Enhanced Perigraft Angiogenesis Prevents Prosthetic Graft Infection

Pre-clinical in vivo Models of Vascular Graft Coating in the Prevention of Vascular Graft Infection: A Systematic Review

OBJECTIVE

Vascular graft infection (VGI) remains an important complication with a high mortality and morbidity rate. Currently, studies focusing on the role of vascular graft coatings in the prevention of VGI are scarce. Therefore, the aims of this study were to survey and summarise key features of pre-clinical in vivo models that have been used to investigate coating strategies to prevent VGI and to set up an ideal model that can be used in future preclinical research.

DATA SOURCES

A systematic review was conducted in accordance with the Preferred reporting items for Systematic Reviews and Meta-Analysis guidelines. A comprehensive search was performed in MEDLINE (PubMed), Embase, and Web of Science.

REVIEW METHODS

For each database, a specific search strategy was developed. Quality was assessed with the Toxicological data Reliability Assessment Tool (ToxRTool). The type of animal model, graft, coating, and pathogen were summarised. The outcome assessment in each study was evaluated.

RESULTS

In total, 4 667 studies were identified, of which 94 papers focusing on in vivo testing were included. Staphylococcus aureus was the organism most used (n = 65; 67.7%). Most of the graft types were polyester grafts. Rifampicin was the most frequently used antibiotic coating (n = 43, 48.3%). In the outcome assessment, most studies mentioned colony forming unit count (n = 88; 91.7%) and clinical outcome (n = 72; 75%). According to the ToxRTool, 21 (22.3%, n = 21/94) studies were considered to be not reliable.

CONCLUSION

Currently published in vivo models are very miscellaneous. More attention should be paid to the methodology of these pre-clinical reports when transferring novel graft coatings into clinical practice. Variables used in pre-clinical reports (bacterial strain, duration of activity coating) do not correspond well to current clinical studies. Based on the results of this review, a proposal for a complete and comprehensive set up for pre-clinical invivo testing of anti-infectious properties of vascular graft coatings was defined.

Nitric oxide-releasing vascular grafts: A therapeutic strategy to promote angiogenic activity and endothelium regeneration

Small-diameter vascular grafts (SDVGs) are associated with a high incidence of failure due to infection and obstruction. Although several vascular grafts are commercially available, specific anatomical differences of defect sites require patient-based design and fabrication. Design and fabrication of such custom-tailored grafts are possible with 3d-printing technology. The aim of this study is to develop 3d-printed SDVGs with a nitric oxide (NO)-releasing coating to improve the success rate of implantation. The SDVGs were printed from polylactic acid and coated with blending of 10 wt% S-nitroso-N-acetyl-D-penicillamine into the polymeric substrate consisting of poly (ethylene glycol) and polycaprolactone. Our results show that NO is released in the physiological range (0.5-4 × 10^-10 mol·cm^-2·min^-1) for 14 days and NO-releasing coating showed significant antibacterial potential against Gram-positive and Gram-negative strains. It was shown that both NO-releasing and control grafts are biocompatible in-vitro and in-vivo. Interestingly, the NO-releasing SDVGs dramatically enhanced ECs proliferation and significantly enhanced ECs migration in-vitro compared to control grafts. In addition, the NO-releasing SDVGs showed angiogenic potential in-vivo which can further prove the results of our in-vitro study. These findings are expected to facilitate tissue regeneration and integration of custom-made vascular implants with enhanced clinical success. STATEMENT OF SIGNIFICANCE: A series of 3d-printed small-diameter vascular grafts (SDVGs, <6 mm) with controlled release of nitric oxide (NO) were prepared to combine the advantages of 3D printing technology and NO-releasing systems. The resulting NO-releasing grafts were promisingly showing sustained NO release in the physiological range over a two weeks period. In addition to the evaluation of endothelial cell migration in-vitro, we implanted for the first time the NO-releasing vascular grafts in a chick chorioallantoic membrane (CAM) to investigate the effect of the prepared grafts on the angiogenesis in-vivo. The fabricated grafts also exhibited bactericidal properties which prevent the formation of a biofilm layer and can thereby enhance the chance of endothelialization on the surface. Taken together, the innovative combination of rapid and highly accurate 3d-printing technology as a patient-specific fabrication method with NO-releasing coating represents a promising approach to develop bactericidal SDVGs with improved endothelialization.

Oesophageal mucosal blood flow changes after thoracic endovascular stent graft implantation using a novel sensor probe

OBJECTIVES

Secondary aorto-oesophageal fistula is a rare, lethal complication occurring after thoracic endovascular aneurysmal repair. The cause of secondary aorto-oesophageal fistula is unknown, but a reduction in local oesophageal mucosal blood flow (OMBF) may be a basis for such a devastating sequela. Our study aims to develop a novel blood flow sensor probe to detect changes in OMBF after thoracic stent graft implantation in an experimental swine model.

METHODS

A novel laser Doppler flowmetry sensor probe incorporating an optical fibre sensor within a nasogastric tube was developed using microelectromechanical system technology. OMBF was measured at various levels using this sensor probe, to test its feasibility before and after thoracic endovascular stent graft implantation covering Th4-Th8 vertebral levels in 6 swine.

RESULTS

In the middle oesophagus (Th5-Th7), where the aorta was covered with a stent graft, the measured OMBFs were significantly decreased after thoracic endovascular stent graft implantation than those of baseline (8.6 ± 2.7 vs 18.4 ± 7.9 ml/min/100 g, P < 0.0001), followed by a plateau period for at least 2 h after stent grafting (8.7 ± 3.3 ml/min/100 g, P < 0.0001 vs baseline). OMBFs in the upper (Th1-Th3) and lower (Th9-Th11) oesophagus, where the aorta was not covered with a stent graft, were unaffected by thoracic endovascular stent grafting.

