Biomaterials and their interactions with biological systems were discussed. Historically, biomaterials consisted of common laboratory materials with little consideration of properties. Modern definitions characterize biomaterials as materials intended to interact with biological systems. An ideal biomaterial is inert, biocompatible, mechanically stable, and elicits an appropriate host response for a specific application. Surface properties and bulk properties were described as important for biomaterial performance and biocompatibility. Characterization techniques for analyzing biomaterial properties were also outlined.

1. Biomaterials and Artificial Organs
Dr. I. Manjubala
1

2. 2
Early Definition (Historical):
“Lack of interaction between material and tissue”
Definition of Biomaterials
“A nonviable material used in a medical device, intended to interact with
biological systems.”
Contemporary Definition:
“Ability of a material to perform with an appropriate host response, in a
specific application”
interdependent mechanisms of interaction between material and tissue
“Ability of material to perform” and not just reside in the body
“Appropriate host response” must be acceptable given the desired function
“Specific application” must be defined
Implies inert, non-toxic, non-carcinogenic, non-allergenic, non-
inflammatory, non-degradable
Thus, material has zero influence…

3. 3
Material used to construct artificial organs, rehabilitation devices, or
prostheses and replace natural body tissues
(The American Heritage® Medical Dictionary, 2007)
Definitions of Biomaterials (modern)
A synthetic material used to replace part of a living system or to function
in intimate contact with living tissue (Park, 1995)
A systemically and pharmacologically inert substance designed for
implantation within or incorporation with living substances
(The Clemson University Advisory Board for Biomaterials)
A nonviable material used in a medical device, intended to interact with
biological systems (Williams, 1987)
A biomaterial is any material, natural or man-made, that comprises whole
or part of a living structure or biomedical device which performs,
augments, or replaces a natural function (Wikipedia)
bi·o·ma·te·ri·al (n)

4. 4
• Historically, biomaterials consisted of materials common in the
laboratories of physicians, with little consideration of material
properties.
• Early biomaterials :
- Gold: Malleable, inert metal (does not oxidize); used in dentistry
by Chinese and Romans--dates 2000 years
- Iron, brass: High strength metals; rejoin fractured femur (1775)
BACKGROUND
- Glass: Hard ceramic; used to replace eye (purely cosmetic)
- Wood: Natural composite; high strength to weight; used for
limb prostheses and artificial teeth
- Bone: Natural composite; uses: needles, decorative piercing
-

5. 5
• Important dates
- 600 BC: Sushruta Samhita, Nose reconstruction
- 1860's: Lister develops aseptic surgical technique, wires and nails
made of iron, gold, silver and platinum
- early 1900's: W.A. Lane, Bone plates used to fix fracture
- 1930's: Introduction of stainless steel, cobalt chromium alloys
- 1938 : P. Wiles, first total hip prosthesis
- 1940's: Polymers (Plastics) in medicine: PMMA bone repair; cellulose
for dialysis; nylon sutures
- 1944 : W. J. Kolff, Hemodialyser
- 1946: J.Judet & R.Judet, Biomechanically designed hip prostheses,
from plastic.
- 1952: A.B. Voorhees, First blood vessel, made of cloth
HISTORY
Vinyon N Copolymer,
(polyvinyl chloride and polyacrylonitrile)
Nylon, Orlon®, Dacron®, Teflon®, Ivalon®

6. 6
- 1953: Dacron (polymer fiber) vascular grafts
- 1958: J. Charnley, Cemented (PMMA) joint, total hip replacement
- 1958: S.Furman & G.Robinson, First direct stimulation of heart
- 1960: A. Starr, M.I. Edwards, first commercial heart valves
- 1976: W.J. Kolff et al., Artificial heart
HISTORY (Contd)
- 1976: FDA amendments governing testing &
production of biomaterials /devices

7. 7
An (ideal) biomaterial must be:
• inert or specifically interactive
• biocompatible
• mechanically and chemically stable or
• biodegradable
• process able (for manufacturability)
• Non-thrombogenic (if blood-contacting)
• sterilizable
Requirements of Biomaterials

