Mats Halvarsson

Raloxifene and alendronate containing thin mesoporous titanium oxide films improve implant fixation to bone

This study tested the hypothesis that osteoporosis drug-loaded mesoporous TiO2 implant coatings can be used to improve bone-implant integration. Two osteoporosis drugs, Alendronate (ALN) and Raloxifene (RLX), were immobilized in nanoporous oxide films prepared on Ti screws and evaluated in vivo in rat tibia. The drug release kinetics were monitored in vitro by quartz crystal microbalance with dissipation and showed sustained release of both drugs. The osteogenic response after 28days of implantation was evaluated by quantitative polymerase chain reaction (qPCR), removal torque, histomorphometry and ultrastructural interface analysis. The drug-loaded implants showed significantly improved bone fixation. In the case of RLX, stronger bone-remodelling activity was observed compared with controls and ALN-loaded implants. The ultrastructural interface analysis revealed enhanced apatite formation inside the RLX coating and increased bone density outside the ALN coating. Thus, this novel combination of a thin mesoporous TiO2 carrier matrix and appropriate drugs can be used to accelerate implant fixation in trabecular bone.

In vivo biomechanical stability of osseointegrating mesoporous TiO(2) implants

Mesoporous materials are of high interest as implant coatings to receive an enhanced osseointegration. In this study, titanium implants coated with mesoporous TiO(2) thin films have been evaluated both in vitro and in vivo. Material characterization showed that, with partly crystalline TiO(2) (anatase), long-range-ordered hydrophilic mesoporous thin films with a pore size of 6nm were obtained. Evaluation of the mechanical resistance showed that the films were robust enough to withstand the standard implantation procedure. In vitro apatite formation was studied using simulated body fluids, showing that the pores are accessible for ions and that formation of apatite was increased due to the presence of the mesopores. An in vivo study using a rabbit model was executed in which the removal torque and histomorphometry were evaluated. The results show that the biomechanical stability of the TiO(2) coating was unaffected by the presence of mesopores and that osseointegration was achieved without any signs of inflammation.

Microstructural investigation of the κ-Al2O3 → α-Al2O3 transformation in multilayer coatings of chemically vapour deposited κ-Al2O3

Abstract The κ→ α transformation in different multilayer coatings of κ-Al 2 O 3 has been investigated. All the multilayers had the same total thickness (8 μm) but a different number of layers (8, 15 and 32). The transformation was studied with respect to (i) rate of transformation, (ii) transformation growth, (iii) morphology and (iv) the adhesion of the different layers. The rate of transformation is highly temperature dependent for all three multilayers and the transformation is 3–4 times faster at 1090 °C than at 1030 °C. The transformation is faster for 32κ, slower for 15κ and slowest for 8κ. There are two different types of preferential nucleations operating simultaneously on the top surface, both along the transgranular cooling cracks and as islands not in contact with cracks. The coatings transformed in all layers simultaneously, with the largest transformed volume in the outermost layer. This is explained by the larger free surface area on the top surface than between the layers where only interfacial pores exist. The α islands on the top surface are larger and have a larger spacing between them than the α islands at the κ-Al 2 O 3 -κ modification layer interfaces. This is attributed to the closely spaced small interfacial pores, which act as preferential nucleation sites for the transformation. For all three types of multilayers, having different surface roughnesses, the surface morphology did not change, except for intergranular cracking, during transformation. The extent of cracking within the layers was smaller than for thick single layers. It was also found that the adhesion decreased with increasing degree of transformation. The adhesion did not depend on the number of layers, but only on the α:κ ratio. In fracture surface specimens, the innermost alumina layer showed full adherence, which indicates that the adhesion is better for thin ( ≈ 1 μ m) transformed alumina layers than for thick transformed layers ( ≈ 4 μ m). All the other alumina layers flaked along the κ modification layers, possibly because of interfacial pores.

