Study Of Injectable Carbonated Hydroxyapatite

PurposeBy adding additives in carbonated hydroxyapatite (CHA) cement to increase its rheology to prepare injectable carbonated hydroxyapatite (ICHA) cement. (1) Test the physicochemistry characteristics of ICHA cement. (2) Evaluate the biocompatibility of ICHA cement. (3) Biomechanical appreciation of ICHA cement used in distal radius fracture. (4) Study the mechanical stability, degradation and bone formation ability of ICHA cement used in goat lateral tibial plateau compression fracture.Materials and MethodsPhysicochemical examination of ICHA cement: Physicochemical characteristics of setting time, compression strength, injectability, anti-washout, consistency, setting temperature and porosity were evaluated in vitro. Product of ICHA cement were tested by scanning electron microscope (SEM), X-ray diffraction and Fouriery transform infrared analysis.Biocompatibility evaluation of ICHA cement: Marrow stroma cells were cultured with ICHA cement extracting solution or cement specimen. Cell relative growth rate was measured by MTT methods. Cement specimen were implanted in rabbit muscle to evaluate inflammation reaction. Hemolytic test and pyrogen test were performed.Biomechanical evaluation of ICHA cement in distal radius fracture: human distal radius fracture models were made and fixed with Kirschner wire, ICHAcement or ICHA cement combined with Kirschner wire. Torsion and compression test were performed. Torsion rigidity, maximum torque, maximum torsion angle, compression rigidity, compression strength of 2mm displacement, maximum compression strength and rotational angle of distal fragment was recorded.Application of ICHA cement in goat lateral tibial plateau compression fracture: Bilateral tibial plateau compression fractures were made in ten goats. The fractures were reduced and fixed with ICHA cement or autograft. Specimens of tibial plateau were retrieved 3 months and 6 months after operation. X-ray and tibia plateau compression rigidity were tested. Degradation of ICHA cement and new bone formation were evaluated in nondecalcified section.ResultsPhysicochemical property examination of ICHA cement: ICHA cement set in situ without heat emission under room temperature. Its initial setting time is 9 min and final setting time is 15 min, which is the same with CHA cement. The compression strength is about 20 MPa on 1 day and reach maximum of 35 MPa on 7 days. Porosity increase a little compared with CHA cement. Compared with CHA cement, ICHA cement has excellent injectability. The injectability coefficient is more than 95% for ICHA, and only 70% for CHA. At the same time, ICHA cement is a kind of anti-washout cement. It can not be washed out if the paste is immersed in distilled waster immediately after mixing. ICHA cement has lower consistency compare with CHA cement during setting process (P<0.01). The push force when injecting ICHA cement from syringe is proportion to syringe diameter and catheter length. The product of ICHA is still CHA as show by SEM, XRD and FITR.Biocompatibility evaluation of ICHA cement: Marrow stroma cells grow well with toxicity rank zero to I when cocultured with ICHA cement extracting solution or cement specimen. The hemolysis rate is no more than 0.05% and no pyrogenetic reaction after injecting extracting solution into vein of rabbit. ICHA cement specimens were implanted in rabbit muscle for 24 weeks. Lymphocytes infiltrating and fibular capsule formation can be seen in the early stage and lymphocytes decrease or disappeared and capsule became stability in the late stage.Biomechanical evaluation of ICHA cement in distal radius fracture: At the range of no more than 10 degree, the torsion rigidity and maximum torque is higher in ICHA group and ICHA combined with Kirschner wire group (P<0.01) than Kirschner wire group. The maximum torsion angle is lower in ICHA group and ICHA combined with Kirschner wire group with 4~5 degree than Kirschner wire group with 9.5 degree (P<0.05). Compression rigidity, distal fragment rotation angle in coronal or sagittal plate has no...