1. CHEG 498/598 Biomaterials Engineering
Required textbook:Integrated Biomaterials Science, Rolando Barbucci, editor, 2002
Web site: www.nd.edu/~aostafin/BIOMAT/biomat.html
Grading: A-F Assessed on Point Accumulation
Scale: 80% of total points A
65% of total points B
45% of total points C
BELOW 45% of total points D or F
Homeworks: 300 points MIDTERM 100 points Newsletter: 200 points
This course is going to be taught in a self-contained modular format. Each week is a new
topic, and the homework assigned weekly A take-home MIDTERM lets me know you have
learned the concepts. Depending on the subject and kind of activity, there may be
overlapping homework deadlines.I may ask you to physically perform a task in order to
complete a particular assignment Homeworks can be late, but lose 5 points a day until there
are no more points. Verifiable participation in the Bioengineering newsletter is mandatory
for all students. This activity replaces the FINAL exam.
2. Tentative Course Outline
Jan 14 16 Biological Materials
Jan 21 23 Polymeric Materials
Jan 28 30 Bioceramics
Feb 4 6 Metals
Feb 11 13 Composites, films, grafts, coatings, fabrics
Feb 18 20 Material/Biochemical interactions
Feb 25 27 Isolation, Characterization, Processing, Preservation
Mar 4 6 Material/Physiological Interactions
Mar 18 20 Tissues:Soft
Mar 25 27 Tissues: Hard
Apr 1 3 Tissue Engineering
Apr 8 10 Devices
Apr 15 17 Drug delivery
Apr 22 24 Biocompatibility Testing, Standards, Patents
Apr 29 no class - Finalize Newsletter
3. The BioEngineering Newsletter 4th Edition
Theme: Biomaterials
Format: Print & Web
Previous Issues: www.nd.edu/~aostafin/benl.html
Participation: Everyone
Grading: Individual, Small Team, & Class
Basis: Essays, Reports, Final Product
Penalty for Lateness: Zero Points for that Part
~100 pts for intermediate team reports
~100 pts for writing & final product
Intermediate Reports and Activities: According to Schedule
Final Publication Due: Last Day of Class
4. Editorial Staff
Layout A Artwork A
Copy Editor A
Layout B Artwork B
Copy Editor B
Assistant Editor A-B
Layout C Artwork C
Copy Editor C
Layout D Artwork D
Copy Editor D
Assistant Editor C-D
Layout E Artwork E
Copy Editor E
Layout F Artwork F
Copy Editor F
Assistant Editor E-F
Editor-in-chief
Publication Staff
1/3 Class
Writing A-B
1/3 Class
Writing C-D
1/3 Class
Writing E-F Printing Financial
Editor-in-chief
BIOENGINEERING NEWSLETTER
Assignments will be made by lottery on Jan 16.
5. Bioengineering Newsletter Staff
Position tasks
Editor-in-chief reads final copy for errors & fixes, makes sure everything is
going on schedule, handles all emergencies
Assistant Editors same as Editor-in-chief
Writing Leaders determines topical content of each of 6 sections; assigns class
members to a given section; and works with them to come up
with topics of relevance to their section; gives initial reading
of first draft of article and makes suggestions for
improvement; must write an article not of their own section,
check for *ORIGINALITY*
Artwork Staff Selects/creates thematic graphics elements for each section;
provides electronic images to L&D staff
6. Position tasks
Layout & Design Staff each person is assigned one section of the newsletter about the
same # of pages (ca. 5);has to learn Microsoft Publisher; has to
complete design layout of own section to mesh with others;can
be unique, but should have overall continuity.
Class each person must write 1 page single-spaced original article on
their section’s theme with suggestions for appropriate 1 or 2
graphics with references and provide electronic
copy,*NO*WEBSITES, *ORIGINAL WORK*
Copy-editing each person has to make their section’s articles fit the allotted
space, are technically correct,understandable,properly
referenced, original; may have to reword some text to fit; may
return to writer for major revision okay.
Financial Staff Obtains funding from student organizations /departments/
advertisers, $350 minimum, if collecting early can be used to
buy pizza, etc.
