E. Pecheva

Peculiarities of hydroxyapatite/nanodiamond composites as novel implants

Hydroxyapatite/detonation nanodiamond composites are created on silica glass and cover glass by simple soaking process in an open deposition type set-up. The supersaturated solution (simulated body fluid, SBF) is prepared in a way to resemble the composition of human blood plasma. The composite growth is carried out through the addition of detonation nanodiamond particles to the SBF. Scanning electron microscopy, X-ray diffraction and FTIR spectroscopy are used to determine the surface morphology and the structure of the hydroxyapatite /detonation nanodiamond composite layers. The applied methods provide evidence that the nanodiamond surface functional groups interact strongly with the biological solution. The detonation nanodiamond surface is chemically multifunctional (surface OH, C-O-H, C = C, C-O-C and C = O groups exist), so that the hydroxyapatite is grown both by physical adsorption and chemical interaction. The OH- groups are regarded to play an important role in the hydroxyapatite growth on a diamonds surface from SBF, as they charge it negatively and attract Ca2+ ions, which in turn attract PO43- ions, thus forming apatite nuclei.

Towards real time 3D quantitative characterisation of in situ layer growth using white light interference microscopy

Quantitative 3D characterisation of layer growth or modification in situ in liquid systems is a challenge because of the changing morphology of the layer and the presence of the growth liquid. Because of the limited bandwidth of many surface profiling techniques, measurement of microscopic surface roughness is generally limited to that of static surfaces. The aim of the present work is to develop a new technique using high speed scanning interference microscopy combined with an adapted immersion head for use in liquid growth systems. For several years we have been developing a real time 3D surface analysis system based on a high speed camera and cabled logic processing, combined with continuous scanning white light interferometry. An optical measurement head is also being developed for use in liquid immersion conditions, with the view of measuring layer growth or modification in biomaterials. In this paper we report on the present status of the development of our second prototype 4D system and also of the optical immersion head for in situ measurements, describing the achievements made and the difficulties still to be overcome.

A novel laser-liquid-solid interaction process for hydroxyapatite formation on porous silicon

The mechanism of hydroxyapatite (HA, Ca10(PO4)6(OH)2) growth on the surface of porous silicon (PS) was examined. PS layers were prepared by electrochemical or chemical etching of n-type Si with (111) orientation, and p-type Si with (100) orientation. HA growth was induced by two methods: a simple soaking process in a simulated body fluid (SBF) and a novel Laser-Liquid-Solid Interaction (LLSI) process which allowed interaction between a scanning laser beam and the PS substrate immersed in the SBF. The grown layers were investigated by light microscopy, electron microprobe analysis, Raman spectroscopy and X-ray diffraction. Differently doped Si substrates with different crystallographic orientation and electrical resistivity were used and their effect on the HA growth, as well as the effect of the laser energy were examined.

Study of Organosilicon Plasma Polymer Used in Composite Layers with Biomedical Application

In this work we study the ability of plasma polymer (PP) films obtained from hexamethyldisiloxane (HMDS) on silica glass (SG) to induce hydroxyapatite (HA)‐based composite layers from a mixture of simulated body fluid (SBF) and clear solution of detonation nanodiamond (DND) by a biomimetic process. The grown composites (PPHMDS/HADND) were studied by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Rutherford backscattering (RBS) techniques. FTIR spectra of the PPHMDS indicated diminishing of the polymer characteristic bands when the polymer is immersed in DND clear solution. Furthermore, after sample immersion in the SBF‐DND mixture, the FTIR spectra showed the presence of carbonate‐containing HA through the characteristic vibration modes of P‐O in the phosphate group and C‐O in the carbonate group. The formation of HA layers, rich in silica and/or carbon was confirmed by RBS and SEM. The cell viability measured after 7 days on the polymer surface is more then 95% for...

Natural Opal as a Model System for Studying the Process of Biomineralization

Opal is a natural nanostructure model. It possesses nanosized close packed silica spheres and a regular sublattice of voids, filled with molecular water and accessible for filling by other substances. Using natural opal as a substrate, no complimentary technique is needed to produce a patterned surface as it is present naturally. Thus, the possession of nano-dimensions for efficient influencing of different biological events can be used in the laboratory and biologically integrated multifunctional devices (biomaterials, sensors) could be created. Additionally, biomineralization mechanisms may be studied using model systems. The main purpose of the work is to use nanostructured or other functionalized materials as models to contribute to the study of biomineralization. Particularly this paper reports on the ability of natural opal from Bulgarias Eastern Rhodopes mountain to induce the deposition of a surface layer of calcium phosphate from simulated body fluid. Raman, infrared spectroscopy and XRD were used to show that opal consists of two main phases: microcrystalline quartz and cristobalite and that the observed with optical microscopy layer deposited from the simulated body fluid on both phases was calcium phosphate.

