Biomaterials for Cartilage Reconstruction and Repair - Biomaterials Fabrication and Processing - page 659

21 Biomaterials for Cartilage

Reconstruction and Repair

Wojciech Swieszkowski, Miroslawa El Fray,
and Krzysztof J. Kurzydlowski

CONTENTS

21.1 Articular Cartilage Biology—Structure and Properties ..................................................... 659
21.2 Repair of Articular Cartilage .............................................................................................. 661
21.3 Cartilage Reconstruction—Artifi cial Cartilage.................................................................. 662
21.3.1 Hydrogels .............................................................................................................. 662
21.3.2 Synthetic Segmented Polyesters and Polyurethanes ............................................. 667
21.4 Tissue Engineering Approach............................................................................................. 668
21.5 Total Joint Replacement ...................................................................................................... 670
21.6 Summary............................................................................................................................. 675
Acknowledgments .......................................................................................................................... 675
References ...................................................................................................................................... 675

21.1 ARTICULAR CARTILAGE BIOLOGY—STRUCTURE AND PROPERTIES
Cartilage is a type of dense connective tissue composed of collagenous or elastic fi bers and chondro-
cytes embedded in a fi rm gel-like matrix of proteoglycans. It is an avascular tissue with extremely
limited capacity for repair. It appears in three different forms in the human body (Figure 21.1):

1. Elastic cartilage —found in noses and ears (contains elastin, a collagen type II, scattered
throughout the matrix);

2. Fibrocartilage —found in ligaments, tendons, intervertebral disks (composed primarily of
collagen type I);

3. Hyaline cartilage —found in lining bones in the joints (called articular cartilage [AC]),
such as the knee, the ankle, the hip, the shoulder, and in any other moving joint such as the
fi ngers (made predominantly of type II collagen).

The hyaline cartilage, the most abundant type, is capable of withstanding repeated load-bearing
activities (resistance to compression) and it evenly distributes this load to the underlying subchon-
dral bone [1].
The main components of mature AC are chondrocyte cells, which make up to 10% of the volume
of the extracellular matrix (containing interstitial fl uid, several forms of collagen, proteoglycans,
noncollagenous proteins, nonspecifi c lipids, glycoproteins, and trace amount of various growth
factors). The collagen is present as woven fi brous network in a polysaccharide matrix contain-
ing hyaluronic acid (HA), chondroitin sulfate, keratin sulfates, and stabilizing proteins. The chon-
droitin and keratin sulfates have hydrophilic groups, which bind water helping to stabilize and
strengthen the system. Collagen fi brils (mainly collagen type II) are responsible for the tensile and
shear stiffness of cartilage, whereas proteoglycans are responsible for the biomechanical properties

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