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Journal of Materials Science: Materials in Medicine: Official Journal of the European Society for Biomaterials (v.17, #11)

Editorial: A forecast of the future for biomaterials by Julian R. Jones; Aldo R. Boccaccini (pp. 963-964).
A Tribute to Professor Larry Hench by William Bonfield (pp. 965-966).

The story of Bioglass® by Larry L. Hench (pp. 967-978).
Historically the function of biomaterials has been to replace diseased or damaged tissues. First generation biomaterials were selected to be as bio-inert as possible and thereby minimize formation of scar tissue at the interface with host tissues. Bioactive glasses were discovered in 1969 and provided for the first time an alternative; second generation, interfacial bonding of an implant with host tissues. Tissue regeneration and repair using the gene activation properties of Bioglass® provide a third generation of biomaterials. This article reviews the 40 year history of the development of bioactive glasses, with emphasis on the first composition, 45S5 Bioglass®, that has been in clinical use since 1985. The steps of discovery, characterization, in vivo and in vitro evaluation, clinical studies and product development are summarized along with the technology transfer processes.

The surface functionalization of 45S5 Bioglass®-based glass-ceramic scaffolds and its impact on bioactivity by Q. Z. Chen; K. Rezwan; D. Armitage; S. N. Nazhat; A. R. Boccaccini (pp. 979-987).
The first and foremost function of a tissue engineering scaffold is its role as a substrate for cell attachment, and their subsequent growth and proliferation. However, cells do not attach directly to the culture substrate; rather they bind to proteins that are adsorbed to the scaffold’s surface. Like standard tissue culture plates, tissue engineering scaffolds can be chemically treated to couple proteins without losing the conformational functionality; a process called surface functionalization. In this work, novel highly porous 45S5 Bioglass®-based scaffolds have been functionalized applying 3-AminoPropyl-TriethoxySilane (APTS) and glutaraldehyde (GA) without the use of organic solvents. The efficiency and stability of the surface modification was assessed by X-ray photoemission spectroscopy (XPS). The bioactivity of the functionalized scaffolds was investigated using simulated body fluid (SBF) and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). It was found that the aqueous heat-treatment applied at 80C for 4 hrs during the surface functionalization procedure accelerated the structural transition of the crystalline Na2Ca2Si3O9 phase, present in the original scaffold structure as a result of the sintering process used for fabrication, to an amorphous phase during SBF immersion. The surface functionalized scaffolds exhibited an accelerated crystalline hydroxyapatite layer formation upon immersion in SBF caused by ion leaching and the increased surface roughness induced during the heat treatment step. The possible mechanisms behind this phenomenon are discussed.

Controlling ion release from bioactive glass foam scaffolds with antibacterial properties by Julian R. Jones; Lisa M. Ehrenfried; Priya Saravanapavan; Larry L. Hench (pp. 989-996).
Bioactive glass scaffolds have been produced, which meet many of the criteria for an ideal scaffold for bone tissue engineering applications, by foaming sol-gel derived bioactive glasses. The scaffolds have a hierarchical pore structure that is very similar to that of cancellous bone. The degradation products of bioactive glasses have been found to stimulate the genes in osteoblasts. This effect has been found to be dose dependent. The addition of silver ions to bioactive glasses has also been investigated to produce glasses with bactericidal properties. This paper discusses how changes in the hierarchical pore structure affect the dissolution of the glass and therefore its bioactivity and rate of ion delivery and demonstrates that silver containing bioactive glass foam scaffolds can be synthesised. It was found that the rate of release of Si and Ca ions was more rapid for pore structures with a larger modal pore diameter, although the effect of tailoring the textural porosity on the rate of ion release was more pronounced. Bioactive glass scaffolds, containing 2 mol% silver, released silver ions at a rate that was similar to that which has previously been found to be bactericidal but not high enough to be cytotoxic to bone cells.

