Polymeric Implant Materials PDF

Polymeric Implant Ch4: Materials Dr Nur Nabilah Shahidan Room: BSP 2.18 This Photo by Unknown Author is licensed under CC BY ...

Polymeric Implant Ch4: Materials Dr Nur Nabilah Shahidan Room: BSP 2.18 This Photo by Unknown Author is licensed under CC BY  FR Outline: 2. Vascular 1.Suture 3. Stents Grafts Add a footer 2  FR natural origin synthetic 1. SUTURES absorbable A strand of material that is used to approximate tissues or to sutures absorption ligate blood vessels during the wound-healing period (Ratner nonabsorbable et al. 2004). They are used to close wounds due to injury or surgery. multifilament Fiber construction 3 monofilament  FR Suture Types & Materials There are three major types of sutures: Monofilament Braided Monofilament Braided  FR Suture Types & Materials There are three major types of sutures: Monofilamented Sutures are prepared from a Monofilament single strand of material Advantages Glides easily through tissue Resist harboring organisms that may cause infection Disadvantages More difficult to tie than braided sutures Must be handled carefully – Crimping may cause nicks that weaken the strand  FR Suture Types & Materials There are three major types of sutures: Braided Sutures are prepared from many small monofilaments woven together Braided Advantages Affords greater strength, pliability & flexibility Generally easier to handle & tie than monofilamented sutures Disadvantages Tend to absorb liquids More likely to harbor pathogens that can lead to Next infection Next  FR Suture Types & Materials There are three major types of sutures: Monofilament Braided Advantages Combines benefits of monofilaments & braided sutures Disadvantages Only available for a few material types Monofilamented Braided Sutures Can still lead to infection are prepared by braiding a small number of monofilament strands  FR Suture Types & Materials There are several materials that are used to make sutures. These materials can be: Synthetic Natural =C Nylon 6 =O =N =H ~or~ Nylon 6,6 Silkworm and its Cocoon http://www.answers.com/topic/nylon6-and-nylon-66-png http://www.msm.cam.ac.uk/doitpoms/tlplib/bioelasticity/printall.php Examples: Nylon, Polyglactin Examples: Silk, Catgut Catgut is extracted from the intestines of sheep or goats. Synthetic materials are generally preferred because they cause lower levels of tissue interaction  FR Suture Types & Materials There are several materials that are used to make sutures. These materials can also be: Non-Absorbable Absorbable ~ or ~ Remain in the wound tissue & are ultimately Degraded by enzymes or through hydrolysis encapsulated by fibroblasts Typically absorb fully within 100 days May be removed after adequate healing Examples: Catgut, Polyglycolic acid, Examples: Silk, Nylon & Polypropylene Polyglactin & Polydioxanone  FR Suture Types & Materials Typical sutures for cutaneous wounds: Natural/ Absorbable/ Material Types Notes/Comments Synthentic Non-Absorbable Glides in tissue more easily than nylon Polypropylene Synthetic Non-absorbable High plasticity, poor knot security (Prolene) Minimal tissue reaction Nylon High tensile strength & easy to handle A cutaneous wound is a Synthetic Non-absorbable Excellent elasticity but high memory defined as a disruption of (Ethilon) Minimal tissue reaction normal anatomic structure Spun by silkworm larvae and function of the skin that Non-absorbable Silk Natural Superior handling characteristics occurs owing to an injury of (but degrades slowly) High levels of tissue reaction the skin. Made from animal intestines Catgut Natural Absorbable Poor knot security & high memory High levels of tissue reaction During cutaneous wound Copolymer of lactide and glycolide healing, the barrier and Polyglactin-910 Synthetic Absorbable Initially strong & then rapidly degrades mechanical properties of (Vicryl) Minimal tissue reaction skin are restored by the Polyglycolic acid Stiff & monofilaments difficult to handle actions of numerous cell Synthetic Absorbable Excellent knot