Significant differences in the material properties between aged human and porcine aortic tissues

Caitlin Martin; Thuy Pham; Wei Sun

doi:10.1016/j.ejcts.2010.08.056

. Author manuscript; available in PMC: 2011 Jul 1.

Published in final edited form as: Eur J Cardiothorac Surg. 2010 Dec 21;40(1):28–34. doi: 10.1016/j.ejcts.2010.08.056

Significant differences in the material properties between aged human and porcine aortic tissues^{^☆}

Caitlin Martin ¹, Thuy Pham ¹, Wei Sun ^1,^*

PMCID: PMC3080441 NIHMSID: NIHMS256762 PMID: 21177118

Abstract

Objectives

Currently, percutaneous aortic valve (PAV) replacement devices are being investigated to treat aortic stenosis in patients deemed to be of too high a risk for conventional open-chest surgery. Successful PAV deployment and function are heavily reliant on the tissue–stent interaction. Many PAV feasibility trials have been conducted with porcine models under the assumption that these tissues are similar to human; however, this assumption may not be valid. The goal of this study was to characterize and compare the biomechanical properties of aged human and porcine aortic tissues.

Methods

The biaxial mechanical properties of the left coronary sinus, right coronary sinus, non-coronary sinus, and ascending aorta of eight aged human (90.1 ± 6.8 years) and 10 porcine (6–9 months) hearts were quantified. Tissue structure was analyzed via histological techniques.

Results

Aged human aortic tissues were significantly stiffer than the corresponding porcine tissues in both the circumferential and longitudinal directions (p < 0.001). In addition, the nearly linear stress–strain behavior of the porcine tissues, compared with the highly nonlinear response of the human tissues at a low strain range, suggested structural differences between the aortic tissues from these two species. Histological analysis revealed that porcine samples were composed of more elastin and less collagen fibers than the respective human samples.

Conclusions

Significant material and structural differences were observed between the human and porcine tissues, which raise questions on the validity of using porcine models to investigate the biomechanics involved in PAV intervention.

Keywords: Percutaneous aortic valve, Aortic sinus, Ascending aorta, Mechanical properties, Animal trials

1. Introduction

Aortic stenosis is the most common valvular heart disease and its prevalence is growing with an aging population. The current treatment, aortic valve replacement with cardio-pulmonary bypass, involves open-chest surgery, which holds significant risks for patients with advanced age and/or comorbidities. A recent review reports operative mortality rates of 9% and 24% for octogenarians undergoing isolated aortic valve repair (AVR) and AVR with coronary artery bypass grafting, respectively [1]. The recent development of percutaneous aortic valve (PAV) replacement devices provides a less-invasive endovascular approach for the treatment of stenosis to target patients unsuitable for surgical intervention. Although the PAV technique holds promise, it remains in its infancy. Successful PAV deployment and function are heavily reliant on the tissue–stent interaction. For instance, excessive radial force of the stent may cause aortic injury, while insufficient force may lead to para-valvular leakage and device migration. Therefore, a thorough biomechanical characterization of the elastic properties of the human aortic root and ascending aorta is critical to PAV success.

Animal trials have shown that PAV replacement is feasible in porcine, ovine, and canine models [2–4]; however, each of these trials was also associated with various adverse effects. Specifically in porcine models, PAV replacement has resulted in cases of device migration, valvular regurgitation, para-valvular leakage, and coronary obstruction [2,3,5]. The mechanical properties of porcine aortic tissues have been investigated by several research groups because the porcine model is considered to be a close approximation of healthy human tissues [6,7]. The 6–9-month-old pig, in particular, is a commonly used animal model for investigating age-specific valvular conditions in humans [8,9]. Porcine tissues make a convenient test model: assuming that these tissues are comparable to human tissues, the porcine model may accelerate the rate of PAV clinical trials and, ultimately, successful PAV device design. Yet, no study has been done to quantify and compare the mechanical properties of human and porcine aortic tissues.