Printing/Distribution Staff Selects a print shop, arranges details, pays, delivers hardcopy to
selected distribution list; learns Microsoft Publisher, and convert
document to html, with hyperlinks for hotspots in the text, and
page advance, etc.
7. Jan 28 Feb 11 Feb 18 Mar 11
Asst. Editor
Writing
Layout
Copy Edit
Financial
Printing
All
Editor
Apr 1 Apr 15 May 1
Artwork
Meeting Deadline Calendar and Report Schedule
********Meetings must take place and reports submitted by no later than the listed date, EARLY is OK
8. Jan 28
Feb 11
Feb 18
Mar 11
Apr 1
Apr 15
May 1
Editor meets with key staff, generates semester calendar, makes assignments, appoints meeting
secretary who prepares 1-page report of meeting and key decisions for instructor
Editor meets with writing and assistant editors to decide on topic/theme/generate list of subjects
students can write about, editor appoints meeting secretary who prepares 1-page report of meeting
and key decisions for instructor, any timeline changes should be noted
Writing staff divides class into groups, and give writing assignment, rules, deadlines. Class time
will be given for this.Each writing staff provides a 1-page report to the instructor listing class
members in their group. Financial staff report to editor of their progress.
Writing staff returns read and critiqued submissions, and gives suggestion for improvements,
and new deadline. Class members return revised manuscript. Writing team also meets with
Layout and artwork team, hands off electronic manuscripts, and gives ideas for final design.
Each writing staff provides a 1-page report to the instructor listing class members who
Have fulfilled their assignment, and final list of titles.
Editor meets with key staff to check on publication progress, finances, printing plans and makes
emergency adjustments to schedule, publication design and content, appoints meeting secretary
who prepares 1-page report of meeting for instructor
Assistant editors meet with editing team and make final edits on electronic manuscript,
appoints meeting secretary who prepares 1-page report of meeting for instructor
Printing meets with copy editors and gets electronic manuscript. Printing converts electronic
manuscript to web format. Finance and Printing exchange money. Printing submits, pays for,
picks up,and distributes hard copies. Editor prepares final 3-page report on team activity, pointing out
problems, and suggested improvements, provides instructor with electronic files of print and web versions
9. Two classes of Biomaterials
1.) Biological materials 1.) of biological origin,
2.) may be used in a biological system
3.) consist of: proteins, nucleic acids,
sugars polyesters, calcium phosphates
2.) Synthetic material 1.) organic or inorganic materials
2.) used in a biological organism or
method
10. Typically complex (multicomponent) materials
Function can be altered by processing of material even though
“design” is unchanged because surface chemistry changes
Function is integrated with complex host chemical environment
-degeneration of supporting tissue, immunicity
Features of Biomaterials
11. Examples of Biological Materials
Disadvantages:
1.) not usually extraordinarily better than synthetics
2.) hard to get in high volume, purity, reproducible
3.) may have higher immunogenic response
4.) could be more expensive, storage issues
13. Non-medical applications for biomaterials:
materials for growing cells in culture
devices for biological material production & handling
tools for biomaterials characterization
biosensors
fertility regulators for cattle, oysters
20. There are 20 common
amino acids
Hydrophobic
Hydrophilic
Special
H2
H2
-H
NH2
21. Figure 1. A Venn diagram showing the relationship of the 20 naturally occurring amino
acids to a selection of physio-chemical properties thought to be important in the
determination of protein structure [2].