security types which undergo (Dexon) Minimal tissue reaction proliferation,differentiation, Soft, pliable – Ideal for soft tissue types migration and apoptosis to Polydioxanone Synthetic Absorbable Difficult to handle & knot (PDS II) Minimal tissue reaction rebuild the skin. Commercials name  FR SUTURES The various types of sutures are summarized in Table 12 a: T, Twisted monofilament; M, monofilamene; B, multifilament braid Reprinted with permission from Roby (1998). Copyright © 1998, Elsevier. FR  FR 2. VASCULAR GRAFT Blood vessel (arteries /veins) transport blood Vascular disease : disorder involving blood vessels 2 main blood vessel disorder are : a) Aneurysms (vascular) b) Atherosclerosis (cardiovascular)  FR Aneurysm: Description of the disease state An aneurysm is a bulge in a blood vessel caused by a weakness in the blood vessel wall. When a weak part of the aorta expands or bulges it is called An Abdominal Aortic Aneurysm (AAA) 40 AAA can stretch the aorta beyond its safety margin after Similarly 41 which it can rupture leading to shock or death Blow too much air into a balloon-IT BURSTS !!  FR What is Atherosclerosis? ▪ Atherosclerosis is a condition in which fatty deposits develop along the inner walls of the arteries (plaque). ▪ These deposits thicken and harden and eventually block the arteries which may prevent the flow of blood.  FR Treatment Options Bypass Surgery using vascular grafts is the most common treatment option Coronary Artery Bypass Peripheral Artery Bypass AsVascular shown in the Atherosclerosis animation, plaque Graft formation blocks the flow of blood in the vessel Plaque Synthetic Graft made of a polymer (E.g. PTFE, Dacron) is sutured in at the site where the blood flow is blocked After the graft attachment The The path ofnormal blood blood flow flow to needs continues be diverted Using a Bypass. VASCULAR GRAFTS are used for this purpose End of Animation End of Animation Types of Vascular Grafts Autograft Synthetic Allograft Xenograft Tissue Engineered Types of Vascular Grafts Autograft is the primary choice of the surgeon before he considers other options Autograft Internal Mammary Synthetic Saphenous Artery Bypass Vein Bypass Allograft 6 Xenograft Tissue Engineered Source: Graft transplanted from one part of patient’s body to another. Example: Saphenous Vein Graft for Bypass, Internal Mammary Artery Bypass Types of Vascular Grafts The main Focus of this module is Synthetic Grafts made from Polymers Autograft Synthetic Allograft Xenograft Tissue Engineered Source: Manufactured Example: Dacron (Polyethylene Terephthalate ePTFE( Expanded Polytetrafluoroethylene) and Other (Nylon, Polyurethane) Types of Vascular Grafts Autograft Femoral Artery Synthetic Vascular Graft Allograft Popliteal Artery Xenograft Tissue Engineered Source: Transplanted vascular graft tissues derived from the same species as recipient Example: Glutaraldehyde treated Umbilical cord vein graft Types of Vascular Grafts Autograft Xenografts are rarely used Synthetic Hemodialysis Machine Allograft From the Dialysis Machine Xenograft Tissue Engineered To the Dialysis Bovine Heterograft inserted as primary method Machine of Vascular Access (Fistula) Source: Surgical Graft of vascular tissues derived from species to a recipient of another species Example: Modified Bovine Heterograft (Mostly used a hemodialysis access shunt) Types of Vascular Grafts The Future of Vascular Graft Prosthesis Autograft 1. Embryonic Stem Cells+ Reprogramming Factors Synthetic Allograft 2. Smooth Muscle Cells + Endothelial Cells Xenograft Tissue Engineered 3. Maturation of vascular graft In a Bioreactor + In Vivo-In Vitro Testing Tissue-Engineered Grafts have mostly been used for animal studies SYNTHETIC POLYMERS Synthetic Polymer Synthetic Polymers Modifications  FR Why Synthetic Polymers? Synthetic Polymers are commonly used for the manufacture of vascular grafts Chemically Compatible at Inert high flow rates Visco-elasticty Non- comparable to Thrombogenic native blood Polymeric vessels textiles