The mechanical properties of human aortic tissues, especially from the aged population, remain largely unknown. Considering that PAV replacement devices are suited for patients with advanced age and/or comorbidities, the mechanical properties of aortic tissues from the aged human population is of particular interest.

The current assumption is that the mechanical properties are homogeneous throughout the entire aortic root [10,11]. However, the significant differences found between the mechanical properties of the porcine ascending aorta and aortic sinuses [7] suggest that this assumption may be invalid. The goal of this study was to quantify the biomechanical properties of aged human and porcine aortic sinuses and ascending aorta through biaxial mechanical testing and histological analysis to determine the relationships between the two species. This study may also provide insight into the biomechanics involved in PAV intervention, and into the efficacy of porcine models in the development of the PAV technique for the treatment of aortic stenosis in the aged human.

2. Methods

2.1. Specimen preparation

Fresh-frozen human cadaver hearts (n = 8) were obtained from the National Disease Research Interchange (NDRI, Philadelphia, PA, USA) and 6–9-month-old porcine hearts (n = 10) were obtained from Animal Technologies Inc. (Tyler, TX, USA). Each heart was submerged in the 37 °C oxygenated low-sodium, high-potassium solution (in mM: 0.4KH₂PO₄; 1.0MgSO₄:7H₂O; 28NaHCO₃; 1.5CaCl₂:2H₂O; 5.6 Dextrose; 117.5 L-Glutamic acid) for 30 min and treated with cryopreservation solution (15% dimethyl sulfoxide) before being stored in a −80 °C freezer until mechanical testing could be performed. Studies have shown that cryopreservation does not significantly modify the biomechanical properties of aortic tissue [12]. Human specimen characteristics are presented in Table 1. The use of human tissues was approved by the Research Compliance Office of the University of Connecticut for this study. Square samples from the ascending aorta (AA), left coronary sinus (LCS), right coronary sinus (RCS), and non-coronary sinus (NCS) were excised from each heart to undergo biaxial mechanical testing. The sample dimensions for the AA, LCS, RCS, and NCS were 21.5 ± 3.5 mm, 13.4 ± 1.1 mm, 13.7 ± 1.8 mm, and 14.1 ± 2.6 mm, respectively (presented as a mean ± standard deviation). Care was taken to align the edges of each specimen along the circumferential and longitudinal directions of the aorta to determine the differences in mechanical properties with respect to anatomical orientation. The thickness of each sample was measured in five places along the center of the specimen with a Mitutoyo rotating thickness gauge (Model 7301) with an accuracy of ± 0.01 mm. Four graphite markers delimiting a square approximately 3 mm × 3 mm in size were glued to the central region of the tissue surface for optical strain measurements.

Table 1.

Human specimen characteristics.

Human heart	1	2	3	4	5	6	7	8
Age	88	96	95	98	87	80	82	95
Sex	F	F	F	F	F	F	M	M
Cause of death	Alz	CPA	RA	RA	unk	unk	AP	NC
Primary disease	CAD	n	n	n	PKD	n	n	n
Risk factors
Diabetes	unk	n	n	y	n	n	n	n
GERD	y	n	n	n	n	n	n	n
Pneumonia	n	n	y	n	n	n	y	n
Dementia	n	n	n	n	y	n	n	n
Atherosclerosis
Coronary	y	n	n	n	n	n	n	n

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Alz: Alzheimer’s, AP: asperation pneumonia, CA: cardiac arrest, CAD: coronary artery disease, CPA: chronic pulmonary aspergillosis, GERD: gastroesophogeal reflux disease, NC: natural causes (old age), RA: respiratory arrest, PKD: polycystic kidney disease, unk: unknown.

