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153 Cards in this Set
- Front
- Back
What are 6 requirements of natural biomaterials? |
1. Non-toxic 2. Non-inflammatory 3. Non-allergenic 4. Good mechanical properties 5. Induces cell attachment and differentiation (if needed) 6. Low cost |
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What is the most abundant protein in the human body? |
Collagen at 30% of the total proteins in the body |
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What is collagen used for in the body? |
Used for maintenance of structural integrity |
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What can collagen do at a certain temperature? Why? |
At the shrinkage temperature, collagen can shrink to less than 33% of its original length due to the collapse of the triple helical structure. |
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Collagen is referred to as what? |
Fibrous protein |
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TRUE OR FALSE: Collagen is found in animals and plants. |
FALSE. Collagen is found exclusively in animals. |
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Collagen is the primary protein of what 4 tissues? |
1. Skin 2. Bone 3. Tendon 4. Ligaments |
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Collagen possesses what 3 desirable properties? |
1. Can be resorbed into the body 2. Non-toxic 3. Minimal immune response, even between different species |
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Collagen exists in what 5 forms? |
1. Gel form (like in the ECM and eye) 2. Tight bundles of tendons 3. Stacked in the cornea 4. Fibers in the bones 5. Loose fibril network in the skin |
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Collagen form is dictated by what? |
Their structural role in a particular organ |
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Collagen fibrils are produced by what? |
Fibroblasts in which collagen is synthesized in the ER. |
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What is the basic unit of collagen? |
Topocollagen which is made up of amino acids |
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In order from smallest to largest, list the four steps of the hierarchy of collagen structures |
Amino acids --> Tropocollagen --> Fibrils --> Fibers |
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In the ER, procollagen is known as what? |
pre-procollagen |
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What is the first event that takes place in post-translational modification of collagen? |
Alpha peptide chains of glycine + Proline + hydroxyproline are formed |
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What is the second event that takes place in post-translational modification of collagen? |
Hydroxylation and glycolysation takes place on the peptide chains:
Hydroxylation of proline and lysine Glycolysation of hydroxyproline |
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What is the third event that takes place in post-translational modification of collagen? |
Alpha chains are twisted around the central axis to form a triple-stranded left-handed helix |
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Of the three alpha chains in each collagen molecule, two of the chains have how many amino acid residues? What are they called? |
1056 residues and are called alpha1-chains |
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Of the three alpha chains in each collagen molecule, one chain has how many amino acid residues? What is it called? |
1029 residues and is called alpha2-chain |
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Together, the triple helix of collagen is called what? |
A gamma-structure |
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What is found in the interior of the helical structure of collagen? What are found on the outside? |
Glycine is found in the interior Proline and hydroxyproline are pointed outward |
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What 4 things further stabilize the triple helix structure of collagen? |
1. tight fit of amino acids in helix 2. Inter-H bonding between carbonyl O atom of proline (X residues) and adjacent amide H atom of glycine 3. Inter-H bonding between hydroxyl group of hydroxyproline and amide H atom of glycine 4. H20 presence to form inter-chain H bonding |
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What is the difference between the polypeptide chains within the collagen molecule? |
The positions of the X and Y amino acids in the triple helix |
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Once procollagen is packaged into transport vesicles, where does it go and why? |
It goes to the Golgi apparatus where oligosaccharides are added and secreted into the ECM |
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How is tropocollagen formed? |
The trimeric globular C-propeptide and trimeric N-propeptide domains are cleave forming tropocollagen. |
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What is the typical length and diameter of tropocollagen? |
300 nm long and 1.5 nm in diameter |
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Tropocollagen self-assembles into what how? |
Self-assembles into fibrils by oxidative deamination of lysine and hydroxylysine using lysyl oxidase which forms aldol cross-linking |
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Which types of collagen are fibril-forming? |
Types I, II, and III |
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Which types of collagen are network-forming? |
Types IV and VII |
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Which types of collagen are fibril-associated? |
Types IX and XII |
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Depending on age and tissue, the diameter of Type I collagen is within what range? |
50 to 500 nm |
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Where is Type I collagen found? |
Skin, dentin, cornea, blood vessels, bone, tendon, ligament, and fibrocartilage |
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Which type of collagen is the most abundant collagen and the most predominant form used in biomedical applications? |
Type I |
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TRUE OR FALSE: Telopeptides do not possess the triple-helical structure nor made up of repeating glycine-X-Y structures. |
TRUE |
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Where is Type II collagen found? |
Articular cartilaginous tissues and inter-vertebral disks |
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Type II collagen forms what structure? |
Dense network arrays of individual thin fibrils with an interfibrillar matrix made of proteoglycans, glycoproteins, non-collagenous proteins, and water.