Study of the calcium phosphate layer grown on AISI 316 stainless steel from simulated body fluid

A calcium phosphate layer was deposited on the surface of AISI 316 stainless steel by immersion in a solution supersaturated with calcium and phosphorus ions. The substrates were pre-modified by ion implantation of Ca and P, in order to induce nuclei for calcium phosphate growth on the surface. The reactivity of these surfaces towards crystal growth in aqueous solution was examined by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. This showed that the deposited layer was a mixture of hydroxyapatite and other calcium phosphates.

Precise femtosecond laser ablation of dental hard tissue: preliminary investigation on adequate laser parameters

This work aims at evaluating the possibility of introducing state-of-the-art commercial femtosecond laser system in restorative dentistry by maintaining well-known benefits of lasers for caries removal, but also in overcoming disadvantages such as thermal damage of irradiated substrate. Femtosecond ablation of dental hard tissue is investigated by changing the irradiation parameters (pulsed laser energy, scanning speed and pulse repetition rate), assessed for enamel and dentin. The femtosecond laser system used in this work may be suitable for cavity preparation in dentin and enamel, due to the expected effective ablation and low temperature increase when using ultra short laser pulses. If adequate laser parameters are selected, this system seems to be promising for promoting a laser-assisted, minimally invasive approach in restorative dentistry.

Hydroxyapatite Reinforced Coatings with Incorporated Detonationally Generated Nanodiamonds

We studied the effect of the substrate chemistry on the morphology of hydroxyapatite‐detonational nanodiamond composite coatings grown by a biomimetic approach (immersion in a supersaturated simulated body fluid). When detonational nanodiamond particles were added to the solution, the morphology of the grown for 2 h composite particles was porous but more compact then that of pure hydroxyapatite particles. The nanodiamond particles stimulated the hydroxyapatite growth with different morphology on the various substrates (Ti, Ti alloys, glasses, Si, opal). Biocompatibility assay with MG63 osteoblast cells revealed that the detonational nanodiamond water suspension with low and average concentration of the detonational nanodiamond powder is not toxic to living cells.

Optimised 3D surface measurement of hydroxyapatite layers using adapted white light scanning interferometry

Biomineralization is intensively studied at present due to its importance in the formation of bones, teeth, cartilage, etc. Hydroxyapatite is one of the most common natural biomaterials and the primary structural component of bones and teeth. We have grown bio-like hydroxyapatite layers in-vitro on stainless steel, silicon and silica glass by using a biomimetic approach (immersion in a supersaturated aqueous solution resembling the ion composition of human blood plasma). Using classical techniques such as stylus profiling, AFM or SEM, it was found difficult, destructive or time-consuming to measure the topography, thickness and profile of the heterogeneous, thick and rough hydroxyapatite layers. White light scanning interferometry, on the other hand, has been found to be particularly useful for analyzing such bio-like layers, requiring no sample preparation and being rapid and non-destructive. The results have shown a typical layer thickness of up to 20 μm and a rms roughness of 4 μm. The hydroxyapatite presents nonetheless a challenge for this technique because of its semi-translucence, high roughness and the presence of cavities within its volume. This results in varying qualities of fringe pattern depending on the area, ranging from classical fringes on smooth surfaces, to complex speckle-like fringes on rough surfaces, to multiple fringe signals along the optical axis in the presence of buried layers. In certain configurations this can affect the measurement precision. In this paper we present the latest results for optimizing the measurement conditions in order to reduce such errors and to provide additional useful information concerning the layer.

Hydroxyapatite Growth on Glass/CdSe/SiOx Nanostructures

The aim of this study was to find if nanocrystal layers obtained by well-established nanotechnology are able to induce deposition of hydroxyapatite [Ca10(PO4)6(OH)2]. It is known that nanosized objects and porous structures influence biological events and they may be used to create biologically integrated multifunctional devices including biomaterials and sensors. In this work, sequential physical vapour deposition of CdSe and SiO, or SiOx film was used to modify glass substrates. To study the ability of the nanostructured surfaces to induce hydroxyapatite deposition, samples were immersed in a simulated body fluid and simultaneously irradiated with a scanning laser beam for a few minutes. This resulted in a porous sponge-like non homogeneous hydroxyapatite layer, consisting of networks of aggregates of nano dimensions on the modified surfaces. Analysis showed higher Ca and P contents in the stripes of the laser-substrate interaction, which indicated the influence of the laser energy. The method of laser-liquid-solid interaction used has led to a synergistic effect due to the simultaneous use of the nanostructured substrate, aqueous solution and laser energy.