2.2. Planar biaxial mechanical testing

Biaxial testing was carried out according to the methods presented in Sacks and Sun [13]. Briefly, tissue samples were submerged in aqueous 0.9% NaCl solution at room temperature, and stress-controlled test protocols were used while the ratio of the normal Lagrangian stress components T₁₁:T₂₂ was kept constant with T₁₂ = T₂₁ = 0. Twenty continuous cycles of preconditioning were performed to reduce tissue hysteresis. Each sample was tested at the maximum load possible without causing tissue damage. At the maximum load, seven consecutive stress protocols were conducted at the following ratios: T₁₁:T₂₂ = 0.75:1, 0.5:1, 0.3:1, 1:1, 1:0.75, 1:0.5, and 1:0.3. Tissue samples were assumed to be incompressible and planar.

2.3. Constitutive modeling

The ascending aorta and aortic sinuses were all assumed to be anisotropic, nonlinear hyperelastic materials. Therefore, the second Piola–Kirchhoff stress (S) can be computed by Eq. (1), where E represents the Green–Lagrangian strain tensor and W is a strain energy function.

S_{i j} = \frac{\partial W}{\partial E_{i j}} with i, j = 1, 2

(1)

In this study, experimental stress–strain data from human ascending aorta and aortic sinus samples was fitted with the generalized Fung-type strain energy function for the planar biaxial response of soft biological tissues given by the following equations [14]:

W = \frac{c}{2} (e^{Q} - 1)

(2)

Q = A_{1} E_{11}^{2} + A_{2} E_{22}^{2} + 2 A_{3} E_{11} E_{22} + A_{4} E_{12}^{2} + 2 A_{5} E_{11} E_{22} + 2 A_{6} E_{22} E_{12}

(3)

where c and A_i are material parameters. The experimental data from stress-controlled protocols was fitted simultaneously to reduce the effect of multiple collinearities, and material parameters were obtained using the Marquardt–Levenberg nonlinear regression algorithm with MYSTAT 12 software (Systat Software, Inc., Chicago, IL, USA).

2.4. Histological analysis

The fibrous structure of human and porcine ascending aorta and aortic sinuses was examined in both the circumferential and longitudinal directions via histological analysis. Tissue specimens were cryopreserved after biaxial tests. After thawing, tissues were fixed in formalin for 24 h prior to the histology process. Each sample was then dehydrated through a process of varied alcohol concentrations, embedded in paraffin, and serially sectioned at 5 μm through the thickness. Samples were then mounted on microscope slides and dried. After deparaffinization, slides were stained with the Verhoeff–Van Gieson (VVG) stain to identify the components of interest: collagen, elastin, and smooth muscle fibers. Digital images of each section were obtained from an Olympus U-TVO.5xC digital camera coupled to an Olympus BX40 light microscope and qualitatively analyzed to compare the relative content and orientation of each component.

2.5. Data analysis

Tissue stiffness was quantified and compared among tissues by means of the secant modulus at a stress value of 60 kPa in both the circumferential and longitudinal directions. In a study by Gundiah et al., the tissue stiffness of porcine aortic sinuses were compared at a Green strain of 0.3 [15], because the expansion of the porcine aorta has been approximated at ~30% from end-diastole to systole through the use of digital sonomicrometry [16,17]. In this study, a stress level of 60 kPa was chosen for the comparison of tissue stiffness, which corresponds to a strain of approximately 0.3 in porcine tissue. This stress level was used rather than a strain level of 0.3 because the human tissues could not be stretched to this extent. Paired Student’s t-tests were used to compare the difference in stiffness between the circumferential and longitudinal direction for each tissue type (AA, LCS, RCS, and NCS) for both the human and porcine sample sets. Independent samples Student’s t-tests were used to compare the stiffness and thickness between human and porcine tissues for each tissue type. Non-parametric tests including Wilcoxon signed-rank tests and Mann–Whitney rank sum tests were used in place of paired Students’ t-tests and independent samples Students’ t-tests, respectively, in cases where the datasets were not approximately normally distributed. For all statistical considerations, a p value <0.05 was deemed to indicate a significant difference between means. All the data given in the following sections are presented as the mean ± standard deviation.