Dacron, ePTFE and Polyurethane  FR Synthetic Polymer The focus of the interactive learning module is the manufacture and use of synthetic vascular grafts in surgery Three primary synthetic polymers are used in the manufacture of vascular grafts Dacron ePTFE PU Polyethylene Terephthalate Expanded-Polytetrafluoroethylene Polyurea Urethane 25 26 24 Dacron, ePTFE and Polyurethane  FR Dacron Properties ▪ Density 1.3-1.4 g/cm3 ▪ Tensile Modulus 2-4 GPa ▪ Tensile Strength 80 MPa ▪ Melting Temperature 265 degree C ▪ Chemically Inert ▪ Treated with Collagen to prevent blood Seepage (modification) ▪ Condensation Polymer 27 ▪ Thermoplastic Dacron Vascular Graft Chemical Structure of Polyethylene Terephthalate (PET)  Dacron is formed by the Dacron (PET): Chemical Reaction Trans-esterification reaction, a type of condensation polymerization Terepthalic Acid Ethylene Glycol (diacid) (diol) 23 Dacron Different Alcohol Ester Alcohol Different Ester  FR Polytetrafluoroethylene (PTFE): Fluoropolymer Properties 28 ▪ Highly crystalline >94% ▪ High Density 2.2 g/cc ▪ Low modulus (0.56 Pa) ▪ Low Tensile Strength 14 MPa ▪ Stiffness of 0.5 GPa Photomicrograph (×1000) of an ePTFE graft. ▪ Low friction co-efficient 0.1 The dark areas are PTFE nodes interconnected by many PTFE fibrils. Average internodal ▪ Low surface tension 18.5 ergs/cm2 distance in grafts in clinical use is now 40µ ▪ High melting Temperature 327 degree C ▪ Flexible, non adhesive, chemically inert ▪ Addition Polymer Chemical Structure of Polytetrafluoroethylene (PTFE)  FR PTFE: Chemical Reaction PTFE is formed by the Addition Polymerization 23 Expanded Polytetrafluoroethylene (ePTFE) is a stretched polymer of PTFE which allows the passage of fluids but not cells  FR ePTFE: Common Use 29 The origin of waterproof and breathable GORE-TEX® outerwear, footwear, and gloves started with ePTFE. ePTFE, or expanded Polytetrafluoroethylene, was created by Bob Gore in 1969 when he rapidly stretched PTFE under certain conditions The result was an incredibly strong, Microporous material with an amazing list of characteristics including low water adsorption and good weathering properties ePTFE: Microstructure FR Microporous structure with Nodules and inter-connected Fibrils  Synthetic Polymer Modifications FR Add Heparin for Add carbon to improve Anti-Thrombogenicity e-PTFE electronegativity- antiplatelet effect. Example of Heparin-coated Graft The BioActive luminal surface of a 3 mm diameter GORE PROPATEN® Vascular Graft (top) remains free of thrombus, while the non-bioactive surface of a control graft (below; 3 mm diameter) is covered with thrombus. Grafts were explanted after 2 hours in a challenging carotid shunt canine model.  FR Synthetic Polymer Modifications Synthetic Materials impregnated with….. (Scroll over the tabs below) Anticoagulant Substances Growth Factors  FR Synthetic Polymer Modifications Synthetic Materials impregnated with... Anticoagulant Substances Growth Factors Heparin Dacron Better Patency Rate ! Heparin ePTFE Reduced Thrombogenicity and better Patency Rate ! Patency is the state or quality of being open, expanded, or unblocked. Patency rate is the main measure of vascular performance  FR Synthetic Polymer Modifications Synthetic Materials impregnated with... Anticoagulant Substances Growth Factors ePTFE Greater Endothelialization and Growth Factors Grafts Tissue Incorporation ! Growth Factors: Example-FGF2 (Fibroblast Growth Factor), Platelet Derived Growth Factor, Vascular Endothelial Growth factor Endothelialization is the lining of the inner vascular surface with endothelial cells. Vendors FR InterGard : Woven & Knitted Dacron Grafts Zenith Flex® AAA Endovascular Zenith Renu® AAA Ancillary Graft  FR Summary slide Dacron Synthesis Autografts (Harvested from patient’s body) and Synthetic grafts are most commonly used for surgery Dacron , PTFE and are the most common graft materials ePTFE (Expanded PTFE Synthesis Polytetrafluoroethylene) is a stretched polymer of PTFE which allows the passage of fluids but not cells  FR Implant Design Check-list of implant design:  Range of sizes to match dimensions of native vessels Biocompatibility  Lack of chemical reactivity  Very low thrombogenicity  Porosity  Sterility and no leaching  Flexibility  Ability to resist kinking and squashing  Tensile and shear strength to avoid tearing  Circumferential strength to withstand pressure  Mechanical properties similar to native vessel  FR Vascular graft Diameter What are the optimal Graft Diameters? 