Docstoc

IN VIVO

Document Sample
IN VIVO Powered By Docstoc
					        BME Experiment
         2010 Summer

            Ming-Long Yeh
              8/25/2010

Biological Testing of Biomaterials

  From: Biomaterials Science by Ratner
                                         1
  5. Biological Testing of Biomaterials
5.1 INTRODUCTION TO TESTING BIOMATERIALS
5.2 IN VITRO ASSESSMENT OF TISSUE
   COMPATIBILITY
5.3 IN VIVO ASSESSMENT OF TISSUE COMPATIBILITY
5.4 EVALUATION OF BLOOD-MATERIALS
   INTERACTIONS
5.5 LARGE ANIMAL MODELS IN CARDIAC AND
   VASCULAR BIOMATERIALS RESEARCH AND
   TESTING
5.6 MICROSCOPY FOR BIOMATERIALS SCIENCE


                                                 2
 5.1 INTRODUCTION TO
TESTING BIOMATERIALS




                       3
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
 How can biomaterials be evaluated to
  determine if they are biocompatible and
  will function in a biologically appropriate
  manner in the in vivo environment?
 This introduction: common to all
  biomaterials biological testing.



                                                4
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
 Evaluation under in vitro (literally "in
  glass") conditions: rapid and inexpensive
  data on biological interaction (Chapter 5.
  2).
 The question: will the in vitro test measure
  parameters relevant to what will occur in
  vivo environment?


                                                 5
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
   For example, tissue culture polystyrene, a
    surface modified polymer, will readily attach and
    grow most cells in culture.
   Untreated polystyrene will neither attach nor
    grow mammalian cells.
   Yet when implanted in vivo, both materials heal
    almost indistinguishably with a thin foreign body
    capsule.
   Thus, the results of the in vitro test do not
    provide information relevant to the implant
    situation.

                                                        6
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
   In vitro tests minimize the use of animals in
    research, a desirable goal.
   Also, in vitro testing is required by most
    regulatory agencies in the device approval
    process for clinical application.
   When appropriately used, in vitro testing
    provides useful insights that can dictate whether
    a device need be further evaluated in expensive
    in vivo experimental models.

                                                        7
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
   Animals are used for testing biomaterials to
    model the environment that might be
    encountered in humans (Chapter 5. 3).
   However, there is great range in animal
    anatomy, physiology, and biochemistry.
   Will the animal model provide data useful for
    predicting how a device performs in humans?
   Without validation to human clinical studies, it is
    often difficult to draw strong conclusions from
    performance in animals.
                                                          8
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
   The first step in designing animal testing
    procedures is to choose an animal model that
    offers a reasonable parallel anatomically or
    biochemically to the situation in humans.
   Experiments designed
       to minimize the number of animals needed,
       ensure that the animals are treated humanely (e. g.,
        NIH guidelines for the use of laboratory animals), and
       maximize the relevant information generated by the
        testing procedure are essential.
                                                                 9
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
   Some biomaterials fulfill their intended function in
    seconds.
   Others are implanted for a lifetime (10 years ? 70
    years?).

   Are 6-month implantation times useful to learn about a
    device intended for 3-minute insertion?

   Will six months implantation in a test model provide
    adequate information to draw conclusions about the
    performance of a device intended for lifetime
    implantation?
                                                             10
5.1 INTRODUCTION TO TESTING
        BIOMATERIALS
   Assistance in the design of many biomaterials
    tests is available through national and
    international standards-organizations.
   Thus, the American Society for Testing Materials
    (ASTM) and the International Standards
    Organization (IS0) can often provide detailed
    protocols for widely accepted, carefully thought
    out testing procedures.
    Other testing protocols are available through
    government agencies (e. g., the FDA) and
    through commercial testing laboratories.
                                                   11
5.2 IN VITRO ASSESSMENT
OF TISSUE COMPATIBILITY




                          12
    5.2 IN VITRO ASSESSMENT OF
        TISSUE COMPATIBILITY
   “Cytotoxicity”: to cause toxic effects (death,
    alterations in cellular membrane permeability,
    enzymatic inhibition, etc.) at the cellular level.
   It is distinctly different from physical factors that
    affect cellular adhesion (surface charge of a
    material, hydrophobicity, hydrophilicity, etc.).
   Evaluation of biomaterials by methods that use
    isolated, adherent cells in culture to measure
    cytotoxicity and biological compatibility.