Gene activation by bioactive glasses by G. Jell; M. M. Stevens (pp. 997-1002).
Bioactive glasses have been shown to regulate gene expression in both hard and soft tissue repair. New resorbable bioactive glass constructs are now being developed that can influence gene expression in the local environment by manipulating material properties such as the surface chemistry, topography and the release of dissolution ions. The success of these scaffolds, however, may depend upon a greater understanding of the bioactive glass stimulated gene expression pathways. This will allow the construction of tissue specific scaffolds with tailored surface chemistry, topography and ion release rates. This paper summarises the advances made in understanding gene expression in response to bioactive glasses and discusses the future steps required for further insights into these molecular mechanisms.

The use of advanced diffraction methods in the study of the structure of a bioactive calcia: silica sol-gel glass by Robert John Newport; Laura J. Skipper; Daniela Carta; David M. Pickup; Frank E. Sowrey; Mark E. Smith; Priya Saravanapavan; Larry L. Hench (pp. 1003-1010).
Sol-gel derived calcium silicate glasses may be useful for the regeneration of damaged bone. The mechanism of bioactivity is as yet only partially understood but has been strongly linked to calcium dissolution from the glass matrix. In addition to the usual laboratory-based characterisation methods, we have used neutron diffraction with isotopic substitution to gain new insights into the nature of the atomic-scale calcium environment in bioactive sol-gel glasses, and have also used high energy X-ray total diffraction to probe the nature of the processes initiated when bioactive glass is immersed in vitro in simulated body fluid. The data obtained point to a complex calcium environment in which calcium is loosely bound within the glass network and may therefore be regarded as facile. Complex multi-stage dissolution and mineral growth phases were observed as a function of reaction time between 1 min and 30 days, leading eventually, via octacalcium phosphate, to the formation of a disordered hydroxyapatite (HA) layer on the glass surface. This methodology provides insight into the structure of key sites in these materials and key stages involved in their reactions, and thereby more generally into the behaviour of bone-regenerative materials that may facilitate improvements in tissue engineering applications.

From the bioactive glasses to the star gels by María Vallet-Regí; Antonio J. Salinas; Daniel Arcos (pp. 1011-1017).
The improvement of bioactive glasses is one of the most important subjects in the field of hard tissue replacement. More than 30 years after being discovered by Prof. Hench, bioactive glasses still attract the attention of many researchers all over the World. With this article we want to pay homage to Prof. Hench by means of reviewing the main contribution of our research team to the field initiated by him in 1969. Our efforts, aimed to go further in the understanding of sol-gel glasses bioactivity as well as to improve the mechanical properties of bioactive materials, are explained.

Progress in Raman spectroscopy in the fields of tissue engineering, diagnostics and toxicological testing by Chris A. Owen; Ioan Notingher; Robert Hill; Molly Stevens; Larry L. Hench (pp. 1019-1023).
This review summarises progress in Raman spectroscopy and its application in diagnostics, toxicological testing and tissue engineering. Applications of Raman spectroscopy in cell biology are in the early stages of development, however, recent publications have demonstrated its utilisation as a diagnostic and development tool with the key advantage that investigations of living cells can be performed non-invasively.Some of the research highlighted here demonstrates the ability of Raman spectroscopy to accurately characterise cancer cells and distinguish between similar cell types. Many groups have used Raman spectroscopy to study tissues, but recently increased effort has gone into single cell analysis of cell lines; the advantages being that cell lines offer ease of handling and increased reproducibility over tissue studies and primary cells. The main goals of bio-Raman spectroscopy at this stage are twofold. Firstly, the aim is to further develop the diagnostic ability of Raman spectroscopy so it can be implemented in a clinical environment, producing accurate and rapid diagnoses. Secondly, the aim is to optimise the technique as a research tool for the non-invasive real time investigation of cell/material interactions in the fields of tissue engineering and toxicology testing.

