Biomaterials - Final Exam
The unrelaxed compliance in a 10 cm long sample of PLLA with a diameter of 5 mm that extends by 0.35 mm when subjected to a force of 100 N is about: a)0.69 GPa^-1 b)1.45 GPa c)50.9 MPa^-1 d)1.45 GPa^-1
0.69 GPa^-1 Compliance J = strain/stress. Strain = 0.035/10. Stress = Force/area = 100/(3.14 x (5x10-3)2 /4)= 5095541 Pa. Compliance = strain/stress. Using this we get 0.69 GPa-1. Remember the units if modulus is GPa (or MPa etc.). While the units of compliance is GPa-1 (or MPa-1 etc.). Similarly, modulus = stress/strain. In this case comes out to be 1.45 GPa, which is inverse of 0.69 GPa-1
The average molecular weight in a PLA-PGA alternating copolymer molecule is 13,000 g/mol. The number of PLA units in the molecule is: a) 100 b)72 c) 1000 d)58
100. weight of PLA mer = 72 g/mol. weight of PGA mer = 58 g/mol. So in PLA-PGA unit, weight = 72+58 g/mol = 130 g/mol. So, DP or the number of PLA-PGA mer pairs is = 13,000/130 = 100. There are 100 such pairs in the molecule since MW is 13,000 g/mol. So there should be 100 PLA unit and 100 PGA units since they alternate.
A biopolymer sample was soft and flexible when implanted inside the body. Based on this information which of the following temperatures is likely to be the Tg of the polymer? (Ignore the effects of water plasticization) a)45C b)38C c)100.2C d)10C e)74C
10C Ignore the effects of water plasticization. Body temperature is 37C. Any polymer with Tg less than 37C will be soft and flexible. Any polymer with Tg > 37C is likely to be hard and rigid.
The approximate number of mers in a single molecule of UHMWPE is: a)2100 b)720000 c)215000 d)10500 e)110000 f)1000
215000 The approximate MW in UHMWPE is 6 x 106 g/mol. mer weight for PE is 28 g/mol. So # of mers in a single molecule is 6 x 106 g/mol/28 g/mol ~ 215000. So there are about 215,000 mers in a single molecule. By comparison, in a plastic bag aslo made of PE, molecular weight is about 60,000 g/mol, so there are 60,000/28 ~ 2150 mers in a single molecule. So you see the effect of MW.
The molecular weight of a silicone polymer is 312650 Daltons. The DP is: a) 6143 b)5000 c)3000 d)4225 e)7000
4225. mer weight is 74 amu. So DP = 312650/74
Lactic acid is a chiral compound. A racemic mixture of lactic acid consists of: a)75% D 25% L enantiomer b)50% D 50% L enantiomer c)25% D 75% L enantiomer d)25% cis, 25%trans isomer, 25% D enantiomer and 25% L enantiomer
50% D 50% L
Which of the following materials can have bioactive, antibacterial and angiogenesis properties? octa calcium phosphate aluminum oxide hydroxyapatatite mesoporous silica Ti-Nb Bioglass Ti-Ta dicalcium phosphate flouridated hydroxy apatite
Bioglass
Alloy that produces osteointegration is: Co-Cr Ti-6Al-4V 316L stainless steel CP Ti Nitinol
CP Ti Commercially pure Ti (CP Ti) is the only alloy that produces osteointegration. Used in dental implants.
Which of the following alloys has a fatigue strength of ~ 900 MPa? Ti6Al4V Nitinol Co-Cr-Mo 316L CP Ti
Co-Cr-Mo The traditional Co-Cr-Mo has one of the highest fatigue strength ~ 900 MPa or greater. Ti6Al4V ~ 700 MPa. 316L ~ 600 MPa. Nitinol not much data, but probably < ~ 300 MPa. Same with CP Ti not much data, but much lower than even 300 MPa.
