Small fiber diameter fibro-porous meshes: Tissue response sensitivity to fiber spacing

The purpose of this research was to determine if fiber spacing for small fiber diameter fibro-porous meshes affected tissue response in vivo. Disk-shaped polyurethane meshes, with mean fiber diameters of 7.6 microm and fiber spacing between 6 and 68 microm, were implanted in rat subcutaneous dorsum for 5-week intervals and then prepared for light microscopy and morphological analysis. Results showed that implants with 12- to 68-microm spacing had no histologically apparent fibrous capsule around the perimeter, a result different from that for 6-microm spacing samples that had a capsule around a mean of 34.2% of the perimeter. For the 12- to 68-microm spacing range, a mean of 21.0% of individual fibers within the meshes were encapsulated. Qualitatively, it appeared that larger fibers were encapsulated more frequently than smaller ones. When nodeless or baggy meshes were implanted, cells tended to cluster three or more fibers into groups and then encapsulate each group. Over the 6- to 68-microm spacing range, cell nuclei volume fraction within the meshes increased from the 6- to the 29-microm spacing (p = 0.000) and then decreased from the 29- to the 68-microm spacing (p = 0.015). There was a trend of an increase in local vessel volume fraction with spacing over the 6- to 68-microm range, though the relationship was weak. The results indicate that the reason for the lack of encapsulation of small-fiber fibro-porous meshes is not exclusively a pore boundary explanation, as is proposed for small-pore porous meshes.

Biomaterial Mesh Seeded with Vascular Remnants from a Quail Embryo Has a Significant and Fast Vascular Templating Effect on Host Implant Tissue

Seeding biomaterial implants with vascular remnants has the potential to facilitate host vessel ingrowth via a vascular templating effect. Vessels from quail embryo were grown into a polyurethane fibroporous mesh and the samples were frozen-thawed and then implanted in rat subcutaneous dorsum. Results show that the process of revascularization, using the quail vessel remnants, occurred over the first 3 days after implantation and resulted in functional vessels. Rat endothelial cells were found in the quail templates on day 1. On day 2 the endothelial cells formed a confluent layer and started producing laminin. By this time approximately 70% of the rat vessel tissue in the implant had grown into quail vascular remnants, indicating that the quail vessels were extensively used as templates for host vessel ingrowth. Laminin production was increased and collagen production started by day 3, at which time the vessels were functional in that rat blood flowed through them. At 2 weeks host vessel density was approximately twice that of control samples; thus the implant substantially enhanced the size of the vascular network. For meshes that additionally received vascular endothelial growth factor (VEGF) seeding before implantation, vessel density at 2 weeks was enhanced over samples with quail embryo alone. However, the quail was found to have the greatest angiogenic effect above any of the implant components-quail, VEGF, and collagen. Tissue engineering of vessel templates may thus be a realistic solution to effective fast vascularization of biomaterials.