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.
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.
Hydroxyapatite (HA) is present in the human body as a mineral constituent of the bones and teeth, as well as a major or minor component of kidney stones. HA deposited on different solid substrates can find applications including biomaterials and biosensors.
This work deals with the kinetics of the HA growth by applying a novel method of laser-liquid-solid-interaction (LLSI) process on three types of materials (stainless stell, silicon and silica glass). The method allows interaction between a pulsed laser and a substrate immersed in a solution (simulated body fluid, SBF). By a scanning system, a design of seven squares at a distance of 200 μm was created at the end of each sample. In this way the center of the substrate (about 6x6 mm) was no irradiated. Following the LLSI process, the samples were left in the irradiated SBF for various intervals of time. Light microscopy (LM) showed surfaces seede with randomly distributed transparent and white particles. The surface seeding increased with the immersion time and was dependent on the substrate type. Fourier transform infrared (FTIR) spectrsocopy showed that in the first stage of soaking (up to 6 h) the observed white particles were calcium phosphate containing. Energy dispersive X-ray (EDX) spectrsocopy revealed that the transparent particles were NaCl. In the next stage (after 12 h) vibrational modes typical for HA were clearly observed. Detailed observation with scanning electron microscopy (SEM) after 12 h showed morphology of sphere-like aggregates, grouped in a porous network. Raman spectroscopy, X-ray diffraction (XRD) and EDX confirmed that after 12 h the grown layer was HA.
It was found that in comparison to the traditionally empoyed prolonged soaking in SBF, the applied LLSI process yielded a synergistic effect due to the simultaneous use of the solid substrate, the aqueous solution and the laser energy.
In this paper the use of stainless steel, silicon and silica glass substrates for the growth of hydroxyapatite (HA, widely used as artificial bone material), induced by a laser-liquid-solid-interaction is reported. The method allows growing of HA layer by using the interaction between a laser beam and a liquid precursor solution, as well as laser irradiation of the substrate during the laser-liquid interaction. The scanned laser beam (pulsed CuBr laser) is directed at the solid substrate, which is immersed in the solution, which resembles the ion composition and concentrations of the human blood plasma (simulated body fluid, SBF). The set-up includes an open deposition system, which allows the introduction of the laser beam led by a scanning system. It is shown that the proposed method enhances the HA formation, in comparison with the traditional methods of prolonged soaking in SBF. The HA layers grown in this manner are investigated by Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) Spectroscopy, X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) and Raman Spectroscopy.
In this study stainless steel, silicon and silica glass are used as representatives of metal, semiconductor and isolator with the purpose to create an experimental model for studying the formation of minerals like hydroxyapatite (HA, the bone and teeth mineral part) from aqueous solutions. The samples are Na+ implanted and consequently subjected to thermal treatment in air at 873 K. Implantation with Na+ is known to lead to formation of hydroxylated surface, i.e. formation of metal- or Si-OH- groups upon immersion in a liquid, simulating the human blood plasma (simulated body fluid, SBF). The negatively charged hydroxylated surfaces induce HA formation in SBF. The samples are immersed in SBF, irradiated through the solution with a scanning laser beam (CuBr pulsed laser equipped with a scanning system) and subsequently soaked in the solution at 37°C for a shorter time, comparing to the traditional methods for HA growing. The grown HA layers are investigated by Fourier Transform Infrared (FTIR) and Raman Spectroscopies, X-ray Diffraction (XRD), Light Microscopy (LM), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) Spectroscopy to evaluate the effect of the surface modification by the thermal treatment following the ion implantation, as well as the effect of the laser irradiation on the process of HA formation.