A superhydrophobic surface is one where (select the best answer): a)contact angle is > 120 degrees b)contact angle is = 180 degrees c)Wenzel equation becomes the Young-Dupree equation d)surface energy is < 100 mJ/m2 e)there is strong wetting of the liquid on the solid surface and there is intimate interaction between the solid and the liquid f)contact angle is < 10 degrees
Contact angle is > 120 degrees Superhydrophobic solid surfaces have a contact angle > 120 degrees. In these surfaces water droplets are likely to roll and bounce from the surface rather than spread or wet the surface
An example of an osteoinductive material is: demineralizaed bone zirconium oxide all the above Hydroxyapatite none of the above tricalcium phosphate alumina
DMB The only osteoinductive material, i.e. that can aid in the transformation of stem cells, immature cells into bone forming cells is demineralized bone
As the molecular weight of a polymer increases, the degree of crystallinity in a polymer a) decreases b) increases c)is unaffected
Decreases. As molecular weight increases, the molecules become more entangled, thus their ability to fold or align to produce crystalline regions decreases. Hence the degree of crystallinity decreases.
At low pressures, the compliance of a vein (large vein, eg. vena cava) is: a) equal to 150x the compliance of a large artery b) equal to 15x the compliance of a large artery c) equal to 0.015x the compliance of a large artery d) equal to the compliance of a large artery
Equal to the compliance of a large artery. At low pressure, the compliance of a vein is ~ 10 to 20 times the compliance of an artery (both large). At high pressures, however, the compliances are comparable for vein and artery.
Skin is highly viscoelastic because: a)its viscosity increases with shear rate b) Er/Eu is much less than 1 c)Hydroxyapatite fibers are highly crosslinked d)Er/Eu is much greater than 1
Er/Eu is much less than 1. Skin is highly viscoelastic because ER/EU ~ 0.3. Structurally it is viscoelastic because it contains significant elastin and because the arrangement of clooagen is different than that in tendons or ligaments. (there are several other structural factors, but these are the prominent ones.)
One of the main advantages of 316L stainless steel is that it exhbits significant hysteresis which can be important when used with bone. True/False
False 316L stainless stell does not exhibit any hysteresis. It is nitinol which exhibits this behavior.
Hydroxyapatite is bioactive and osteoinductive True/false
False HA is not Osteoinductive, it's osteconductive
The Tg of PGA is likely to be higher than the Tg of PLA.
False PLA has a bigger pendant group (CH3), so higher Tg, but lower degree of crystallinity than PGA.
PMMA bone cements can be injected to the targeted site while ceramic bone cement cannot be injected. True/false
False PMMA bone cement can be formed as a tooth paste consistency material and pushed into the location. Can't be injected easily. Ceramic based bone cement can be injected much more easily or produces as a putty and pushed into location or can be produced as a solid foam and positioned.
As the surface roughness increases, the contact angle of a liquid on a hydrophobic solid decreases True false
False In hydrophobic surfaces, as the roughness increases, contact angle increases and the liquid does not wet the solid as much
PMMA is an important biomedical polymer. Based on its mer structure only, it is fair to say that it is likely to have a high degree of crystallinity.
False See the different pendant groups on either side.
Polylactide is produced by condensation polymerization
False. Poly lactic acid is produced by condensation polymerization. Poly lactide is produced by ring opening polymerization.
When a polymer implant is placed inside the body, the effective glass transition temperature increases.
False. When a polymer implant is implanted inside the body, physiological fluids can penetrate the polymer and lower the effective Tg, thus leading to softening of the implant. This is called water plasticization. How much will the Tg decrease, how much will the polymer soften? In hydrophobic polymers, there is very little softening or change in Tg, while in Hydrophyllic polymers, there can be significant decrease in Tg and thus significant softening.
An example of a bioactive material is: hydroxyapatite CP Ti alumina Co-Cr nitinol
HA A bioactive material is one that establishes a chemical bond at the surface. Two of the inorganic materials that are bioactive are bioglass and synthetic hydroxyapatite.
One of the clinical methods to increase the wear resistance of UHMWPE is: a)increase molecular weight b)use UHMWPE-PEO block copolymer c)increase surface crosslinking d)PEG-ylate the surface e)increase surface crystallinity
Increase surface crosslinking
Which of the following is NOT a characteristic associated with PMMA? a)When used as bone cement, the temp of the surrounding area increases during polymerization b)It's highly hydrophyllic c)It's an amorphous polymer d)It has an E that is much lower than that of bone e)It has a relatively low resistance to creep
It is highly hydrophyllic. PMMA because of the two CH3 groups in the pendant positions, is not hydophyllic. It can classified as moderately hydrophobic polymer. The highly hydrophyllic polymer in the acrylic group is HEMA.