22. Alanine A, Ala 71.079 CH3- 7.49
Arginine R, Arg 156.188 HN=C(NH2)-NH-(CH2)3- 5.22
Asparagin N, Asn 114.104 H2N-CO-CH2- 4.53
Aspartic acid D, Asp 115.089 HOOC-CH2- 5.22
Cysteine C, Cys 103.145 HS-CH2- 1.82
Glutamine Q, Gln 128.131 H2N-CO-(CH2)2- 4.11
Glutamic acid E, Glu 129.116 HOOC-(CH2)2- 6.26
Glycine G, Gly 57.052 H- 7.10
Histidine H, His 137.141 N=CH-NH-CH=C-CH2- |__________| 2.23
Isoleucine I, Ile 113.160 CH3-CH2-CH(CH3)- 5.45
Leucine L, Leu 113.160 (CH3)2-CH-CH2- 9.06
Lysine K, Lys 128.17 H2N-(CH2)4- 5.82
Methionine M, Met 131.199 CH3-S-(CH2)2- 2.27
Phenylalanine F, Phe 147.177 Phenyl-CH2- 3.91
Proline P, Pro 97.117 -N-(CH2)3-CH- |_________| 5.12
Serine S, Ser 87.078 HO-CH2- 7.34
Threonine T, Thr 101.105 CH3-CH(OH)- 5.96
Tryptophan W, Trp 186.213 Phenyl-NH-CH=C-CH2-
|___________|
1.32
Tyrosine Y, Tyr 163.176 4-OH-Phenyl-CH2- 3.25
Valine V, Val 99.133 CH3-CH(CH2)- 6.48
Name abbrev. MW R-group pKa
23. Polypeptide’s sequence defines its hierarchical structure in 4
dimensions (6 if you include macrostructure & time).
2-D array
of a-actinin
24. SEA = Solvent Exposed Area
Amino acid SEA > 30 Å2 SEA < 10 Å2 30 > SEA > 10 Å2
S 0.70 0.20 0.10
T 0.71 0.16 0.13
A 0.48 0.35 0.17
G 0.51 0.36 0.13
P 0.78 0.13 0.09
C 0.32 0.54 0.14
D 0.81 0.09 0.10
E 0.93 0.04 0.03
Q 0.81 0.10 0.09
N 0.82 0.10 0.08
L 0.41 0.49 0.10
I 0.39 0.47 0.14
V 0.40 0.50 0.10
M 0.44 0.20 0.36
F 0.42 0.42 0.16
Y 0.67 0.20 0.13
W 0.49 0.44 0.07
K 0.93 0.02 0.05
R 0.84 0.05 0.11
H 0.66 0.19 0.15
The numbers indicate the probability that a particular
residue will be positioned in real proteins so that its
solvent exposed area meets the particular criterion in the
column’s title.
25. Post-translational changes either inside a cell or outside the
cell are important in determining final material properties.
1.) Even in the body proteins are not synthesized in their final form
2.) There are many possible structures.
(# bond angles allowed)#residues or 8n possible peptide conformations
3.) Many proteins need CHAPERONES to assist their folding
molecular chaperones – protect some regions transiently
chaperonins – actively fold
5.) Some protein sequences contain INTEINS which self-excise to allow
correct folding.
A diagram showing the bond angles, bond
lengths and general geometry of a peptide bond.
Bond angles are given in degrees.
26. Molecular
Chaperone
Hsp70 is a common
molecular chaperone
that binds to the protein
as it is made. Release is
ATP dependent
Chaperonins
TCiP, is made of a
circular array of Hsp60
units, and is a
chaperonin. Its inside
attracts the misfolded
protein, other spot
attracts ATP, which
cause the barrel
structure to change and
pull the misfolded
protein into shape
27. Types of Post-translational Chemical Modification
Acetylation (80% of all protein’s N-terminus is acetylated)
Glycosylation
Phosphorylation (ATP dependent)
Hydroxylation
Methylation
Carboxylation
Can occur in or outside the cell,
i.e. can be engineered
30. Post-translational Digestion:
1.) Can be Extracellular and Intracellular
2.) Extracellular digestion involves proteases
Endoprotease
- cleave protein backbone next to basic and aromatic residues.
-chymotrypsin, trypsin
Exopeptidase
-remove amino acids sequentially from the end of the chain
-aminopeptidase removes from amino end
-carboxy peptidase removes from carboxy-end
Peptidases
-split oligopeptides into di- and tri-peptides and single units
3.) Used to correct folding mistakes
- can occur in lysosomes (acidic lipid sacks) or the cytosol
4.) In the body mis-folds and degradation fragment accumulation
lead to disease like Alzheimers
31. Functional Design of Proteins
1.) The structure of proteins is designed for function
2.) The role of proteins in the body can inspire their use as a biomaterial
Nuclear pore
Topoisomerase
Chaperonin
Reverse
transcriptase
133 nm
70 nm
Lets genetic material
enter/leave nucleus
RNA
Copies viral RNA into
DNA, found only in RNA
viruses
GroEL/ES is a circle
of 21 subunits that
helps fold proteins
3.3 nm
Prevents DNA from
overtwisting during
replication
32. Protein structure can be grouped by function
Proteins bind molecules (ligands or substrates) with high affinity
(strength, Keq, Kd) and high specificity (discrimination).