The influence of the nucleation surface on the growth of CVD α-Al2O3 and κ-Al2O3

In this work, in order to increase the understanding of the nucleation and growth of CVD alumina, three different types of specimen have been investigated by cross-section TEM. The alumina layers were deposited onto Ti(C,N) (i) with and (ii) without an intermediate α-bonding layer, and (iii) onto an intermediate Ti 2 O 3 layer. It was found that pure κ-Al 2 O 3 was obtained on the Ti(C,N) layer, while pure α-Al 2 O 3 was obtained on the α-bonding and Ti 2 O 3 layers. As the process parameters of the alumina deposition were the same in all cases, this demonstrates that the resulting alumina polymorph is governed by its nucleation on the intermediate layers. Pores could frequently be observed at the Ti(C,N)-Ti 2 O 3 layer interfaces, while no pores could be detected at the Ti 2 O 3 -α-Al 2 O 3 , Ti(C,N)-α-Al 2 O 3 or α-bonding-α-Al 2 O 3 interfaces. No orientation relationships between the grains in the α-bonding and the α-Al 2 O 3 layer could be found, while epitaxial growths of κ-Al 2 O 3 on Ti(C,N) and α-Al 2 O 3 on Ti 2 O 3 were frequently observed and are described as : (001) κ //(111) Ti(C,N) [010] κ1 , [310] κ2 and [310] κ3 //[011] Ti(C,N) (0001) α //(0001) Ti2O3 [1100] α //[1100] Ti2O3 Both orientation relationships describe close-packed planes growing on close-packed planes, with close-packed directions being parallel.

Microstructural investigation of CVD α-Al2O3/κ-Al2O3 multilayer coatings

Abstract Chemically vapour deposited multilayer κ-Al2O3 and multilayer α microscopy. Cross-section thin foils were prepared from alumina-coated cemented carbide cutting tool inserts. Special emphasis has been given to the examination of the α and κ polymorphs in the differen The thickness of each alumina layer was 1 μm. Grain refinement was obtained by the renucleation of Al2O3 on each modification layer. The microstructure of the α-Al2O3 layers consisted of equiaxed grains with a large number of dislocations and pores, while the κ-Al2O3 layers consisted of columnar twinned grains which were di randomly distributed, while the preferred growth direction of κ-Al2O3 was along the c axis. Observation of the growth of α-Al2O3 on both α- and κ-bonding a needle-shaped bonding layer. In both the α and κ multilayers, the occ the first alumina layer was directly related to the morphology of the bonding layer.

TEM investigation of the oxide scales formed on a FeCrAlRE alloy (Kanthal AF) at 900°C in dry O2 and O2 with 40% H2O

Abstract The base oxide scales on a commercial FeCrAl alloy oxidized isothermally at 900°C in dry O2 or O2 with 40% H2O were studied in detail using analytical electron microscopy. Electron transparent cross-section foils prepared with a FIB/SEM in-situ lift-out technique were investigated using STEM/EDX and CBED. The oxide scales on the samples exposed to dry O2 are slightly thinner than the scales formed in O2+H2O. The oxide scales exhibit a multilayered structure, with a Cr-rich layer in the middle, indicating the original metal/gas interface. An almost pure inner α-Al2O3 layer, containing columnar grains, was formed by inward oxygen diffusion, after exposures in both the dry and wet atmospheres. The outer oxide layer consisted of γ-Al2O3 in the wet case and of α-Al2O3/MgAl2O4 in the dry case. It is suggested that the α-Al2O3/MgAl2O4 phases resulted from a phase transformation of initially grown γ-Al2O3. The observations indicate that water vapour may stabilize the γ-Al2O3 phase.