One of the main advantages of using Al2O3 in hip implants is: its high degree of crystallinity its high degree of wear resistance its very high modulus its very high compressive strength its high degree of bioactivity
Its high degree of wear resistance Al2O3 balls are used quite frequently in hip joint replacements as the ball and sometime the acetabular shell. It can either have Al2O3-UHMWPE articulating surface or Al2O3 -Al2O3 articulating surface. Both of these have a better wear resistance than Co-UHMWPE Ti-UHMWPE joints. They also have a lower coefficient of friction. However, Al2O3 balls have a tendency to break under sudden loads.
Pluronic is an important class of block (mostly triblock) copolymers used in many applications. It consists of PPO and PEO blocks. The central PPO portion of the molecular block: a)higher grain size than outter PEO b)more hydrophyllic than outter PEO c)more crosslinked than outter PEO d)more hydrophobic than outter PEO
More hydrophobic than outter PEO segment Pluronic is a block copolymer, (PEO)x-(PPO)y-(PEO)x
Nb stents are attracting a lot of attention because of: a)the biodegradability of the stent at a much slower rate than Mg b)Answer Nb has a low magnetic susceptibility c)Nb surface oxide is bioactive d)ENb < EMg e)Nb can produce magneto and electro viscoelastic modulus variations f)Niobum is osteoinductive
Nb has a low magnetic susceptibility because of the low magnetic susceptibility, MRI images are very sharp and this is a major advantage.
One of the most common materials used in cardiovascular stents is: alumina Co-Cr nitinol CP Ti Ti-6Al-4V
Nitinol Nitinol is becoming the most common material for both regular and drug coated stents. Although stainless steel is still being used in many cases, nitinol is gradually starting to dominate the market. Mostly because of the superelastic effect, low E, hysteresis stc.
A stimuli sensitive polymer that can respond to pH is: a)PGA b)PMMA c)Nylon d)PAA e)PLLA
PAA PAA or polyacrylic acid is the smart polymer that can respond to pH or ionic strength.
The Tg of PLA is about 55°C. The Tg of PCL is about -60°C. At body temperature (Ignore water plasticization): a)PCL is rubbery and PLA is hard and brittle b)PLA and PCL are both hard and brittle c)PLA is rubbery and PCL is hard and brittle d)Both are rubbery
PCL is rubbery and PLA is hard and brittle
Which is more likely to be crystalline: PDLLA or PLLA?
PDLLA consists of both racemic forms, so not as crystalline. PLLA consists of only one enantiomer, so more crystalline because it can be arranged more easily. (But remember that PLLA is not as crystalline as PGA).
Water driven shape memory can be achieved with Polyetherurethane copolymers by incorporating: PGA particles PCL particles Nylon particles NaCl particles PEG particles PLGA particles
PEG Particles Low MW PEG particles have been used in these polymers. When water comes in contact with the sample, PEG dissolves and shape memory is inititated.
The polymer that is likely to be most hydrophyllic among the following is: a)PDLLA b)PLLA c)PMMA d)PGA e)PEO
PEO
A polymer that can be used in a synthetic vascular graft used for repairing blood vessels is: a)PMMA b)Nylon 6 c)PPO d)HEMA e)PAN f)PET g)UHMWPE h)PEEK
PET
The material that you would select for a resorbable bone plate and screw for the treatment of a long bone fracture is: a)PDLLA b)PMMA c)PCL d)HEMA e)PAA f)PLLA
PLLA PMMA, HEMA and PAA are not resorbable. PLLA, PDLLA and PCL are resorbable and FDA approved for use in the body. PDLLA and PCL are relatively soft polymers and thus cannot be used in orthopedic implants. PLLA and PGA have the required mechanical properties (E, strength, creep resistance) for orthopedic applications.
During the degradation of a bioresorbable polymer under physiological conditions: a) Primary covalent bonds in the molecule are broken b)the polymer becomes bionert due to enhanced phagocytosis c)molecular weight of the polymer increases d)the polymer becomes a thermoset
Primary covalent bonds in the molecule are broken.
