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Bioabsorbalbe coronary stents
Bioabsorbable stents are manufactured from materials that dissolve in the body over time. They serve the same purpose as traditional metal stents by expanding a blocked blood vessel, but eventually degrade so the vessel is freed from the scaffold. Polymer-based materials like PLLA and absorbable metals such as magnesium alloys are being tested. Bioabsorbable stents could overcome limitations of permanent metal stents by eliminating risk of late thrombosis and local inflammation once dissolved. Several types are currently in clinical trials and projected to gain significant market share as they receive FDA approval.
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Bioabsorbalbe coronary stents
- 1. Bioabsorbable Coronary Stents Submitted To:Dr. Shagufta Naz Roll no:329 BS-IV (8th Semester) Department of Zoology Lahore College for Women University
- 2. Introduction In medicine,a stent is 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. A bioresorbable, biodegradable, or bioabsorbable stent serves 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.
- 3. Introduction Unique abilityto 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.
- 4. Material Characteristic s for Stents The 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.
- 5. Bioabsorbable Stent Design Theideal design should have: Mechanical properties Must 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.
- 6. Mechanism of Absorption Degradation ofpolymers 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.
- 7. Types of Stents Regardingthe 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.
- 8. Bioabsorbable Polymeric Stents They employa 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.
- 10. Dissolvable Metallic Stents Thebiodegradable 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.
- 11. 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 patients…no thrombosis, heart attack
- 12. Iron based Bioabsorbable Stents Thisstent 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 candidate…… Mechanical 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
- 13. Bioabsorbable Coronary Stents: Current Status & Clinical Trials Presently, 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.
- 14. Conclusion Bioabsorbable Scaffoldhave 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 6–12 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.
- 15. Put down theremote and go for walk………… Thanks…..
Editor's Notes
- #6 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 an Adequate 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 itself
- #7 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.
- #10 Rezolve….sirolimus or paclitaxel IDEAL…….both properties anti proliferative anf inflammatory DESolve….plla based polymer drug matrix
- #12 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
- #13 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
- #15 Since metallic stents provide better treatment but it is required to last for 6–12 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 approach