions. In this way the lysozyme concentration in the gel and the surrounding tissue as a function of time and distance was obtained. The presence of cross-linked ge latin in Dacron did lead to an increased uptake of lysozyme and a delayed r elease during 30 h after implantation, whereas a burst release took place f rom Dacron, gas plasma-treated Dacron, or Dacron containing non-cross-linke d gelatin. (C) 2000 Elsevier Science B.V. All rights reserved.