Computational analysis of mechanical stress-strain interaction of a bioresorbable scaffold with blood vessel

Crimping and deployment of bioresorbable polymeric scaffold, Absorb, were modelled using finite element method, in direct comparison with Co-Cr alloy drug eluting stent, Xience V. Absorb scaffold has an expansion rate lower than Xience V stent, with a less outer diameter achieved after balloon deflation. Due to the difference in design and material properties, Absorb also shows a higher recoiling than Xience V, which suggests that additional post-dilatation is required to achieve effective treatment for patients with calcified plaques and stiff vessels. However, Absorb scaffold induces significantly lower stresses on the artery-plaque system, which can be clinically beneficial. Eccentric plaque causes complications to stent deployment, especially non-uniform vessel expansion. Also the stress levels in the media and adventitia layers are considerably higher for the plaque with high eccentricity, for which the choice of stents, in terms of materials and designs, will be of paramount importance. Our results imply that the benefits of Absorb scaffolds are amplified in these cases

Effect of two-year degradation on mechanical interaction between a bioresorbable scaffold and blood vessel

This paper aims to evaluate the mechanical behaviour of a bioresorbable polymeric coronary scaffold using finite element method, focusing on scaffold-artery interaction during degradation and vessel remodelling. A series of nonlinear stress-strain responses was constructed to match the experimental measurement of radial stiffness and strength for polymeric scaffolds over 2-year in-vitro degradation times. Degradation process was modelled by incorporating the change of material property as a function of time. Vessel remodelling was realised by changing the size of artery-plaque system manually, according to the clinical data in literature. Over degradation times, stress on the scaffold tended to increase firstly and then decreased gradually, corresponding to the changing yield stress of the scaffold material; whereas the stress on the plaque and arterial layers showed a continuous decrease. In addition, stress reduction was also observed for scaffold, plaque and artery in the simulations with the consideration of vessel remodelling. For the first time, the work offered insights into mechanical interaction between a bioresorbable scaffold and blood vessel during two-year in-vitro degradation, which has significance in assisting with further development of bioresorbable implants for treating cardiovascular diseases

Treating medical conditions by polymerizing macromers to form polymeric materials

Water soluble macromers are modified by addition of free radical polymerizable groups, such as those containing a carbon-carbon double or triple bond, which can be polymerized under mild conditions to encapsulate tissues, cells, or biologically active materials. The polymeric materials are particularly useful as tissue adhesives, coatings for tissue lumens including blood vessels, coatings for cells such as islets of Langerhans, and coatings, plugs, supports or substrates for contact with biological materials such as the body, and as drug delivery devices for biologically active molecules. A medical condition at a localized site is treated by applying a polymerization initiator and then applying a substantially water-soluble, degradable macromer of at least 200 mw and having at least two crosslinkable substituents, and polymerizing the macromer to form a crosslinked polymeric material at the site. The crosslinked polymeric material may adhere two surfaces together, or be a barrier that provides immunoisolation or prevents adhesion of the site to another surface such as post-surgical adhesion. A biologically active material may be present when the macromer is polymerized to provide for delivery of the biologically active material, or to provide the polymeric material with a desired property such as resistance to bacterial growth or a decrease in inflammatory response.Board of Regents, University of Texas Syste

Quantifying the mechanical properties of polymeric tubing and scaffold using atomic force microscopy and nanoindentation

Measurement of mechanical parameters of polymeric scaffolds presents a significant challenge due to their intricate shape and small characteristics dimensions of their elements – around 100μm. In this study, mechanical properties of polymeric tubing and scaffold, made of biodegradable poly (l-lactic) acid (PLLA), were characterised using atomic force microscopy (AFM) and nanoindentation, complemented with tensile testing. AFM was employed to assess the properties of the tube and scaffold locally, whilst nanoindentation produced results with a dependency on the depth of indentation. As a result, the AFM-measured elastic modulus differs from the nanoindentation data due to a substantial difference in indentation depth between the two methods. With AFM, a modulus between 2 and 2.5 GPa was measured, while a wide range was obtained from nanoindentation on both the tube and scaffold, depending on the indentation scale. Changes in the elastic modulus with in-vitro degradation and ageing were observed over the one-year period. To complement the indentation measurements, tensile testing was used to study the structural behaviour of the tube, demonstrating the yielding, hardening and fracture properties of the material

Mechanical and chemical characterisation of bioresorbable polymeric stent over two-year in vitro degradation