The future of biomedical materials by James M. Anderson (pp. 1025-1028).
The purpose of this communication is to present the author’s perspectives on the future of biomedical materials that were presented at the Larry L. Hench Retirement Symposium held at Imperial College, London, in late September 2005. The author has taken a broad view of the future of biomedical materials and has presented key ideas, concepts, and perspectives necessary for the future research and development of biomedical polymers and their future role as an enabling technology for the continuing progress of tissue engineering, regenerative medicine, prostheses, and medical devices. This communication, based on the oral presentation, is meant to be provocative and generate discussion. In addition, it is targeted for students and young scientists who will play an ever-increasing role in the future of biomedical materials.

Historic and current strategies in bone tissue engineering: Do we have a hope in Hench? by Eileen Gentleman; Julia M. Polak (pp. 1029-1035).
Professors Larry Hench and Julia Polak formed the Tissue Engineering and Regenerative Medicine Centre (TERM) at Imperial College London to foster collaborations between biologists and materials scientists. Early work at the center elucidated the biomolecular interactions between primary human osteoblasts and 45S5 Bioglass® . As research efforts expanded, the team discovered that the dissolution products of both 45S5 Bioglass® and 58S sol-gel bioactive glasses had osteoblastic stimulatory properties. To address the shortage of appropriate cells for bone tissue engineering applications, TERM scientists also demonstrated the differentiation of embryonic stem (ES) cells to osteoblasts when treated with the dissolution products of bioactive glasses. They also found that the soluble factors ascorbic acid, β -glycerophosphate, and dexamethasone preferentially differentiated ES cells to osteoblasts, and their combination with the dissolution products of bioactive glasses stimulated differentiation even further. Taken together, these results demonstrate the suitability of bioactive glasses as scaffolds for bone tissue engineering as they not only provide an osteoconductive and osteoproductive substrate, but also actively stimulate cells to express appropriate osteoblastic phenotypes. Professor Hench’s vision to pioneer regenerative medicine research continues with the aim of developing novel therapeutics to treat musculoskeletal disability.

Clinical applications of glass-ceramics in dentistry by Wolfram Höland; Volker Rheinberger; Elke Apel; Christian van ’t Hoen; Marlies Höland; Alex Dommann; Marcel Obrecht; Corinna Mauth; Ursula Graf-Hausner (pp. 1037-1042).
Glass-ceramics featuring special properties can be used as a basis to develop biomaterials. It is generally differentiated between highly durable biomaterials for restorative dental applications and bioactive glass-ceramics for medical use, for example, bone replacements. In detail, this paper presents one biomaterial from each of these two groups of materials.In respect to the restorative dental biomaterials, the authors give an overview of the most important glass-ceramics for clinical applications. Leucite, leucite-apatite, lithium disilicate and apatite containing glass-ceramics represent biomaterials for these applications. In detail, the authors report on nucleation and crystallization mechanisms and properties of leucite-apatite glass-ceramics. The mechanism of apatite nucleation is characterized by a heterogeneous process. Primary crystal phases of α - and β -NaCaPO4 were determined.Rhenanite glass-ceramics represent biomaterials with high surface reactivity in simulated body fluid, SBF, and exhibit reactive behaviour in tests with bone cells. Cell adhesion phenomena and cell growth were observed. Suitable colonization and proliferation and differentiation of cells as a preliminary stage in the development of a material for bone regeneration applications was established. The authors conclude that the processes of heterogeneous nucleation and crystallization are important for controlling the required reactions in both biomaterial groups.

Skeletal tissues as nanomaterials by L. Bozec; M. A. Horton (pp. 1043-1048).
Collagen is the most abundant protein in the body and, though the fibre-forming collagens have a ‘common’ structure, it is adapted to perform a large range of functions—from the differing mechanical needs of tendon versus bone to forming a transparent support structure in the cornea. This perfidy also suggests that collagen could form a generic basis for a range of scaffold needs for tissue engineering or medical device coating applications. We at the London Centre for Nanotechnology—a joint venture between University College London and Imperial College—are taking a bottom-up approach having decided that many of the ‘accepted dogmas’ of collagen biology may not be quite as soundly based as currently held. We are using several of the tools of ‘hard’ nanotechnology—such as atomic force microscopy—to re-examine collagen structure with the longer term aim of using such information to design materials with appropriate physical attributes. Examples of our current research on mineralised and soft tissue collagens are presented.

