Biomedical Engineering Reference
In-Depth Information
Many of the arthroscopic repair strategies employed utilize the intrinsic repair response to
induce the formation of a repair tissue within the defect [8].
Arthroscopic lavage and debridement are often used to alleviate joint pain. Lavage involves
irrigation of the joint during arthroscopy. Debridement is the arthroscopic removal of damaged tis-
sue from the joint, which has also been shown to alleviate pain and when used in conjunction with
lavage, pain relief appears to last longer [9]. Both lavage and debridement, however, do not induce
repair of AC in full-thickness defects.
Soft tissue grafts involving the transplantation of periosteum and perichondrium to full-
thickness defects of AC have been used extensively in animal models and human clinical trials. It
must be noted that periosteum has chondrogenic potential.
Osteochondral transplantation of autogenic and allogeneic tissues has been widely used to
treat predominately large osteochondral defects. Though allogenic material derived from cadaveric
donors has been used to treat osteochondral defects, an immune response is still a potential problem
with this approach [10]. Autologous osteochondral grafts involve the removal of cylindrical plugs
of osteochondral tissue from nonload-bearing regions of the AC, such as the femoral trochlear
groove, and transplantation of the debrided full-depth defect. This procedure is limited by: 1) insuf-
fi cient supply of donor tissue, 2) the diffi culty of carving the host cartilage into the desired three-
dimensional (3D) structure, 3) the chemical and mechanical instabilities of the graft, 4) mismatch of
the articular surface of the donor and the host, and 5) an unfavorable immune response by synovial
fl uid [4].
Cell-based transplantation methods currently involve the transplantation of expanded autolo-
gous chondrocytes to the defects to form a repair tissue.
Autologous chondrocyte transplantation (ACT) in humans is a procedure involving the excision
of a healthy biopsy by arthroscopy from a nonload-bearing region of the AC. The chondrocytes
are then released by enzymatic digestion and expanded in culture. A second procedure is then per-
formed by arthrotomy. The defect is debrided back to the healthy cartilage but not to the subchon-
dral bone. A periosteal graft is taken from the medial tibia, sutured over the defect, and cultured
autologous chondrocytes are then injected under the periosteal fl ap. Although, the ACT method is
used very often, the repair tissue differs in structure from normal cartilage due to the lack of the
preferential collagen arrangement, which could be found in the normal cartilage.
21.3 CARTILAGE RECONSTRUCTION—ARTIFICIAL CARTILAGE
Various materials, including biological and synthetic matrices with growth factors or chondrocytes,
are used to restore, maintain, or improve tissue functions. Much attention is focused on the use of
biocompatible synthetic matrices. Inorganic materials such as carbon fi bers and hydroxyapatites,
various polymers such as polytetrafl uoroethylene, polyesters, poly(lactic acid) (PLA), and hydrogels
such as poly(vinyl alcohol) (PVA) (Figure 21.3) have been used as artifi cial cartilage [11].
These materials are used very often as artifi cial osteochondral substitutes (“plugs”) implanted
in the cartilage defects to stop further fracture [12,13]. Meyer et al. [14] reported the clinical appli-
cation of the plugs made of PVA hydrogel (SaluCartilage).
21.3.1 H
YDROGELS
Hydrogels, both degradable and nondegradable, are widely studied for biomedical applications,
including tissue engineering (TE), drug delivery, or cartilage repair. The network structure of poly-
meric hydrogels is made of cross-linked polar chains. This structure allows them to hold large
amount of fl uids (i.e., water) without dissolving. The hydrogels have a high permeability to small
molecules and viscoelastic behaviors. These properties make hydrogels similar to biological tis-
sues. These materials also show good biocompatibility. Cartilage reconstruction is generally
based on polymeric hydrogels, which could form 3D porous scaffolds. Hydrogels for biomedical
applications based on natural and synthetic polymers are hydrophilic polymer networks that may
