Download Biomaterials Based on Polymers, Fibers, and Textiles

Welcome Biomaterials
Based on Polymers, Fibers,
and Textiles !
TXMI 8000
Professor Leonid Ionov
College of Engineering, College of Family & Consumer
Sciences, The University of Georgia
Office: 303 Dawson Hall, 305 Sanford Dr, Athens, GA 30602
Lab: Riverbend Research North, Room 107
110 Riverbend Rd. Athens, GA 30602
Phone: 706-542-4885
E-mail: [email protected]
Web: www.ionov-lab.com
Office Hours: By appointment via email
My group
Administrative details
• Course Text: Biomaterials Science, An Introduction to Materials in
Medicine: Authors: Ratner & Hoffman & Schoen & Lemons, 2012,
3rd Edition, ISBN: 9780123746269.
•
26 lectures + 3 midterm tests + 1 day for consultation for
preparation to exam
•
Grading: 25% midterm tests, 25% homework, 50% final exam
•
Homework: Generally assigned on Thursday and be due on the
following Tuesday.
•
Midterm tests: 3 tests
•
Final test: May
•
Lecture notes, problem sets (and answers), supplementary material
will be posted on eLearning Commons.
Introduction
The goal is to improve the quality of life
Ancient history of implants and biomaterials.
• 3500 - 1800 BC warrior Vishpla, (Rig Veda, Sanskrit) with iron
leg
• 600 BC Sushruta, a renowned Indian physician,- nose
reconstruction using a rotated skin flap
• 600 BC Sutures made of vegetable fibers, leather, tendons,
• Egypt 4000 years ago - linen sutures
• 600 AD – dental implants
Modern history of implants and biomaterials.
Examples
hip replacement
knee replacement
drug release
Examples
Increasing Need For Tissue and Organ Replacement
13.000
12.000
And:
Waitinglist Organ-Transplantation
USA 1990: 20.481 Patients
06/2006: 92.265 Patients
11.000
10.000
9.000
Waitinglist
Kidney-Tx
Germany
UNOS, June 07 2006
8.000
7.000
Kidney - Transplantation in Germany
Need ca. 3.500 / Year
 2516 in 2003
 2478 in 2004
6.000
5.000
4.000
3.000
2.000
1.000
0
1979
'81
'83
'85
'87
'89
'91
Year
'93
'95
'97
'99
2001 03
DSO 2006
1970-4
Increasing Need For Tissue and Organ Replacement
MEDICAL DEVICE EXAMPLES
Sutures (temporary or bioresorbable)
Catheters (fluid transport tubes)
Blood Bags
Contact Lenses
Intraocular Lenses
Coronary Stents
Knee and Hip Prostheses
Breast Prostheses (cancer or cosmetic)
Dental Implants
Renal Dialyzers (patients)
Oxygenators/CPB’s (cardiopulmonary bypass system facilitates open heart
ANNUAL # (U.S.)*
250 M**
200 M
40 M
30 M
2.5 M
1.2 M***
0.5 M
0.25 M
0.9 M
0.3 M
0.3 M
Vascular Grafts
Pacemakers (pulse generators)
0.3 M
0.4 M
surgery)
Bio…materials
Biomaterials do not necessarily have to be natural materials as the name may suggest.
Biomaterials are defined by their application, NOT chemical make-up
Biomaterials cover all classes of materials – metals, ceramics, polymers
In 1974, at the 6th Annual International Biomaterials Symposium held at Clemson University,
a biomaterial was defined as
… a systemically, pharmacologically inert substance designed for implantation within
or incorporation with a living system.
In 1986, at a consensus conference of the European Society for Biomaterials, a biomaterial
was defined as
… a nonviable material used in a medical device, intended to interact with biological
Systems
definition was provided by Williams
… material intended to interface with biological systems to evaluate, treat, augment,
or replace any tissue, organ, or function of the body
Bio…materials
What governs materials choice?
Subject
One needs to know
how body works (chemistry, physics, biology)
internal and surface structure of implants (material science)
interaction between body and implant = f (body, implant)
- mass exchange (transport),
- changes in body (immune response),
- changes in implant (degradation)
Subject
• Structure of body, tissues, cells and molecules (overview)
• Biomaterials (metals, ceramics, solid polymers, hydrogels, composites,
different scale) – chemical and physical properties, structure,
• Methods of bulk characterization
• Interactions between biomaterials and body (changes in biomaterials,
controlled release, active interfaces)
• Methods of surface characterization and modification
• Applications (drug delivery, implants, scaffolds)
Cells
• self-organization
• regeneration
• adaptation
Scales
Structural Hierarchies
8 Order of magnitude
Length scales of structure
1. Primary Chemical Structure
(Atomic & Molecular: 0.1–1 nm)
Length scale of bonding – strongly dictates
biomaterial performance
Primary
Ionic: e-donor, e-acceptor ceramics, glasses (inorganic)
Covalent: e-sharing glasses, polymers
Metallic: e-“gas” around lattice of + nuclei
Secondary/Intermolecular
Electrostatic
H-bonding
Van der Waals (dipole-dipole, dipole-induced dipole, London dispersion)
Hydrophobic Interactions (entropy-driven clustering of nonpolar gps in H2O)
Physical Entanglement (high MW polymers)
Covalent bonds
Covalent bonds : non - polar and polar ( - > dipoles )
■ covalent bonds ,
formed by electron pairs ,
fixed orientation ,
Relatively high dissociation energy ( 210-840 kJ / mol )
■ polar bonds ,
different electronegativity of the atoms ,
binding electrons unequally distributed ,
one end of a polar bond has a partial positive charge and the other end is a
partial negative charge
Non covalent bonds
■ Four main types of non-covalent interactions in biological systems :
ionic bonds ,
Hydrogen bonds ,
van -der- Waals interactions ,
hydrophobic interactions.
