Suntharavathanan Mahalingam

Forming of Polymer Nanofibers by a Pressurised Gyration Process

A new route consisting of simultaneous centrifugal spinning and solution blowing to form polymer nanofibers is reported. The fiber diameter (60-1000 nm) is shown to be a function of polymer concentration, rotational speed, and working pressure of the processing system. The fiber length is dependent on the rotational speed. The process can deliver 6 kg of fiber per hour and therefore offers mass production capabilities compared with other established polymer nanofiber generation methods such as electrospinning, centrifugal spinning, and blowing.

Formation of protein and protein-gold nanoparticle stabilized microbubbles by pressurized gyration.

A one-pot single-step novel process has been developed to form microbubbles up to 250 μm in diameter using a pressurized rotating device. The microbubble diameter is shown to be a function of rotational speed and working pressure of the processing system, and a modified Rayleigh-Plesset equation has been derived to explain the bubble-forming mechanism. A parametric plot is constructed to identify a rotating speed and working pressure regime, which allows for continuous bubbling. Bare protein (lysozyme) microbubbles generated in this way exhibit a morphological change, resulting in microcapsules over a period of time. Microbubbles prepared with gold nanoparticles at the bubble surface showed greater stability over a time period and retained the same morphology. The functionalization of microbubbles with gold nanoparticles also rendered optical tunability and has promising applications in imaging, biosensing, and diagnostics.

Coupling Infusion and Gyration for the Nanoscale Assembly of Functional Polymer Nanofibers Integrated with Genetically Engineered Proteins

Nanofibers featuring functional nanoassemblies show great promise as enabling constituents for a diverse range of applications in areas such as tissue engineering, sensing, optoelectronics, and nanophotonics due to their controlled organization and architecture. An infusion gyration method is reported that enables the production of nanofibers with inherent biological functions by simply adjusting the flow rate of a polymer solution. Sufficient polymer chain entanglement is obtained at Berry number > 1.6 to make bead‐free fibers integrated with gold nanoparticles and proteins, in the diameter range of 117–216 nm. Integration of gold nanoparticles into the nanofiber assembly is followed using a gold‐binding peptide tag genetically conjugated to red fluorescence protein (DsRed). Fluorescence microscopy analysis corroborated with Fourier transform infrared spectroscopy (FTIR) data confirms the integration of the engineered red fluorescence protein with the nanofibers. The gold nanoparticle decorated nanofibers having red fluorescence protein as an integral part keep their biological functionality including copper‐induced fluorescence quenching of the DsRed protein due to its selective Cu+2 binding. Thus, coupling the infusion gyration method in this way offers a simple nanoscale assembly approach to integrate a diverse repertoire of protein functionalities into nanofibers to generate biohybrid materials for imaging, sensing, and biomaterial applications.

Facile synthesis of both needle-like and spherical hydroxyapatite nanoparticles: effect of synthetic temperature and calcination on morphology, crystallite size and crystallinity.

Synthetic hydroxyapatite (HA) nanoparticles, that mimic natural HA, are widely used as biocompatible coatings on prostheses to repair and substitute human bones. In this study, HA nanoparticles are prepared by precipitating them from a precursor solution containing calcium sucrate and ammonium dihydrogen orthophosphate, at a Ca/P mole ratio of 1.67:1, at temperatures, ranging from 10°C to 95°C. A set of products, prepared at different temperatures, is analyzed for their crystallinity, crystallite size, morphology, thermal stability and composition, by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopic techniques, while the other set is analyzed after calcining the respective products, soon after their synthesis, for 3h, at 700°C. The as-prepared products, after 2h of drying, without any calcination, are not crystalline, but they grow very slowly into needle-like morphologies, as they are ripened with time. The percentage crystallinity of the final products increases from 15% to 52%, with increasing the preparative temperature. The calcined samples always produce spherical nanoparticles of essentially the same diameter, between 90 nm and 100 nm, which does not change due to aging and preparative temperatures. Therefore, the same method can be utilized to synthesize both spherical and needle-like nanoparticles of hydroxyapatite, with well-defined sizes and shapes. The ability to use readily available cheap raw materials, for the synthesis of such well-defined crystallites of hydroxyapatite, is an added advantage of this method, which may be explored further for the scaling up of the procedures to suit to industrial scale synthesis of such hydroxyapatite nanoparticles.

Antibacterial Activity and Biosensing of PVA-Lysozyme Microbubbles Formed by Pressurized Gyration

In this work, the biosensing and antibacterial capabilities of PVA-lysozyme microbubbles have been explored. Gas-filled PVA-lysozyme microbubbles with and without gold nanoparticles in the diameter range of 10 to 250 μm were produced using a single-step pressurized gyration process. Fluorescence microscopy showed the integration of gold nanoparticles on the shell of the microbubbles. Microbubbles prepared with gold nanoparticles showed greater optical extinction values than those without gold nanoparticles, and these values increased with the concentration of the gold nanoparticles. Both types of microbubbles showed antibacterial activity against Gram-negative Escherichia coli (E. coli), with the bubbles containing the gold nanoparticles performing better than the former. The conjugation of the microbubbles with alkaline phosphatase allowed the detection of pesticide paraoxon in aqueous solution, and this demonstrates the biosensing capabilities of these microbubbles.

Generation of poly(N-vinylpyrrolidone) nanofibres using pressurised gyration

The ability to generate nanofibres useful for biomedical applications at bench and at a larger scale is a significant manufacturing challenge. In this study, we demonstrate that it is possible to generate nanofibre meshes of poly(N-vinylpyrrolidone) (PVP) using pressurised gyration. The effects of altering polymer molecular weight and concentration on fibre morphology and size have been investigated, with identification of minimum values for both parameters for successful fibre fabrication. In addition, we note that changing the molecular weight may result in changes to the Fourier Transform Infrared (FTIR) spectra associated with changes in fibre intramolecular bond strength and arrangement. Overall the study has demonstrated that pressure gyration represents a feasible means of producing nanofibres (470-970nm) on a scale commensurate with commercial viability and have identified key parameters that influence mesh structure.