3. Results

Anatomic differences were analyzed among the samples of each type. The specimen thickness was relatively constant within tissue type for the human sample set. However, in most cases, the ascending aorta specimen from each heart was thicker than the respective sinus samples (1.53 ± 0.19 mm vs 1.35 ± 0.30 mm in humans and 2.61 ± 0.37 mm vs 1.62 ± 0.31 mm in porcine). In the human hearts, the ascending aorta (1.53 ± 0.19 mm) was significantly thicker than the LCS (1.35 ± 0.30 mm) (p = 0.006) and the RCS (1.29 ± 0.31 mm) (p = 0.016), but no such distinction could be made between the ascending aorta and the NCS (1.41 ± 0.32 mm) samples (p = 0.177). This trend also carried over to the porcine samples: the AA specimens (2.61 ± 0.37 mm) were significantly thicker than the respective LCS (1.72 ± 0.18 mm), RCS (1.76 ± 0.36 mm), and NCS (1.37 ± 0.20 mm) specimens, all with p-values less than 0.001. A significant difference in mean thickness was also found among the porcine sinus samples: the LCS and the RCS were thicker than the NCS with p values of 0.001 and 0.01, respectively. No difference was found between the LCS and the RCS. Additional differences were found to exist between human and porcine samples: the porcine tissues were thicker than the corresponding human LCS (p = 0.005), RCS (p = 0.01), and AA (p < 0.001) samples. There was no significant difference in mean thickness between human and porcine NCS (p = 0.742).

It was also noted that, in several of the human aortic specimens tested, crystalline calcium deposits were found along the edges of the sinuses and leaflets. However, the belly of the sinus, which was the portion subjected to biaxial testing, did not exhibit this calcification. No calcification was observed in any of the porcine samples tested in this study.

3.1. Biaxial mechanical response

Representative experimental data generated from the biaxial mechanical testing of human and porcine samples are presented in Fig. 1 to illustrate the loading portion of the equibiaxial nonlinear stress–strain behavior in the circumferential and longitudinal directions of each human and porcine specimen. In general, both human and porcine tissues exhibited anisotropic behavior, a common characteristic of biological materials. All the human tissues were much stiffer than the corresponding porcine tissues (Fig. 2) with a very rapid transition from the low-toe region to the deeper stress–strain curve. Conversely, porcine tissues behave nearly linearly with greater extensibility at low stresses. The most pronounced linear response was observed in the stress–strain behavior of porcine AA in the low stress range of <40 kPa (see Fig. 2, last row), which agrees well with Gundiah et al., who reported a nearly linear stress–strain response of the porcine AA over a range of approximately 0–60 kPa [7]. In addition, within the range of 0–60 kPa, each of the porcine sinus samples also demonstrated a nearly linear stress–strain response as compared with the nonlinear response of human sinuses. Overall, the obtained biaxial results showed that all of the human tissues exhibited much lower strains than the corresponding porcine tissues.

Fig. 2 — Complete experimental biaxial test data of human (closed dots) and porcine (open dots) LCS (a and b), RCS (c and d), NCS (e and f) and AA (g and h) in the circumferential (left) and longitudinal (right) direction presented as the mean and standard deviation.

To further illustrate the differences in mechanical properties between human and porcine aortic tissues, the stiffness of each specimen was determined at a stress of 60 kPa. There was no statistically significant difference in the stiffness of the porcine AA (219 ± 17 kPa) with the LCS (222 ± 48 kPa), RCS (198 ± 24 kPa) or NCS (206 ± 83 kPa) in the circumferential direction unlike in the results published by Gundiah et al. [7]; however, the AA was significantly more compliant in the longitudinal direction with a stiffness of 133 ± 12 kPa, than the LCS (177 ± 43 kPa), and the RCS (147 ± 32 kPa), with p values of 0.003 and 0.04, respectively. No difference was found between the stiffness of the AA and the NCS (146 ± 40 kPa) in the longitudinal direction (p = 0.099). There were no significant differences between the mean tissue stiffness of the three porcine sinuses. One trend consistent throughout all porcine samples, including the LCS, RCS, NCS, and AA, was higher stiffness in the circumferential direction than in the longitudinal direction with p values of 0.004, 0.002, 0.005, and 0.001, respectively.

