Kajal K. Mallick

3D printing of porous hydroxyapatite scaffolds intended for use in bone tissue engineering applications.

A systematic characterisation of bone tissue scaffolds fabricated via 3D printing from hydroxyapatite (HA) and poly(vinyl)alcohol (PVOH) composite powders is presented. Flowability of HA:PVOH precursor materials was observed to affect mechanical stability, microstructure and porosity of 3D printed scaffolds. Anisotropic behaviour of constructs and part failure at the boundaries of interlayer bonds was highlighted by compressive strength testing. A trade-off between the ability to facilitate removal of PVOH thermal degradation products during sintering and the compressive strength of green parts was revealed. The ultimate compressive strength of 55% porous green scaffolds printed along the Y-axis and dried in a vacuum oven for 6h was 0.88 ± 0.02 MPa. Critically, the pores of 3D printed constructs could be user designed, ensuring bulk interconnectivity, and the imperfect packing of powder particles created an inherent surface roughness and non-designed porosity within the scaffold. These features are considered promising since they are known to facilitate osteoconduction and osteointegration in-vivo. Characterisation techniques utilised in this study include two funnel flow tests, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), compressive strength testing and computed tomography (CT).

Phase transition in BiVO4

Abstract Monophasic zircon-type tetragonal BiVO 4 was prepared by a new co-precipitation method that employs accurate control of pH and temperature. The highly crystalline phase converts irreversibly to its monoclinic isomorph when heated between 350 and 400 °C. Mechanical grinding at room temperature also resulted in the tetragonal BiVO 4 to transform irreversibly to the monoclinic form. The amount transformed was found to be dependant on the duration of grinding.

Preparation and characterisation of nanophase Sr, Mg, and Zn substituted hydroxyapatite by aqueous precipitation.

Hydroxyapatite (HA) substituted with 2 mol% Sr, 10 mol% Mg, and 2 mol% Zn were precipitated under identical alkaline conditions (pH 11) at 20°C from an aqueous solution. As-synthesised materials were confirmed to be phase pure by XRD and samples prepared in air contained surface adsorbed CO2 as observed by FTIR. SEM studies revealed a globular morphology and agglomeration behaviour, typical of precipitated nHA. EDS spectra confirmed nominal compositions and substitution of Sr, Mg and Zn. At the levels investigated cationic doping was not found to radically influence particle morphology. An indication of the potential in-vivo bioactivity of samples was achieved by analysing samples immersed in SBF for up to 28 days by interferometry and complementary SEM micrographs. Furthermore, a live/dead assay was used and confirmed the viability of seeded MC3T3 osteoblast precursor cells on HA and substituted HA substrates up to 7 days of culture.

Sol gel preparation, structure and thermal stability of crystalline zirconium titanate microspheres

Very pure and crystalline ZrTiO4 microspheres (15–50 μm) were prepared by two sol gel methods using a zirconia sol and two types of titania sols and characterized by scanning electron microscopy, X-ray diffraction and simultaneous differential thermal and thermogravimetric analysis. On gelation of the mixed sols, microspheres of an amorphous material with Zr/Ti ratio of ∼ 1.0 were obtained by each route. The amorphous materials obtained by the two routes transformed to fully crystalline ZrTiO4 at 500 and 600 °C, respectively. The high temperature thermal stabilities of these materials were also studied.

Biomaterial scaffolds for tissue engineering

Reconstruction and regeneration of new tissues are challenges facing scientists, technologists and clinicians. This review describes strategies of selection and design of biomaterials having significant impact on various possible synthesis routes for scaffold fabrication. The criteria for three-dimensional (3D) scaffold architectures are explored in tandem with biomaterial properties such as porosity, interconnectivity and mechanical integrity. The cell-surface biointerface is outlined in terms of biomaterial composition, target tissues and biological evaluation with emphasis on bone tissue engineering. Comparative merits and demerits of conventional and rapid prototyping (RP) approaches of fabrication are discussed. The conventional methods are often simple to design, inexpensive and flexible to optimise or modulate physicochemical properties. Despite being expensive and suffering from certain drawbacks of choice of materials and capital costs many generic RP techniques are extremely attractive in their ability to mimic new tissue structures and possibility of incorporating pharmaceutical agents. The future directions include scaffold development using nanobiomaterial based biosystems /biointerfaces where cell biology including genetically modified tissue engineering approaches can play a cross-disciplinary role for the success of tissue augmentation.