Physio-chemical and antibacterial characteristics of pressure spun nylon nanofibres embedded with functional silver nanoparticles

A novel and facile approach to prepare hybrid nanoparticle embedded polymer nanofibers using pressurised gyration is presented. Silver nanoparticles and nylon polymer were used in this work. The polymer solutions physical properties, rotating speed and the working pressure had a significant influence on the fibre diameter and the morphology. Fibres in the range of 60-500nm were spun using 10wt.%, 15wt.% and 20wt.% nylon solutions and these bead-free fibres were processed under 0.2MPa and 0.3MPa working pressure and a rotational speed of 36,000rpm. 1-4wt.% of Ag was added to these nylon solutions and in the case of wt.% fibres in the range 50-150nm were prepared using the same conditions of pressurised gyration. Successful incorporation of the Ag nanoparticles in nylon nanofibres was confirmed by using a combination of advanced microscopical techniques and Raman spectrometry was used to study the bonding characteristics of nylon and the Ag nanoparticles. Inductively coupled plasma mass spectroscopy showed a substantial concentration of Ag ions in the nylon fibre matrix which is essential for producing effective antibacterial properties. Antibacterial activity of the Ag-loaded nanofibres shows higher efficacy than nylon nanofibres for Gram-negative Escherichia coli and Pseudomonas aeruginosa microorganisms, and both Ag nanoparticles and the Ag ions were found to be the reason for enhanced cell death in the bacterial solutions.

Rheology and pressurised gyration of starch and starch-loaded poly(ethylene oxide)

This work investigates the rheology and spinning of starch and starch-loaded poly(ethylene oxide) (PEO) by pressurised gyration in order to prepare nanofibres. The spinning dopes rheological properties played a crucial role in fibre formation. Newtonian behaviour is observed in 1-20 wt% starch suspensions and non-Newtonian behaviour is found in all the PEO-starch mixtures. Pressurised gyration of the starch suspensions produced beads only but PEO-starch mixtures generated fibres. The fibre diameter of the PEO-starch samples is shown to be a function of polymer concentration and rotating speed of the gyration system. Fibre formation can only be facilitated below a certain working pressure. The concentration of starch in the PEO-starch mixtures is crucial in defining whether beaded or continuous fibres were generated and this is related to the composition of the spinning dope. FT-IR, XRD and microscopy studies indicated very good miscibility of starch and PEO in the nanofibres. The storage modulus of the PEO-starch were also studied as a function of temperature (30-150°C) and showed interesting results but it was not possible to deduce general trends valid for the entire temperature range.

Development and Characterization of Amorphous Nanofiber Drug Dispersions Prepared Using Pressurized Gyration

Nanofibrous systems are attracting increasing interest as a means of drug delivery, although a significant limitation to this approach has been manufacture on a scale commensurate with dosage form production. However, recent work has suggested that nanofibers may be successfully manufactured on a suitable scale using the novel process of pressurized gyration (PG). In this study, we explore the potential of PG as a novel means of generating amorphous solid dispersions of poorly water-soluble drugs with enhanced dissolution performance. We examine the effect of increasing drug loading on fiber properties including size, surface characteristics, and the physical state of both components. Dispersions of ibuprofen in poly(vinylpyrrolidone) (PVP) were prepared (up to 50% w/w loading) and characterized using a range of imaging, thermal, diffraction, and spectroscopic techniques, while the release profiles were studied using sink and non-sink (pH 1.0) conditions. The drug was found to be dispersed on a molecular basis within the fibers; attenuated total reflection FTIR indicated evidence for a direct interaction between the drug and polymer at lower drug loading by the identification of a strong single band in the carbonyl region and amide region of ibuprofen and PVP respectively. Dissolution studies under sink conditions indicated a substantial increase in release rate, while non-sink studies showed evidence for supersaturation. It is concluded that PG presents a viable method for the production of drug-loaded nanofibers for oral administration with enhanced in vitro dissolution rate enhancement.

Preparation of bone-implants by coating hydroxyapatite nanoparticles on self-formed titanium dioxide thin-layers on titanium metal surfaces

Preparation of hydroxyapatite coated custom-made metallic bone-implants is very important for the replacement of injured bones of the body. Furthermore, these bone-implants are more stable under the corrosive environment of the body and biocompatible than bone-implants made up of pure metals and metal alloys. Herein, we describe a novel, simple and low-cost technique to prepare biocompatible hydroxyapatite coated titanium metal (TiM) implants through growth of self-formed TiO2 thin-layer (SFTL) on TiM via a heat treatment process. SFTL acts as a surface binder of HA nanoparticles in order to produce HA coated implants. Colloidal HA nanorods prepared by a novel surfactant-assisted synthesis method, have been coated on SFTL via atomized spray pyrolysis (ASP) technique. The corrosion behavior of the bare and surface-modified TiM (SMTiM) in a simulated body fluid (SBF) medium is also studied. The highest corrosion rate is found to be for the bare TiM plate, but the corrosion rate has been reduced with the heat-treatment of TiM due to the formation of SFTL. The lowest corrosion rate is recorded for the implant prepared by heat treatment of TiM at 700 °C. The HA-coating further assists in the passivation of the TiM in the SBF medium. Both SMTiM and HA coated SMTiM are noncytotoxic against osteoblast-like (HOS) cells and are in high-bioactivity. The overall production process of bone-implant described in this paper is in high economic value.