Although the human tissues also exhibited different stress–strain responses in both directions with the circumferential direction being stiffer in most specimens, no statistically significant differences were found between the mean stiffness in either direction for the LCS (p = 0.055), RCS (p = 0.945), NCS (p = 0.641), or AA (p = 0.66). There were also no significant differences found in the mean tissue stiffness among the human sinuses or between the sinuses and the ascending aorta, aside from the RCS (1.24 × 10³ ± 563 kPa) being stiffer than the AA (734 ± 680 kPa) in the circumferential direction (p = 0.029).

Dramatic differences in mean tissue stiffness were found while comparing human tissues to the corresponding porcine tissues. The human aortic tissues were significantly stiffer than each of the respective porcine tissues in both directions (see Fig. 3).

Fig. 3 — Stiffness (secant modulus) of human and porcine AA and aortic sinuses in the circumferential and longitudinal directions at a stress of 60 kPa presented as a mean and standard deviation.

3.2. Constitutive modeling

The Fung strain–energy function was able to capture the biaxial mechanical properties of the human and porcine aortic tissues with a high degree of accuracy (see Fig. 4). Material parameters obtained from fitting the experimental data to the model are listed in Table 2. Each set of parameters was checked for convexity and condition number per Sun and Sacks [14], which could facilitate the incorporation of the material model (Eq. (2)) into commercial finite element code. The average correlation coefficient for each porcine tissue type was greater than 0.950, while all the respective human values were greater than 0.900.

Fig. 4 — Representative experimental data (open circles) fit by Fung strain energy function (solid line) for human (a–d) and porcine (e–h) sinus and AA.

Table 2.

Coefficients used to fit experimentally generated human (a) and porcine (b) data by Fung strain energy function.

Parameter	LCS	RCS	NCS	AA
(a)
C	5.652 ± 3.346	5.820 ± 4.799	4.275 ± 2.596	5.858 ± 4.256
A1	77.958 ± 16.254	100.049 ± 26.559	65.984 ± 38.748	60.494 ± 52.257
A2	77.393 ± 55.043	105.940 ± 57.058	72.378 ± 59.671	58.927 ± 34.513
A3	21.322 ± 14.154	29.245 ± 25.641	24.343 ± 22.046	17.552 ± 21.689
A4	46.109 ± 20.853	56.375 ± 29.218	38.250 ± 31.331	35.751 ± 19.551
A5	5.303 ± 14.433	−2.103 ± 7.382	0.159 ± 3.879	−2.388 ± 7.239
A6	0.426 ± 10.314	−7.470 ± 14.916	2.567 ± 5.979	−2.512 ± 3.060
R²	0.924 ± 0.072	0.955 ± 0.030	0.928 ± 0.043	0.966 ± 0.024
(b)
C	60.055 ± 26.330	71.562 ± 36.336	61.103 ± 22.267	109.402 ± 43.680
A1	2.133 ± 0.815	1.648 ± 0.782	1.665 ± 0.550	1.194 ± 0.549
A2	1.766 ± 0.690	1.442 ± 0.680	1.330 ± 0.492	0.878 ± 0.396
A3	0.415 ± 0.155	0.391 ± 0.133	0.343 ± 0.171	0.305 ± 0.130
A4	5.520 ± 4.727	5.697 ± 4.114	1.731 ± 0.468	2.365 ± 1.510
A5	0.185 ± 0.737	−0.062 ± 0.480	−0.057 ± 0.218	−0.114 ± 0.400
A6	0.296 ± 0.383	−0.189 ± 0.663	−0.133 ± 0.194	−0.089 ± 0.140
R²	0.974 ± 0.032	0.973 ± 0.031	0.961 ± 0.041	0.974 ± 0.032