                                                            13
          HISTORICAL REVIEW
 Cell culture methods: more than two
  decades (Northup, 1986).
 Most often today the cells used for culture
  are from established cell lines purchased
  from biological suppliers or cell banks.
 Primary cells are seldom used
       less assay repeatability, reproducibility,
        efficiency, and, in some cases, availability.

                                                        14
     BACKGROUND CONCEPT
                            Toxicity
   A toxic material is defined as a material that releases a
    chemical in sufficient quantities to kill cells either directly
    or indirectly through inhibition of key metabolic
    pathways.
   The number of cells that are affected is an indication of
    the dose and potency效力 of the chemical.
   Although a variety of factors affect the toxicity of a
    chemical (e.g., compound, temperature, test system),
    the most important is the dose or amount of chemical
    delivered to the individual cell.


                                                                  15
     BACKGROUND CONCEPT
          Delivered and Exposure Doses
   Delivered dose: the dose that is actually absorbed by the
    cell.
   Exposure dose: the amount applied to a test system.

   For example, if an animal is exposed to an atmosphere
    containing a noxious有毒的 substance (exposure dose),
    only a small portion of the inhaled substance will be
    absorbed and delivered to the internal organs and cells
    (delivered dose).


                                                              16
Delivered and Exposure Doses
   The cells that are most sensitive are referred to
    as the target cells.
   Cell culture methods: evaluate target cell toxicity
    by using delivered doses of the test substance.
   This distinguishes cell culture methods from
    whole- animal studies, which evaluate the
    exposure dose and do not determine the target
    cell dose of the test substance.



                                                      17
                Safety Factors
   A highly sensitive test system is desirable for
    evaluating the potential hazards of biomaterials
    because the inherent characteristics of the
    materials often do not allow the dose to be
    exaggerated.
   There is a great deal of uncertainty in
    extrapolating from one test system to another,
    such as from animals to humans.
   To allow for this, toxicologists have used the
    concept of safety factors to take into account
    intra- and interspecies variation.
                                                       18
               Safety Factors
   This practice requires being able to exaggerate
    the anticipated預期 human clinical dosage in the
    nonhuman test system.
   Local toxicity model in animals: there is ample
    opportunity for reducing the target cell dose by
    distribution, diffusion, metabolism, and changes
    in the number of exposed cells (because of the
    inflammatory response).
   Cell culture models: the variables of metabolism,
    distribution, and absorption are minimized, the
    dosage per cell is maximized to produce a highly
    sensitive test system.
                                                    19
ASSAY METHODS




                20
           ASSAY METHODS
   Three primary cell culture assays are
    used for evaluating biocompatibility:
     direct contact,
     agar diffusion,
     elution (also known as extract dilution).
   These are morphological assays, meaning
    that the outcome is measured by
    observations of changes in the
    morphology of the cells.
                                                  21
             cell culture assays
   http://en.wikipedia.org/wiki/Cell_Culture_Assays


     direct contact,
     agar diffusion,
     elution




                                                       22
         Direct contact method
1.   A near confluent layer of fibroblasts are prepared in a
     culture plate
2.   Old cell culture media (agar generally) is removed
3.   Fresh media is added
4.   Material being tested is placed onto the cultures, which
     are incubated for 24 hours at 37 degrees Celsius
5.   The material is removed
6.   The culture media is removed
7.   The remaining cells are fixed and stained, dead cells
     are lost during fixation and only the live cells are stained
8.   The toxicity of the material is indicated by the absence
     of stained cells around the material

