Mechanically tuned vascular graft demonstrates rapid endothelialization and integration into the porcine iliac artery wall.

Mechanical properties of vascular grafts likely play important roles in healing and tissue regeneration. Healthy arteries are compliant at low pressures but stiffen rapidly with increasing load, ensuring sufficient volumetric expansion without overstretching the vessel. Commercial synthetic vascular grafts are stiff and unable to expand under physiologic loads, which may result in altered hemodynamics, deleterious cellular responses, and compromised clinical performance.

Hierarchical Mechanisms of Lateral Interactions in High-Performance Fibers.

The processing conditions used in the production of advanced polymer fibers facilitate the formation of an oriented fibrillar network that consists of structures spanning multiple length scales. The irregular nature of fiber tensile fracture surfaces suggests that their structural integrity is defined by the degree of lateral (interfacial) interactions that exist within the fiber microstructure. To date, experimental studies have quantified interfacial adhesion between nanoscale fibrils measuring 10-50 nm in width, and the global fracture energy through applying peel loads to fiber halves.

Quantifying Polymer Chain Orientation in Strong and Tough Nanofibers with Low Crystallinity: Toward Next Generation Nanostructured Superfibers.

Advanced fibers revolutionized structural materials in the second half of the 20th century. However, all high-strength fibers developed to date are brittle. Recently, pioneering simultaneous ultrahigh strength and toughness were discovered in fine (<250 nm) individual electrospun polymer nanofibers (NFs).

Role of Mechanical Factors in Applications of Stimuli-Responsive Polymer Gels - Status and Prospects.

Due to their unique characteristics such as multifold change of volume in response to minute change in the environment, resemblance of soft biological tissues, ability to operate in wet environments, and chemical tailorability, stimuli responsive gels represent a versatile and very promising class of materials for sensors, muscle-type actuators, biomedical applications, and autonomous intelligent structures. Success of these materials in practical applications largely depends on their ability to fulfill application-specific mechanical requirements. This article provides an overview of recent application-driven development of covalent polymer gels with special emphasis on the relevant mechanical factors and properties.

Biomimetic substrate control of cellular mechanotransduction.

Extracellular mechanophysical signals from both static substrate cue and dynamic mechanical loading have strong potential to regulate cell functions. Most of the studies have adopted either static or dynamic cue and shown that each cue can regulate cell adhesion, spreading, migration, proliferation, lineage commitment, and differentiation. However, there is limited information on the integrative control of cell functions by the static and dynamic mechanophysical signals.

Focal adhesion kinase regulation in stem cell alignment and spreading on nanofibers.

While electrospun nanofibers have demonstrated the potential for novel tissue engineering scaffolds, very little is known about the molecular mechanism of how cells sense and adapt to nanofibers. Here, we revealed the role of focal adhesion kinase (FAK), one of the key molecular sensors in the focal adhesion complex, in regulating mesenchymal stem cell (MSC) shaping on nanofibers. We produced uniaxially aligned and randomly distributed nanofibers from poly(l-lactic acid) to have the same diameters (about 130 nm) and evaluated MSC behavior on these nanofibers comparing with that on flat PLLA control.

Effects of age on the physiological and mechanical characteristics of human femoropopliteal arteries.

Surgical and interventional therapies for peripheral artery disease (PAD) are notorious for high rates of failure. Interactions between the artery and repair materials play an important role, but comprehensive data describing the physiological and mechanical characteristics of human femoropopliteal arteries are not available. Fresh femoropopliteal arteries were obtained from 70 human subjects (13-79 years old), and in situ vs.

Three-dimensional bending, torsion and axial compression of the femoropopliteal artery during limb flexion.

High failure rates of femoropopliteal artery reconstruction are commonly attributed to complex 3D arterial deformations that occur with limb movement. The purpose of this study was to develop a method for accurate assessment of these deformations. Custom-made stainless-steel markers were deployed into 5 in situ cadaveric femoropopliteal arteries using fluoroscopy.

