Bioresorbable and bioactive polymer/Bioglass® composites with tailored pore structure for tissue engineering applications

An overview about the development of porous bioresorbable composite materials for applications as scaffolds in tissue engineering is presented. A thermally induced phase separation method was developed to fabricate porous foam-like structures of poly(lactide-co-glycolide) (PLGA) containing bioactive glass particle additions (up to 50 wt.%) and exhibiting well-defined, oriented and interconnected porosity. The in vitro bioactivity and the degradability of the composite foams were investigated in contact with phosphate buffer saline (PBS). Weight loss, water absorption and molecular weight measurements were used to monitor the polymer degradation after incubation periods of up to 7 weeks in PBS. It was found that the presence of bioactive glass retards the polymer degradation rate for the time period investigated. The present results show a way of controlling the in vitro degradation behaviour of PLGA porous composite scaffolds by tailoring the concentration of bioactive glass.     

Electrophoretic deposition of carbon nanotubes

Electrophoretic deposition (EPD) has been gaining increasing interest as an economical and versatile processing technique for the production of novel coatings or films of carbon nanotubes (CNTs) on conductive substrates. The purpose of the paper is to present an up-to-date comprehensive overview of current research progress in the field of EPD of CNTs. The paper specifically reviews the preparation and characterisation of stable CNT suspensions, and the mechanism of the EPD process; it includes discussion of pure CNT coatings and CNT/nanoparticle composite films. A complete discussion of the EPD parameters is presented, including electrode materials, deposition time, electrode separation, deposition voltage and resultant electric field. The paper highlights potential applications of the resulting CNT and CNT/composite structures, in areas such as field emission devices, fuel cells, and supercapacitors.     

A Glass–Ceramic Derived from High TiO2-Containing Slag: Microstructural Development and Mechanical Behavior

A novel glass–ceramic material was developed from the melt of a TiO₂-containing iron-making slag with additional waste glass. The high percentage (∼20 wt% TiO₂) of this network-modifying oxide has promoted a crystallization of the parent glass, resulting in a fine-grained, homogeneous polycrystalline material with high mechanical properties ( E =120 GPa, flexural strength=∼180 MPa, and Vickers hardness=7 GPa) after a heat treatment at 1100°C for 2 h. The room temperature and elevated temperature fracture toughness were also studied. The main crystalline phases of the glass–ceramic material were of the pyroxene series until heat-treatment temperature reached 1000°C, at which titanium-rich perovskite and armalcolite crystals became the dominant phases. The end material is high-strength, aesthetically acceptable (metallic gray or opaque brown colored), and suitable for structural and architectural applications.     

Processing ceramic-matrix composites using electrophoretic deposition

A novel, cost-effective processing technique for manufacturing ceramic-matrix composites (CMCs) containing two-dimensional woven-fiber reinforcement has been developed. The technique relies on the electrophoretic deposition (EPD) of ceramic sols on/into the fiber preforms to achieve the required impregnation. The laboratory-scale results achieved thus far indicate that the processing approach offers great potential for the manufacture of high-quality, composite products with dual-component oxide matrices for high-temperature structural applications.     

Sintering of glass matrix composites containing Al2O3 platelet inclusions

The effect of alumina platelet inclusions on the sintering behaviour of a commercial aluminosilicate glass powder has been investigated by means of a heating microscope at 850°C. For platelet volume fractions 0.15, no significant influence of the inclusions on the densification behaviour of the composite was found. Scherer's model for viscous sintering with rigid inclusions, which uses the Hashin-Shtrikman approximation for the composite shear viscosity, can be conveniently used to interpret the experimental results. However, the composite densification rate and the stresses caused by the inclusions can be correctly predicted using this model only for inclusion volume fractions lower than a critical value, given by the percolation threshold. For platelet volume fractions 0.15, high-density glass matrix composites can be fabricated by simple pressureless sintering.     

Processing and mechanical properties of biocompatible Al2O3 platelet-reinforced TiO2

The mechanical behaviour of Al₂O₃ platelet-reinforced TiO₂ bioceramics produced by hot-pressing has been investigated. The variation of the elastic constants, fracture strength and fracture toughness with the volume fraction of platelet content was studied. The addition of platelets did not affect the critical flaw size of the composites. This fact, and the good matrix/platelet interfacial bond resulted in a simultaneous increase of the fracture strength and toughness. The mechanical properties increased from K_Ic=2.4 MPa m^1/2 and ₀=215 MPa for pure TiO₂ to K_Ic=3.3 MPa m^1/2 and ₀=265 MPa for a 30 vol% platelet-containing composite. The indentation technique demonstrated the anisotropic behaviour of the fracture toughness in the composites due to platelet orientation during hot-pressing. Load transfer was identified as the main reinforcing mechanism and the toughening effect could be assessed by a load transfer-based model equation. Fracture surface analysis showed mainly intercrystalline fracture for the TiO₀ matrix, whilst with the composites, fracture became more transcrystalline with increasing platelet content.     

Prediction of the Poisson's ratio of porous materials

An equation is presented for the prediction of the Poisson's ratio of porous materials. The equation is strictly derived for spherical porosity and isotropic materials and it is valid for the whole porosity range. For low porosity, the equation coincides with a published equation, which has been verified in the past by comparison with extensive experimental data. For the high-porosity range, the theoretical variation of the Poisson's ratio exhibits a trend converging to a value _P =0.5, when the porosity increases to P=1, A similar converging trend has been found in other theoretical studies, but a rigorous experimental verification of such variations has still to be carried out.