Time course of membrane microarchitecture-driven neovascularization

The host response to a microporous material that induces neovascularization at the material-tissue interface was studied in terms of the number and types of cells invading the membrane, the degree of vascularization at the material-tissue interface, and the characteristics of the surrounding connective tissue as a function of time following implantation. Millipore-MF mixed esters of cellulose membranes with a nominal pore diameter of 8.0 μm were implanted subcutaneously into male Sprague-Dawley rats and explanted at 3, 5, 7, 10, 21 and 329 days post-implantation. Two samples from each of two devices at each implantation time were embedded in paraffin, sectioned to a thickness of 5 μm, and stained with haematoxylin and eosin for light microscopic observation. The density of cells in the membrane increased up to 7 days following implantation, then remained roughly constant through 21 days and decreased at the 329 day time point. The vascularity of the material-tissue interface increased up to 10 days and remained at this level even at 329 days post-implantation. The connective tissue was disorganized, loose and avascular at 3 days, resembled granulation tissue at 5 days, and underwent fibrous capsule formation and maturation starting at 7 days following implantation.