Orthopaedic Implants – Demonstrations of the Capabilities of Surface Analysis Techniques
DSIMS Analysis of an Orthopaedic Implant
The aim of this work was to investigate the presence and depth distribution of silicon on an orthopaedic implant.
DSIMS analysis concluded:
Silicon is apparently present on and within the coating. However, the major contribution to this silicon level is from areas of exposed substrate. Silicon is therefore present within the chromium - cobalt alloy or is present at the coating / alloy interface as a contaminant.
Analysis of Contamination on a Femoral Knee Joint
This work was commissioned in order to ascertain the origin of a greasy stain over the entire polished surface of a femoral knee joint that had been vacuum packed in a heat sealed polymer bag.
XPS and ToFSIMS analysis concluded:
Most of the stain material on the knee joint is unfunctionalised, saturated hydrocarbon-based. There is a significant amount of silicone and sodium on both the polished knee joint surface and the heat shrink-wrapped polymer bag surface with which it was in contact.
There are also traces of sulphur, chlorine and calcium which are typical of detergents that have been dispersed in domestic tap water.
In contrast, there is only polymer, erucamide slip agent and other additives on an unused bag surface.
It is thought possible that the detergent contamination has arisen because the knee joint may have been wrapped whilst still damp or contaminated after the washing/cleaning treatments used.
There is evidence that the level of hydrocarbon contamination is higher in the areas of the surface of the knee joint which are in intimate contact with the wrapper. This suggests that the origin of the contamination is the polymer material itself and the high levels of hydrocarbon material contaminant on the surface correspond to degradation product from the packaging resulting from application of heat during sealing or irradiation.
Surface Analysis of Two Knee Implants
The aim of this work was to investigate the surface composition of two knee implants.
ToFSIMS and XPS analysis showed:
The surfaces of both implants exhibited high levels of silicone.
Species attributable to the implant alloy were also detected indicating that the silicone overlayer was less than 5nm thick or patchy
Traces of other species, including Al, Ca, Na and a range of organic contaminants, were also detected.
A LIMA Investigation of Brown Stains on Shot Blasted Prosthesis Components
The aim of this work was to analyse a brown stain on knee femoral and hip joint components.
LIMA analysis concluded:
The bulk alloy contains titanium and aluminium.
The brown deposit consists of a material, which contains sodium, potassium, calcium, aluminium, chlorine and traces of iron in an organic matrix. The matrix consists of long chain hydrocarbons including amine (and possibly amide) - like compounds, possibly also with carboxylic acid functionality.
Perovskite with High Dielectric Constant May Lead to High Performance Capacitors
Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory are studying a mysterious material that may lead to significant advances in the miniaturisation of electronics. This work may lead to applications using the material to store electrical charge in high-performance capacitors, and offer insight into how charges behave on the nanoscale - on the order of billionths of a meter.
The material - a perovskite-related oxide containing calcium (Ca), copper (Cu), titanium (Ti), and oxygen (O) in the formula CaCu3Ti4O12 - is unusual in that it has an extremely high dielectric constant, a property that determines its ability to become electrically polarised (i.e., separate positive and negative electrical charges). The higher the dielectric constant, the more charge you can store, and the smaller you can make electronic circuits.
In addition, unlike most dielectric materials, this one retains its enormously high dielectric constant over a wide range of temperatures, from 100 to 600 Kelvin (K), or -173 to 327°C, making it ideal for a wide range of applications. Yet the material’s dielectric constant drops precipitously - 1,000-fold - below 100K, with no evidence of structural or phase changes in the atoms. Therein lies the mystery.
“Such a large change in the way charge is distributed within the material implies that the atomic structure should change as well,†said Christopher Homes, the lead physicist on the Brookhaven study. “It’s difficult to imagine how one property can undergo such a large change while the other remains unaffected.â€
Previously, scientists have looked for hints of changes using x-rays, neutron beams, and other methods - to no avail. But Homes’ technique, measuring optical conductivity, or the material’s ability to reflect and absorb varying frequencies of infrared light, revealed a number of unusual changes in the way the atomic structure vibrates.
