Int J Colorectal Dis (2011) 26:729–735 733 Fig. 3 Light microscopy of anastomoses from different groups. A control anastomosis at 3 and 7 days follow-up (a and b, respectively). At 3 days follow-up, a collagen fleece (asterisk) induced an intense inflammatory reaction (c, v=villi). At 7 days follow-up, the control (d) and the fibrin glue (e) groups showed comparable wound healing at might remodel further, possibly leading to resolution of the obstruction. Nevertheless, based on our findings, we consider the early period after colonic anastomosis with a collagen fleece at risk for obstruction. Many sheet-like structures have been tested for their ability to enhance anastomotic healing including collagen fleeces, dura mater fleeces, free peritoneal grafts, polyglycolic acid meshes, and an amniotic membrane [20, 21, 23–25]. Collagen fleeces are derived from the submuscular layer of porcine small bowel or from equine tendons, the latter being the source for the collagen fleeces in this study. At follow-ups longer than 30 days, a collagen fleece seems to be safe, but no significant improvements in bursting pressures have been observed [12]. At shorter follow-up, an impaired healing around the collagen fleece was found in our study and by others [26]. Comparable results were also found after application of dura mater, free peritoneal grafts, and polyglycolic meshes [21, 25]. A possible explanation is the intraluminal confinement of bacteria together with reduced peritoneal contact. Furthermore, one might argue that the avascular and xenograft nature of these sheets is a likely cause for the problems encountered. However, omentoplasties—both vascular and the patient's own—were not able to prevent anastomotic leakages in a large randomized clinical trial either [27]. So far, an amniotic membrane is the only fleece showing potential the luminal interface. In the collagen group (f), a more severe inflammation was still present (H&E staining, bars represent 500 μm (a and b, original magnification ×40) and 100 μm (c–f, original magnification ×100)) for anastomotic healing improvement in experimental studies [23, 28]. In this study, no significant differences were found between the fibrin glue group and the control and collagen fleece groups. Other experimental studies have demonstrated an inhibited anastomotic healing due to fibrin glue [14, 29]. In a randomized clinical trial, fibrin glue did not show any improvements on anastomotic leakage after laparoscopic rectal cancer resection [30]. Equally, fibrin glue did not show any improvements in two studies involving laparoscopic gastric bypasses [31, 32]. Yet, leakages after (colo) esophageal anastomoses in children were significantly reduced by fibrin glue [33, 34]. We used four polypropylene sutures in this rat model with colonic anastomoses. We chose unresorbable sutures for this short term follow-up study since we wanted to exclude as much as possible the possible interactions with resorbable materials other than fibrin glue and collagen fleece. Furthermore, apart from a single study in rats, experimental studies typically involved six or more sutures resulting in spontaneous leakage rates equal or close to zero [14]. Our model resulted in a 15% leakage rate which is comparable with leakage rates in humans. Although this mimics the clinical scenario better, outcomes may be less comparable with other experimental studies.