Avijit Guha

Mesenchymal cell response to nanosized biphasic calcium phosphate composites

Biphasic calcium phosphate nanoparticles comprising both hydroxyapatite (HA) and beta polymorph of tricalcium phosphate (beta-TCP) have been synthesized together by a polymer matrix mediated process. The process, based on in situ mineralization of poly (vinyl alcohol), exerts a good control over the morphological features of biphasic nanoparticles. By controlling the reaction chemistry (Ca:P ratios), nanobioceramic particles having three different HA/beta-TCP ratios of 50:50, 55:45 and 60:40 respectively. As the two constituents of biphasic system (HA and beta-TCP) facilitate series of signaling cascades in osteoblast division and differentiation, the adhesion and differentiation properties of mesenchymal cells (MSCs) derived from bone marrow has been studied.

Evaluation of nano-biphasic calcium phosphate ceramics for bone tissue engineering applications: In vitro and preliminary in vivo studies

Reconstruction of critical sized bone injuries is a major problem that continues to inspire the design of new materials and grafts. Natural ceramics (hydroxyapatite (HA) coralline HA, or synthetic HA) and β-tricalcium phosphate (β-TCP) are being explored for use as scaffolds in bone tissue engineering, among several other materials. The present study evaluated the bone forming capacity of nanosize bioceramics synthesized in situ in poly-vinyl alcohol (PVA) with different ratios of HA and β-TCP; the Ca/P ratio was 1.62 for bioceramic P1, 1.60 for P2 and 1.58 for P3. Further osteogenesis in vitro with mesenchymal stem cells (MSC) acquired from different sources for osteogenesis in vitro and their bone healing properties in vivo were also evaluated. MSC isolated from human placenta, Wharton’s jelly from umbilical cord, fetal bone marrow and adipose tissue, cultured in the presence of nanosize bioceramic particles, were monitored for osteogenic differentiation. Placental cells showed the best osteogenic potential of the different MSC studied on the basis of expression of osteogenic markers. Complete regeneration of the damaged region was observed in vivo when MSC derived from placenta were used with nanoceramic (Ca/P ratio 1.58) in the experimental defect created in the femur of Wistar rats. Even small variation in the Ca/P ratio can alter the outcome of tissue constructs.

Composition dependent structural modulations in transparent poly(vinyl alcohol) hydrogels.

Transparent and stable Poly(vinyl alcohol) hydrogels were synthesized from polymer aqueous solution without resorting to a mixed solvent such as dimethyl sulfoxide and water. Contrary to the reported methods involving hydrogen bond induced physical crosslinking by repeated freeze-thawing at -20 degrees C, the present process demonstrates the gelation taking place at relatively higher temperature, i.e. 0 degrees C. While maintaining transparency in all the synthesized hydrogels, the present paper reports systematic structural and morphological variations in the hydrogels as a function of polymer concentration.

Microwave irradiation enhances kinetics of the biomimetic process of hydroxyapatite nanocomposites

In situ synthesized hydroxyapatite-poly(vinyl) alcohol nanocomposite was subjected to microwave irradiation, post synthesis. Interestingly, the aging time of 1 week required for the normal biomimetic process was reduced to 1 h post microwave irradiation, as characterized by x-ray powder diffraction and transmission electron microscopy. The surface topography shows the tendency of tubules to cross-link with the help of microwave energy. The microwave energy seems to provide a directional pull to the polymer chains which could have led to an enhancement of the kinetics of phase formation.

Bovine serum albumin binding and drug delivery studies with PVA-ferrofluid

This paper describes a single-step method for the biomimetic synthesis of stably suspended magnetite nanoparticles in poly(vinyl alcohol) termed ferrofluids. The challenge is to synthesize water based stable magnetic colloids with a control over the particle size and morphology for biomedical applications. The polymer possibly plays a dual role of a surfactant and a functionalizing agent. Transmission electron microscopy, infrared spectroscopy and vibrating sample magnetometry were used to investigate the properties of the synthesized ferrofluids. It has a strong affinity towards the tryptophan residues in bovine serum albumin protein as determined from the fluorescence emission studies. For in vivo applications this could indirectly mean a resistance to immune response and thus ensure long-term circulation. The ability of the synthesized ferrofluid to bind a chemotherapeutic drug ceftriaxone and its ionic release was observed. The polymer hydroxyl group allows drug-binding and the magnetic property allows targeting to specific sites. Magnetic hybrid fluids with combined advantages of magnetism and polymer open up new perspectives for applications.

Low-Temperature Biomimetic Synthesis of β-Tricalcium Phosphate by Altering pH

Biomimetic synthesis of β-tricalcium phosphate (β-TCP) in polyvinyl alcohol is done at a much lower temperature of 450°C compared with conventional synthesis. By varying the pH of the reaction in a patented process for hydroxyapatite synthesis, the authors synthesized β-TCP with controlled particle morphology at a very low temperature. The synthesized powder has been structurally characterized and cell studies with mesenchymal stem cells shows good adhesion.