Does PGA external stenting reduce compliance mismatch in venous grafts?

A review on the treatment of intimal hyperplasia with perivascular medical devices: role of mechanical factors and drug release kinetics

INTRODUCTION

Intimal hyperplasia (IH) is a significant factor limiting the success of revascularization surgery for blood flow restoration. IH results from a foreign body response and mechanical disparity that involves complex biochemical reactions resulting in graft failure. The available treatment option utilizes either different pharmacological interventions or mechanical support to the vascular grafts with limited success.

AREAS COVERED

This review explains the pathophysiology of IH, responsible mechanical and biological factors, and treatment options, emphasizing perivascular devices. They are designed to provide mechanical support and pharmacology actions. The perivascular drug delivery concept has successfully demonstrated efficacy in various animal studies. Accurate projections of drug release mechanisms using mathematical modeling could be used to formulate prolonged drug elution devices. Numerical modeling aspects for the prediction of design outcomes have been given due importance that fulfills the unmet clinical need for better patient care.

EXPERT OPINION

IH could be effectively prevented by simultaneous mechanical scaffolding and sustained local drug delivery. Future perivascular medical devices could be designed to integrate these essential features. Numerical modeling for device performance prediction should be utilized in the development of next-generation perivascular devices.

Biaxial Stretch Improves Elastic Fiber Maturation, Collagen Arrangement, and Mechanical Properties in Engineered Arteries

Tissue-engineered blood vessels (TEVs) are typically produced using the pulsatile, uniaxial circumferential stretch to mechanically condition and strengthen the arterial grafts. Despite improvements in the mechanical integrity of TEVs after uniaxial conditioning, these tissues fail to achieve critical properties of native arteries such as matrix content, collagen fiber orientation, and mechanical strength. As a result, uniaxially loaded TEVs can result in mechanical failure, thrombus, or stenosis on implantation. In planar tissue equivalents such as artificial skin, biaxial loading has been shown to improve matrix production and mechanical properties. To date however, multiaxial loading has not been examined as a means to improve mechanical and biochemical properties of TEVs during culture. Therefore, we developed a novel bioreactor that utilizes both circumferential and axial stretch that more closely simulates loading conditions in native arteries, and we examined the suture strength, matrix production, fiber orientation, and cell proliferation. After 3 months of biaxial loading, TEVs developed a formation of mature elastic fibers that consisted of elastin cores and microfibril sheaths. Furthermore, the distinctive features of collagen undulation and crimp in the biaxial TEVs were absent in both uniaxial and static TEVs. Relative to the uniaxially loaded TEVs, tissues that underwent biaxial loading remodeled and realigned collagen fibers toward a more physiologic, native-like organization. The biaxial TEVs also showed increased mechanical strength (suture retention load of 303 ± 14.53 g, with a wall thickness of 0.76 ± 0.028 mm) and increased compliance. The increase in compliance was due to combinatorial effects of mature elastic fibers, undulated collagen fibers, and collagen matrix orientation. In conclusion, biaxial stretching is a potential means to regenerate TEVs with improved matrix production, collagen organization, and mechanical properties.

Management of extracranial carotid artery disease

Stroke is the third leading cause of death in developed nations. Up to 88% of strokes are ischemic in nature. Extracranial carotid artery atherosclerotic disease is the third leading cause of ischemic stroke in the general population and the second most common nontraumatic cause among adults younger than 45 years. This article provides comprehensive, evidence-based recommendations for the management of extracranial atherosclerotic disease, including imaging for screening and diagnosis, medical management, and interventional management.

Expression of versican isoform V3 in the absence of ascorbate improves elastogenesis in engineered vascular constructs

A promising method to fabricate tissue-engineered blood vessels is to have cells synthesize the supportive extracellular matrix scaffold of the tissue-engineered blood vessel; however, a shortcoming of this method has been limited elastogenesis. Previously, we found that arterial smooth muscle cells (ASMCs) produced significant quantities of elastin when transduced with splice variant 3 of the proteoglycan versican (V3). In this study, we assessed whether elastogenesis and the structural properties of entirely cell-derived engineered vascular constructs could be improved by the incorporation of V3-transduced rat ASMCs. After 18 weeks of culture, V3 constructs had more tropoelastin, more elastin crosslinks, higher burst strengths, greater elasticity, and thicker collagen fiber bundles compared with empty-vector controls. The expression of elastin and elastin-associated proteins was increased in V3 and control ASMC monolayer cultures when ascorbic acid, which promotes collagen synthesis and inhibits elastogenesis, was removed from the medium. Engineered vascular constructs with ascorbate withdrawn for 14 weeks, after an initial 4-week exposure to ascorbate, exhibited increased elastin, desmosine content, elasticity, and burst strength compared with constructs exposed continuously to ascorbate. Our results show that V3 coupled with limited exposure to ascorbate promotes elastogenesis and improves the structural and functional properties of engineered vascular constructs.

Inhibition of neointimal formation and hyperplasia in vein grafts by external stent/sheath

Synthetic and to a lesser extent vein graft failure is still a major problem in the treatment of peripheral arterial disease, with neointimal hyperplasia being the main cause for graft occlusion in the medium and long term. This review aims to establish the current status of external stents or sheaths in the prevention of intimal hyperplasia in small diameter (< 6 mm) vein grafts.

Tracheal compliance and limit flow rate changes in a murine model of asthma

Trachea is the unique passage for air to flow in and out. Its tone is of importance for the respiration system. However, investigation on how tracheal tone changes due to asthma is limited. Aiming at studying how the mechanical property changes due to asthma as well as the compliance and flow limitation, the following methods are adopted. Static and passive pressure-volume tests of rats' trachea of the asthmatic and control groups are carried out and a new type of tube law is formulated to fit the experimental data, based on which changes of compliance and limit flow rate are investigated. In order to give explanation to such changes, histological examinations with tracheal soft tissues are made. The results show that compliance, limit flow rate and material constants included in the tube law largely depend on the longitudinal stretching ratio. Compared with the control group, the tracheal compliance of asthmatic animals decreases significantly, which results in an increased limit flow rate. Histological studies indicate that asthma can lead to hyperplasia/hypertrophy of smooth muscle cells, and increase elastin and collagen fibres in the muscular membrane. Though decreasing compliance increases stability, during the onset of asthma, limit flow rate is much smaller due to the lower transmural pressure. Asthma leads to a stiffer trachea and the obtained results reveal some aspects relevant to asthma-induced tracheal remodelling.