Host response - Orthopaedic Biomaterials in Research and Practice - page 339

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Host response

In addition to satisfying the physical and functional requirements
imposed by implant designs, biomaterials must be easily accepted by
the body. In fact, lack of acceptance—adverse host response—is com-
monly the limiting factor in the application of materials to solve biomed-
ical problems. For this reason, it is extremely important to gauge host
response, particularly materials aspects that are not directly dependent
on design details but that enlighten us concerning more general relation-
ships between biomaterials and living systems.
Implants must “couple” with the host to produce a host response; this
may happen in a variety of ways. The most obvious is through direct
chemical effects owing to corrosion, dissolution, or elution of the implant
component materials. Implants in particulate form, as in wear debris,
produce different tissue responses than they do in bulk form, with the
response to a degree independent of the chemical composition of the
particles. Mechanical factors, principally seen in remodeling responses
to initial changes in stress distribution, are also important to the require-
ments for biologic ingrowth and to local chemical, thermal, or pressure
necrosis. Electrical factors are usually not appreciated, except in the spe-
cial case of the use of implanted electrodes to stimulate osteogenesis.
The host responses may be classified as structural, physiological,
bacteriologic, immunologic, and carcinogenic. The responses are seen
most frequently in the immediate vicinity of the implant but may occur
systemically or at remote sites, such as the regional lymph nodes. The
following discussion will deal with responses primarily by location.
Most of what is known about host response to implanted biomaterials
results from animal studies. However, the emphasis will be placed on
what can be reliably deduced by comparing these laboratory results to
clinical findings.

Local host response

Normal response Implants are placed in intimate contact with soft tissue and bone. The

process of placing them (implantation) produces a wound. Thus, the