The scientists detected the vibrations by illuminating samples of the substance with varying wavelengths of infrared light at Brookhaven’s National Synchrotron Light Source, and measuring which wavelengths were reflected and which were absorbed. The absorbed wavelengths are those that match the atoms’ natural vibration frequencies. As the temperature of the substance was cooled below the 100K mark, the absorbed frequencies - and therefore the vibrations - changed.
“Since the vibrations in a solid depend a great deal on how the charges are distributed, the changes in vibrations suggest that the charges can be rearranged without causing a structural distortion,†Homes said. “The fact that we see these changes offers the first real glimpse of why this material has such a large dielectric constant, and the mechanism by which it decreases so dramatically below 100K.â€
The scientists speculate that at temperatures above 100K, pairings of positive and negative electric charges, called dipoles, can flip around quickly, independent of one another. This property and the high concentration, or density, of dipoles within the solid both contributes to the large dielectric constant. If you put the material in an electric field, all the individual dipoles flip into alignment to separate the charges.
But as the material cools, the dipoles “freeze out†in random positions, losing their ability to flip quickly into alignment. This “electronic phase transition†happens in the absence of a structural change. “Additional research will help us understand this effect and the range of ways this material might be used in microelectronics and other fields,†Homes said.
Patent for Nano - Biomaterials
It was announced today that Orthovita, a biomaterials manufacturer has been granted a U.S. patent for its fine particle synthesis or nano-structured technology.
The patent covers 12 new claims for the production and use of the unique minerals and biomaterials. It also provides additional patent protection to the core solution-based chemistry technology utilised in the development of Vitoss(TM). Vitoss is a calcium phosphate based material used for filling voids in cancellous bone.
“This patent further protects our efficient technique for producing homogeneous ceramics,” said Dr. Erik Erbe, Vice President, Research and Development of Orthovita. The techniques described in the patent provide exacting control over production parameters enabling excellent control over product structure, purity, and yield and are incorporated into the Vitoss product. The technology also allows cells and signaling molecules, such as growth factors, to absorb our material so that the body can effectively remodel it into natural bone over time.”
Timken Premium Mill Grease
The Timken Company, probably best known for it bearings, have also been actively researching and developing lubricants for the last 70 years.
Work from this division has yielded a calcium sulfonate complex grease specifically formulated for protecting steel and aluminium mills under intense operating environments. The premium mill grease is available in three grades, NLGI grades 1.0, 1.5 and 2.0. They have been designed to provide a barrier to protect from water and hence oxidation and corrosion, while maintaining optimal lubricating properties.
Properties of these products include:
·        Strong anti-wear properties
·        High oxidation resistance
·        Excellent load-bearing properties
This range of products is suited to anti-friction bearings, roll necks, drive shafts, vertical edgers, liners and other grease requiring applications.
Superwool Ceramic Fibre is Here!
Thermal Ceramics has launched Superwool 607 MAX, a new insuÂlation material that extends the maximum short term use temperÂature of calcium magnesium siliÂcate fibres to 1300°C. Available in bulk fibre, flexible blanket and pre‑fabricated furnace module forms, Superwool 607 MAX has a variety of features that help maxÂimise the performance of thermal insulation. Applications include in heat treatment, furnace insulaÂtion in the steel and aluminium industries, and launder systems in non‑ferrous metal transfer.
New Range of Low Biopersisent Refractory Textiles
Thermal Ceramics has introduced Textiles 607 MAX, a new range of textile products produced from its Superwool 607 MAX low biopersistence insulation fibre. Using Superwool 607 MAX fibre produces textile products capable of operating at a maximum continuous use temperature of 1200°C to 50°C above the typical maximum continuous use temperature limit of standard grade refractory ceramic fibre (RCF) products. Textiles 607 MAX products are available in the following forms: tape; rope; lagging; twisted rope; braided sleeving; cloth; round; and square or rectangular braided packing.
Natural and Synthetic Bone Graft Materials – Autogenous, Allograft, Demineralised Bone Matrix and Synthetic Mixture Bone Grafts
Bone Grafts
Bone grafting is currently used in orthopaedic and maxillofacial surgery for the treatment of bridging diaphyseal defects, non-union, filling metaphyseal defects and mandibular reconstruction.