Zonal release of proteins within tissue engineering scaffolds by Tri Suciati; Daniel Howard; John Barry; Nicola M. Everitt; Kevin M. Shakesheff; Felicity RAJ Rose (pp. 1049-1056).
The manufacture of a scaffold for tissue engineering applications that can control the location and timing of growth factor release is described. The scaffold is formed by the sintering of poly(DL-lactic acid) (PDLLA) microparticles, plasticized with poly(ethylene glycol) (PEG), although the method can be used for many other polymer types. The microparticles were loaded with model proteins, trypsin and horseradish peroxidase (HRP), or recombinant human bone morphogenetic protein-2 (rhBMP-2). Entrapment efficiencies above 75% were achieved using a solid-in-oil-in-water system. Controlled release of active protein was achieved for at least 30 days. Microparticles were built into protein-loaded or protein-free layers and release of the protein was restricted to zones within the scaffold. Cell response to rhBMP-2 was tuneable by changing the dose of the rhBMP-2 released by varying the ratio of protein-loaded and protein-free microparticles within scaffolds. Zonal activity of rhBMP-2 on C2C12 cells was demonstrated. The scaffolds may find utility in applications where gradients of growth factors within 3D templates are required or where zonation of tissue growth is required.

Surface behaviour of biomaterials: The theta surface for biocompatibility by Robert Edward Baier (pp. 1057-1062).
“Biomaterials” are non-living substances selected to have predictable interactions with contacting biological phases, in applications ranging from medical/dental implants to food processing to control of biofouling in the sea. More than 30 years of empirical observations of the surface behaviours of various materials in biological settings, when correlated with the contact-angle-determined Critical Surface Tensions (CST) for these same materials, support the definition of the “theta surface”. The “theta surface” is that characteristic expression of outermost atomic features least retentive of depositing proteins, and identified by the bioengineering criterion of having measured CST between 20 and 30 mN/m. Biomaterials applications requiring strong bioadhesion must avoid this range, while those requiring easy release of accumulating biomass should have “theta surface” qualities. Selection of blood-compatible materials is a main example. It is forecast that future biomaterials will be safely and effectively translated directly to clinical use, without requiring animal testing, based on laboratory data for CST, protein denaturation, and cell spreading alone.

Synthesis and sintering of biomimetic hydroxyapatite nanoparticles for biomedical applications by Suprabha Nayar; M. K. Sinha; D. Basu; Arvind Sinha (pp. 1063-1068).
Synthesis of monodisperse nanoparticles with uniform morphology and narrow size distribution as achieved by nature is a challenge to materials scientists. Mimicking the process of biomineralization has led to the development of biomolecules mediated synthesis of nanoparticles that overcomes many of the problems associated with nanoparticle synthesis. Termed as biomimetics this paradigm shift in the philosophy of synthesis of materials is very advantageous for the design-based synthesis of nanoparticles. The effect of concentration of a protein named bovine serum albumin on particle size, morphology and degree of crystallinity of biomimetically synthesized hydroxyapatite particles, has been studied. Results establish 0.5% protein as the required concentration to produce 30–40 nm sized hydroxyapatite particles with an optimum degree of crystallinity as required for biomedical applications. These particles synthesized under certain stringent conditions are found to have stoichiometric calcium:phosphorus ratio of 1.67 and exhibit restricted grain growth during sintering.

