How does the human body respond to a biomaterial

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15 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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MECH 500:

Bionic Implants and Devices



Sumitra Rajagopalan

sumitra.rajagopalan@polymtl.ca



Office Hours:


5pm


5:30 pm Mondays

4 pm
-

5pm Fridays



Office : B
-

364



Lecture 2 : Functional Biomaterials

Lecture 2: Functional Biomaterials


How does the human body respond to a biomaterial ?



What materials are currently used as biomaterials?


How are these biomaterials characterised? What happens
to the biomaterial once implanted?


What kind of surface modification can improve the
biocompatibility of the biomaterial?


What changes in the bulk can improve the performance of
the biomaterial?


How does nature
"
design
"

biological materials?


Mimicking Nature: Biomimetic (Bionic) Material Design


Where do we go from here ?


Lecture 3: Combining materials with living tissues


tissue
engineering.

Human Blood: A Hostile Environment


Blood: Red Blood Cells +
White Blood Cells


ONLY White Blood Cells
(LEUKOCYTES) are
involved in the body’s
response


Neutrophiles (poly) engulf
and destroy foreign
material :
PHAGOCYSTOSIS


Monocytes turn into giant
MACROPHAGES to gulp
foreign body particles


Biomaterial debris often
targetted by macrophages


Scavenger Cells!




Site becomes red


Site becomes swollen


The site becomes warm


The site becomes painful


Blood clots, Polys appear at
the site of injury: ACUTE
INFLAMMATION


If splinter is removed, then
tissue returns to normal


If splinter is not removed,
polys recruit monocytes, then
macrophages


Inflammation turns into
CHRONIC INFLAMMATION




tutor.lscf.ucsb.edu/.../ chapter02/monocyte.htm



Inflammation Reaction:Splinter in Finger

After the clean
-
up: Wound Healing


Blood vessels begin to grow at site


Tissue called fibroblasts synthesize
collagen


***************


Normal Tissue Repair cannot
happen if biomaterial persists in
body





First Reaction ?


Fibroblasts then lay down a layers
of fibrous tissue to wall
-
off the
implant


The thinner the capsule the more it
is biocompatible


Serious complications if the
inflammation persists: CHRONIC
INFLAMMATION







In what instances would this fibrous capsule
impede the preformance of the implant?


Porous or textured surfaces do not provoke
capsule formation. Why?

Lecture 2: Functional Biomaterials


How does the human body respond to a biomaterial ?


What materials are currently used as biomaterials?


How are these biomaterials characterised? What happens
to the biomaterial once implanted?


What kind of surface modification can improve the
biocompatibility of the biomaterial?


What changes in the bulk can improve the performance of
the biomaterial?


How does nature
"
design
"

biological materials?


Mimicking Nature: Biomimetic (Bionic) Material Design


Where do we go from here ?


Lecture 3: Combining materials with living tissues


tissue
engineering.

BIO
-
MATERIALS


POLYMERS


METALS/ALLOYS


CERAMICS


COMPOSITES








"

Smart Materials
"

will be dealt with along with Bioactive Implants

Polymers


Long
-
chained molecule


Repeating units called
monomers


Highly versatile: gels, foams,
rubbers, cements, glass


Most biological materials are
polymers : DNA, proteins,
peptides, ALL soft tissue





What is the difference
between a synthetic polymer
and a biological polymer?


Metals, Ceramics and Glasses


Metals: Platinum, Nickel, Stainless Steel, Titanium, commonly
used



Metals can corrode in the human body? How ?



How can this be averted ?



Ceramics are oxides of metals :alumina, sappire, silica


Carbon, graphite,


Mineral phase of bone(hydroxyapatite)



What are the mechanical properties of metal vs. Ceramics?


What are the advantages of ceramic vs. Metals?




Lecture 2: Functional Biomaterials


How does the human body respond to a biomaterial ?



What materials are currently used as biomaterials?


How are these biomaterials characterised? What happens
to the biomaterial once implanted?


What kind of surface modification can improve the
biocompatibility of the biomaterial?


What changes in the bulk can improve the performance of
the biomaterial?


How does nature
"
design
"

biological materials?


Mimicking Nature: Biomimetic (Bionic) Material Design


Where do we go from here ?


Lecture 3: Combining materials with living tissues


tissue
engineering.

Characterisation of Biomaterials


Bulk: FTIR, DMA, DSC, TGA



Surface: X
-
Ray Photoelectron
spectroscopy, TOF
-
SIMS,



In
-
vitro: Simulated Body Fluid



In
-
vivo: Biocompatibility, Cytotoxicity

Lecture 2: Functional Biomaterials


How does the human body respond to a biomaterial ?



