X-ray microtomography reveals a lattice-like network within aortic elastic lamellae

Structural and physical basis for the elasticity of elastin

Elastin function is to endow vertebrate tissues with elasticity so that they can adapt to local mechanical constraints. The hydrophobicity and insolubility of the mature elastin polymer have hampered studies of its molecular organisation and structure-elasticity relationships. Nevertheless, a growing number of studies from a broad range of disciplines have provided invaluable insights, and several structural models of elastin have been proposed. However, many questions remain regarding how the primary sequence of elastin (and the soluble precursor tropoelastin) governs the molecular structure, its organisation into a polymeric network, and the mechanical properties of the resulting material. The elasticity of elastin is known to be largely entropic in origin, a property that is understood to arise from both its disordered molecular structure and its hydrophobic character. Despite a high degree of hydrophobicity, elastin does not form compact, water-excluding domains and remains highly disordered. However, elastin contains both stable and labile secondary structure elements. Current models of elastin structure and function are drawn from data collected on tropoelastin and on elastin-like peptides (ELPs) but at the tissue level, elasticity is only achieved after polymerisation of the mature elastin. In tissues, the reticulation of tropoelastin chains in water defines the polymer elastin that bears elasticity. Similarly, ELPs require polymerisation to become elastic. There is considerable interest in elastin especially in the biomaterials and cosmetic fields where ELPs are widely used. This review aims to provide an up-to-date survey of/perspective on current knowledge about the interplay between elastin structure, solvation, and entropic elasticity.

Non-destructive 3D characterization of the blood vessel wall microstructure in different species and blood vessel types using contrast-enhanced microCT and comparison with synthetic vascular grafts

To improve the current treatment for vascular diseases, such as vascular grafts, intravascular stents, and balloon angioplasty intervention, the evaluation of the native blood vessel microstructure in full 3D could be beneficial. For this purpose, we used contrast-enhanced X-ray microfocus computed tomography (CECT): a combination of X-ray microfocus computed tomography (microCT) and contrast-enhancing staining agents (CESAs) containing high atomic number elements. In this work, we performed a comparative study based on staining time and contrast-enhancement of 2 CESAs: Monolacunary and 1:2 Hafnium-substituted Wells-Dawson polyoxometalate (Mono-WD POM and Hf-WD POM, respectively) for imaging of the porcine aorta. After showing the advantages of Hf-WD POM in terms of contrast enhancement, we expanded our imaging to other species (rat, porcine, and human) and other types of blood vessels (porcine aorta, femoral artery, and vena cava), clearly indicating microstructural differences between different types of blood vessels and different species. We then showed the possibility to extract useful 3D quantitative information from the rat and porcine aortic wall, potentially to be used for computational modeling or for future design optimization of graft materials. Finally, a structural comparison with existing synthetic vascular grafts was made. This information will allow to better understand the in vivo functioning of native blood vessels and to improve the current disease treatments. STATEMENT OF SIGNIFICANCE: Synthetic vascular grafts, used as treatment for some cardiovascular diseases, still often fail clinically, potentially because of a mismatch in mechanical behaviour between the native blood vessel and the graft. To better understand the causes of this mismatch, we studied the full 3D microstructure of blood vessels. For this, we identified Hafnium-substituted Wells-Dawson polyoxometalate as contrast-enhancing staining agent to perform contrast-enhanced X-ray microfocus computed tomography. This technique allowed to show important differences in the microstructure of different types of blood vessels and in different species, as well as with that of synthetic grafts. This information can lead to a better understanding of the functioning of blood vessels and will allow to improve current disease treatments, such as vascular grafts.

Technical options in surgery for artery-involving pancreatic cancer: Invasion depth matters

Background

The artery involvement explains the majority of primary unresectability of non-metastatic pancreatic cancer patients and both arterial resection and artery-sparing dissection techniques are utilized in curative-intent pancreatectomies for artery-involving pancreatic cancer (ai-PC) patients.

Methods

This narrative review summarized the history of resectability evaluation for ai-PC and attempted to interpret its current pitfalls that led to the divergence of resectability prediction and surgical exploration, with a focus on the rationale and the surgical outcomes of the sub-adventitial divestment technique.

Results

The circumferential involvement of artery by tumor currently defined the resectability of ai-PC but insufficient to preclude laparotomy with curative intent. The reasons behind could be: 1. The radiographic involvement of tumor to arterial circumference was not necessarily resulted in histopathological artery wall invasion; 2. the developed surgical techniques facilitated radical resection, better perioperative safety as well as oncological benefit. The feasibility of periadventitial dissection, sub-adventitial divestment and other artery-sparing techniques for ai-PC depended on the tumor invasion depth to the artery, i.e., whether the external elastic lamina (EEL) was invaded demonstrating a hallmark plane for sub-adventitial dissections. These techniques were reported to be complicated with preferable surgical outcomes comparing to arterial resection combined pancreatectomies, while the arterial resection combined pancreatectomies were considered performed in patients with more advanced disease.

Conclusions

Adequate preoperative imaging modalities with which to evaluate the tumor invasion depth to the artery are to be developed. Survival benefits after these techniques remain to be proven, with more and higher-level clinical evidence needed.

Key message

The current resectability evaluation criteria, which were based on radiographic circumferential involvement of the artery by tumor, was insufficient to preclude curative-intent pancreatectomies for artery-involving pancreatic cancer patients. With oncological benefit to be further proven, periarterial dissection and arterial resection have different but overlapping indications, and predicting the tumor invasion depth in major arteries was critical for surgical planning.

Early Alterations of Intra-Mural Elastic Lamellae Revealed by Synchrotron X-ray Micro-CT Exploration of Diabetic Aortas

Diabetes is a major concern of our society as it affects one person out of 11 around the world. Elastic fiber alterations due to diabetes increase the stiffness of large arteries, but the structural effects of these alterations are poorly known. To address this issue, we used synchrotron X-ray microcomputed tomography with in-line phase contrast to image in three dimensions C57Bl6J (control) and db/db (diabetic) mice with a resolution of 650 nm/voxel and a field size of 1.3 mm³. Having previously shown in younger WT and db/db mouse cohorts that elastic lamellae contain an internal supporting lattice, here we show that in older db/db mice the elastic lamellae lose this scaffold. We coupled this label-free method with automated image analysis to demonstrate that the elastic lamellae from the arterial wall are structurally altered and become 11% smoother (286,665 measurements). This alteration suggests a link between the loss of the 3D lattice-like network and the waviness of the elastic lamellae. Therefore, waviness measurement appears to be a measurable elasticity indicator and the 3D lattice-like network appears to be at the origin of the existence of this waviness. Both could be suitable indicators of the overall elasticity of the aorta.