Transcript Slide 1

Dr. Alagiriswamy A A, (M.Sc, PhD, PDF)
Asst. Professor (Sr. Grade),
Dept. of Physics, SRM-University,
Kattankulathur campus,
Chennai
ABCs of Biomaterials
UNIT III
Lecture 4
July 18, 2015
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CLASSIFICATION OF BIOMATERIALS
Biomaterials can be divided into three major classes of
materials:
Metals
Polymers
Ceramics (including carbons, glass ceramics, and glasses).
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Biological responses ; requirements
 Changing the chemistry at the surface
 Inducing roughness/porosity at the surface
 Incorporate surface reactive materials (bioresorbable;
helps in slow replacement by tissue)
 Should not secrete oxidizing agents
 Reduce corrosion rate of biomaterials
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METALLIC IMPLANT MATERIALS
 Stainless steel
 Must be corrosion resistant
 Cobalt-chromium alloys  Good fatigue properties
 Titanium alloys
 Other compatible issues
Metallic implants are used for two primary purposes.
To replace a portion of the body such as joints, long bones and
skull plates.
Fixation devices are used to stabilize broken bones
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CONSTITUENTS OF STEEL
Type
%C
%Cr
% Ni
%Mn
% other elements
301
0.15
16-18
6-8
2.0
1.0Si
304
0.07
17-19
8-11
2.0
1-Si
316, 18-8sMo
0.07
16-18
10-14
2.0
2-3 Mo, 1.0 Si
316L
0.03
16-18
10-14
2.0
2.3 Mo, 0.75Si
430F
0.08
16-18
1.0-1.5
1.5
1.0 Si, 0-6 Mo
LECTURE 3
5
Other features
 less chromium content should be utilized (because Cr is a
highly reactive metal)
 Make use of austenite type steel (less magnetic properties)
 Lowered carbon content
 Inclusion of molybdenum helps corrosion resistance
 Electroplating technique (increases corrosion resistance)
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Devices
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Alloy Type
Jewitt hip nails and plates
316 L
Intramedullary pins
316 L
Mandibular staple bone plates
316L
Heart valves
316
Stapedial Prosthesis
316
Mayfield clips (neurosurgery)
316
Schwartz clips (neurosurgery)
420
Cardiac pacemaker electrodes
304
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COBALT CHROMIUM ALLOYS
Cobalt based alloys are used in one of three forms
•Cast; as prepared
•Wrought (fine structure with low carbon contents ;
pure forms)
•Forged
Cobalt based alloys are better than stainless steel devices
because of low corrosion resistance
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More details
Cast alloy:
• a wax model of the implant is made and
ceramic shell is built around the wax model
• When wax is melted away, the ceramic mold has the shape
of the implant
• Molten metal alloy is then poured in to the
shell, cooling, the shell is removed to obtain
metal implant.
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 Wrought alloy:
 possess a uniform microstructure with fine grains.
 Wrought Co-Cr –Mo alloy can be further strengthened by
cold work.
 Forged Alloy:
 produced from a hot forging process.
 Forging of Co-Cr –Mo alloy requires
sophisticated press and complicated tooling.
 Factors make it more expensive to fabricate a device
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TITANIUM BASED ALLOYS
The advantage of using titanium based alloys as implant
materials are
 low density
 good mechano-chemical properties
The major disadvantages
o relatively high cost
oreactivity.
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More details
• a light metal
• Titanium exists in two allotropic forms,
• The low temperature -form has a close-packed hexagonal
crystal structure with a c/a ratio of 1.587 at room temperature
• Above 882.50C -titanium having a body centered cubic
structure which is stable
• Ti-6 Al-4V alloy is generally used in one of three conditions
wrought, forged or cast
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THREE CLASSES OF CERAMICS (according to their reactivity)
 completely resorbable
•
More reactive (Calcium phosphate) – over a span of times
•
Yielding mineralized bone growing from the implant surface
 surface reactive
•
Bioglass ceramics ; Intermediate behavior
•
Soft tissues/cell membranes
 nearly inert
•
Less reactive (alumina/carbons) even after thousands of hours
•
how minimal interfacial bonds with living tissues.
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DIFFERENT VARIETIES OF CARBON (NEARLY INERT CERAMICS)

Pyrolitic carbon;
• Pyrolysis of hyrdocarbon gas (methane) ≤ 15000 degrees
• Low temperature isotropic (LTI) phase
• Good bonding strength to metals (10 Mpa – 35 Mpa)
• Inclusion of Si with C, wear resistance increases drastically