CONCLUSIONS

The novel laser Doppler flowmetry sensor probe was useful to monitor precise changes of OMBF in a swine model, demonstrating a significant reduction in OMBF after thoracic endovascular stent graft implantation.

Suppression of aortic expansion and contractile recovery in a rat abdominal aortic aneurysm model by biodegradable gelatin hydrogel sheet incorporating basic fibroblast growth factor

Biodegradable gelatin hydrogel sheet (BGHS) incorporating basic fibroblast growth factor (bFGF) may inhibit the progression of abdominal aortic aneurysm (AAA). We investigated whether AAA in a rat model treated with BGHS soaked with bFGF can suppress aortic expansion and recover the contractile response of aneurysmal aortic wall. Experimental AAA was induced in 10-week-old male Sprague-Dawley rats with intra-aortic elastase infusion. Aortas of these rats were assigned to 4 groups (n = 6 each) as follows: Control group, aortas infused with saline; Elastase only group, aortas infused with elastase; Hydrogel group, aortas wrapped with saline-soaked BGHS after elastase infusion; and bFGF group, aortas wrapped with bFGF (100 μg)-soaked BGHS after elastase infusion. Preoperatively and on postoperative day (POD)7 and POD14, mean aortic maximal diameter was measured ultrasonographically. Aortic expansion ratio was calculated as: (post-infusion aortic diameter on POD14/pre-infusion aortic diameter × 100). Aortas were stained with Elastica van Gieson and α-smooth muscle actin to measure the ratio of elastic fibers and α-smooth muscle actin-positive cells area to the media area. Aortas on POD14 were cut into 2-mm rings and treated with contractile agent, then tension was recorded using myography. Maximum aorta diameters were significantly greater in Elastase only group, Hydrogel group, and bFGF group than in Control group (on POD14). Maximum diameter was significantly lower in bFGF group (3.52 ± 0.4 mm) than in Elastase only group (6.21 ± 1.4 mm on POD14, P < .05). On histological analysis, ratio of the area staining positively for elastic fibers was significantly greater in bFGF group (7.43 ± 1.8%) than in Elastase only group (3.76 ± 2.9%, P < .05). The ratio for α-smooth muscle actin-positive cells was significantly lower in Elastase only group (38.3 ± 5.1%) than in Control group (49.8 ± 6.7%, P < .05). No significant differences were seen between Elastase only group and bFGF group, but ratios tended to be increased in bFGF group. Consecutive mean contractile tensions were significantly higher in bFGF group than in Elastase only group. Maximum contractile tension was significantly higher in bFGF group (1.3 ± 0.4 mN) than in Elastase only group (0.4 ± 0.2 mN, P < .05). Aortic expansion can be suppressed and contractile responses of aneurysmal aortic wall recovered using BGHS incorporating bFGF.

Multidisciplinary Treatment Approach for Prosthetic Vascular Graft Infection in the Thoracic Aortic Area

Prosthetic vascular graft infection in the thoracic aortic area is a rare but serious complication. Adequate management of the complication is essential to increase the chance of success of open surgery. While surgical site infection is suggested as the root cause of the complication, it is also related to decreased host tolerance, especially as found in elderly patients. The handling of prosthetic vascular graft infection has been widely discussed to date. This paper mainly provides a summary of literature reports published within the past 5 years to discuss issues related to multidisciplinary treatment approaches, including surgical site infection, timing of onset, diagnostic methods, causative pathogens, auxiliary diagnostic methods, antibiotic treatment, anti-infective structures of vascular prostheses, surgical treatment, treatment strategy against infectious aortic aneurysms, future surgical treatment, postoperative systemic therapy, and antimicrobial stewardship. A thorough understanding of these issues will enable us to prevent prosthetic vascular graft infection in the thoracic aortic area as far as possible. In the event of its occurrence, the early introduction of appropriate treatment is expected to cure the disease without worsening of the underlying pathological condition.

In vivo detection of Staphylococcus aureus in biofilm on vascular prostheses using non-invasive biophotonic imaging

OBJECTIVES

Biophotonic imaging was compared to standard enumeration method both for counting Staphylococcus aureus in biofilm and bacterial susceptibility tests of different graft materials.

DESIGN

Prospective, randomized, controlled animal study.

MATERIAL AND METHODS

Five types of vascular grafts were placed subcutaneously in 35 mice and challenged with bioluminescent S. aureus. The mice were divided into equal groups as follows: group A (polyester), group B (polytetrafluoroethylene), group C and D (two types of silver acetate-coated polyester) and group E (bovine pericardium). Controls were given only the bacteria. The bioluminescence signal of S. aureus, able to predict number of viable bacteria in biofilm without any manipulation, was measured at different time points. Five days postinfection, regular cultures of adherent bacteria on grafts were obtained. Comparative analyses between bioluminescence activity and culture enumeration were performed.

RESULTS

The number of viable bacteria on silver-coated prostheses was the slightest, indicating superior bacterial resistance. The density of bacteria on polytetrafluoroethylene and polyester was comparable, with a non-significant advantage for polytetrafluoroethylene. Moreover, bioluminescence detected the number of viable S. aureus in biofilm more exactly compared to enumeration of bacteria.

CONCLUSION

Bioluminescence imaging can be considered a useful tool to characterize susceptibility of any graft material to bacterial biofilm prior to implantation.