In the last 50 years the Biomedical Engineering, and in particular the vascular surgery, has grown more and more. One of the major challenges of contemporary research in biomechanics is to assess the material properties of human arteries and studying them is essential to design prosthesis that resemble the original vessels. Since it is hard to estimate the Elastic Modulus of the arteries in vivo, several embalming methods have been developed to preserve the tissues and to allow an accurate biomechanical study. In this work, the effectiveness of a new embalming method performed through perfusion is evaluated, analysing the mechanical behaviour of human brachial, femoral and popliteal arteries. Moreover, this Master’s Thesis evaluates the influence of the arteries’ geometry in the resistance of an external stress. To verify it, the arteries were tested in two different configurations and the results obtained, in terms of elasticity, were compared. Some arteries were tested in the closed configuration and they were stretched as tubes, while other arteries were tested in the opened configuration. In the second case, the arteries were firstly cut along the longitudinal axis and then tested as rectangles. To evaluate the mechanical properties of the biological tissues, uniaxial tensile tests were performed. A force was applied to each specimen and the maximum stress and strain before failure were measured. Elastic modulus, E1 and E2, were assessed using two linear regression fits separated by the transition point. The protocol has been carefully studied and verified testing 12 silicon tubes, in both configurations, before testing the arteries. The elastic modulus of the human arteries tested was compared with the values in the literature. Embalmed brachial arteries showed no significant difference in the elastic moduli E2 in the closed and in the opened configurations (1.227 ± 1.46 MPa and of 1.400 ± 1.01 MPa respectively). The results obtained are not in accordance (p-value 0.02) with the literature: 3.8 ± 1.7 MPa (Leguy, 2010). Regarding the femoral arteries, the E2 obtained were of the same order of magnitude (1.145 ± 0.49 MPa in the closed configuration and 1.590 ± 1.16 MPa in the opened one) and it did not show a significant difference with respect to the one of fresh femoral arteries in (Pukacki et al., 2000). The popliteal arteries showed a stiffer behaviour compared to the brachial and the femoral ones. Anyway, there was no significant difference between the two configurations (3.547 ± 1.20 MPa and 3.250 ± 1.53 MPa). In the literature, the fresh popliteal arteries tested have a softer elastic response, 1.01 ± 0.54 MPa. This difference could be due to the embalming technique (p-value 0.02). Despite the small sample size, very promising results were obtained. Further research should focus on testing more specimens to increase the numerosity of the sample and to confirm that the embalming method through perfusion preserves a good elasticity of blood vessels, as well as the colour of the tissue, its quality and the consistency of the embalmed bodies.
Negli ultimi 50 anni l’Ingegneria Biomedica, e in particolar modo la chirurgia vascolare, è cresciuta sempre di più. Una delle sfide principali dell’attuale ricerca in biomeccanica riguarda la determinazione delle proprietà delle arterie umane e il loro studio è essenziale ai fini della progettazione e della produzione di prostesi quanto più simile al tessuto originale. Siccome è molto difficile stimare il Modulo Elastico delle arterie in vivo, nel corso degli anni sono stati sviluppati diversi metodi di imbalsamazione volti alla conservazione dei corpi, per permettere più accurati studi biomeccanici. In questo elaborato è stata valutata l’efficacia di un nuovo metodo di imbalsamazione per perfusione, sviluppato per la prima volta nell’Universidade Nova de Lisboa, analizzando le proprietà meccaniche di arterie brachiali, femorali e poplitee umane. Inoltre, in questo lavoro di tesi è stato studiato l’effetto che la geometria delle arterie può avere sulla risposta a stimoli meccanici esterni. Per valutare questo aspetto, le arterie sono state testate in due differenti configurazioni e i risultati ottenuti sono stati confrontati. Alcune arterie sono state testate in una configurazione chiusa, e quindi testate a trazione come tubi, mentre altre in una configurazione aperta. Nel secondo caso, le arterie sono state tagliate lungo l’asse longitudinale, aperte a formare un rettangolo e sottoposte a trazione. Per valutare le proprietà meccaniche di tessuti biologici, sono stati svolti test a trazione uniassiale. La forza applicata al provino, necessaria per allungarlo, e i valori di σ e ε fino a rottura sono stati registrati durante il test. Il modulo elastico (E1 e E2) sono stati misurati applicando due differenti rette di regressione, separate dal punto di transizione caratteristico di ogni arteria. Il protocollo utilizzato durante il test è stato accuratamente studiato e verificato, testando 12 tubi di silicone, in entrambe le configurazioni, prima di lavorare sulle arterie. Il modulo