Vitreous carbon (glassy carbon);
• controlled pyrolysis of a polymer such as phenol formaldehyde
resin, rayon and polyacrylonitrile
• Low temperature isotropic phase
• Good biocompatibility, but strength and wear resistance are not good as LTI carbons

Turbostratic carbon (Ultra low temperature isotropic carbons (ULTI))
• Carbon atoms are evaporated from heated carbon source and
condensed into a cool substrate of ceramic, metal or polymer.
• Good biocompatibility
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Alumina (Aluminium oxide)
 Natural single crystal alumina known as sapphire
 High-density alumina ; prepared from purified alumina
powder by isostatic pressing and subsequent firing at 150017000C.
 -alumina has a hcp crystal structure (a=0.4758 nm and
c=1.2999nm)
 load bearing hip prostheses and dental implants, hip and knee
joints, tibial plate, femur shaft, shoulders, vertebra, and ankle
joint prostheses
Alumina ceramic
femoral
component
Porous network ;
SEM images
•high corrosion resistance
•wear resistance
• Surface finishing
•small grain size
•biomechanically correct design
•exact implantation technique
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Glass Ceramics
To achieve a controlled surface reactivity that will
induce a direct chemical bond between the implant and the
surrounding tissues.
Bioglass
Also known as 45S5 glass. It is composed of SiO2, Na2O,
CaO and P2O5.
45 wt.% of SiO2 and 5:1 ratio of CaO to P2O5. Lower Ca/P
ratios do not bond to bone.
Bioglass and Ceravital; fine-grained structure with
excellent mechanical and thermal properties
The composition of Ceravital is similar to bioglass in Sio2
content but differ in CaO,MgO,Na2O.
Ceravital
Bioglass implants have several advantages like
•
high mechanical properties
•
surface biocompatible properties.
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Resorbable Ceramics (first resorbable implant material-Plaster of Paris).
•
Should not have variable resorption rates
•
Should not have poor mechanical properties.
Two types of orthophosphoric acid salt namely -tricalcium phosphate (TCP)
and hydroxyapatite (HAP) (classified on the basis of Ca/P ratio).
The apatite- [Ca10 (PO4)6 (OH)2] crystallizes into the hexagonal rhombic
system. The unit cell has dimensions of a = 0.9432 mm and c = 0.6881 nm.
The ideal Ca/P ratio of hydroxyapatite is 10/6 and the calculated density is
3.219 g/ml.
The substitution of OH- with F- gives a greater structural stability due to the
fact that F- has a closer coordination than the hydroxyl, to the nearest calcium.
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POLYMERS
Elastomers; able to withstand large deformations and
return to their original dimensions after releasing the
stretching force.
Plastics; are more rigid
materials
 Thermoplastic (can be
reused, melted)
 Thermosetting (can’t)
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Elastomers
include,
butyl
rubber,
chlorosulfonated
polyethylene,
epichlorohydrin,rubber,
polyurethane,natural rubber and silicone
rubber.
Polymers toxicity
Residual monomers due to incomplete
polymerization/catalyst
used
for
polymerization may cause irritations.
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Polymer
Specific Properties
Biomedical uses
Polyethylene
Low cost, easy Possibility excellent
electrical
insulation
properties,
excellent
chemical
resistance,
toughness and flexibility even at low
temperatures
Tubes for various
catheters, hip
joint, knee joint
prostheses
Polypropylene
Excellent chemical resistance, weak
permeability to water vapors good
transparency and surface reflection.
Yarn for surgery,
sutures
Tetrafluoroethylene Chemical
inertness,
exceptional
weathering and heat resistance,
nonadhesive, very low coefficient of
friction
Vascular and
auditory
prostheses,
catheters tubes
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Polyethylene structures
The first polyethylene [PE,(-CH2-CH2-)n] was made by
reacting
ethylene gas at high pressure in the presence of a peroxide
catalyst for starting polymerization; yielding low density
polyethylene (LDPE).
By using a Ziegler-Natta catalyst, high-density polyethylene
(HDPE)
can be produced at low pressure; (first titanium-based
catalysts)
The crystallinity usually is 50-70% for low density PE and
70-80% or high density PE
ultra high molecular weight polyethylene (UHMWPE)
…??????
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ACRYLIC RESINS (organic glass)
The most widely used polyacrylate is poly(methyl
methacrylate, PMMA) ; The features of acrylic polymers ;
 high toughness/strength,
 good biocompatibility properties
 brittle in comparison with other polymers
 excellent light transparency
 high index of refraction.
Causes allergic reactions
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BONE CEMENT MIXING AND INJECTION
 PMMA powder + MMA liquid
mixed in a ratio of 2:1 in a dough, to
cure
Injected in the femur (thigh bone)
The monomer polymerizes and
binds
together
the
preexisting
polymer particles.
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Hydrogels
