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Transcript of Vascular Grafts
BIEN 010 Section 021
•What We Learned
(cc) image by anemoneprojectors on Flickr
Cardiovascular Disease affects 26.8 million adults in the U.S.
Statistic is still on the rise.
Bioengineers need to find how to reduce the deaths caused by cardiovascular disease.
Unlike other treatment options vascular grafts enable doctors to quickly repair damaged vessels.
Causes of Death
(cc) image by anemoneprojectors on Flickr
Annual Deaths in 2009
To address the current Dacron graft that is on the market and attempt to solve its problems and criticisms.
Specific goals of the project:
•Improve the durability of the graft.
•Avoid clotting and breakage at the points of connection.
•Reduce poor blood flow that is caused by the graft.
Cardiovascular Disease = Having damaged arteries and veins.
Damage can result from:
Breakage of vessels due to aneurysms (ballooning of weakened vessel walls)
Failure of blood vessels over time.
Diabetes, high blood pressure, high cholesterol, and smoking.
Solution = Vascular Grafts
A graft is not a complete replacement but will serve its purpose by acting as a blood vessels to help continue blood flow.
Vascular Grafting is the use of biological/synthetic blood vessels to replace damaged, natural ones.
Deaths, caused by restricted vessels, can be reduced.
Types of Grafts:
To patch up damaged vessels and avoid allografting and autografting.
To replace extremely damaged portions of blood vessels. Without replacement, the patient would most certainly die.
So What Was Done in the Past?
Vascular Surgery was defined by Alexis Carrel.
Vascular Grafts, made out of Vinyon-N Cloth, first used by Arthur Voorhees.
Dacron, a synthetic vascular graft, was used and developed by Dr. De Bakey
Hyperplasia (increase in number of cells) at the distal and proximal end causes stenosis (narrowing of blood vessels) and thrombosis (blood clotting) of arterial bypass grafts.
Caused by compliance mismatch between the graft and artery and leads to stress.
Formation of aneurysms after graft implantation:
•Formed by thrombosis (blood clots due to blood platelets attaching to the wall).
• Symptoms are hard to detect and possible only when patient feels symptoms such as pain.
•Aneurysms can expand greatly.
•Failure to treat can lead to rupture and bleeding.
•Failure of Dacron grafts caused by material fatigue (gradual breakdown of individual fibers = weak prosthetic fabric).
Much improvements needed on today's grafts still .
So, some problems need solutions for current grafts.
True and False Aneurysms
Formation of Clots
Distal Embolization (Decreased blood flow) caused by Occlusions (Clotting of the blood).
Breakages and leakage of blood vessels at the site of anastomisis (the connections of two blood vessels).
Additional blood clots may form after the Heparin dissolves away.
Addition of Heparin.
Reinforcement of anastomosis site using drug eluting stents.
Dissolving layer that releases Heparin.
Results: Better blood flow through the veins by the thinning of the blood, thus clearing the occlusions.
•May cause profuse bleeding as well as headaches, dizziness, and chest pain.
•Can be minimized by the use of low molecular weight heparin (LMWH).
• The Heparin will eventually run out.
Results: The structure will be less likely to break or allow blood to leak through.
Coated with Heparin
Adding stents will cause scar tissue formation.
The blood vessel must be of at least a certain size.
Dacron Graft, bonded with Heparin
Degradable Polylactic Acid with Heparin
Results: Blood clots may be avoided for a longer duration of time, without subjecting the rest of the body to blood thinners.
Polyactic acid may degrade sooner than expected, releasing a larger dose of Heparin which may result in bleeding .
The degrading of PLA (though very slow) is determined by its environmental factors, so there is no control over degradation.
•$64 per 0.8ml of Low Molecular Weight Heparin.
•About $410 Dacron graft.
•$12 per lb polyactic acid.
•$1000 per stent.
Blood clotting, True and False Aneurysms, and eventual disappearance of Heparin.
Use of Heparin, addition of stents at the sites of aneurysms, and usage of a polyactic acid layer to introduce Heparin over time.
Increased blood flow, a reduced blood loss due to aneurysms, and increased protection against blood clots.
Synthetic grafts still fail eventually.
Future graft will be biodegradable and allows regeneration of blood vessel.
What We Learned
•Most products are not perfect
•Many require several improvements
•However, some improvements have side effects, so balance between what is improved and what is worsened is key.
•Bioengineering is not easy!!
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Blood vessels; includes arteries