biostudies-literaturePanpho PBritish Heart FoundationRoyal Academy of Engineering/Leverhulme TrustJillian Madine and Mark FieldRoyal Thai Government Scholarship892-901https://www.ebi.ac.uk/biostudies/studies/S-EPMC9070530biostudies-literatureUnknown34(5)<h4>Objectives</h4>The transition of aortic dissection from acute to chronic is poorly understood. We examined time-dependent mechanical behaviour and biochemical properties of chronic dissection tissues.<h4>Methods</h4>Aorta samples were obtained from 14 patients with mixed aetiology who were undergoing elective surgery for chronic dissected aneurysms, ranging from 3 months to 15 years post-dissection. The tissue elastic modulus and tissue deformation following application of loading for 5 h were measured for the false lumen (FL), true lumen (TL) and flap (FP) tissues with a custom-indentation technique. Collagen, elastin and glycosaminoglycan levels were determined with established biochemical assays. Elastin fragmentation was graded from histological sections. The number of tissues characterized was as follows: FP (n = 10), TL (n = 5 for biomechanical testing, n = 8 for biochemical analysis, n = 8 for histological assessment) and FL (n = 4).<h4>Results</h4>Tissues stiffness was highest in FP [59.8 (14.8) kPa] as compared with TL [50.7 (6.2) kPa] and FL [40.5 (4.7) kPa] (P = 0.023 and P = 0.006, respectively). FP [0.5 (0.08) mm] also exhibited reduced deformation relative to TL [0.7 (0.02) mm] and FL [0.9 (0.08) mm] (P = 0.003 and P = 0.006, respectively), lowest collagen concentration [FP: 40.1 (19.6) µg/mg, TL: 59.9 (19.5) µg/mg, P = 0.008; FL: 79.1 (32.0) µg/mg, P = 0.006] and the lowest collagen: elastin ratio [0.4 (0.1)] relative to the other tissues [TL; 0.6 (0.3), P = 0.006, FL; 1.5 (0.4); P = 0.003]. Significant elastin loss was evident in the FL-stained tissue sections whereas highly aligned, long fibres were visible in the FP and TL. A linear relationship was found between the stiffness, deformation and the time from the dissection event to surgical intervention for the FP. All data are presented as median (interquartile range).<h4>Conclusions</h4>FP exhibited reduced time-dependent deformation and distinct biochemical properties relative to TL and FL irrespective of connective tissue disorder or the anatomical region of the dissection.Interactive cardiovascular and thoracic surgeryTime-dependent mechanical behaviour of the aortic chronic dissection flap.PMC9070530FS/12/61/29877LTSRF1617/13/76PG/16/107/32681Panpho PTorella FYang YDavies HANawaytou OField MAkhtar RHarky AMadine JfalseTime-dependent mechanical behaviour of the aortic chronic dissection flap.<h4>Objectives</h4>The transition of aortic dissection from acute to chronic is poorly understood. We examined time-dependent mechanical behaviour and biochemical properties of chronic dissection tissues.<h4>Methods</h4>Aorta samples were obtained from 14 patients with mixed aetiology who were undergoing elective surgery for chronic dissected aneurysms, ranging from 3 months to 15 years post-dissection. The tissue elastic modulus and tissue deformation following application of loading for 5 h were measured for the false lumen (FL), true lumen (TL) and flap (FP) tissues with a custom-indentation technique. Collagen, elastin and glycosaminoglycan levels were determined with established biochemical assays. Elastin fragmentation was graded from histological sections. The number of tissues characterized was as follows: FP (n = 10), TL (n = 5 for biomechanical testing, n = 8 for biochemical analysis, n = 8 for histological assessment) and FL (n = 4).<h4>Results</h4>Tissues stiffness was highest in FP [59.8 (14.8) kPa] as compared with TL [50.7 (6.2) kPa] and FL [40.5 (4.7) kPa] (P = 0.023 and P = 0.006, respectively). FP [0.5 (0.08) mm] also exhibited reduced deformation relative to TL [0.7 (0.02) mm] and FL [0.9 (0.08) mm] (P = 0.003 and P = 0.006, respectively), lowest collagen concentration [FP: 40.1 (19.6) µg/mg, TL: 59.9 (19.5) µg/mg, P = 0.008; FL: 79.1 (32.0) µg/mg, P = 0.006] and the lowest collagen: elastin ratio [0.4 (0.1)] relative to the other tissues [TL; 0.6 (0.3), P = 0.006, FL; 1.5 (0.4); P = 0.003]. Significant elastin loss was evident in the FL-stained tissue sections whereas highly aligned, long fibres were visible in the FP and TL. A linear relationship was found between the stiffness, deformation and the time from the dissection event to surgical intervention for the FP. All data are presented as median (interquartile range).<h4>Conclusions</h4>FP exhibited reduced time-dependent deformation and distinct biochemical properties relative to TL and FL irrespective of connective tissue disorder or the anatomical region of the dissection.2022-01-01T00:00:00Z2022 May2025-04-22T07:50:37.775Z2025-04-05T22:17:54.892ZS-EPMC90705303514175710.1093/icvts/ivac029