S.A.J. Zaat

In vitro and in vivo evaluation of gelatin-chondroitin sulphate hydrogels for controlled release of antibacterial proteins.

Chemically cross-linked gelatin-chondroitin sulphate (ChS) hydrogels, impregnated in Dacron, were evaluated as drug delivery systems for antibacterial proteins. The gelatin-chondroitin sulphate gels, plain or impregnated in Dacron, were cross-linked with a water-soluble carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The release of lysozyme and recombinant thrombocidin (rTC-1), an antibacterial protein derived from human blood platelets, from the gelatin-ChS gels in Dacron in phosphate-buffered saline at 37 degrees C was determined, and compared to the release from gelatin gels in Dacron and plain gelatin-ChS gels. The incorporation of chondroitin sulphate into gelatin gels, caused a marked increase in lysozyme loading capacity, and a slower release rate. The relative release profiles for rTC-1 and lysozyme were equal for cross-linked gelatin as well as for cross-linked gelatin-ChS gels. Furthermore, rTC-1 showed no loss of antibacterial activity after 1 week of release. The lysozyme concentration profiles in the samples and in the surrounding medium as a function of time were calculated using mathematical solutions for Ficks second law of diffusion for a semi-infinite composite medium, which is a schematic representation of a slab in a surrounding medium. The biocompatibility and degradation of the Dacron matrices impregnated with gelatin-ChS gels was studied after implantation in subcutaneous pockets in rats. Chemically cross-linked gelatin-Ch5 gels showed a mild tissue reaction, and almost complete degradation within 18 weeks of implantation.

In vivo compatibility and degradation of crosslinked gelatin gels incorporated in knitted Dacron

Gelatin gels were applied to porous Dacron meshes with the aim of using these gels for local drug delivery. In this article, the biocompatibility and degradation of gelatin gels with different crosslink densities applied in Dacron were studied in vivo by subcutaneous implantation in rats. Dacron discs were treated with carbon dioxide gas plasma to improve hydrophilicity, and subsequently impregnated with gelatin type B. The gelatin samples were crosslinked to different extents using various amounts of water-soluble carbodiimide (EDC) and N-hydroxysuccinimide (NHS). After 6 h, 2, 5, and 10 days, and 3, 6, and 10 weeks of postimplantation, the tissue reactions and biodegradation were studied by light microscopy. The early reaction of macrophages and polymorphonuclear cells to crosslinked gelatin was similar to or milder than Dacron. Giant cell formation was predominantly aimed at Dacron fibers and was markedly reduced in the presence of a crosslinked gelatin coating. At week 10 of implantation, the crosslinked gelatin gels were still present in the Dacron matrix. The gelatin degradation was less for samples with the highest crosslink density. The gelatin gel with the lowest crosslink density showed clear cellular ingrowth, starting after 6 weeks of implantation. The intermediate and high crosslinked gelatin gels showed little or no ingrowth. In these gels, giant cells were involved in the phagocytosis of gelatin parts at week 10. Application of carbodiimide crosslinked gelatin gels in Dacron is suitable for medical applications because of the good biocompatibility of the gels and the possibility of adapting the degradation rate of gelatin to a specific application.

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 antibacterial proteins from the Dacron sewing ring of a prosthetic heart valve. Dacron discs were treated with a carbon dioxide gas plasma to improve the hydrophilicity and thereby enabling homogeneous impregnation with gelatin type B. The gelatin samples were cross-linked to different degrees using various amounts of water-soluble carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Lysozyme, a model protein for antibacterial proteins, was loaded into (non)-cross-linked gelatin gels incorporated in Dacron, or adsorbed onto non-treated and gas plasma-treated Dacron. The in vivo lysozyme release was measured after subcutaneous implantation of lysozyme-loaded samples in rats. The lysozyme content of the samples, and the lysozyme level of the surrounding 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 solution under sink conditions was in good agreement with the in vivo lysozyme release profiles, and therefore considered a good model to describe in vivo release characteristics. The release was modelled with a solution of Ficks 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 gelatin in Dacron did lead to an increased uptake of lysozyme and a delayed release during 30 h after implantation, whereas a burst release took place from Dacron, gas plasma-treated Dacron, or Dacron containing non-cross-linked gelatin.

Presence of a biomaterial implant facilitates induction of experimental infective endocarditis due to streptococci and staphylococci

Infective endocarditis (IE) usually is studied using animals with catheters inserted into the heart, which causes formation of platelet-fibrin thrombi (vegetations, VGs). We used two rabbit models to study the respective roles of the catheter and the VGs in the development of IE. The influence of the catheter was studied by either removing the catheter before bacterial challenge, or leaving the catheter in place. In all cases, removal of the catheter caused a strong decrease in the frequency of IE. The presence of the catheter stimulated population increase of streptococci within 4 h after challenge. As most catheters were sterile 4 h after challenge, they did not serve as a reservoir of bacteria. To study the requirement of a preformed VG catheters were inserted either 24 h or 30 min before bacterial challenge. In the former model VGs were present, in the latter VGs were not yet formed when bacteria were injected. The frequencies of IE due to 2 S. sanguis and 2 S.epidermidis strains in the 24 h model or 30 min model were similar, indicating that a preformed VG is not necessary for development of IE. Five coagulase-negative stains were shown to vary in their capacity to cause IE in the 30 min model. Variation was not caused by differences in early adhesion or colonization of the aortic valve, but reflects differences in persistence after initial colonization. Like in the 24 h model, persistence of the bacteria was greatly enhanced by the continuous presence of the catheter. Possible mechanisms of the infection-potentiating effect of the catheters are discussed.

Biomimetic implants for pelvic floor repair

Polypropylene implants are used for the reconstructive surgery of urogynaecological disorders like pelvic organ prolapse, but severe complications associated with their use have been reported. There is evidence that surface properties and a difference in mechanical stiffness between the implant and the host tissue contribute to these adverse events. Electrospinning is an innovative engineering alternative that provides a biomimetic microstructure for implants, resulting in a different mechano‐biological performance.