-antibodies (part of immunoglobulin family)
-enzymes
35. Biomaterial created by PT modification: Collagen
One of the three component of the ECM (extracellular matrix)
Proteoglycans (cushion)
Collagen (strengthen)
Multiadhesive matrix proteins(controll cell interactions)
16 types (80% are type I, II,& III)
Forms a triple helix 3 peptides
Comprised of general sequence: (Gly-X-Y-)n where X,Y
are other amino acids but most frequently X= proline, and Y= hydroxyproline
Electroneutral- equal number of positive and negative amino acids
Hydrophobic regions help stabilize chains
Type I collagen found in bone, skin, ligament, tendons of many species
75% dry weight collagen 20% dry weight proteoglycans and polysaccharides
<5% glycoproteins and elastin
36. Single chain left handed helix
Triple stranded helix
a1 1056 AA
a2 1029 AA
Tropocollagen
(280 kDa)
Collagen fibril
Many linked into fibers
Fiber diameters:
50 nm to 300 nm
Structure of Type I Collagen
Rise per residue: 0.286 nm; unit twist 108o, 10 residues in 3 turns, helical pitch 8.68 nm
95% Gly-X-Y, except at N and C termini where 9-26 residues form telopeptides
37. Reasons for Collagen Stability
1.) Amino acids fit very tightly
between strands
2.) Hydrogen bonding between
carboxylic and amine backbone
groups
3.) Embedded water increases
hydrogen bonding
4.) Telopeptides make strong
intermolecular crosslinks through
allysine (hydroxylysine converted
to aldehyde) is crosslinked with
hydroxyllysine of other strand
peptidases (pepsin) used to remove
telopeptides to get atelocollagen
SEM
rabbit bone
TEM
tendon
TEM
skin
38. Collagen Material Properties
1.) Material properties of collagen when it is outside
the body differ from those inside
2.) 3-D arrangment is tailored for function
3.) Fibers are arranged in different directions
depending on the kind of tissue
tendon & ligament = paralell for highest tensile
strength
skin = random greatest resiliency to stress
Cartilage = mixed with proteoglycan gel to
form material with low friction coefficient
< 0.01
4.) Glass transition temperature at 40oC, melting at
56oC
5.)Stress- strain curves exhibit non-linear behavior
Alignment of fibers
Breaking of fibers
Stretching of fibers
Alignment of fibers
Lamella
align and stretch
Weak stress gives high strain
Weak stress gives low strain
39. Overview of materials concepts that are important
Stress: normalized load (force/area)
Strain: normalized deformation (extension/original length)
s Tensile stress: (force/area perpendicular to force)
e Tensile strain: (extension/original length parallel to the extension)
t Shear stress: (force/area parallell to force)
s Shear strain: (extension/ original length perpendicular to extension)
Extension is proportional to load according to Hooke’s law.
40. s=E e E = Young’s modulus or elastic stress
t=G g G = Shear modulus or elastic shear
E&G can be related to microstructure and bonding, elastic strain increases when bonds are
stretched. A material can have high or low resistance to interatomic stretch
Elastic materials
Ductile materials
Using Hooke’s Law these properties can be related
Typical stress/strain curves
44. Physiochemical Properties of collagen
Electrostatic
~240 charged AA under physiological conditions
can be changed by changing the pH above 10 or below 4
fibers swell
can be prevented by chemically crosslinking the electrostatic attachments
Electrostatic properties can be adjusted by acetylating lysines and hydroxylysines,and
methylating negative residues
Ion binding
~60 free carboxylic groups are present in native collagen at physiological conditions
can bind metal cations if hydrogen bonding is prevented by pH or by lyotropic agents or by
reacting all positive or negative charges (removing electroneutrality)
Fiber forming
By digesting native collagen, and then subjecting it to one or more treatments above, fibers
can be reformed by dehydrating in high salt or in non-aqueous solvents
45. Biological Properties of collagen
Hemostatic
Attracts platelets
Cell interaction
Interacts with surface adhesion proteins on cells
Immunogenic
Very low level response by immune system
46. Biotechnology of collagen
1.) Isolation & Purification
molecular
pepsinize to remove telopeptides and solubilize collagen fibers
repetitive precipitation with high salt
solubilize in buffer at physiological pH
fibrillar
remove non-collagen materials from tissue with salt extraction
remove lipids with extraction with ether or alcohol
remove acidic proteins and glycosamines with acid extractions
remove basic proteins and weaken fibrils by base extractions
enzymes can be used to remove specific protein components
2.) Matrix fabrication
approach depends on application
47.
