One major class of drug delivery systems is materials that encapsulate drugs to protect
them during transit in the body. Drug encapsulation materials include liposomes and
polymers (i.e. Polylactide (PLA) and Lactide-co-Glycolide (PLGA)) which are used as
microscale particles. The materials form capsules around the drugs and permit timed drug
release to occur as the drug diffuses through the encapsulation material. The drugs can
also be released as the encapsulation material degrades or erodes in the body.
When encapsulation materials are produced from nanoparticles in the 1 to 100nm size
range instead of bigger microparticles, they have a larger surface area for the same
volume, smaller pore size, improved solubility, and different structural properties. This can improve both the diffusion and degradation characteristics of the encapsulation
material.

In addition to liposomes and polymers, other types of nanoparticles are available for
encapsulation. Materials such as silica and calcium phosphate (hydroxyapatite) have
demonstrated superior properties at the nanoscale than the microscale, and can potentially
be better suited for certain drug delivery challenges mentioned above.
Nanoparticle encapsulation is also being investigated for the treatment of neurological
disorders to deliver therapeutic molecules directly to the central nervous system beyond
the blood-brain barrier, and to the eye beyond the blood-retina barrier. Applications could
include Parkinson’s, Huntington’s, Alzheimer’s, ALS and diseases of the eye. In
particular, ophthalmic disorders represent a rapidly growing area that is threatened by
various diseases such as age related macular degeneration (AMD), diabetic retinopathy,
glaucoma, and retinitis pigmentosa (RP).
Neurotech is developing an encapsulated cell therapy to treat eye diseases. It uses a semipermeable
membrane to encapsulate cells, which also permits therapeutic agents
produced by the cells to diffuse through the membrane. The membrane isolates the cells
from the local environment and minimizes immune rejection. The encapsulated cells are
administered by a device implanted in the eye to permit the continuous release of
therapeutic molecules from living cells. This avoids direct injections into the eye, which
may not be practical for regular administrations.

Advectus Life Sciences is developing a nanoparticle-based drug delivery system for the
treatment of brain tumors. The anti-tumor drug doxorubicin is adhered to a nanopolymer
Poly ButylCyano Acrylate (PBCA) particle and coated with polysorbate 80. The drug is
injected intravenously and circulates through the blood stream. The polysorbate 80
attracts plasma apolipoproteins and is used by the blood stream to carry lipids. This is
intended to create a camouflage effect similar to LDL cholesterol, which allows the drug
to pass the blood-brain barrier.