Roslina Ahmad

Advances in fabrication of TiO2 nanofiber/nanowire arrays toward the cellular response in biomedical implantations: a review

The nanotopography of biomedical implants is known to play a pivotal role in the cell–implant interactions for successful clinical implantations. Recently, due to the morphological similarity to natural extracellular matrix, titania (TiO2) nanofibers/nanowires have shown great promise as a preferred platform in the field of biomedical implants. In this study, we first review recent progress pertaining to fabrication techniques for producing TiO2 nanofibrous surface topographies. Subsequently, we outline the effect of this on cellular response, using several examples of current in vitro studies, noting that these remarkable results greatly support the potential use of such a surface as a substrate for implantation. However, further in vitro and in vivo studies will be required to realize their full potential in clinical use. Finally, we anticipate that the future direction in this field will be shaped by better analysis and understanding of cellular interactions with TiO2 nanowires/nanofibers surface structure.

Enhanced in vitro angiogenic behaviour of human umbilical vein endothelial cells on thermally oxidized TiO2 nanofibrous surfaces

One of the major challenges in bone grafting is the lack of sufficient bone vascularization. A rapid and stable bone vascularization at an early stage of implantation is essential for optimal functioning of the bone graft. To address this, the ability of in situ TiO2 nanofibrous surfaces fabricated via thermal oxidation method to enhance the angiogenic potential of human umbilical vein endothelial cells (HUVECs) was investigated. The cellular responses of HUVECs on TiO2 nanofibrous surfaces were studied through cell adhesion, cell proliferation, capillary-like tube formation, growth factors secretion (VEGF and BFGF), and angiogenic-endogenic-associated gene (VEGF, VEGFR2, BFGF, PGF, HGF, Ang-1, VWF, PECAM-1 and ENOS) expression analysis after 2 weeks of cell seeding. Our results show that TiO2 nanofibrous surfaces significantly enhanced adhesion, proliferation, formation of capillary-like tube networks and growth factors secretion of HUVECs, as well as leading to higher expression level of all angiogenic-endogenic-associated genes, in comparison to unmodified control surfaces. These beneficial effects suggest the potential use of such surface nanostructures to be utilized as an advantageous interface for bone grafts as they can promote angiogenesis, which improves bone vascularization.

Proliferation and stemness preservation of human adipose-derived stem cells by surface-modified in situ TiO2 nanofibrous surfaces

Two important criteria of an ideal biomaterial in the field of stem cells research are to regulate the cell proliferation without the loss of its pluripotency and to direct the differentiation into a specific cell lineage when desired. The present study describes the influence of TiO2 nanofibrous surface structures on the regulation of proliferation and stemness preservation of adipose-derived stem cells (ADSCs). TiO2 nanofiber arrays were produced in situ onto Ti-6Al-4V substrate via a thermal oxidation process and the successful fabrication of these nanostructures was confirmed by field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), and contact angle measurement. ADSCs were seeded on two types of Ti-6Al-4V surfaces (TiO2 nanofibers and flat control), and their morphology, proliferation, and stemness expression were analyzed using FESEM, AlamarBlue assay, flow cytometry, and quantitative real-time polymerase chain reaction (qRT-PCR) after 2 weeks of incubation, respectively. The results show that ADSCs exhibit better adhesion and significantly enhanced proliferation on the TiO2 nanofibrous surfaces compared to the flat control surfaces. The greater proliferation ability of TiO2 nanofibrous surfaces was further confirmed by the results of cell cycle assay. More importantly, TiO2 nanofibrous surfaces significantly upregulate the expressions of stemness markers Sox-2, Nanog3, Rex-1, and Nestin. These results demonstrate that TiO2 nanofibrous surfaces can be used to enhance cell adhesion and proliferation while simultaneously maintaining the stemness of ADSCs, thereby representing a promising approach for their potential application in the field of bone tissue engineering as well as regenerative therapies.

Optical Studies on Multiwalled Carbon Nanotubes via Modified Wolff-Kishner Reduction Process

Multiwalled carbon nanotubes (MWCNTs) have been successfully synthesized by using a relatively simple method, known as modified Wolff-Kishner reduction process. Transmission electron microscopy (TEM) has shown the as-prepared MWCNTs possess straight morphologies with average inner and outer diameters, between 2 to 7 nm and 5 to 15 nm, respectively. Ultraviolet-visible (UV-Vis) absorption measurement has been conducted for the first time. The correlation between energy of the π plasmon absorbance (Eπ) and nanotube diameter (dCNT) for the as-prepared MWCNTs shows contradiction to the empirical relationship as Eπ = 4.8 + 0.7 / (dCNT)2. Other optical characteristics like transmittance, reflectance and refraction index also have been studied. This work explores the optical property of the as-prepared MWCNTs and thus provides better understanding about the feasibility of this synthesis technique.

