540 - Drug Delivery Systems - Exam Iii - Polymeric Implants

Front 1

Name four types of polymeric implants.

Back 1

1) Diffusion-controlled drug release, 2) Stimuli-sensitive drug release, 3) Biodegradation-controlled drug release, & 4) Sol-gel polymers for drug release

Front 2

What is the most salient advantage of drug delivery via polymeric implant?

Back 2

Polymeric implants facilitate controlled drug release over an extended time frame.

Front 3

Describe the composition of a diffusion-controlled drug release “matrix system.”

Back 3

The polymer and active agent have been mixed to form a homogeneous system.

Front 4

Describe three prominent factors that define the properties of a diffusion-controlled drug release from a matrix system.

Back 4

First, drug release depends on the content of the drug in the polymer matrix. “Content” refers mainly to the drug concentration, but also entails properties specific to the given drug, such as whether it is dissolved or dispersed. Second, drug release depends on “size,” as in the size of the drug molecule, which influences the rate of diffusion, and the size of the implant, which, along with its shape, influences the volume-to-surface area. Third, drug release depends on the structure of the polymer.

Front 5

What is the prominent design feature of a diffusion-controlled drug release “reservoir system?”

Back 5

The reservoir is surrounded by a release rate-controlling membrane.

Front 6

What are three types of stimuli that have been utilized to facilitate the release of drugs from polymeric implants designed for stimuli-sensitive drug release?

Back 6

Polymeric implants exhibiting stimuli sensitive drug release have been designed to do so in response to changes in temperature, pH, or the concentration of a specific chemical species.

Front 7

What are hydrogels?

Back 7

Hydrogels are cross-linked, hydrophilic polymers that swell by absorbing water. These can often be designed to do so in response to a stimulus, such as a change in pH.

Front 8

What is the process by which most biodegradable polymers are designed to degrade?

Back 8

Hydrolysis. Most biodegradable polymers are designed to degrade as a result of hydrolysis.

Front 9

Describe the two contrasting processes by which biodegradable polymers may degrade.

Back 9

Degradation that occurs in a relatively uniform manner throughout the matrix is known as bulk erosion, while degradation limited to the surface is referred to as surface erosion. The extent to which a polymer degrades via bulk erosion vs. surface erosion is dictated by the degree to which water is able to penetrate the polymer matrix.

Front 10

What is a predominant factor influencing the rate of release from a biodegradable polymer that degrades only at the surfaces?

Back 10

Surface area. The rate of drug release from a polymer that degrades only at the surface is directly proportional to the surface area.

Front 11

What class of biodegradable polymers is most notable for degrading at the surface?

Back 11

Polyanhydrides degrade only at the surfaces.

Front 12

What is meant by a Type I erosion mechanism of polymer biodegradation?

Back 12

“Type I erosion refers to water-soluble polymers that have been insolubilized by covalent cross-links and that solubilize as the cross-links (Type IA) or the backbone (Type IB) undergoes a hydrolytic cleavage.” Heller J, Crit Rev Ther Drug Carrier Syst, 1984;1(1):39-90

Front 13

What is meant by a Type II erosion mechanism of polymer biodegradation?

Back 13

“Type II erosion refers to polymers that are initially water insoluble that are solubilized by hydrolysis, ionization, or protonation of a pendant group.” Heller J, Crit Rev Ther Drug Carrier Syst, 1984;1(1):39-90

Front 14

What is meant by a Type III erosion mechanism of polymer biodegradation?

Back 14

In Type III erosion, hydrophobic polymers are converted to small, water-soluble molecules by cleavage of the polymer’s backbone. Heller J, Crit Rev Ther Drug Carrier Syst, 1984;1(1):39-90

Front 15

As a general rule, how does the crystallinity and the rate of degradation for an enantiomerically-pure poly(lactic acid), such as the L form, compare with one consisting of a mixture of D & L chiral centers on the repeat units?

Back 15

Enantiomerically-pure poly(lactic acid) has a semicrystalline structure, while a racemic mixtures of repeat units give the polymer an amorphous structure. The semicrystalline, enantiomerically-pure PLA form degrades more slowly than the amorphous, racemic PLA form.

Front 16

How does the ratio of lactic acid units and glycolic acid units influence the degradation rate of poly(lactic-co-glycolic acid)?

Back 16

The degradation rate of poly(lactic-co-glycolic acid), i.e. PLGA, is inversely proportional to the equality of the ratio of the lactic acid and glycolic acid units. In other words, both pure poly(lactic acid) and pure poly(glycolic acid) degrade more slowly than a mixture of the two, and an equal ratio of the two has the fastest rate of degradation.

Front 17

As a general rule, how does the degradation rate of a polymer, such as poly(lactic-co-glycolic acid), correlate to the molecular weight?

Back 17

The degradation rate of a polymer is inversely proportional to the molecular weight of the polymer. In other words, the heavier the molecular weight of the polymer, the slower its degradation rate will be.

Front 18

What is a sol-gel polymer?

Back 18

A sol-gel polymer, of the type used for pharmaceutical applications, is one that is initially a solution at room temperature, but solidifies into a biodegradable gel at body temperature.