Charles Thomas Stent, 1807, London dentist (gutta percha,
Charles Thomas Stent, 1807, London dentist (gutta percha, gum Palaquium gutta) . Stents Material Studies in Plastic Surgery of the Face Annals of Surgery , 1917 Stent Dr Stents () ( )
Mulliken JB, Goldwyn RM: Impressions of Charles Stent. Plastic & Reconstructive Surgery 62:173176, 1978. stent Charles T. Dotter, 1969. stent . Dotter CT: Transluminally placed coilspring endarterial tube grafts. Invest Radiol 4:327332, 1969.
Dotter and Judkins : 1964: 1977: Grntzig : 1985. Palmaz et al. : 1986: Schatz et al. Palmaz stent, stent, the PalmazSchatz stent. 1986:Puel and Sigwart stent a self expanding mesh device. 1987
. stent : a) ( ) b) () stent : Self expanded Balloon expanded stent Balloon expanded stents (Pre-mounted)
Non mounted , ( Spring load ) (Plastic deformation) (Thermal memory) (Expansibility ratio ) H stent :
(shortening) stent stent A stent with an expansibility ratio of 4 and an optimal expanded diameter of 5 mm will have an unexpanded diameter of 1 .25 mm, or 3.75 French. Hoop stress stent the hoop stress (residual circumferential elasticity) collapse , .
stent ( Method of deployment) (Flexibility) (Crush -not crush- on external pressure Radial strength, Hoop stress ) (Radiopacity) , (Predictability of final deployment location and length) (Ability to be repositioned prior to complete deployment) (Material of construction)
High hoop strength , , ( High expansion ratio)
Side branch accessibility stent stent 5-20 nm ()
PLT, Balloon expanded stents Palmaz stent Non mounted High expandability Only few diameters (4-9mm, 8-12mm) Final diameter depends on the size of balloon used to deploy it Ability to use in areas of vessel size changes e.g. common to external iliac artery? Balloon expanded stents Palmaz stent Risk of dislodgment (undeployd stent from the balloon) WHEN? Turns in the vascular system
Solution Always advancement within a sheath or G Catheter Technique for secure fixation in the balloon? Balloon expanded stents Palmaz stent If partial or complete dislodgment occurs Inside sheath Outside sheath SOLUTION If possible deploy the stent in other vessel Balloon expanded stents Palmaz stent Risk to open forward or backward of the balloon Solution Ensure that the stent remains centered on the balloon before initiating deployment Balloon expanded stents
Palmaz stent Risk of delivery fail at aortic bifurcation Flexibility related Use only short length balloons Palmaz Schatz (articulated stent flexibility) Balloon expanded stents Corinthian stent (pre-mounted) Self expanding stents , Self expanding stents
Nitinol coil stent used by Dotter A coil wound to a small diameter and delivered through a catheter into the vessel would expand to a larger diameter, upon warming with 60C saline solution Self expanding stents Wallstent 1st self-expandable stent Braided wires Made of a cobalt (Co)chromium (Cr) alloy (Elgiloy), Mo was clinically applied in 1986 Low strength at end-points Corrosion resistance Narrow range of expansion (large inventory of
stents) Maximal foreshortening , Accuracy only distally Can be recaptured during deployment Self expanding stents Wallstent Good flexibility but Apposition () to vessel wall fair, may not make adequate wall contact Avoid its use in tortous vessels Modular designs (Laser cut Nitinol ) offer better apposition Ni-Ti (nitinol) '60 William Buehler, Naval Ordnance Laboratory Silver Springs, Maryland, , Andreasen '70 "Nitinol". Nitinol"Nitinol". .
(Ni Ti) Naval Ordnance Laboratory. 55% Ni 45% Ti, ( 1-1 .) Nitinol stents They are superelastic (crush recoverable) 10% - , . , , .
Constant force, Dynamic interference Flat unloading curve over a wide deflection (strain) range Importance Exert a gentle chronic outward force . stent Nitinol Properties Kink Resistance Extreme deformation of a Nitinol stent (Cordis SMART). The stent will recover after the load is removed Suitable in superficial vessels
Ni-Ti (nitinol) Ni-Ti . . Co 1.6%. Nitinol stents Temperature - dependent stiffness. Nitinol stents with a transition temperature of 30C Weak when squeezed at low temperature. Much stiffer when squeezed at temp. above 30. Wire-based stent designs Wire-based stent designs
ZA stent (Cook) Symphony stent (Boston Scientific) wire formed design with struts welded to form hexagonal cells Braided or weld wire struts: larger catheters Wire-based stent designs stents Sheet-based stent designs When Nitinol sheet became available, Angiomed (Bard) developed the first laser-cut Nitinol stent by cutting a pattern from sheet, rolling it up, and welding at specific strut locations
Memotherm stent Sheet-based stent designs Vascular architects Aspire stent dual-rail ladder type frame from Nitinol sheet and covered with ePTFE. Proposed to keep vessel side branches open. Suitable in distal SFA, popliteal territory Tube-based stent designs Presently Most self-expanding Nitinol stents are produced by laser cutting of Nitinol tubing. Tube-based stent designs Laser-cut Nitinol tubular stents. Top: Memotherm (Bard Angiomed) bottom: SMART (Cordis) Laser-cut Nitinol tubular stents. Top: Jostent SelfX (Jomed)
bottom: DynaLink (Guidant) DES Components of a drug eluting stent a)Platform (stent itself) b)Carrier (usually a polymer) c) Agent (drug) DES Currently investigational for non coronary applications Results from ZILVER PTX and STRIDES non randomized controlled trials are anticipated DES in SFA provide no additional benefit over current nitinol BMS (COMPLEX LESIONS?) Preliminary results in the BK arteries are encouraging (Siamblis 2005,Bosiesr 2006,Commeau 2006) Bioabsorbable stents Stent
() , .. Bioabsorbable stents The bioabsorbable magnesium-alloy stent (BIOTRONIK AG) was first implanted safely in infrapopliteal and human coronary arteries Bioabsorbable stents POLYMERS Polylactic, polyglycolic acid Limitation Lower strength Greater bulk Atrophic changes of the arterial wall may lead to aneurysmal dilatation METALS Mg
Metals Limitation: Inflammatory response elicited after implantation Bioabsorbable stents Second generation AMS is under development Optimization of the Mg alloy resulting in a longer degradation time Stent design with increased radial force Stent sizes should be better adapted to peripheral lesions. Bioabsorbable stents Duke biodegradable stent IgakiTamai biodegradable stent poly-L-lactide (BAS plus DES) STENT
2. Activity of the Solvent. When a solution is made infinitely dilute, it can be considered to consist essentially of pure solvent. Therefore, X. 1 = 1, and the solvent behaves ideally in conformity with Raoult's law.. Under this condition,...
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