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Among the various techniques that have been investigated to produce Hydroxyapatite (HA) coatings in order to promote fixation and osteointegration of cementless prosthesis, the plasma spray (PS) technique is the most popular method commercially in use. PS presents some disadvantages such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, an approach on how to bind HA to the Ti alloy will be introduced in this work, using a well-known technique in the metallurgical field: laser surface cladding. Different techniques were applied to characterize the coated samples, including x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray analysis. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: A new deposition method is presented, based on electrospraying, that can build bioceramic structures with desirable surface properties. This technology allows nanoapatite crystals, including hydroxyapatite (nHA), carbonate-substituted HA (nCHA) and silicon-substituted HA (nSiHA), to be electrosprayed on glass substrates. Human osteoblast cells cultured on nSiHA showed enhanced cell attachment, proliferation and protein expression, namely alkaline phosphatase, type 1 collagen and osteocalcin, as compared to nHA and nCHA. The modification of nanoapatite by the addition of silicon into the HA lattice structure renders the electrosprayed surface more hydrophilic and electronegatively charged. [Copyright &y& Elsevier]

Abstract: Hydroxyapatite containing levels of titanium (TiHA) of up to 1.6 wt.% has been produced via a chemical co-precipitation route. The distribution of Ti was seen by transmission electron microscopy/energy-dispersive X-ray analysis to be uniform throughout as-prepared nanosized TiHA particles (20nm×100nm). The incorporation of Ti into the HA structure was found to influence the ceramic microstructure on sintering and the grain size was found to decrease from 0.89μm with HA to 0.63μm with 0.8 wt.% TiHA (0.8 TiHA) and 0.45μm with 1.6 wt.% TiHA (1.6 TiHA). Rietveld refinement analysis showed that there was a proportional increase in both the a and c axis with incorporation of Ti into the HA lattice structure, leading to an increase in the cell volume with the addition of Ti. Fourier transform-Raman analysis showed a slight increase in the ratio of O–H/P–O peaks on TiHA, in comparison with HA. A bone-like apatite layer was formed on the surface of TiHA after immersion in simulated body fluid for 3days, which demonstrated the high in vitro bioactivity of TiHA. In vitro culture with primary human osteoblast (HOB) cells revealed that TiHA was able to support the growth and proliferation of HOB cells in vitro, with a significantly higher cell activity being observed on 0.8 TiHA after 7days of culture in comparison with that on HA. Well-organized actin cytoskeletal protein was developed after 1day of culture, and an increase in cell filopodia (attachment) was observed on TiHA sample surfaces. The results indicate that TiHA has great potential for biomedical applications. [Copyright &y& Elsevier]

Electrohydrodynamic spraying is a well established process used to deposit, coat, analyse and synthesise materials within the biomedical remit. Recently, electrohydrodynamic printing has been developed to afford structures for potential applications in the biomedical and medical engineering fields. Both of these processes rely on the formation of an electrically-induced jet, however the resulting products can be made strikingly different and offer potential in broader applications. Here we show how spraying and printing are linked by elucidating the ease of transition between the processes. Changes in the deposition distance can result in either spray (>10 mm) or print formation (<3 mm), with an overlap of the two in between this range. For the optimal printing distance of 0.5 mm, gradual changes in the applied voltage (0–4.5 kV) encounters transitional printing modes (dripping, micro-dripping, rapid micro-dripping, unstable and stable jetting) which can be utilised for patterning. The results indicate the robustness of the electrohydrodynamic route in the nano-materials processing arena, with emphasis on biomedical materials. [ABSTRACT FROM AUTHOR]

