Biomedical Engineering Reference
In-Depth Information
it is beneficial to culture cells on scaffolds rather than mixing them
just prior to the operation. 42 Accordingly, the scaffolds should be
highlybiocompatibletoallowcellattachment,growth,anddifferen-
tiation of the cells. Since the induction period is two to three weeks,
thematerialsshouldalsobestableforthisculture/inductionperiod.
Aftercelltransplantation,thescaffoldsaredegradedasnewbone
formation occurs, which continues until the scaffold is completely
degraded. This is the phase of actual bone regeneration. When
β
-
TCPgranulesareused,boneregenerationmaycontinueforuptoone
year. During this stage, the scaffold seems to be directly degraded
by resorption by osteoclastic cells. Compared with the dissolution
by interstitial fluid, this process might be favorable since morphol-
ogy of the tissue is maintained. To accelerate this active resorption
process of the scaffold, the scaffold should mimic bone and be pre-
sented as a target tissue for osteoclasts. Ceramic-based materials
might be advantageous since osteoclastic activities were confirmed
from in vivo studies.
The third phase starts when the scaffold is completely degraded
and the newly formed bone enters the normal remodeling process.
For clinical cases, stability of the regenerated bone for a longer
period is important. However, factors which affect stability are not
well known. It is known that mechanical stimuli such as dental
implant placement may help to maintain the volume of regener-
ated bone. Importantly, the shape of hard tissue should be compat-
ible with the covering soft tissues. Long-term changes of atrophic
alveolar bone shape result in a soft-tissue environment that con-
forms. Accordingly, immediate morphological changes after bone
regeneration may lead to increased pressure on the regenerated
bone and cause unexpected absorption. To prevent late absorption
of the regenerated bone, the resorption of the scaffold should be
longenoughuntilthesofttissuesurroundingthenewlyformedbone
becomes stabilized. From this point of view, scaffolds with a rela-
tively short degradation time, such as collagen, have disadvantages,
andtheirapplicationislimitedtoareaswithoutpressurefromadja-
cent soft tissues. Conversely, if scaffold degradation takes too long,
the bone regeneration process may be delayed and the mechanical
strengthoftheregeneratingtissuemaynotbeenoughtosupportthe
 
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