                                                                23
          Agar diffusion method
1.   A near confluent layer of fibroblasts are prepared in a
     culture plate
2.   Old cell culture media is removed
3.   The cells are covered with a solution of 2% agar,
     which often contains red vital stain
4.   When the agar solidifies the cells will have dispersed
     throughout its volume
5.   The material is then placed on the surface of the agar
     and incubated for 24 hours at 37 degrees Celsius
6.   Live cells take up the vital stain and retain it, dead cells
     do not
7.   The toxicity of the material is evaluated by the loss of
     vital stain under and around the material
8.   Surface microscopy is also needed to evaluate the
     material-cell interfacae
                                                               24
                 Elution method
1.   A near confluent layer of fibroblasts are prepared in a
     culture plate
2.   An extract of the material which is being tested is
     prepared using physiological saline or serum free media
     (the latter is generally preferred)
3.   Extraction conditions are used which are appropriate for
     the type of exposure which the cells would receive in
     the in vivo environment if the material were to be
     implanted
4.   The extract is placed on the cells and incubated for 48
     hours at 37 degrees Celsius
5.   After 48 hours the toxicity is evaluated using either a
     histochemical or vital stain

                                                            25
            ASSAY METHODS
   To standardize the methods and compare the
    results of these assays, the variables
      number of cells,
      growth phase of the cells (period of frequent
       cell replication),
      cell type,
      duration of exposure,
      test sample size (e.g., geometry, density,
       shape, thickness), and
      surface area of test sample
                                                       26
            ASSAY METHODS
   In general, cell lines that have been developed
    for growth in vitro are preferred to primary cells
    that are freshly harvested from live organisms
    because the cell lines improve the reproducibility
    of the assays and reduce the variability among
    laboratories.
   That is, a cell line is the in vitro counterpart of
    inbred近親交配的 animal strains used for in vivo
    studies.
   Cell lines maintain their genetic and
    morphological characteristics throughout a long
    (sometimes called infinite) life span.
                                                      27
            ASSAY METHODS
   Cell lines from other tissues or species may also
    be used.
   Selection of a cell line is based upon the type of
    assay, the investigator’s experience,
    measurement endpoints (viability, enzymatic
    activity, species specific receptors, etc.), and
    various other factors.
   It is not necessary to use human cell lines for
    this testing because, by definition, these cells
    have undergone some dedifferentiation and lost
    receptors and metabolic pathways in the
    process of becoming cell lines.
                                                     28
            ASSAY METHODS
   Positive and negative controls are often included
    in the assays to ensure the operation and
    suitability of the test system.

   The negative control of choice: high-density
    polyethylene material.
   The positive controls: low-molecular-weight
    organotin-stabilized poly (vinyl chloride), gum
    rubber, and dilute solutions of toxic chemicals,
    such as phenol and benzalkonium chloride.
                                                       29
30
            CLINICAL USE
 The in vitro cytotoxicity assays are the
  primary biocompatibility screening tests for
  a wide variety of elastomeric, polymeric,
  and other materials used in medical
  devices.
 After the cytotoxicity profile of a material
  has been determined, then more
  application specific tests are performed to
  assess the biocompatibility of the material.

                                             31
                  CLINICAL USE
   Current experience indicates that a material that is
    judged to be nontoxic in vitro will be nontoxic in in vivo
    assays.
   This does not necessarily mean that materials that are
    toxic in vitro could not be used in a given clinical
    application.
   The clinical acceptability of a material depends on many
    different factors, of which target cell toxicity is but one.
   For example, glutaraldehyde-fixed porcine valves
    produce adverse effects in vitro owing to low residues of
    glutaraldehyde; however, this material has the greatest
    clinical efficacy for its unique application.

                                                               32
      5.3 IN VIVO
ASSESSMENT OF TISSUE
    COMPATIBILITY



                       33
  5.3 IN VIVO ASSESSMENT OF
     TISSUE COMPATIBILITY
               INTRODUCTION
 The goal of in vivo assessment of tissue
  compatibility of a biomaterial, prosthesis,
  or medical device is to determine the
  biocompatibility or safety of the
  biomaterial, prosthesis, or medical device
  in a biological environment.


