Debasis Bhattacharya

Rapid synthesis and characterization of mesoporous nanocrystalline MgAl2O4 via flash pyrolysis route

Abstract In this work, we demonstrate an effective, fast and low-cost route for the synthesis of mesoporous MgAl2O4 powder. This synthesis procedure successfully reduces the overall synthesis time for nanosized MgAl2O4 powder from days to a few hours. The as-synthesized powder was found to be amorphous in nature. Upon calcination at 700 °C (2 h) and 900 °C (4 h) in presence of air, the as-synthesized MgAl2O4 amorphous powder was transformed into a disorder and order nanocrystalline phase respectively. The structural information of evolvement phase was analyzed through Rietveld refinement technique and Fourier transform infrared spectroscopy. The specific surface area of MgAl2O4 powder calcined at 700 °C and 900 °C was found to be 118.14 m2/g and 74.67 m2/g, respectively.

Silk scaffolds in bone tissue engineering: An overview

Bone tissue plays multiple roles in our day-to-day functionality. The frequency of accidental bone damage and disorder is increasing worldwide. Moreover, as the world population continues to grow, the percentage of the elderly population continues to grow, which results in an increased number of bone degenerative diseases. This increased elderly population pushes the need for artificial bone implants that specifically employ biocompatible materials. A vast body of literature is available on the use of silk in bone tissue engineering. The current work presents an overview of this literature from materials and fabrication perspective. As silk is an easy-to-process biopolymer; this allows silk-based biomaterials to be molded into diverse forms and architectures, which further affects the degradability. This makes silk-based scaffolds suitable for treating a variety of bone reconstruction and regeneration objectives. Silk surfaces offer active sites that aid the mineralization and/or bonding of bioactive molecules that facilitate bone regeneration. Silk has also been blended with a variety of polymers and minerals to enhance its advantageous properties or introduce new ones. Several successful works, both in vitro and in vivo, have been reported using silk-based scaffolds to regenerate bone tissues or other parts of the skeletal system such as cartilage and ligament. A growing trend is observed toward the use of mineralized and nanofibrous scaffolds along with the development of technology that allows to control scaffold architecture, its biodegradability and the sustained releasing property of scaffolds. Further development of silk-based scaffolds for bone tissue engineering, taking them up to and beyond the stage of human trials, is hoped to be achieved in the near future through a cross-disciplinary coalition of tissue engineers, material scientists and manufacturing engineers. STATEMENT OF SIGNIFICANCE The state-of-art of silk biomaterials in bone tissue engineering, covering their wide applications as cell scaffolding matrices to micro-nano carriers for delivering bone growth factors and therapeutic molecules to diseased or damaged sites to facilitate bone regeneration, is emphasized here. The review rationalizes that the choice of silk protein as a biomaterial is not only because of its natural polymeric nature, mechanical robustness, flexibility and wide range of cell compatibility but also because of its ability to template the growth of hydroxyapatite, the chief inorganic component of bone mineral matrix, resulting in improved osteointegration. The discussion extends to the role of inorganic ions such as Si and Ca as matrix components in combination with silk to influence bone regrowth. The effect of ions or growth factor-loaded vehicle incorporation into regenerative matrix, nanotopography is also considered.

Nanofibrous nonmulberry silk/PVA scaffold for osteoinduction and osseointegration

Poly‐vinyl alcohol and nonmulberry tasar silk fibroin of Antheraea mylitta are blended to fabricate nanofibrous scaffolds for bone regeneration. Nanofibrous matrices are prepared by electrospinning the equal volume ratio blends of silk fibroin (2 and 4 wt%) with poly‐vinyl alcohol solution (10 wt%) and designated as 2SF/PVA and 4SF/PVA, respectively with average nanofiber diameters of 177 ± 13 nm (2SF/PVA) and 193 ± 17 nm (4SF/PVA). Fourier transform infrared spectroscopy confirms retention of the secondary structure of fibroin in blends indicating the structural stability of neo‐matrix. Both thermal stability and contact angle of the blends decrease with increasing fibroin percentage. Conversely, fibroin imparts mechanical stability to the blends; greater tensile strength is observed with increasing fibroin concentration. Blended scaffolds are biodegradable and support well the neo‐bone matrix synthesis by human osteoblast like cells. The findings indicate the potentiality of nanofibrous scaffolds of nonmulberry fibroin as bone scaffolding material.

