Biomedical Engineering Reference
In-Depth Information
ing bone implants. Nanotechnology has been shown to be one of the few
technologies that can promote the functions of numerous bone implant materials
(regardless of chemistry).
9.3 Nanostructured biomaterials for cartilage
applications
9.3.1 Cartilage biology, defects and implants
Cartilage is a type of dense connective tissue existing within many joints. It is
composed of specialized cells called chondrocytes that produce a large amount
of an extracellular matrix composed of collagen fibers (mainly collagen type II),
abundant ground substances rich in proteoglycans, and elastin fibers. Chondro-
genesis is a natural process in the formation and growth of articular cartilage
tissue [70, 71]. The chondrocyte occupies less than 10% of native tissue but is
responsible for the creation and maintenance of the extracellular matrix
[70, 72, 73]. Chondrocytes have a spherical shape when in the native
extracellular matrix [73]. Destruction or removal of the extracellular matrix
will result in the loss of differentiated chondrocyte function [74].
Articular cartilage defects are widespread because of intensive sports activi-
ties, genetic disorders (like rheumatoid arthritis) and osteoarthritis. Due to
cartilage loss, patients usually have significant pain and are limited in joint
motion. Today, more than 20 million Americans suffer from arthritis and it is
estimated that the worldwide arthritis market will reach nearly $21 billion by
2010 [75]. It is the leading cause of disability in people over the age of 55 in the
US [76].
Except for artificial joint replacements (usually including metals as
mentioned in the previous section) with their associated short lifespans, there
is no appropriate long-lasting treatment for cartilage damage. Currently, many
researchers have focused on promoting cartilage tissue growth to repair joints
instead of metallic replacement surgeries [77, 78]. To treat cartilage defects, a
key step is to repair the damaged extracellular matrix of cartilage.
To successfully repair or replace the cartilage extracellular matrix, it is very
important to first understand the structure of cartilage. As shown in Fig. 9.9, just
like bone, cartilage also has a self-organized hierarchical structure from macro/
micro- to nano-size. Nanotechnology today can help produce nanostructured
scaffolds which better mimic the organization of the natural cartilage structure.
Tissue-engineered nanostructured scaffolds for cartilage applications need to
meet several criteria in order to adequately regenerate cartilage including cell
seeding, cell growth and in vivo use. The scaffold should be readily processed
into 3D structures uniquely designed for their particular use. The scaffold
surface and porosity must permit cell adhesion, infiltration, proliferation and
differentiation for the synthesis of cartilage tissue. Neither the polymer nor its