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Type II collagen acts as what? |
Shock absorbers |
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What does Type III collagen consist of? |
3 identical polypeptide alpha1 chains |
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The elastic properties of type III collagen may be due to what? |
Disulfide bonds |
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Where is Type III collagen found? |
Distensible tissues, fetal skin, blood vessels |
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What is the second most abundant collagen found in humans? |
Type III |
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Where is Type IV collagen found? |
In the basement membranes of the eye lens, walls of blood vessels, kidneys, and skin (beneath stratified squamous epithelia) |
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Type IV collagen interacts with non-collagenous components to form what? What does this allow? |
Form meshes or networks allowing a filtration system for cells, molecules, and light. |
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Type IV collagen consists of what? |
Polypeptide chains of dissimilar size |
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What are the 2 disadvantages of using collagen? |
1. Unpredictable degradation rate 2. No adequate mechanical properties |
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What are 4 biomedical uses of collagen? |
1. Artificial skin 2. Guided tissue regeneration membranes 3. Tube allographs for peripheral nerve regeneration 4. Carriers for BMP-2 in INFUSE |
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What is Elastin? |
It is an insoluble, fibrous protein composed of fibrillin and soluble tropoelastin monomers containing about 786 amino acids. |
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Elastin is found in organs requiring what 3 properties? |
1. Elasticity 2. Flexibility 3. Strength |
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Elastin has resistance to what 3 things? |
1. Acid 2. Alkalis 3. Most proteolytic enzymes (except elastase) |
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In Elastin, the elasticity of fibers is dependent on what? |
The entropy of the relaxation of elastin |
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Where is Elastin found? |
Lungs, blood vessels, elastic ligaments and in small amounts in the ear and skin |
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The presence of elastin allows organs to do what? |
Retain their shape after stretching or contracting |
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Flexibility allows the organs to do what 3 things? |
1. Undergo repetitive strain and deformation without rupture 2. To store energy involved in deformation 3. to recover to their original state when stress is removed |
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Tropoelastin is produced by what 4 things? |
1. Endothelial cells 2. Smooth muscle cells 3. Fibroblasts 4. Chondrocytes |
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Is tropoelastin soluble or insoluble? |
Soluble |
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Tropoelastin is rich in what 5 amino acids? |
Glycine, proline, lysine, valine, and alanine |
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Is the tropoelastin amino acid sequence structured or unstructured? |
Unstructured |
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Catalyzed by lysyl oxidases, elastin is stabilized how? |
By inter-chain cross-linking the side chains of lysine residues |
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In tropoelastin, oxidative deamination converts the amine groups of lysine into what? |
Reactive aldehydes or allysine residues by lysyl oxidase |
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In tropoelastin, what form a desmosine cross-link? |
3 allysyl side chains and 1 unaltered lysyl side chain |
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Tropoelastin becomes highly what as a result of cross-linking? |
INSOLUBLE |
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What aspect of elastin allows it to stretch and bend in any direction when stressed? |
It's relatively loose, highly interconnected, and rubbery network |
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What are 5 similarities between collagen and elastin? |
1. Protein-based 2. Contains proline and lysine 3. Stable after cross-linking 4. Monomer secreted into EC space 5. Self-assembly and cross-linking occur in the EC space |
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Is carbohydrates present in elastin? What about collagen? |
Elastin - NO Collagin - YES |
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How many types of elastin are there? |
1 |
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What are the types of cross links found in collagen and elastin? |
Collagen - Intramolecular aldol cross-links Elastin - Intramolecular desmosine cross-links
