Biomedical Engineering Reference
In-Depth Information
TABLE 9.17
Major Causes of Failure of Total Joint Replacement Devices
Causes of failure for total joint replacement devices
Biological reaction at implant/tissue interface
Properties of the implant surface
Infection
Surgical technique employed
Dislocation and implant fracture
Host tissue fracture
nonmineralized connective tissue forms in the border zone in contact with the implant,
resulting in micromotion at the implant/tissue site and eventual implant failure.
The brittleness of bioactive glasses and glass-ceramics coupled with their limited com-
positional ranges for bioactivity have limited their possible improvement in mechanical
properties. However, there continues to be interest in their development and application
as coatings on load-bearing metallic implant surfaces due to their inherent bioactivity and
surface reaction layers, which have the potential to significantly retard the rate at which
the border zone is converted into nonmineralized connective tissue.
Bioactive glass or glass-ceramic coatings on metallic substrates offer significant improve-
ments in bioactivity but have been difficult to develop due to thermal expansion coefficient
(TEC) mismatch, limited coating adhesion, and difficulty in precisely controlling the coat-
ing structure (heterogeneous coatings) [25].
Topological Modifications (Surface Roughness)
The development of dental implants from machine-smoothed parts into parts with pre-
cisely defined surface roughness provides an indication to possible benefits of topological
modifications.
Surface roughness has been attributed to providing better mechanical stability due to
higher interfacial surface contact for protein absorption, resulting in enhanced stimulation
of bone during the healing process. Surface roughness has also been shown to directly
regulate cell-material interactions by effecting cell shape, cellular attachment and result-
ing proliferation, and ECM production.
Engineered topological (surface roughness) features can be divided into two features of
scale:
1. Micron to submicron features (1- to 10-μm-sized grooves, microthreaded designs,
and macroporosity; 0.1- to 1.0-μm-sized etched features)
2. Nanofeatures
Nanofeatures have been shown to directly affect adsorption of proteins and will be dis-
cussed in Section 9.7.
Bioactive Glass Coatings on Metallic Implants
An approach to introduce surface bioactivity on load-bearing surface of metallic implants
(e.g., dental and total joints) has been to apply thick (>100 μm) bioactive glasses as coatings
on metallic implant surfaces. These coating can be useful for a number of reasons:
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