https://www.seas.upenn.edu/%7Edischer/pdfs/Cell_on_Gel-CELLpaper.pdf

Matrix elasticity directs stem cell lineage specification.

Gold, enigmatically represented by the target-like design of its ancient alchemical symbol, has been considered a mystical material of great value for centuries. Nanoscale particles of gold now command a great deal of attention for biomedical applications. Depending on their size, shape, degree of aggregation, and local environment, gold nanoparticles can appear red, blue, or other colors. These visible colors reflect the underlying coherent oscillations of conduction-band electrons (“plasmons”) upon irradiation with light of appropriate wavelengths. These plasmons underlie the intense absorption and elastic scattering of light, which in turn forms the basis for many biological sensing and imaging applications of gold nanoparticles. The brilliant elastic light-scattering properties of gold nanoparticles are sufficient to detect individual nanoparticles in a visible light microscope with ∼102 nm spatial resolution. Despite the great excitement about the potential uses of gold nanoparticles for medical diag...

Gold nanoparticles in biology: beyond toxicity to cellular imaging

Mechanical properties of the adventitia are largely determined by the organization of collagen fibers. Measurements on the waviness and orientation of collagen, particularly at the zero-stress state, are necessary to relate the structural organization of collagen to the mechanical response of the adventitia. Using the fluorescence collagen marker CNA38-OG488 and confocal laser scanning microscopy, we imaged collagen fibers in the adventitia of rabbit common carotid arteries ex vivo. The arteries were cut open along their longitudinal axes to get the zero-stress state. We used semi-manual and automatic techniques to measure parameters related to the waviness and orientation of fibers. Our results showed that the straightness parameter (defined as the ratio between the distances of endpoints of a fiber to its length) was distributed with a beta distribution (mean value 0.72, variance 0.028) and did not depend on the mean angle orientation of fibers. Local angular density distributions revealed four axially symmetric families of fibers with mean directions of 0°, 90°, 43° and −43°, with respect to the axial direction of the artery, and corresponding circular standard deviations of 40°, 47°, 37° and 37°. The distribution of local orientations was shifted to the circumferential direction when measured in arteries at the zero-load state (intact), as compared to arteries at the zero-stress state (cut-open). Information on collagen fiber waviness and orientation, such as obtained in this study, could be used to develop structural models of the adventitia, providing better means for analyzing and understanding the mechanical properties of vascular wall.

/pdf/experimental-investigation-of-collagen-waviness-and-35sv8tu15v.pdf

Experimental investigation of collagen waviness and orientation in the arterial adventitia using confocal laser scanning microscopy.

Fibroblast biology in three-dimensional collagen matrices.

The use of bone grafts is the standard to treat skeletal fractures, or to replace and regenerate lost bone, as demonstrated by the large number of bone graft procedures performed worldwide. The most common of these is the autograft, however, its use can lead to complications such as pain, infection, scarring, blood loss, and donor-site morbidity. The alternative is allografts, but they lack the osteoactive capacity of autografts and carry the risk of carrying infectious agents or immune rejection. Other approaches, such as the bone graft substitutes, have focused on improving the efficacy of bone grafts or other scaffolds by incorporating bone progenitor cells and growth factors to stimulate cells. An ideal bone graft or scaffold should be made of biomaterials that imitate the structure and properties of natural bone ECM, include osteoprogenitor cells and provide all the necessary environmental cues found in natural bone. However, creating living tissue constructs that are structurally, functionally and mechanically comparable to the natural bone has been a challenge so far. This focus of this review is on the evolution of these scaffolds as bone graft substitutes in the process of recreating the bone tissue microenvironment, including biochemical and biophysical cues.

Scaffold Design for Bone Regeneration

Prediction of equibiaxial loading stress in collagen-based extracellular matrix using a three-dimensional unit cell model.