A facile, bio-based, novel approach for synthesis of covalently functionalized graphene nanoplatelet nano-coolants toward improved thermo-physical and heat transfer properties

In this study, we synthesized covalently functionalized graphene nanoplatelet (GNP) aqueous suspensions that are highly stable and environmentally friendly for use as coolants in heat transfer systems. We evaluated the heat transfer and hydrodynamic properties of these nano-coolants flowing through a horizontal stainless steel tube subjected to a uniform heat flux at its outer surface. The GNPs functionalized with clove buds using the one-pot technique. We characterized the clove-treated GNPs (CGNPs) using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). We then dispersed the CGNPs in distilled water at three particle concentrations (0.025, 0.075 and 0.1wt%) in order to prepare the CGNP-water nanofluids (nano-coolants). We used ultraviolet-visible (UV-vis) spectroscopy to examine the stability and solubility of the CGNPs in the distilled water. There is significant enhancement in thermo-physical properties of CGNPs nanofluids relative those for distilled water. We validated our experimental set-up by comparing the friction factor and Nusselt number for distilled water obtained from experiments with those determined from empirical correlations, indeed, our experimental set-up is reliable and produces results with reasonable accuracy. We conducted heat transfer experiments for the CGNP-water nano-coolants flowing through the horizontal heated tube in fully developed turbulent condition. Our results are indeed promising since there is a significant enhancement in the Nusselt number and convective heat transfer coefficient for the CGNP-water nanofluids, with only a negligible increase in the friction factor and pumping power. More importantly, we found that there is a significant increase in the performance index, which is a positive indicator that our nanofluids have potential to substitute conventional coolants in heat transfer systems because of their overall thermal performance and energy savings benefits.

Osteoblast and stem cell response to nanoscale topographies: a review

Abstract To understand how cells respond to the nanoscale extracellular environment in vivo, cells from various sources have been cultured on nanoscale patterns fabricated using bottom-up and top-down techniques. Human fetal osteoblasts (hFOBs) and stem cells are some of them and they are known to be overtly responsive to nanoscale topographies – allowing us to investigate the hows and whys of the response in vitro. Information gathered from these in vitro studies could be used to control the cells, i.e. make the stem cells differentiate or retain their characteristics without the use of medium supplements. In this review, hFOB and stem cell responses to nanotopographies are summarized and discussed to shed some light on the influence of patterns on the reactions. Although both types of cells are responsive to nanoscale topographies, the responses are found to be unique to topographical dimension, shape, orientation and the types of cells used. This implies that cellular responses are influenced by multitude of factors and that if done right, cheaper self-assembled nanotopographies can be tailored to control the cells. A new self-assembly, powder-based technique is also included to provide an insight into the future of nanofabrication.

Synthesis of bioactive titania nanofibrous structures via oxidation

Abstract Titania (TiO2) nanofibres with controllable diameters have been successfully fabricated in situ on a Ti–6Al–4 V substrate by a thermal oxidation process. Their morphology, elemental composition, crystal structure, surface roughness and surface wettability were characterized by field-emission scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffractometer, atomic force microscope and contact angle goniometer. The results showed that the diameter of the resulting TiO2 nanofibres can be controlled within the range of 45–65 nm by changing the flow rate of argon gas. The results of material characterization studies revealed that TiO2 nanofibres with smaller diameter possessed greater surface roughness and hydrophilicity, as well as the degree of crystallinity. Therefore, we envisage that such surfaces can be ideally used as biomedical implants for size-dependent cellular response.

Diffusion of Palm Biodiesel in Elastomers Undergoing Multiaxial Large Deformations

Petroleum-based fuel is facing significant depletion issue due to its limited reserves and increasing demand from various industries. Thus, various considerations from economical, environmental and political concerns have motivated researchers to develop alternative energy sources such as biofuel to decrease dependence on petroleum-based fuel. However, the changes in the fuel composition of biofuel affect the material compatibility. In engineering applications where elastomeric components are exposed to hostile environment such as palm biodiesel medium, at least two aspects contribute to the degradation of the materials during the service: diffusion of the liquids leading to swelling and fluctuating multiaxial mechanical loading leading to fatigue failure. Therefore, it is of utmost importance to study the mechanical responses of elastomers under this coupled diffusion-mechanical loading in order to predict accurately their fatigue failure. The present work investigates the swelling of elastomers under simultaneous diffusion of palm biodiesel and multiaxial large deformations.

Evaluation of Surface Properties and In Vitro Characterization of Surface Modified In Situ TiO2 Nanofibers

In situ TiO2 nanofiber arrays have been successfully produced directly on a Ti-6Al-4V substrate by using thermal oxidation under a limited supply of oxygen. Their morphology, elemental composition, crystal structure, surface roughness and surface wettability were characterized by field-emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometer (XRD), atomic force microscope (AFM) and contact angle goniometer, respectively. The results of material characterization studies revealed that TiO2 nanofibers possessed greater surface roughness and wettability, as well as the degree of crystallinity. In vitro characterization have also been evaluated by using bovine articular chondrocytes on the resulting TiO2 nanofibrous surface at different time points. Cell adhesion was observed qualitatively by using FESEM and cell proliferation was determined quantitatively by using AlamarBlue reduction assay. The results showed that the TiO2 nanofibrous substrate triggers enhanced chondrocytes adhesion, proliferation, and production of extracellular matrix (ECM) fibrils compared to untreated substrate. These results suggest that the oxidation process produces a surface structure to which chondrocytes affinity, and thus this surface would has potential use in implants designed for cartilaginous applications.

Surface Properties and Cell Response of Bioactive Thermally Grown TiO2 Nanofibers

Titania nanofiber (TiO2 NFs) arrays were fabricated in situ on a Ti-6Al-4V substrate by an oxidation process. Their surface morphology, crystallographic structure, surface roughness and wettability were characterized, as well as their in vitro interaction with bovine articular chondrocytes at different time points. Results showed that TiO2 NFs possessed greater surface roughness, hydrophilicity and degree of crystallinity. The in vitro cell studies revealed that TiO2 NFs substrate triggers enhanced cell adhesion, proliferation and extracellular matrix (ECM) formation compared to the untreated control sample. These results showed that chondrocytes have an affinity to the nanofibrous substrate surface and thus we suggest that such surfaces are suited to be used as an implant designed for cartilage growth.