Biomedical Engineering Reference
In-Depth Information
On state
erapeutic window
Off state
FIGURE 5.1
Pulsatile release profile.
Externally regulated pulsatile delivery systems may be considered open-loop systems
(Figure 5.2a) and the internal or self-regulated systems may be considered closed-loop
systems (Figure 5.2b). It is obvious that the closed-loop system is a more suitable choice
because of its ability to be self-controlled. Overdose of hormone drugs such as insulin
is highly undesirable because it leads to coma and death [4]. A good control over the
release rate, especially at off-state, is thus the key issue in pulsatile/controlled delivery
systems to minimize any leakage. To realize pulsatile drug delivery and to control its
release rate at different states, a responsive material can be coated onto the conventional
drug carrier.
This chapter is devoted to address four fundamental questions: (1) What mecha-
nisms are used to control release by coating? (2) What materials are usually used for
coating the drug delivery systems? (3) How are different release profiles achieved,
and can their release rates by different types of coatings be controlled? (4) What tech-
niques are used to realize different coatings in both large-scale production and research
laboratories?
External controlling
signal
-
System
Resulting
glucose
concentration
+
Glucose from
food
(a)
-
System
Resulting
glucose
concentration
+
Glucose from
food
(b)
FIGURE 5.2
Open- and closed-loop control systems.
