Introduction to Biomaterials

Prof. Wendy Liu

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  1    
 What are biomaterials?

•  “A nonviable material used in a medical device, intended

to interact with biological systems” – European Society
for Biomaterials, 1986

•  “Any substance, synthetic or natural in origin which

treats, augments, or replaces any tissue, organ or
function of the body” – Greco, 1994

•  “A material intended to interface with biological systems

to evaluate, treat, augment, or replace any tissue, organ
or function of the body” – Williams, 1999

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  2    
 FDA definition of a biomaterial
“... an instrument, apparatus, implement, machine, contrivance,
implant, in vitro reagent, or other similar or related article, including a
component part, or accessory which is recognized in the official
National Formulary or the United States Pharmacopoeia, or any
supplement to them, intended for use in the diagnosis of disease or
other conditions, or in the cure, mitigation, treatment, or prevention of
disease, in man or other animals, or intended to affect the structure or
any function of the body of man or other animals, and which does not
achieve any of it’s primary intended purposes through chemical action
within or on the body of man or other animals and which is not
dependent upon being metabolized for the achievement of any of its
primary intended purposes.”

note:  FDA  does  not  approve  biomaterials,    

they  approve  devices  containing  biomaterials  
 
BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  3    
 Examples of biomaterials

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  4    
 Historical Biomaterials
•  Pre World War II
–  Wooden prosthetics (~1000 BC)
–  Gold and iron dental implants (200 AD)
–  Linen or animal tendon sutures

Huebsch  and  Mooney,  Nature  2009  

•  Post World War II

–  Materials originally developed for military tested as biomaterials
–  Shards of airplane canopies (Plexiglass) embedded in eyes of
pilots did not show rejection

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  5    
 Intraocular Lens
•  Replace lens in
patients with cataracts
•  Originally made of
polymethyl
methacrylate

cornea  

lens  
•  Evolved to become
made of silicone or
opJc  nerve   acrylic, which are soft
iris  
and foldable and can
be inserted with a
smaller incision

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  6    
 Sutures
Poly(lacJc-­‐co-­‐glycolic)  acid  

•  Absorbable sutures degrade or get absorbed into the

body over time

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  7    
 Total hip replacement

•  Combination of metal, ceramic and polymer, to provide

adequate mechanical strength and wear properties
•  Integration with bone is important.

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  8    
 Vascular stent
Abbot  Vascular’s  Self-­‐Expanding  Stent    

•  Stents need to withstand forces

present in arteries
•  Vascular devices interact with
cells of the vessel and blood
Image  from  www.nhlbi.nih.gov  

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  9    
 Pyramid of Materials Science & Engineering

Performance/Applica/on  

Structure  

Synthesis  &  Processing   Physical  &  Chemical  

Proper/es  

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  10    
 Class Syllabus

•  Bulk Materials - metals, ceramics, polymers

–  Chemical properties
–  Physical properties
–  Mechanical properties
–  Degradation characteristics
•  Surface Phenomena
–  Protein-biomaterial interactions
–  Cell-biomaterial interactions
•  Applications of biomaterials
•  Detailed syllabus available on the class website

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  11    
 Class Schedule
•  Lectures: Tue/Thu 11 – 12:20 pm in RH101
–  April 16 and 21 are “flipped”
•  Discussion Sections:
–  Mondays 11am, 12pm or 1pm in ET204 – just 2 of these?
–  Opportunity to review lecture material, go over practice problems
•  Office Hours:
–  Liu: Mondays 2-4pm, EH2406
–  Andrew: Wednesdays 4-5 pm, NSII3212
–  Xiaolong: Time TBA, NSII3212 Andrew  

•  Quizzes/Exams: Xiaolong  
–  April 21: Quiz 1 on lectures 1-6
–  May 14: Quiz 2 on lectures 7-12
–  June 9: Final Exam is cumulative
BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  12    
 Text Book

•  Readings from text book outlined in syllabus.

•  Additional readings may be assigned.
•  Material covered in lecture is most important, text book is a reference.