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What are the 2 advantages of elastin? |
1. Ability to stretch and relax 2. High stability with half-life of 70 years |
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What are 3 uses of elastin? |
1. Vascular stents 2. Skin repair 3. Cosmetic implantation |
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What becomes a problem of elastin-based biomaterials in vivo? Why? |
Calcification because elastin serves as a nucleation site for mineralization |
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Precipitation in synthetic elastin-like polypeptides as a result of a change in phase occurs when? |
When the mixture is heated above the lower critical solution temperature |
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What is silk used for? |
Maintenance of structural integrity |
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How is silk made? |
Made by silkworms, spiders, scorpions, mites, and flies |
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Silk is composed of what 2 things? |
Sericin and fibroin |
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Composition of sericin and fibrion is dependent on what? |
The location of the silk: Outer layer of silk contains more sericin |
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Silk may contain what 4 impurities? |
1. Carbohydrates 2. Waxes 3. Inorganic salts 4. Pigment |
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Which is more soluble: sericin or fibroin? |
Sericin (but sericin is not soluble in cold water) |
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What does Sericin do? |
It acts as a gum binder to surround the fibroin and for maintenance of structure |
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What are 5 properties of sericin? |
1. Easily hydrolyzed 2. Resists oxidation 3. Antimicrobial 4. Easily absorbs and releases moisture 5. UV resistant |
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Fibroin is made up of what 3 primary peptides? |
1. Heavy chain 2. Light chain 3. Fibrohexamerin |
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What is fibrohexamerin? |
A glycoprotein linked by disulfide bonds |
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What are the four regions of fibroin? |
3 Crystalline regions and 1 amorphous region |
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What are the three crystalline regions of fibroin made of? |
Anti-parallel beta-sheet structures, primarily with Gly, Ala, Ser sequences |
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Fibroin is considered to be what kind of polymer? Why? |
A block co-polymer because fibroin contains crystalline regions with amorphous regions. |
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What allows silk to stretch? |
Bulky regions with valine and tyrosine that interrupt the beta-sheet |
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The crystalline regions of fibroin are responsible for what 2 things? |
1. Tensile strength 2. Toughness |
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Silk has what 7 properties? |
1. Insoluble in water, dilute acids, alkalis, and most organic solvents 2. Resistant to degradation 3. Hydrolyzable in concentrated sulfuric acid 4. Hygroscopic 5. Tensile strength of 650 MPa and modulus of 15 GPa (higher than steel) 6. Elastic 7. Poor conductor of electricity |
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What does Region 1 of fibroin consist of? |
Highly crystalline region with repetative Gly-Ala-Gly-Ala-Gly-Ser sequence (GAGAGS) |
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What does Region 2 of fibroin consist of? |
Less crystalline than region 1 but contains repetative GAGAGT or GAGAGVGT sequences |
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What does Region 3 of fibroin consist of? |
Highly crystalline and contains AAS sequences |
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What is Region 4 of Fibroin? |
Amorphous region with amino acid residues that are negatively charged, polar, hydrophobic and aromatic. |
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Region 4 of Fibroin exhibits what? |
Helical, spring-like properties allowing the fibers to be elastic or extended |
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Spider silk is composed of what? |
Long amino acid chains that form beta-pleated sheet crystals and amorphous or semi-amorphous regions or network chains |
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What are beta-pleated sheet crystals? |
Stacks of amino acids rich in alternating G and Ala or Ala blocks |
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What is the problem with spider silk? |
It's difficult to harvest thus cannot be produced large scale |
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What are 5 uses of silk? |
1. Artificial tendons, ligaments 2. Tissue repair 3. Wound healing 4. Sutures for eye or neurosurgery 5. Substitute for kevlar fibre |