Polylactide is generally produced by: a)cross linking polymerization b)ring opening c)polymerization d)condensation polymerization e)addition polymerization
Ring opening polymerization
An example of a resorbable ceramic is: Al2O3 hydroxyapatite bioglass ZrO2 tricalcium phosphate
TCP Most of the ceramic/glass are NOT resorbable. There is some controversy over hydroxyapatite (HA). While most papers indicate that HA does not resorb, some say that it degrades very, very, very slowly. The only ceramic that has definitely been shown to be degradable is tricalcium phosphate (TCP). As a result, it is now being used in many drug delivery systems.
Which of the following alloys has a E of ~ 55 GPa? Ti-Ta-Nb Co-Cr CP Ti 316L Ti6Al4V SR-PLLA
Ti-Ta-Nb Both CP Ti and Ti6Al4V between 100 to 110 GPa. 316L ~ 220 GPa, Co-Cr ~ 240 GPa. SR-PLLA ~ 14 GPa. Ti-Nb-Ta alloys have E ~ 50 to 65GPa. Some compositions also superelastic.
In the Biomaterials lab, E for an orthopedic material was measured to be ~ 112 GPa. This material is most likely: UHMWPE Til-6Al-4V Co-Cr alloy PEEK 316L stainless steel PMMA Mg alloy PLLA
Til-6Al-4V E for cortical bone is ~ 20 GPa. The polymers are generally < 20 GPa (except may be for some PEEK composites) and the metals are > 20 GPa. The closer the E to 20 GPa in the orthopedic biomaterial, the less is the stress shielding. Co-Cr ~ 200 GPa. Ti6Al4V ~ 100 GPa.
In general, for a hydrogel, finer the polymer network forming the gel, greater is the probability of transparency in the gel.
True Hydrogels are typically hydrophyllic polymer networks (physical or chemical) that can trap a lot of water (or a solution of water). In most cases, finer the polymer network greater is the probability of transparency in the gel. This is usually true, but there are some exceptions.
Contact angle between synovial fluid and a Ti alloy on a blasted surface and a polished surface were measured to be 82.4 degrees and 77.3 degrees respectively. Based on this information, synovial fluid will spread better (i.e. better contact with the Ti alloy) on a polished surface. True, false
True Lower the contact angle, better is spreading. So better spreading likely on polished surface. However, since the difference is small, it is likely that the difference in spreading between the two cases is minimal.
In a metallic alloy, atoms at the surface are in a much higher energy state than atoms in the bulk: True/false
True Because bonds are broken at the surface and the coordination number has been reduced, atoms are in a much higher state of energy.
Biopolymers undergo creep when subjected to stresses inside the body. During this creep, the compliance increases with increasing time.
True. During creep stress is constant, strain increases with time. Since compliance is strain/stress, (and strain is increasing with time and stress is constant), compliance (J) increases with increasing time during creep. Since the modulus (E or G) is stress /strain (and strain is increasing with time and stress is constant), E (or G) decreases with increasing time
Tg of a biopolymer is around 55C. At body temperature it likely to be hard and rigid.
True. Let us ignore the water plasticization effect. Body temperature is 37C, which is < 55C the Tg. Since we are below the Tg, the polymer will be in its hard and rigid state.
Based only on the mer structure, PLA is stronger than PCL.
True. PLA has a CH3 group and has fewer CH2s in the main chain.
Two pieces of tendon are tested under tension. The first peice is tested at a strain rate of 1%/s and the second piece is tested at 100%/s. The elastic modulus measured at a strain rate of 100%/s will be greater than the elastic modulus measured at 1%/s.
True. The elastic modulus, strength measured at a higher strain rate will be greater than the modulus and strength measured at a lower strain rate. Viscoelastic materials show a strong depenedence on strain rate. So when you obtain data on modulus, strength etc. for tissues, always check the strain rate. Depending on strain rate, you can find widely differing numbers. Metals and ceramics on the other hand are not viscoelastic and so do not show such dependence on strain rate.
In UHXPE used in total hip replacement, the surface is crosslinked to improve a)Biofunctionality of the implant b)E of the implant c)Wear resistance of the implant d)Fatigue strength of the implant e)Resorption rate of the implant
Wear resistance of the implant
Because of the potential toxicity of Ni, Ni free superelastic Ti alloys are being developed for medical applications. Some of the common elements added to replace Ni were mentioned in class. Which of the following elements is NOT commonly added in place of Ni in superelastic Ti alloys? Zn Mo Nb Ta Zr Sn
Zn Some of the common elements added are Nb, Ta, Zr, Sn, Mo added in various amounts and in various combinations. Many commercial alloys are now being tested. The maximum elastic strain varies from ~ 2 to 7% (compared with 8 - 10% for nitinol).