Interaction with H2O, but
not soluble
PHEMA; absorbs 60 % of Water,
machinable when dry
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Interesting features
HYDROGELS
(1) The soft, rubbery nature coupled with minimal
mechanical/frictional irritation to the
surrounding
tissues.
(2) Low or zero interfacial tension with surrounding
biological fluids and tissues, thereby, minimizing the
driving force for protein adsorption and cell adhesion
(3) Hydrogels allow the permeating and diffusion of low
molecular weight metabolities,waste products and salts
as do living tissues.
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POLYURETHANES
 Polyther-urethanes; block copolymers (variable length blocks that
aggregate in phase domains)
 Good physical and mechanical characteristics
 Are hydrophilic in nature
 Good biocompatibility (blood compatibility)
 Hydrolytic heart assist devices
 Non-cytotoxic therapy
Consists of hard and soft segments
LECTURE 5
BIOMATERIALS
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POLYAMIDES (Nylons)
Obtained through condensation of diamine and
diacid derivative.
Excellent fiber forming properties due to interchain hydrogen bonding and high degree of
crystallinity, which increases the strength in the
fiber direction.
Hydrogen bonds play a major role
As a catheter
Hypodermic syringes
Diamino hexane + adipic acid
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BIOMATERIALS
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Biological responses ; requirements
 Changing the chemistry at the surface
 Inducing roughness/porosity at the surface
 Incorporate surface reactive materials (bioresorbable;
helps in slow replacement by tissue)
 Should not secrete oxidizing agents
 Reduce corrosion rate of biomaterials
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Biosensors (invitro/in vivo);
 analytical devices which convert
biological response into a useful electrical
signal
 to determine the concentration of
substances either directly or indirectly
 areas of biochemistry, bioreactor
science,
physical
chemistry,
electrochemistry, electronics and software
engineering, and others
http://www.lsbu.ac.uk/biology/enztech/
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Principle of biosensors (bio-recognition systems)
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WORKING PRINCIPLE OF BIOSENSOR
 biocatalyst (a) converts the substrate to product.
 This reaction is determined by the transducer (b)
which converts it to an electrical signal.
The output from the transducer is amplified (c),
output
 distribution of charges
 light-induced changes
 mass difference
 processed (d) and displayed (e).
LECTURE 6
BIOMATERIALS
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Three so-called 'generations' of biosensors;
 First generation; normal product of the reaction diffuses to
the transducer and causes the electrical response.
 Second generation; involve specific 'mediators' between
the reaction and the transducer in order to generate
improved response.
 Third generation; reaction itself causes the response and no
product or mediator diffusion is directly involved.
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Brief applications of biosensor(s)
 Clinical diagnosis and biomedicine
 Farm, garden and veterinary analysis
 Process control: fermentation control and
analysis food and drink
 production and analysis
 Microbiology: bacterial and viral analysis
 Pharmaceutical and drug analysis
 Industrial effluent control
 Pollution control and
monitoring/Mining, industrial and toxic
gases
 Military applications
LECTURE 3
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Tissue engineering (also referred to as
“regenerative medicine)
 By
restoring,
maintaining,
enhancing the tissue, and finally
functionalize the organs
 Tissue can be grown inside or
outside
To create products that improve tissue
function or heal tissue defects.
 Replace diseased or damaged tissue
 Finally to exploit the living cells in
many ways
Because……
Donor tissues and organs are in short
supply
We want to minimize immune system
response by using our own cells or
novel ways to protect transplant
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Tissue engineering
 Regenerate
 Identify the cues that allow for



regeneration without scarring
 Like growing a new limb
 Repair
 Stimulate the tissue at a cell or
molecular level, even at level of
DNA, to repair itself.
 Replace
 A biological substitute is created
in the lab that can be implanted
within the extracellular
to replace the tissue or organ of
as laminins,collagens,and
interest
The cells themselves
Non-soluble factors
matrix (ECM) such
other molecules
Soluble factors such as cytokines, hormones,
nutrients, vitamins, and minerals
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Normal strategies
 cell isolation
 cell culture
 scaffold material choice
 cell scaffold co-culture studies
 implantation in animals
 human trials
SUCCESSFULLY ENGINEERED
TO SOME EXTENT
Skin
Bone
Cartilage
Intestine
Questions?
July 18, 2015