Autogenous Bone Grafts
Autogeneous bone graft is osteogenic (which forms bone, due to living cells such as osteocytes or osteoblasts), osteoconductive (have no capacity to induce or form bone but they provide an inert scaffold which osseous tissue can regenerate bone), osteoinductive (stimulate cells to undergo phenotypic conversion to osteoprogenitor cell types capable of formation of bone). There are no substitutes for autogenous bone; there are, however, synthetic alternatives.
Bone Allograft Materials
Allografts have been used as an alternative, but it has low or no osteogenicity, increased immunogenicity and resorbs more rapidly than autogenous bone. In clinical practice, fresh allografts are rarely used because of immune response and the risk of transmission of disease. The frozen and freeze-dried types are osteoconductive but are considered, at best, to be only weakly osteoinductive. Freeze drying diminishes the structural strength of the allograft and renders it unsuitable for use in situations in which structural support is required. Allograft bone is a useful material in patients who require bone grafting of a non-union but have inadequate autograft bone. Bulk allografts can be utilised for the treatment of segmental bone defects. Their use is well documented for reconstruction after resection of bone tumours, however not common in reconstruction after trauma in which bone lengthening and transport are usually required.
Demineralised Bone Matrix
Demineralised bone matrix (DBM) was first observed by Urist in 1965 to induce heterotopic bone. The active components of DBM are a series of glycoproteins, which belong to a group of transforming growth factor family (TGF-β). The members of this group are responsible for the morphogenic events involved in the development of tissue and organs. Urist later isolated a protein from the bone matrix, which was termed as the bone morphogenic protein (BMP). DBM is commercially available and used in management of non-union of fractures. They are not suitable where structural support is required. To date, the main delay in developing clinical products has been the need to find a suitable carrier to deliver the BMP to the site at which its action is required. New generation ceramic composites/hybrids could fill this gap. Experimentally, BMP-2 and OP-1® (BMP-7) have been shown to stimulate the formation of new bone in diaphysical defects in the rat, rabbit, dog, sheep and non-human primates. The use of BMP’s with new calcium phosphate derivatives or composites could be used for bone remodelling where bone regeneration and remodelling is needed such as therapeutic applications in osteoporosis.
Bovine Collagen/Hydroxyapatite Mixtures
Bovine collagen mixed with hydroxyapatite is marketed as a bone-graft substitute, which can be combined with bone marrow aspirated from the site of the fracture. Although no transmission of disease has been recorded, their use will continue to be a source of concern. This material is osteogenic, osteoinductive and osteoconductive however it lacks the structural strength required.
Nanostructures and Osteoblast Behavior of Thermal Sprayed Calcium Phosphate Splats
Introduction
Calcium phosphate (CP), especially hydroxyapatite (Ca10(PO4)6(OH)2, HA), coatings deposited on titanium alloy implants have shown promising effects on rapid bone remodeling and suitable functional life in orthopedic and dental applications. There is no doubt that the microstructure of the coatings significantly influences their mechanical properties [1, 2]. It is well known that a thermal sprayed coating shows a layered structure composed of individual accumulated splats. Due to this anomalous inhomogeneously-layered structure, the coatings show a significant dependence of their mechanical performances on microstructure. Generally, splat formation is an isolated procedure, which means a minor influence of the subsequent splat on the phases of the former one. Therefore, the overall in vitro behavior and microstructure of a bulk HA coating should be directly related to those of an individual HA splats. Consequently, a good understanding of the in vitro behavior and microstructure of an individual HA splat would significantly contribute to knowledge on HA coatings.  To date, some interesting results have been reported by many researchers on the microstructure of thermal sprayed splats [3-5]. In order to reveal detailed structural features of a single splat, transmission electron microscopy (TEM) must be adequately involved. Furthermore, in vitro study of individual CP splats can probably give insight into the mechanism of biocompatible CP interaction with cells. In addition, a previous in vitro study has shown that nano-sized ceramics have a significant ability to enhance osteoblast adhesion on them [6]. Nanostructures within a biocompatible coating could therefore show the same effect. In the present study, the nanostructures and in vitro osteoblast behavior of individual CP splats were characterized. The splats were deposited using both plasma spraying and HVOF onto polished Ti-6Al-4V substrates.