5 ✗ ✓ < 6mm ≥ 6mm ▪ Size was decided according to experimental patency rates ▪ Blood vessels below the knee are smaller and occlude more easily Increasing Vessel Diameter ▪ Vascular graft surgeries above the knee exhibit greater patency rates as compared to those below the knee. Patency is the state or quality of being open, expanded, or unblocked.  FR Porosity What is a desirable graft pore size? A larger pore size is more desirable in vascular grafts, which can be achieved by knitting rather than weaving synthetic fiber. Large pores promote tissue ingrowth and are more compliant. Knitted Grafts are easier to suture in than woven grafts. 6 7 Woven Dacron prosthetic vascular graft. Knitted Dacron prosthetic vascular graft. This graft is relatively impervious to blood because of the tightness of the weave.  FR Low Thrombogenicity Platelet activation and thrombus What is Thrombogenicity? formation Synthetic graft materials causes platelet adhesion and activation of fibrin and the coagulation cascade. Synthetic vascular This causes blood to clot and block vessels. graft Commercially available heparin-bonded ePTFE has been developed to decrease Legend: Thrombogenicity Platelet Fibrin Red Blood Cell End of Animation  FR Gore PROPATEN® Vascular Graft (Heparin Coated) Vs. Normal ePTFE Graft Both ePTFE and heparin coated ePTFE grafts exhibit similar microstructure (SEM images on the left) A. Sem image of untreated vascular graft (Gore Stretch Vascular Graft) showing platelet adhesion and fibrin deposition perfused or 6 minutes with whole blood B. Adhesion or deposition absent on Gore Propaten Vascular Graft  FR What IS A Stent? A coronary stent is a tube usually a metal mesh or polymer that is placed in the blood vessel to clear out plaque and keep the channel open in cases of cardiovascular disease. An average stent has a diameter of 2-3 mm and is 25 mm long The procedure for inserting a stent is called: Percutaneous Coronary intervention (PCI)  FR Percutaneous Coronary intervention The stent is inserted via a catheter usually through the groin artery. The stent is placed at the tip of the catheter tube often along with an oval shaped balloon. The catheter is guided to the appropriate vessel location and the stent is decompressed. The decompression of the stent rearranges the plaque so that blood can flow easily. It remains in place to support the blood vessel *polymer : absorbable polymer FR Drug-Eluting Stent In 2003 the FDA approved the use of drug eluting stents(DES). DES address the problem of restenosis by a drug coating on the surface of the stent that prevents tissue re-growth. Restenosis: Occurs when a treated blood vessel becomes blocked again  FR Parts of the Drug Eluting Stent Drug Eluting Stents consist of three parts: 1. Expandable Metal Alloy Framework: This part of the stent is usually very similar to a BMS, sometimes the mesh designs are more complex in DES. 2. Stent Coating: This coating is where the drug is released from. It is typically a polymer in which the drug is embedded. 3. The Drug: Suppresses the bodies natural immune response thus resisting restenosis.  FR Bioabsorbable Stent This type of stent is very similar to a bare metal stent with the addition of it being able to degrade in the vessel after a certain amount of time This would decrease the risk of blood clot formation on the implanted stent as well as make it easier to re-stent the same vein multiple times Biodegradable stents are especially useful when the patient is younger and will probably need another stent in their lifetime