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Mechanisms of foam cell formation in atherosclerosis
Low-density lipoprotein (LDL) and cholesterol homeostasis in the peripheral blood is maintained by specialized cells, such as macrophages. Macrophages express a variety of scavenger receptors (SR) that interact with lipoproteins, including SR-A1, CD36, and lectin-like oxLDL receptor-1 (LOX-1). These cells also have several cholesterol transporters, including ATP-binding cassette transporter ABCA1, ABCG1, and SR-BI, that are involved in reverse cholesterol transport. Lipids internalized by phagocytosis are transported to late endosomes/lysosomes, where lysosomal acid lipase (LAL) digests cholesteryl esters releasing free cholesterol. Free cholesterol in turn is processed by acetyl-CoA acetyltransferase (ACAT1), an enzyme that transforms cholesterol to cholesteryl esters. The endoplasmic reticulum serves as a depot for maintaining newly synthesized cholesteryl esters that can be processed by neutral cholesterol ester hydrolase (NCEH), which generates free cholesterol that can exit via cholesterol transporters. In atherosclerosis, pro-inflammatory stimuli upregulate expression of scavenger receptors, especially LOX-1, and downregulate expression of cholesterol transporters. ACAT1 is also increased, while NCEH expression is reduced. This results in deposition of free and esterified cholesterol in macrophages and generation of foam cells. Moreover, other cell types, such as endothelial (ECs) and vascular smooth muscle cells (VSMCs), can also become foam cells. In this review, we discuss known pathways of foam cell formation in atherosclerosis.
Journal Article
Foam roller workbook : illustrated step-by-step guide to stretching, strengthening and rehabilitative techniques
\"Amplify your stretches and exercise using the foam roller. Once used exclusively in physical therapy settings, the foam roller has made its way into yoga and pilates studios, gyms and homes. With this simple device, you can: Improve core strength, Increase flexibility, Release tension, Alleviate pain, Rehabilitate injuries. Foam Roller Workout offers 50 effective exercises paired with clear captions and step-by-step photos that will help you roll your way to better posture, balance and relaxation. In addition, special programs will enhance your sporting life, whether you hit the track, the court, or the slopes\" -- Back jacket.
Book
Polyurethane foams from vegetable oil-based polyols: a review
Polyurethane is a versatile material that can be converted into various forms according to applications. PU foams or PUFs are the most commonly used polyurethanes. These are materials of low density and low thermal conductivity that make them highly suitable for thermal insulating applications. Most of the synthesis of PUFs is still based on the petrochemical industry. There are issues associated with the oil industry, such as environmental pollution, sustainability, and market instability. More recently, we have experienced the COVID-19 pandemic which has destroyed the global supply chain of raw materials. Such sudden disruption of the supply chain affects the global economy. To eliminate the reliance on special ingredients, it is important to find and produce alternate and domestic raw materials. Vegetable oils are organic, cost-effective, and economically viable and present in abundant amounts. The oil consists of triglycerides. It can be functionalized to provide polyol for PU foam synthesis. Herein, we review the literature on factors influencing the properties of PUFs depending on polyols from vegetable oil as well as present a glimpse of the conversion of vegetable oils into polyols for PUF synthesis.
Journal Article
Supramolecular metallic foams with ultrahigh specific strength and sustainable recyclability
Porous materials with ultrahigh specific strength are highly desirable for aerospace, automotive and construction applications. However, because of the harsh processing of metal foams and intrinsic low strength of polymer foams, both are difficult to meet the demand for scalable development of structural foams. Herein, we present a supramolecular metallic foam (SMF) enabled by core-shell nanostructured liquid metals connected with high-density metal-ligand coordination and hydrogen bonding interactions, which maintain fluid to avoid stress concentration during foam processing at subzero temperatures. The resulted SMFs exhibit ultrahigh specific strength of 489.68 kN m kg
−1
(about 5 times and 56 times higher than aluminum foams and polyurethane foams) and specific modulus of 281.23 kN m kg
−1
to withstand the repeated loading of a car, overturning the previous understanding of the difficulty to achieve ultrahigh mechanical properties in traditional polymeric or organic foams. More importantly, end-of-life SMFs can be reprocessed into value-added products (e.g., fibers and films) by facile water reprocessing due to the high-density interfacial supramolecular bonding. We envisage this work will not only pave the way for porous structural materials design but also show the sustainable solution to plastic environmental risks.
Porous materials with high strength are desirable for many applications. Here, the authors present a supramolecular metallic foam enabled by nanostructured liquid metals connected with high-density metal-ligand coordination to exhibit ultrahigh specific strength and recyclability.