Hydroxyapatite [Ca10(PO4)6(OH)2], (HA) is similar in composition to bone mineral and has been found to promote new bone formation when implanted in a skeletal defect. However, its use in biomedical applications is limited by its relatively slow rate of biological interaction, and there is also a requirement to improve the success rate of HA implants in younger active patients, particularly where implants will be in place long-term. The addition of silicon (Si) into HA has been demonstrated to enhance the speed, and quality of the bone repair process. This paper describes the synthesis and detailed characterisation of nanocrystalline silicon-substituted hydroxyapatite (SiHA) thin coatings applied to a titanium substrate via a magnetron co-sputtering process. Amorphous SiHA coatings (∼1 μm thick) with varying Si content up to 4.9 wt% were produced before being transformed into crystalline films by heat-treatment. The crystalline coating was characterised by X-ray diffraction (XRD) and infrared (IR) analysis, and confirmed to be a single-phase apatite. The substitution of Si into HA resulted in an increase in both the a- and c-axes of the unit cell parameters, but a decrease in the crystallite size, with increasing Si substitution. This substitution also caused a decrease in the intensities of both the O–H and P–O bands in the IR spectra. Hence, these findings confirmed that the crystal structure of HA was altered with Si substitution. In vitro cell culture work showed that these SiHA thin coatings exhibited enhanced bioactivity and biofunctionality. An increase in the attachment and growth of human osteoblast-like (HOB) cells on these coatings was observed throughout the culture period, with the formation of extracellular matrix. In addition, confocal microscopy revealed that HOBs developed mature cytoskeletons with clear evidence of actin stress fibres, along with defined cell nuclei. [ABSTRACT FROM AUTHOR]

Reports on the production of biocompatible submicrometer sized relics containing nanosized hydroxyapatite (HA) by electrospraying. Procedure's offer of the potential to create both micro- and nano- scale surface topography and coverage for a favorable cell response; Exploration of the processing of nHA suspensions using different modes of electrospraying and a variety of substrates having different surface porosities.

A detailed study has been undertaken of the anisotropic mechanical behaviour of oriented hydroxyapatite reinforced polymer composite (HAPEXTM). The oriented material was produced by hydrostatic extrusion of isotropic HAPEXTM. It was found that the tensile and shear moduli and strengths of the oriented HAPEXTM are substantially increased compared with isotropic HAPEXTM. In particular, the properties along the extrusion direction exceed the lower range of the properties of cortical bone, showing that the oriented HAPEXTM is suitable for use in skeletal major load bearing applications. [ABSTRACT FROM AUTHOR]

Hydroxyapatite reinforced high density polyethylene composite (HAPEX™) has been developed for bone substitution. To improve its mechanical properties, HAPEX™ was hydrostatically extruded at different extrusion ratios after compression moulding. Substantial increases in the tensile and flexural properties of both unfilled polyethylene and HAPEX™ were achieved. It was evident that the higher the extrusion ratio, the stiffer and the stronger the extruded rods. The ductility of HAPEX™ was also significantly enhanced by hydrostatic extrusion. Hydrostatically extruded HAPEX™ possesses mechanical properties that are within the bounds for human cortical bone, which indicates its potential for load-bearing skeletal implant applications. [ABSTRACT FROM AUTHOR]

A hydroxyapatite (HA) reinforced polyethylene (PE) composite (designated HAPEX™), with high mechanical specification and a bioactive HA phase, has been optimised as a bone analogue material. Manufacturing conditions and machining of the materials were carefully controlled to give a reproducible material surface roughness with minimal batch variation. The effect of surface composition was examined in vitro using primary human osteoblasts (HOB). HOBs were cultured in direct contact with the test materials containing 20% and 40% vol. HA. The results showed that 40% HA/PE enhanced cellular activity by increasing proliferation rate and differentiation compared to the 20% vol. HA composite. The cytoskeletal organisation of the cells was also examined and HOBs cultured on 40% HA/PE were flatter and had an enhanced rate of cytoskeletal organisation and an increase in focal contact points compared to the 20% HA/PE. [Copyright &y& Elsevier]

