Biomedical Engineering Reference
In-Depth Information
CHAPTER
2
Cartilage Aging and Pathology:
The Impetus for Tissue
Engineering
This chapter examines how cartilage develops, and it then describes tissue changes that occur with
age and pathology. As explained, cartilage inherently lacks an adequate healing response, motivat-
ing efforts in tissue engineering. Cartilage healing is difficult and deceptive. It is difficult because
chondrocytes do not mount a sufficient healing response. It is also deceptive because, depending
on the type of injuries, temporary functional restoration can last for years before the mechanically
inferior repair tissue degenerates to result in significant pain and even disability. What is clear is that
long-lasting functional restoration is naturally absent, and, if one judges “healing” by this criterion,
then cartilage is devoid of a complete healing response.
2.1 CARTILAGE FORMATION
As animals with bilateral symmetry, human embryos develop three germ layers during embryogen-
esis. In between the ectoderm and endoderm is the mesoderm, from which cartilages arise. We will
begin our discussion of cartilage formation from this point. Ossification will also be briefly discussed
in relation to chondrogenesis, as knowledge on how cartilage calcifies may aid in developing methods
to prevent unwanted calcification in tissue engineering efforts.
2.1.1 CHONDROCYTE CONDENSATIONANDDIFFERENTIATION
From the mesoderm, the axial skeleton forms from the somites, the lateral plate mesoderm generates
the limbs, and the craniofacial cartilages arise from the neural crest. Examples of axial skeleton
cartilages include rib, intervertebral disc, and facet joint cartilages. The temporomandibular joint
cartilages (i.e., disc, condyle, and fossa), along with auricular and nasal cartilages, are examples of
craniofacial cartilages that are retained in the adult. One of the most essential articulations for
maintaining quality of life is the temporomandibular joint. Diseases associated with this joint pose
significant costs both financially and in terms of morbidity; a separate topic in this series has been
devoted to its treatment through tissue engineering [
99
]. The majority of the information provided
below, though derived from many studies using cells of neural crest origin has been generalized to
cartilage formation in the lateral plate mesoderm, i.e., cartilages of the knee, hip, and ankle.
