Biomedical Engineering Reference
In-Depth Information
this characteristic crystalline structure of TiO 2 , it was mentioned that good osseo-
integration, bony apposition, and cell attachment of Ti implant systems [Meachim
et al., 1973; Albrektsson et al., 1987] are partially due to the fact that the oxide
layer, with unusually high dielectric constant of 50-117, depending on the TiO 2
concentration, may be the responsible feature [Kasemo, 1983; Lausmaa, 1986].
5.4 OSSEOINTEGRATION AND BONE/IMPLANT INTERFACE
Broadly speaking, two types of anchorage mechanisms have been described:
biomechanical and biochemical. Biomechanical binding is when bone in-growth
occurs into micrometer sized surface irregularities. Realistically, the term osseo-
integration probably best describes this biomechanical phenomenon. Biochemi-
cal bonding may occur with certain bioactive materials where there is primarily
a chemical bonding, with possible supplemental biomechanical interlocking. The
distinct advantage with the biochemical bonding is that the anchorage is accom-
plished within a relatively short period of time, while biomechanical anchorage
takes weeks to develop. This would clinically translate into the possibility of
earlier restorative loading of implants. Most commercially available implants
depend on biomechanical interlocking for anchorage. All implants must exhibit
biomechanical as well as morphological compatibility [Albrektsson, 1983; Oshida
et al., 1994].
Defi ning the nature of biomaterial surfaces is crucial for understanding inter-
actions with biological systems. Surface analysis requires special techniques and
instruments considering the analysis of a 50 Å thick region in one mm, two areas
on the surface of a specimen that is one mm in total thickness. Devices intended
to be implanted or interfaced intimately with living tissue may be composed of
a variety of materials. Understanding the biological performance and effi cacy of
these biomaterials requires a thorough knowledge of the nature of their surfaces.
The nature of the surface can be described in terms of surface chemistry, surface
energy, and morphology [Ratner et al., 1987].
The biological events occurring at the bone-implant interface are infl uenced
by the topography, chemistry, and wettability of the implant surface, as seen in
the above. A goal of biomaterials research has been, and continues to be, the
development of implant materials which are predictable, controlled, guided, with
rapid healing of the interfacial tissues, both hard and soft. The performance of
biomaterials can be classifi ed in terms of the response of the host to the implant,
and of the behavior of the material in the host. This is actually related to which
side is being observed at the host (vital tissue)/foreign materials (implant)
interface.
The event that occurs almost immediately upon implantation of metals, as
with other biomaterials, is adsorption of proteins. These proteins come fi rst from
blood and tissue fl uids at the wound site, and later from cellular activity in the
interfacial region. Once on the surface, proteins can desorb (undenatured or
denatured, intact or fragment), remain, or mediate tissue-implant interaction
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