8. 8
Generalproperties and Criteria
1. Mechanical properties (strength)
2. Toxicity and Biocompatibility
3. Tissue response
4. Interfacial response
5. Performance
6. Regulation and ethics

9. 9
1. Mechanical properties of Biological materials and biomaterials

10. 10
2. Toxicity and Biocompatibility
A biomaterial should not be toxic
It deals with the substances that migrate out of biomaterials.
• There is no general set of criteria, for a material to qualify as being
biocompatible
– The time scale over which the host is exposed to the material or device
must be considered
material contact time
syringe needle 1-2 s
tongue depressor 10 s
contact lens 12 hr - 30 days
bone screw / plate 3-12 months
total hip replacement 10-15 yrs
intraocular lens 30 + yrs

11. 11
3. Tissue Response to Implants

12. 12
3. Tissue Response to Implants - Contd
1. Minimal Response: Thin layer of fibrous tissue
Silicon rubber, PTFE, PMMA, Ceramics, alloys
2. Chemically Induced response: Acute, mild inflammation
Absorbable sutures, resins
4. Physically Induced response: Inflammation to particulates
PTFE, PMMA, Nylon, Metals
3. Chemical (2) : Chronic and Severe Inflammation
Degradable material, Metallic corrosion
5. Physical (2) : Tissue growth into porous material
Polymer, ceramic, metal, Composites
6. Necrotic response: Layer of necrotic Debris
Bone cement, surgical adhesives

13. 13
4. Interfacial Response
Based on Interfacial response, there are four types of biomaterials:
1. Nearly inert, smooth surface
2. Nearly inert, microporous surface
3. Controlled reactive surface
4. Resorbable

14. 14
5. Performance of Implants

15. 15
5. Performance of Implants (contd)
Schematic illustration
showing probability of
failure vs implant period
The performance of an implant after insertion can be considered in terms of
reliability.
there are four major factors contributing to the failure of hip joint replacements
fracture, wear, infection, and loosening of implants

16. 16
6. Regulation
Different standards:
ISO – International Standards Organisation
ASTM – American Soceity for Testing Materials
BSI – British Standards Institute
AISI – American Institute of Steel and Iron
BIS – The Bureau of Indian Standards

17. 17
6. Regulation (contd.)

18. 18
Inert, Interactive, Living and replacing materials
Inert biomaterials: Implantable materials with little or no counter reaction
from the body.
Interactive biomaterials: Implantable materials designed to elicit a specific
benign tissue reaction, such as integration, adhesion, etc.
Living biomaterials: Implantable materials that possibly contain living cells at
time of implantation, regarded by the host tissue as tolerable tissue, and are
actively resorbed and/or remodeled.
Replacement biomaterial: Implantable materials made of living tissue that
has been cultivated from the patient own cells outside the body.
Classification of Biomaterials

19. 19
Material Advantages Disadvantages
POLYMERS:
Nylon, silicones, PTFE,
UHMWPE
Resilient, easy to
fabricate
Not strong, deform with
time, may degrade
METALS:
Titanium, stainless steels,
CoCr alloys, gold
Strong, tough, ductile May corrode, high
density
CERAMICS:
Aluminum oxide, carbon,
hydroxyapatite
Highly biocompatible,
inert, high modulus and
compressive strength,
good esthetic properties
Brittle, difficult to make,
poor fatigue resistance
COMPOSITES:
Various combinations
Strong, tailor-made Difficult to make
Classes of Biomaterials

20. 20
Important Definitions
• Biological response: host response towards a material.
• Biodegradation: breakdown of a material in a biological system.
• Bioactive material: A biomaterial intended to cause or modulate a biological activity.
• Bioactivity: Degree of wanted (positive) reaction from tissues.
• Inherent thrombogenicity: establishment of a thrombus that is controlled by material
surface properties (thrombus=blood plug, genicity=”cause”).
• Osseointegration: is a description of the clinical performance of bone that interact
with a biomaterial (ossus=bone).
• Bone bindning: the establishment of a continuity between implants and living bone
through physical/biochemical processes.