The use of endovascular treatment in the thoracic aorta has revolutionized the clinical approach for treating Stanford type B aortic dissection. The endograft procedure is a minimally invasive alternative to traditional surgery for the management of complicated type-B patients. The endograft is first deployed to exclude the proximal entry tear to redirect blood flow toward the true lumen and then a stent graft is used to push the intimal flap against the false lumen (FL) wall such that the aorta is reconstituted by sealing the FL. Although endovascular treatment has reduced the mortality rate in patients compared to those undergoing surgical repair, more than 30% of patients who were initially successfully treated require a new endovascular or surgical intervention in the aortic segments distal to the endograft. One reason for failure of the repair is persistent FL perfusion from distal entry tears. This creates a patent FL channel which can be associated with FL growth. Thus, it is necessary to develop stents that can promote full re-apposition of the flap leading to complete closure of the FL. In the current study, we determine the radial pressures required to re-appose the mid and distal ends of a dissected porcine thoracic aorta using a balloon catheter under static inflation pressure. The same analysis is simulated using finite element analysis (FEA) models by incorporating the hyperelastic properties of porcine aortic tissues. It is shown that the FEA models capture the change in the radial pressures required to re-appose the intimal flap as a function of pressure. The predictions from the simulation models match closely the results from the bench experiments. The use of validated computational models can support development of better stents by calculating the proper radial pressures required for complete re-apposition of the intimal flap.

Validated Computational Model to Compute Re-apposition Pressures for Treating Type-B Aortic Dissections.

In this issue of the JEVT, Torres-Blanco and colleagues and Lindstrom and colleagues alert us to the disconnection of the proximal suprarenal uncovered stent in the Zenith abdominal aortic aneurysm (AAA) stent-grafts (Cook Medical, Bloomington, IN, USA). Disconnections of the proximal uncovered stent are indeed infrequent but were noted with the first generation of the stent prior to 2002. At that time, the device was modified with double suture reinforcement to secure the uncovered stent. Since this modification was introduced, the problem of uncovered stent disconnection has become very rare. Failure of aortic stent-grafts is most often multifactorial (Figure 1). Although there is usually a leading cause, stentgraft failure is often due to overlapping factors. These can be grouped in 3 categories: patient (eg, poor anatomy or progression of aortic disease), physician (eg, selection of improper treatment, faulty or inaccurate deployment or device selection), and device factors (eg, integrity or design issues). The proximal suprarenal stent was designed to optimize seal by adding fixation to the aorta to stop migration. The problem highlighted in this issue of the JEVT reflects a device integrity issue, ultimately disconnection of the uncovered stent. An aortic stent-graft is subjected to longterm cyclic forces acting to displace the stent-graft. Moreover, these forces must be overcome in the setting of continual changes in aortic neck configuration. Albeit rare, this structural failure highlights the importance of continued lifelong surveillance of endografts, regardless of specific type or manufacturer. It is critical that we analyze device successes or failures in the context of the specific anatomic conditions for which the devices are approved. The Cook Zenith AAA stent-graft was tested clinically and approved for use in normal aortic segments of at least 15-mm length with <60° angulation. Although these requirements represent ideal conditions, numerous reports indicate that technical and clinical success can sometimes be achieved outside these strict anatomic recommendations. It is important to note that prospective trials of AAA devices to support Food and Drug Administration (FDA) approval include only patients treated within the instructions for use (IFU). These patients are followed for 5 years. There is a paucity of prospective clinical data on outside IFU use of any AAA device. Use of any AAA device outside the IFU should be undertaken with extreme caution. 636029 JETXXX10.1177/1526602816636029Journal of Endovascular TherapyOderich and Roeder research-article2016

Commentary: Proximal Uncovered Stent Disconnections With the Standard and Low-Profile Zenith AAA Stent-Grafts.

A prosthesis having a tubular body of a biocompatible graft material having a proximal end, a distal end, a lumen therethrough, and a sidewall. The prosthesis includes at least one perfusion branch extending from the sidewall of the tubular body and having a proximal end, a distal end, and a lumen therethrough, where the lumen of the perfusion branch is in temporary fluid communication with the lumen of the tubular body. The perfusion branch comprises a self-sealing component, that after predetermined period of time precludes fluid flow out of the distal end of the perfusion branch.

Blayne A. Roeder

Papers

Prediction of equibiaxial loading stress in collagen-based extracellular matrix using a three-dimensional unit cell model.

Validated Computational Model to Compute Re-apposition Pressures for Treating Type-B Aortic Dissections.

Commentary: Proximal Uncovered Stent Disconnections With the Standard and Low-Profile Zenith AAA Stent-Grafts.

Endovascular stent graft with self-closing perfusion branch

Local, Three-Dimensional Strain Measurements Within Largely