Key Engineering Materials Vols. 330-332

Abstract: In this study, an exclusive sodium titanate (Na2Ti6O13) coating on titanium was fabricated by sol-gel method and evaluated in vitro. The coating was characterized by SEM and XRD. The bioactivity of the Na2Ti6O13 coating was evaluated by the biomimetic growth of apatite on its surface after soaked in an acellular simulated body fluid (SBF) for a period of time. In vitro osteoblasts culture was carried out to determine cytocompatibility by the measurement of the proliferation and alkaline phosphatase (ALP) activity of the cells. XRD patterns showed that Na2Ti6O13 was well crystallized when the coating was heated at 800°C. SEM observation exhibited that the Na2Ti6O13 coated titanium had a homogeneous surface without any cracks. After immersion in SBF, the apatite layer can be formed on the coating. The cells culture showed that the osteoblasts grew well on the Na2Ti6O13 coated titanium. It can be concluded that Na2Ti6O13 coating on titanium obtained by sol-gel method is bioactive.

Abstract: The adhesion of bone cells on substrate materials is generally measured by the removal torque and/or contact area between bone and implants. In this study, collagen was used as a surfacegrafting material on hydroxyapatite (HA) substrates to enhance the cell adhesion because the collagen is a major constituent of connective tissues and has been regarded as one of the most excellent coating materials for bone bonding. First, HA disks (10mmΦ x 1mm) were prepared and then collagen was immobilbized on the HA surface using an 3-APTES coupling agent to improve the adhesiveness of cells on HA disk surfaces. NIH 3T3 fibroblasts were seeded on the collagengrafted and non-grated HA disks and cultured in a Dulbecco’s modified eagle medium containing 10% fetal bovine serum for 3 hrs to evaluate the cell adhesion on the HA samples. The fibroblasts on the collagen-grafted sample were more spread than those on the non-grafted sample. It is believed that collagen-grafted HA surface provides suitable sites for cell attaching due to the high biocompatibility of collagen.

Abstract: Bone is a kind of biomaterial in nature. It behaves favorable strength, stiffness and fracture toughness which are closely related to its fine microstructure. SEM observation on a shankbone shows that the bone is a kind of natural bioceramic composite consisted of hydroxyapatite layers and collagen matrix. The observation also shows that the hydroxyapatite layers consist of many hydroxyapatite sheets and are arranged in a parallel distribution. The fracture toughness of the bone is analyzed based on the representative model of the microstructure of the bone and the idea of maximum pullout force. The analytical result shows that the long and thin shape as well as the parallel distribution of the hydroxyapatite sheets improves the maximum pullout force of the sheets and the fracture toughness of the bone.

Abstract: The antibacterial brushite-forming calcium phospahte cements (CPC) were prepared using an equimolar mixture of β-tricalcium phosphate (β-TCP) and monocalcium phosphate monohydrate (MCPM) with chlorine dioxide (ClO2) generating powders (sodium chlorite and mixed acid activator). The effect of ClO2 on cement setting time, compressive strength, and antibacterial property of novel antibacterial CPC was investigated. The use of 0.3M citric acid solutions as liquid phase enabled final setting times of 5~10 min. The setting time of antibacterial cement systems was prolonged with increasing the amount of antibiotic used. Dry compressive strength was found to be in the range between 9~15 MPa and increased with addition of ClO2 generating powders. Wet compressive strength was slightly decreased compared to dry compressive strength after immersion of cement samples in water for 24 h. The antimicrobial potency of the different cement formulations was investigated using the agar diffusion method. The acidic brushite cement itself showed the inhibitory effect for Streptococcus mutans. The inhibition zone was increased with the amount of ClO2 generating powders. These results indicate that our novel antibacterial CPC have the great potential to avoid the development of infections for preventive antibiotic therapy.

Abstract: The purpose of this study was to determine if a strontium (Sr)-containing mixing liquid could be used as an exchanging agent for calcium phosphate cement crystallized with Sr-replacing hydroxyapatite (Sr-HAP). Alpha-tricalcium phosphate (α-TCP) powder was mixed with Srcontaining and phosphorous (P)-containing solutions, that is, SrCl2 or SrCl2+CaCl2 solution and NaH2PO4 or Na2HPO4 solution. After storage in the incubator for 7 days, the α-TCP crystals in all set cements were confirmed to have been transformed to HAP crystals by the mixing liquids. The XRD patterns of the set cements implied that the Sr-HAP could be precipitated by using Srcontaining solutions as the mixing liquid because of the chemical shift of a peak (002) in XRD of the HAP crystal. The solubility (shaking immersion in physiological saline) of set cements containing Sr was markedly higher than that of set cement not containing Sr. These results revealed that the Sr-containing solutions used as mixing liquids for α-TCP cement acted as precipitating agents for Sr-HAP. Sr-HAP-precipitating cement could be useful because of its pharmacological activity with high solubility.

Abstract: The aim of this work was to assess the mixing, transfer and handling, properties, injectability, set time, wash-out characteristics, acceptance of hardware (i.e. stainless screws), and their delivery/transfer systems of self hardening synthetic bone cements made from calcium phosphate and calcium sulphate. Surgical procedures (i.e. cranioplasty) were performed on adult Labrador dogs using seven different bone cements from various manufacturers. Direct comparison of the defined intraoperative properties were evaluated and recorded. There is considerable variability with respect to application properties among commercially available injectable synthetic bone cements. Only one product was rated good to excellent in seven of the eight categories evaluated (6-excellent, 1-good, 1-fair) based on in-vivo tests. This study outlines the critical parameters required for successful implantation of cements that have to be understood when designing new injectable bone cements for the future.

Abstract: In this study, we attempted preparation and assessments of composite pastes of demineralized bone matrix (DBM) and calcium phosphate cement (CPC). While the composite pastes presented self-setting behavior up to a certain DBM content without significant differences in setting time, temperature increase and phase transformation, compressive strength and injection capability decreased in general with the DBM content. The DBM particulates were observed to uniformly disperse in the composite cross-sections, suggesting a new model of bioactive paste with tissue regenerative function.

Abstract: N,O-carboxymethyl chitosan (CMCTS) was added in Calcium phosphate bone cement (CPC). A preliminary study was carried out in order to evaluate the biocompatibility of CPC containing CMCTS. In vitro tests were done using extract liquid from normal saline. The result showed that the biological reaction complied with standards of GB/16886 and the composite might have good biocompatibility.

Abstract: Acrylic bone cements are used to fix joint replacements to bone. The main substance in acrylic bone cement is biologically inert poly(methylmethacrylate), PMMA. The dense PMMA polymer structure of cement does not allow bone ingrowth into cement. Therefore, the main focus of our studies is to modify acrylic bone cement in order to improve its biological properties e.g., by creating porosity in the cement matrix. The porous structure is in situ created using pore-generating filler (i.e., 20 wt% of an experimental biodegradable polyamide) that is incorporated in acrylic bone cement. The aim of this in vitro study was to investigate the biomineralization of acrylic bone cement modified using an experimental biodegradable polyamide.