21. 21
Material properties

22. 22
• To introduce the fundamental mechanical and surface chemistry properties
of biomaterials
• OUTLINE
– Mechanical Properties (bulk)
• elasticity, viscoelasticity, brittle fracture, fatigue
– Surface Properties
– List of Characterization techniques
Material properties
The bulk of a biomaterial presents physical and chemical properties of the
material that remain during the lifetime of the implant.
The surface properties is mainly defined by chemical, microstructure and it
interacts with the host tissue directly.

23. Biomaterial Properties
• Surface properties
• Bulk properties
• Biological properties
23

24. 24
Surface Properties
The surface region of a material is known to be uniquely reactive
 The surface of a material is inevitably different from the bulk
 Surfaces readily contaminate
 The surface structure of a material is often mobile.
•Biomaterial surface is extremely important in determining the biological
response.
•Some of the biomedical devices and materials do not leach undesirable
substances in sufficient quantities to influence cells and tissue.
•Therefore, the surface structure play an important role in attract the
cells and tissue to respond with the materials.
Surface properties

25. 25
Parameters:
roughness, wettability, surface mobility,
chemical composition, electrical charge,
crystallinity, and heterogeneity to biological
reaction
Surface is a material, near interface,
having different properties from bulk. (few
nm layers)
Surface Sensitivity
This is usually relative to the penetration
depth of the probe.

26. 26
Physical Description of Biomaterial Surfaces
Biomaterial surfaces exhibit remarkable heterogeneity in physical structure:
Material dependant: Metals vs. Polymers vs. Ceramics vs. Gels
Chemistry: Polar vs. Apolar, Charge, Reactivity, Patterned
Morphology: Smooth, Rough, Stepped, Patterned, Diffuse
Order: Crystalline, Amorphous, Semi-Crystalline, Phases
Environment: Hydration, Solvent Quality
Bumpy with Phases
Hydration
Glassy

27. • Some Possibilities for Surface Structure
27

28. 28
• Parameters to be measured:
a) Roughness, smoothness
b) Chemical composition
(atomic, supramolecular,
macromolecular)
Surface properties

29. 29
c) Surfaces may be structurally or
compositionally inhomogeneous in
the plane of the surface such as
phase-separated domains or
microcontact printed lanes.
d) Surfaces may be
inhomogeneous with depth
into the specimen or simply
over layered with a thin film.
Surface properties

30. 30
e) Crystallinity f) Unreconstructed surface or
reconstructed surface
Surface properties

31. 31
Common Methods to Characterize Biomaterial Surfaces
Surface Characterization

32. SURFACE PROPERTIES
The surface properties for the biomaterials
which are being considered for discussion are
Surface Energy
Contact Angle
Critical Surface Tension
32

33. 33
• Interface
– boundary between 2 layers
• significance
– protein adsorption to materials
– blood coagulation/thrombosis due to material contact
– cellular response to materials
Surface Energy

34. SURFACE ENERGY
Surface energy quantifies the disruption of
intermolecular bonds that occurs when a surface is
created.
In other words surface energy is a measure of the
extent to which bonds are unsatisfied at the surface of
material. At the surface, there is an asymmetric force
field, which results in an attraction of atoms which are
there on the surface in to the bulk.
This tends to deplete the surface of atoms putting the
surface in tension.
34

35. SURFACE ENERGY
Metals and ceramics have surfaces with high
surface energies ranging from 102 to 104
ergs/cm2.
In contrast, most polymers and plastics have
much smaller surface energies, usually <100
ergs/cm2.
The surface energy values are subject to
much experimental variation due to
adsorption of gases or organic species.
35

36. CONTACT ANGLE
The contact angle is the angle at which a
liquid/vapor interface meets the solid
surface.
The contact angle is specific for any given
system and is determined by the
interactions across the three interfaces.
36