■ non- covalent interactions between the atoms are much weaker than covalent
bonds with bond energy in the range of about 4 - 20 kJ / mol
Ionic bonds
Kation+ … Anion-
Kations :
Anions :
H+, Na+, K+, Mg2+, Ca2+
Cl-, OH-
ionic bonds = electrostatic attractions
between the positive and negative charges
of the ions.
In aqueous solutions, all cations and anions
are surrounded by a shell of water
molecules bound .
Increasing the salt (eg NaCl ) concentration
weakens the ionic bonds . Binding energy
about 787 kJ / mol ( NaCl )
Metallic bonds
Common conduction electrons
Metal atoms are good donors of electrons and metallic bonds
are characterized by tightly packed positive ions or cores
surrounded by electrons
Hydrogen bonds
• Hydrogen bonds are longer and weaker than covalent bonds between the same atoms .
• The hydrogen bond between water molecules ( about 20-40 kJ / mol ) is much weaker
than a covalent bond OH ( approximately 460 kJ / mol ) .
•
The solubility of the neutral substances in an aqueous environment depends on their
ability to form hydrogen bonds with water .
Van der Waals interactions
Nonspecific interactions lead to instantaneous random variations in the distribution of
the electrons of an atom = unequal distribution of electrons .
Van der Waals interactions are based on interactions of temporary or permanent
electrical dipoles .
0.5-5 kJ / mol
Hydrophobic interactions
„Like dissolves like “
hydrophobic substances
• In an aqueous environment , the association of polar or non - polar molecules is brought
about by the hydrophobic effect state.
• The contact of hydrophobic molecules with water molecules to be reduced .
Binding energy
1x100 kJ
1x101 kJ
1x102 kJ
1x103 kJ
Examples
used for hard tissue replacement
e.g., dental implants
Ex. 1: alumina Al2O3
– (corundum)
Properties:
• corrosion resistant
• high strength derived from
• wear resistant ionic bonding
• “biocompatible”
derived from
ionic bonding
Examples
Ex. 2: polyethylene oxide (PEO)
(CH2CH2O)n
Properties:
• flexible
• hydrolysable
• water soluble
• bioinert
used for protein resistant coatings, hydrogels
Derived from primary &
secondary bonding
2. Higher Order Structure (1 – 100 nm)
Crystals: 3D periodic arrays of atoms or molecules
metals, ceramics,
polymers (semicrystalline)
crystallinity decreases solubility and
bioerosion
(biogradable polymers & bioresorbable
ceramics)
Networks
exhibit short range order & characteristic lengths
Ex. 1: Bioactive Glasses
used for hard connective tissue replacement
Network formers (~50wt%): SiO2, P2O5
Network modifiers (high! ~50wt%): Na2O, CaO
Properties:
• partially soluble in vivo (facilitates bone
bonding)
• easily processed (complex shapes)
inorganic glasses, gels
Networks
Ex. 2: Hydrogels
used for contact lenses, drug delivery
matrices, synthetic tissues
x-linked, swollen polymer network
Properties:
• shape-retaining
• flexible
• slow release of entrapped molecules
derived from crosslinked network
Self-Assemblies
aggregates of amphiphilic molecules micelles, lyotropic liquid crystals, block copolymers
Ex.: Cationic Liposomes used for gene therapy
Properties:
• water dispersible
• can contain/release DNA
• can penetrate cell membrane (-)
derived from supramolecular assembly
Molecular complementarity
Geometry , shape + non-covalent bonds
3. Microstructure (1μm + )
Crystal “grains”: crystallites of varying
orientation
Ex: Stainless steels Fe-Ni-Cr
Spherulites: radially oriented crystallites
interspersed w/ amorphous phase
semicrystalline polymers, glass-ceramics
used for fracture
fixation plates,etc., &
angioplasty stents
Porosity
often desirable in biomaterials applications
Ex. 1: Porous Bioresorbable Scaffolds
polylactide (PLA)
Properties:
• Penetrable to body fluids, cells
• Structurally stable
Pore dimensions: 10100 μm derived from
pore microstructure
used for tissue
regeneration