Non-mulberry silk fibroin grafted poly(ε-caprolactone) nanofibrous scaffolds mineralized by electrodeposition: an optimal delivery system for growth factors to enhance bone regeneration

Mineralization of scaffolds enables them to mimic the chemistry of natural bone. Mineralizing nanofibrous scaffolds can successfully replicate both the architecture and chemical composition of bones and prove suitable for bone reconstruction. Non-mulberry silk fibroin (NSF) (from Antheraea mylitta) grafted poly(e-caprolactone) (PCL) nanofibrous scaffolds (NSF-PCL) are fabricated using electrospinning, followed by aminolysis. Electrodeposition, due to its speed and simplicity is used to deposit calcium phosphate on these scaffolds at two deposition voltages: 3 V and 5 V. The deposition of nano-hydroxyapatite (nHAp) obtained is of high quality and its topology is dependent upon the voltage of electrodeposition. Along with scaffolds of nHAp deposited on a NSF-PCL matrix at 3 V and 5 V (NSF-PCL/3V and NSF-PCL/5V respectively), the unmodified NSF-PCL matrix is used as a control. The results of mechanical characterization and certain basic cell culture using the MG-63 cell line show the merits of NSF-PCL/5V over the other two compositions. The NSF-PCL/5V scaffold is then used for detailed cell culture studies after being loaded with growth factors like bone morphogenic protein-2 (rhBMP-2) and transforming growth factor beta (TGF-β) in a 1:1 (potency) proportion. Outcomes from these studies show a clear advantage of using a combination of the growth factors over using any one of them individually. Dual growth factor loaded matrices promote more significant expression of genes related to bone growth and better facilitate early differentiation of cells. The mineralized scaffolds thus created are mechanically suitable for bone tissue engineering and in combination with growth factors significantly enhance bioactivity, proliferation and differentiation of osteoblast-like cells. The engineered scaffolds hold the potential, with further development, to serve as an optimal alternative for bone tissue engineering.

Synthesis and fabrication of MgAl2O4 ceramic foam via a simple, low-cost and eco-friendly method

Abstract The MgAl2O4 nanocrystalline powder was synthesized using naturally available egg white and inexpensive metal nitrate salts. During this process, the freshly extracted egg white was mixed with metal nitrate salt and subsequently heated at 350 °C in a pit furnace. The entire dehydration of the aqueous solution thus facilitates the low-density fluffy mass. From TGDTG results, it was observed that maximum decomposition of the precursors occurred below 600 °C. Therefore, the calcination temperature of as-synthesized powder was set at 600 °C. The MgAl2O4 bulk ceramic foam was fabricated by dispersing different loading of MgAl2O4 nanoparticles in the egg white, and then coating on polyurethane sponge prior to drying and sintering at a higher temperature. The ceramic suspensions exhibit a typical shear thinning behavior, and its viscosity was found to be significantly influenced by MgAl2O4 powder content. An optimum loading of 40 wt% MgAl2O4 nanoparticles in the egg white was found to show maximum porosity up to 90%. The obtained ceramic foam has potential applications in catalysis, absorption and sensor.

Electrical properties of BaZrO3 ceramic synthesized by flash pyrolysis process

Barium Zirconate (BaZrO3) nanoparticles are synthesized by flash pyrolysis combustion process. Rietveld refinement of XRD pattern of calcined powder at 900 °C, 1100 °C and sintered at 1600 °C describes that a single-phase compound is formed of an Pm-3m cubic crystal structure with a lattice constant a = 4.19102, 4.192693, and 4.195276 A respectively. Crystallize size of calcined powder at 900 °C, 1100 °C and sintered at 1600 °C is found 34.28, 37.7 and 47.14 nm respectively using Scherrer formula. The FESEM image of sintered pellet at 1600 °C for 4 h describes porous nature of the sample. The Nyquist plots indicate the dominant grain boundary effect in electrical processes in the sample. A decrease in the bulk resistance with increasing temperature demonstrates a semiconducting behavior. The temperature dependent relaxation and conduction mechanism brief involvements of different types of the charge species in the 250 to 500 °C temperature region as studied at different frequencies over 100 Hz to 1 MHz.

A green fabrication strategy for MgAl2O4 foams with tunable morphology

Porous ceramics have several industrial applications; however, most of them are prepared using toxic chemicals and submicron size ceramic particles. Here, an environmentally friendly gel casting method is employed by dispersing magnesium aluminate (MgAl2O4) nanoparticles in egg albumin-based aqueous solution in the presence of sucrose, to develop porous ceramic structures. The sintered ceramic foams are found to be cellular in nature and porous, as confirmed by scanning electron microscopy and mercury porosimetry studies, respectively. MgAl2O4 nanoparticle loading plays a significant role in controlling microstructural properties i.e. cell size, pore size distribution, the amount of porosity, and pore morphology in the final sintered bodies. The rheological measurements are carried out to understand the morphological changes in the sintered body. The obtained porous MgAl2O4 foam with an interconnected cellular structure could find potential applications as an adsorptive material, catalyst support or in humidity sensors. In the present study, the as-prepared ceramic body with multimodal porosity is found to be an efficient separator for Congo red removal from contaminated water.