37. CONTACT ANGLE
When a liquid drop is placed on to the surface of a solid or the
surface of the liquid, the processes which occur are:
1.The liquid may sit on the surface in the form of a droplet
or
2. It may spread out over the entire surface depending on the
interfacial free energies of the two substances.
At equilibrium contact angle or Young Dupree equation
is given by
s / g = s / l + l / g cos 
Where s / g, s / l and l / g are the interfacial free energy between
the solid and gas; solid and liquid, liquid and gas respectively and
 the contact angle. 37

38. CONTACT ANGLE
The wetting characteristic can be generalized
as
 = 0, complete wetting ;
  0  900, partial wetting ;
 > 900 , no wetting.
The contact angle can be affected greatly by
the surface roughness and adsorption of polar
gases or organic species or contamination by
dirt.
38

39. 39
Superhydrophobicity

40. CRITICAL SURFACE TENSION
The critical surface tension is defined as that value of
surface tension of a liquid below which the liquid will
spread on a solid and is expressed in dynes/cm.
The critical surface tension of a material is determined
by measuring the different values of contact angle 
formed by liquids with different values of l / g.
A plot of cos  versus l / g is usually a straight line
40

41. 41
The critical surface tension is the surface tension of a
liquid that would completely wet the solid of interest.
Material c (dyne/cm)
Co-Cr-Mo 22.3
Pyrex glass 170
Gold 57.4
poly(ethylene) 31-33
poly(methylmeth
acrylate)
39
Teflon 18
Critical Surface Tension
The l / g at which cos  =1 is defined as the critical surface-tension (c).

42. CRITICAL SURFACE TENSION
Blood compatibility of material surfaces has been shown
to vary in the same order as the critical surface tension.
It is found that the amount of thrombus formation
increases and blood clotting time decreases as c
increases.
42

43. 43
At the surface (interface) there are intermolecular forces and
intramolecular forces of attraction and repulsion.
• van der Waals forces : Hydrogen Bonds : Coulombic :
Surface Chemistry
How surfaces interact with molecules?
 Nonspecific interaction
 Specific binding
 Surface topology
Nonspecific Interaction
• attractive van der Waals force that arises from dipole-dipole type interactions;
• Electrostatic forces resulting from charged molecules
• Hydration or solvation force that results from expulsion of water between the
two surfaces
• Hydrophobic effects that non‐polar molecules tend to form intermolecular
aggregates in an aqueous medium
• Repulsive steric forces that arise due to proteins on both surfaces forming
spikes of up to 10 nm.

44. 44
• surface may become charged by
– adsorption of ionic species present in sol’n or preferential
adsorption of OH-
– ionization of -COOH or -NH2 group
-
-
-
-
-
-
solid
+
+
+
+
+
+ hydroxyl ion
Surface Electrical properties

45. 45
-
-
-
-
-
-
+
+
+
+
+
+
+
-
+
+
-
+ - -
++
-
+
-
- +
+ - +
+
gegenion
Nernst potential
zeta potential
tightly
bound
diffuse
electroneutral
bulk
Electric Double Layer

46. 46
Surface Analysis Techniques for Biomaterials
• Contact Angle Measurements
• Electron Spectroscopy for Chemical Analysis (ESCA / XPS)
• Auger Electron Spectroscopy (Auger)
• Near Edge X-ray Absorption Fine Structure (NEXAFS)
• Secondary Ion Mass Spectroscopy (SIMS)
• Scanning Probe Microscopy (AFM)
• Sum Frequency Generation (SFG)
• Surface Plasmon Resonance (SPR)
• Optical Imaging and Spectroscopy (microscopy, TIRF)
• Ellipsometry
• Scanning Electron Microscopy (SEM)
• Infrared Spectroscopy (FTIR)
• Many more...

