Key Engineering Materials Vols. 336-338

Abstract: Porous biodegradable scaffolds are widely used in bone tissue engineering to provide temporary templates for cellular attachment and matrix synthesis. Ideally, the degradation rate in vivo may be similar or slightly less than that of tissue formation, allowing for the maintenance of the scaffold structure and the mechanical support during early stages of tissue formation. Eventually, the 3-D spaces occupied by the porous scaffolds will be replaced by newly formed tissue. In this work, β-tricalcium phosphate/Poly-L lactide (β-TCP/PLLA) scaffolds with different proportions of β-TCP to PLLA were investigated. The effects of β-TCP proportions on degradation rate and mechanical strengths of the scaffolds were evaluated in simulated body fluid (SBF) at 37°C up to 42 days. Results show that: different proportions of β-TCP to PLLA have significant influence on degradation behaviors of the scaffolds, and mechanical strengths of the scaffolds with weight proportion of β-TCP to PLLA being 2 to 1 are much higher than those of the others during the degradation period. And in this period, the scaffolds biodegrade slowly, and Hydroxyl Carbonate Apatite (HCA) forms in the surface of the material.

Abstract: In this article, a multilayer tissue engineering scaffold has been fabricated. The uppermost layer is consisted by the collagen and the downmost layer is consisted by the collagen/hydroxyapatide. Between the two layers, there have several continues changed collagen/HA layers at different ratio. These gradient scaffolds have been made by the freeze dried method. The morphology of the multiphase scaffold has been observed by the SEM. The chondrocytes from New Zealand rabbit knee joint were separated, harvested and cultured on the top layer of the scaffold. The histological and the immunohistochemical testing show that the chondrocytes keep its normal type in the 2 culture weeks.

Abstract: The surface dissolution of hydroxyapatite ceramics in distilled water was investigated by using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The disks made of hydroxyapatite powder were sintered at 1200oC for 2 h in air with under moisture protection. After sintering, the disks were polished to smoothness using 1 μm diamond and they were soaked in 40 ml of pH 7.4 distilled water at 37oC for certain period of time. The morphological change of hydroxyapatite surface, specifically at the initial stage of immersion, and related surface roughness were observed with immersion time. The present study suggested that an artificial fact like surface scratch in this case initiated to be eliminated prior to the surface dissolution along grain boundary. That is, the surface roughness decreased at the initial stage of immersion, and then increased due to the surface dissolution.

Abstract: In order to assess the behavior of ceramic fibers that are respired and accumulate in the lung, the solubility of bio-soluble CaO-MgO-SiO2 system ceramic fibers was determined by measuring the concentrations of the main components in the Gamble solution after different solution periods. The effect of ZrO2, TiO2, B2O3, Al2O3 and the different CaO/MgO ratio of fibers on the solubility of the ceramic fibers were investigated. The results indicated that the pH value of the Gamble solutions increase with the increasing of solution time. CaO, MgO, SiO2 in the ceramic fiber have greater solubility. The existence of ZrO2 and Al2O3 in the fibers would reduce the solubility of the fibers, and the existence of TiO2, and B2O3 in fibers will benefit the solubility of the fibers.

Abstract: Ag+-doped TiO2 films on stainless steel were prepared by a sol-gel method and their microstructures and compositions were studied with X-Ray Diffractometer, Scanning Electron Microscope (SEM) and X-ray Photoelectron Spectroscopy. It was shown that Fe atoms in untreated stainless steel react with Ag+ in the TiO2 film and form FeTiO3, which has an acicular crystal form under SEM observation. As a result, Ag+ in the film is reduced to the silver atom, which degrades the antibacterial property of the film. However, after an oxidization of the substrate, a layer of ferric oxide is formed, which reacts with Fe atoms that would otherwise react with and reduce Ag+, and then forms FeTiO3. Thus, the penetration of Fe atoms is stopped and Ag+ in the anatase-structure TiO2 film is protected from the reduction, which enhanced antibacterial property of the film.

Abstract: In this paper, antibacterial agent of silver-carrying nano-hydroxyapatite is synthesized by an ion exchange reaction, which is mixed thoroughly with a commercial glaze for antibacterial ceramics. The valence states of Ag in antibacterial agent are confirmed to be +1 and 0 by XPS. Antibacterial effect against bacterium of E. coli is also tested. Experimental results indicate that the antibacterial ceramics exhibit excellent antibacterial performances, with bactericidal rate of 99.92%.

Abstract: Porous HAp scaffolds have been prepared by using the slurry including HAp and magnesia based on the replication of polymer sponge substrate. The influence of HAp and MgO content in slurry on the pore morphology and size, and density, porosity, and mechanical strength of porous HAp scaffolds was investigated. The obtained scaffolds with average pore sizes ranging 150 to 300 μm had open, relatively uniform, and interconnected porous structure regardless of HAp and MgO content. As the MgO content increased, the pore network frame of scaffolds became to be relatively stronger, even though the pore size was not much changed. The compressive strength of the scaffolds increased rapidly with the increase of MgO content at a fixed HAp content because of increasing the pore wall thickness and density of the scaffolds. As a result, the porosity, density, and compressive strength of the porous HAp scaffolds scaffolds prepared by the sponge method were significantly affected by the addition of MgO.

Abstract: Stir-froth-polymerization is a novel technique for producing highly porous ceramics, in which bubbles are formed by a mechanical frothing in aqueous slurry of ceramic powders. Many work had be done about the porosity, the permeability and the mechanical strength of the porous ceramics derived from this method, but there are still a lot of things remain unclear. This paper focuses on the mechanism of frothing, and the influence of parameters in the mechanical frothing. It was found that the stir time, the stir speed and the viscosity of the slurry have influence on the average cell-size and the distribution of them respectively. The average cell-size can be controlled in the range from 60 to 160 μm by adjusting the parameters.

Abstract: The bone tissue engineering scaffold was developed by compounded the type I collagen with the porous scaffold of the sol-gel derived bioactive glass (BG) in the system CaO-P2O5-SiO2. The resultant porous scaffold was treated in supersaturated calcification solution (SCS) to form the surface layer of hydroxyl-carbonate-apatite (HCA) since the type I collagen possessed good biocompatibility and bio-absorbability, and also, the ability of inducting calcium phosphates to precipitated inside and outside the collagen fibers where the collagen fibers acted as bio-macromolecules template for formation of bone-like inorganic minerals in nature bone such as: octo-calcium phosphate (OCP), tri-calcium phosphate (TCP) and hydroxyl-carbonate-apatite (HCA). On the other hand, the sol-gel derived bioactive glass also played an important role in formation of the above bio-minerals owing to its serial chemical reactions with the body fluid. The in vitro study in supersaturated calcification solution SCS indicated that the surface of the porous scaffold was able to induce formation of bone-like HCA crystals on the pore walls of the scaffold which possessed satisfactory cells biocompatibility.

Abstract: Tetrahedral amorphous carbon (ta-C) films were deposited onto Si(100) wafers by using filtered cathodic vacuum arc technique (FCVA). The influence of the negative bias voltage applied to substrates on film structures was studied by Raman spectroscopy, X-ray photoemission spectroscopy (XPS). The ta-C films showed maximal sp3 fractions 87%, the hardness and elastic modulus of the ta-C film is 72 and 480 GPa, respectively. In vitro measurements of contact angle and platelet adhesion were applied to evaluate the biocompatibility of the ta-C films in comparison with that of NiTi, 316L and pure titanium. The results show that the ta-C films have hydrophobicity and exhibit better hemocompatibility which are very suitable for biomedical applications.