Ti-Nb alloys are receiving a lot of attention because: a)addition of Nb increases the elastic modulus b)addition of Nb enables photothermal drug release c)Addition of Nb makes the alloy resorbable as Mg alloys d)addition of Nb prevents the release of V ions e)addition of Nb makes the alloy photosensitive
addition of Nb prevents release of V ions Conventional Ti-6Al-4V alloys have a problem in terms of potential V ion release, which can have adversely affect biocompatibility. Nb ions if released are not thought to adversely affect biocompatibility. Keep in mind that Ti-6Al-4V has been used in millions of people and has been FDA approved for over 30 years. So, it will be a long time before Ti-Nb alloys can even be considered as a standard clinical option (if ever). Nb also lowers the E, which reduces stress shielding as we have discussed.
The extent of bioactivity in bioglass depends on the: Ca/P ratio amounts of SiO2, CaO, Na2O grain size level of self reinforcement amounts of Al2O3, ZrO2 and TCP
amounts of SiO2, CaO, Na2O
An oleogel consists of (select the best answer as discussed in class): a) hydrophobic polymer network that has trapped a lot of water b)a hydrophobic polymer network that has trapped a lot of oil c)a hydrophyllic polymer network that has trapped a lot of oil d)a hydrogel with physical crosslinks
b)a hydrophobic polymer network that has trapped a lot of oil
Natural hydroxyapatite in bone: a)crystallinity changes depending on how the bone is loaded b)has a constant crystallinity of 50% c)is completely crystalline d)completely amorphous e)has a crystallinity that is much greater than in synthetic hydroxyapatite
crystallinity changes depending on how the bone is loaded
At high pressures, the compliance of a vein (large vein, eg. vena cava) is: a) equal to 150x the compliance of a large artery b) equal to 15x the compliance of a large artery c) equal to 0.015x the compliance of a large artery d) equal to the compliance of a large artery
equal to the compliance of a large artery. At low pressure, the compliance of a vein is ~ 10 to 20 times the compliance of an artery (both large). At high pressures, however, the compliances are comparable for vein and artery.
Poly(N-ethylmethacrylamide) (PNEMAM) is a polymer with a LCST of 58C. So if a solution of this polymer is injected into a physiological site, it will form a gel because of phase separation. True/false
false Since LCST is 58C, phase separation only occurs above 58C. So it will remain a solution at body temperature (37C) and will not gel.
Tricalcium phosphate is resorbable, osteoconductive and osteoinductive. true/false
false Tricalcium phosphate is resorbable and osteoconductive. It is NOT osteoinductive. The only osteoinductive material is demineralized bone.
Ti alloys are considered biocompatible because they: a) crosslink with collagen at the surface and form a osteogenic blend b) the V in the alloy leads to surface grafting with osteocytes c) they are osteoinductive d) produce acidic by products during degradation e) form a stable oxide layer that can also be functionalized f) lead to an increase in pH at the surface suring degradation that is conducive to surface calcification
form a stable oxide layer that can also be functionalized Ti forms TiO2 on the surface which can transform to hydroxides (in aqeous mediums) that may enable surface functionalization.
The primary advantage of Epoxy in SMP is: a)good shape retention b)hydrophyllic c)resorbable d)it is a thermoplastic e)Large shape changes with high f)strains possible g)exhibits LCST h)can form good gels
good shape retention PU and Epoxy are the 2 most common SMP's. PU is much more common. PU can produce large shape changes. The advantage of Epoxy, a thermoset, is good shape retention.
A very highly lipophyllic compound: a) is always a weak acid b) has a P<1 c)has a P>3000 d) Has a low pKa e) is always a weak base
has a P>3000 because when P<1, it's highly hydrophyllic. So when P>3000 it's likely highly lipophyllic.
