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Biodegradable implants have shown great promise for the repair of bone defects and have been commonly used as bone substitutes, which traditionally would be treated using metallic implants. The need for a second surgery exacerbated by the stress shielding effect caused by an implant has led researchers to consider more effective, synthetic biodegradable graft substitutes. The hierarchical structures commonly designed are inspired by nature in human bones, which consist of minerals such as hydroxyapatite, a form of calcium phosphate and protein fiber. The bone graft bio-substitutes should possess a combination of properties for the purpose of facilitating cell growth and adhesion, a high degree of porosity, which would facilitate the transfer of nutrients and excretion of the waste products, and the scaffold should have high tensile strength and high toughness in order to be consistent with human tissues. Blending of polycaprolactone and hydroxyapatite has demonstrated great potential as bone substitutes. It is essential to identify a standardized processing methodology for the composite, which would result in optimum mechanical property for the biocomposite. In this study, biocomposites made of polycaprolactone (PCL) and hydroxyapatite (HAP) are reviewed for their applications in bone tissue engineering. The processing methodologies are discussed for the purpose of obtaining the porosity and pore size required in an ideal tissue scaffold. The properties of the composite can be varied based on the change in pore size, porosity, and processing methodology. This paper reviews and evaluates the methods to produce the hydroxyapatite-polycaprolactone scaffolds.

Morphological and mechanical properties of hydroxyapatite (HAP)-reinforced polycaprolactone (PCL) were studied. The objective was to examine how morphological features alter the bulk mechanical properties in our laboratory-synthesized HAP-reinforced PCL. HAP crystals were synthesized by hydrolysis of mixtures of calcium and phosphate salts in the laboratory with wet chemical methods. The properties of the commercially available hydroxyapatite (HAP(1)) are compared with that of laboratory-synthesized hydroxyapatite (HAP(2)). The HAP crystals and composition were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectrometry (FTIR). The HAP(1) and HAP(2) crystals were dispersed into polymers to examine the mechanical behavior of bioactive composites, and the interfacial interactions between the polymer and HAP crystals are addressed. The FTIR results confirmed that the two forms of HAP crystals are consistent in terms of the functional chemical groups. The wide angle X-ray diffraction study was performed to determine the crystallinity of the bioactive composites. It was observed that the crystallinty of HAP-filled PCL steadily increased as the filler concentration increased. Generally, HAP(2) has a particle size considerably smaller than HAP(1) and the composite derived had higher modulus than conventional HAP-filled polymers. This increase in modulus is attributed to better interfacial interaction. Bioresorbability tests performed on HAP particles found that the synthesized HAP had higher resorption rates. It is clear that the mechanical properties are influenced by the particle size and therefore by the processing method used.

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In the present study, an attempt has been made to tailor the properties of monolithic magnesium by initially reinforcing it with a predetermined amount of nanosize yttria particulates followed by hybridising it with nanocopper particulates in two different volume percentages of 0?3 and 0?6 vol.-% respectively. Both the monolithic magnesium and magnesium nanocomposites were synthesised using the blend press sinter powder metallurgy technique followed by hot extrusion. For sintering of the materials, an innovative hybrid microwave sintering method was chosen with the objective of realising savings in both time and energy. Test results revealed that both strength and ductility of pure magnesium increased with the addition of yttria and a hybrid reinforcement mixture of yttria and copper nanoparticulates. The best combination of properties in uniaxial tension was obtained for the Mg/(0?7Y 2 O 3 z0?3Cu) hybrid nanocomposite. The observed improvement in properties is attributed to synergistic influences of a noticeable reduction in grain size of the hybrid nanocomposite, coexistence of both Y 2 O 3 and copper to a reasonable extent, and a fairly uniform distribution of the reinforcement particulates and intermetallics. A scientific attempt is made in this study to highlight the significance of using hybrid reinforcements, at nanolength scale, in a pure magnesium matrix to obtain a noticeable increase in tensile properties.