Chemistry Reference
In-Depth Information
a
b
Fig. 1.6
Structural formulae of camptothecin [
95
] (
a
), and karenitecin (
b
) [
85
,
86
]
brief glimpse at some of the roles that silicon-based species have played and con-
tinue to play in the biomedical field. A comprehensive treatment of this field could
undoubtedly be the subject of several texts in its own right.
Related to the use of silicon-containing bioactive molecules (Sect. 1.3.2.2.1) sili-
cone matrices have been explored for the controlled release of biologically active
molecules since the 1960s typically as matrix or reservoir devices [
97
]. For example,
Norplant® is a sub-cutaneous implant designed to release the contraceptive levo-
norgestrel over a 5-year period [
98
]. A related system, Estring®, is a vaginal insert
that is used to treat the symptoms of menopause by releasing 17-β-estradiol [
99
].
More recently silicone hydrogel contact lenses were doped with levofloxacin (an
antibiotic) and chlorhexidine (an antiseptic) for delivery of these materials directly
to the eye. Given the successful release of these materials from the contact lens the
development of a daily disposable therapeutic contact lens may be possible [
100
].
In addition to the polymeric silicone systems, porous silicon has also garnered
attention as drug delivery vectors because of their biocompatibility, biodegradabil-
ity, ease of fabrication, their tunable structure, and the porous nature of the network
[
101
,
102
]. These types of materials have been used to deliver localized radioactive
32
P to tumors. Chemotherapy agents such as cisplatin and doxorubicin have also
been delivered from porous silicon
in vitro
[
103
,
104
].
In addition to its uses as a drug delivery vehicle, porous silicon has also received
attention as a platform onto which various tissues can adhere and ultimately grow
[
105
,
106
]. Voelcker and colleagues have utilized porous silicon as a non-toxic,
biodegradable scaffold onto which they have promoted the adhesion of cells related
to the human eye. Similarly, silicon is often incorporated into medical implants and
bone grafts to promote adhesion between the implant and the existing bone tissue
[
107
]. Similar research has looked at using porous silicon as a means of effecting
soft and cartilage tissue repair [
108
].
Silicone polymers based on a Si-O-Si backbone are perhaps the widely known
and widely applied silicon-based system in biomedical devices. A number of rea-
sons account for this observation [
3
,
109
]:
