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e1
QUESTIONS
1. The transformation of a solid implant into water-sol-
uble material(s) is best described by the term “bioero-
sion”. Which of the following events may or may not
accompany bioerosion?
(a) Changes in the physico-mechanical properties of
the polymer.
2. The statement that polyanhydrides are surface erod-
ing is not always true. Likewise, the statement that
poly(lactic acid) is bulk eroding is not always true.
(a) What determines if a polymer is surface or bulk
eroding?
3. Poly(L-lactic acid) is known to be highly crystalline
and not to be completely resorbed over periods of
4. How does the fact that a material is biodegradable
affect the evaluation of toxicity for a given degradable
material? The conventional testing for the toxicity of
5. Virtually all currently available implant materials
erode due to the hydrolytic cleavage of the polymer
6. Identify the potential advantages (or disadvantages)
of surface eroding biomaterials over bulk eroding
ANSWERS
1. Satement (b). The backbone cleavage is one of the
mechanisms of chemical degradation. Chemical deg-
radation may lead to bioerosion, but is a separate
process and is not required for bioerosion of some
biomaterials. Bioerosion refers to physical changes in
the material.
if the rate of degrading agent influx is much higher
than the bond cleavage rate, the material will be
bulk eroding, and the degradation process will occur
simultaneously throughout the volume of the medical
device.
that it could permeate through the volume of the
device before signiticant degradation begins, making
out to the surrounding fluid is slower than the chain
degradation rate, the acidic byproducts of the PLA
degradation will be trapped within the bulk of the
water must be able to enter the polymer network
to cleave the ester bonds. The crystalline regions of
regions, the polymer backbone degrades much more
slowly than an amorphous polymer, and thus con-
CHAPTER I.2.6
Degradable and Resorbable Biomaterials
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4. One must know each of the possible degradation
products due to cleavage of bonds by hydrolysis and
enzymatic action. The toxicity of each of the poten-
tial degradation products and the toxicity of the
intermediate oligomer byproducts must be evaluated.
Furthermore, one must know how these products
5. Temperature and pH levels are very consistent
between individuals and most body compartments,
while the concentration of particular enzymes, bacte-
under superior control and with more consistency
than devices that erode as a result of biodegradation.
6. (a) Many hydrophobic drug molecules have sufticient
retention within hydrophobic polymer matrices. Sur-
face eroding biomaterials can provide near zero-order
release kinetics (linear cumulative release) as the sur-
tion decreases over time. In contrast, bulk eroding
materials lose molecular weight consistently through
the volume of the device, typically becoming brittle