Polymeric stent is a temporary cardiovascular scaffold, made of biodegradable poly (l-lactic) acid, to treat coronary artery stenosis, with expected resorption by the human body over two to three years. In this paper, the mechanical properties of a polymeric stent over two-year in vitro degradation were studied and characterised using atomic force microscopy and nanoindentation techniques, complemented with analyses of weight loss, gel permeation chromatography and differential scanning calorimetry. Atomic force microscopy assessed stent degradation at the surface, whilst nanoindentation was able to investigate the property at a greater depth into the material. No significant changes to the Young’s modulus were observed with the atomic force microscopy due to bulk degradation nature of the polymer. Chemical analyses demonstrated a reduction of molecular weight and an increase of crystallinity, indicating degradation of the stents. Berkovich nanoindentation showed a trend of reduction in modulus over in vitro degradation, which was, however, not continuous due to the variations of measurements associated with the pyramidal indenter tip and the semi-crystalline structure of the polymer

Computational analysis of mechanical stress–strain interaction of a bioresorbable scaffold with blood vessel

This paper was accepted for publication in the journal Journal of Biomechanics and the definitive published version is available at http://dx.doi.org/10.1016/j.jbiomech.2016.05.035Crimping and deployment of bioresorbable polymeric scaffold, Absorb, were modelled using finite element method, in direct comparison with Co-Cr alloy drug eluting stent, Xience V. Absorb scaffold has an expansion rate lower than Xience V stent, with a less outer diameter achieved after balloon deflation. Due to the difference in design and material properties, Absorb also shows a higher recoiling than Xience V, which suggests that additional post-dilatation is required to achieve effective treatment for patients with calcified plaques and stiff vessels. However, Absorb scaffold induces significantly lower stresses on the artery-plaque system, which can be clinically beneficial. Eccentric plaque causes complications to stent deployment, especially non-uniform vessel expansion. Also the stress levels in the media and adventitia layers are considerably higher for the plaque with high eccentricity, for which the choice of stents, in terms of materials and designs, will be of paramount importance. Our results imply that the benefits of Absorb scaffolds are amplified in these cases

Modelling the impact of atherosclerosis on drug release and distribution from coronary stents

Although drug-eluting stents (DES) are now widely used for the treatment of coronary heart disease, there remains considerable scope for the development of enhanced designs which address some of the limitations of existing devices. The drug release profile is a key element governing the overall performance of DES. The use of in vitro, in vivo, ex vivo, in silico and mathematical models has enhanced understanding of the factors which govern drug uptake and distribution from DES. Such work has identified the physical phenomena determining the transport of drug from the stent and through tissue, and has highlighted the importance of stent coatings and drug physical properties to this process. However, there is limited information regarding the precise role that the atherosclerotic lesion has in determining the uptake and distribution of drug. In this review, we start by discussing the various models that have been used in this research area, highlighting the different types of information they can provide. We then go on to describe more recent methods that incorporate the impact of atherosclerotic lesions

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac

Surface-immobilized polyethylene oxide for bacterial repellence

Polyethylene terephthalate films were surface-modified with polyethylene oxide (18,500 g/mol) using a solution technique described previously. These films were investigated for their resistance to bacterial adhesion. Three bacterial strains most commonly associated with implant infections, Staphylococcus epidermidis, Staphylococcus aureus and Pseudomonas aeruginosa, were cultured in tryptic soya broth, human plasma and human serum on the polymeric substrates. Significant reductions (between 70 and 95%) in adherent bacteria were observed on the polyethylene oxide-modified substrates compared to the untreated control polyethylene terephthalate. Surface modification with polyethylene oxide may reduce the risk of implant-associated infections. Plasma fibrinogen was observed to play an important role in the adhesion of all three of these species on both the polyethylene oxide-modified and control polyethylene terephthalate materials. [on SciFinder (R)

Resistance to noise-induced gap detection impairment in FVB mice is correlated with reduced neuroinflammatory response and parvalbumin-positive neuron loss

Exposure to loud noises results in neuroinflammatory responses in the central auditory pathway. Noise-induced neuroinflammation is implicated in auditory processing deficits such as impairment in gap detection. In this study, we examined whether strain differences between the FVB and C57BL/6 mice in noise-induced impairment in gap detection are correlated with strain differences in neuroinflammatory responses. We found that noise induced more robust TNF-α expression in C57BL/6 than in FVB mice. Noise-induced microglial deramification was observed in C57BL/6 mice, but not in FVB mice. Furthermore, noise exposure resulted in a reduction in parvalbumin-positive (PV+) neuron density in the C57BL/6 mice, but not in FVB mice. These results suggest that neuroinflammatory responses and loss of PV+ neurons may contribute to strain differences in noise-induced impairment in gap detection. © 2020, The Author(s).Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]