Key Engineering Materials Vols. 361-363

Abstract: For dental/orthopedic implants to achieve better bone apposition and bone-implant bonding, various approaches to improve titanium surfaces have been developed. Recently, a fluoridated hydroxyapatite (FHA) coating on titanium (Ti) implants was made by sol–gel method and shown to be a possible applicative bone implant. The purpose of the current study was to evaluate biological responses and biomechanical bonding strength of FHA coated Ti implants as compared with that of the conventional Ti alloys and hydroxyapatite (HA) coated Ti implants. In vitro assays were made using human osteoblast-like cell (MG63) culture on different implants with cell attachment, morphology and differentiation evaluations. The implant plates were also implanted into the proximal metaphysis of New Zealand White rabbit tibiae. After 8 and 16 weeks implantation, mechanical and histological assessments were performed to evaluate biomechanical and biological behavior in vivo. The results showed that the cell adhesion and cell growth rate on the FHA and HA surface was higher than that on cp Ti surface (p<0.01), and insignificant difference was observed between two coated groups. Mechanical test demonstrated that the FHA implants had a higher interface shear strength than the both controls at 8 and 16 wks, with no significant difference with HA-Ti. Histologically, the coated implants revealed a significantly greater percentage of bone-implant contact when compared with the uncoated implants. Results demonstrated that the new FHA surface improved cell adhesion and proliferation. The coating exhibited a bioactive mechanical and histological behavior at bone-implant interface, suggesting that a useful approach by combined coating processes could optimize implant surfaces for bone deposition and early implant fixation.

Abstract: One of the techniques for modifying Ti implant surface is an anodization. This method is an electrochemical one that forms rough, thick, and porous oxide films. To compare the gene expression from the cells cultured on the different implant surface, cDNA microarray have been performed. MC3T3-E1 cells were cultured on titanium disks. The control groups were cultured on the machined surfaces(MS). The experimental groups cultured on the anodized titanium surfaces(AS). Microarray assay 48 hours after culturing the cells on the machined surface and anodized surface revealed that osteoinductive molecules appeared more prominent on the anodized surface, whereas the adhesion molecules on the biomaterial were higher on the machined surface than anodized surface, which will affect the phenotype of the plated cells depending on the surface morphology.

Abstract: Because of its high biocompatibility, hydroxyapatite(HA) has been considered as a good blasting material. DNA microarray is a new molecular technology that enables the analysis of gene expression in parallel on a very large number of genes, spanning a significant fraction of the human genome. It is a qualitive analysis (e.g. it can differentiate each single gene) and quantitative, since it has the sensitivity to detect a change of expression level in the investigated cells when compared to normal samples. The aim of this study is to define the cell attachment and the genetic effect of machined surface implant and RBM (resorbable blast media) surface implant on the osteoblastic cell (MC3T3-E1 osteoblastic cell line) by cDNA microarray slide containing 21575 genes. Cells were cultured on machined grade 4 titanium disks(Group 1, machined surface) and disks of RBM (Group 2) and the samples were moved to new dishes and media were added and the plated disks were cultured for 24 hours. Total RNA extraction was performed with Qiagen mini kit (Qiagen, Chatsworth, CA, USA) for microarray assay. Microarray assay after culturing the cells on the machined surface and RBM surface revealed that osteoinductive molecules appeared more prominent on the RBM surface, whereas the adhesion molecules on the biomaterial were higher on the machined surface than RBM surface.

Abstract: The aim of this study was to evaluate the biocompatibility with the proliferation of osteoblast-like cell (MC3T3-E1) on zirconia/alumina nanocomposite (NANOZR) in comparison to yttria stabilized zirconia (3Y-TZP) and titanium (Ti). Cellular proliferations after 1-, 3-, 6-, and 9-day incubation were calculated from the measurement of the MTT activities of the proliferated cell and were analyzed by two-way ANOVA. Time-dependent proliferation of MC3T3-E1 in all the sample was observed in all three materials with culture days. However, these were no significant differences in the proliferation between three kinds of material, indicating all the materials have a similar-good biocompatibility.

Abstract: The purpose of this study was to evaluate the cytotoxicity of nanometer magnetic composite via being cultured with osteoblast-like cells (MG-63). The osteoblast-like cell (MG-63) was utilized as the seed cell. The cells were cultured on the surface of nanometer magnetic composite. After union culturing, on the day 1, 3, 5, 7, the cytotoxicity of nanometer magnetic composite was evaluated by MTT method and the cell morphology was observed by SEM. Meanwhile, on the day 4, 7, 10, the alkaline phosphatase (ALP) activity was tested respectively. These results demonstrated that the typical cell morphology could be observed when the osteoblast-like cells were cultured on nanometer magnetic composite substrate in vitro. Cell proliferation and ALP activity became higher as the prolongation of cultivate time in the group of nanometer magnetic composite. The study showed that nanometer magnetic composite had a little inhibition to cell proliferation and ALP activity in vitro cell culture, as compared with the chitin and PLA fiber substrate. So the feasibility of nanometer magnetic composite as scaffold for bone tissue engineering should be studied further.