What materials are currently used as biomaterials?


How are these biomaterials characterised? What happens
to the biomaterial once implanted?


What kind of surface modification can improve the
biocompatibility of the biomaterial?


What changes in the bulk can improve the performance of
the biomaterial?


How does nature
"
design
"

biological materials?


Mimicking Nature: Biomimetic (Bionic) Material Design


Where do we go from here ?


Lecture 3: Combining materials with living tissues


tissue
engineering.

Architecture of Soft Tissue vs. Synthetic Gel


Ordered microstructure
and nanostructure



Anisotropic



Self
-
assembly of small
molecules



High Charge density



Tough




Amorphous




Isotropic



Crosslinking of long
chains



Low charge density



Fragile

Hard Tissue Architecture: Some numbers

What is the paradox here?

Hard Tissue Architecture: Nature, The
Original Nanotechnologist?


Biological Materials exhibit
many levels of heirarchical
structures from macroscopic
to microscopic length scales.


Bone has 7 orders of
heirarchy


Hard Tissue: Mineral crystals
embedded in soft organic
matrix


The protein matrix behaves
like a soft wrap around the
mineral plateltes and
HOMOGENIZES the stress
distribution within the
composite


Architecture of Hard Tissue


Staggered mineral platelets
(hydroxyapataite) embedded in a
collagen matrix



Arrangement of platelets in
preferred orientations makes
biocomposites intrinsically
anisotropic



Under an applied tensile stress,
the mineral platelets carry most
of the tensile load



Protein matrix transfers the load
between mineral crystals via
shear



Biocomposites can be describes
through tension
-
shear model
described by Ji et. al.



B. Ji, H. Gao / J. Mech. Phys. Solids 52 (2004) 1963


1990


Lecture 2: Functional Biomaterials


How does the human body respond to a biomaterial ?



What materials are currently used as biomaterials?


How are these biomaterials characterised? What happens
to the biomaterial once implanted?


What kind of surface modification can improve the
biocompatibility of the biomaterial?


What changes in the bulk can improve the performance of
the biomaterial?


How does nature
"
design
"

biological materials?


Mimicking Nature: Biomimetic (Bionic) Material
Design


Where do we go from here ?


Lecture 3: Combining materials with living tissues


tissue
engineering.

Example 1:

Biomimetic Deposition of Apatite Coating on
Surface
-
Modified NiTi Alloy


High content of Ni is of
concern with regards to
biocompatibility


TiO2 is method of choice to
modify NiTi


The heat
-
treated alloy was
immersed in SBF to allow for
biomimetic deposition of the
apatite layer on the surface
of the coating


Heat
-
treated NiTi induced a
layer of microcrystalline
carbonate containing
hydroxyapatite


How so?



Fig. 3. Surface morphologyof 800 1C heat
-
treated NiTi alloy
before and after immersion in SBF for various periods of time. (a)
before immersion,

(b) 7 days in SBF, and (c) 28 days in SBF.


Example 2: Synthesis of bone
-
like
apatite/collagen nanocomposite


Bone
-
like nanoapatite
was prepared by
addition of calcium
nitrate aqueous
solution into the
neutral collgen sol
containing ammonium
phosphate



Composite showed
features of natural
bone

Lin, X. et al. Materials Letters 58(2004) 356903572

Cartilage : Active Material?

Lecture 2: Functional Biomaterials


How does the human body respond to a biomaterial ?



What materials are currently used as biomaterials?


How are these biomaterials characterised? What happens
to the biomaterial once implanted?


What kind of surface modification can improve the
biocompatibility of the biomaterial?


What changes in the bulk can improve the performance of
the biomaterial?


How does nature
"
design
"

biological materials?


Mimicking Nature: Biomimetic (Bionic) Material Design


Where do we go from here ?


Lecture 3: Combining materials with living tissues


tissue
engineering.

Bionic Implant & Device


Implant that mimics


as far as possible



the structure AND
function of the body part it replaces.



Interacts with the human body in a bidirectional fashion



Examples of Bionic Devices: Artificial Heart, Artificial Muscle,
Cochlear Implant, Bioelectrodes, Mechanoactive Cartilage



Towards seamless integration of implant with physiological
environment



Describe the evolution of a conventional bone implant towards
a bionic bone implant,

What surface modifications would you suggest to mitigate debris
formation in existing metallic implants ?


What fundamental changes would you bring about?


What material combination would you use to replicate the
spongy interior and the tough exterior of the bone?