                                                34
          INTRODUCTION
 Biocompatibility has been defined as the
  ability of a medical device to perform with
  an appropriate host response in a specific
  application, and
 biocompatibility assessment is considered
  to be a measurement of the magnitude
  and duration of the adverse alterations in
  homeostatic mechanisms that determine
  the host response.

                                                35
             INTRODUCTION
   From a practical perspective, the in vivo
    assessment of tissue compatibility of medical
    devices is carried out to determine that the
    device performs as intended and presents no
    significant harm to the patient or user.
   Thus, the goal of the in vivo assessment of
    tissue compatibility is to predict whether a
    medical device presents potential harm to the
    patient or user by evaluations under conditions
    simulating clinical use.
                                                      36
             INTRODUCTION
   Recently, extensive efforts have been made by
    government agencies, i. e., FDA, and regulatory
    bodies, i.e., ASTM, IS0, and USP, to provide
    procedures, protocols, guidelines, and standards
    that may be used in the in vivo assessment of
    the tissue compatibility of medical devices.
   This chapter draws heavily on the IS0 10993
    standard, Biological Evaluation of Medical
    Devices, in presenting a systematic approach to
    the in vivo assessment of tissue compatibility of
    medical devices.
                                                    37
List of the standards in the 10993 series
 ISO 10993-1:2003 Biological evaluation of
  medical devices Part 1: Evaluation and testing
 ISO 10993-2:2006 Biological evaluation of
  medical devices Part 2: Animal welfare
  requirements
 ISO 10993-3:2003 Biological evaluation of
  medical devices Part 3: Tests for genotoxicity,
  carcinogenicity and reproductive toxicity
 ISO 10993-4:2002/Amd 1:2006 Biological
  evaluation of medical devices Part 4: Selection
  of tests for interactions with blood
 ISO 10993-5:1999 Biological evaluation of
  medical devices Part 5: Tests for in vitro
  cytotoxicity
                                                    38
   ISO 10993-6:1994 Biological evaluation of medical
    devices Part 6: Tests for local effects after
    implantation
   ISO 10993-7:1995 Biological evaluation of medical
    devices Part 7: Ethylene oxide sterilization residuals
   ISO 10993-8:2001 Biological evaluation of medical
    devices. Part 8: Selection and qualification of
    reference materials for biological tests
   ISO 10993-9:1999 Biological evaluation of medical
    devices Part 9: Framework for identification and
    quantification of potential degradation products
   ISO 10993-10:2002/Amd 1:2006 Biological evaluation
    of medical devices Part 10: Tests for irritation and
    delayed-type hypersensitivity


                                                             39
   ISO 10993-11:2006 Biological evaluation of medical
    devices Part 11: Tests for systemic toxicity
   ISO 10993-12:2002 Biological evaluation of medical
    devices Part 12: Sample preparation and reference
    materials (available in English only)
   ISO 10993-13:1998 Biological evaluation of medical
    devices Part 13: Identification and quantification of
    degradation products from polymeric medical
    devices
   ISO 10993-14:2001 Biological evaluation of medical
    devices Part 14: Identification and quantification of
    degradation products from ceramics
   ISO 10993-15:2000 Biological evaluation of medical
    devices Part 15: Identification and quantification of
    degradation products from metals and alloys

                                                            40
   ISO 10993-16:1997 Biological evaluation of medical
    devices Part 16: Toxicokinetic study design for
    degradation products and leachables
   ISO 10993-17:2002 Biological evaluation of medical
    devices Part 17: Establishment of allowable limits
    for leachable substances
   ISO 10993-18:2005 Biological evaluation of medical
    devices Part 18: Chemical characterization of
    materials
   ISO/TS 10993-19:2006 Biological evaluation of
    medical devices Part 19: Physico-chemical,
    morphological and topographical characterization of
    materials
   ISO/TS 10993-20:2006 Biological evaluation of
    medical devices Part 20: Principles and methods for
    immunotoxicology testing of medical device
                                                          41
INTRODUCTION




