Tissue storage ex vivo significantly increases vascular fusion bursting pressure.

INTRODUCTION: Harvested biological tissue is a common medium for surgical device assessment in a laboratory setting; this study aims to differentiate between surgical device performance in the clinical and laboratory environments prior to and following tissue storage. Vascular tissue fusion devices are sensitive to tissue-device temperature gradients, tissue pre-stretch in vivo and tissue water content, each of which can vary during tissue storage. In this study, we compare the results of tissue fusion prior to and following storage using a standardized bursting pressure protocol. METHODS: Epigastric veins from seven porcine models were subject to identical bursting pressure protocols after fusion. One half of each vein was fused in vivo, harvested and immediately analyzed for burst pressure; the remainder was stored (0.9% Phosphate Buffered Saline, 24h, 4 °C) and then analyzed ex vivo. Histological slides were prepared for qualitative analysis of in versus ex vivo fusions. RESULTS: Bursting pressures of vessels fused ex vivo (514.7 ± 187.0 mmHg) were significantly greater than those of vessels fused in vivo (310 ± 127.7 mmHg, p = 2.06 E-10). Histological imaging of venous axial cross-sections indicated the lamination of adventitia and media layers ex vivo, whereas in vivo samples consisted only of adventitia. CONCLUSION: These findings suggest that the fusion of porcine venous tissue ex vivo may overestimate the clinical performance of fusion devices. Prior work has indicated that increased tissue hydration and the lamination of tissue layers both positively affect arterial fusion bursting pressures. The bursting pressure increase observed herein may therefore be due to storage-induced alterations in tissue composition and mechanics of the fusion interface. While harvested tissue provides an accessible medium for comparative study, the fusion of vascular tissue in vivo may avoid storage-induced biomechanical alterations and is likely a better indicator of fusion device performance in a clinical setting.

Strength and Persistence of Energy-Based Vessel Seals Rely on Tissue Water and Glycosaminoglycan Content.

Vessel ligation using energy-based surgical devices is steadily replacing conventional closure methods during minimally invasive and open procedures. In exploring the molecular nature of thermally-induced tissue bonds, novel applications for surgical resection and repair may be revealed. This work presents an analysis of the influence of unbound water and hydrophilic glycosaminoglycans on the formation and resilience of vascular seals via: (a) changes in pre-fusion tissue hydration, (b) the enzymatic digestion of glycosaminoglycans (GAGs) prior to fusion and (c) the rehydration of vascular seals following fusion. An 11% increase in pre-fusion unbound water led to an 84% rise in vascular seal strength. The digestion of GAGs prior to fusion led to increases of up to 82% in seal strength, while the rehydration of native and GAG-digested vascular seals decreased strengths by 41 and 44%, respectively. The effects of increased unbound water content prior to fusion combined with the effects of seal rehydration after fusion suggest that the heat-induced displacement of tissue water is a major contributor to tissue adhesion during energy-based vessel sealing. The effects of pre-fusion GAG-digestion on seal integrity indicate that GAGs are inhibitory to the bond formation process during thermal ligation. GAG digestion may allow for increased water transport and protein interaction during the fusion process, leading to the formation of stronger bonds. These findings provide insight into the physiochemical nature of the fusion bond, its potential for optimization in vascular closure and its application to novel strategies for vascular resection and repair.

Evaluating temperature and duration in arterial tissue fusion to maximize bond strength.

Tissue fusion is a growing area of medical research that enables mechanical closure of tissues without the need of foreign bodies such as sutures or staples. Utilizing heat and pressure applied for a specified time, a bond can be formed between adjacent tissues. The success or failure of tissue fusion is contingent upon the strength of the bond it creates between opposing tissues, yet little characterization has been done to measure the strength of this interface as a function of the input parameters, such as heat and pressure. Previous studies have examined the strength of tissue fusion using clinically relevant outcomes such as bursting pressure or tearing strength, but none have explored metrics more appropriate for determining the mechanics of the actual bond such as peel or shear strengths. The goal of this study is to establish methodology for T-peel and lap shear testing of fused tissues and measure the fusion bonding strength as a function of temperature and time using the ConMed Altrus(®) laparoscopic thermal fusion device. Across five temperatures (120, 140, 150, 160, 170°C) and four time durations (500, 1000, 1800, 3000ms) the mean peeling strength, ultimate shear strength, and bursting pressure of fused porcine splenic arteries were measured. The shear strength increased with increasing temperature and time with an ultimate shear strength at 160°C and 3000ms equal to 290 ± 99Pa. No trend was observed between the input parameters of time and applied temperature and the mean peeling force, although there were significant differences between groups. The bursting pressure increased significantly with increasing durations, but no trend was noted between temperature and bursting pressure. The shear strength data suggest there is some physical or chemical reaction which occurs in the tissue between 120°C and 150°C which provides a stronger bond. The shear and peel results also reveal that the fusion bond undergoes brittle failure. This study suggests that the tissue fusion bond is maximized at temperatures over 150°C and at a time of 3000ms using the ConMed Altrus(®) and that input parameters can be tuned to optimize the strength of the bonded region.

Temperature measurement methods during direct heat arterial tissue fusion.

Fusion of biological tissues through direct and indirect heating is a growing area of medical research, yet there are still major gaps in understanding this procedure. Several companies have developed devices which fuse blood vessels, but little is known about the tissue's response to the stimuli. The need for accurate measurements of tissue behavior during tissue fusion is essential for the continued development and improvement of energy delivery devices. An experimental study was performed to measure the temperatures experienced during tissue fusion and the resulting burst pressure of the fused arteries. An array of thermocouples was placed in the lumen of a porcine splenic artery segment and sealed using a ConMed Altrus thermal fusion device. The temperatures within the tissue, in the device, and at the tissue-device interface were recorded. These measurements were then analyzed to calculate the temperature profile in the lumen of the artery. The temperature in the artery at the site of tissue fusion was measured to range from 142 to 163 °C using the ConMed Altrus. The corresponding burst pressure for arteries fused at this temperature was measured as 416 ± 79 mmHg. This study represents the first known experimental measurement of temperature at the site of vessel sealing found in the literature.