Tissue engineering - Orthopaedic Biomaterials in Research and Practice - page 234

Osteochondral allografting emerged in the 1970s as an option for
treating large post-traumatic injuries, osteonecrosis, and tumors adja-
cent to articular joints. Osteochondral allografting involves transplant-
ing mature hyaline cartilage containing living chondrocytes that can
support the hyaline cartilage matrix indefinitely. The osseous portion of
the graft serves as an osteoconductive scaffold for graft incorporation
and for restoring absent bone.
Other approaches to the use of tissue engineering for bone and soft
tissue healing involve concentrated platelets in plasma-rich platelet
injections. Plasma-rich platelet has been used in rotator cuff surgeries,
meniscal repairs, and allograft anterior cruciate ligament reconstruc-
tions to accelerate healing. However, the positive actions of plasma-rich
platelet are still unclear. The findings in the literature are mixed. Some
researchers have reported no benefits for bone healing in animal models,
while others have found effective augmentation of porous biomaterials
after plasma-rich platelet use. Some commercially available plasma-rich
platelet preparation systems include gravitational platelet separation by
Cell Factor Technologies/Biomet Biologics, Magellan by Medtronic, and
Symphony II by DePuy. The potential role of plasma-rich platelets in
healing musculoskeletal injuries is an exciting frontier that may even
lead to newer improved therapies, but studies are still being conducted
to establish effectiveness, indications, and protocols.
Stem cells
Over the last decade, there has been considerable interest in the use of
mesenchymal stem cells and tissue-engineering principles in orthopae-
dics and musculoskeletal sciences. Stem cells are an attractive option
because of their potential for a high rate of proliferation, with the abil-
ity to undergo chondrogenic, osteogenic, and adipogenic differentiation.
Cells with mesenchymal stem cell characteristics can be isolated from
different adult tissues, such as bone marrow, periosteum, skin, adipose
tissue, skeletal muscle, synovial tissue, the infrapatellar fat pad, and
cartilage. Stem cells have demonstrated excellent gene transfer with
the capability to be transduced for the tissue engineering of bone. Gene
transfer could enable growth factors and bone morphogentic proteins to
enhance bone repair. Stem cells are implanted onto scaffolds, which help
support tissue formation by allowing cell migration, proliferation, and
differentiation. These scaffolds are required to deliver and retain cells,
allow for cell attachment, and have adequate biodegradability, biocom-
patibility, and nonimmunogenicity.
Cell-based clinical therapies using mesenchymal stem cells have
used several approaches. Tissue-engineering approaches have been used
where stem cells are seeded into 3D scaffolds in order to generate func-
tional tissues for replacement of defective tissues. Another approach has
used stem cell transplantation to replace defective host cells. The proper-
ties of stems acting as cytokine/growth factor producers have also been
investigated to stimulate repair or inhibit degenerative processes.