Sarit B. Bhaduri

Novel microwave synthesis of amorphous calcium phosphate nanospheres

Amorphous calcium phosphate (ACP) is an important precursor phase in tissue mineralization. It shows high solubility and excellent remineralization ability. Commercially viable techniques for producing ACP are high-cost/low-efficiency process. This article describes a novel microwave (MW)-assisted ACP synthesis route as an alternative to current ACP synthesis methods. An important feature of the process is the use of supersaturated biomimetic fluids (SBFs), which are based on Kokubo-like simulated body fluids. However, our present compositions are substantially different in that they no longer simulate the body fluid compositions. The effects of solution composition and processing parameters were studied. The mechanism of ACP synthesis under MW irradiation process is also discussed. The as-synthesized ACP nanospheres were characterized and showed good reactivity and biocompatibility. These as-synthesized nanoparticles can be potential candidates for biomedical applications and remineralization mechanism study.

Fabrication of novel PLA/CDHA bionanocomposite fibers for tissue engineering applications via electrospinning

The main theme here is to fabricate PLA (poly lactic-acid)/CDHA (carbonated calcium deficient hydroxyapatite) bionanocomposites, where both the constituents are biocompatible and biodegradable with one dimension in nanometer scale. Such materials are important in tissue engineering applications. The bionanocomposite fibers were fabricated via electrospinning. There are two important signatures of this paper. First, CDHA, rather than HA, is added to PLA as the second phase. As opposed to HA, CDHA mimics the bone mineral composition better and is biodegradable. Therefore, PLA/CDHA fibers should have better biodegradability while maintaining a physiological pH during degradation. To the best of our knowledge, this is the first attempt of electrospinning of such a composite. Second, the CDHA nanoparticles were synthesized using the benign low temperature biomimetic technique, the only route available for the retention of carbonate ions in the HA lattice. The structural properties, degradation behavior, bioactivity, cell adhesion, and growth capability of as-fabricated PLA/CDHA bionanocomposites were investigated. The results show that the incorporation of CDHA decreased PLA fiber diameters, accelerated PLA degradation, buffered pH decrease caused by PLA degradation, improved the bioactivity and biocompatibility of the scaffold. These results prove that PLA/CDHA bionanocomposites have the potential in tissue regeneration applications.

Rapid coating of AZ31 magnesium alloy with calcium deficient hydroxyapatite using microwave energy.

Due to their unique biodegradability, magnesium alloys have been recognized as suitable metallic implant materials for degradable bone implants and bioresorbable cardiovascular stents. However, the extremely high degradation rate of magnesium alloys in physiological environment has restricted its practical application. This paper reports the use of a novel microwave assisted coating technology to improve the in vitro corrosion resistance and biocompatibility of Mg alloy AZ31. Results indicate that a dense calcium deficient hydroxyapatite (CDHA) layer was uniformly coated on a AZ31 substrate in less than 10min. Weight loss measurement and SEM were used to evaluate corrosion behaviors in vitro of coated samples and of non-coated samples. It was seen that CDHA coatings remarkably reduced the mass loss of AZ31 alloy after 7days of immersion in SBF. In addition, the prompt precipitation of bone-like apatite layer on the sample surface during immersion demonstrated a good bioactivity of the CDHA coatings. Proliferation of osteoblast cells was promoted in 5days of incubation, which indicated that the CDHA coatings could improve the cytocompatibility of the AZ31 alloy. All the results suggest that the CDHA coatings, serving as a protective layer, can enhance the corrosion resistance and biological response of magnesium alloys. Furthermore, this microwave assisted coating technology could be a promising method for rapid surface modification of biomedical materials.

A microwave-assisted solution combustion synthesis to produce europium-doped calcium phosphate nanowhiskers for bioimaging applications

Biocompatible nanoparticles possessing fluorescent properties offer attractive possibilities for multifunctional bioimaging and/or drug and gene delivery applications. Many of the limitations with current imaging systems center on the properties of the optical probes in relation to equipment technical capabilities. Here we introduce a novel high aspect ratio and highly crystalline europium-doped calcium phosphate nanowhisker produced using a simple microwave-assisted solution combustion synthesis method for use as a multifunctional bioimaging probe. X-ray diffraction confirmed the material phase as europium-doped hydroxyapatite. Fluorescence emission and excitation spectra and their corresponding peaks were identified using spectrofluorimetry and validated with fluorescence, confocal and multiphoton microscopy. The nanowhiskers were found to exhibit red and far red wavelength fluorescence under ultraviolet excitation with an optimal peak emission of 696 nm achieved with a 350 nm excitation. Relatively narrow emission bands were observed, which may permit their use in multicolor imaging applications. Confocal and multiphoton microscopy confirmed that the nanoparticles provide sufficient intensity to be utilized in imaging applications.

Effect of electrospinning parameters on the characterization of PLA/HNT nanocomposite fibers

Halloysite nanotubes (HNT) reinforced polylactic acid (PLA) nanocomposite fibers were produced using an electrospinning approach for biomedical applications. The PLA/HNT nanocomposite fibers were characterized using x-ray diffraction (XRD) and scanning electron microscopy (SEM). The various factors such as type of solvent, solution concentration, HNT loading and feed rate, affecting the electrospinning process, and the morphology of the nanofibers were investigated, and the optimum values for these parameters are suggested. The results indicated that the addition of dimethylformamide (DMF) to chloroform facilitated the electrospinning process because of the improvement in electrical conductivity and viscosity of the solution. Nanometer-sized fibers were obtained by the addition of HNT to PLA. HNT loadings had a significant effect on the morphology of the nanofibers. Bead-free fibers were produced at feed rates between 1 and 4 mL/h.