Macroporous bioactive glass-ceramic scaffolds for tissue engineering by C. Vitale Brovarone; E. Verné; P. Appendino (pp. 1069-1078).
Highly bioactive scaffolds for tissue engineering were synthesized using a glass belonging to the SiO2-CaO-K2O (SCK) system. The glass SCK was prepared by a traditional melting-quenching route and its bioactivity was assessed by in vitro tests in a simulated body fluid (SBF). The glass was ground and sieved to obtain powders of specific size that were subsequently mixed with polyethylene particles of two different dimensions. The powders were then uniaxially pressed to obtain a crack free green compact that was thermally treated to remove the organic component and to sinter the inorganic phase. The obtained biomaterial was characterised by means of X-ray Diffraction, SEM equipped with EDS, mercury intrusion porosimetry, density measurements, image analysis, mechanical tests and in vitro evaluations. A glass-ceramic macroporous scaffold with a homogenously distributed and highly interconnected porosity was obtained. The amount and size of the introduced porosity could be tailored using various amounts of polyethylene powders of different size.

Crystallinity in apatites: how can a truly disordered fraction be distinguished from nanosize crystalline domains? by Giancarlo Celotti; Anna Tampieri; Simone Sprio; Elena Landi; Luca Bertinetti; Gianmario Martra; Caterina Ducati (pp. 1079-1087).
In the last decade synthetic apatites mimicking the human natural one have been widely prepared and characterized from the physico-chemical point of view; however a shading zone is still remaining related to the evaluation and distinction of the less crystalline part, almost amorphous, and the crystallographically well ordered, nano-sized part, inside the apatite itself. Actually natural apatite forming bone tissue can include both types of crystals whose prevalence is dependent from the specific bone evolution stage and the specialized tissue performance. The quantitative description of such a combination usually represents a puzzling problem, but the result can also clarify the definition of “crystallinity in apatite” that appears still controversial. Many different synthetic apatites, including those nucleated on organic templates, were analyzed with different techniques (X-ray diffraction, transmission electron microscopy, and so on) to clarify the true nature of the disordered part. The results, manipulated by the classical methodologies devised for substances with highly perturbed structural order, led to establish that only specifically prepared amorphous calcium phosphate is really a glass, while the distorted portion coexisting with more or less crystalline regions is simply nanocrystalline. Moreover, at the conceptual limit of crystallinity tending to zero, the two models surprisingly cease to be conflicting.

The effect of pressure during sintering on the strength and the fracture toughness of hydroxyapatite ceramics by Satoshi Kobayashi; Wataru Kawai; Shuichi Wakayama (pp. 1089-1093).
Hydroxyapatite (HA) is known to be biocompatible and osteoconductive, and can be synthesized chemically. The objective of the present study is to clarify the effect of pressure during sintering on the mechanical properties of HA. HA was sintered using a hot press system at a uniaxial pressure ranging from 7.81 to 62.5 MPa at a maximum temperature of 1200C with a heating rate of 10C/min. The density of the HA increased with increasing pressure and peaked at the sintering pressure of 31.2 MPa. Four-points bending tests and fracture toughness measurements with indentation method were conducted to clarify the effect of sintering pressure. Bending strength decreased at the pressure > 31.2 MPa. This result indicates that residual stress generated during sintering process became larger with increasing pressure. Fracture toughness were also lower with high density HA.

Cytotoxicity study of plasma-sprayed hydroxyapatite coating on high nitrogen austenitic stainless steels by C. P. O. Ossa; S. O. Rogero; A. P. Tschiptschin (pp. 1095-1100).
Stainless steel has been frequently used for temporary implants but its use as permanent implants is restricted due to its low pitting corrosion resistance. Nitrogen additions to these steels improve both mechanical properties and corrosion resistance, particularly the pitting and crevice corrosion resistance. Many reports concerning allergic reactions caused by nickel led to the development of nickel free stainless steel; it has excellent mechanical properties and very high corrosion resistance. On the other hand, stainless steels are biologically tolerated and no chemical bonds are formed between the steel and the bone tissue. Hydroxyapatite coatings deposited on stainless steels improve osseointegration, due their capacity to form chemical bonds (bioactive fixation) with the bone tissue. In this work hydroxyapatite coatings were plasma-sprayed on three austenitic stainless steels: ASTM-F138, ASTM-F1586 and the nickel-free Böhler-P558. The coatings were analyzed by SEM and XDR. The cytotoxicity of the coatings/steels was studied using the neutral red uptake method by quantitative evaluation of cell viability. The three uncoated stainless steels and the hydroxyapatite coated Böhler-P558 did not have any toxic effect on the cell culture. The hydroxyapatite coated ASTM-F138 and ASTM-F1586 stainless steels presented cytotoxicity indexes (IC50%) lower than 50% and high nickel contents in the extracts.

