Nanocomposite foams are an attractive prospect in a number of fields including biomedical science, catalysis and filtration. In biomedical engineering, porous nanocomposite scaffolds can potentially mimic aspects of the nanoscale architecture of the extra-cellular matrix, as well as enhance the mechanical properties required for successful weight-bearing implants. Thermoplastic polyurethane-multi-walled carbon nanotubes (CNTs) foams were manufactured by thermally induced phase separation (TIPS). TIPS proved to be a successful manufacturing route to three-dimensional, highly porous polymers containing well-dispersed CNTs. Some CNTs are trapped perpendicular to the pore surface creating a rough, nanotextured surface. The surface character of the nanocomposites became more acidic with increasing loading fraction of oxidised CNTs. However, due to the heterogeneity of the nanocomposite surface, its wetting behaviour was not affected. CNT incorporation significantly improved the compression strength and stiffness of the nanocomposite scaffold. The biological properties of these scaffolds were studied in vitro and revealed that increasing MWNT loading fraction did not cause osteoblast cytotoxicity or detrimental effects on osteoblast differentiation or mineralisation. However, osteoblast production of the potent angiogenic factor VEGF (vascular endothelial growth factor) increased in proportion to CNT loading (after 3 days in culture), revealing the potential of the nanocomposite scaffolds to influence cellular behaviour.

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The remarkable intrinsic properties of carbon nanotubes, including their high mechanical strength, electrical conductivity, and nanoscale 3D architecture, create promising opportunities for the use of nanotube composites in a number of fields, particularly for composites in which conventional fillers cannot be accommodated. In the current study, 3D polyurethane (PU) nanocomposite foams were developed, and their potential biomedical applications were investigated. Multiwalled carbon nanotubes (CNTs) were synthesized by chemical vapor deposition and, following suitable chemical modification, uniformly distributed within the walls of PU foams produced by direct reaction. Although the loading fraction was too low to observe significant mechanical effects, CNT incorporation improved the wettability of the nanocomposite surfaces in a concentration-dependent manner, supporting the claim that the nanotubes are active at the pore surface. Studies of bone cell interactions with the nanocomposite foams revealed that increasing CNT loading fraction did not cause osteoblast cytotoxicity nor have any detrimental effects on osteoblast differentiation or mineralization. The application of "fixed" or embedded CNTs in nondegradable scaffolds is likely advantageous over "loose" or unattached CNTs from a toxicological point of view.

Polymer scaffolds tailored for tissue engineering applications possessing the desired pore structure require reproducible fabrication techniques. Nondestructive, quantitative methods for pore characterization are required to determine the pore size and its distribution. In this study, a promising alternative to traditional pore size characterization techniques is presented. We introduce a quantitative, nondestructive and inexpensive method to determine the pore size distribution of large soft porous solids based on the on the displacement of a liquid, that spreads without limits though a porous medium, by nitrogen. The capillary pressure is measured and related to the pore sizes as well as the pore size distribution of the narrowest bottlenecks of the largest interconnected pores in a porous medium. The measured pore diameters correspond to the narrowest bottleneck of the largest pores connecting the bottom with the top surface of a given porous solid. The applicability and reproducibility of the breakthrough technique is demonstrated on two polyurethane foams, manufactured using the thermally induced phase separation (TIPS) process, with almost identical overall porosity (60-70%) but very different pore morphology. By selecting different quenching temperatures to induce polymer phase separation, the pore structure could be regulated while maintaining the overall porosity. Depending on the quenching temperature, the foams exhibited either longitudinally oriented tubular macropores interconnected with micropores or independent macropores connected to adjacent pores via openings in the pore walls. The pore size and its distribution obtained by the breakthrough test were in excellent agreement to conventional characterization techniques, such as scanning electron microscopy combined with image analysis, BET technique, and mercury intrusion porosimetry. This technique is suitable for the characterization of the micro- and macropore structure of soft porous solids intended for tissue engineering applications. The method is sensitive for the smallest bottlenecks of the largest continuous pores throughout the scaffold that contributes to fluid flow.

Porous 3D polymer scaffolds prepared by TIPS from PLGA (53:47) and PS are intrinsically hydrophobic which prohibits the wetting of such porous media by water. This limits the application of these materials for the fabrication of scaffolds as supports for cell adhesion/spreading. Here we demonstrate that the interior surfaces of polymer scaffolds can be effectively modified using atmospheric air plasma (AP). Polymer films (2D) were also modified as control. The surface properties of wet 2D and 3D scaffolds were characterised using zeta-potential and wettability measurements. These techniques were used as the primary screening methods to assess surface chemistry and the wettability of wet polymer constructs prior and after the surface treatment. The surfaces of the original polymers are rather hydrophobic as highlighted but contain acidic functional groups. Increased exposure to AP improved the water wetting of the treated surfaces because of the formation of a variety of oxygen and nitrogen containing functions. The morphology and pore structure was assessed using SEM and a liquid displacement test. The PLGA and PS foam samples have central regions which are open porous interconnected networks with maximum pore diameters of 49 microm for PLGA and 73 microm for PS foams.