The Cell–Surface Interaction - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 22

adherent endotoxin to potentiate cytokine production, osteoblast differentiation
and bone loss induced by wear particles.
4 Tissue-Implant Interface
4.1 Interface Structure and Composition
The formation of bone at the implant interface was first defined by Osborne and
Newesley [ 110 ] in their description of distance and contact osteogenesis. Distance
osteogenesis describes the phenomenon whereby bone surfaces adjacent to the
implant provide a population of osteogenic cells, which through the process of
appositional bone growth encroach upon the implant. Ultimately, therefore, the
implant becomes surrounded by bone rather than bone forming de novo on the
implant surface. It is postulated that the outcome of distance osteogenesis is that
the surface will never actually have direct bone bonding since it will always be
obscured by ECM and prevailing cells. In contrast to distance osteogenesis,
contact osteogenesis describes the phenomenon whereby bone forms de novo on
the implant surface. Essentially, therefore, the implant must become populated by
osteogenic cells prior to matrix production can be initiated. Although both theories
describe distinct methods for bone to become juxtaposed to an implant surface, it
is likely that both methods are actually involved in implant osseointegration.
Since the peri-implant site becomes primarily encased in blood, the migration
of the cells will be via the fibrin network that is produced during clot formation,
and it is these cells that will ultimately afford the basis for the osteogenic cell
population required for differentiation. What is interesting is that since fibrin is a
by-product released into the implantation site to promote healing, one could
therefore assume that this protein would adhere to virtually all surfaces, and thus
osteoconduction could theoretically occur for any biomaterial; however, this is not
the case. As is the case with dermal wound healing, cell migration is associated
with subsequent wound contraction; thus, migration of cells on a provisional fibrin
matrix results in its subsequent withdrawal (Fig. 6 ), preventing further migration,
and ultimately osteogenesis (see [ 111 ] for a review). It seems increasingly
apparent, therefore, that implant design is important in providing the correct
degree of anchorage for a transitory scaffold for the purpose of cell migration.
Therefore, the ability of a biomaterial surface to retain fibrin attachment during
this retraction phase is crucial in determining if migrating cells will reach the
device. It is suggested that the complexity of a microrough surface provides a 3D
topography so that fibrin remains sufficiently attached to the implant to withstand
retraction, allowing cell migration.
Once an osteogenic cell population is present at the surface, the next critical
step is the initial formation of a mineralized matrix. The method of de novo bone
formation at the implant interface is described by four principal phases and is