               42
   BIOMATERIALS AND DEVICE
PERSPECTIVES IN IN VIVO TESTINGS




                                   43
   BIOMATERIALS AND DEVICE
PERSPECTIVES IN IN VIVO TESTINGS




                                   44
          Sensitization, irritation刺激, and
     intracutaneous (intradermal) Reactivity
   Exposure to or contact with even minute
    amounts of potential leachables from medical
    devices or biomaterials can result in allergic or
    sensitization reactions.
   Sensitization tests estimate the potential for
    contact sensitization to medical devices,
    materials, and/or their extracts.
   Symptoms of sensitization are often seen in skin
    and tests are often carried out topically in guinea
    pigs.

                                                      45
    Sensitization, irritation, and intracutaneous
              (intradermal) Reactivity
   The most severely irritating chemical leachables may be
    discovered prior to in vivo studies by careful material
    characterization and in vitro cytotoxicity tests.
   Irritant tests emphasize utilization of extracts of the
    biomaterials to determine the irritant effects of potential
    leachables.
   Intracutaneous (intradermal) reactivity tests determine
    the localized reaction of tissue to intracutaneous
    injection of extracts of medical devices, biomaterials, or
    prostheses in the final product form.
   Intracutaneous tests may be applicable where
    determination of irritation by dermal or mucosal tests are
    not appropriate.
   Albino rabbits are most commonly used.
                                                              46
              Systemic Toxicity:
    Acute, Subacute, and Subchronic Toxicity
   Mice, rats, or rabbits are the usual animals
    of choice for the conduct of these tests
    and oral, dermal, inhalation, intravenous,
    intraperitoneal, or subcutaneous
    application of the test substance may be
    used, depending on the intended
    application of the biomaterial.

       Peritoneal 腹膜的

                                               47
                Systemic Toxicity:
    Acute, Subacute, and Subchronic Toxicity
   Acute toxicity is considered to be the adverse effects that
    occur after administration of a single dose or multiple
    doses of a test sample given within 24 hours.
   Subacute toxicity (repeat-dose toxicity) focuses on
    adverse effects occurring after administration of a single
    dose or multiple doses of a test sample per day during a
    period of from 14 to 28 days.
   Sub-chronic toxicity is considered to be the adverse
    effects occurring after administration of a single dose or
    multiple doses of a test sample per day given during a
    part of the life span, usually 90 days but not exceeding
    10 % of the life span of the animal.

                                                              48
                  Systemic Toxicity:
     Acute, Subacute, and Subchronic Toxicity
  Pyrogenicity tests are also included in the
   systemic toxicity category to detect
   material-mediated fever-causing reactions
   to extracts of medical devices or materials.
  It is noteworthy that no single test can
   differentiate pyrogenic reactions that are
   material-mediated from those due to
   endotoxin contamination

Pyrogenicity: producing or produced by heat or fever   49
                    Genotoxicity
   In vivo genotoxicity tests are carried out if indicated by
    the chemistry and/or composition of the biomaterial (see
    Table 1) or if in vitro test results indicate potential
    genotoxicity [changes in deoxyribonucleic acid (DNA)].
   Initially, at least three in vitro assays should be used and
    two of these assays should utilize mammalian cells.
   The initial in vitro assays should cover the three levels of
    genotoxic effects:
      DNA destruction,
      gene mutations, and
      chromosomal aberrations .


                                                               50
           Implantation




Dystrophic: 營養不良的         51
              Implantation
 For short-term implantation evaluation
  out to 12 weeks, mice, rats, guinea pigs,
  or rabbits are the usual animals utilized in
  these studies.
 For longer-term testing in subcutaneous
  tissue, muscle, or bone, animals such as
  rats, guinea pigs, rabbits, dogs, sheep,
  goats, pigs, and other animals with
  relatively long life expectancy are suitable.