Surface morphology and adsorbed proteins affect phagocyte responses to nano-porous alumina by M. Karlsson; L. Tang (pp. 1101-1111).
This study evaluates human neutrophil responses to aluminum oxide membranes with different pore sizes (20 nm and 200 nm in diameter) uncoated and pre-coated with serum, collagen I, or fibrinogen. The effect of released neutrophil granule components on the survival of osteoblastic cells (MG63) bound to the alumina membranes has also been evaluated. Without protein coatings the 20 nm pore-size membranes prompt higher reactive oxygen species (ROS) production as assessed by luminol-amplified chemiluminescence than the 200 nm pore-size membranes. Such pore-size depending responses were also found on membranes pre-coated with fibrinogen, but not with collagen or serum were in fact a much lower ROS production was observed. In addition, uncoated and fibrinogen-coated membranes prompt stronger release of the granule enzymes, myeloperoxidase and elastase, than collagen or serum-coated alumina. Equally important, we found that surface-mediated phagocyte activation and the subsequent release of granule components had a significant affect on the adhesion, viability and proliferation of osteoblasts. This stresses the importance of studying not only cell/surface interactions but also cell/cell interactions in wound healing and tissue regeneration processes.

The properties of biomimetically processed calcium phosphate on bioactive ceramics and their response on bone cells by M. Vaahtio; T. Peltola; T. Hentunen; H. Ylänen; S. Areva; J. Wolke; J. I. Salonen (pp. 1113-1125).
This study looks for grounds to alter the chemical composition (phosphate, calcium, silica and carbonate), dissolution properties, structure and nanotopography of the biomimetically processed surfaces on bioactive ceramics to optimize their shown ability to influence bone cell behaviour and production of new bone. In the bone environment desirable characteristic of these materials is their ability to be remodeled by natural osteoclastic resorption. Different silica and carbonate containing calcium phosphate layers were prepared on bioactive glasses 9 (S53P4) and 1-98 (S53P2) and sol-gel processed pure silica SiO2 in C- and R-SBF (conventional and revised simulated body fluid) for varying periods of time. It was shown that in R-SBF the CaP layer formed faster compared to C-SBF. The CaP layer in the R-SBF contained more carbonate (CO3 2−) compared to that formed with the same immersion time in C-SBF. The CaP so formed in R-SBF with faster precipitation is more amorphous than the bonelike HCA formed in C-SBF. The results indicate that the most suitable surface for both osteoblasts and osteoclasts was found to be an amorphous CaP having mesoporous nanotopography and proper dissolution rate of calcium and silica.

Characterization of a novel calcium phosphate composite bone cement: Flow, setting, and aging properties by M. L. Roemhildt; S. D. Wagner; T. D. McGee (pp. 1127-1132).
The flow, setting, and aging characteristics of a newly developed calcium phosphate/calcium aluminate composite orthopaedic cement were studied. The effect of vibration on the flow of the cement paste was studied and found to greatly enhance placement. The setting times of this cement were dependent on temperature and decreased with increasing temperatures. At 37C, the working and setting times were 6.3 ± 0.3 and 12.8 ± 0.4 minutes, respectively.Hydration and conversion of the cement phases continued while specimens were stored under simulated, physiological conditions. A cumulative increase in mass of 8.23 ± 0.65% was observed over a 14 month test period. During this time, the cement was found to expand slightly, 0.71 ± 0.39%. X-ray diffraction was used to characterize the crystalline phases present during hydration and conversion. The calcium aluminate in the cement hydrated and formed calcium aluminate chloride hydrates, while no changes were observed in the β-tricalcium phosphate during the testing period.