Microstructural investigation of as-deposited and heat-treated CVD Al2O3

In this work, two different CVD A1203 coatings have been investigated: (i) as-deposited α-Al 2 O 3 ; and (ii) α-Al 2 O 3 produced by heat-treatment of as-deposited α-Al 2 O 3 . The aim was to describe and compare the detailed microstructure of these two α-Al 2 O 3 coatings using transmission electron microscopy (TEM). In the as-deposited α-Al 2 O 3 layer, the grains were columnar with a width of 1-2 μm, and a length of up to 5 μm. The grains in the transformed α-Al 2 O 3 layer were equiaxed, with a grain size of about 1 μm. Both α-Al 2 O 3 layers contained a large number of dislocations and voids. Linkage of voids was most apparent in the transformed α-Al 2 O 3 layer, which also contained a number of large cracks. During the κ-Al 2 O 3 → α-Al 2 O 3 phase transformation, the columnar grains in the κ-A1203 layer were transformed into columns of smaller equiaxed α-Al 2 O 3 grains, separated by low angle grain boundaries. It was concluded that the close-packed oxygen ion planes are preserved during the κ → α phase transformation, but the stacking sequence of these planes is changed from...ABAC... as in κ-Al 2 O 3 to...ABAB... as in α-Al 2 O 3 .

Determination of the thermal expansion of κ-Al2O3 by high temperature XRD

Abstract In this work, the thermal expansion of κ -Al 2 O 3 has been characterised using high temperature X-ray diffraction of κ -Al 2 O 3 powder obtained from crushed chemical vapour deposited κ -Al 2 O 3 coatings. The lattice parameters, volume, thermal linear and volume expansion coefficients have been determined in the range 23 to 840 °C. It was found that κ -Al 2 O 3 expands anisotropically, the expansion being about equal along the b - and c -axis, while it is significantly lower along the a -axis. Compared with α -Al 2 O 3 , the expansion is slightly lower along c κ than along c α , similar along b κ and a α , while it is significantly lower along a κ than along a α . The expansion data imply that all aluminium ions in κ-Al 2 O 3 are not ordered in a hexagonal mesh as in α -Al 2 O 3 , but are ordered in lines along the a -axis.

Microstructural changes in CVD κ-Al2O3 coated cutting tools during turning operations

Abstract This work is concerned with the microstructural evolution in CVD κ-Al2O3 coatings during high speed metal cutting. The wear characteristics and the κ-Al2O3 to α-Al2O3 phase transformation during metal cutting have been studied in detail by means of transmission electron microscopy and scanning electron microscopy. Based on the results of these investigations, the different wear mechanisms of κ-Al2O3 coated cemented carbide tools in metal cutting are discussed. Under the cutting conditions studied, flank wear depth developed at about twice the speed of rake face wear. No phase transformation occurred on the flank face, leading to wear of the non-transformed κ-Al2O3 of a more abrasive nature. On the rake face, a region of the κ-Al2O3 coating was transformed to α-Al2O3, and the wear crater was positioned inside the transformed α-Al2O3 area. The surface zone in the crater displayed a higher dislocation density, an indication of the occurrence of plastic deformation. It is concluded that the transformation from κ-Al2O3 to α-Al2O3, and the wear of the transformed α-Al2O3 by plastic deformation, are characteristic of the rake face wear.

Microstructural investigation of the effect of water vapour on the oxidation of alloy 353 MA in oxygen at 700 and 900°C

Abstract The objective of this work was to study the impact of water vapour on the corrosion behaviour of the austenitic stainless steel 353MA at 700 and 900°C through a detailed microstructural characterisation of the oxide scales formed, after 168 hours, in O2 and O2 with 40% H2O. The oxidized samples were investigated by scanning electron microscope/energy dispersive X-ray, focused ion beam and transmission electron microscope/energy dispersive X-ray. At 700°C 353MA forms a Cr-rich protective (Fe,Cr)2O3 oxide scale, with some silica at the oxide/metal interface. Breakaway oxidation occurs in H2O/O2 mixtures because the oxide scale is depleted in Cr due to the formation of CrO2(OH)2(g). However, the microstructural investigation indicated that a healing Cr-rich oxide layer formed beneath the Fe-rich oxide after some time. This could be a result of the high Cr/Fe ratio of 353MA. The behaviour at 900°C was different. In spite of the loss of Cr from the oxide scale, breakaway oxidation did not occur, i.e. the oxide scale remained protective. The microstructural investigation showed a thick, almost continuous silica layer at the oxide/metal interface, which may act as a diffusion barrier at the higher temperature.