In a study model that aims to evaluate the effect of nanotopography on bone formation, micrometer structures known to alter bone formation, should be removed. Electropolished titanium implants were prepared to obtain a surface topography in the absence of micro structures, thereafter the implants were divided in two groups. The test group was modified with nanosize hydroxyapatite particles; the other group was left uncoated and served as control for the experiment. Topographical evaluation demonstrated increased nanoroughness parameters for the nano-HA implant and higher surface porosity compared to the control implant. The detected features had increased size and diameter equivalent to the nano-HA crystals present in the solution and the relative frequency of the feature size and diameter was very similar. Furthermore, feature density per microm(2) showed a decrease of 13.5% on the nano-HA implant. Chemical characterization revealed calcium and phosphorous ions on the modified implants, whereas the control implants consisted of pure titanium oxide. Histological evaluation demonstrated significantly increased bone formation to the coated (p < 0.05) compared to uncoated implants after 4 weeks of healing. These findings indicate for the first time that early bone formation is dependent on the nanosize hydroxyapatite features, but we are unaware if we see an isolated effect of the chemistry or of the nanotopography or a combination of both.

Early bone response to cylindrical smooth titanium implants (S(a)=0.1 microm) inserted into the rabbit tibia was compared in a stable and nonstable regime. Surface roughness parameters were calculated from measurements obtained with optical interferometry and atomic force microscopy. Contrary to our hypothesis, the nonstable implant showed higher bone to metal contact and increased bone area in the endosteal region compared with the stable implant after 4 weeks of healing. Bone area measurements in the cortical region revealed similar values. Primitive woven bone was found in close contact with both implants, but significantly more with the nonstable implant. Finding more bone-to-implant contact (BIC) need not necessarily indicate that unstable implants were more strongly integrated. Primitive bone stage development observed indicates less strong implant anchorage than could be expected from BIC percentage alone. Stable implant design used in this study is a reliable model to evaluate submicron and nanostructures in vivo, as implant stability was achieved in the absence of microirregularaties.

The current study indicates that the presence of open scaffold microporosity in HA, as determined by the fabrication process, enhances the ability of ceramic scaffolds to promote bone ingrowth and bone contact.

Nanohydroxyapatite materials show similar chemistry to the bone apatite and depending on the underlying topography and the method of preparation, the nanohydroxyapatite may simulate the specific arrangement of the crystals in bone. Hydroxyapatite (HA) and other CaP materials have been indicated in cases in which the optimal surgical fit is not achievable during surgery, and the HA surface properties may enhance bone filling of the defect area. In this study, very smooth electropolished titanium implants were used as substrata for nano-HA surface modification and as control. One of each implant (control and nano HA) was placed in the rabbit tibia in a surgical site 0.7 mm wider than the implant diameter, resulting in a gap of 0.35 mm on each implant side. Implant stability was ensured by a fixating plate fastened with two side screws. Topographical evaluation performed with an optical interferometer revealed the absence of microstructures on both implants and higher resolution evaluation with AFM showed similar nanoroughness parameters. Surface pores detected on the AFM measurements had similar diameter, depth, and surface porosity (%). Histological evaluation demonstrated similar bone formation for the nano HA and electropolished implants after 4 weeks of healing. These results do not support that nano-HA chemistry and nanotopography will enhance bone formation when placed in a gap-healing model. The very smooth surface may have prevented optimal activity of the material and future studies may evaluate the synergic effects of the surface chemistry, micro, and nanotopography, establishing the optimal parameters for each of them.

