Nanomedical Devices - Nanomaterials for Medical Applications - page 267

of protein ligands (e.g. transferrin) could increase endocytic uptake and, thus,
the transfection efficiency of the polycation-DNA complexes. 320 The location
of genes in nanostructures within a scaffold would provide spatial control of
growth factors to guide the behavior of specific cell populations. 321 The incor-
poration of gene delivery vectors within structured delivery vehicles, such as
fibrous scaffolds, would also allow for the spatial delivery of genes to cells
seeded or recruited from the host. 322
6.6.2 Nerve Cell Repair
Another area where nanomaterials can be very useful are in peripheral nerve
injuries which are a major financial burden for the public. 323 The frequency of
these injuries have increased steadily over the past few decades reaching several
hundred thousand cases across the world. 324 Frequently, these injuries cause dis-
ability for life because there are no efficient therapeutic repair measures, espe-
cially in severe nerve damages. Usually, end-to-end suturing and autologous
nerve grafting are the most common means of treatment 325 with unsatisfactory
outcomes such as reduced stretching capacity of up to 24% with end-to-end
sutured nerves. 326 Nerve gaps that are not amenable to suturing are repaired
using autologous nerve grafting which is the current gold standard but it is asso-
ciated with morbidity, loss of sensation, painful neuroma formation, and scarring
at the donor site. 327 Initial success of substitute tissues for bridging small-sized
nerve gaps are dampened by the observation that the foreign tissue grafts are
unsuitable to support nerve regeneration over critical size nerve injuries because
they lack the appropriate biochemical and topographical elements. 323
The peripheral nerves link the brain and spinal cord to various parts of the
body. A peripheral nerve injury refers to destruction, damage, or crushing of the
peripheral nerve which is a serious health problem that affects 2.8% of trauma
patients annually. 328 Peripheral neuropathy is a common disease that affects
about 8% of the US population. 329,331 Peripheral nerves exhibit the capacity of
self-regeneration for less severe injury but serious cases can potentially lead
to lifelong disabilities. Various strategies for better recovery of nerve func-
tions have been developed including end-to-end suturing which is one effec-
tive method for short nerve gaps whereas tubular structures are necessary for
bridging longer gaps. 332,333 Many kinds of bioengineered nerve grafts have been
developed from polymeric materials that have conducive properties and dimen-
sions to meet the requirements for peripheral nerve regeneration. Such materials
include naturally derived polymers to conventional nondegradable and biode-
gradable synthetic polymers that are noncytotoxic, highly permeable, and suffi-
ciently flexible with appropriate degradation rate and degradation products that
cater to regenerative axons that minimize swelling and inflammation. 333
Chitosan is one of the natural polymers that is utilized for fabricating nerve
conduits (NCs). 334,335 Other natural polymers include collagen, 336,337 hyal-
uronic acid (HyA), 338 gelatin, 339 and silk fibroin. 340 Because these are natural