Abstract: It is well known that the cellular responses are related with both physical and chemical characteristics of substrate, including surface topography. In the present study，the effect of surface topography of hydroxyapatite (HA) on rat bone marrow cell (rBMCs) response was investigated. HA disc-shaped pellets with various topography were manufactured by single-axis pressing methods. The rBMCs responses on materials including cell morphology and proliferation were evaluated by SEM and MTT methods respectively, and the differentiation potential was assessed by total protein content and alkaline phosphatase (ALP) activity testing. The results showed that the cell porliferation was higher on HA surfaces with macropore structure, while ALP activity was lower. No significant difference in the cellular responses on the pore distribution and orietation was observed. However, the pore structure had a potential to guide cell orientation by gathering the cells inside the pores rather than on the ridges. Since ALP served as an indicator of early osteoblast differentiation, in this study its higher expression on HA surface with micropores suggested that surface microtopograhy exhibited an important effect on early osteoblast differentiation process.

Abstract: The aim of this study was to evaluate the cytocompatibility, cell ingrowth and extracellular matrix deposition of a newly developed porous bioactive glass as a bone substitute. Two types of bioactive glass, different in their pore size (75 and 20 ppi, resp. ~350 and ~1200 $m), were used in this study. The materials were seeded with human osteoblastic (MG63) and fibroblastic (M-228 F01 and M-191 F01) cell lines. The cells were visualized by two techniques, scanning electron microscopy and confocal microscopy. For confocal microscopy cell nuclei were labeled with propidium iodide (IP) and the extracellular matrix components (type I collagen and osteocalcin) by specific antibodies. Cells and matrix were visualized by fluorescence. The bioactive glass used in this study was shown to be non cytotoxic. Cell growth and colonization at the surface and in the depth of the material were observed. Extracellular matrix deposition was also demonstrated which proved the proper biofunctionality of the biomaterial. Scanning electron microscope allowed us to visualize cells at a high magnification at the surface of the bioglass and evidenced that the biomaterials were covered by a sheet of cells with their matrix; on the other hand, confocal microscopy permitted us to observe cell ingrowth and matrix deposition within the depth of the substitute. We showed that extracellular matrix was synthesized mainly in the upper levels where the cell population was the most confluent. In summary, this porous bioglass appears promising for bone substitution.

Abstract: The initial osteoblast like cell response to bioactive nano-sized hydroxyapatite (HAp) and bioinert zirconia was evaluated with the cell morphology by SEM and cell adhesion proteins by fluorescence microscopy. Surface roughness also measured by a confocal laser microscopy. The surface roughness and topography was almost identical among specimens. The nano-sized HAp specimens showed better initial cell adhesion and activity than bioinert zirconia ceramics.

Abstract: Real time adsorption behaviors of six proteins with different isoelectric points on hydroxyapatite (HAp) nanocrystal surfaces have been investigated by using HAp sensors for quartz crystal microbalance with dissipation technique (QCM-D). The dissipation (D)–frequency (f) plots clearly showed that the different types of protein adsorption behaviors; the D-f plots of acidic proteins lie on one straight line with a constant slope under all initial protein concentrations, while those of neutral and basic proteins lie on two straight lines with different slopes. The acidic proteins formed a monolayer, while the neutral and basic proteins could cause conformational changes with the adsorbed amount of proteins. The QCM-D technique with novel HAp nanocrystal sensor is useful for the liquid phase changes of proteins on the surface.

Abstract: Bone remodelling is a coupled process of bone formation and resorption. This process is physiologically controlled and involves the synthesis of bone matrix by osteoblasts and bone resorption by giant cells called osteoclasts. It includes a complex interaction of cells, with specific chemokine signalling. In order to study bone remodelling in vitro, we cultivated two precursor cellline types in a model coculture system on synthetic hydroxyapatite ceramic (HA) for 14 days. The monocytes have the capacity to differentiate into osteoclast-like cells, and the bone marrow stromal cells can differentiate into osteoblast-like cells. This coculture was used to analyse the in vitro cell interaction between monocytes and stromal cells. Furthermore, the attachment of the bone marrow stromal cells to the resorbed HA-surfaces was studied. In this in vitro study we demonstrated osteoclast-like differentiation and bone marrow stromal growth in a coculture system on a synthetic bone substitute material. Under optimal conditions, HA can be resorbed and bone marrow cells can grow into the lacunas to form new bone. These results give important cues for the adjustment of synthetic bone substitute materials for optimal remodelling behaviour.