Maxillofacial Bone Regeneration Using Tissue Engineering Concepts - Engineered Bone: Tissue Engineering Intelligence Unit - page 193

replicating extracellular matrix. Growth factors are added to the in vitro system to encourage stem
cell proliferation. The engineered structure is then transplanted to the recipient.
For bone formation induced by marrow-derived MSCs has long been recognized to be
useful. 18,19 Recently, a method has been developed involving enzymatic liberation of marrow
cells from explants and their introduction into cell culture with subsequent expansion in cell
number. These cultured cells eventually differentiated into mature osteoblasts. 20,21 Therefore,
on this basis, it was considered advantageous here to transplant cultured MSC as a source of
osteoblasts, but the cellular implantation procedure was complicated by problems associated
with delivery vehicles. Optimally, delivery substances to be used for bone or cartilage replace-
ment or repair through tissue engineering would provide the same environment as bone matrix
in vivo and, additionally, would combine an appropriate rate of biodegradability with the
capacity of the respective cells to multiply.
Vacanti 22 and his group have engineered structures such as ear cartilage and a composite
distal interphalangeal joint among other structures using collagen gel. In our laboratory induc-
tion of bone tissue in athymic mice was attempted with MSCs and fibrin glue. Yamada 15 has
cultivated mesenchymal stem cells in vitro and seeded them in an injectable scaffold and fibrin.
After 16 weeks, the construct closely resembles the bone. The engineered structure is hard and
bone is evident histologically when the specimen is sectioned. Various growth factors in fibrin
glue related to wound healing have been found recently to support the growth, adhesion,
migration, differentiation, and vascularization. 23 There may be an advantage, then, to using a
cell/fibrin composite in that it has been suggested as more osteoinductive than cell suspension,
although both the composite and cell suspensions sequester and retain osteoinductive proteins
required to trigger molecular signals for local morphodifferentiation to promote calcification.
In the presence of fibrin glue, the results here support the greater osteoinductive capacity of
cell/extracellular matrix composites.
From these series of experiments, I can conclude that the cell and fibrin mixture can be a
interesting alternative to the conventional autogenous cancellous bone grafting especially in
category I bone defect. However, in categories II or II, the regenerated bone cell/fibrin mixture
have not enough mechanical strength. Tissue engineering is just at the beginning and many
problems remain to be solved before its clinical use.
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