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  13    
 Other recommended texts
An excellent introduction to materials science: The biomaterials “Bible”:

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  14    
 Grading

1  problem  graded  each  assignment.    

Homeworks 12% May  work  together,  but  each  hand  
in  1  HW  
Quiz 1 24%

Quiz 2 24%

Final 40%

Total 100%

Stay  tuned  for  extra  credit  assignments  

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  15    
 BREAK

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  16    
 Classes of materials

•  Inorganic vs. organic

Ceramic   Metal   Polymer  

•  Synthetic vs. Natural

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  17    
 Chemical Bonding

•  Chemical bonds form by the interactions between the

valence electrons, or electrons in the outermost shell
–  Atoms want to fill their outermost shell of electrons
–  Primary bonds – ionic, metallic, covalent – involve sharing or
transfer of electrons
–  Secondary bonds – involve attraction between atoms, no
sharing/transfer of electrons

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  18    
 Electronegativity
•    Columns:    Similar  Valence  Structure  

inert  gases  
give  up  1e-­‐  
give  up  2e-­‐  

accept  2e-­‐  
accept  1e-­‐  
•  F  is  highly  
electronegaJve,  
give  up  3e-­‐  

value  is  4.0  

•  Na  is  electroposiJve,  
H   He   value  is  0.9  
Li   Be   O   F   Ne  
Na   Mg   S   Cl   Ar  
K   Ca   Sc   Se   Br   Kr  
Rb   Sr   Y   Te   I   Xe  
Cs   Ba   Po   At   Rn  
Fr   Ra  

ElectroposiJve  elements:   ElectronegaJve  elements:   Adapted  from  

Fig.  2.6,  
Readily  give  up  electrons   Readily  acquire  electrons   Callister  &  
to  become  +  ions. to  become  -­‐  ions. Rethwisch  8e.  

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  19    
 Ionic Bonding
•  Occur by transfer of electrons
e- Na+ Cl- between two atoms of
Na Cl disparate electronegativities
electrostatic interaction (difference is greater than 2.0)

•  Charge is distributed in three-

dimensions surrounding the
atoms, each anion is
surrounded by as many
cations as possible and vice
versa, to reduce the anion-
anion or cation-cation
repulsion.
•  Bonds are non-directional
•  Usually crystalline but
sometimes amorphous
structures result
BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  20    
Ceramic materials are characterized by ionic
bonds
–  Because atoms cannot move in response to forces, materials
are hard but brittle, and are resistant to degradation
–  Electrons are held in place, so materials are bad conductors
–  High bond energies result in high melting temperatures

Ceramic   Applica/on  
Alumina  (Al2O3),  zirconia   Total  joint  replacements,  
(ZrO2)     dental  implants,  implant  
coaJngs  
 
Calcium  phosphate  (CaPO4)   Tissue  regeneraJon  scaffolds,  
cements,  drug  delivery  
 

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  21    
 Covalent Bonding
•  Covalent bonding results from sharing of electrons between two
atoms of similar (and high) electronegativities, the difference is less
than 1.6
•  Side note – if the difference is between 1.6 and 2.0 and a metal is
involved, then it is considered ionic; if only nonmetals are involved,
bond is covalent
•  Directionality is determined by geometry of subshells

H
H C H
H
C  has  electron  configuraJon  1s22s22p2  

BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  22    
 Polymers are characterized by covalent
bonds
–  Bonds are strong, but ability to rotate atoms around single bonds
generates flexibility, materials are easily deformed
–  Ways to prevent movement, for example crosslinking, so a wide
range of properties are possible
–  Electrons held in place, so not good conductors

Polymer   Applica/on  
Polyethylene   Total  joint  replacements  
 
Polytetrafluorethylene   Vascular  grais  
(teflon)    
Polydimethyl  siloxane   Contact  lens,  breast  implants  
(silicone)  
Poly(lacJc  co-­‐glycolic)  acid   Resorbable  sutures,  stents  
(PLGA)  
Collagen   Tissue  engineered  scaffolds,  cosmeJc  agents  
BME111  Design  of  Biomaterials  Spring  2015                    March  31    Lecture  1    Slide  23