Alumina is used in dental implants because: a)it can hydrate and form hydroxides which can be PEGylated. b)it has an exceptionally high compressive strength c)it is highly bioactive d)it it has an exceptionally high tensile strength e)it has an exceptionally high tensile modulus
it has an exceptionally high compressive strength Aluminum oxide has a very compressive strength > 4000 MPa. It also produces the lowest amount of foreign body repsonse. Although it does not produce osteointegration of CP Ti, comes close.
Among the following, the polymer that can be used clinically as a tissue adhesive is a)n-bca b)PMMA c)PAA d)PTFE e)ePTFE f)PEEK g)PVDF h)UHMWPE
n-bca
One of the most important materials used in cardiovascular stents is: nitinol Co-Cr Ti-6Al-4V alumina CP Ti
nitinol Nitinol is becoming the most common material for both regular and drug coated stents. Although stainless steel is still being used in some cases, nitinol is gradually starting to dominate the market. Mostly because of the superelastic effect, low E, hysteresis stc.
Which of the following materials is osteoinductive? 316L stainless steel nitinol bioglass HA Alumina none of the above Ti-6Al-4V zirconia all of the above PLLA PGA TCP CP Ti
none of the above. Osteoinductive materials are able enhance/partake/influence the biological processes associated with bone formation. They can facilitate osteoblastic activity at the surface. The only material that is osteoinductive is demineralized bone. In order to impart/enhance osteoinductive property, we can also inject bone morphogenic proteins into the implant. The other property that we discussed is the osteoconductive property. Osteoconductive materials act as a scaffold similar to the extra cellular matrix in the body. Bioglass, HA and to a lesser extent TCP are examples of osteoconductive materials.
Bioactive molecules can be immobilized on the surface of some orthopedic implants by: a)incorporation of ionomers with covalent double bonds at the surface b)chemical crosslinking to form mesopeptides c)plasma etching with tetrahydrofuran (THF) d)physical adsorption e)acid etching followed by reaction with amine containing bases f)grafting with orthoesters and anhydrides
physical absorption Immobilization of biomolecules at the surface is important for osteointegration of the implant. It is possible in Ti alloys because of the surface TiO2 layer. There are many techniques including physical absorption, chemical covalent bonding and biomimetic processes. Physical absorption is the easiest at the current stage.
Ceramic bone cement hardens by the: a)chemical crosslinking between the brushitei and hydroxyapatite crystals b)chemical crosslinking between the di and tri calcium phosphate crystals c)chemical crosslinking between the brushite and tricalcium phosphate crystals d)crosslinking between Ca+2 ions and the OH- ions from neighboring crystals e)physical interlocking of the needle like crystals from neighboring crystals f)physical interlocking between the glassy core and the crystalline shell
physical interlocking of the needle like crystals from neighboring crystals
One of the disadvantages of polyacrylamide hydrogel contact lenses is: a)polyacrylamide gel lenses have a negative surface charge which can attract protein buildup b)polyacrylamide can breakdown and interact with the tear film to form micelles which cloud the vision c)it can interact with the tear film to form an IPN d)polyacrylamide is a hydrophobic polymer with a contact angle close to 168 degrees e)polyacrylamide lenses can reduce the pKa of the tear film f)polacryamide gels are very rigid and so uncomfortable in the eye
polyacrylamide gel lenses have a negative surface charge which can attract protein buildup Polyacryamide and HEMA hydrogels were one of the first hydrogel lenses that were introduced in the 80's and are still being used. The gels can contain over 90% water and are very comfortable. But they have a relatively low oxygen permeability. Also, polyacrylamide, a weak polyelectrolyte can have a residual negative surface charge and thus attract protein buildup.
On which of the following solid surfaces will a liquid with a surface tension of 1700 mN/m spread the most? solid with a surface energy = 2500 mJ/m2 solid with a surface tension of 1500 mN/m solid with a surface tension = 2100 mN/m solid with a surface energy = 1500 mJ/m2 solid with a surface energy = 1300 mJ/m2 solid with a surface energy = 1000 mJ/m2
solid with a surface energy = 2500 mJ/m2 The solid with the highest surface energy will produce the greatest wetting.
A new way being explored to improve the integration of Ti alloy implant with bone in orthopedic implants is: a)production of superoleophobic surfaces b)surface coating with pluronic c)surface PEGylation with corsslinked micelles d)surface coating with CaSO4 e)surface coating with Co to obtain in magnetostrictive properties f)surface coating with conducting polymers such as polypyrrole g)Surface coating with nitinol
surface coating with conducting polymers such as polypyrrole In order to make the surface biofunctional, conducting polymer coatings on Ti alloys are being explored. Biomolecules or cells can then attach to the polymer and thus enhance osteointegration.
