Table 1.

Mechanical test protocols for different aged specimens

Age (days)	Average systolic P from (Le et al. 2011)		Constant-length inflation protocols				Constant-pressure axial stretch protocols		PL and PH values (mmHg) for parameter fitting
	WT	Eln+/−	Max P (mmHg)	Wait time (s)	Step P (mmHg)	Typical axial stretch	P (mmHg)	Typical axial stretch	WT	Eln+/−
3	31	33	90	8	9	1.1, 1.2, 1.3	20, 40, 60	1.1–1.3	PL = 9	PL = 9
									PH = 45	PH = 45
7	46	48	120	8	12	1.1, 1.2, 1.3	25, 50, 75	1.1–1.3	PL = 12	PL = 12
									PH = 60	PH = 48
14	57	65	140	9	14	1.1, 1.2, 1.3	30, 60, 90	1.1–1.3	PL = 14	PL = 14
									PH = 98	PH = 70
21	84	90	160	10	20	1.1, 1.25, 1.4	40, 80, 120	1.1–1.4	PL = 20	PL = 20
									PH = 120	PH = 100
30	99	108	175	12	25	1.1, 1.3, 1.5	50, 100, 150	1.1–1.5	PL = 25	PL = 25
									PH = 125	PH = 100
60	112	127	175	12	25	1.1, 1.3, 1.5	50, 100, 150	1.1–1.5	PL = 25	PL = 25
									PH = 125	PH = 100

For constant-length inflation cycles, the myograph system (Danish Myotechnology) was programmed to cyclically inflate the aorta three times from 0 mmHg to the maximum (max) pressure (P) in discrete pressure steps. Deflation occurred in a single step over 60 s for all aortas, allowing the aorta to fully return to the starting dimensions, while minimizing total cycle time. The maximum pressure avoids damage to the aorta from overinflation and ranges from 1.5 to 3 times the average systolic pressure for each age (Le et al. 2011). The wait time provides enough time for the system to stabilize at each pressure and allows operator intervention if necessary to correct diameter tracking problems. The pressure steps provide an overall rate of 1–2 mmHg/s from a starting pressure of 0 mmHg. The constant-length values were chosen to provide a range of axial stretch ratios at and above the in vivo value and were varied for each aorta. Typical values are presented above. The average in vivo axial stretch ratio is approximately 1.1 for all ages and genotypes (Supplemental Table 1). For constant- pressure axial stretch cycles, the aorta was cyclically lengthened manually three times from the same minimum and maximum axial stretches used in the inflation cycles by turning a micrometer attached to one of the artery mounting rods at a constant rate of approximately 20 µm/s. The constant-pressure values were chosen to provide a range of values above and below the physiologic value. P_L and P_H values were used to constrain the elastin and collagen circumferential stress contributions in the constitutive model for the “low” and “high” pressure regions. Note that the P_L values are similar between genotypes, but P_H is lower in Eln+/− aorta compared with WT at all ages above P3