Key Engineering Materials Vols. 396-398

Abstract: Particle size is one of the most important factors to the successful application of calcium phosphate bioceramics as it may have an important role on its final properties such as mechanical resistance and reactivity. Thus, a process which results on very small and homogeneous particles is required, since it avoids further contamination derived from long milling times. On this context, a process such as sol-gel synthesis may be feasible, due to its simplicity on handling and its well known characteristic of producing homogeneous nanoparticles. Moreover, precipitated HA also may lead to satisfactory results regarding particle size and phase purity. The aim of this article was to demonstrate a preliminary characterization study of powders obtained by both methods and to compare them to a commercial sample available in Brazil. Characterization was made by XRD, Scherrer’s equation, XRF, SEM-LV, SEM-FEG and SEM-EDS. It has been found out that all samples consist of pure nanostructured hydroxyapatite with crystallite size between 37nm and 62nm.

Abstract: A three-layer coating for stents with a nanostructured surface of calcium phosphate (CaP) is pre-sented. The coating stack consists of (a) a TiNbN layer deposited by physical vapour deposition and acting as diffusion barrier against allergenic ions, (b) a SiO2 xerogel layer providing good adhesion properties and designing the nanoporosity of the outer CaP layer (c) precipitated electrochemically. The verification of the SiO2-layer (and therewith its influence onto adhesion and structure of the outer CaP layer) succeeded only by use of XPS because of the very small amount of the xerogel. SEM results verified a homogeneous nanoscale nanoporous structure of the CaP coating. It is char-acterised by high adhesion strength. If applied for stent covering the nanoscale CaP coating has promising properties to initiate rapid endothelium formation and reduced risk of restenosis.

Abstract: A novel bone scaffolding material was successfully fabricated by electrospinning from hyperbranched polyglycerol (HPGL) solutions containing nanoparticles of hydroxyapatite (HA). The potential use of the electrospun fibrous HPGL-HA scaffolds for bone regeneration was evaluated in vitro with human osteoblasts in terms of alkaline phosphatase (ALP) activity of the cells that were cultured directly on the scaffolds. The results were compared with those on corresponding HPLG-HA solution-cast film scaffolds. It was found that all of the fibrous scaffolds promoted much better adhesion and proliferation of cells than the corresponding film scaffolds.

Abstract: This paper describes the use of micro-computed tomography for determining in vitro degradation of calcium-phosphate ceramic materials. Samples were immersed in a simulated body fluid and scanned at the initial and final timepoints. Analysis indicates degradation of material density as well as changes in mineral content and mineral density. Findings are confirmed with known methods of materials characterization (SEM, mass analysis, and Archimedes’s density calculations), indicating changes in surface morphology, mass, and pore volume.

Abstract: Bioactive ceramics have the ability to chemically bond to bone. This class of biomaterials can be used as coatings on metallic implants, alloplastic bone defect fillers and as scaffold for tissue engineering. The most widely used bioactive ceramics are hydroxyapatite, Ca10(PO4)6(OH)2 and tricalcium phosphate, Ca3(PO4)2. This study presents new bioactive ceramics based on Nb2O5 and Ta2O5. These materials were produced from bioinert ceramics chemically activated by an alkali hydrothermal treatment. Scanning electron microscopy, energy dispersion X-ray spectroscopy and X-ray diffraction analyses on samples incubated in simulated body fluid showed the presence of bone-like apatite, confirming that the modified ceramics surface became bioactive.

Abstract: Three types of calcium phosphate porous materials were prepared by the applied hydrothermal method. One of them was non-stoichiometric hydroxyapatite (HA) with calcium deficient composition and the others were β-tricalcium phosphate (β-TCP) and HA/β-TCP bi-phase material. Granules with several millimeter in size of calcium deficient HA, β-TCP and HA/β-TCP could be prepared. These granules with porosity over 70 % were composed of rod-shaped particles with aspect ratio about 10. Rod-shaped particles were locked together to make sub-micro-sized pores of about 0.1 to 0.5 µm in size. These materials must be suitable for the bone graft materials and as the scaffolds of cultured bone.