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How does polymerization occur in chitosan? |
Linking monosaccharides together via O-glycosidic bonds between hydroxyl groups |
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Chitosan is derived from what? |
Chitin |
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What is a major tensile element of the exoskeleton? |
Chitin |
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Chitin is made up of what? |
Long linear polymeric chains of N-acetyl-D-glucosamine |
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Deacetylation of chitosan allows for what 4 things? |
1. Tighter packaging 2. Increased crystallinity 3. Different biodegradation rates 4. Different levels of osteogenesis |
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What is the chemical difference between cellulose and chitosan? |
Chitosan has an amine group Cellulose has a hydroxyl group |
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What is the difference between cellulose and chitin? |
Cellulose has an hydroxyl group Chitin has an acetyl group |
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What are the 2 differences between chitin and chitosan? |
Chitosan has an amine group and no oxygen double bond
Chitin has an acetyl group and has an oxygen double bond |
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Chitosan is made up of what? |
Linear polysaccharide chains of beta-1,4,D-glucosamine and N-acetyl-d-glucosamine. |
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What is the degree of deacetylation? |
Is the measure of molar fraction of glucosamines to N-acetyl glucosamines in Chitosan. |
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Chitosan possesses what 4 favorable properties for use as a biomaterial? |
1. Elicits minimal foreign body reaction 2. Can be dissolved in water, depending on pH 3. Has available side groups for attachment of growth factors 4. Controllable mechanical and biodegradation properties |
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Although tougher and more flexible than ceramics, chitosan tends to be what? |
Tends to swell when immersed in physiologic solution and is mechanically weak. |
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Degradation of chitosan is dependent on what? |
Its crystallinity and the degree of deacetylation. |
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An increase in the degree of deacetylation causes what to crystallinity and rate of degradation? |
Increases crystallinity and decreases rate of degradation. |
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Does cell viability improve on chitosan with higher degrees of deacetylation or lower degrees of deacetylation? |
Higher degrees! |
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What is the formula for cellulose? |
(C6H10 O5)n |
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Cellulose is what kind of compound? |
Beta-glucan |
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Why is cellulose rigid and rod-like? |
Due to orientation of the glycosidic bond |
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What is Cellulose? |
Highly abundant organic polymer found in cell walls of plants that is comprised of glucose units linked beta-1,4-glycosidic bonds |
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Why does cellulose possess hygroscopic properties? |
Because of less crystalline regions that allow for swelling when immersed in water |
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Extensive hydrogen bonding between cellulose chains causes native cellulose to be what? |
Roughly 70% crystalline |
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What are three off label properties of cellulose? |
1. Tasteless 2. Odorless 3. Hydrophilic |
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Where is Cellulose I found? |
Plants |
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Cellulose I contains more of what kind of structure? |
More beta sheets than alpha helix |
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Cellulose I consists of what kind of glucan chains? |
Parallel beta-1,4-linked |
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Where is Cellulose II found? |
Algae, mold, and bacteria |
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Cellulose II contains more of what kind of structure? |
More alpha helix than beta sheets |
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Cellulose II consists of what kind of glucan chains? |
Anti-parallel beta-1,4 linked |
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Why is Cellulose II thermodynamically stable? |
High hydrogen bonding |
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Cellulose II can be converted from Cellulose I via what? |
Alkali treatment |
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How is cellulose III formed? |
By treating Cellulose I and II with liquid ammonia |
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How is cellulose IV formed? |