Microwave assisted synthesis of amorphous magnesium phosphate nanospheres

Magnesium phosphate (MgP) materials have been investigated in recent years for tissue engineering applications, attributed to their biocompatibility and biodegradability. This paper describes a novel microwave assisted approach to produce amorphous magnesium phosphate (AMP) in a nanospherical form from an aqueous solution containing Mg2+ and HPO42−/PO43−. Some synthesis parameters such as pH, Mg/P ratio, solution composition were studied and the mechanism of AMP precursors was also demonstrated. The as-produced AMP nanospheres were characterized and tested in vitro. The results proved these AMP nanospheres can self-assemble into mature MgP materials and support cell proliferation. It is expected such AMP has potential in biomedical applications.

Microwave assisted preparation of magnesium phosphate cement (MPC) for orthopedic applications: A novel solution to the exothermicity problem

There are two interesting features of this paper. First, we report herein a novel microwave assisted technique to prepare phosphate based orthopedic cements, which do not generate any exothermicity during setting. The exothermic reactions during the setting of phosphate cements can cause tissue damage during the administration of injectable compositions and hence a solution to the problem is sought via microwave processing. This solution through microwave exposure is based on a phenomenon that microwave irradiation can remove all water molecules from the alkaline earth phosphate cement paste to temporarily stop the setting reaction while preserving the active precursor phase in the formulation. The setting reaction can be initiated a second time by adding aqueous medium, but without any exothermicity. Second, a special emphasis is placed on using this technique to synthesize magnesium phosphate cements for orthopedic applications with their enhanced mechanical properties and possible uses as drug and protein delivery vehicles. The as-synthesized cements were evaluated for the occurrences of exothermic reactions, setting times, presence of Mg-phosphate phases, compressive strength levels, microstructural features before and after soaking in (simulated body fluid) SBF, and in vitro cytocompatibility responses. The major results show that exposure to microwaves solves the exothermicity problem, while simultaneously improving the mechanical performance of hardened cements and reducing the setting times. As expected, the cements are also found to be cytocompatible. Finally, it is observed that this process can be applied to calcium phosphate cements system (CPCs) as well. Based on the results, this microwave exposure provides a novel technique for the processing of injectable phosphate bone cement compositions.

Fabrication of novel poly(lactic acid)/amorphous magnesium phosphate bionanocomposite fibers for tissue engineering applications via electrospinning.

Fibrous bionanocomposites consisting of amorphous magnesium phosphate (AMP) nanospheres and polylactic acid (PLA) were fabricated by electrospinning. There are two important signatures of this paper. First, AMP, as an alternative to well-known calcium phosphate (CaP) materials, is added to PLA as the second phase. To the best of our knowledge, it is the first attempt to fabricate magnesium phosphate (MgP)/biopolymer composite. This is made possible by our previously reported research on the successful synthesis of AMP nanospheres via microwave processing. Second, the sustained release of magnesium and phosphate ions from PLA matrix can stimulate a series of cell responses. The structure of the composites and their bone-like apatite-forming abilities in simulated body fluid (SBF) were examined. Additionally, the effects on the proliferation and differentiation of preosteoblast cells were evaluated by performing in vitro cell culture and monitoring markers such as Osteocalcin (OCN), Osteopontin (OPN), Alkaline phosphatase (ALP) and Collagen type-I (Col I) using real-time polymerase chain reaction (PCR). For better dispersion of AMP in the fibers, a surfactant, 12-hydroxysteric acid (HSA), as previously reported in the literature, was used. However, HSA significantly inhibited the proliferation and differentiation of preosteoblast cells, indicating the potential risk in using HSA in the combination of AMP or MgP in tissue engineering applications.

Biomimetic coating of bisphosphonate incorporated CDHA on Ti6Al4V

Bi-functional coatings of carbonated calcium deficient hydroxyapatite (CDHA) on Ti alloys were developed by using a biomimetic coating process. The bi-functionality was achieved by loading alendonate sodium (AS), an approved bisphosphonate drug used for the treatment of osteoporosis, into the inner layers of CDHA coatings. Three possible methods of loading AS into CDHA coatings were systematically studied and compared. The results indicated that the co-precipitation method had greater benefits and can modify the release profile of AS by incorporating AS in the inner layers of the coatings. As a preliminary study, the influences of applied AS dosage to CDHA coatings were evaluated using XRD and SEM. In vitro tests indicated that the AS content on CDHA coatings played a significant role, and optimum AS content in local area is beneficial for osteoblast cells proliferation. It is expected that the CDHA–AS coatings via the co-precipitation approach have potential for bone tissue engineering applications.

Microwave assisted apatite coating deposition on Ti6Al4V implants

In this work we report a novel microwave assisted technology to deposit a uniform, ultra-thin apatite coating without any cracks on titanium implants in minutes. This method comprises of conventional biomimetic coating in synergism with microwave irradiation to result in alkaline earth phosphate nucleation. The microwave assisted coating process mainly follows the initial stages of biomimetic coating until the step of the Ca-P nuclei formation. After that, due to microwave irradiation more Ca-P nuclei are formed to cover the whole surface of the implant instead of the growth of deposited Ca-P nuclei to Ca-P globules and coatings. It is interesting to note the doping of Mg(2+) to Ca-P apatite coating can significantly change the properties and performances of as-deposited coatings. The hydrophilicity, physical properties, bioactivity, cell adhesion, and growth capability of as-deposited microwave assisted coatings were investigated. The study shows that this coating technology has great potential in biomedical applications. Additionally, since biomimetic coating can be applied to series of implant materials such as polymer, metals and glass, it is expected this microwave assisted coating technology can also be applied to these materials if they can remains stable at 100 °C, the boiling point of water.