Study on machinable glass-ceramic containing fluorophlogopite for dental CAD/CAM system by Hong Li; De-Qiang You; Chang-Ren Zhou; Jun-Guo Ran (pp. 1133-1137).
The glass-ceramic mainly containing fluorophlogopite is one of widely used dental ceramics. In the K2O-CaO-MgO-Al2O3-SiO2-F system, a new-type glass-ceramic containing fluorophlogopite Ca-mica has been synthesized. Its crystalline was studied by XRD and EDS. The fluorophlogopite whose formula postulated K1 − X Ca X/2Mg3AlSi3O10F2 was its main crystalline. The microstructure of the glass-ceramic displayed typical machinable microstructure with lath like crystals isolated and interlocking with different aspect ratio. The material also showed better bending strength (228.11 ± 7.55 MPa). It took less than 12 minutes to fabricate a whole crown by dental CAD/CAM system with the glass-ceramic.

Bone-like apatite coating on Mg-PSZ/Al2O3 composites using bioactive systems by A. A. Nogiwa; D. A. Cortés (pp. 1139-1144).
A biomimetic method was used to promote bioactivity on zirconia/alumina composites. The composites were composed of 80 vol% Mg-PSZ and 20 vol% Al2O3. Samples of these bioinert materials were immersed in simulated body fluid (SBF) for 7 days on either a bed of wollastonite ceramics or bioactive glass. After those 7 days, the samples were immersed in a more concentrated solution (1.4 SBF) for 14 days. Experiments were also performed without using a bioactive system during the first stage of immersion. A bone-like apatite layer was formed on the surface of all the materials tested, using wollastonite the bioactive layer was thicker and its morphology was close to that observed on the existing bioactive systems. A thinner apatite layer consisting of small agglomerates was obtained using bioactive glass. The thickness of the ceramic layers was within the range of 15 to 30 μm.

Injectable bone substitute to preserve alveolar ridge resorption after tooth extraction: A study in dog by D. Boix; P. Weiss; O. Gauthier; J. Guicheux; J.-M. Bouler; P. Pilet; G. Daculsi; G. Grimandi (pp. 1145-1152).
The aim of the present study was to assess the efficacy of a ready-to-use injectable bone substitute on the prevention of alveolar ridge resorption after tooth extraction. Maxillary and mandibular premolars were extracted from 3 Beagle dogs with preservation of alveolar bone. Thereafter, distal sockets were filled with an injectable bone substitute (IBS), obtained by combining a polymer solution and granules of a biphasic calcium phosphate (BCP) ceramic. As a control, the mesial sockets were left unfilled. After a 3 months healing period, specimens were removed and prepared for histomorphometric evaluation with image analysis. Histomorphometric study allowed to measure the mean and the maximal heights of alveolar crest modifications. Results always showed an alveolar bone resorption in unfilled sockets. Resorption in filled maxillary sites was significantly lower than in control sites. Interestingly, an alveolar ridge augmentation was measured in mandibular filled sockets including 30% of newly-formed bone. It was concluded that an injectable bone substitute composed of a polymeric carrier and calcium phosphate can significantly increase alveolar ridge preservation after tooth extraction.

