A medical device stent is a small mesh tube placed into a hollow structure in the body. A stent restores flow in a blocked passage. Narrowing or blockage of a structure is known as stenosis. It can occur due to cholesterol build-up in the blood vessels or narrowing of the vessel—stents aid in preventing a reoccurrence of stenosis in the structure. There are a variety of sizes and materials used for making stents. Location, size, and individual case factors determine the type of stent used in a procedure.
Medical Device Stent Types
The most used medical device stents are bare-metal stents (BMS), drug-eluting stents (DES), stent-grafts, and polymer stents.
Bare metal stents (BMS) are mesh-like tubes made of thin metal without coatings or coverings. Different metals used to create stents are stainless steel, cobalt-chromium, platinum chromium, and other suitable metals. These metals may come in the form of wires, tubes, or sheets. Sheets are made into tubular configurations by welding or special mechanical locking features.
Drug-eluting stents (DES) are metal stents coated with medicine. The medicine can be coated directly on the metal stent, or a medicine-infused polymer coating can be applied to the metal. The medicine is released over time to prevent restenosis and other post-implantation complications. The new generation of drug-eluting stents uses the -limus family of drugs. These drugs include everolimus, zotarolimus, umirolimus, novolimus, and amphilimus. Each differs in structure, potency, molecular weight, and lipophilicity.
Dual therapy stents (DTS) are similar to drug-eluting stents. The difference between the two is the amount of drug coating. Dual therapy stents have a coating on both sides of the stent. This stent is the latest type of coronary stent developed.
Bioresorbable vascular scaffolds are a drug-eluting stent with a few more additions. They are made with a dissolvable scaffold which is absorbed over time. Drug coated polymers are used in bioresorbable vascular scaffolds. Many materials are used for the scaffolding backbone, but magnesium alloys, PLLA, and tyrosine polycarbonate are the most used.
Stent grafts are metal stents covered with a fabric tube, also known as the covering or graft. A metal stent supports the fabric tube. The stent can be covered by a graft or synthetic materials sewn into the metallic stent frame. Stent grafts are more commonly used in larger vessels, such as the aorta and aneurysms.
Polymer stents are made of an array of polymer materials. These stents are easily moldable to create and hold desired shapes. Polymer stents have a widespread application. They are used as stent platforms, also known as scaffolds, and coating for drug-eluting stents. Apart from the permanent polymers used to create scaffolds and coatings for drug-eluting stents, polylactide, a biodegradable polymer, is used to make biodegradable stents.
Medical Device Stent Uses
Medical device stents are not universal. One stent type cannot be used for all anatomical procedures. Each area has unique characteristics and functions that are considered when making stents. Stents can also have anatomical categories depending on the stent characteristics and uses.
Coronary (heart) stents are placed into the arteries leading into the heart to keep them open, a coronary angioplasty procedure. A build-up of plaque in the arteries can reduce blood flow into the heart resulting in a blood clot. Blocking the blood flow to the heart could lead to a heart attack and heart disease. Coronary stents can be bare-metal stents or drug-eluting stents. Drug-eluting stents are used more commonly to aid in the prevention of future artery blockage or narrowing. Drug-eluting coronary stents can be permanent polymer drug-eluting stents or bioabsorbable polymer drug-eluting stents. In the case of permanent polymer drug-eluting stents, the polymer stays on the stent, even after the drug has been released. The body fully absorbs bioabsorbable polymer drug-eluting stents after the drug has been fully released.
Carotid artery stents are placed in carotid arteries located in the neck, which allow blood flow to the brain. This procedure is called carotid artery angioplasty. Plaque build-up in these arteries could increase the risk of strokes which may cause further damage to the brain. Based on the situation, carotid stents may be bare metal or drug-eluting. The use of Nitinol is widespread for carotid artery stents as they are known for it is known for its self-expanding characteristics.
Peripheral vascular stents are placed in the legs or arms where the peripheral arteries are located. This procedure is called a peripheral artery angioplasty. Build-up, or blockage, in these arteries, or veins, can reduce blood flow to the limbs resulting in pain and loss of function over time. Bare metal stents or stent-grafts are used to restore the blood flow in peripheral arteries.
Ureteral stents are placed in the ureter, tubes that transport urine from the kidneys to the bladder. Blockage in the ureter, build-up, or kidney stones, may result in a stent placement to restore normal urine flow. Ureteral stents are soft and flexible long polymer stents. These stents may only be placed for a few days in some instances.
Prostatic stents are placed in the prostate when blockage or narrowing of the urethra, the tube that carries urine out of the body, occurs. Prostatic stents are typically metal stents that may be placed temporarily or, in some cases, permanently.
Esophageal stents are placed in the esophagus, the tube that connects the throat to the stomach. These stents are placed due to the constriction (narrowing) of the esophagus or a blockage. The blockage or narrowing may cause pain, difficulty swallowing and even choking. Esophageal stents are typically metal stents or polymer stents.
Airway stents help open the air passages to the lungs. These stents include laryngeal stents to open the larynx (voice box), tracheal stents, to open the trachea (windpipe), and bronchial stents, to open the bronchia. Airway stents may be a polymer, bare metal, or hybrid stents.
Medical Procedures for Stents
While there are a variety of medical device stents, the procedures for stent placements are relatively similar. The process of placing a stent is known as stenting. Some stenting procedures also include an angioplasty. An angioplasty involves a balloon catheter being inserted into the vessel through a small incision in the body. The catheter is guided to the artery where the build-up/blockage has occurred. Once in place, the balloon is inflated, expanding the balloon, compressing the build-up, and restoring the flow.
Coronary stents, carotid artery stents, and peripheral vascular stents are inserted by an angioplasty procedure. The critical difference between a stent angioplasty and a regular angioplasty is the placement of the stent onto the balloon catheter before it is initially inserted into the body. When the balloon is inflated at the blockage site, the stent expands with the balloon. When the balloon is deflated for removal, the stent remains in the expanded shape, keeping the plaque compressed and the artery open.
Ureteral, prostatic, esophageal, and airway stents are placed using stenting. Stenting typically involves a guidewire or catheter being put into the body along with a stent and moved to the desired anatomical location. Once in the desired location, the stent expands and coils slightly to ensure it stays in the proper area. The guidewire or catheter is removed once the stent is placed and supporting the passageway.
Specific medical device stent types are used for specific medical procedures. The procedure is a critical factor in determining the type of stent that would need to be manufactured. Regardless of the stent type and use, the end purpose of a stent is to keep a passageway open to restore the original flow and function of the structure and prevent future recurrences.
If you want to learn more information and discuss how ProPlate® can collaborate with you on your stent development project, please contact our Business Development Team at Sales@proplate.com or (763) 427-0112.