Biaxial mechanical properties of the human thoracic and abdominal aorta, common carotid, subclavian, renal and common iliac arteries.

The biomechanics of large- and medium-sized arteries influence the pathophysiology of arterial disease and the response to therapeutic interventions. However, a comprehensive comparative analysis of human arterial biaxial mechanical properties has not yet been reported. Planar biaxial extension was used to establish the passive mechanical properties of human thoracic (TA, [Formula: see text]) and abdominal (AA, [Formula: see text]) aorta, common carotid (CCA, [Formula: see text]), subclavian (SA, [Formula: see text]), renal (RA, [Formula: see text]) and common iliac (CIA, [Formula: see text]) arteries from 11 deceased subjects ([Formula: see text] years old).

Passive biaxial mechanical properties and in vivo axial pre-stretch of the diseased human femoropopliteal and tibial arteries.

Surgical and interventional therapies for atherosclerotic lesions of the infrainguinal arteries are notorious for high rates of failure. Frequently, this leads to expensive reinterventions, return of disabling symptoms or limb loss. Interaction between the artery and repair material likely plays an important role in reconstruction failure, but data describing the mechanical properties and functional characteristics of human femoropopliteal and tibial arteries are currently not available.

A mathematical evaluation of hemodynamic parameters after carotid eversion and conventional patch angioplasty.

Carotid endarterectomy has a long history in stroke prevention, yet controversy remains concerning optimal techniques. Two methods frequently used are endarterectomy with patch angioplasty (CEAP) and eversion endarterectomy (CEE). The objective of this study was to compare hemodynamics-related stress and strain distributions between arteries repaired using CEAP and CEE.

Effects of carotid artery stenting on arterial geometry.

Background: The role of carotid artery stenting (CAS) for the treatment of carotid artery disease continues to evolve, despite higher stroke and restenosis risks for CAS compared with conventional open endarterectomy. Understanding the effects of CAS on arterial geometry, which strongly influence hemodynamics and wall mechanics, can assist in better stratifying the inherent risk of CAS to individual patients.

Study Design: Fifteen consecutive patients undergoing CAS had pre- and post-stenting CT angiograms.

The role of RhoA kinase (ROCK) in cell alignment on nanofibers.

While the potential of nanofibers as tissue engineering scaffolds has been demonstrated, very little has been revealed as regards the molecular mechanism by which cells sense and respond to nanofibers. It was hypothesized that RhoA kinase (ROCK), one of the vital cell tension signaling cascades, plays a role in regulating cell alignment on nanofibers. To test this, unidirectionally aligned and randomly distributed nanofibers, both with an average diameter of ∼130nm, were fabricated with poly(l-lactic acid) (PLLA).

Simultaneously strong and tough ultrafine continuous nanofibers.

Strength of structural materials and fibers is usually increased at the expense of strain at failure and toughness. Recent experimental studies have demonstrated improvements in modulus and strength of electrospun polymer nanofibers with reduction of their diameter. Nanofiber toughness has not been analyzed; however, from the classical materials property trade-off, one can expect it to decrease.

Extraordinary improvement of the graphitic structure of continuous carbon nanofibers templated with double wall carbon nanotubes.

Carbon nanotubes are being widely studied as a reinforcing element in high-performance composites and fibers at high volume fractions. However, problems with nanotube processing, alignment, and non-optimal stress transfer between the nanotubes and surrounding matrix have so far prevented full utilization of their superb mechanical properties in composites. Here, we present an alternative use of carbon nanotubes, at a very small concentration, as a templating agent for the formation of graphitic structure in fibers.

Hemodynamically motivated choice of patch angioplasty for the performance of carotid endarterectomy.

Patch angioplasty is the most common technique used for the performance of carotid endarterectomy. A large number of materials are available, but little is known to aid the surgeon in choosing a patch while caring for a patient with carotid disease. The objective of this study was to investigate biomechanics of the carotid artery (CA) repaired with patch angioplasty, study the influence of patch width and location of closure on hemodynamics, and to select the optimal patch material from those commonly used.