                                              52
                 Implantation
 If a complete medical device is to be
  evaluated, larger species may be utilized
  so that human-sized devices may be used
  in the site of intended application.
 For example,
     substitute heart valves are usually tested as
      heart valve replacements in sheep,
     whereas calves are usually the animal of
      choice for ventricular assist devices and total
      artificial hearts.
                                                        53
            Hemocompatibility
   Hemocompatibility tests evaluate effects on
    blood and/or blood components by blood-
    contacting medical devices or materials.
   In vivo hemocompatibility tests are usually
    designed to simulate the geometry, contact
    conditions, and flow dynamics of the device or
    material in its clinical application.
   From the IS0 standards perspective, five test
    categories are indicated for hemocompatibility
    evaluation : thrombosis血栓, coagulation凝結,
    platelets, hematology血液學, and immunology
    (complement and leukocytes).
                                                     54
            Hemocompatibility
   In vivo testing in animals may be
    convenient, but species' differences in
    blood reactivity must be considered and
    these may limit the predictability of any
    given test in the human clinical situation.




                                                  55
               Chronic Toxicity
   Chronic toxicity tests determine the effects of
    either single or multiple exposures to medical
    devices, materials, and/or their extracts during a
    period of at least 10 % of the lifespan of the test
    animal, e.g. over 90 days in rats.
   Chronic toxicity tests may be considered an
    extension of subchronic (subacute) toxicity
    testing and both may be evaluated in an
    appropriate experimental protocol or study.

                                                      56
                 Carcinogenicity
   Carcinogenicity tests determine the tumorigenic potential
    of medical devices, materials, and/or their extracts from
    either single or multiple exposures or contacts over a
    period of the major portion of the lifespan of the test
    animal.
   Since tumors associated with medical devices have
    been rare (see Chapter 4. 7) carcinogenicity tests should
    be conducted only if data from other sources suggest a
    tendency for tumor induction.
   In addition, both carcinogenicity (tumorigenicity) and
    chronic toxicity may be studied in a single experimental
    study.

                                                            57
    Reproductive and Developmental Toxicity

   These tests evaluate the potential effects of
    medical devices, materials, and/or their extracts
    on reproductive function, embryonic
    development (teratogenicity), and prenatal產前的
    and early postnatal development.
   The application site of the device must be
    considered and tests and/or bioassays should
    only be conducted when the device has a
    potential impact on the reproductive potential of
    the subject.
                                                    58
                  Biodegradation
   Biodegradation tests determine the effects of a
    biodegradable material and its biodegradation
    products on the tissue response.
   They focus on
       the amount of degradation during a given period of
        time (the kinetics of biodegradation),
       the nature of the degradation products,
       the origin of the degradation products (e. g.,
        impurities, additives, corrosion products, bulk
        polymer), and
       the qualitative and quantitative assessment of
        degradation products and leachables in adjacent
        tissues and in distant organs.
                                                             59
             Immune Response
   Immune response evaluation is not a component of the
    standards currently available for in vivo tissue
    compatibility assessment.
   However, ASTM, IS0, and the FDA currently have
    working groups developing guidance documents for
    immune response evaluation where pertinent.
   Synthetic materials are not generally immunotoxic.
   However, immune response evaluation is necessary with
    modified natural tissue implants such as collagen, which
    has been utilized in a number of different types of
    implants and may elicit immunological responses.


                                                           60
過敏的




      61
SELECTION OF ANIMAL MODELS FOR IN
           VIVO TESTS




                              蕁麻疹




                                62
            Immune Response
   Direct measures of immune system activity by
    functional assays are the most important types
    of tests for immunotoxicity.
   Functional assays are generally more important
    than tests for soluble mediators, which are more
    important than phenotyping.
   Signs of illness may be important in in vivo
    experiments but symptoms may also have a
    significant role in studies of immune function in
    clinical trials and postmarket studies.