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3.3. Histology

Histological analysis showed structural differences between the human and porcine tissues. Images (Fig. 5) were taken of human and porcine AA ((a)–(d)) and NCS ((e)–(h)) specimens through the tissue thickness in the longitudinal direction at an objective magnification of 40×. Verhoeff–Van Gieson stain effectively rendered elastin fibers black, collagen fibers pink, and smooth muscle brown (Fig. 5). The porcine tissues contain a higher proportion of elastin than the human tissues, which contain a higher proportion of collagen. The elastin fibers in the porcine tissues also appeared to be more undulated than the elastin fibers in the human samples, which were thinner and straighter.

4. Discussion

Dramatic differences were found between the mechanical properties of human and porcine aortic tissues. These differences will influence PAV–host tissue interactions. Considering that a stent is typically oversized by 15–20% in the radial direction with respect to the native artery to ensure safe anchoring [18], the reaction force of the expanded stent against the arterial wall will be low in a porcine model because porcine aortic tissues can stretch up to 20% under very little stress (20–30 kPa), and high in a human patient because these tissues are much stiffer (20% extension corresponds to stress of >100 kPa). As a result, the same PAV device may dislodge and migrate in a porcine model, yet cause aortic injury in a human patient. Therefore, the porcine model may not be a reliable model to predict the biomechanics involved in PAV stent–tissue interactions in humans.

The high stiffness of human aortic tissues might be accounted for by several factors. One factor is the advanced age of the patients selected in this study (90.1 ± 6.8 years): tissue stiffness has been shown to increase with age, due to an increase of collagen content. Age was also a likely contributor to the histological differences seen between the human and porcine aortic tissues, and may explain the increased collagen content as well as the high stiffness found in the human samples. Stephens and Grande-Allen show that porcine tissues also experience an increase in collagen content with age [8]. They suggest that the collagen matrix organization and turnover in a 6-month-old pig is comparable to that of a 17-year-old female and a 19-year-old male human, while a 6-year-old pig corresponds to an aged human [8]. Therefore, it is possible that the mechanical properties of a 6-year-old pig are more closely similar to those of an aged human, although this has not been assessed.

In addition, structural differences between the human and porcine aortic root may explain the differences found in their mechanical properties. Elastin dominates the stress–strain behavior of soft tissues at low stresses allowing for large strains, and, as the stress increases, the crimped collagen fibers straighten out to greatly increase tissue stiffness. Therefore, the high elastin content of the porcine samples may explain the linearity and greater compliance seen in the stress–strain behavior, while the high collagen content of the human samples explains the high stiffness and nonlinearity in the stress–strain behavior. The crimping of collagen fibers observed in the porcine tissue may also explain the high compliance. The collagen and elastin fibers in the human tissues were relatively straight; therefore, when loaded, more collagen fibers were recruited to bear tension, attributing to higher stiffness. Wuyts et al. suggested that the collagen fibers of the aorta become less wavy as a result of aging [19].

Another factor to consider is calcification present in some of the human aortic tissues: calcium deposition will increase tissue stiffness. Many studies show that calcification is associated with regions subjected to high stress concentration or large deformations [20–22]. Assuming a similar physiological strain range in both the human and porcine aortic root, the lower stresses in the porcine aortic root may lead to less calcification of these tissues. As stenosis is associated with calcium deposits in the aortic valve in many patients, a sufficient PAV replacement test platform should take high stiffness induced by calcification into consideration.

Furthermore, disease state may contribute to differences or changes in the mechanical properties of the aortic root. Results from Choudhury et al. show that samples from the aorta in patients associated with dilated tricuspid or bicuspid aortic valves are different from those in healthy patients in thickness, stress–strain response, and fibrous content [23]. Higher aortic stiffness in adults with congenital aortic valvular stenosis has also been documented [24]. The effect that disease state had on the mechanical properties of the aortic root in this study is unclear due to the limited sample size and patient information. Together, these factors may have contributed to variability in the experimental data.