Ta has reemerged as a candidate for orthopedic implants because: a)surface oxide layer readily absorb hydroxyl groups which can lead to hydroxyapatite nucleation b)surface oxide layer can readily bond with osteoclasts which elminate necrotic bone around the implant c)it can be alloyed with Mg to produce wear resistant biodegradable alloys d)it can now be formed into an amorhous glass which can bond better with bioglass and establish a strong bond with bone. e)It can now be nade degradable by the addition of Y f)it can be combined with calcium phosphates to form cermets with high shear strength
surface oxide layer can readily bond with osteoclasts which elminate necrotic bone around the implant
Hyperthermia with magnetic nanoparticles refers to: a)temperature increase in the particle in a magnetic field b)nanoparticle degradation with the application of a voltage c)sol-gel reversion with the application of a voltage d)Shape memory effect with NIPAAM in distal tibia e)gel formation with the application of a voltage
temperature increase in the particle in a magnetic field Hyperthermia is becoming an important means of drug delivery with nanoparticles. In this case, nanoparticles are heated in the presence of a magnetic field (to ~45C) and cancer cells which are extremely temperature sensitive can be killed.
The drawback of syntheitc hydroxyapatite is that it does not perform as effectively as natural hydroxyapatite. This deficiency is because of structural differences between natural and synthetic forms. One of this structural difference is that: a)Only crystalline HA can be produced by synthetic processes. b)the degree of crystallinity in synthetic HA is much higher than in natural HA c)the degree of crystallinity in natural HA is much higher than in synthetic HA d)substitutional ions in synthetic HA such as F-1, CO3 -2 and OH-1 can increase the crystallinity substantially compared to natural HA. e)the degree of crystallinity in natural HA can change depending on the local remodeling conditions.
the degree of crystallinity in natural HA can change depending on the local remodeling conditions. Natural HA has crystallites whose size is in nm. It has also has many carefully selected substitutions both in the cationic and anionic sites. These substitutions are very important in determining the rate of degradtion based on physiological conditions. Further natural HA changes the degree of crystallinity based on physological conditions. All these conitions cannot be met by synthetic HA and so it is never as effective.
One of the problems associated with porous ingrowth used for fixation of metallic implants is: a)the pore size cannot be controlled to maximize osteoblastic activity b)the surface area increases and so corrosion resistance decreases c)the alloy cannot be sterilized easily. d)the resorption rate and crosslinking increase significantly. e)the pores are not spherical
the surface area increases and so corrosion resistance decreases Porous ingrowth is effective as a fixation technique, but can increase surface area and thus increase the release of metallic ions. Beads or felt may break off and only 10 to 20% pores filled. These are some of the disadvantages.
One of the problems with Mg alloys is that: a)they have a low magnetic suceptibility like Nb b)they are non-degradable c)they degrade at a much smaller rate when compared to PLLA d)when they degrade, pH decreases e)they produce acidic by products during degradation f) there is copious evolution of Hydrogen gas during degradation g)the surface of Mg alloys is superhydrophyllic h)because of their magnetostriction, the impants can break after implantation
there is copius evolution of hydrogen gas during degredation Mg alloys degrade very rapidly. As a result there are large gas bubbles produced which can accumulate at the implant, bone interafce, cause pressure and this enable failure.
Nitriding of Ti-6Al-4V alloys is conducted primarily to increase: tensile strength ductility E osteointegration potential wear resistance
wear resistance Ti based alloys and nitrided to improve wear resistance. In addition, the fatigue properties are also improved.
Which of these is likely to have the highest resorption rate? aluminum oxide β-tricalcium phosphate α-tricalcium phosphate synthetic hydroxyapatite zirconium oxide
α-tricalcium phosphate The most often used tricalcium phosphate is β-TCP. This is resorbable. However there is also another variety, which can be produced by processing at a higher temperature called α-TCP. This is difficult to produce, but can have a higher resorption rate than the β-TCP. Note also that amophous calcium phosphate (and thus SOME ceramic bone cements) can degrade even faster than α-TCP.