An X-ray diffraction and Mossbauer study of nano-crystalline Fe2O3–Cr2O3 solid solutions

A series of gels with nominal composition Fe2−xCrxO3 (x=0–2) was prepared at room temperature by an inorganic sol–gel route and studied by X-ray diffraction and Mossbauer spectroscopy. The gels dried at 105°C were found to be X-ray amorphous, but Mossbauer studies revealed the gels to be nano-crystalline solid-solution particles of the composition above, with super-paramagnetic properties. Further heating to 600°C gave crystalline X-ray patterns which allowed lattice parameter and crystallite size calculations to be made. It was found that lattice parameters and crystallite sizes decreased with increasing chromia content, and that at the higher chromia/iron ratios, a partially collapsed Mossbauer pattern results, indicating reductions in crystallite size and hyperfine field with increasing chromia content.

Low-temperature synthesis and characterization of ceria-based oxide ion conductors

Solid solutions of the general formula Ce1−xLnxO2−x/2□x/2 (Ln = lanthanide (III) and □ = anion vacancy), were prepared by a novel sol-gel route. These materials were characterized by powder diffraction and scanning electron microscopy. The gels formed on sol evaporation were found to be solid solutions with the fluorite structure and a crystallite size of approximately 6 nm. This is the lowest temperature of formation to date. The gels densified readily at 700 °C and the lattice parameter of these materials was found to be directly proportional to the ionic radius of the dopant.

Preparation and characterization of Ln2Zr2O7 microspheres by an inorganic sol-gel route

Free-flowing Ln2Zr2O7 microspheres (Ln=lanthanide) were prepared by an aqueous inorganic sol-gel route without any intermediate phase formation. The gel spheres obtained at room temperature were shown by X-ray diffraction to be amorphous but calcination to 750 °C produced fully crystalline fluorite phases. On calcination to 850 °C, pyrochlore phases were formed with suitable lanthanides. The microspheres were characterized by X-ray diffraction and scanning electron microscopy with energy dispersive analysis of X-rays to give accurate determination of structure, composition and crystallite size.

Combustion synthesis, powder characteristics and crystal structure of phases in Ce-Pr-O system

The combustion method has been employed to produce homogeneous, single phased mixed rare-earth oxides in Ce1 − xPrxO2−y system for x ranging from 0 to 0.7. A cubic fluorite structure is formed for the compositions 0 ≤ x ≤ 0.7, while for x > 0.7 mixed phases are obtained. The mixed oxides are formed at the furnace temperature of 500 °C in a short duration of 10 min. In view of the importance of these powders in catalysis, crystallite size, surface area and porosity measurements have been carried out. The crystallite size of the powders increases with x while the surface area decreases. As the temperature is increased to 850 °C, the surface area decreases and the effect is much pronounced in cerium rich oxides. The powders on calcination above 900 °C in air results in the demixing of Ce and Pr to give two fluorite phases.

Three‐dimensional porous bioscaffolds for bone tissue regeneration: Fabrication via adaptive foam reticulation and freeze casting techniques, characterization, and cell study

Highly interconnected and 3D porous bioactive hydroxyapatite (HAP) and Bioglass scaffolds have been fabricated by an adaptive version of camphene based foam reticulation (ARM) and camphene freeze casting (CFC) methods. Controlled sublimation of camphene during freeze casting at -78°C produced process optimized bioscaffolds with open, uniform, and interconnected porous structures. HAP and Bioglass scaffolds with desired porosity, pore size, and microtopography were successfully fabricated using polyurethane foam templates of appropriate structures. Macropores of 50-1100 μm with microporosity of 1-10 μm, known to facilitate cell adhesion and proliferation, were obtained. Compressive yield strength of 0.8 MPa close to the upper range of cancellous bone was achieved. The mean compressive strength of HAP scaffolds compared favorably with the theoretical model of porosity variation with strength and was higher than reported values. The nature of pore development, morphology, porosity, crystal structure, chemical composition, and thermal behavior were characterized using scanning electron and optical microscopy, X-ray diffraction, thermal analysis, and mercury porosimetry. These scaffolds are suited for nonstructural graft and were not cytotoxic in vitro when osteoblast-like MG63 cells were cultured with the HAP constructs. The cells attached indicated by cell metabolic activity by resazurin assay and spread well when cultured on the surface of the materials.