Joseph G. Lawrence

Elastic properties and morphology of individual carbon nanofibers.

The structural complexity of vapor-grown carbon nanofibers means that they require a method that determines both their elastic properties and their corresponding morphology. A three-point bending test method was developed combining atomic force microscopy, transmission electron microscopy (TEM) and focused ion beam techniques to suspend individual nanofibers and measure their deflection coupled with accurate determinations of inner and outer diameters and morphology using high resolution TEM. This resulted in much improved accuracy and reproducibility of the measured values of the elastic modulus which ranged from 6 to 207 GPa. The data showed two distinct trends, with higher values of the modulus when the outer wall thickness of the nanofibers is larger than that of the inner wall, with the values decreasing with the overall wall thickness. These results suggest that the more ordered layers of the outer wall, closest to the inner wall, are mostly responsible for the nanofiber strength. For large nanofiber wall thicknesses of greater than 80 nm, the elastic modulus becomes independent of the thickness with a value of approximately 25 GPa. The results also demonstrate that this technique can be a standardized one for the detailed study of mechanical properties of nanofibers and their relationship to morphology.

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.

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.

Polycaprolactone nanofiber interspersed collagen type-I scaffold for bone regeneration: a unique injectable osteogenic scaffold

There is an increasing demand for an injectable cell coupled three-dimensional (3D) scaffold to be used as bone fracture augmentation material. To address this demand, a novel injectable osteogenic scaffold called PN-COL was developed using cells, a natural polymer (collagen type-I), and a synthetic polymer (polycaprolactone (PCL)). The injectable nanofibrous PN-COL is created by interspersing PCL nanofibers within pre-osteoblast cell embedded collagen type-I. This simple yet novel and powerful approach provides a great benefit as an injectable bone scaffold over other non-living bone fracture stabilization polymers, such as polymethylmethacrylate and calcium content resin-based materials. The advantages of injectability and the biomimicry of collagen was coupled with the structural support of PCL nanofibers, to create cell encapsulated injectable 3D bone scaffolds with intricate porous internal architecture and high osteoconductivity. The effects of PCL nanofiber inclusion within the cell encapsulated collagen matrix has been evaluated for scaffold size retention and osteocompatibility, as well as for MC3T3-E1 cells osteogenic activity. The structural analysis of novel bioactive material proved that the material is chemically stable enough in an aqueous solution for an extended period of time without using crosslinking reagents, but it is also viscous enough to be injected through a syringe needle. Data from long-term in vitro proliferation and differentiation data suggests that novel PN-COL scaffolds promote the osteoblast proliferation, phenotype expression, and formation of mineralized matrix. This study demonstrates for the first time the feasibility of creating a structurally competent, injectable, cell embedded bone tissue scaffold. Furthermore, the results demonstrate the advantages of mimicking the hierarchical architecture of native bone with nano- and micro-size formation through introducing PCL nanofibers within macron-size collagen fibers and in promoting osteoblast phenotype progression for bone regeneration.

Focused ion beam and electron microscopy characterization of nanosharp tips and microbumps on silicon and metal thin films formed via localized single-pulse laser irradiation

Cross-sections of laser fabricated nanosharp tips and microbumps on silicon and metal thin films are produced and examined in this work. These structures are formed with a Q-switched neodymium doped yttrium aluminum garnet nanosecond-pulse laser, emitting at its fourth harmonic of 266 nm, using a mask projection technique to generate circular laser spots, several microns in diameter. Cross-section of selected structures were produced using a focused ion beam and were characterized via electron microscopy. The diffraction patterns of the silicon samples indicate that the laser formed tip maintains the same single crystal structure as the original silicon film. Examinations of the laser formed structures in metal films confirm that the microbumps are hollow, while revealing that the vertical protrusions are solid.

Development and Commercialization of Vapor Grown Carbon Nanofibers: A Review

The lack of a low cost, high volume method to produce carbon nanotubes has greatly limited their commercialization. Carbon nanofibers have a similar structure and properties as nanotubes and are a commercially viable alternative to them. In recent years many of the difficulties of commercial nanofiber production have been overcome through innovations in their manufacturing process. It is now possible to produce carbon nanofibers of different grades, such as thinner and thicker walled ones, and low heat treated and high heat treated ones. Most significantly, commercial quantities can now be produced of carbon nanofibers that have been surface functionalized with carboxylic acid groups, making them suitable for further functionalization and new classes of applications, such as biomedical sensors and drug delivery. Despite their cost advantages and availability more widespread use of carbon nanofibers has been hampered by uncertainties in their molecular structure and a lack of physical property measurements. However, recent theoretical and experimental studies have addressed these deficiencies showing that these fibers have a cone-helix structure under the usual manufacturing conditions. Additionally, small amounts of a segmented carbon nanotube structure, commonly called a bamboo structure, are also present. When the conical nanofibers were heat treated they were found to transform to a stacked cone structure. Advances in surface functionalization have allowed a variety of groups to be incorporated on them, significantly enhancing their properties and potential applications. Finally, the recent development of a new method to measure the elastic properties and morphology of single nanofibers has clearly demonstrated the high strength of these fibers. These nanofibers now represent a well understood and well characterized graphitic carbon nanomaterial that can be manufactured at low cost in large quantities, and have the potential to bring widespread use of nanotechnology to a variety of fields.

Physico-chemical characterisation, cytotoxic activity, and biocompatibility studies of tamoxifen-loaded solid lipid nanoparticles prepared via a temperature-modulated solidification method

Abstract Context: Solid lipid nanoparticles (SLNs) can efficiently and efficaciously incorporate anti-cancer agents. Objective: To prepare and characterise tamoxifen (TAM)-loaded SLNs. Materials and methods: Glyceryl monostearate, Tween-80, and trehalose were used in SLNs. SLNs were tested via dynamic light scattering (DLS), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Results: Characterisation studies revealed SLNs of about 540 nm with a negative surface charge and confirmed the entrapment of TAM in the SLNs. The entrapment efficiency was estimated to be 60%. Discussion: The in vitro drug release profile demonstrated a gradual increase followed by a release plateau for several days. A drug concentration-dependent increase in cytotoxic activity was observed when the SLNs were evaluated in cell cultures. Conclusion: Biocompatible and stable lyophilised SLNs were successfully prepared and found to possess properties that may be utilised in an anti-cancer drug delivery system.

Role of enhanced solubility in esterification of 2,5-furandicarboxylic acid with ethylene glycol at reduced temperatures: energy efficient synthesis of poly(ethylene 2,5-furandicarboxylate)

Poly(ethylene 2,5-furandicarboxylate) (PEF) has garnered considerable industrial and academic interest as a renewable alternative to traditional polyesters due to its superior barrier and thermal properties. While efforts for the industrial scale production of PEF from 2,5-furandicarboxylic acid (FDCA) and ethylene glycol (EG) are underway, most of the published literature on PEF follows the conventional terephthalic acid (TPA) based polyester synthesis protocol. In this study, we reveal for the first time that the solubility of FDCA is an order of magnitude higher in EG compared to that in TPA at the process temperatures. The enhanced solubility of FDCA in EG results in improved esterification kinetics especially at temperatures from 180–210 °C to yield complete end group conversion. We further demonstrate that it is advantageous to perform the direct esterification step of PEF synthesis in a lower temperature range than that in previous reports reducing the potential side reactions in addition to cost and energy savings at the industrial scale. This work can provide new insights into the sustainable synthesis of FDCA-based polyesters for bio-based packaging.