                                                    63
SELECTION OF ANIMAL MODELS
     FOR IN VIVO TESTS
   Animal models are used to predict the clinical
    behavior, safety, and biocompatibility of medical
    devices in humans (Table7).
   The selection of animal models for the in vivo
    assessment of tissue compatibility must consider
    the advantages and disadvantages of the animal
    model for human clinical application.
   Several examples follow, which exemplify the
    advantages and disadvantages of animal
    models in predicting clinical behavior in humans
    (also see Chapter 5. 5).
                                                    64
SELECTION OF ANIMAL MODELS FOR IN
           VIVO TESTS




                                65
SELECTION OF ANIMAL MODELS
     FOR IN VIVO TESTS
 Thus, the choice of this animal model for
  bioprosthetic heart valve evaluation is
  made on the basis of accelerated
  calcification in rapidly growing animals,
  which has its clinical correlation in young
  and adolescent humans.
 Nevertheless, normal sheep may not
  provide a sensitive assessment of the
  propensity of a valve to thrombosis,

                                                66
SELECTION OF ANIMAL MODELS
     FOR IN VIVO TESTS
 The in vivo assessment of tissue
  responses to vascular graft materials is
  an example in which animal models
  presents particularly misleading
  picture of what generally occurs in
  humans.
 Virtually all animal models, including
  nonhuman primates, heal rapidly and
  completely with an endothelial blood-
  contacting surface.
                                             67
SELECTION OF ANIMAL MODELS
     FOR IN VIVO TESTS
   Humans, on the other hand, do not show
    extensive endothelialization of vascular graft
    materials and the resultant pseudointima from the
    healing response in humans has potential
    thrombogenicity.
   Consequently, despite favorable results in animals,
    small-diameter vascular grafts (less than 4mm in
    internal diameter) yield early thrombosis in humans,
    the mayor mechanism of failure, which is secondary
    to the lack of endothelialization in the luminal
    surface healing response.
       intima 內膜
                                                       68
STANDARDS




            69
70
71
SELECTION OF ANIMAL MODELS FOR IN
           VIVO TESTS




                                72
73
             Preoperative Care
   Anesthesia Dogs should be fasted for 12
    hours prior to their operation to reduce the risk
    of aspiration肺內異物的吸入 during anesthetic
    induction and endotracheal intubation氣管內插管.
   Preparation of the animal involves administration
    of a mild intramuscular (IM) sedative such as
    acepromazine, a phenothiazine tranquillizer.
   Peripheral intravenous (IV) accesses can then
    be established.

                                                    74
Preoperative Care Anesthesia
   Prior to intubation, 0.05 mg/kg of atropine阿托品,
    an anticholinergic抗副交感神經藥., may be
    administered to reduce the amount of oral
    secretions and ease endotracheal (ET)
    intubation.
   Once a secure airway has been obtained,
    anesthesia can be fully induced with a
    barbiturate such as thiopental sodium (12.5 mg /
    kg IV).
   Table 3 lists several of the recommended drugs
    and doses for sedation and anesthesia in dogs.
                                                   75
76
             Preoperative Care
   Anesthesia Dogs should be fasted for 12
    hours prior to their operation to reduce the risk
    of aspiration肺內異物的吸入 during anesthetic
    induction and endotracheal intubation氣管內插管.
   Preparation of the animal involves administration
    of a mild intramuscular (IM) sedative such as
    acepromazine, a phenothiazine tranquillizer.
   Peripheral intravenous (IV) accesses can then
    be established.

                                                    77
Preoperative Care Anesthesia
   Prior to intubation, 0.05 mg/kg of atropine阿托品,
    an anticholinergic抗副交感神經藥., may be
    administered to reduce the amount of oral
    secretions and ease endotracheal (ET)
    intubation.
   Once a secure airway has been obtained,
    anesthesia can be fully induced with a
    barbiturate such as thiopental sodium (12.5 mg /
    kg IV).
   Table 3 lists several of the recommended drugs
    and doses for sedation and anesthesia in dogs.
                                                   78
79
Swine vascular graft




                       80
81
82
83
84
85
86
87
88
89
90
Thanks!




          91
92

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:5
posted:11/26/2012
language:English
pages:92