In this study, we did not observe any statistical difference in the thickness among the human aortic sinuses. However, the porcine NCS (1.37 ± 0.20 mm) was significantly thinner than the respective LCS (1.72 ± 0.18 mm) and RCS (1.76 ± 0.36 mm). Gundiah et al. [15] found that the porcine LCS (2.36 ± 0.39 mm) was significantly thicker than the NCS (1.79 ± 0.48 mm). However, in a later study, Gundiah et al. [7] found that there was no significant difference in thickness among any of the porcine aortic sinuses (mean thickness of sinuses: 1.99 ± 0.57 mm). Clearly, further study is required to clarify the difference between the NCS and the left (LCS) and right coronary sinuses (RCS).

In general, the significant differences between human and porcine tissue properties presented here suggest that the porcine model may not be suitable to assess PAV–tissue mechanics. However, the 6–9-month-old porcine model may still be a reliable model to assess biocompatibility and thrombogenicity of PAV devices in vivo. Additionally, the porcine model may be beneficial for surgeons to practice PAV implantation and deployment techniques. The constitutive models developed throughout this study, which describe the mechanical behavior of human and porcine aortic tissues to a high degree of accuracy, may now be implemented in finite element models to study the biomechanics of the human and porcine aortic root.

4.1. Study limitations

The sample size for each species and tissue type was relatively small: a larger sample size would provide more conclusive results. Possible regional property differences within each aortic sinus and ascending aorta selected for study were not considered in order to simplify the experimental procedure. Although care was taken to prepare a test specimen that was roughly planar, each biaxial test sample was assumed to be planar for subsequent calculations even though the AA and aortic sinuses are curved anatomically, which may have also affected results. Finally, considering the effects that age and disease state have on the mechanical properties of aortic tissues, the results presented here can only offer insight into the comparison between aortic tissues from 6- to9-month-old pigs and elderly humans. Although vast differences were seen between the porcine and human tissues tested in this study, older pigs may have tissue properties that are more similar to humans. It should also be noted that the mean age of the patients included in this study was 90 years old, whereas the reported mean age of the PAV patient population is around 80 years [25].

5. Conclusions

The progression and success of the PAV technique is reliant on the quantification of the mechanical properties of the aortic root. Porcine models have been used in clinical studies to approximate PAV delivery/function in humans. However, there are significant differences between human and porcine ascending aorta and aortic sinuses with regard to the mechanical properties and structural composition, thus questioning the validity of using porcine models to investigate the biomechanics involved in PAV intervention. Therefore, the future use of porcine models in PAV clinical trials must be considered with caution.

Footnotes

^☆

This work was supported in part by a State of Connecticut Department of Public Health biomedical research grant DPH 2010-0085 and a NIH Pre-doctoral Fellowship.

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[R19] 19.Wuyts FL, Vanhuyse VJ, Langewouters GJ, Decraemer WF, Raman ER, Buyle S. Elastic properties of human aortas in relation to age and atherosclerosis: a structural model. Physics in Medicine and Biology. 1995;40:1577–97. doi: 10.1088/0031-9155/40/10/002. [DOI] [PubMed] [Google Scholar]

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[R22] 22.Levy RJ, Schoen FJ, Levy JT, Nelson AC, Howard SL, Oshry LJ. Biologic determinants of dystrophic calcification and osteocalcin deposition in glutaraldehyde-preserved porcine aortic valve leaflets implanted subcutaneously in rats. American Journal of Pathology. 1983;113:143–55. [PMC free article] [PubMed] [Google Scholar]

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PERMALINK

Significant differences in the material properties between aged human and porcine aortic tissues^{^☆}

Caitlin Martin

Thuy Pham

Wei Sun