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A comparison of fibrous tissue formation surrounding intraperitoneal and subcutaneous implantation of ALCAP, HA, and TCP ceramic devices.

It is well demonstrated in the literature that ceramic drug delivery systems are highly compatible and non-immunogenic. Recent studies in our laboratory have documented the need of an experiment comparing foreign body reactions of several different types of ceramics used for implantation and/or drug delivery. The specific objective of this study was to compare the subcutaneous (s.c.) and intraperitoneal (i.p.) foreign body reactions and biocompatibility of the following implantable materials presently used in orthopedics: ALCAP (aluminum calcium phosphate), HA (hydroxyapatite), and TCP (tricalcium phosphate). The rats were divided into four groups: Group I consisted of 10 rats implanted with ALCAP i.p. and s.c., Group II (n = 10) animals were implanted i.p. and s.c. with HA, Group III consisted of 10 rats implanted i.p. and s.c. with TCP, and Group IV consisted of 10 control animals that were housed under the same environmental conditions as the three experimental groups. At 90 days post-implantation, rats in all four groups were euthanized. The microscopic evaluation of the fibrous tissue surrounding i.p. and s.c. implants revealed the following: 1) all of the ceramic devices had varying degrees of fibrous capsule formation at the time of sacrifice, 2) the thickness of the fibrous tissue capsule was dependent on the type of ceramic used, and 3) the thickness of the fibrous tissue capsules around the subcutaneous devices differed remarkably from implants placed intraperitoneally. The data from this study indicates that capsule formation is dependent upon factors such as ceramic composition and surgical implantation site.