By heat treating Cellulose III. |
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What are 4 uses of cellulose? |
1. Pill tablet binders (less viscous = rapid drug release) 2. Artificial skin 3. Hemodialysis membranes 4. Control of hemorrage during surgery |
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TRUE OR FALSE: Chitosan is used in bulk. |
FALSE. It's too mechanically weak. |
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What are 3 uses of chitosan? |
1. Gel to repair cartilage 2. Bandages 3. Scaffolds |
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What is alginate? |
Non-branched polysaccharide polymers derived from bacterial and marine algae. |
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Alginate is made up of what 2 monomers? |
1. B-D-mannuronic acid (M) 2. a-L-guluronic acid (G) |
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Alginate monomers are epimers with a difference where? |
C5 |
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TRUE OR FALSE: a-L-guluronic acid (G) cannot be modified. |
TRUE |
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How can M alginate be modified? |
It can undergo acetylation at C2 and C3 hydroxyl groups and undergo epimerization forming G monomers |
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What are 8 properties of Alginate monomers? |
1. Dependent on co-monomer blocks and degree of acetylation 2. Non-toxic 3. Non-inflammatory 4. Hygroscopic 5. Easily processed in water 6. Biodegradable 7. Controllable porosity 8. Able to attach biological cues |
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If the pH is too low, what happens to alginate? |
It shrinks and does not release encapsulated cells or growth factors |
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If the pH is too high, what happens to alginate? |
Rapid degradation of alginate |
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Hyaluronic acid is found naturally in what 7 places? |
1. ECM 2. Connective tissues 3. Epithelial tissues 4. Neural tissues 5. Synovial fluid 6. Vitreous humor 7. Umbilical cord |
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Hyaluronic acid is made up of what 2 things? |
1. a-1,4-D-glucuronic acid 2. b-1,3-N-acetyl-D-glucosamine |
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What are the 4 roles of hyaluronic acid? |
1. Viscoelastic property and ability to swell to serve as lubricant and shock absorber 2. Resistant to compression 3. Regulates tissue and matrix water during wound repair 4. Antioxidant effect and helps mediate inflammation |
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What are 3 uses for hyaluronic acid? |
1. Lubricants and mechanical support 2. Viscoelastic gel for dermal ulcers, wounds, and burns 3. Opthalmic surgical aid in cataract extraction, intraocular lens implantation, and retinal attachment surgery |
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What is Chondroitin Sulfate? |
Sulfated, unbranched polysaccharide polymer found in the ECM that is used for maintaining structural integrity of tissues |
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Chondroitin Sulfate is made of what two things? |
1. N-acetyl-D-galactosamine 2. D-glucoronic acids |
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Sulfation of the N-acetyl-D galacosamine in Chondroitin Sulfate occurs where? |
At the OH group in the C4 (type A) or C6 (type B) position |
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What are 5 properties of Chondroitin Sulfate? |
1. Bind and modulate growth factors 2. Involved with cell adhesion, migration, proliferation, and differentiation 3. Non-immunogenic 4. Degradable in water 5. By-products are oligosaccharides |
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What are 3 uses of Chondroitin Sulfate? |
1. Nutritional supplements for osteoarthritic patients 2. Delivery carrier for tissue engineering 3. Opthalmic applications due to viscoelastic properties |
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Corals are found naturally in coral reefs as what? |
Crystalline calcium carbonate |
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Depending on species, what percentage is the open pore structure of coral? |
20 to 80% open pores |
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Depending on species, what is the pore size range of coral? |
150 um to 500 um |
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What are 3 issues with using corals? |
1. Unstable if untreated 2. Brittle 3. Lacks mechanical integrity for load bearing applications |
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What are 2 uses of corals? |
1. Fillings of defects in orthopedics, crainofacial bones, dental, neurosurgery (spinal) 2. Bone graft substitutes |
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What improves the stability of coral? |
Hydrothermal treatment improves stability by converting CaCO3 to carbonated hydroxyapatite but it still has an unstable degradation time. |