lecture_6 - Biomaterials Consideration and Selection S...

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Unformatted text preview: Biomaterials Consideration and Selection S. Laguette ME 128 Fall 2007 October 17, 2007 Biomaterials Biomaterials have been in existence for centuries The use of gold dates back about 2000 and is one of the first known substances to be used in dentistry The use of wooden and ivory dentures date to the Middle Ages Metal bone plates in 1900 and joint replacements in 1930 IOL implant materials date to WWII shattered airplane canopies 10/17/07 ME 128 2 Ivory dentures 18th century ivory denture with human teeth, BDA Museum 10/17/07 ME 128 3 IOL implant material 10/17/07 ME 128 4 Hip implant 10/17/07 ME 128 5 Biomaterials A common definition of Biomaterials: Synthetic or natural materials that can replace or augment tissues, organs or body functions. There has been significant attention in the area of biomaterials in last few decades. Previously a successful biomaterial exhibited an "bioinert" performance or "tolerance" by the body Current applications intend to mimic, simulate, or to stimulate a "bio-active" response 10/17/07 ME 128 6 Biomaterials Society of Biomaterials since 1975 Well known university programs include: University of Washington University of Utah Clemson University Johns Hopkins 10/17/07 ME 128 7 Biomaterials Example uses of biomaterials include: Silicone elastomer (tubing, shunts, mammary implants, IOL) Polyurethane (catheters, cardiovascular implants) PMMA (IOL) Stainless steel (orthopedic implants, implant housings) PTFE (cardiovascular stents and grafts) 10/17/07 ME 128 8 Biomaterials Current examples include: Drug eluting cardiovascular stents to improve performance Hydrophilic coating of implants to improve ease of use Porous materials to induce biological reaction (adhesive-less implants) Coated materials with antibiotics to inhibit infection 10/17/07 ME 128 9 Drug eluting stents 10/17/07 ME 128 10 The FDA and Biocompatibility The primary intent of the regulations and guidance documents is to ensure that the benefits provided by a final product exceed any potential risks Evaluation of any new device intended for human use requires data from systematic testing The systematic testing is based upon the intended use of the device 10/17/07 ME 128 11 The FDA and Biocompatibility The Federal Food, Drug, and Cosmetic Act of 1976 introduced the FDA as a regulatory agency responsible for medical devices http://www.fda.gov/cdrh/index.html http://www.fda.gov/oc/industry/default.htm In 1986 the Tripartite Biocompatibility Guidance for Medical Devices was issued US, Canada, UK http://www.fda.gov/cdrh/g951.html 10/17/07 ME 128 12 The FDA and Biocompatibility Required Biocompatibility Training and Toxicology Profiles for Evaluation of Medical Devices (G95-1), May 1, 1995 Guidance Document for Dura Substitute Devices: November 9, 2000 Recognized Standard ISO 7197:1997 Neurosurgical Implants Recognized Standard ISO 11979-1:1999 Ophthalmic implants Intraocular lenses Recognized Standard ANSI Z80.20-1998 Ophthalmics: Contact lenses 10/17/07 ME 128 13 International Regulatory Efforts International Standards Organization (ISO) developed ISO 10993 to harmonize biocompatibility testing ISO 10993:1 provides categorizing and performance testing ISO 10993:2 provides animal welfare requirements ISO 10993:12 provides sample preparation and reference materials 10/17/07 ME 128 14 Device Categories ISO 10993-1 categorizes devices into three main categories: Surface device Externally communicating device Implant device Within each category, identify body contact: Skin, Mucosal membrane, Blood path, Tissue/bone, etc 10/17/07 ME 128 15 Device Categories The choice of the test program for device in a given category depends on the duration of contact: Limited contact (<24 hrs) Prolonged contact (24 hrs to 30 days) Permanent contact (>30 days) 10/17/07 ME 128 16 Test Matrix 10/17/07 ME 128 17 Device Categories Example: Voice Prosthesis Device is intended to be placed into the fistula and removed every day for cleaning 10/17/07 ME 128 18 ENT 10/17/07 ME 128 19 Voice Prosthesis External Communicating Tissue communicating Limited (24hr) Recommended Tests Cytotoxicity, Sensitization, Irritation, Hemocompatibility Possibly Acute Systemic Toxicity 10/17/07 ME 128 20 Device Categories Example: Hydrocephalic Shunt Device is intended to be permanently implanted 10/17/07 ME 128 21 Neurosurgery 10/17/07 ME 128 22 Shunt Implant Device Blood contact Permanent Recommended Tests Cytotoxicity, Sensitization, Irritation, Systemic toxicity, Genotoxicity, Implantation, Hemocompatibility Possibly Chronic toxicity, Carcinogenicity 10/17/07 ME 128 23 Device Categories Example: Tissue Expander injection site locator Device is intended to be placed over the skin to locate the injection site 10/17/07 ME 128 24 Tissue Expanders 10/17/07 ME 128 25 Tissue Expander Locator Surface Skin Limited Recommended Tests Cytotoxicity, Sensitization, Irritation 10/17/07 ME 128 26 Tests Cytotoxicity Detect the potential ability of a device to induce effects at the cellular level Elution, Direct Contact, Agar Diffusion Basic screening test Sensitization Allergic contact dermatitis manifest in animals as redness (erythema) and swelling (edema) Most recognized is guinea pig maximization test (GPMT) Skin Irritation Detect a skin reaction to irritant contact caused by the primary and direct effect of a substance on the skin Preferred animal is the albino rabbit from several hours to several days 10/17/07 ME 128 27 Tests Intracutaneous reactivity Designed to asses the localized reaction of tissue to leachable substances Solvent extracts and intracutaneous injections to rabbits to assess redness and swelling Acute systemic toxicity Considered for all blood contact devices and an initial step in the assessment of toxic characteristics Extracts are administered intravenously or intraperitoneally in rabbits or mice Genotoxicity Investigate materials for possible mutagenic effects damage to the body's genes or chromosomes Simplest and most sensitive assays use cultured mammalian cells 10/17/07 ME 128 28 Tests Implantation Testing methods attempt to imitate the intended use conditions of the material Intramuscular implantation in the rabbit is most common Detect possible undesirable changes in the blood caused directly by a medical device or by chemicals leaching from a device Hemolysis, thrombus formation, coagulation, immunological changes Tests are dependent upon the device Some uncertainty of regulatory requirements ME 128 29 Hemocompatibility 10/17/07 Tests Subchronic and Chronic toxicity Detect potential adverse effects as a result of repeated daily dosing Testing is conducted after acute testing in appropriate animal model Carcinogenicity Objective is long-term Normally conducted with oral dosing in mice or rats An increased incidence to induce tumors Very few products for which this test is justified 10/17/07 ME 128 30 ...
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