Targeted Drug Delivery - Nanomaterials for Medical Applications - page 208

as a surface stabilizer. 165 NP suspensions were evaluated to determine if tar-
geted drug delivery to sebaceous glands and hair follicles could be achieved.
In vitro delivery of UK-157,147 to the follicles on rabbit ear tissue was dem-
onstrated with limited distribution to the surrounding dermis. Delivery to hair
follicles was demonstrated in vivo following stimulation of hair growth with
100-nm NPs with a C3H mouse model. The NPs were completely biocompat-
ible without visible skin irritation. In vivo tests of smaller NPs with a hamster
ear model indicated targeted delivery to sebaceous glands. The NPs released
drug rapidly in in vitro tests and were stable in suspension for 3months. The
results showed selective drug delivery to the follicles through follicular trans-
port of NPs and rapid release of a poorly water-soluble drug showing a promis-
ing approach for targeted topical delivery of low-solubility compounds to hair
follicles.
In as much as liposomes have been shown to be biocompatible, safe, and
biodegradable, its potential of liposomes as a drug delivery system for use
in the oral cavity has been investigated. 166 For the specific in vitro targeting
of the teeth, formulations based on the adsorption of charged liposome to
hydroxyapatite (HA) which is a model substance for the dental enamel, has
been conducted in human parotid saliva to simulate oral-like conditions. The
results showed that precipitation occurred in the presence of the lipids dipal-
mitoyl phosphatidylcholine (DPPC)/dipalmitoyl trimethylammoniumpropane
or DPPC/dipalmitoyl phosphatidylglycerol-liposomes in parotid saliva with
no HA which indicated that constituents of parotid saliva reacted with the
liposomes. 166 Based on these studies, the constituents of saliva may interact
with liposomes resulting in aggregation that can be circumvented by adding
various ions to create ionic stability in the medium. The results of the stud-
ies by Nguyen et al. indicated that negatively charged DPPC/DPPA-liposomes
showed the elast reactive to the components of parotid saliva and may be the
most suitable for use in the oral cavity. Additional investigations as to how
these liposomes affect the various components and physiological conditions in
the oral cavity especially the cells must be conducted in vitro to evaluate the
safety of the NMs for dental drug delivery.
5.9.1.3 Polymersomes
Polymersomes are hollow shell NPs that can be sued for the delivery of drugs.
Biodegradable polymersomes for loading, delivery, and cytosolic uptake of
drug mixtures were shown to exploit the thick membrane of these block copo-
lymer vesicles, their aqueous lumen, and pH-triggered release within endolyso-
somes. 1 Target-specific and biodegradable polymersomes break down in acidic
environments and release the drugs within tumor cell endosomes. Unlike cell
membranes and liposomes that are created from a double layer of phospholip-
ids, a polymersome is comprised of two layers of synthetic polymers where the
individual polymers are considerably larger than individual phospholipids but
have many of the same chemical features.