47. 47
Biomaterials Surface Analysis

48. 48
Property Technique(s)
Composition ESCA, Auger, SIMS, NEXAFS
Structure SIMS, ESCA, NEXAFS, FTIR, SFG
Orientation NEXAFS, FTIR, SFG
Spatial Distribution Imaging SIMS, AFM, microscopy
Topography AFM
Thickness ESCA, AFM, ellipsometry, SPR
Energetics Contact angle
Surface Information

49. Biocompatibility and
Sterilization
49

50. 50
• Protocol for biomaterial test provide by:
– American Society for Testing Material (ASTM)
– International Standards Organization (ISO)
– Government agencies, e.g., the FDA

51. 51
STANDARDS
• 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.
• 20 parts of the ISO 10993 standard
• are either accepted or under preparation. Tests that may be used in
the assessment of medical device biocompatibility include
procedures for cytotoxicity, sensitization, irritation, acute systemic
toxicity, subchronic toxicity, mutagenicity, geno toxicity,
hemocompatibility etc. The testing procedures can be performed in
vitro as well as in vivo

52. 52
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

53. 53
• 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

54. 54
• 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

55. 55
• 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

56. Biocompatibility
• Defined as the compatibility between a material and the biological
system.
• “the ability of a material to perform with an appropriate host response
in a specific application”
• Two principal elements.
• First there is the absence of a cytotoxic effect and second, there is the
aspect of functionality.
• Cytotoxicity - survival of cells and the maintenance of specific cellular
functions under the influence of a material and/or its degradation
products.
• Functionality - integration of the biomaterial into a biological system.
assumes the absence of impairment of cellular function requires that
the mechanical, chemical and physical features of the material are
sufficient for the performance of cell-specific functions.
56

57. 57
TESTING OF 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?
• in vitro (literally "in glass") conditions: rapid and inexpensive
data on biological interaction
– Cells attach and grow on MODIFIED Tissue culture
polystyrene, a surface modified polymer, not on untreated
polystyrene.
• 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 in vivo implant situation.

58. 58
Advantages of in vitro:
• 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.
In vivo Experiments:
• 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.

59. 59
IN VITRO ASSESSMENT
• “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.
• Cells 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.

60. 60
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 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.

61. 61
Delivered and Exposure Doses
• Delivered dose: the dose that is actually absorbed by the cell.
• Exposure dose: the amount applied to a test system.
• 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.

62. 62
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.

63. 63
Direct contact method
1. A near confluent layer of fibroblasts are prepared in a culture
plate
2. Fresh media is added
3. Material being tested is placed onto the cultures, which are
incubated for 24 hours at 37 degrees Celsius
4. The material is removed
5. The culture media is removed
6. The remaining cells are fixed and stained, dead cells are lost
during fixation and only the live cells are stained
7. The toxicity of the material is indicated by the absence of
stained cells around the material

64. 64
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
interface

65. 65
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
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

66. 66
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

67. 67

68. 68
IN VIVO ASSESSMENT BIO-
COMPATIBILITY
• 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.

69. 69
In Vivo Assessment of Tissue Compatibility
• The goal of in vivo assessment of a biomaterial,
prosthesis or medical devices is:
– to determine that the device performs as intended
and presents no significant harm to the patient or
user.
• In vivo test for assessment of tissue biocompatibility
are chosen to stimulate end-use applications.
• To facilitate the selection of appropriate tests,
medical devices with their components of
biomaterial can be categorized by:
– The nature of body contact of the medical device
– Duration of contact of the medical device

70. 70
Medical device categorization by tissue contact and
contact duration
Tissue Contact
Surface devices
External communicating
devices
Implant devices
Contact duration
Skin
Mucosal membrane
Breached or compromised surface
Blood path
Tissues/Bone/dentin communicating
Circulating blood
Tissue/bone
Blood
Limited, ≤ 24 hours
Prolonged, ≥ 24 hours and < 30 days
Permanent, >30 days
In Vivo Assessment of Tissue Compatibility

71. 71
In vivo test for tissue compatibility
1. Sensitization
2. Irritation
3. Intracutaneous reactivity
4. Systemic toxicity (acute toxicity)
5. Subcronic toxicity (subacute toxicity)
6. Genotoxicity
7. Implantation
8. Hemocompatibility
9. Chronic toxicity
10. Carcinogenicity
11. Reproductive and developmental toxicity
12. Biodegradation
13. Immune responses

72. 72
In Vivo Assessment of Tissue Compatibility
1. Sensitization
• Sensitization test estimate the potential for contact
sensitization to medical devices or materials.
• Symptom of sensitization are often seen in skin.
• Sensitization is a immune system response to chemicals
2. Irritation
• Irritant test emphasize utilization of extracts of
biomaterials to determine the irritant effects of potential
leachables
• Irritation is a local tissue inflammation response to
chemical.
3. Intracutaneous (intradermal) reactivity
• Determine the localized reaction of tissue to
intracutaneous injection of extracts of medical devices,
biomaterials, or prosthesis in the final product form.

73. 73
4. Systemic toxicity (acute toxicity)
– Estimate the potential harmful effects in vivo on target
tissues and organs away from the point of contact with
either single or multiple exposure to medical devices or
biomaterials.
– Acute toxicity is considered to be the adverse effects
occurring after administration test sample within 24
hours.
5. Subacute toxicity
– Focuses on adverse effect occuring after administration
of a single dose or multiple doses of a test sample per
day during a period of from 14 to 28 days.
6. Subcronic toxicity
– adverse effect occuring 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.
In Vivo Assessment of Tissue
Compatibility

74. 74
7. Genotocity
• Genocity tests are carried out if in vitro test results
indicate potential genotoxicity.
• The in vitro assay should cover three levels of
genotoxicity effects: DNA destruction, Gene mutation,
Chromosomal aberrations (abnormality)
8. Implantation
• Implantation test assess the local pathological effects on
the structure and function of living tissue induced by a
sample of a material or final product at site where it is
surgically implanted.
In Vivo Assessment of Tissue Compatibility

75. 9. Hemocompatibility
– This test evaluate effect on blood and/or blood
component by blood contacting medical devices or
materials.
– From the ISO standard prospective, five test
categories for hemocompatibility evaluation:
• Thrombosis (blood coagulation)
• Coagulation
• Platelets
• Haematology
• Immunology
In Vivo Assessment of Tissue Compatibility
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Alternative scenario that can be applied for interpreting results
of blood-material interaction assay
Alternate
interpretation
Result implying
poor blood
compatibility
Evaluation
method
Result implying
good blood
compatibility
Alternate
interpretation
Many platelet
adhere, but the
platelets are not
activated and
form passivating
natural biological
layer on the
surface
Many adherent
platelets
Measure
platelet
adhesion
No adherent
platelets
Platelets
aggregate and
embolize
downstream
The thrombus
layer forms a non-
reactive natural
biological film on
the surface
Surface coated
with adherent
thrombus
Measure the
mass of
adherent
thrombus
No adherent
thrombus
Thromus detaches
and embolizes
downstream.
Therefore it not
seen on the
surface
Released factors
stimulated
desirable
endothelial cell
growth
Extensive platelet
granule release
Measure the
platelet
granule
release
No release Release actually
occurs but its
diluted by the
flowing blood

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10. Carcinogenity
– This test determine the tumorigenic potential of medical
devices and biomaterial.
11. Reproductive and Developmental Toxicity
– These test evaluate the potential effects of medical
devices and biomaterials on reproductive function,
embryonic development and prenatal and postnatal
development.
12. Biodegradation
• This test determine the effects of biodegradation materials
and its biodegradation products on the tissue response.
• This test focus on:
– Amount of degradation during a period of time
– The nature of the degradation products
– The origin of the degradation product
– Leachable in adjacent tissue and in distant organ.
In Vivo Assessment of Tissue Compatibility

78. 78
13. Immune response
– Immune response evaluation is not a component of
the standards currently in vivo tissue compatibility
assessment.
– However, ASTM, ISO and FDA currently have
working groups developing guidance documents for
immune response evaluation.
– Synthetic material are not generally immunogenic
– However, immune response evaluation is necessary
with modified natural tissue implant such as
collagen.
In Vivo Assessment of Tissue
Compatibility

