Synthesis of monodisperse nanoparticles with uniform morphology and narrow size distribution as achieved by nature is a challenge to materials scientists. Mimicking the process of biomineralization has led to the development of biomolecules mediated synthesis of nanoparticles that overcomes many of the problems associated with nanoparticle synthesis. Termed as biomimetics this paradigm shift in the philosophy of synthesis of materials is very advantageous for the design-based synthesis of nanoparticles. The effect of concentration of a protein named bovine serum albumin on particle size, morphology and degree of crystallinity of biomimetically synthesized hydroxyapatite particles, has been studied. Results establish 0.5% protein as the required concentration to produce 30-40 nm sized hydroxyapatite particles with an optimum degree of crystallinity as required for biomedical applications. These particles synthesized under certain stringent conditions are found to have stoichiometric calcium:phosphorus ratio of 1.67 and exhibit restricted grain growth during sintering.
In situ precipitation of microporous and nanosized hydroxyapatite particles (5–40 nm) has been conducted in poly(vinyl alcohol) and bovine serum albumin gels. The process, which is similar to biomineralization, is highly controlled with respect to microstructural features, such as size and shape, and to precipitation of hydroxyapatite phase having a calcium:phosphorus stoichiometric ratio of 1.67. Nanosized precipitated hydroxyapatite particles show remarkable thermal stability and do not decompose to other calcium phosphate phases, even at higher temperatures.
The nucleation and growth of hydroxyapatite is closely associated with the extracellular matrix environment. Bovine Serum Albumin, Collagen and poly vinyl alcohol were used to mimic the extracellular matrix. An attempt to understand the role of these matrices on the synthesis and function of Hydroxyapatite has been made. XRD, FT-IR, XPS, TG-DTA, SEM and TEM confirmed the formation of hydroxyapatite synthesized by the biomimetic route. Further the role of organic matrix in controlling the nucleation and growth of hydroxyapatite particles in the nano level is understood by the in-depth analysis of the XPS spectra. The in vitro release of the anti-cancer drug methotrexate, in aqueous solution was studied and the in vitro release profile was assayed by elution in phosphate buffered saline with pH 7.4 and pH 5 at 37 º C. The percentage of loading and release profiles of drug were evaluated. The results show that the use of matrix increased the drug release efficiency from 44.5% to 66% at pH 7.4 and 78% to 98.92% at pH 5. These results suggest that the synthesized hydroxyapatite can be used as a pH responsive vehicle for delivering drugs. Further the release profile was predicted by Higuchi and Peppas model. The results suggested that the release mechanism was governed by the Fickian diffusion for initial 8 hrs followed by anomalous transport for longer time. The cytocompatibility of the materials was evaluated by in vitro cytotoxicity test. Both MTT and live/dead assay observations indicated that the material had no adverse impact on the cell proliferation. The results imply these composites to be bioactive having a good cytocompatibility. Although all the matrices showed good results, the one with poly vinyl alcohol exhibited higher biocompatibility and drug release efficiency. A plausible explanation was proposed for the enhanced drug delivery efficiency of these materials.
In the current study, an optimized in vitro blood–brain barrier (BBB) model was established using mouse brain endothelial cells (b.End3) and astrocytes (C8-D1A). Before measuring the permeability of superparamagnetic iron oxide nanoparticle (SPION) samples, the BBB was first examined and confirmed by an immunofluorescent stain and evaluating the transendothelial electrical resistance. After such confirmation, the permeability of the following five previously synthesized SPIONs was determined using this optimized BBB model: 1) GGB (synthesized using glycine, glutamic acid, and bovine serum albumin [BSA]), 2) GGC (glycine, glutamic acid, and collagen), 3) GGP (glycine, glutamic acid, and polyvinyl alcohol), 4) BPC (BSA, polyethylene glycol, and collagen), and 5) CPB (collagen, polyvinyl alcohol, and BSA). More importantly, after the permeability test, transmission electron microscopy thin section technology was used to investigate the mechanism behind this process. Transmission electron microscopy thin section images supported the hypothesis that collagen-coated CPB SPIONs displayed better cellular uptake than glycine and glutamine acid-coated GGB SPIONs. Such experimental data demonstrated how one can modify SPIONs to better deliver drugs to the brain to treat a wide range of neurological disorders.
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