Three-dimensional geometry of the human carotid artery.

Accurate characterization of carotid artery geometry is vital to our understanding of the pathogenesis of atherosclerosis. Three-dimensional computer reconstructions based on medical imaging are now ubiquitous; however, mean carotid artery geometry has not yet been comprehensively characterized. The goal of this work was to build and study such geometry based on data from 16 male patients with severe carotid artery disease.

Comparative analysis of the biaxial mechanical behavior of carotid wall tissue and biological and synthetic materials used for carotid patch angioplasty.

Patch angioplasty is the most common technique used for the performance of carotid endarterectomy. A large number of patching materials are available for use while new materials are being continuously developed. Surprisingly little is known about the mechanical properties of these materials and how these properties compare with those of the carotid artery wall.

Nonlinear mechanical behavior of the human common, external, and internal carotid arteries in vivo.

Background: The mechanical environment and properties of the carotid artery play an important role in the formation and progression of atherosclerosis in the carotid bifurcation. The purpose of this work was to measure and compare the range and variation of circumferential stress and tangent elastic moduli in the human common (CCA), external (ECA), and internal (ICA) carotid arteries over the cardiac cycle in vivo.

Methods: Measurements were performed in the surgically exposed proximal cervical CCA, distal ECA, and distal ICA of normotensive patients (n = 16) undergoing carotid endarterectomy.

Highly efficient rapid ethanol sensing based on Co-doped In₂O₃ nanowires.

Pristine and Co-doped In(2)O(3) nanowires were synthesized via electrospinning with subsequent calcination. Scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were used to characterize nanowire morphology and structure. Ethanol sensing performance analyzed in the range of temperatures and concentrations showed that Co-doped In(2)O(3) nanowires exhibited significantly enhanced sensitivity and rate of performance with the response and recovery times of 2s and 3s, respectively.

In vivo three-dimensional blood velocity profile shapes in the human common, internal, and external carotid arteries.

Objective: True understanding of carotid bifurcation pathophysiology requires a detailed knowledge of the hemodynamic conditions within the arteries. Data on carotid artery hemodynamics are usually based on simplified, computer-based, or in vitro experimental models, most of which assume that the velocity profiles are axially symmetric away from the carotid bulb. Modeling accuracy and, more importantly, our understanding of the pathophysiology of carotid bifurcation disease could be considerably improved by more precise knowledge of the in vivo flow properties within the human carotid artery.

Finite element model of the patched human carotid.

Introduction: The hemodynamic effects of carotid artery patching are not well known. Our objective was to develop a fluid-solid finite element model of the endarterectomized and patched carotid artery.

Methods: Hyperelastic materials parameters were determined from studies of 8 cadaveric carotids.

Rippling of polymer nanofibers.

This paper studies the evolution mechanism of surface rippling in polymer nanofibers under axial stretching. This rippling phenomenon has been detected in as-electrospun polyacrylonitrile in recent single-fiber tension tests, and in electrospun polyimide nanofibers after imidization. We herein propose a one-dimensional nonlinear elastic model that takes into account the combined effect of surface tension and nonlinear elasticity during the rippling initiation and its evolution in compliant polymer nanofibers.

Analysis of the effects of the residual charge and gap size on electrospun nanofiber alignment in a gap method.

In this paper, the effects of residual charges on nanofiber alignment in a gap method are studied and presented. The gap method was presented by Li and Xia (2003 Nano Lett. 3 1167); in it, a gap is introduced into a traditional collector.

Phase-field modeling of the formation of lamellar nanostructures in diblock copolymer thin films under inplanar electric fields.

Recent experiments show that external inplanar electric field can be employed to guide the molecular self-assembly in diblock copolymer (BCP) thin films to form lamellar nanostructures with potential applications in nanotechnology. We study this self-assembly process through a detailed coarse-grained phase-separation modeling. During the process, the free energy of the BCP films is modeled as the Ginzburg-Landau free energy with nonlocal interaction and electrostatic coupling.