Biodegradable polyurethane urea (PUU) elastomers are ideal candidates for fabricating tissue engineering scaffolds with mechanical properties akin to strong and resilient soft tissues. PUU with a crystalline poly(ε-caprolactone) (PCL) macrodiol soft segment (SS) showed good elasticity and resilience at small strains (<50%), but showed poor resilience under large strains due to stress-induced crystallization of the PCL segments, with a permanent set of 677±30% after tensile failure. To obtain softer and more resilient PUUs, noncrystalline poly(trimethylene carbonate) (PTMC) or poly(δ-valerolactone-co-ε-caprolactone) (PVLCL) macrodiols of different molecular weights were used as SSs that were reacted with 1, 4-diisocyanatobutane and chain extended with 1, 4-diaminobutane. Mechanical properties of the PUUs were characterized by tensile testing with static or cyclic loading and dynamic mechanical analysis. All the PUUs synthesized showed large elongations at break (800–1400%) and high tensile strength (30–60 MPa). PUUs with non-crystalline SSs all showed improved elasticity and resilience relative to the crystalline PCL-based PUU, especially for the PUUs with high molecular weight SSs (PTMC 5400 Mn and PVLCL 6000 Mn), of which the permanent deformation after tensile failure was only 12±7% and 39±4%, respectively. The SS molecular weight also influenced the tensile modulus in an inverse fashion. Accelerated degradation studies in PBS containing 100 U/mL lipase showed significantly greater mass loss for the two polyester-based PUUs versus the polycarbonate-based PUU, and for PVLCL versus PCL polyester PUUs. Basic cytocompatibility was demonstrated with primary vascular smooth muscle cell culture. The synthesized families of PUUs showed variable elastomeric behavior that could be explained in terms of the underlying molecular design and crystalline behavior. Depending upon the application target of interest, these materials may provide options or guidance for soft tissue scaffold development.

Background Ascending thoracic aortic aneurysm (ATAA) predisposes patients to aortic dissection and has been associated with diminished tensile strength and disruption of collagen. ATAA arising in patients with bicuspid aortic valve (BAV) develop earlier than those with tricuspid aortic valves (TAV) and have a different risk of dissection. The purpose of this study was to compare aortic wall tensile strength between BAV and TAV ATAAs and determine if the collagen content of the ATAA wall is associated with tensile strength and valve phenotype. Methods Longitudinally and circumferentially oriented strips of ATAA tissue obtained during elective surgery were stretched to failure and collagen content was estimated by hydroxyproline assay. Experimental stress-strain data were analyzed for failure strength and elastic mechanical parameters: α, β and maximum tangential stiffness. Results The circumferential and longitudinal tensile strengths were higher for BAV ATAA when compared with TAV ATAA. The α and β were lower for BAV ATAA when compared with TAV ATAA. The maximum tangential stiffness was higher for circumferential when compared with longitudinal orientation in both BAV and TAV ATAA. Amount of hydroxyproline was equivalent in BAV and TAV ATAA specimens. While there was a moderate correlation between the collagen content and tensile strength for TAV, this correlation is not present in BAV. Conclusion The increased tensile strength and decreased values of α and β in BAV ATAAs despite uniform collagen content between groups indicate that micro-structural changes in collagen contribute to BAV-associated aortopathy.

The circumferential tensile strength of the ureter was found to be significantly lower than the longitudinal strength. Circumferential tensile strength was also lower with more proximal parts of the ureter. This information may be important for the design of "intelligent" devices and simulators to prevent complications.

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Abdominal aortic aneurysm (AAA) is a degenerative disease of the aorta characterized by severe disruption of the structural integrity of the aortic wall and its major molecular constituents. From the early stages of disease, elastin in the aorta becomes highly degraded and is replaced by collagen. Questions persist as to the contribution of collagen content, quality and maturity to the potential for rupture. Here, using our recently developed Fourier transform infrared imaging spectroscopy (FT-IRIS) method, we quantified collagen content and maturity in the wall of AAA tissues in pairs of specimens with different wall stresses. CT scans of AAAs from 12 patients were used to create finite element models to estimate stress in different regions of tissue. Each patient underwent elective repair of the AAA, and two segments of the AAA tissues from anatomic regions more proximal or distal with different wall stresses were evaluated by histology and FT-IRIS after excision. For each patient, collagen content was generally greater in the tissue location with lower wall stress, which corresponded to the more distal anatomic regions. The wall stress/collagen ratio was greater in the higher stress region compared to the lower stress region (1.01 ± 1.09 vs. 0.55 ± 0.084, p = 0.02). The higher stress region also corresponded to the location with reduced intraluminal thrombus thickness. Further, collagen maturity tended to decrease with increased collagen content (p = 0.068, R = 0.38). Together, these results suggest that an increase in less mature collagen content in AAA patients does not effectively compensate for the loss of elastin in the aortic wall, and results in a reduced capability to endure wall stresses.

Current commercial tensile testing systems use spring-loaded or other compression-based grips to clamp materials in place posing a problem for very soft or delicate materials that cannot withstand this mechanical clamping force. In order to perform uniaxial tensile tests on soft tissues or materials, we have created a novel vacuum-assisted anchor (VAA). Fibrin gels were subjected to uniaxial extension, and the testing data was used to determine material mechanical properties. Utilizing the VAA, we achieved successful tensile breaks of soft fibrin gels while finding statistically significant differences between the mechanical properties of gels fabricated at two different fibrinogen concentrations.

Coil embolization has become a widely accepted endovascular procedure for intracranial aneurysms, as an alternative to surgical clipping [1,2]. This procedure involves treating an aneurysm from the inside out, whereby metallic coils are placed into the aneurysm to induce thrombosis of the lumen and eliminate the risk of rupture and hemorrhage. Successful endosaccular packing mainly depends on the morphological features and size of the aneurysm, and the relationship of the aneurysm to the cerebral arteries.

Bicuspid aortic valve (BAV) is the most common congenital heart malformation occurring in 1–2% of the population with a high rate of morbidity [1]. There is a significantly higher rate of dilation of the aortic root in adults with a BAV when compared to the normal population and this condition is often associated with ascending thoracic aortic aneurysm (ATAA). ATAA is characterized as an enlargement of the aorta to twice its normal diameter. If left untreated, ATAA can lead to aortic dissection or rupture. Therefore, ATAA is recommended for prophylactic surgery when its diameter reaches about 5.5 cm. However, in certain high-risk cases, such as patients with BAV, ATAA may rupture when its diameter is less than 5.5 cm. Since ATAA dissection and rupture are biomechanical phenomena, better mechanical models are needed to more accurately predict these events over the predictive capability of diameter alone.