Abstract: Silicon-substituted hydroxyapatite (Si–HA) coatings with three different Si compositions (0.8, 2.2 and 4.9 wt.%) were produced as thin films on titanium substrates by magnetron co-sputtering. Following heat-treatment, a crystalline, single-phase apatite structure was obtained for all coatings, as evidenced by the presence of characteristic peaks for HA in X-ray diffraction traces, and infrared absorption P–O and O–H bands. A human osteoblast-like (HOB) cell model was employed to assess the biocompatibility of these Si–HA coatings. Unsubstituted HA thin coatings were used as a control. The results demonstrated that Si–HA elicited a significantly more rapid growth response by the HOBs as compared to HA, although cells spread well on both coatings, with the formation of extracellular matrix. The cytoskeletons on Si–HA showed clear and distinct actin filaments that were parallel to the long axis of the cells. In contrast, a more diffuse actin cytoskeleton organisation was observed on HA. Biomineralisation was seen on both coatings after 42 days of culturing, with a higher level observed on the Si–HA samples. In conclusion, Si–HA offers great potential as a coating material for future medical applications in hard and soft tissue replacements. [Copyright &y& Elsevier]

Abstract: The use of silicon-substituted hydroxyapatite (Si-HA) as a biomaterial has been reported recently. In vivo testing has shown that Si-HA promotes early bonding of the bone/implant interface. In order to extend its usage to major load-bearing applications such as artificial hip replacement implants, it has been proposed that the material could be used in the form of a coating on implant surfaces. This paper reports a preliminary study of the biocompatibility of magnetron co-sputtered silicon-containing hydroxyapatite (Si-HA) coatings on a metallic substrate. Magnetron co-sputtered Si-HA films of thickness 600nm with a Si content of approximately 0.8wt% were produced on titanium substrates. X-ray diffraction analysis showed that the as-deposited Si-HA films were either amorphous or made up of very small crystals. The crystallinity of Si-HA films was increased after post-deposition heat treatment at 700°C for 3h, and the principal peaks were attributable to HA. The formation of nano-scale silicon–calcium phosphate precipitates was noted on the heat-treated films. In vitro cell culture has demonstrated that human osteoblast-like cells attached and grew well on all films, with the highest cell growth and signs of mineralisation observed on the heat-treated Si-HA films. In addition, many focal contacts were produced on the films and the cells had well-defined actin cytoskeletal organisation. This work shows that as-deposited and heat-treated Si-HA films have excellent bioactivity and are good candidates when rapid bone apposition is required. Furthermore, heat-treated Si-HA films have improved biostability compared to as-deposited films under physiological conditions. [Copyright &y& Elsevier]

The incorporation of silicate into hydroxyapatite (HA) has been shown to significantly increase the rate of bone apposition to HA bioceramic implants. However, uncertainty remains about the mechanism by which silicate increases the in vivo bioactivity of HA. In this study, high-resolution transmission electron microscopy was used to observe dissolution from HA, 0.8 wt% Si-HA and 1.5 wt% Si-HA implants after 6 and 12 weeks in vivo. Our observations confirmed that defects, in particular those involving grain boundaries, were the starting point of dissolution in vivo. Dissolution was observed to follow the order 1.5 wt% Si-HA>0.8 wt% Si-HA>pure HA and it was found to be particularly prevalent at grain boundaries and triple-junctions. These observations may help to explain the mechanism by which silicate ions increase the in vivo bioactivity of pure HA, and highlight the enhanced potential of these ceramics for biomedical applications. [Copyright &y& Elsevier]

Poly(methylmethacrylate) (PMMA) is the current standard for cement held prostheses. It forms a strong bond with the implant, but the bond between the cement and the bone is considered to be weak, with fibroblastic cells observed at the implant site, rather than direct bone contact, a contributing factor leading to implant failure. Incorporation of hydroxyapatite (HA) increases the biological response to the cement from tissue around the implant site, thus giving increased bone apposition. In this study, PMMA discs with 0, 4.6 and 8.8 vol% HA were examined. Primary human osteoblast-like cells (HOBs) were used for the biological evaluation of the response to the cements in vitro. Morphology was observed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Measurement of tritiated thymidine (3H-TdR) incorporation and alkaline phosphatase (ALP) activity were used to assess proliferation and differentiation. A synergy between increasing focal contact formation, cytoskeletal organisation, cell proliferation and expression of phenotype was observed with increasing HA volume. Preferential anchorage of HOBs to HA rather than PMMA was a prominent observation. [Copyright &y& Elsevier]