In vitro testing of Nd:YAG laser processed calcium phosphate coatings by A. De Carlos; F. Lusquiños; J. Pou; B. León; M. Pérez-Amor; F. C. M. Driessens; K. Hing; S. Best; W. Bonfield (pp. 1153-1160).
Nd:YAG laser cladding is a new method for deposition of a calcium phosphate onto metallic surfaces of interest in implantology. The aim of this study was to compare the biologic response of MG-63 human osteoblast-like cells grown on Ti-6Al-4V substrates coated with a calcium phosphate layer applied using different methods: plasma spraying as reference material and Nd:YAG laser cladding as test material. Tissue culture polystyrene was used as negative control. The Nd:YAG laser clad material showed a behaviour similar to the reference material, plasma spray, respective to cell morphology (SEM observations), cell proliferation (AlamarBlue assay) and cytotoxicity of extracts (MTT assay). Proliferation, as measured by the AlamarBlue assay, showed little difference in the metabolic activity of the cells on the materials over an 18 day culture period. There were no significant differences in the cellular growth response on the test material when compared to the ones exhibited by the reference material. In the solvent extraction test all the extracts had some detrimental effect on cellular activity at 100% concentration, although cells incubated in the test material extract showed a proliferation rate similar to that of the reference material. To better understand the scope of these results it should be taken into account that the Nd:YAG clad coating has recently been developed. The fact that its in vitro performance is comparable to that produced by plasma spray, a material commercially available for more than ten years, indicates that this new laser based method could be of commercial interest in the near future.

Bond-coating in plasma-sprayed calcium-phosphate coatings by F. N. Oktar; M. Yetmez; S. Agathopoulos; T. M. Lopez Goerne; G. Goller; I. Ipeker; J. M. F. Ferreira (pp. 1161-1171).
The influence of bond–coating on the mechanical properties of plasma-spray coatings of hydroxyatite on Ti was investigated. Plasma-spray powder was produced from human teeth enamel and dentine. Before processing the main apatite coating, a very thin layer of Al2O3/TiO2 was applied on super clean and roughened, by Al2O3 blasting, Ti surface as bond-coating. The experimental results showed that bond-coating caused significant increase of the mechanical properties of the coating layer: In the case of the enamel powder from 6.66 MPa of the simple coating to 9.71 MPa for the bond-coating and in the case of the dentine powder from 6.27 MPa to 7.84 MPa, respectively. Both tooth derived powders feature high thermal stability likely due to their relatively high content of fluorine. Therefore, F-rich apatites, such those investigated in this study, emerge themselves as superior candidate materials for calcium phosphate coatings of producing medical devices. The methods of apatite powder production and shaping optimization of powder particles are both key factors of a successful coating. The methods used in this study can be adopted as handy, inexpensive and reliable ways to produce high quality of powders for plasma spray purposes.

Precipitation of octacalcium phosphates on artificial enamel in artificial saliva by Y. Sato; T. Sato; M. Niwa; H. Aoki (pp. 1173-1177).
The natural saliva samples were collected from 30 Japanese men and women aged between 20 and 30, and the inorganic components in the saliva were analyzed chemically. Artificial saliva (AS) was prepared based on the chemical analysis using chemical reagents. The calcium/phosphate molar ratio of the AS was 0.28 with pH = 7.0. Artificial enamel (AE) was prepared by sintering hydroxyapatite powder at 1,200C. The AE was placed in the AS at 37C. XRD, SEM and EDX investigated precipitation on the AE. The precipitation was always identified as being OCP. As decrease in the pH of the surface of the AE and increase in the concentration of phosphate ions were observed by chemical analysis, it was concluded that the OCP occurs by the pH decrease and phosphate ion concentration increase on the surface of AE.

Calcium phosphate fibres synthesized from a simulated body fluid by E. C. Kolos; A. J. Ruys; R. Rohanizadeh; M. M. Muir; G. Roger (pp. 1179-1189).
The biomimetic coating method was used for fabricating calcium phosphate fibres for biomedical applications such as bone defect fillers. Natural cotton substrate was pre-treated with phosphorylation and a Ca(OH)2 saturated solution. The pre-treated samples were then soaked in simulated body fluid (SBF) of two different concentrations, 1.5 times and 5.0 times the ion concentration of blood plasma. The cotton was then burnt out via sintering of the ceramic coating at 950C, 1050C, 1150C, and 1250C. The results demonstrated that osteoblastic cells were able to cover the entire surface cotton fibres, and the cell coverage appeared to be independent of surface roughness and Ca/P ratio of fibres.
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