elastico stimato durante i test è stato poi confrontato con i valori presenti in letteratura. Le arterie brachiali imbalsamate non hanno mostrato una differenza significativa in E2 tra la configurazione chiusa e quella aperta (1.227 ± 1.46 MPa e 1.400 ± 1.01 MPa rispettivamente). Inoltre, i risultati ottenuti sono in disaccordo (p-value 0.02) con i valori presenti in letteratura: 3.8 ± 1.7 MPa (Leguy, 2010). Per quanto riguarda le arterie femorali, il valore di E2 ottenuto è dello stesso ordine di grandezza nelle due configurazioni (1.145 ± 0.49 MPa in quella chiusa e 1.590 ± 1.16 MPa in quella aperta). In questo caso non è stata registrata una differenza significativa con la letteratura (Pukacki et al., 2000). Le arterie poplitee, invece, hanno mostrato un comportamento più rigido rispetto alle arterie brachiali e femorali imbalsamate con la stessa tecnica. Non è stata comunque riscontrata una differenza significativa tra le due configurazioni (3.547 ± 1.20 MPa e 3.250 ± 1.53 MPa). In letteratura, le arterie poplitee fresche risultano essere più deformabili, 1.01 ± 0.54 MPa. Questa differenza potrebbe essere dovuta dal metodo di imbalsamazione utilizzato (p-value 0.02). Nonostante la bassa numerosità del campione, sono stati ottenuti dei risultati molto promettenti. Sviluppi futuri potrebbero concentrarsi sulla realizzazione di ulteriori test di trazione per aumentare la dimensione del campione in modo tale da confermare quanto riscontrato in questo studio, ovvero che il metodo via perfusione mantiene una buona elasticità dei vasi sanguigni, così come il colore e la qualità del tessuto e la consistenza dei corpi imbalsamati.
Experimental study of the biomechanical properties of human arteries
BRACHETTI, ENRICO
2017/2018
Abstract
In the last 50 years the Biomedical Engineering, and in particular the vascular surgery, has grown more and more. One of the major challenges of contemporary research in biomechanics is to assess the material properties of human arteries and studying them is essential to design prosthesis that resemble the original vessels. Since it is hard to estimate the Elastic Modulus of the arteries in vivo, several embalming methods have been developed to preserve the tissues and to allow an accurate biomechanical study. In this work, the effectiveness of a new embalming method performed through perfusion is evaluated, analysing the mechanical behaviour of human brachial, femoral and popliteal arteries. Moreover, this Master’s Thesis evaluates the influence of the arteries’ geometry in the resistance of an external stress. To verify it, the arteries were tested in two different configurations and the results obtained, in terms of elasticity, were compared. Some arteries were tested in the closed configuration and they were stretched as tubes, while other arteries were tested in the opened configuration. In the second case, the arteries were firstly cut along the longitudinal axis and then tested as rectangles. To evaluate the mechanical properties of the biological tissues, uniaxial tensile tests were performed. A force was applied to each specimen and the maximum stress and strain before failure were measured. Elastic modulus, E1 and E2, were assessed using two linear regression fits separated by the transition point. The protocol has been carefully studied and verified testing 12 silicon tubes, in both configurations, before testing the arteries. The elastic modulus of the human arteries tested was compared with the values in the literature. Embalmed brachial arteries showed no significant difference in the elastic moduli E2 in the closed and in the opened configurations (1.227 ± 1.46 MPa and of 1.400 ± 1.01 MPa respectively). The results obtained are not in accordance (p-value 0.02) with the literature: 3.8 ± 1.7 MPa (Leguy, 2010). Regarding the femoral arteries, the E2 obtained were of the same order of magnitude (1.145 ± 0.49 MPa in the closed configuration and 1.590 ± 1.16 MPa in the opened one) and it did not show a significant difference with respect to the one of fresh femoral arteries in (Pukacki et al., 2000). The popliteal arteries showed a stiffer behaviour compared to the brachial and the femoral ones. Anyway, there was no significant difference between the two configurations (3.547 ± 1.20 MPa and 3.250 ± 1.53 MPa). In the literature, the fresh popliteal arteries tested have a softer elastic response, 1.01 ± 0.54 MPa. This difference could be due to the embalming technique (p-value 0.02). Despite the small sample size, very promising results were obtained. Further research should focus on testing more specimens to increase the numerosity of the sample and to confirm that the embalming method through perfusion preserves a good elasticity of blood vessels, as well as the colour of the tissue, its quality and the consistency of the embalmed bodies.File | Dimensione | Formato | |
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Experimental study of the biomechanical properties of human arteries, Brachetti Enrico.pdf
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https://hdl.handle.net/10589/142614