Experimental
HA powders synthesized in-house via the wet chemical method were utilized for splat deposition employing both HVOF and plasma spray processes. The starting powder particles have typical nanostructures with cylindrical grains <500 nm in length and 40-70 nm in diameter (Figure 1). A nanostructured HA particle is formed by the agglomeration of individual nanosized cylindrical HA grains. The splats were collected on Ti6Al4V plate substrates polished using 1 mm diamond paste. The microstructure of the samples was analyzed using scanning electron microscopy (SEM, JEOL JSM-5600LV), field emission SEM (FESEM, JEOL JSM-6340F), and transmission electron microscopy (TEM, JEOL, JEM-2010) operated at 200 kV. The in vitro cell culture work was conducted using the commercially available hFOB 1.19 cell line. The splat samples were incubated in Dulbecco’s modified eagle medium (DMEM) containing 10% fetal bovine serum (FBS) and 0.5% antibiotics with 5´104 cells. Cells were cultured in an atmosphere of 100% humidity, 5% CO2 at 37°C in 24-well culture plates with 1 ml of medium contained in each well. After 2 days’ incubation, the morphology of the cells attached onto the samples was observed using SEM. Prior to the SEM observation, 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer was used for pre-fixing the cells, followed by post-fixation with 1% osmium tetroxidein in 0.1 M cacodylate buffer. The final steps for fixing the samples were dehydration and critical point drying.
AZoJomo - The AZO Journal of Materials Online - Typical topographical morphology of the starting nSD-HA particles (a). Close examination of the HA particle (b) shows the agglomeration of nanosized HA grains
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AZoJomo - The AZO Journal of Materials Online - Typical topographical morphology of the starting nSD-HA particles (a). Close examination of the HA particle (b) shows the agglomeration of nanosized HA grains
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Figure 1. Typical topographical morphology of the starting nSD-HA particles (a). Close examination of the HA particle (b) shows the agglomeration of nanosized HA grains.
Results and Discussion
Figure 2 shows typical topographical nanostructures within the CP splats observed by TEM (Figure 2a) and FESEM (Figure 2b). It is seen that the HA splat is composed of nanostructured ~30 nm grains. FESEM observation of the HA coatings reveals consistent nanostructures (Figure 3). This further suggests that during the accumulation of individual HA splats to form the bulk coating, there is no obvious grain growth of the nanosized grains. However, it must be noted that for the nanostructures in the splats, there are a lot of phases apart from HA, e.g. a-TCP (tricalcium phosphate) and b-TCP. This may not be desirable since these phases result from HA decomposition and are less bioactive than HA. Furthermore, it is noted that the nanostructures in the splats/coatings are not the same as those present in the starting feedstock. After the high temperature spray processing, the nano-fibers have changed to nanosized spheres with a size range of 40 nm ~ 120 nm. This suggests that during the melting/resolidification process, the nano-fibers were mostly split into one or more individual parts form which by surface tension, the nanosized spheres were formed. The results may also indicate the importance of existing nanostructures in the starting powders on the final nanostructures in the coatings.
AZoJomo - The AZO Journal of Materials Online - Typical TEM morphology at the splat’s fringe (a) and FESEM morphology taken at the splat’s surface (b) of the CP splat showing the consistent nanostructures
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AZoJomo - The AZO Journal of Materials Online - Typical TEM morphology at the splat’s fringe (a) and FESEM morphology taken at the splat’s surface (b) of the CP splat showing the consistent nanostructures
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Figure 2. Typical TEM morphology at the splat’s fringe (a) and FESEM morphology taken at the splat’s surface (b) of the CP splat showing the consistent nanostructures.
AZoJomo - The AZO Journal of Materials Online - FESEM photo of the HA coating showing consistent nanostructures inside the coating
Figure 3. FESEM photo of the HA coating showing consistent nanostructures inside the coating.
