Distribution of cells in soft tissue and fluid space around hollow and solid implants in the rat

The development of the tissue surrounding an implanted material is anticipated to be regulated by the biological factors in the interface as well as the physicochemical properties of the implant material. In the present study light microscopic morphometry and transmission electron microscopy were used to evaluate the distribution of cells adjacent to the implant surface of different implant designs (hollow and solid implants) and materials (titanium and polytetrafluoroethylene). An increased number of leukocytes, predominantly PMN, was retrieved from the exudate inside hollow implants 1 and 9 days after surgery. In contrast, the increased cellularity in the soft tissue around the hollow implants was mainly due to an increased number of monocytes/macrophages and fibroblasts. The presence of a fluid space around both hollow and solid implants was revealed by the use of an electropolishing technique and ground sections. In the fluid space around solid titanium the concentration of leukocytes and the proportion of PMN decreased between 1 and 7 days. After 1 day the majority of leukocytes were freely suspended in the fluid and were rarely directly apposed to the implant surface. A majority of the monocytes/macrophages present in the fluid space after 7 days were attached to the fibrin matrix at the border between the fluid space and the reorganized tissue. Our studies demonstrate that hollow implants promote the influx and a persistence of PMN in the interior of the implant in comparison with the tissue surrounding the hollow and solid implants. Furthermore, during the first week after implantation inflammatory cells are not preferentially distributed directly on the titanium implant surface.