Key Engineering Materials Vols. 309-311

Abstract: Apatite pattern was prepared by electrophoretic deposition (EPD) transcribing resist pattern. A porous polytetrafluoroethylene (PTFE) film was used as a substrate and attached on a cathode. The cathode for EPD was stainless plate with resist pattern. EPD was performed with a suspension of wollastonite particles in acetone and wollastonite particles were deposited on the substrate in the form of the resist pattern. When the wollastonite-deposited substrate was soaked in simulated body fluid (SBF), apatite was induced and then replaced wollastonite at the wollastonite deposited region on the substrate. As a result, apatite was formed in the pattern that traced the resist pattern. The minimum line width of the apatite pattern was about 100 µm.

Abstract: Apatite micropattern was fabricated by a combination of biomimetic process and transcription of resist pattern. We optimized some fabrication conditions such as the height of resist pattern, temperature, concentrations and pH of simulated body fluid(SBF). Consequently, we successfully obtained apatite micropattern widely and homogeneously on a substrate in a short fabrication period.

Abstract: Particulate layers of hydroxyapatite were deposited on the inner and outer surfaces of porous poly(L-lactic acid) monolith, PLLA, by using enzymatically derived ammonia as the precipitant. PLLA specimens were surface-modified with urease and were impregnated with aqueous solutions containing Ca2+, PO4 3- and urea. As ammonia was produced by hydrolysis of urea with the aid of the urease, hydroxyapatite precipitated predominantly on the surfaces of the porous PLLA. In contrast to the conventional biomimetic method or the alternate soaking method, it took shorter time period for hydroxyapatite particles to cover the surfaces of PLLA. The resultant hydroxyapatite was proved to be bone-like apatite because it had low crystallinity, contained carbonate ion in the lattice, and had a calcium-deficient composition.

Abstract: Organic-inorganic hybrids composed of organic polymer and apatite is quite attractive as novel bone-repairing materials since it has mechanical performance analogous to those of natural bone as well as bone-bonding ability, i.e. bioactivity. To fabricate such an apatite-polymer hybrid, biomimetic process has been recently paid much attention. In this process, bone-like apatite is deposited on the surfaces of organic substrates in simulated body fluid (SBF, Kokubo solution) having ion concentrations analogous to those of human extracellular fluid or more concentrated solutions. Previous studies showed that the apatite deposition is triggered by a catalytic effect of carboxyl groups (COOH) on the surfaces of the organic substrates. In this study, we examined apatite deposition on natural polypeptides derived from crops in a biomimetic solution. We selected gluten derived from wheat and zein derived from corn. Both of gluten and zein formed bone-like apatite on their surfaces in a solution that has inorganic ion concentrations 1.5 times those of simulated body fluid, when they were treated with 1 mol/L calcium chloride solution. High content of acidic amino acids such as glutamic acid and aspartic acid in gluten and zein would give large amount of carboxyl groups effective for the apatite nucleation.

Abstract: Natural bone has excellent mechanical properties such as high fracture toughness and high flexibility. These properties are achieved by specific microstructure of natural bone that is composed of the organic collagen and inorganic apatite. On the basis of these findings, apatite-polymer hybrids are expected as novel bone substitutes having excellent mehcanical performances and high bone-bonding ability, i.e. bioactivity. In this study, we attempted preparation of apatite-polyglutamic acid hybrids through biomimetic process that mimics the principle of biomineralization. Simple chemical modification of the polyglutamic acid gel with 1 M (= mol/L) calcium chloride solution provided the gel with apatite-forming ability in simulated body fluid (SBF, Kokubo solution). This type of hybrid is also useful for designing bioactive bone substitutes with injectability, since viscosity of the polyglutamic acid gel can be easily controlled according to degree of cross-linking.

Abstract: An apatite coating by an alternate soaking was undertaken on commercially pure titanium (cpTi) treated with concentrated acid and alkaline solutions. X-ray diffraction (XRD) patterns indicated that the diffraction peak intensities assigned to hydroxyapatite (HAp) increased with the reaction cycle. Fourier transform infrared spectroscopic study (FTIR) showed similar results with XRD. Scanning electron micrographs (SEM) of the deposits showed no observable change after the vacuum firing. It was confirmed that the reaction cycle greatly affected on the deposited amount of apatite on cpTi plates using the alternate soaking and the vacuum firing erased TiH2 formed during the acid etching, but was irrelevant to the crystallinity of the apatite.

Abstract: Surface topography plays an important role in determining the functional performance of engineering materials as well as cell-material interactions. In this work is investigated the surface topography of an apatite layer that was developed on Bioglass® (PerioGlas® Synthetic Bone Graft Particulate, US Biomaterials)-modified dental ceramics, used in fixed prosthetic restorations, after immersion in a Simulated Body Fluid (SBF). The visualization of the surface morphology and structure and the gradual formation of the apatitic layer were followed by CLSM, as well as by ESEM and EDS. Topography profiles on specimens’ surface revealed high surface roughness and a fluctuation of RMS values in relation to immersion time in SBF, due to the continuing process of apatite precipitation.

Abstract: The biomaterial surface represents the first contact point for proteins and cells and is thus critical to optimise the features to transmit the best signals for tissue and organ regeneration. Both chemistry and topography are surface characteristics that can be modified by the manufacturing process and provide signals to cells. While chemistry and crystallinity have received attention for thermally sprayed hydroxyapatite coatings, the control of the surface microtopography has not been addressed. This study collected a range of implants with a coating and assessed the topography on dental implants, orthopaedic screws and hip prostheses. The surface was found to be composed of large topographic features (angular particulate and smooth areas) and micron sized aspects (fine grains, cracks and ridges). Thermal spray experiments were designed to determine the influence of processing conditions on droplet spreading. This knowledge was then applied to see the effect of different parameters on the final coating topography. The parameters investigated for their influence on the surface topography included substrate roughness, substrate temperature, spray distance and particle size. The particle size showed the largest influence on altering the roughness, Ra of the coating. A two-fold increase in particle size doubled the roughness from Ra of 4.8 µm when the powder was sprayed under the same conditions.

Abstract: Fluoride, when incorporated in the apatite, stabilizes the structure. The purpose of this study was to determine the consequences of fluoride (F) substitution on the physico-chemical properties of apatites. F-containing apatites were prepared by precipitation or by hydrolysis of CaHPO4 in solutions containing different F concentrations and characterized using x-ray diffraction, FT-IR spectroscopy, scanning electron microscopy, thermogravimetry and chemical analyses. Results showed that F incorporation have the following effects: (a) decrease in a-axis dimension, (b) increase in crystal size and thickness, (c) decrease in calcium deficiency, and (d) lower solubility.