Properties of the Arterial Wall
Wilmer W Nichols, Michael F O'Rourke, Elazer R Edelman, Charalambos Vlachopoulos in McDonald's Blood Flow in Arteries, 2022
Another way of analyzing the behavior of the arterial wall is to treat it as an elastomer, a class of substances that covers the long molecular chain polymers. Elastomers are grouped (Stacy et al., 1955) by the properties they have in common. Elastin is a representative ideal protein elastomer (Urry et al., 2002): They have a low Young’s modulus, of the order of 107 dyne/cm2. Most other solids have moduli of the order of 1010 to 1011 dyne/cm2. They thus include all highly extensible rubber-like substances.They can be stretched to great lengths before their breaking point or ultimate strength is reached.Their stress–strain curve is usually sigmoid, or S-shaped.
Baroreceptors: Morphology and Mechanics of Receptor Zones and Discharge Properties of Baroafferents*
Irving H. Zucker, Joseph P. Gilmore in Reflex Control of the Circulation, 2020
I have reviewed in some detail the viscoelastic properties of arteries in order to caution against premature conclusions about the tension–strain relations of the geometrically and structurally rather complex carotid sinus receptor regions where the assumptions underlying the incremental approaches (isotropy, homogeneity of the vessel wall) are no longer valid. These obstacles can possibly be circumvented by using “strain energy density” per wall volume as a scalar quantity for expressing wall deformation. This approach derives from finite deformation theory and has been applied to describing the behavior of elastomers. It relates the work done on the wall (volume–pressure relations) to wall deformation in all directions, and requires information about wall volume, pressure, length, and diameter. Strain energy density of the carotid sinus wall follows both circumferential and longitudinal stretch but continues to increase above 200 mmHg when length has already reached its plateau (Koushanpour and Kelso, 1972).
Surgical Models of Stroke Induced by Intraluminal Filament Implantation
Yanlin Wang-Fischer in Manual of Stroke Models in Rats, 2008
Silicone elastomers have been employed for many years in the manufacture of medical devices, including device components and tubing. These elastomers are commercially available in two types: millable high-consistency silicone rubber and pumpable liquid silicone rubber. Low-viscosity silicone liquid is 100% polydimethylsiloxanes. It makes liquid silicone rubbers suitable for molding applications. (Silicone rubber can be purchased as Provil-L®, Bayer Dental D-5090, from Leverkusen, Germany, or Dow Corning, Midland, Michigan, or GE Sealant and Adhesives, Huntersville, North Carolina). Monofilament nylon sutures can be purchased from Ethicon, Somerville, New Jersey, or other companies. Here, we describe the method of Koizumi et al.1 and Takano et al. (1997).13
Controlled release of bioactive IL-2 from visible light photocured biodegradable elastomers for cancer immunotherapy applications
Published in Pharmaceutical Development and Technology, 2022
Mohamed A. Shaker, Jules J. E. Doré, Husam M. Younes
We have previously reported on the elastomers’ long-term degradation using dog-bone-shaped samples in PBS (Shaker et al. 2010). The elastomers were found to follow slow zero-order degradation rate kinetics and exhibited the ability to maintain their shape and extensibility over the studied period. Water absorption and change in weight of blank PDET50 and PDET100 microcylinders over 12 weeks were further investigated in this study to assess the exact possible contribution of degradation on the device geometry and the overall drug release mechanism. As seen from Figure 7, the samples exhibited a two-stage of water absorption and weight-loss behavior. In the first stage (4 weeks), the water absorption and weight-loss proceeded rapidly due to the diffuse out of the samples’ sol phase. However, in the second stage, the water absorption and weight loss took place at a slower rate. By the end of the study period, the average cumulative water absorption was equivalent to 68% and 45% in the PDET50 and PDET100, respectively. At the end of the 12 weeks, the mean weight loss was equivalent to 29% and 14% in micro-cylinders in the PDET50 and PDET100, respectively. Such results confirm that matrices underwent bulk erosion, similar to what we reported previously. The obtained data indicate that water diffusion and mass loss are inversely proportional to the polymer’s crosslinking density (Shaker et al. 2010).
Therapeutic advances in cardiac targeted drug delivery: from theory to practice
Published in Journal of Drug Targeting, 2021
Cuican Li, Muhammad Naveed, Kashif Dar, Ziwei Liu, Mirza Muhammad Faran Ashraf Baig, Rundong Lv, Muhammad Saeed, Chen Dingding, Yu Feng, Zhou Xiaohui
In 2010, Liao and colleagues implanted artificial patches on the surface of the heart after chronic myocardial infarction through a thoracotomy, which gave mechanical support to the heart and physically restricted left ventricular remodelling, thus improving heart function [92]. Compared with ordinary materials, Antonio and his colleagues found that elastomeric materials can effectively achieve the above effects [93]. In addition to physical support, conductive biomaterials can avoid ventricular dysfunction caused by electrophysiological conduction disorders, help ventricular synchronous contraction [90,91]. Taimoor and companions proved that conductive composites could regulate the cellular function through in-vitro experiments and proposed that transport can be achieved by combining 3-D porous scaffolds [94]. Combining the patch and cells has obtained an extremely remarkable therapeutic effect [95,96]. To improve patch delivery efficiency, William and associates changed from the patch to a sustained-release reservoir and connected it with the body surface through a subcutaneously implanted pathway to facilitate multiple cell deliveries to the heart [97]. A growing body of evidence showed [98,99] that patch delivers cells addressed not only the shortcomings of low retention, low survival, and easy removal but also provided more effective cardiac function enhancement and cardiac structural recovery than epicardial or intramyocardial injections.
Developing a process for assessing equivalency of wheelchair cushion pressure redistribution performance
Published in Assistive Technology, 2020
Stephen Sprigle, Steven Pubillones
Future work. This work represents early effort in the potential development of a test method for measuring cushion performance with the intent of establishing thresholds for defining equivalency of cushions with similar performance. Most importantly, the value of measuring stress and strain as a reflection of wheelchair cushion performance must be evaluated. Relatedly, the value of defining cushion equivalency must be assessed. The development of such a test method requires addressing myriad issues related to instrumentation, procedures and data analysis. With respect to instrumentation, the use of a compliant indentor must be addressed as its use is more complicated than that of a rigid model. This includes assessment of whether and how the mechanical properties of the elastomer changes over time. If properties change in a manner that impacts stress and strain measurements, the indentor will have to have a defined useful life, after which it must be retired. Testing procedures must address factors such as the conditioning of cushions prior to testing, the load and time parameters used during testing and the number of trials needed to report reliable stress and strain measurements. The means by which stress and strain measurements are analyzed with respect to equivalency must be studied and finalized. Multiple equivalency options have been presented, all of which have benefits and drawbacks.
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