Bioabsorbalbe coronary stents

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Bioabsorbable Coronary Stents

Submitted To: Dr. Shagufta NazRoll no:329 BS-IV (8th Semester) Department of ZoologyLahore College for Women University

IntroductionIn medicine, astentis any device which is inserted into a blood vessel or other internal duct in order to expand the vessel to prevent or alleviate a blockage. Abioresorbable, biodegradable, or bioabsorbable stentserves the same purpose, but is manufactured from a material that may dissolve or be absorbed in the body.Bioabsorbable scaffolds have been heralded as the fourth revolution interventional cardiology----a novel concept in the treatment of coronary artery disease.

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IntroductionUnique ability to permit the restoration of vascular physiology and integrity as they provide a temporary scaffold.That is necessary to maintain the patency of the vessel after intervention, and then they gradually dissolve, liberating the vessel from its cage. Thus, it is expected that Bioabsorbable stents will potentially overcome the limitations of the traditional stents, such as the risk of late stent thrombosis, and the local inflammation caused by the presence of a foreign body.

Material Characteristics for StentsThe material for bioabsorbable stents is requested to have at least the following characteristics: It must be biocompatible.Degradation products of the material must also be biocompatible. The material must stay in the place for several months before its complete bioabsorption.

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Bioabsorbable Stent DesignThe ideal design should have:Mechanical propertiesMust be biocompatible and would be made of biocompatible Adequate degradation time, have good deliverability.Ideally, it should be able to carry an antiproliferative drug in order to reduce restenosis.

Both the selection of the material and the design are going to influence the success of the device. Mechanical properties----provide the necessary vessel support during the required period.Must be biocompatible and would be made of biocompatible material to prevent vessel irritation, and should have anAdequate degradation time, disappearing without creating an intense inflammatory response. have good deliverability.Ideally, it should be able to carry an antiproliferative drug in order to reduce restenosis.The majority of bioabsorbable materials have low radio-opacity, but the visualization of the device under fluoroscopy can be increased by the use of radio-opaque markers in the balloon or in the device itself5

Mechanism of Absorption

Degradation of polymers generally refers to cleavage of covalent bonds between repeating units.During this chemical process, long backbones break into smaller oligomers (or monomers) by hydrolysis, oxidation, and enzymatic mechanisms.

Degradation of polymers (fig.4) generally refers to cleavage of covalent bonds between repeating units.During this chemical process, long backbones break into smaller oligomers (or monomers) by hydrolysis, oxidation, and enzymatic mechanisms. The small oligomers are phagocytosed by macrophages and further metabolized to carbon dioxide and water by the human body. The polymerization byproducts (initiators, stabilizers, and catalysts) are also released into surrounding tissues, which may cause an adverse response.Increased toxicity due to elevated local concentrations of acid has been reported. The degradation rate is accelerated as water accessibility into the polymer matrix becomes feasible. Water accessibility depends on the chemical structure (hydrophobicity of the polymer, molecular weight), dimension, morphology (crystallinity and porosity), and the local tissue environment.These degradation products are natural metabolites and finally degrade to carbon dioxide and water via the Krebs cycle. 6

Types of StentsRegarding the material, there are two possibilities that are being tested: Polymer-based materials Among the polymers, the one that has been used more frequently is Poly-L-lactic acid (PLLA).Absorbable metals such as magnesium-based alloys.

Bioabsorbable Polymeric StentsThey employ a wide variety of polymers, such as those made from lactic acid, glycolic and caprolactone. The most used polymer for is composed of poly-L-lactic acid (PLLA). PLLA is already found in many medical items, including dissolvable sutures and various implants, and itself has a degradation time of 12-18 months. Another polymer used is the polymer-tyrosine derived polycarbonate and it primarily degrades into L-tyrosine.

Rezolve.sirolimus or paclitaxelIDEAL.both properties anti proliferative anf inflammatoryDESolve.plla based polymer drug matrix9

Dissolvable Metallic StentsThe biodegradable or dissolvable metallic stents consist of either magnesium-based (Mg) or iron-based (Fe) alloys.These metals are alloyed with calcium (Ca), zinc (Zn) and manganese (Mn) as they are well tolerated in the human body. The alloying of Fe with other metals is necessary to alter its ferromagnetism which can reduce MRI compatibility. As for magnesium, it is alloyed to decrease its degradation rate and increase its ductility and strength.

Magnesium based Bioabsorbable Stent

Mg has low thrombogenicity + good compatibility The first metallic bioabsorbable stent implanted in humans was studied in the PROGRESS-AMS trial where 71 magnesium stents, were implanted in 63 patientsno thrombosis, heart attack

There were no deaths, myocardial infarctions, or stent thrombosis, and the stent was no longer. Magnesium is another attractive metal for biodegradable implants because of its low thrombogenicity and well-known biocompatibility. It is an essential trace element and has a high systemic toxic level which is about 7 to 10 millimols per liter of serum [16]. The use of magnesium as a biodegradable stent material was also based on the fact that it is a structural constituent of the tissue and essential element in the living organism. Magnesium is a substantial intercellular cation which is involved in more than 300 biological reactions of cell. Magnesium is also regarded as a non-carcinogenic element [31]. However, magnesium has a rapid degradation in aggressive chloride environments like body fluid. Rapid degradation of magnesium implant results in tissue overload with degradation prTherefore, magnesium is alloyed with other elements such as aluminum, manganese and rare earth elements in order to decrease the degradation rate oducts and this can lead to neointimal formation

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Iron based Bioabsorbable StentsThis stent is made of 41mg pure iron and was implanted in New Zealand white rabbits into its descending aorta.The results from the implantation showed no significant evidence of inflammatory response or neointimal (scar tissue formation) proliferation.Iron is also an interesting candidateMechanical properties. It has a high radial strength and high ductility because of its higher elastic modulus. Iron can interconvert between ferric (Fe2+) and ferrous (Fe3+) ,making it a useful component for cytochromes, oxygen-binding molecules (hemoglobin and myoglobin), and many enzymes

Iron can interconvert between ferric (Fe2+) and ferrous (Fe3+) ions by accepting and donating electrons quite readily, which makes it a useful component for cytochromes, oxygen-binding molecules (hemoglobin and myoglobin), and many enzymes

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Bioabsorbable Coronary Stents: Current Status & Clinical TrialsPresently, 14 different bioabsorbable stents are in preclinical and clinical testing worldwide. As bioabsorbable stents receive FDA approval, the US will acquire market share and steadily become the largest market through 2018 and beyond.Global Data estimates bioabsorbable stent sales to be US$4.2m in 2012 across the US, France, Germany, Italy, Spain and the UK, growing to over US$700m by the end of 2018.

ConclusionBioabsorbable Scaffold have been announced as the fourth revolution in interventional cardiology, introduce a new concept in the treatment of coronary artery disease. Since metallic stents provide better treatment but it is required to last for 612 months. After this period, the presence of stent within the body cannot provide any beneficial effects. Thus, the development of bioabsorbable stents, which can fulfill the mission and step away, is the logical approach.The advantages of the BAS are manifold, with the most key being that it provides no triggers for stent thrombosis.Lastly, the use of this stent will allow a level of psychological relief of concern to patients who dislike the idea of having a foreign material in their bodies for the rest of their lives.

Since metallic stents provide better treatment but it is required to last for 612 months during which arterial remodeling and healing is achieved. After this period, the presence of stent within the body cannot provide any beneficial effects. Thus, the development of bioabsorbable stents, which can fulfill the mission and step away, is the logical approach14

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