Journal Article
TREM2 promotes cholesterol uptake and foam cell formation in atherosclerosis
Disordered lipid accumulation in the arterial wall is a hallmark of atherosclerosis. Previous studies found that the expression of triggering receptor expressed on myeloid cells 2 (TREM2), a transmembrane receptor of the immunoglobulin family, is increased in mouse atherosclerotic aortic plaques. However, it remains unknown whether TREM2 plays a role in atherosclerosis. Here we investigated the role of TREM2 in atherosclerosis using
ApoE
knockout (
ApoE
−/−
) mouse models, primary vascular smooth muscle cells (SMCs), and bone marrow-derived macrophages (BMDMs). In
ApoE
−/−
mice, the density of TREM2-positive foam cells in aortic plaques increased in a time-dependent manner after the mice were fed a high-fat diet (HFD). Compared with
ApoE
−/−
mice, the
Trem2
−/−
/
ApoE
−/−
double-knockout mice showed significantly reduced atherosclerotic lesion size, foam cell number, and lipid burden degree in plaques after HFD feeding. Overexpression of TREM2 in cultured vascular SMCs and macrophages exacerbates lipid influx and foam cell formation by upregulating the expression of the scavenger receptor CD36. Mechanistically, TREM2 inhibits the phosphorylation of p38 mitogen-activated protein kinase and peroxisome proliferator activated-receptor gamma (PPARγ), thereby increasing PPARγ nuclear transcriptional activity and subsequently promoting the transcription of CD36. Our results indicate that TREM2 exacerbates atherosclerosis development by promoting SMC- and macrophage-derived foam cell formation by regulating scavenger receptor CD36 expression. Thus, TREM2 may act as a novel therapeutic target for the treatment of atherosclerosis.
Graphical abstract
Journal Article
Chemical upcycling of commodity thermoset polyurethane foams towards high-performance 3D photo-printing resins
Polyurethane thermosets are indispensable to modern life, but their widespread use has become an increasingly pressing environmental burden. Current recycling approaches are economically unattractive and/or lead to recycled products of inferior properties, making their large-scale implementation unviable. Here we report a highly efficient chemical strategy for upcycling thermoset polyurethane foams that yields products of much higher economic values than the original material. Starting from a commodity foam, we show that the polyurethane network is chemically fragmented into a dissolvable mixture under mild conditions. We demonstrate that three-dimensional photo-printable resins with tunable material mechanical properties—which are superior to commercial high-performance counterparts—can be formulated with the addition of various network reforming additives. Our direct upcycling of commodity foams is economically attractive and can be implemented with ease, and the principle can be expanded to other commodity thermosets.Current strategies for recycling cross-linked polyurethane foam waste are economically unattractive and/or lead to recycled products with inferior properties. Now it has been shown that a cost-effective chemical strategy can be used to turn the foam into high-performance value-added three-dimensional photo-printing resins.
Journal Article
Glycolysis: an efficient route for recycling of end of life polyurethane foams
The increased applications of Polyurethane
(
PU) materials give rise to a higher amount of wastes, which have a devastating effect on the earth in turn; therefore, the management of end-of-life wastes is one of the most important issues in the modern world. Although incineration and landfilling are the most common procedure adopted for waste disposal, but both of them caused environmental problems such as air and soil pollution. Moreover, the former triggers global warming, and the latter causes water pollution making the problem worst. As a consequence, finding economical and environmentally friendly methods are a high priority topic for researchers to overcome this problem. Fortunately, recycling is an environmentally attractive solution, and there is an increased interest by the researchers in recycling PU wastes. Several recycling techniques for PUs have been described in the technical and scientific literature. Without any doubt, glycolysis reaction is one of the most important recycling method, especially for rigid and flexible PUs. In this review, glycolysis of waste polyurethane foam (PUF) materials with different glycols and catalysts, especially metallic ones were considered, and the effect of some additional parameters such as the nature of glycol, catalyst, temperature and material ratio were discussed too. In addition, a brief description on characterization of recycled products, and potential application of regenerated products is carried out.
Graphical abstract
Journal Article
A Review of Rigid Polymeric Cellular Foams and Their Greener Tannin-Based Alternatives
This review focuses on the description of the main processes and materials used for the formulation of rigid polymer foams. Polyurethanes and their derivatives, as well as phenolic systems, are described, and their main components, foaming routes, end of life, and recycling are considered. Due to environmental concerns and the need to find bio-based alternatives for these products, special attention is given to a recent class of polymeric foams: tannin-based foams. In addition to their formulation and foaming procedures, their main structural, thermal, mechanical, and fire resistance properties are described in detail, with emphasis on their advanced applications and recycling routes. These systems have been shown to possess very interesting properties that allow them to be considered as potential substitutes for non-renewable rigid polymeric cellular foams.
Journal Article
Recycling of Polyurethane Foams via Glycolysis: A Review
Polyurethane foams constitute highly problematic waste due to their low density and consequently large volume. Among the most promising recycling approaches, the glycolysis of polyurethane waste stands out and was extensively discussed in this article. Existing literature reviews lack a detailed analysis of glycolysis processes and a clear presentation of the most important data. However, in this review, the scientific literature on glycolysis has been thoroughly examined and updated with the latest research in the field. The article provides an overview of glycolysis methods, categorized into rigid and flexible foams, along with a review of the catalysts and process conditions employed. Additionally, this study offers a comprehensive analysis of industrial methods protected by active patents, which has not been previously explored in the literature. This detailed examination of patent information adds significant value to the review and distinguishes it from others. Furthermore, this review also aims to introduce the main types of polyurethanes and their properties. It outlines the fundamentals of recycling strategies, thermomodernization trends, and environmental considerations, highlighting the critical role of recycling in the industry. The article serves as a complete foundation for exploring new alternative methods in this field.
Journal Article