Bicomponent Vascular Grafts Consisting of Synthetic Absorbable Fibers: Part II: In Vivo Healing Response

Abstract

The objectives of this research were (I) to determine whether the use of partially absorbable vascular grafts would improve their nonthrombogenic performance and whether they are more prone to aneurysmal dilation and subsequent failure in vivo. and (2) to find out the relationships, if any. between these in vivo and the previously reported in vitro data with an emphasis on how the in vitro changes in fabric structure and properties related to these in vivo data. Bicomponent vascular fabrics were made from Dacron and polyglycolic acid (PGA) yarns with a range of composition ratios of the PGA to Dacron. Both woven and single Jersey knit fabrics were made, and implanted in dogs for 4 months. The following findings and relationships were obtained. (1) The bicomponent vascular fabrics resulted in a full-wall healing in the thoracic aorta of dogs. All bicomponent vascular grafts in survived dogs exhibited 100% patency, no thrombus or aneurysmal formation, no hematoma or seroma around the grafts, and no fibrin coagula in the inner capsules. The gross morphology of the regenerated tissues was very similar visually to the adjacent original arterial tissue. Histologically, the luminal surface was lined with a layer of endothelial cells with myofibroblasts, fibroblasts. and collagens underneath. (2) The extent of the full-wall healing depended on the type of fabric structure. the concentration of absorbable yarns, the location of absorbable yarns (for the woven group only), and initial water permeability. It is believed that the concentration effect was related to the level of macrophage activation from the degradation products of the absorbable yarns, while the location effect was attributed to the various types of fabric structure change on the degradation of the absorbable yarns. (3) In general, the knitted group (K), was better than the woven group (W). K3 showed the best in vivo performance in the knitted group. (4) In the woven group, W3 was the best. The incorporation of absorbable yarns in the weft direction of the bicomponent fabrics (W3) resulted in a velourlike, loose and porous fabric surface for facilitating tissue ingrowth. The placement of absorbable yarns in the warp direction (W1), however, did not show this unique surface morphology. Calcification was, however, occasionally observed in the woven samples with low initial water permeability. These observed in vivo performances correlated well with our previously reported in vitro study.

Key Words:

• synthetic vascular grafts
• absorbable fibers
• biodegradation
• animal implantation
• tissue ingrowth
• endothelial cell lining