48. Cellulose is part of the Cell Wall of Plants.
Glucan chain
Cellobios
Microfibril
First recognized by Anselm Payen in
1838.
It occurs in almost pure form in
cotton fiber and in combination with
other materials, such as lignin and
hemicelluloses, in wood, plant
leaves and stalks, etc.
Although generally considered a
plant material, cellulose is also
produced by some bacteria.
Glucose units are joined by single
oxygen atoms (acetal linkages)
between the C-1 of one pyranose
ring and the C-4 of the next ring.
Since a molecule of water is lost
when an alcohol and a hemiacetal
react to form an acetal, the glucose
units in the cellulose polymer are
referred to as anhydroglucose units.
49. Chemistry of Cellulose.
3 hydroxyls groups on each anhydroglucose ring
Derivatives are usually characterized in terms of a
“degree of substitution” (DS), which is an average for
the whole chain and can range between 0 and 3.
In most cases, partial reaction to DS < 3 gives
products that are essentially block copolymers, where
virtually all of the hydroxyls occurring in the less
ordered regions may be derivatized, while those in the
crystalline regions remain unreacted. Higher degrees of
substitution, or reaction conditions which disrupt the
crystalline regions, can be used to reduce inter-chain
hydrogen bonding and force the chains apart. This can
result in a cellulose derivative that is soluble in
common solvents, and thus capable of extrusion to
form filaments, or other structures.
Esterification
Etherification
Acetal Formation
Hydrolysis
Oxidative Degradation
Non-flaming combustion (or glowing combustion)
Thermal Degradation
When the hydroxyl group at C-1 is on the opposite side of
the ring as the C-6 carbon, it’s the b configuration.
This b configuration, with all functional groups in equatorial
positions, causes the molecular chain of cellulose to extend
in a more-or-less straight line, making it a good fiber-
forming polymer. Amylase is in the a configuration and
tends to form coiled fibers.
Reactions of Cellulosecan occur at:
1.) the reducing end with a free hemi-acetal (or
aldehyde) group at C-1,
2.) the non-reducing end with a free hydroxyl at C-4,
3.) the internal rings joined at C-1 and C-4.
4.) 3 dominates but experiences steric hindrance
50. 1.) Chitin is a linear chain of N-acetyl glucosamine, (acetyl group, -COCH3). Chitin is a
major component of the cell walls of many fungi and of the exoskeletons of invertebrates
such as crabs, lobsters and insects.
2.) Chitosan is obtained by removing enough acetyl groups for the molecule to be soluble
in most diluted acids. Chitosan, the major component of the cells walls of the fungal
phylum Zygomycota. Chitosans are characterised by two principal factors :viscosity and
degree of deacetylation.
3.) Deacetylation, exposes amine groups (NH) and gives the chitosan a cationic
characteristic. This is especially interesting in an acid environment where the majority of
polysaccharides are usually neutral or negatively charged. Why?
Chitin Chitosan
Chemistry of Chitin.
51. Chemistry of Silk Fibroin.
Crystalline protein formed as a non-Newtonian
liquid at 25% w/v. Easily handled and stored at
room temperature.
When a critical shear stress is applied molecules
undergo partial denaturation, generating the dense
form found in silk fiber.
Spider dragline contains domains of b-sheet and
random coil, when the completed dragline is
stretched, some of the remaining random coil
converts transiently into a-helix.Silkworm fiber is
almost all rigid and inextensible b-sheet
The protein has alternating alanine and glycine
residues in the primary structure.Small, non-polar
side chains allow the sheets to pack very close
together, stabilized by the hydrophobic effect.