79. 79
Advantages and Limitation of
Biocompatibility Test
Test/Assay Advantages Limitations
In vitro tests Quick turnover (days), high
throughput screening,
standardized with
appropriate protocols
Relevance to in vivo
In vivo test Provide multi-system
interactions, more
comprehensive than
ioutcome inconsistent
In vitro test
Relevance to clinical
use questionable, low
turnover (week to
months), high cost
and low throughput,
animal use concerns,
outcome can be
difficult to interpret

80. STERILIZATION
• One of the greatest challenges for devices
is ensuring sterility
• Many in-vivo degradation schemes have
been linked to loss of mechanical
properties due to post-sterilization aging
80

81. Sterilization
Sterility Definition:
Sterility can be defined as the absence of all living organisms,
particularly microorganisms.
“the state in which the probability of any one bacterial endospore
surviving is 10-6 or lower”
The sterility assurance level (SAL) minimum, that the probability
of a given implant will remain non-sterile after exposure to a given
sterilization process, is one in a million implants.
Example: In operating theatre area: Under aseptic
conditions,
5,000–50,000 skin particles are delivered daily from each
physician’s flora in intensive care units and pathogenic
bacteria such as Staphylococcus aureus can be recovered
from about 90% of “clean” wounds at the time of closure 81

82. 82

83. STERILIZATION SCHEMES
• Steam
• Autoclaving
• Eto Gas
• E-beam radiation
• Gamma Radiation
83

84. Steam Autoclaves
• Steam sterilizers (autoclaves) are instruments that produce
superheated steam under high pressure, and are used for both
decontamination and sterilization
• Material to be sterilized must come in contact with steam and
heat
• Tight-fitting containers do not permit steam penetration, and thus
are not acceptable for use in autoclaves.
• The use of autoclave tape alone however is not an adequate
monitor of efficiency.
• Indicator such as Bacillus stearothermophilus spore strips. The
spores, which can survive 121 ◦C for 5min, but are killed at 121
◦C in 13min,
84

85. Dry Heat
• Dry heat is less efficient than wet heat and requires longer times
and/or higher temperatures to achieve sterilization.
• Sterilization of glassware by dry heat can usually be accomplished
at 160–170 ◦C for 2–4 h.
Radiation
• Gamma and electron-beam irradiation are among the most popular
and well established
• Gamma radiation kills microorganisms by attacking their DNA.
• Processes for sterilizing polymer-based medical devices.
• These techniques can lead to significant alterations in the materials
being treated
85

86. Ethylene Oxide
• 100% ethylene oxide (EtO) gas remains one of the most popular.
• kills microorganisms by destruction of proteins and nucleic acids
• EtO is suitable for heat-labile instruments such as endoscopes with
sensitive optics, medical utensils or implants.
• Disadvantage: Ethylene oxide is an explosive and toxic gas, and a
long degassing period
New Technologies
• gaseous chlorine dioxide, low-temperature gas plasma, gaseous
ozone and vapor-phase hydrogen peroxide
• machine-generated X-rays are being investigated as a substitute to
gamma radiation
86

87. Infections of Biomaterials
• First contact of biomaterial in the body- fluids
• Bacterial organisms have the ability to adhere to all types of materials
that are made of polymers, glasses, ceramics and metals.
• Biofilms account accounts or over 65% of human bacterial infections
• Biofilms: Three major problems.
– First, a reservoir of bacteria that can be shed into the body, - a chronic
infection.
– Second, biofilm bacteria are highly resistant to treatment with
antibiotics; extremely difficult to eliminate with conventional
antimicrobial therapies.
– Finally, unable to eliminate bacteria growing in a biofilm, a chronic
inflammatory response at the site of the biofilm may be produced.-
– may account for tissue damage due to host response
– A non-shedding surface on a medical device encourages the
establishment of biofilms.
87

88. Biofilm-Classes of Bacteria
• Staphylococci
• streptococci
• Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and
• Pseudomonas aeruginosa
These organisms may originate from the skin of patients or
health-care workers, tap water to which entry points are
exposed, or other sources in the environment.
88

89. 89