The physical and biological properties of laser/light activated soldered micro-anastomoses

The ideal anastomosis is one that reproduces the continuity of the vessel, causing the least disruption of blood How and retains the endothelial lining of the vessel without inducing a foreign body or immune reaction. Laser anastomosis caused aneurysm formation and led to the introduction of tissue solder. These reduced the complications but had found limited application in clinical practice. In conjunction with Tissuemed, it was hoped to produce a commercially viable tissue solder that could be used in the formation of vascular anastomoses. Due to the commercial nature of the project, much of the experimental design and rationale were dictated by the requirements of the regulatory authorities (LRQA) for CE marking. Initial work focused on the precise proportions of MB in the solder, while PSA proportions were well reported in literature. Changes in the concentration of solder chromophores had not been investigated or reported by other groups. It was therefore proposed to characterise the solder strength as a function of MB concentration and solder absorption. The solder was seen to deviate from a linear Beer-Lambert relationship. As a result of this study, MB concentration of 0.24%w/w was chosen for inclusion into the solder to be submitted to LRQA. The requirements of the regulatory authorities included data on the solder reabsorbtion, as well as histological evidence of its biocompatibility. In order to determine the lifespan of the solder in vivo radio-labeling was undertaken and histological markers, such as thrombosis, intimal hyperplasia and chronic inflammation, were investigated. The hypothesis for this experiment was that the solder did not remain in the body for more than 90 days and could therefore be classified as a temporary implant (EU Council directive 93/42eeu) and would not induce an adverse tissue reaction. As a result of this study it was noted that improved patency could be achieved with a lower laser power. For reasons of cost and safety a move away from lasers was made. In place a filtered xenon arc lamp was constructed. Equivalence with the laser was demonstrated both in vitro and in vivo, showing that the lamp was able to produce a soldered anastomosis of similar burst strength and histological appearance to lasered anastomoses. Previous studies had not looked at solders in vivo beyond 90 days. Since the onset of aneurysms from lasered anastomoses were a late event, it was essential to demonstrate that this had been resolved with the use of solders. Three and six month anastomoses were produced and showed a complete absence of aneurysms or other complications. The solder contains porcine albumin and therefore a measure of the antigenicity of this protein was determined by observing the immune response. A worst-case scenario was produced with pre-sensitised and naive animals. No pathological effects were observed either systemically or in immune complex deposition in the kidneys. These results together with the previous data contributed to the solder and white light source being awarded CE marks. Vascular compliance is an important factor in both short and long term patency. Therefore the physical characteristics of the solder were investigated by measuring the compliance compared to a continuous sutured anastomosis. It was determined that there was an increase in compliance associated with the use of solder over continuous but not interrupted suture techniques. The use of the solder as a sealant was seen to leave the sutured anastomotic compliance unchanged. Finally, as a prelude to clinical studies, the use of solder as a haemostatic sealant was studied in cases of anastomoses formed using ePTFE graft material. There was a significant reduction in blood loss (p<0.05) and bleeding time (p<0.05) but the difference in overall haemostatic time was not significantly altered over simple compression (p=0.065).