Abstract: Precipitation routes for HA production result in the formation of suspensions of nano-scale hydroxyapatite particles in water. During this work, suspensions of phase-pure and carbonate-substituted hydroxyapatite were produced using a precipitation reaction with calcium hydroxide and orthophosphoric acid as reactants. The chemistry of the apatites was analysed using XRD and FTIR after heat treatment in various atmospheres and the particle morphology investigated using TEM. The thermal stability of the carbonate HA was found to be significantly less than the phase-pure HA and dependent upon the heat-treatment atmosphere. Suspensions were used directly for replication of polymer foam templates with a dip-coating technique. Good replication of the foam structure was achieved with the phase pure hydroxyapatite, but no structural integrity was achieved with the carbonate-HA structure possibly a result of limits on the sintering temperature.

Abstract: Silk has been used in biomedical applications for centuries. The potential of silk for application in tissue engineering is currently being explored. The purpose of this study was to develop new method of mineralizing silk with carbonate apatite and determine cell response. The cocoons were placed in sodium bicarbonate solution and heat treated. The treated silk fibers were mineralized with carbonate apatite (CHA) using precipitation and new microwave methods. The mineralized and non-mineralized silks were characterized using SEM, EDS, XRD, FT-IR, and TGA. Cell response to mineralized silk and non-mineralized silk was determined using human osteoblast like cells (MG-63). The microwave method was more efficient than the precipitation method in terms of the amount of minerals incorporated with the silk and time required for mineralization. EDS, FT-IR and XRD identified CHA in the mineralized silk. In terms of cell response, greater production of type 1 collagen was observed with CHA mineralized silk compared with non-mineralized silk.

Abstract: Selective laser sintering (SLS) has the potential to fabricate bioresorbable polymer / ceramic composite scaffolds with pre-designed external and internal architecture that can be used for bone tissue engineering applications. Scaffolds were fabricated using poly-ε-caprolactone as the base material. The effect of 15 and 30 wt% of hydroxyapatite (HA) addition was investigated in terms of compressive properties, accuracy, surface topology, and wettability. Fabricated dimensions of PCL microstructures showed great deviations from their nominal values. Average surface roughness was found to be Ra=25±4 µm. Increased HA content had no statistically significant effect on accuracy and surface roughness. However the addition of HA had a significant influence on compressive properties, hydrophobicity and wettability of the samples. Addition of 30 wt% HA improved initial compressive modulus of pure PCL scaffolds from 1.31±0.08 MPa to 1.58±0.18 MPa. Yield strength values increased from 0.14±0.07 MPa to 0.17±0.01 MPa by adding 15 wt% of HA, but decreased with further HA addition. Yield strain for all compositions was over ε=0.06. Increased HA content decreased hydrophobicity and increased wettability of scaffold surfaces. The study demonstrated the ability of SLS to fabricate tissue engineering scaffolds, and the positive effect of HA particle reinforcement in terms of compressive mechanical properties and surface characteristics

Abstract: Three dimensional printing was investigated for fabricating hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) composite scaffolds using calcium phosphate based ceramics and calcium phosphate cement chemistry. Scaffolds were formed by printing an aqueous sodium phosphate solution on the powder bed consisting of a mixture of dicalcium phosphate anhydrous (DCPA) and calcium hydroxide powders. The sodium phosphate solution was functioning as a binder material and also as the initiator of the wet chemical reaction. Compressive mechanical properties of printed samples were examined as a function of saturation level that was inversely proportional to the powder to liquid ratio. To increase mechanical properties and obtain hydroxyapatite and β-TCP composites, the printed samples were sintered. The effect of sintering parameters including dwell time and sintering temperature were also examined. X-ray diffraction (XRD) was used to examine material composition at different stages of the manufacturing process and to confirm the presence of HA and β-TCP in the final stage. The effect of sintering procedure on the surface topology of the samples was examined using scanning electron microscopy (SEM).