Furthermore, amorphous CP was revealed at the extreme surrounding areas of the splat (Figure 4), which indicates very rapid cooling of the droplet upon impingement on the substrate.
AZoJomo - The AZO Journal of Materials Online - Typical TEM microstructure of the HA splat (a) taken at the splat fringe, showing the predominant presence of amorphous calcium phosphate (ACP), as suggested by a selected diffraction pattern (b).
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AZoJomo - The AZO Journal of Materials Online - Typical TEM microstructure of the HA splat (a) taken at the splat fringe, showing the predominant presence of amorphous calcium phosphate (ACP), as suggested by a selected diffraction pattern (b).
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Figure 4. Typical TEM microstructure of the HA splat (a) taken at the splat fringe, showing the predominant presence of amorphous calcium phosphate (ACP), as suggested by a selected diffraction pattern (b).
It has also been revealed that, for the HVOF HA coatings/splats, the areas inside the HA splats with intimate contact with the substrate surface exhibited a typical cuboid structure (Figure 5). Most of the grains are <250 nm in length and <50 nm in diameter. Very few of them have a larger size of 0.4-1.2 mm in length and 80-120 nm in width. The appearance of such cuboid shape structures only in the HVOF coating possibly indicates a critical condition for formation of the structure: full molten state, rapid cooling, and fast impingement.
AZoJomo - The AZO Journal of Materials Online - Typical FESEM photos taken at the bottom of the HVOF coating (with intimate contact with the substrate) showing a cuboid structureAZoJomo - The AZO Journal of Materials Online - Typical FESEM photos taken at the bottom of the HVOF coating (with intimate contact with the substrate) showing a cuboid structure
Figure 5. Typical FESEM photos taken at the bottom of the HVOF coating (with intimate contact with the substrate) showing a cuboid structure.
The primary cell culture testing suggests that the HA splats are bioactive such that they attracted marked cell attachment and proliferation after 2 days’ incubation (Figure 6). However, there is significant dissolution of the splats prior to the attachment and proliferation of the cells on the substrate. This may suggest that the (partial) dissolution of the splats into the culture media enhances the proliferation of the cells.
AZoJomo - The AZO Journal of Materials Online - Obvious attachment and proliferation of the osteoblast cells on the HA splats, (a) SEM picture before the incubation and (b) after the incubation.
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AZoJomo - The AZO Journal of Materials Online - Obvious attachment and proliferation of the osteoblast cells on the HA splats, (a) SEM picture before the incubation and (b) after the incubation.
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Figure 6. Obvious attachment and proliferation of the osteoblast cells on the HA splats, (a) SEM picture before the incubation and (b) after the incubation.
For comparison purpose, the HA coatings were also incubated in the media for 2 days. The cells also proliferated well on the coating surface (Figure 7). However, there is no remarkable dissolution of the coating. It is noted that the number of the cells proliferated on the coating is less than that on the splats. It hence indicates that dissolution of the Ca-P-rich phase into the medium might promote cell proliferation. The dissolution behavior of the CP splats has been discussed in another paper from our laboratory [7]. It must be noted that the phases inside the splats that act as the first layer of the coating consist of less HA than in the coating surface. This might partially account for the dissolution. The resorbable CPs would promote the uniform deposition of new mineralized bone matrix, thus enabling rapid integration with the surrounding host bone tissue in vivo. Other researchers have found that dissolution of the CP coating was accompanied by good goat bone marrow stromal cell attachment [8] and high proliferation rate and ALP activity of osteoblast-like cells [9].
AZoJomo - The AZO Journal of Materials Online - SEM picture showing attachment of the osteoblast cells on the HA coating
Figure 7. SEM picture showing attachment of the osteoblast cells on the HA coating.
Conclusion
The thermal sprayed HA splats are actually composed of ~30 nm nanostructures. The nanostructures in HA feedstock were retained and re-organized after the coating deposition. The melting/solidification of the nanosized fibers resulted in formation of spherical nanosized grains in the coatings. The nanostructured HA splats are capable of enhancing the attachment and proliferation of the osteoblast cells. The present study also revealed that the dissolution of the Ca/P-rich phases into the culture medium might promote the proliferation/differentiation of the cells.
