Self-setting apatite bone substitute is calcium phosphate hardening, biocompatible, super formative material. This material is made of a mixture of a-tricalcium phosphate and tetracalcium phosphate as powder, and a solution of 65%, 83%, or 98% deacetylated chitosan in citric acid as liquid. The kneaded material first becomes gum-like, and then hardens in about 8 minutes.
The sample rods were 1.5mm in diameter and 3mm in length. They were implanted in the subcutaneous tissue in the backs of rats.
1) control: sintered hydroxylapatite.
2) samples:
(1) hardening material: mixture of the powder and each solution, implanted after hardening.
(2) non hardening material: mixture of the powder and each solution, implanted before hardening.
Decalcified sections of tissue, taken from the backs at 1, 2, and 4 weeks and 3 months, were stained by hematoxylin and eosin, and evaluated.
The results are summarized as follows.
1) At 1 week postoperative, small round cells (SRC) were very prominent in all materials.
2) At 2 weeks postoperative, SRC were seen less around the control and 98% or 83% deacetylated chitosan hardened materials than around 65% deacetylated chitosan or non-hardened materials.
3) At 4 weeks postoperative, fibrous tissues were seen around all materials but were less prominent around 65% deacetylated chitosan hardened material and 3 types of non-hardening materials.
4) At 3 months postoperative, fibrous tissue was seen around allmaterials, but SRC were also seen, with the fibrous tissue, around non-hardening material.
We concluded that no SRC were seen around the 83% or 98% deacetylated chitosan in citric acid as the liquid for the hardening materials, and this was responsible for the fibrous tissues. SRC was seen around the non-hardening materials for a long time. From these findings, it was concluded that it is desirable to use the highly deacetylated chitosan in citric acid as the liquid for hardening materials, or wait until after the material has hardened for clinical application.
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