Study Of Macroporous Carbonated Hydroxyapatite Cement

ObjectiveTo increase the macroporosity by adding polyglycolide acid(PGA) microspheres into carbonated hydroxyapatite(CHA) cement to prepare macroporous carbonated hydroxyapatite (MCHA) cement. (1) Test the physicochemistry characteristics of MCHA cement. (2) Test the Biomechanical and macroporous characteristics of MCHA cement after PGA degraded. (3) Evaluate the biocompatibility of MCHA cement. (4) Study the degradation and bone formation ability of MCHA cement used in rabbit distal femoral bone defect.MethodsPhysicochemical examination of MCHA cement: Preparation and physicochemical characteristics of setting time, compression strength, setting temperature and porosity were evaluated in vitro. Product of MCHA cement were tested by scanning electron microscope (SEM), X-ray diffraction and Fouriery transform infrared analysis.Biomechanical and macroporous characteristics of MCHA cement after PGA degraded: Measure length, width and height of specimens;then the specimens were immersed in physiological solutions for 16 weeks. Three dimensions were measured again. The macroporosity MCHA was obtained by formulas. Strength, PH of solution measured and the morphous of pores was observed by SEM.Biocompatibility evaluation of MCHA cement: hemolytic test, thrombotest and pyrogen test was performed with MCHA cement extracting solution. Rabbit marrow stroma cells were cultured with MCHA cement extracting solution or cement specimen. Cell relative growth rate was measured by MTT methods. Cement specimens were implanted in rabbit muscle to evaluate inflammation reaction.Application of MCHA cement in rabbit distal femoral bone defect as graft: Bilateral distal femoral bone defects of rabbits were made. The defects were filled with MCHA or CHA. Specimens of distal femoral were retrieved at 1, 2 and 3 months after operation. X-ray were tested. Degradation of MCHA cement and new bone formation morphometry and dynamic parameter were evaluated in nondecalcified section.ResultsPhysicochemical property examination of MCHA cement: MCHA cement set in situ without heat emission under room temperature. As the increasing of PGAvolumn fraction, initial setting time and final setting time was shorter. When PGA volumn fraction was 60%, initial setting time was 4.5min and final setting time was 9.1min. The compression strength reach maximum of 30 MPa on 7 days more than 1 day. As the increasing of PGA, the compression strength descended. Porosity increase a little compared with CHA cement. The product of MCHA was still CHA as show by SEM, XRD and FITR.Biomechanical and macroporous characteristics of MCHA cement after PGA degraded: After 16 weeks, PGA micropheres was almost degraded. Macropores appeared on the surface and in the MCHA cement. When PGA volumn fraction was 60%, the macroporosity was 56.1% and the total porosity reached 70.4%;while seldom macropores in CHA. The compression strength was 6.8Mpa more than the strength of cancellous bone graft. Partially interconnected network of macropores formed in MCHA(300um) were observed by SEM. The solution PH was almost neutral.Biocompatibility evaluation of MCHA cement: Hemolytic test, thrombotest and pyrogen test was normal. Rabbit marrow stroma cells grew well when cocultured with MCHA cement extracting solution or cement specimen. No cytotoxity was found in cell culture. MCHA cement specimens were implanted in rabbit muscle. Lymphocytes infiltrating and fibular capsule formation could be seen in the early stage and lymphocytes decreased or disappeared and capsule became stability in the late stage.Application of MCHA cement in rabbit distal femoral bone defect as graft: There was no animals died in the test. No articular surface collapsed and no bone fracture in 1, 2 and 3 months specimens. The bone infiltration was obvious in MCHA, bone infiltration and cement degradation was observed by naked eyes. Only some bone ingrowth in edge of CHA was found and the degradation was not obvious. X-ray show the MCHA cement resorbed rapidly and bone ingrowth was obvious while the CHA resorbed slowly. There were more osteoblasts and osteoclasts in MCHA cement group than CHA group. The cement area decreased to 78.8% at 1 month and 31.69% at 3 month. A lot of fluorescence materials were observed in MCHA, showed the new bone formation was active and bone rebuilding was also active.Conclusion1. MCHA has good performance of setting in situ without heat emission. It has moderate compression strength before degradation. It has enough strength to fill non bearing bone defect.2. Partially interconnected network of macropores formed in MCHA(300um) after degradation and the compression strength is still more than cancellous bone graft. There is no acid injury after MCHA degradation.3. MCHA cement has good Biocompatibility.4. MCHA cement is rapidly resorbed in animal and new bone form at the same time.