Molybdenum
Background
Originally molybdenum was confused with graphite and lead ore, and was not prepared till 1782 by Hjelm in the impure state. Molybdenum does not occur native, and is obtained mainly from molybdenite (MoS2). Other minor commercial ores of molybdenum are powellite (Ca(MoW)O4) and wulfenite (PbMoO4). It may also be recovered from copper and tungsten operations as a by-product.
The metal is prepared from the powder made by the hydrogen reduction of purified molybdic trioxide or ammonium molybdate. Molybdenum the metal is silvery-white, and very hard. However, it is softer and more ductile than tungsten and is readily worked or drawn into very fine wire. It cannot be hardened by heat treatment, only by working. It exhibits a high elastic modulus and a very high melting point. Above temperatures of 760°C (1400°F) molybdenum the metal forms an oxide that evaporates as it is formed and its resistance to corrosion is high. It has a low thermal expansion and its heat conductivity is twice that of iron. It is one of the few metals that has some resistance to hydrofluoric acid.
Key Properties
Molybdenum is a refractory metal typically used in high temperature applications. Key properties include:
·        Low co-efficient of thermal expansion (5.1×10-6 m/m/°C) which is about half that of most steels
·        Good thermal conductivity
·        Good electrical conductivity
·        Good stiffness, greater then that of steel (Young’s Modulus 317MPa)
·        High melting point (2615°C)
·        Good hot strength
·        Good strength and ductility at room temperature
·        High density (10.2 g/cm3)
Its ability to withstand high temperatures and maintain strength under these conditions are responsible for the fact that molybdenum finds most of its application at elevated temperatures. In fact, it can work at temperatures above 1100°C (in non-oxidising conditions), which is higher than steels and nickel-based superalloys.
When exposed to temperatures in excess of 760°C in air rapid oxidation can result. Under these conditions, the oxide layer sublimes and the base metal is attacked. Thus, molybdenum performs best in inert of vacuum environments.
Applications
Molybdenum Metal
Molybdenum metal is used in:
·        Alloying agent – contributing hardenability, toughness to quenched/tempered steels. It also improves the strength of steels at high temperatures (red-hardness).
·        In nickel-based alloys (such as Hastelloys®) and stainless steels it imparts heat-resistance and corrosion-resistance to chemical solutions.
·        Electrodes for electrically heated glass furnaces and forehearths.
·        Nuclear energy applications, as missile and aircraft parts (where high temperature resistance is vital).
·        As a catalyst in the refining of petroleum.
·        As a filament material in electronic/electrical applications.
·        As a support members in radio and light bulbs.
·        Arc resistant electric contacts.
·        Thermocouple sheaths
·        Flame- and corrosion-resistant coatings for other metals (generally arc deposited for metallising).
Molybdenum Compounds
Molybdenum and its compounds are used in:
·        Molybdenum sulphide and selenites are used as a high temperature lubricant in favour to petroleum based oils, due to its superior high temperature resistance.
·        Sodium molybdate (Na2MoO4) in the anhydrous form is used as a dry powdered fertiliser.
·        Calcium molybdate (CaMoO4), Molyte, molybdic oxide, molybdenum-chromium are used as sources of molybdenum for steels.
Liquifier from Bayer for Self-Levelling Calcium Sulfate Screeds
The new flow promoter Anhyplan® P extends the range of products from Bayer Chemicals AG, Leverkusen, Germany; as a result of the restructuring of the Bayer Group, this subgroup will soon be part of Lanxess, the newly-forming global chemical company.
The powdered high-performance liquifier is used for the formulation of calcium sulfate self-levelling screeds conforming to DIN EN 13813/DIN 18560, the new European screed standard, as factory-made or site-made mortars and mortars for truck mixers or double-chamber silos.
Anhyplan® P liquefies the screed mortar and reduces the amount of water required. Mortar density is increased, as is the compressive and flexural strength of the hardened screed. The additive is non-freezing and suitable for the formulation of dry mortars.