Effect of nanostructure on biodegradation behaviors of self-setting apatite/collagen composite cements containing vitamin K2 in rats.

Apatite cement and collagen were combined by a mechanochemical method to create a new self-setting apatite/collagen composite cement, and menatetrenone (VK2) was loaded into a drug-delivery system to test biocompatibility in rats. Powder X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and electron probe microanalyzer (EPMA) were performed to characterize the physicochemical properties of apatite/collagen composite cements. The XRD results suggested that ground apatite/collagen cement was completely transformed into bone-like hydroxyapatite, but that without grinding was incomplete. The SEM and EPMA results suggested that ground apatite/collagen cement was homogeneously dispersed of nanoapatite crystals in collagen matrices, similar to that in natural bone. In contrast, the cement without grinding was heterogeneously distributed. To evaluate in-vivo cement density (CMM), microradiograms were measured for 72 days after implanting apatite/collagen composite cements in intramuscular tissue on the backs of rats, and cross sections of the cements and surrounding soft tissues were observed by microscope. The CMM results of the apatite/collagen composite cements suggested that the biodegradation rate was dependent on the cement quality and nanogeometrical structure. The CMM result of VK2-loaded apatite/collagen cements suggested that the biodegradation rates of the cements were significantly dependent on their formulation. The CMM of ground apatite/collagen cement increased until 7 days and then decreased, and bone-like cells penetrated deeply in the center. The microphotograph and CMM results of apatite/collagen without grinding indicated that a lot of bone-like cells penetrated into the cement and the cement shape was totally deformed.