No abstract

The aim of the study was to compare Ca and P formation (CaP) and subsequent bone cell response of a blasted and four different possibly bioactive commercially pure (cp) titanium surfaces; 1. Fluoride etched (Fluoride), 2. Alkali-heat treated (AH), 3. Magnesium ion incorporated anodized (TiMgO), and 4. Nano HA coated and heat treated (nano HA) in vitro. Furthermore, to evaluate the significance of the SBF formed CaP coat on bone cell response. The surfaces were characterized by Optical Interferometry, Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). CaP formation was evaluated after 12, 24 and 72 h in simulated body fluid (SBF). Primary human mandibular osteoblast-like cells were cultured on the various surfaces subjected to SBF for 72 h. Cellular attachment, differentiation (osteocalcin) and protein production (TGF-beta(1)) was evaluated after 3 h and 10 days respectively. Despite different morphological appearances, the roughness of the differently modified surfaces was similar. The possibly bioactive surfaces gave rise to an earlier CaP formation than the blasted surface, however, after 72 h the blasted surface demonstrated increased CaP formation compared to the possibly bioactive surfaces. Subsequent bone cell attachment was correlated to neither surface roughness nor the amount of formed CaP after SBF treatment. In contrast, osteocalcin and TGF-beta(1) production were largely correlated to the amount of CaP formed on the surfaces. However, bone response (cell attachment, osteocalcin and TGF-F production) on the blasted controls were similar or increased compared to the SBF treated fluoridated, AH and TiMgO surface.

A B S T R A C T Aluminium is a lightweight material with high strength and good corrosion resistanceamong other beneficial properties. Thanks to these properties, aluminium is more extensively used in the vehicle industry. High-pressure die casting of aluminium is a manufacturing process that makes it possible to attain complex, multi-functional components with near-net shape. However, there is one disadvantage of such castings, that is, the presence of various defects such as porosity and its effect on mechanical properties. The aim of this work was to investigate the influence of porosity on the fatigue strength of high-pressure die cast aluminium. The objective was to derive the influence of defect size with respect to the fatigue load, and to generate a model for fatigue life in terms of a Kitagawa diagram. The aluminium alloy used in this study is comparable to AlSi9Cu3. Specimens were examined in X-ray prior to fatigue loading and classified with respect to porosity level and eventually fatigue tested in bending at the load ratio, R, equal to −1. Two different specimen types with a stress concentration factor of 1.05 and 2.25 have been tested.It has been shown that the fatigue strength decreases by up to 25% as the amount of porosity of the specimen is increased. The results further showed that the influence of defects was less for the specimen type with the higher stress concentration. This is believed to be an effect of a smaller volume being exposed to the maximum stress for this specimen type. A Kitagawa diagram was constructed on the basis of the test results and fracture mechanics calculations. A value of 1.4 Mpa m 1/2 was used for the so-called stress intensity threshold range. This analysis predicts that defects larger than 0.06 mm 2 will reduce the fatigue strength at 5 × 10 6 cycles for the aluminium AlSi9Cu3 material tested. A = area of the defect a = 'crack length', defect radius da d N = crack growth rate N = number of cycles to failure K = stress intensity factor K t = elastic stress concentration factor R = stress ratio (=σ min /σ max ) K = stress intensity range K th = stress intensity threshold range at approximately 10 −9 m/cycles σ n = nominal stress range σ an = nominal stress amplitude σ FL = fatigue strength at N = 5 × 10 6 cycles

The aim of the present study was to compare the nucleating and growing behaviour on four types of bioactive surfaces by using the simulated body fluid (SBF) model. Titanium discs were blasted and then prepared by alkali and heat treatment, anodic oxidation, fluoridation, or hydroxyapatite coating. The discs were immersed in SBF for 1, 2, 4 and 6 weeks. Calcium phosphates were found on all specimens, as analysed with scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX). After 1 and 2 weeks of SBF immersion more titanium was accessible with SEM/EDX on the blasted surfaces than the four bioactive surface types, indicating a difference in coverage by calcium phosphates. The Ca/P mean ratio of the surfaces was approximately 1.5 after 1 week, in contrast to the fluoridated specimens which displayed a Ca/P mean ratio of approximately 2. Powder X-ray diffraction (P-XRD) analyses showed the presence of hydroxyapatite on all types of surfaces after 4 and 6 weeks of immersion. The samples immersed for 6 weeks showed a higher degree of crystallinity than the samples immersed for 4 weeks. In conclusion, differences appeared at the early SBF immersion times of 1 and 2 weeks between controls and bioactive surface types, as well as between different bioactive surface types.